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-rw-r--r--tvix/store/Cargo.toml59
-rw-r--r--tvix/store/README.md63
-rw-r--r--tvix/store/build.rs38
-rw-r--r--tvix/store/default.nix34
-rw-r--r--tvix/store/docs/api.md288
-rw-r--r--tvix/store/protos/LICENSE21
-rw-r--r--tvix/store/protos/default.nix55
-rw-r--r--tvix/store/protos/pathinfo.proto128
-rw-r--r--tvix/store/protos/rpc_pathinfo.proto76
-rw-r--r--tvix/store/src/bin/tvix-store.rs401
-rw-r--r--tvix/store/src/import.rs156
-rw-r--r--tvix/store/src/lib.rs8
-rw-r--r--tvix/store/src/nar/import.rs351
-rw-r--r--tvix/store/src/nar/mod.rs27
-rw-r--r--tvix/store/src/nar/renderer.rs216
-rw-r--r--tvix/store/src/pathinfoservice/from_addr.rs187
-rw-r--r--tvix/store/src/pathinfoservice/fs/mod.rs79
-rw-r--r--tvix/store/src/pathinfoservice/grpc.rs204
-rw-r--r--tvix/store/src/pathinfoservice/memory.rs84
-rw-r--r--tvix/store/src/pathinfoservice/mod.rs52
-rw-r--r--tvix/store/src/pathinfoservice/nix_http.rs312
-rw-r--r--tvix/store/src/pathinfoservice/sled.rs140
-rw-r--r--tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs116
-rw-r--r--tvix/store/src/proto/mod.rs368
-rw-r--r--tvix/store/src/proto/tests/grpc_pathinfoservice.rs74
-rw-r--r--tvix/store/src/proto/tests/mod.rs2
-rw-r--r--tvix/store/src/proto/tests/pathinfo.rs448
-rw-r--r--tvix/store/src/tests/fixtures.rs125
-rw-r--r--tvix/store/src/tests/mod.rs3
-rw-r--r--tvix/store/src/tests/nar_renderer.rs231
-rw-r--r--tvix/store/src/tests/utils.rs16
-rw-r--r--tvix/store/src/utils.rs35
32 files changed, 4397 insertions, 0 deletions
diff --git a/tvix/store/Cargo.toml b/tvix/store/Cargo.toml
new file mode 100644
index 000000000000..9065465af622
--- /dev/null
+++ b/tvix/store/Cargo.toml
@@ -0,0 +1,59 @@
+[package]
+name = "tvix-store"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+anyhow = "1.0.68"
+async-stream = "0.3.5"
+blake3 = { version = "1.3.1", features = ["rayon", "std"] }
+bytes = "1.4.0"
+clap = { version = "4.0", features = ["derive", "env"] }
+count-write = "0.1.0"
+data-encoding = "2.3.3"
+futures = "0.3.30"
+lazy_static = "1.4.0"
+nix-compat = { path = "../nix-compat", features = ["async"] }
+pin-project-lite = "0.2.13"
+prost = "0.12.1"
+opentelemetry = { version = "0.21.0", optional = true}
+opentelemetry-otlp = { version = "0.14.0", optional = true }
+opentelemetry_sdk = { version = "0.21.0", features = ["rt-tokio"], optional = true}
+sha2 = "0.10.6"
+sled = { version = "0.34.7" }
+thiserror = "1.0.38"
+tokio = { version = "1.32.0", features = ["fs", "macros", "net", "rt", "rt-multi-thread", "signal"] }
+tokio-listener = { version = "0.2.2", features = [ "tonic010" ] }
+tokio-stream = { version = "0.1.14", features = ["fs"] }
+tokio-util = { version = "0.7.9", features = ["io", "io-util", "compat"] }
+tonic = { version = "0.10.2", features = ["tls", "tls-roots"] }
+tower = "0.4.13"
+tracing = "0.1.37"
+tracing-opentelemetry = "0.22.0"
+tracing-subscriber = { version = "0.3.16", features = ["json"] }
+tvix-castore = { path = "../castore" }
+url = "2.4.0"
+walkdir = "2.4.0"
+async-recursion = "1.0.5"
+reqwest = { version = "0.11.22", features = ["rustls-tls", "stream"], default-features = false }
+xz2 = "0.1.7"
+
+[dependencies.tonic-reflection]
+optional = true
+version = "0.10.2"
+
+[build-dependencies]
+prost-build = "0.12.1"
+tonic-build = "0.10.2"
+
+[dev-dependencies]
+test-case = "3.3.1"
+tempfile = "3.3.0"
+tokio-retry = "0.3.0"
+
+[features]
+default = ["fuse", "otlp", "tonic-reflection"]
+fuse = ["tvix-castore/fuse"]
+otlp = ["dep:opentelemetry", "dep:opentelemetry-otlp", "dep:opentelemetry_sdk"]
+tonic-reflection = ["dep:tonic-reflection", "tvix-castore/tonic-reflection"]
+virtiofs = ["tvix-castore/virtiofs"]
diff --git a/tvix/store/README.md b/tvix/store/README.md
new file mode 100644
index 000000000000..a9d29671d8bb
--- /dev/null
+++ b/tvix/store/README.md
@@ -0,0 +1,63 @@
+# //tvix/store
+
+This contains the code hosting the tvix-store.
+
+For the local store, Nix realizes files on the filesystem in `/nix/store` (and
+maintains some metadata in a SQLite database). For "remote stores", it
+communicates this metadata in NAR (Nix ARchive) and NARInfo format.
+
+Compared to the Nix model, `tvix-store` stores data on a much more granular
+level than that, which provides more deduplication possibilities, and more
+granular copying.
+
+However, enough information is preserved to still be able to render NAR and
+NARInfo when needed.
+
+## More Information
+The store consists out of two different gRPC services, `tvix.castore.v1` for
+the low-level content-addressed bits, and `tvix.store.v1` for the Nix and
+`StorePath`-specific bits.
+
+Check the `protos/` subfolder both here and in `castore` for the definition of
+the exact RPC methods and messages.
+
+## Interacting with the GRPC service manually
+The shell environment in `//tvix` provides `evans`, which is an interactive
+REPL-based gPRC client.
+
+You can use it to connect to a `tvix-store` and call the various RPC methods.
+
+```shell
+$ cargo run -- daemon &
+$ evans --host localhost --port 8000 -r repl
+  ______
+ |  ____|
+ | |__    __   __   __ _   _ __    ___
+ |  __|   \ \ / /  / _. | | '_ \  / __|
+ | |____   \ V /  | (_| | | | | | \__ \
+ |______|   \_/    \__,_| |_| |_| |___/
+
+ more expressive universal gRPC client
+
+
+localhost:8000> package tvix.castore.v1
+tvix.castore.v1@localhost:8000> service BlobService
+
+tvix.castore.v1.BlobService@localhost:8000> call Put --bytes-from-file
+data (TYPE_BYTES) => /run/current-system/system
+{
+  "digest": "KOM3/IHEx7YfInAnlJpAElYezq0Sxn9fRz7xuClwNfA="
+}
+
+tvix.castore.v1.BlobService@localhost:8000> call Read --bytes-as-base64
+digest (TYPE_BYTES) => KOM3/IHEx7YfInAnlJpAElYezq0Sxn9fRz7xuClwNfA=
+{
+  "data": "eDg2XzY0LWxpbnV4"
+}
+
+$ echo eDg2XzY0LWxpbnV4 | base64 -d
+x86_64-linux
+```
+
+Thanks to `tvix-store` providing gRPC Server Reflection (with `reflection`
+feature), you don't need to point `evans` to the `.proto` files.
diff --git a/tvix/store/build.rs b/tvix/store/build.rs
new file mode 100644
index 000000000000..cfeda59698a0
--- /dev/null
+++ b/tvix/store/build.rs
@@ -0,0 +1,38 @@
+use std::io::Result;
+
+fn main() -> Result<()> {
+    #[allow(unused_mut)]
+    let mut builder = tonic_build::configure();
+
+    #[cfg(feature = "tonic-reflection")]
+    {
+        let out_dir = std::path::PathBuf::from(std::env::var("OUT_DIR").unwrap());
+        let descriptor_path = out_dir.join("tvix.store.v1.bin");
+
+        builder = builder.file_descriptor_set_path(descriptor_path);
+    };
+
+    // https://github.com/hyperium/tonic/issues/908
+    let mut config = prost_build::Config::new();
+    config.bytes(["."]);
+    config.extern_path(".tvix.castore.v1", "::tvix_castore::proto");
+
+    builder
+        .build_server(true)
+        .build_client(true)
+        .compile_with_config(
+            config,
+            &[
+                "tvix/store/protos/pathinfo.proto",
+                "tvix/store/protos/rpc_pathinfo.proto",
+            ],
+            // If we are in running `cargo build` manually, using `../..` works fine,
+            // but in case we run inside a nix build, we need to instead point PROTO_ROOT
+            // to a sparseTree containing that structure.
+            &[match std::env::var_os("PROTO_ROOT") {
+                Some(proto_root) => proto_root.to_str().unwrap().to_owned(),
+                None => "../..".to_string(),
+            }],
+        )?;
+    Ok(())
+}
diff --git a/tvix/store/default.nix b/tvix/store/default.nix
new file mode 100644
index 000000000000..35d2a22bb2ce
--- /dev/null
+++ b/tvix/store/default.nix
@@ -0,0 +1,34 @@
+{ depot, pkgs, ... }:
+
+let
+  mkImportCheck = p: expectedPath: {
+    label = ":nix :import ${p} with tvix-store import";
+    needsOutput = true;
+    command = pkgs.writeShellScript "tvix-import-check" ''
+      export BLOB_SERVICE_ADDR=memory://
+      export DIRECTORY_SERVICE_ADDR=memory://
+      export PATH_INFO_SERVICE_ADDR=memory://
+      TVIX_STORE_OUTPUT=$(result/bin/tvix-store import ${p})
+      EXPECTED='${/* the vebatim expected Tvix output: */expectedPath}'
+
+      echo "tvix-store output: ''${TVIX_STORE_OUTPUT}"
+      if [ "$TVIX_STORE_OUTPUT" != "$EXPECTED" ]; then
+        echo "Correct would have been ''${EXPECTED}"
+        exit 1
+      fi
+
+      echo "Output was correct."
+    '';
+  };
+in
+
+(depot.tvix.crates.workspaceMembers.tvix-store.build.override {
+  runTests = true;
+  # virtiofs feature currently fails to build on Darwin.
+  # we however can ship it for non-darwin.
+  features = if pkgs.stdenv.isDarwin then [ "default" ] else [ "default" "virtiofs" ];
+}).overrideAttrs (_: {
+  meta.ci.extraSteps = {
+    import-docs = (mkImportCheck "tvix/store/docs" ./docs);
+  };
+})
diff --git a/tvix/store/docs/api.md b/tvix/store/docs/api.md
new file mode 100644
index 000000000000..c1dacc89a598
--- /dev/null
+++ b/tvix/store/docs/api.md
@@ -0,0 +1,288 @@
+tvix-[ca]store API
+==============
+
+This document outlines the design of the API exposed by tvix-castore and tvix-
+store, as well as other implementations of this store protocol.
+
+This document is meant to be read side-by-side with
+[castore.md](../../tvix-castore/docs/castore.md) which describes the data model
+in more detail.
+
+The store API has four main consumers:
+
+1. The evaluator (or more correctly, the CLI/coordinator, in the Tvix
+   case) communicates with the store to:
+
+   * Upload files and directories (e.g. from `builtins.path`, or `src = ./path`
+     Nix expressions).
+   * Read files from the store where necessary (e.g. when `nixpkgs` is
+     located in the store, or for IFD).
+
+2. The builder communicates with the store to:
+
+   * Upload files and directories after a build, to persist build artifacts in
+     the store.
+
+3. Tvix clients (such as users that have Tvix installed, or, depending
+   on perspective, builder environments) expect the store to
+   "materialise" on disk to provide a directory layout with store
+   paths.
+
+4. Stores may communicate with other stores, to substitute already built store
+   paths, i.e. a store acts as a binary cache for other stores.
+
+The store API attempts to reuse parts of its API between these three
+consumers by making similarities explicit in the protocol. This leads
+to a protocol that is slightly more complex than a simple "file
+upload/download"-system, but at significantly greater efficiency, both in terms
+of deduplication opportunities as well as granularity.
+
+## The Store model
+
+Contents inside a tvix-store can be grouped into three different message types:
+
+ * Blobs
+ * Directories
+ * PathInfo (see further down)
+
+(check `castore.md` for more detailed field descriptions)
+
+### Blobs
+A blob object contains the literal file contents of regular (or executable)
+files.
+
+### Directory
+A directory object describes the direct children of a directory.
+
+It contains:
+ - name of child (regular or executable) files, and their [blake3][blake3] hash.
+ - name of child symlinks, and their target (as string)
+ - name of child directories, and their [blake3][blake3] hash (forming a Merkle DAG)
+
+### Content-addressed Store Model
+For example, lets consider a directory layout like this, with some
+imaginary hashes of file contents:
+
+```
+.
+├── file-1.txt        hash: 5891b5b522d5df086d0ff0b110fb
+└── nested
+    └── file-2.txt    hash: abc6fd595fc079d3114d4b71a4d8
+```
+
+A hash for the *directory* `nested` can be created by creating the `Directory`
+object:
+
+```json
+{
+  "directories": [],
+  "files": [{
+    "name": "file-2.txt",
+    "digest": "abc6fd595fc079d3114d4b71a4d8",
+    "size": 123,
+  }],
+  "symlink": [],
+}
+```
+
+And then hashing a serialised form of that data structure. We use the blake3
+hash of the canonical protobuf representation. Let's assume the hash was
+`ff0029485729bcde993720749232`.
+
+To create the directory object one layer up, we now refer to our `nested`
+directory object in `directories`, and to `file-1.txt` in `files`:
+
+```json
+{
+  "directories": [{
+    "name": "nested",
+    "digest": "ff0029485729bcde993720749232",
+    "size": 1,
+  }],
+  "files": [{
+    "name": "file-1.txt",
+    "digest": "5891b5b522d5df086d0ff0b110fb",
+    "size": 124,
+  }]
+}
+```
+
+This Merkle DAG of Directory objects, and flat store of blobs can be used to
+describe any file/directory/symlink inside a store path. Due to its content-
+addressed nature, it'll automatically deduplicate (re-)used (sub)directories,
+and allow substitution from any (untrusted) source.
+
+The thing that's now only missing is the metadata to map/"mount" from the
+content-addressed world to a physical path.
+
+### PathInfo
+As most paths in the Nix store currently are input-addressed [^input-addressed],
+and the `tvix-castore` data model is also not intrinsically using NAR hashes,
+we need something mapping from an input-addressed "output path hash" (or a Nix-
+specific content-addressed path) to the contents in the `tvix-castore` world.
+
+That's what `PathInfo` provides. It embeds the root node (Directory, File or
+Symlink) at a given store path.
+
+The root nodes' `name` field is populated with the (base)name inside
+`/nix/store`, so `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-pname-1.2.3`.
+
+The `PathInfo` message also stores references to other store paths, and some
+more NARInfo-specific metadata (signatures, narhash, narsize).
+
+
+## API overview
+
+There's three different services:
+
+### BlobService
+`BlobService` can be used to store and retrieve blobs of data, used to host
+regular file contents.
+
+It is content-addressed, using [blake3][blake3]
+as a hashing function.
+
+As blake3 is a tree hash, there's an opportunity to do
+[verified streaming][bao] of parts of the file,
+which doesn't need to trust any more information than the root hash itself.
+Future extensions of the `BlobService` protocol will enable this.
+
+### DirectoryService
+`DirectoryService` allows lookups (and uploads) of `Directory` messages, and
+whole reference graphs of them.
+
+
+### PathInfoService
+The PathInfo service provides lookups from a store path hash to a `PathInfo`
+message.
+
+## Example flows
+
+Below there are some common use cases of tvix-store, and how the different
+services are used.
+
+###  Upload files and directories
+This is needed for `builtins.path` or `src = ./path` in Nix expressions (A), as
+well as for uploading build artifacts to a store (B).
+
+The path specified needs to be (recursively, BFS-style) traversed.
+ * All file contents need to be hashed with blake3, and submitted to the
+   *BlobService* if not already present.
+   A reference to them needs to be added to the parent Directory object that's
+   constructed.
+ * All symlinks need to be added to the parent directory they reside in.
+ * Whenever a Directory has been fully traversed, it needs to be uploaded to
+   the *DirectoryService* and a reference to it needs to be added to the parent
+   Directory object.
+
+Most of the hashing / directory traversal/uploading can happen in parallel,
+as long as Directory objects only refer to Directory objects and Blobs that
+have already been uploaded.
+
+When reaching the root, a `PathInfo` object needs to be constructed.
+
+ * In the case of content-addressed paths (A), the name of the root node is
+   based on the NAR representation of the contents.
+   It might make sense to be able to offload the NAR calculation to the store,
+   which can cache it.
+ * In the case of build artifacts (B), the output path is input-addressed and
+   known upfront.
+
+Contrary to Nix, this has the advantage of not having to upload a lot of things
+to the store that didn't change.
+
+### Reading files from the store from the evaluator
+This is the case when `nixpkgs` is located in the store, or IFD in general.
+
+The store client asks the `PathInfoService` for the `PathInfo` of the output
+path in the request, and looks at the root node.
+
+If something other than the root of the store path is requested, like for
+example `maintainers/maintainer-list.nix`, the root_node Directory is inspected
+and potentially a chain of `Directory` objects requested from
+*DirectoryService*. [^n+1query].
+
+When the desired file is reached, the *BlobService* can be used to read the
+contents of this file, and return it back to the evaluator.
+
+FUTUREWORK: define how importing from symlinks should/does work.
+
+Contrary to Nix, this has the advantage of not having to copy all of the
+contents of a store path to the evaluating machine, but really only fetching
+the files the evaluator currently cares about.
+
+### Materializing store paths on disk
+This is useful for people running a Tvix-only system, or running builds on a
+"Tvix remote builder" in its own mount namespace.
+
+In a system with Nix installed, we can't simply manually "extract" things to
+`/nix/store`, as Nix assumes to own all writes to this location.
+In these use cases, we're probably better off exposing a tvix-store as a local
+binary cache (that's what `//tvix/nar-bridge` does).
+
+Assuming we are in an environment where we control `/nix/store` exclusively, a
+"realize to disk" would either "extract" things from the `tvix-store` to a
+filesystem, or expose a `FUSE`/`virtio-fs` filesystem.
+
+The latter is already implemented, and particularly interesting for (remote)
+build workloads, as build inputs can be realized on-demand, which saves copying
+around a lot of never- accessed files.
+
+In both cases, the API interactions are similar.
+ * The *PathInfoService* is asked for the `PathInfo` of the requested store path.
+ * If everything should be "extracted", the *DirectoryService* is asked for all
+   `Directory` objects in the closure, the file structure is created, all Blobs
+   are downloaded and placed in their corresponding location and all symlinks
+   are created accordingly.
+ * If this is a FUSE filesystem, we can decide to only request a subset,
+   similar to the "Reading files from the store from the evaluator" use case,
+   even though it might make sense to keep all Directory objects around.
+   (See the caveat in "Trust model" though!)
+
+### Stores communicating with other stores
+The gRPC API exposed by the tvix-store allows composing multiple stores, and
+implementing some caching strategies, that store clients don't need to be aware
+of.
+
+ * For example, a caching strategy could have a fast local tvix-store, that's
+   asked first and filled with data from a slower remote tvix-store.
+
+ * Multiple stores could be asked for the same data, and whatever store returns
+   the right data first wins.
+
+
+## Trust model / Distribution
+As already described above, the only non-content-addressed service is the
+`PathInfo` service.
+
+This means, all other messages (such as `Blob` and `Directory` messages) can be
+substituted from many different, untrusted sources/mirrors, which will make
+plugging in additional substitution strategies like IPFS, local network
+neighbors super simple. That's also why it's living in the `tvix-castore` crate.
+
+As for `PathInfo`, we don't specify an additional signature mechanism yet, but
+carry the NAR-based signatures from Nix along.
+
+This means, if we don't trust a remote `PathInfo` object, we currently need to
+"stream" the NAR representation to validate these signatures.
+
+However, the slow part is downloading of NAR files, and considering we have
+more granularity available, we might only need to download some small blobs,
+rather than a whole NAR file.
+
+A future signature mechanism, that is only signing (parts of) the `PathInfo`
+message, which only points to content-addressed data will enable verified
+partial access into a store path, opening up opportunities for lazy filesystem
+access etc.
+
+
+
+[blake3]: https://github.com/BLAKE3-team/BLAKE3
+[bao]: https://github.com/oconnor663/bao
+[^input-addressed]: Nix hashes the A-Term representation of a .drv, after doing
+                    some replacements on refered Input Derivations to calculate
+                    output paths.
+[^n+1query]: This would expose an N+1 query problem. However it's not a problem
+             in practice, as there's usually always a "local" caching store in
+             the loop, and *DirectoryService* supports a recursive lookup for
+             all `Directory` children of a `Directory`
diff --git a/tvix/store/protos/LICENSE b/tvix/store/protos/LICENSE
new file mode 100644
index 000000000000..2034ada6fd9a
--- /dev/null
+++ b/tvix/store/protos/LICENSE
@@ -0,0 +1,21 @@
+Copyright © The Tvix Authors
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+“Software”), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
diff --git a/tvix/store/protos/default.nix b/tvix/store/protos/default.nix
new file mode 100644
index 000000000000..56345d9338b2
--- /dev/null
+++ b/tvix/store/protos/default.nix
@@ -0,0 +1,55 @@
+{ depot, pkgs, ... }:
+let
+  protos = depot.nix.sparseTree {
+    name = "store-protos";
+    root = depot.path.origSrc;
+    paths = [
+      # We need to include castore.proto (only), as it's referred.
+      ../../castore/protos/castore.proto
+      ./pathinfo.proto
+      ./rpc_pathinfo.proto
+      ../../../buf.yaml
+      ../../../buf.gen.yaml
+    ];
+  };
+in
+depot.nix.readTree.drvTargets {
+  inherit protos;
+
+  # Lints and ensures formatting of the proto files.
+  check = pkgs.stdenv.mkDerivation {
+    name = "proto-check";
+    src = protos;
+
+    nativeBuildInputs = [
+      pkgs.buf
+    ];
+
+    buildPhase = ''
+      export HOME=$TMPDIR
+      buf lint
+      buf format -d --exit-code
+      touch $out
+    '';
+  };
+
+  # Produces the golang bindings.
+  go-bindings = pkgs.stdenv.mkDerivation {
+    name = "go-bindings";
+    src = protos;
+
+    nativeBuildInputs = [
+      pkgs.buf
+      pkgs.protoc-gen-go
+      pkgs.protoc-gen-go-grpc
+    ];
+
+    buildPhase = ''
+      export HOME=$TMPDIR
+      buf generate
+
+      mkdir -p $out
+      cp tvix/store/protos/*.pb.go $out/
+    '';
+  };
+}
diff --git a/tvix/store/protos/pathinfo.proto b/tvix/store/protos/pathinfo.proto
new file mode 100644
index 000000000000..b03e7e938e33
--- /dev/null
+++ b/tvix/store/protos/pathinfo.proto
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+syntax = "proto3";
+
+package tvix.store.v1;
+
+import "tvix/castore/protos/castore.proto";
+
+option go_package = "code.tvl.fyi/tvix/store-go;storev1";
+
+// PathInfo shows information about a Nix Store Path.
+// That's a single element inside /nix/store.
+message PathInfo {
+  // The path can be a directory, file or symlink.
+  tvix.castore.v1.Node node = 1;
+
+  // List of references (output path hashes)
+  // This really is the raw *bytes*, after decoding nixbase32, and not a
+  // base32-encoded string.
+  repeated bytes references = 2;
+
+  // see below.
+  NARInfo narinfo = 3;
+}
+
+// Represents a path in the Nix store (a direct child of STORE_DIR).
+// It is commonly formatted by a nixbase32-encoding the digest, and
+// concatenating the name, separated by a `-`.
+message StorePath {
+  // The string after digest and `-`.
+  string name = 1;
+
+  // The digest (20 bytes).
+  bytes digest = 2;
+}
+
+// Nix C++ uses NAR (Nix Archive) as a format to transfer store paths,
+// and stores metadata and signatures in NARInfo files.
+// Store all these attributes in a separate message.
+//
+// This is useful to render .narinfo files to clients, or to preserve/validate
+// these signatures.
+// As verifying these signatures requires the whole NAR file to be synthesized,
+// moving to another signature scheme is desired.
+// Even then, it still makes sense to hold this data, for old clients.
+message NARInfo {
+  // This represents a (parsed) signature line in a .narinfo file.
+  message Signature {
+    string name = 1;
+    bytes data = 2;
+  }
+
+  // This size of the NAR file, in bytes.
+  uint64 nar_size = 1;
+
+  // The sha256 of the NAR file representation.
+  bytes nar_sha256 = 2;
+
+  // The signatures in a .narinfo file.
+  repeated Signature signatures = 3;
+
+  // A list of references. To validate .narinfo signatures, a fingerprint needs
+  // to be constructed.
+  // This fingerprint doesn't just contain the hashes of the output paths of all
+  // references (like PathInfo.references), but their whole (base)names, so we
+  // need to keep them somewhere.
+  repeated string reference_names = 4;
+
+  // The StorePath of the .drv file producing this output.
+  // The .drv suffix is omitted in its `name` field.
+  StorePath deriver = 5;
+
+  // The CA field in the .narinfo.
+  // Its textual representations seen in the wild are one of the following:
+  //  - `fixed:r:sha256:1gcky5hlf5vqfzpyhihydmm54grhc94mcs8w7xr8613qsqb1v2j6`
+  //    fixed-output derivations using "recursive" `outputHashMode`.
+  //  - `fixed:sha256:19xqkh72crbcba7flwxyi3n293vav6d7qkzkh2v4zfyi4iia8vj8
+  //    fixed-output derivations using "flat" `outputHashMode`
+  //  - `text:sha256:19xqkh72crbcba7flwxyi3n293vav6d7qkzkh2v4zfyi4iia8vj8`
+  //    Text hashing, used for uploaded .drv files and outputs produced by
+  //    builtins.toFile.
+  //
+  // Semantically, they can be split into the following components:
+  //  - "content address prefix". Currently, "fixed" and "text" are supported.
+  //  - "hash mode". Currently, "flat" and "recursive" are supported.
+  //  - "hash type". The underlying hash function used.
+  //    Currently, sha1, md5, sha256, sha512.
+  //  - "digest". The digest itself.
+  //
+  // There are some restrictions on the possible combinations.
+  // For example, `text` and `fixed:recursive` always imply sha256.
+  //
+  // We use an enum to encode the possible combinations, and optimize for the
+  // common case, `fixed:recursive`, identified as `NAR_SHA256`.
+  CA ca = 6;
+
+  message CA {
+    enum Hash {
+      // produced when uploading fixed-output store paths using NAR-based
+      // hashing (`outputHashMode = "recursive"`).
+      NAR_SHA256 = 0;
+      NAR_SHA1 = 1;
+      NAR_SHA512 = 2;
+      NAR_MD5 = 3;
+
+      // Produced when uploading .drv files or outputs produced by
+      // builtins.toFile.
+      // Produces equivalent digests as FLAT_SHA256, but is a separate
+      // hashing type in Nix, affecting output path calculation.
+      TEXT_SHA256 = 4;
+
+      // Produced when using fixed-output derivations with
+      // `outputHashMode = "flat"`.
+      FLAT_SHA1 = 5;
+      FLAT_MD5 = 6;
+      FLAT_SHA256 = 7;
+      FLAT_SHA512 = 8;
+
+      // TODO: what happens in Rust if we introduce a new enum kind here?
+    }
+
+    // The hashing type used.
+    Hash type = 1;
+
+    // The digest, in raw bytes.
+    bytes digest = 2;
+  }
+}
diff --git a/tvix/store/protos/rpc_pathinfo.proto b/tvix/store/protos/rpc_pathinfo.proto
new file mode 100644
index 000000000000..c1c91658ada2
--- /dev/null
+++ b/tvix/store/protos/rpc_pathinfo.proto
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+syntax = "proto3";
+
+package tvix.store.v1;
+
+import "tvix/castore/protos/castore.proto";
+import "tvix/store/protos/pathinfo.proto";
+
+option go_package = "code.tvl.fyi/tvix/store-go;storev1";
+
+service PathInfoService {
+  // Return a PathInfo message matching the criteria specified in the
+  // GetPathInfoRequest message.
+  rpc Get(GetPathInfoRequest) returns (PathInfo);
+
+  // Upload a PathInfo object to the remote end. It MUST not return until the
+  // PathInfo object has been written on the the remote end.
+  //
+  // The remote end MAY check if a potential DirectoryNode has already been
+  // uploaded.
+  //
+  // Uploading clients SHOULD obviously not steer other machines to try to
+  // substitute before from the remote end before having finished uploading
+  // PathInfo, Directories and Blobs.
+  // The returned PathInfo object MAY contain additional narinfo signatures, but
+  // is otherwise left untouched.
+  rpc Put(PathInfo) returns (PathInfo);
+
+  // Calculate the NAR representation of the contents specified by the
+  // root_node. The calculation SHOULD be cached server-side for subsequent
+  // requests.
+  //
+  // All references (to blobs or Directory messages) MUST already exist in the
+  // store.
+  //
+  // The method can be used to produce a Nix fixed-output path, which contains
+  // the (compressed) sha256 of the NAR content representation in the root_node
+  // name (suffixed with the name).
+  //
+  // It can also be used to calculate arbitrary NAR hashes of output paths, in
+  // case a legacy Nix Binary Cache frontend is provided.
+  rpc CalculateNAR(tvix.castore.v1.Node) returns (CalculateNARResponse);
+
+  // Return a stream of PathInfo messages matching the criteria specified in
+  // ListPathInfoRequest.
+  rpc List(ListPathInfoRequest) returns (stream PathInfo);
+}
+
+// The parameters that can be used to lookup a (single) PathInfo object.
+// Currently, only a lookup by output hash is supported.
+message GetPathInfoRequest {
+  oneof by_what {
+    // The output hash of a nix path (20 bytes).
+    // This is the nixbase32-decoded portion of a Nix output path, so to substitute
+    // /nix/store/xm35nga2g20mz5sm5l6n8v3bdm86yj83-cowsay-3.04
+    // this field would contain nixbase32dec("xm35nga2g20mz5sm5l6n8v3bdm86yj83").
+    bytes by_output_hash = 1;
+  }
+}
+
+// The parameters that can be used to lookup (multiple) PathInfo objects.
+// Currently no filtering is possible, all objects are returned.
+message ListPathInfoRequest {}
+
+// CalculateNARResponse is the response returned by the CalculateNAR request.
+//
+// It contains the size of the NAR representation (in bytes), and the sha56
+// digest.
+message CalculateNARResponse {
+  // This size of the NAR file, in bytes.
+  uint64 nar_size = 1;
+
+  // The sha256 of the NAR file representation.
+  bytes nar_sha256 = 2;
+}
diff --git a/tvix/store/src/bin/tvix-store.rs b/tvix/store/src/bin/tvix-store.rs
new file mode 100644
index 000000000000..ecee8d78f3b7
--- /dev/null
+++ b/tvix/store/src/bin/tvix-store.rs
@@ -0,0 +1,401 @@
+use clap::Parser;
+use clap::Subcommand;
+
+use futures::future::try_join_all;
+use std::path::PathBuf;
+use std::sync::Arc;
+use tokio_listener::Listener;
+use tokio_listener::SystemOptions;
+use tokio_listener::UserOptions;
+use tonic::transport::Server;
+use tracing::info;
+use tracing::Level;
+use tracing_subscriber::fmt::writer::MakeWriterExt;
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
+
+use tvix_castore::proto::blob_service_server::BlobServiceServer;
+use tvix_castore::proto::directory_service_server::DirectoryServiceServer;
+use tvix_castore::proto::GRPCBlobServiceWrapper;
+use tvix_castore::proto::GRPCDirectoryServiceWrapper;
+use tvix_store::pathinfoservice::PathInfoService;
+use tvix_store::proto::path_info_service_server::PathInfoServiceServer;
+use tvix_store::proto::GRPCPathInfoServiceWrapper;
+
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+use tvix_store::pathinfoservice::make_fs;
+
+#[cfg(feature = "fuse")]
+use tvix_castore::fs::fuse::FuseDaemon;
+
+#[cfg(feature = "otlp")]
+use opentelemetry::KeyValue;
+#[cfg(feature = "otlp")]
+use opentelemetry_sdk::{
+    resource::{ResourceDetector, SdkProvidedResourceDetector},
+    trace::BatchConfig,
+    Resource,
+};
+
+#[cfg(feature = "virtiofs")]
+use tvix_castore::fs::virtiofs::start_virtiofs_daemon;
+
+#[cfg(feature = "tonic-reflection")]
+use tvix_castore::proto::FILE_DESCRIPTOR_SET as CASTORE_FILE_DESCRIPTOR_SET;
+#[cfg(feature = "tonic-reflection")]
+use tvix_store::proto::FILE_DESCRIPTOR_SET;
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+struct Cli {
+    /// Whether to log in JSON
+    #[arg(long)]
+    json: bool,
+
+    #[arg(long)]
+    log_level: Option<Level>,
+
+    #[command(subcommand)]
+    command: Commands,
+}
+
+#[derive(Subcommand)]
+enum Commands {
+    /// Runs the tvix-store daemon.
+    Daemon {
+        #[arg(long, short = 'l')]
+        listen_address: Option<String>,
+
+        #[arg(long, env, default_value = "sled:///var/lib/tvix-store/blobs.sled")]
+        blob_service_addr: String,
+
+        #[arg(
+            long,
+            env,
+            default_value = "sled:///var/lib/tvix-store/directories.sled"
+        )]
+        directory_service_addr: String,
+
+        #[arg(long, env, default_value = "sled:///var/lib/tvix-store/pathinfo.sled")]
+        path_info_service_addr: String,
+    },
+    /// Imports a list of paths into the store, print the store path for each of them.
+    Import {
+        #[clap(value_name = "PATH")]
+        paths: Vec<PathBuf>,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        blob_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        directory_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        path_info_service_addr: String,
+    },
+    /// Mounts a tvix-store at the given mountpoint
+    #[cfg(feature = "fuse")]
+    Mount {
+        #[clap(value_name = "PATH")]
+        dest: PathBuf,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        blob_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        directory_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        path_info_service_addr: String,
+
+        /// Number of FUSE threads to spawn.
+        #[arg(long, env, default_value_t = default_threads())]
+        threads: usize,
+
+        /// Whether to list elements at the root of the mount point.
+        /// This is useful if your PathInfoService doesn't provide an
+        /// (exhaustive) listing.
+        #[clap(long, short, action)]
+        list_root: bool,
+    },
+    /// Starts a tvix-store virtiofs daemon at the given socket path.
+    #[cfg(feature = "virtiofs")]
+    #[command(name = "virtiofs")]
+    VirtioFs {
+        #[clap(value_name = "PATH")]
+        socket: PathBuf,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        blob_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        directory_service_addr: String,
+
+        #[arg(long, env, default_value = "grpc+http://[::1]:8000")]
+        path_info_service_addr: String,
+
+        /// Whether to list elements at the root of the mount point.
+        /// This is useful if your PathInfoService doesn't provide an
+        /// (exhaustive) listing.
+        #[clap(long, short, action)]
+        list_root: bool,
+    },
+}
+
+#[cfg(all(feature = "fuse", not(target_os = "macos")))]
+fn default_threads() -> usize {
+    std::thread::available_parallelism()
+        .map(|threads| threads.into())
+        .unwrap_or(4)
+}
+// On MacFUSE only a single channel will receive ENODEV when the file system is
+// unmounted and so all the other channels will block forever.
+// See https://github.com/osxfuse/osxfuse/issues/974
+#[cfg(all(feature = "fuse", target_os = "macos"))]
+fn default_threads() -> usize {
+    1
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let cli = Cli::parse();
+
+    // configure log settings
+    let level = cli.log_level.unwrap_or(Level::INFO);
+
+    let subscriber = tracing_subscriber::registry()
+        .with(
+            cli.json.then_some(
+                tracing_subscriber::fmt::Layer::new()
+                    .with_writer(std::io::stderr.with_max_level(level))
+                    .json(),
+            ),
+        )
+        .with(
+            (!cli.json).then_some(
+                tracing_subscriber::fmt::Layer::new()
+                    .with_writer(std::io::stderr.with_max_level(level))
+                    .pretty(),
+            ),
+        );
+
+    // Add the otlp layer (when otlp is enabled), then init the registry.
+    // Or if the feature is disabled, just init without adding the layer.
+    // It's necessary to do this separately, as every with() call chains the
+    // layer into the type of the registry.
+    #[cfg(feature = "otlp")]
+    {
+        subscriber
+            .with({
+                let tracer = opentelemetry_otlp::new_pipeline()
+                    .tracing()
+                    .with_exporter(opentelemetry_otlp::new_exporter().tonic())
+                    .with_batch_config(BatchConfig::default())
+                    .with_trace_config(opentelemetry_sdk::trace::config().with_resource({
+                        // use SdkProvidedResourceDetector.detect to detect resources,
+                        // but replace the default service name with our default.
+                        // https://github.com/open-telemetry/opentelemetry-rust/issues/1298
+                        let resources =
+                            SdkProvidedResourceDetector.detect(std::time::Duration::from_secs(0));
+
+                        // SdkProvidedResourceDetector currently always sets
+                        // `service.name`, but we don't like its default.
+                        if resources.get("service.name".into()).unwrap() == "unknown_service".into()
+                        {
+                            resources.merge(&Resource::new([KeyValue::new(
+                                "service.name",
+                                "tvix.store",
+                            )]))
+                        } else {
+                            resources
+                        }
+                    }))
+                    .install_batch(opentelemetry_sdk::runtime::Tokio)?;
+
+                // Create a tracing layer with the configured tracer
+                tracing_opentelemetry::layer().with_tracer(tracer)
+            })
+            .try_init()?;
+    }
+
+    // Init the registry (when otlp is not enabled)
+    #[cfg(not(feature = "otlp"))]
+    {
+        subscriber.try_init()?;
+    }
+
+    match cli.command {
+        Commands::Daemon {
+            listen_address,
+            blob_service_addr,
+            directory_service_addr,
+            path_info_service_addr,
+        } => {
+            // initialize stores
+            let (blob_service, directory_service, path_info_service) =
+                tvix_store::utils::construct_services(
+                    blob_service_addr,
+                    directory_service_addr,
+                    path_info_service_addr,
+                )
+                .await?;
+
+            let listen_address = listen_address
+                .unwrap_or_else(|| "[::]:8000".to_string())
+                .parse()
+                .unwrap();
+
+            let mut server = Server::builder();
+
+            #[allow(unused_mut)]
+            let mut router = server
+                .add_service(BlobServiceServer::new(GRPCBlobServiceWrapper::new(
+                    blob_service,
+                )))
+                .add_service(DirectoryServiceServer::new(
+                    GRPCDirectoryServiceWrapper::new(directory_service),
+                ))
+                .add_service(PathInfoServiceServer::new(GRPCPathInfoServiceWrapper::new(
+                    Arc::from(path_info_service),
+                )));
+
+            #[cfg(feature = "tonic-reflection")]
+            {
+                let reflection_svc = tonic_reflection::server::Builder::configure()
+                    .register_encoded_file_descriptor_set(CASTORE_FILE_DESCRIPTOR_SET)
+                    .register_encoded_file_descriptor_set(FILE_DESCRIPTOR_SET)
+                    .build()?;
+                router = router.add_service(reflection_svc);
+            }
+
+            info!(listen_address=%listen_address, "starting daemon");
+
+            let listener = Listener::bind(
+                &listen_address,
+                &SystemOptions::default(),
+                &UserOptions::default(),
+            )
+            .await?;
+
+            router.serve_with_incoming(listener).await?;
+        }
+        Commands::Import {
+            paths,
+            blob_service_addr,
+            directory_service_addr,
+            path_info_service_addr,
+        } => {
+            // FUTUREWORK: allow flat for single files?
+            let (blob_service, directory_service, path_info_service) =
+                tvix_store::utils::construct_services(
+                    blob_service_addr,
+                    directory_service_addr,
+                    path_info_service_addr,
+                )
+                .await?;
+
+            // Arc the PathInfoService, as we clone it .
+            let path_info_service: Arc<dyn PathInfoService> = path_info_service.into();
+
+            let tasks = paths
+                .into_iter()
+                .map(|path| {
+                    tokio::task::spawn({
+                        let blob_service = blob_service.clone();
+                        let directory_service = directory_service.clone();
+                        let path_info_service = path_info_service.clone();
+
+                        async move {
+                            if let Ok(name) = tvix_store::import::path_to_name(&path) {
+                                let resp = tvix_store::import::import_path_as_nar_ca(
+                                    &path,
+                                    name,
+                                    blob_service,
+                                    directory_service,
+                                    path_info_service,
+                                )
+                                .await;
+                                if let Ok(output_path) = resp {
+                                    // If the import was successful, print the path to stdout.
+                                    println!("{}", output_path.to_absolute_path());
+                                }
+                            }
+                        }
+                    })
+                })
+                .collect::<Vec<_>>();
+
+            try_join_all(tasks).await?;
+        }
+        #[cfg(feature = "fuse")]
+        Commands::Mount {
+            dest,
+            blob_service_addr,
+            directory_service_addr,
+            path_info_service_addr,
+            list_root,
+            threads,
+        } => {
+            let (blob_service, directory_service, path_info_service) =
+                tvix_store::utils::construct_services(
+                    blob_service_addr,
+                    directory_service_addr,
+                    path_info_service_addr,
+                )
+                .await?;
+
+            let mut fuse_daemon = tokio::task::spawn_blocking(move || {
+                let fs = make_fs(
+                    blob_service,
+                    directory_service,
+                    Arc::from(path_info_service),
+                    list_root,
+                );
+                info!(mount_path=?dest, "mounting");
+
+                FuseDaemon::new(fs, &dest, threads)
+            })
+            .await??;
+
+            // grab a handle to unmount the file system, and register a signal
+            // handler.
+            tokio::spawn(async move {
+                tokio::signal::ctrl_c().await.unwrap();
+                info!("interrupt received, unmounting…");
+                tokio::task::spawn_blocking(move || fuse_daemon.unmount()).await??;
+                info!("unmount occured, terminating…");
+                Ok::<_, std::io::Error>(())
+            })
+            .await??;
+        }
+        #[cfg(feature = "virtiofs")]
+        Commands::VirtioFs {
+            socket,
+            blob_service_addr,
+            directory_service_addr,
+            path_info_service_addr,
+            list_root,
+        } => {
+            let (blob_service, directory_service, path_info_service) =
+                tvix_store::utils::construct_services(
+                    blob_service_addr,
+                    directory_service_addr,
+                    path_info_service_addr,
+                )
+                .await?;
+
+            tokio::task::spawn_blocking(move || {
+                let fs = make_fs(
+                    blob_service,
+                    directory_service,
+                    Arc::from(path_info_service),
+                    list_root,
+                );
+                info!(socket_path=?socket, "starting virtiofs-daemon");
+
+                start_virtiofs_daemon(fs, socket)
+            })
+            .await??;
+        }
+    };
+    Ok(())
+}
diff --git a/tvix/store/src/import.rs b/tvix/store/src/import.rs
new file mode 100644
index 000000000000..588a0108931e
--- /dev/null
+++ b/tvix/store/src/import.rs
@@ -0,0 +1,156 @@
+use std::path::Path;
+
+use data_encoding::BASE64;
+use tracing::{debug, instrument};
+use tvix_castore::{
+    blobservice::BlobService, directoryservice::DirectoryService, proto::node::Node,
+};
+
+use nix_compat::store_path::{self, StorePath};
+
+use crate::{
+    pathinfoservice::PathInfoService,
+    proto::{nar_info, NarInfo, PathInfo},
+};
+
+pub fn log_node(node: &Node, path: &Path) {
+    match node {
+        Node::Directory(directory_node) => {
+            debug!(
+                path = ?path,
+                name = ?directory_node.name,
+                digest = BASE64.encode(&directory_node.digest),
+                "import successful",
+            )
+        }
+        Node::File(file_node) => {
+            debug!(
+                path = ?path,
+                name = ?file_node.name,
+                digest = BASE64.encode(&file_node.digest),
+                "import successful"
+            )
+        }
+        Node::Symlink(symlink_node) => {
+            debug!(
+                path = ?path,
+                name = ?symlink_node.name,
+                target = ?symlink_node.target,
+                "import successful"
+            )
+        }
+    }
+}
+
+/// Transform a path into its base name and returns an [`std::io::Error`] if it is `..` or if the
+/// basename is not valid unicode.
+#[inline]
+pub fn path_to_name(path: &Path) -> std::io::Result<&str> {
+    path.file_name()
+        .and_then(|file_name| file_name.to_str())
+        .ok_or_else(|| {
+            std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                "path must not be .. and the basename valid unicode",
+            )
+        })
+}
+
+/// Takes the NAR size, SHA-256 of the NAR representation and the root node.
+/// Returns the path information object for a content addressed NAR-style (recursive) object.
+///
+/// This [`PathInfo`] can be further filled for signatures, deriver or verified for the expected
+/// hashes.
+#[inline]
+pub fn derive_nar_ca_path_info(nar_size: u64, nar_sha256: [u8; 32], root_node: Node) -> PathInfo {
+    // assemble the [crate::proto::PathInfo] object.
+    PathInfo {
+        node: Some(tvix_castore::proto::Node {
+            node: Some(root_node),
+        }),
+        // There's no reference scanning on path contents ingested like this.
+        references: vec![],
+        narinfo: Some(NarInfo {
+            nar_size,
+            nar_sha256: nar_sha256.to_vec().into(),
+            signatures: vec![],
+            reference_names: vec![],
+            deriver: None,
+            ca: Some(nar_info::Ca {
+                r#type: nar_info::ca::Hash::NarSha256.into(),
+                digest: nar_sha256.to_vec().into(),
+            }),
+        }),
+    }
+}
+
+/// Ingest the given path [`path`] and register the resulting output path in the
+/// [`PathInfoService`] as a recursive fixed output NAR.
+#[instrument(skip_all, fields(store_name=name, path=?path), err)]
+pub async fn import_path_as_nar_ca<BS, DS, PS, P>(
+    path: P,
+    name: &str,
+    blob_service: BS,
+    directory_service: DS,
+    path_info_service: PS,
+) -> Result<StorePath, std::io::Error>
+where
+    P: AsRef<Path> + std::fmt::Debug,
+    BS: AsRef<dyn BlobService> + Clone,
+    DS: AsRef<dyn DirectoryService>,
+    PS: AsRef<dyn PathInfoService>,
+{
+    let root_node =
+        tvix_castore::import::ingest_path(blob_service, directory_service, &path).await?;
+
+    // Ask the PathInfoService for the NAR size and sha256
+    let (nar_size, nar_sha256) = path_info_service.as_ref().calculate_nar(&root_node).await?;
+
+    // Calculate the output path. This might still fail, as some names are illegal.
+    // FUTUREWORK: express the `name` at the type level to be valid and move the conversion
+    // at the caller level.
+    let output_path = store_path::build_nar_based_store_path(&nar_sha256, name).map_err(|_| {
+        std::io::Error::new(
+            std::io::ErrorKind::InvalidData,
+            format!("invalid name: {}", name),
+        )
+    })?;
+
+    // assemble a new root_node with a name that is derived from the nar hash.
+    let root_node = root_node.rename(output_path.to_string().into_bytes().into());
+    log_node(&root_node, path.as_ref());
+
+    let path_info = derive_nar_ca_path_info(nar_size, nar_sha256, root_node);
+
+    // This new [`PathInfo`] that we get back from there might contain additional signatures or
+    // information set by the service itself. In this function, we silently swallow it because
+    // callers doesn't really need it.
+    let _path_info = path_info_service.as_ref().put(path_info).await?;
+
+    Ok(output_path.to_owned())
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{ffi::OsStr, path::PathBuf};
+
+    use crate::import::path_to_name;
+    use test_case::test_case;
+
+    #[test_case("a/b/c", "c"; "simple path")]
+    #[test_case("a/b/../c", "c"; "simple path containing ..")]
+    #[test_case("a/b/../c/d/../e", "e"; "path containing multiple ..")]
+
+    fn test_path_to_name(path: &str, expected_name: &str) {
+        let path: PathBuf = path.into();
+        assert_eq!(path_to_name(&path).expect("must succeed"), expected_name);
+    }
+
+    #[test_case(b"a/b/.."; "path ending in ..")]
+    #[test_case(b"\xf8\xa1\xa1\xa1\xa1"; "non unicode path")]
+
+    fn test_invalid_path_to_name(invalid_path: &[u8]) {
+        let path: PathBuf = unsafe { OsStr::from_encoded_bytes_unchecked(invalid_path) }.into();
+        path_to_name(&path).expect_err("must fail");
+    }
+}
diff --git a/tvix/store/src/lib.rs b/tvix/store/src/lib.rs
new file mode 100644
index 000000000000..2fa86ff6a468
--- /dev/null
+++ b/tvix/store/src/lib.rs
@@ -0,0 +1,8 @@
+pub mod import;
+pub mod nar;
+pub mod pathinfoservice;
+pub mod proto;
+pub mod utils;
+
+#[cfg(test)]
+mod tests;
diff --git a/tvix/store/src/nar/import.rs b/tvix/store/src/nar/import.rs
new file mode 100644
index 000000000000..20b922a61f2e
--- /dev/null
+++ b/tvix/store/src/nar/import.rs
@@ -0,0 +1,351 @@
+use bytes::Bytes;
+use nix_compat::nar;
+use std::io::{self, BufRead};
+use tokio_util::io::SyncIoBridge;
+use tracing::warn;
+use tvix_castore::{
+    blobservice::BlobService,
+    directoryservice::{DirectoryPutter, DirectoryService},
+    proto::{self as castorepb},
+    B3Digest,
+};
+
+/// Accepts a reader providing a NAR.
+/// Will traverse it, uploading blobs to the given [BlobService], and
+/// directories to the given [DirectoryService].
+/// On success, the root node is returned.
+/// This function is not async (because the NAR reader is not)
+/// and calls [tokio::task::block_in_place] when interacting with backing
+/// services, so make sure to only call this with spawn_blocking.
+pub fn read_nar<R, BS, DS>(
+    r: &mut R,
+    blob_service: BS,
+    directory_service: DS,
+) -> io::Result<castorepb::node::Node>
+where
+    R: BufRead + Send,
+    BS: AsRef<dyn BlobService>,
+    DS: AsRef<dyn DirectoryService>,
+{
+    let handle = tokio::runtime::Handle::current();
+
+    let directory_putter = directory_service.as_ref().put_multiple_start();
+
+    let node = nix_compat::nar::reader::open(r)?;
+    let (root_node, mut directory_putter, _) = process_node(
+        handle.clone(),
+        "".into(), // this is the root node, it has an empty name
+        node,
+        &blob_service,
+        directory_putter,
+    )?;
+
+    // In case the root node points to a directory, we need to close
+    // [directory_putter], and ensure the digest we got back from there matches
+    // what the root node is pointing to.
+    if let castorepb::node::Node::Directory(ref directory_node) = root_node {
+        // Close directory_putter to make sure all directories have been inserted.
+        let directory_putter_digest =
+            handle.block_on(handle.spawn(async move { directory_putter.close().await }))??;
+        let root_directory_node_digest: B3Digest =
+            directory_node.digest.clone().try_into().unwrap();
+
+        if directory_putter_digest != root_directory_node_digest {
+            warn!(
+                root_directory_node_digest = %root_directory_node_digest,
+                directory_putter_digest =%directory_putter_digest,
+                "directory digest mismatch",
+            );
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "directory digest mismatch",
+            ));
+        }
+    }
+    // In case it's not a Directory, [directory_putter] doesn't need to be
+    // closed (as we didn't end up uploading anything).
+    // It can just be dropped, as documented in its trait.
+
+    Ok(root_node)
+}
+
+/// This is called on a [nar::reader::Node] and returns a [castorepb::node::Node].
+/// It does so by handling all three kinds, and recursing for directories.
+///
+/// [DirectoryPutter] is passed around, so a single instance of it can be used,
+/// which is sufficient, as this reads through the whole NAR linerarly.
+fn process_node<BS>(
+    handle: tokio::runtime::Handle,
+    name: bytes::Bytes,
+    node: nar::reader::Node,
+    blob_service: BS,
+    directory_putter: Box<dyn DirectoryPutter>,
+) -> io::Result<(castorepb::node::Node, Box<dyn DirectoryPutter>, BS)>
+where
+    BS: AsRef<dyn BlobService>,
+{
+    Ok(match node {
+        nar::reader::Node::Symlink { target } => (
+            castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+                name,
+                target: target.into(),
+            }),
+            directory_putter,
+            blob_service,
+        ),
+        nar::reader::Node::File { executable, reader } => (
+            castorepb::node::Node::File(process_file_reader(
+                handle,
+                name,
+                reader,
+                executable,
+                &blob_service,
+            )?),
+            directory_putter,
+            blob_service,
+        ),
+        nar::reader::Node::Directory(dir_reader) => {
+            let (directory_node, directory_putter, blob_service_back) =
+                process_dir_reader(handle, name, dir_reader, blob_service, directory_putter)?;
+
+            (
+                castorepb::node::Node::Directory(directory_node),
+                directory_putter,
+                blob_service_back,
+            )
+        }
+    })
+}
+
+/// Given a name and [nar::reader::FileReader], this ingests the file into the
+/// passed [BlobService] and returns a [castorepb::FileNode].
+fn process_file_reader<BS>(
+    handle: tokio::runtime::Handle,
+    name: Bytes,
+    mut file_reader: nar::reader::FileReader,
+    executable: bool,
+    blob_service: BS,
+) -> io::Result<castorepb::FileNode>
+where
+    BS: AsRef<dyn BlobService>,
+{
+    // store the length. If we read any other length, reading will fail.
+    let expected_len = file_reader.len();
+
+    // prepare writing a new blob.
+    let blob_writer = handle.block_on(async { blob_service.as_ref().open_write().await });
+
+    // write the blob.
+    let mut blob_writer = {
+        let mut dst = SyncIoBridge::new(blob_writer);
+
+        file_reader.copy(&mut dst)?;
+        dst.shutdown()?;
+
+        // return back the blob_writer
+        dst.into_inner()
+    };
+
+    // close the blob_writer, retrieve the digest.
+    let blob_digest = handle.block_on(async { blob_writer.close().await })?;
+
+    Ok(castorepb::FileNode {
+        name,
+        digest: blob_digest.into(),
+        size: expected_len,
+        executable,
+    })
+}
+
+/// Given a name and [nar::reader::DirReader], this returns a [castorepb::DirectoryNode].
+/// It uses [process_node] to iterate over all children.
+///
+/// [DirectoryPutter] is passed around, so a single instance of it can be used,
+/// which is sufficient, as this reads through the whole NAR linerarly.
+fn process_dir_reader<BS>(
+    handle: tokio::runtime::Handle,
+    name: Bytes,
+    mut dir_reader: nar::reader::DirReader,
+    blob_service: BS,
+    directory_putter: Box<dyn DirectoryPutter>,
+) -> io::Result<(castorepb::DirectoryNode, Box<dyn DirectoryPutter>, BS)>
+where
+    BS: AsRef<dyn BlobService>,
+{
+    let mut directory = castorepb::Directory::default();
+
+    let mut directory_putter = directory_putter;
+    let mut blob_service = blob_service;
+    while let Some(entry) = dir_reader.next()? {
+        let (node, directory_putter_back, blob_service_back) = process_node(
+            handle.clone(),
+            entry.name.into(),
+            entry.node,
+            blob_service,
+            directory_putter,
+        )?;
+
+        blob_service = blob_service_back;
+        directory_putter = directory_putter_back;
+
+        match node {
+            castorepb::node::Node::Directory(node) => directory.directories.push(node),
+            castorepb::node::Node::File(node) => directory.files.push(node),
+            castorepb::node::Node::Symlink(node) => directory.symlinks.push(node),
+        }
+    }
+
+    // calculate digest and size.
+    let directory_digest = directory.digest();
+    let directory_size = directory.size();
+
+    // upload the directory. This is a bit more verbose, as we want to get back
+    // directory_putter for later reuse.
+    let directory_putter = handle.block_on(handle.spawn(async move {
+        directory_putter.put(directory).await?;
+        Ok::<_, io::Error>(directory_putter)
+    }))??;
+
+    Ok((
+        castorepb::DirectoryNode {
+            name,
+            digest: directory_digest.into(),
+            size: directory_size,
+        },
+        directory_putter,
+        blob_service,
+    ))
+}
+
+#[cfg(test)]
+mod test {
+    use crate::nar::read_nar;
+    use std::io::Cursor;
+    use std::sync::Arc;
+
+    use tokio_stream::StreamExt;
+    use tvix_castore::blobservice::BlobService;
+    use tvix_castore::directoryservice::DirectoryService;
+    use tvix_castore::fixtures::{
+        DIRECTORY_COMPLICATED, DIRECTORY_WITH_KEEP, EMPTY_BLOB_DIGEST, HELLOWORLD_BLOB_CONTENTS,
+        HELLOWORLD_BLOB_DIGEST,
+    };
+    use tvix_castore::proto as castorepb;
+    use tvix_castore::utils::{gen_blob_service, gen_directory_service};
+
+    use crate::tests::fixtures::{
+        NAR_CONTENTS_COMPLICATED, NAR_CONTENTS_HELLOWORLD, NAR_CONTENTS_SYMLINK,
+    };
+
+    #[tokio::test]
+    async fn single_symlink() {
+        let blob_service = gen_blob_service();
+        let directory_service = gen_directory_service();
+
+        let handle = tokio::runtime::Handle::current();
+
+        let root_node = handle
+            .spawn_blocking(|| {
+                read_nar(
+                    &mut Cursor::new(&NAR_CONTENTS_SYMLINK.clone()),
+                    blob_service,
+                    directory_service,
+                )
+            })
+            .await
+            .unwrap()
+            .expect("must parse");
+
+        assert_eq!(
+            castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+                name: "".into(), // name must be empty
+                target: "/nix/store/somewhereelse".into(),
+            }),
+            root_node
+        );
+    }
+
+    #[tokio::test]
+    async fn single_file() {
+        let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+        let directory_service = gen_directory_service();
+
+        let handle = tokio::runtime::Handle::current();
+
+        let root_node = handle
+            .spawn_blocking({
+                let blob_service = blob_service.clone();
+                move || {
+                    read_nar(
+                        &mut Cursor::new(&NAR_CONTENTS_HELLOWORLD.clone()),
+                        blob_service,
+                        directory_service,
+                    )
+                }
+            })
+            .await
+            .unwrap()
+            .expect("must parse");
+
+        assert_eq!(
+            castorepb::node::Node::File(castorepb::FileNode {
+                name: "".into(), // name must be empty
+                digest: HELLOWORLD_BLOB_DIGEST.clone().into(),
+                size: HELLOWORLD_BLOB_CONTENTS.len() as u64,
+                executable: false,
+            }),
+            root_node
+        );
+
+        // blobservice must contain the blob
+        assert!(blob_service.has(&HELLOWORLD_BLOB_DIGEST).await.unwrap());
+    }
+
+    #[tokio::test]
+    async fn complicated() {
+        let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+        let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+
+        let handle = tokio::runtime::Handle::current();
+
+        let root_node = handle
+            .spawn_blocking({
+                let blob_service = blob_service.clone();
+                let directory_service = directory_service.clone();
+                || {
+                    read_nar(
+                        &mut Cursor::new(&NAR_CONTENTS_COMPLICATED.clone()),
+                        blob_service,
+                        directory_service,
+                    )
+                }
+            })
+            .await
+            .unwrap()
+            .expect("must parse");
+
+        assert_eq!(
+            castorepb::node::Node::Directory(castorepb::DirectoryNode {
+                name: "".into(), // name must be empty
+                digest: DIRECTORY_COMPLICATED.digest().into(),
+                size: DIRECTORY_COMPLICATED.size(),
+            }),
+            root_node,
+        );
+
+        // blobservice must contain the blob
+        assert!(blob_service.has(&EMPTY_BLOB_DIGEST).await.unwrap());
+
+        // directoryservice must contain the directories, at least with get_recursive.
+        let resp: Result<Vec<castorepb::Directory>, _> = directory_service
+            .get_recursive(&DIRECTORY_COMPLICATED.digest())
+            .collect()
+            .await;
+
+        let directories = resp.unwrap();
+
+        assert_eq!(2, directories.len());
+        assert_eq!(DIRECTORY_COMPLICATED.clone(), directories[0]);
+        assert_eq!(DIRECTORY_WITH_KEEP.clone(), directories[1]);
+    }
+}
diff --git a/tvix/store/src/nar/mod.rs b/tvix/store/src/nar/mod.rs
new file mode 100644
index 000000000000..c1a7fc2a933f
--- /dev/null
+++ b/tvix/store/src/nar/mod.rs
@@ -0,0 +1,27 @@
+use data_encoding::BASE64;
+use tvix_castore::B3Digest;
+
+mod import;
+mod renderer;
+pub use import::read_nar;
+pub use renderer::calculate_size_and_sha256;
+pub use renderer::write_nar;
+
+/// Errors that can encounter while rendering NARs.
+#[derive(Debug, thiserror::Error)]
+pub enum RenderError {
+    #[error("failure talking to a backing store client: {0}")]
+    StoreError(#[source] std::io::Error),
+
+    #[error("unable to find directory {}, referred from {:?}", .0, .1)]
+    DirectoryNotFound(B3Digest, bytes::Bytes),
+
+    #[error("unable to find blob {}, referred from {:?}", BASE64.encode(.0), .1)]
+    BlobNotFound([u8; 32], bytes::Bytes),
+
+    #[error("unexpected size in metadata for blob {}, referred from {:?} returned, expected {}, got {}", BASE64.encode(.0), .1, .2, .3)]
+    UnexpectedBlobMeta([u8; 32], bytes::Bytes, u32, u32),
+
+    #[error("failure using the NAR writer: {0}")]
+    NARWriterError(std::io::Error),
+}
diff --git a/tvix/store/src/nar/renderer.rs b/tvix/store/src/nar/renderer.rs
new file mode 100644
index 000000000000..313397dcf31b
--- /dev/null
+++ b/tvix/store/src/nar/renderer.rs
@@ -0,0 +1,216 @@
+use super::RenderError;
+use async_recursion::async_recursion;
+use count_write::CountWrite;
+use nix_compat::nar::writer::r#async as nar_writer;
+use sha2::{Digest, Sha256};
+use std::{
+    pin::Pin,
+    task::{self, Poll},
+};
+use tokio::io::{self, AsyncWrite, BufReader};
+use tokio_util::compat::{TokioAsyncReadCompatExt, TokioAsyncWriteCompatExt};
+use tvix_castore::{
+    blobservice::BlobService,
+    directoryservice::DirectoryService,
+    proto::{self as castorepb, NamedNode},
+};
+
+/// Invoke [write_nar], and return the size and sha256 digest of the produced
+/// NAR output.
+pub async fn calculate_size_and_sha256<BS, DS>(
+    root_node: &castorepb::node::Node,
+    blob_service: BS,
+    directory_service: DS,
+) -> Result<(u64, [u8; 32]), RenderError>
+where
+    BS: AsRef<dyn BlobService> + Send,
+    DS: AsRef<dyn DirectoryService> + Send,
+{
+    let mut h = Sha256::new();
+    let mut cw = CountWrite::from(&mut h);
+
+    write_nar(
+        // The hasher doesn't speak async. It doesn't
+        // actually do any I/O, so it's fine to wrap.
+        AsyncIoBridge(&mut cw),
+        root_node,
+        blob_service,
+        directory_service,
+    )
+    .await?;
+
+    Ok((cw.count(), h.finalize().into()))
+}
+
+/// The inverse of [tokio_util::io::SyncIoBridge].
+/// Don't use this with anything that actually does blocking I/O.
+struct AsyncIoBridge<T>(T);
+
+impl<W: std::io::Write + Unpin> AsyncWrite for AsyncIoBridge<W> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _cx: &mut task::Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(self.get_mut().0.write(buf))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut task::Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(self.get_mut().0.flush())
+    }
+
+    fn poll_shutdown(
+        self: Pin<&mut Self>,
+        _cx: &mut task::Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+/// Accepts a [castorepb::node::Node] pointing to the root of a (store) path,
+/// and uses the passed blob_service and directory_service to perform the
+/// necessary lookups as it traverses the structure.
+/// The contents in NAR serialization are writen to the passed [AsyncWrite].
+pub async fn write_nar<W, BS, DS>(
+    w: W,
+    proto_root_node: &castorepb::node::Node,
+    blob_service: BS,
+    directory_service: DS,
+) -> Result<(), RenderError>
+where
+    W: AsyncWrite + Unpin + Send,
+    BS: AsRef<dyn BlobService> + Send,
+    DS: AsRef<dyn DirectoryService> + Send,
+{
+    // Initialize NAR writer
+    let mut w = w.compat_write();
+    let nar_root_node = nar_writer::open(&mut w)
+        .await
+        .map_err(RenderError::NARWriterError)?;
+
+    walk_node(
+        nar_root_node,
+        proto_root_node,
+        blob_service,
+        directory_service,
+    )
+    .await?;
+
+    Ok(())
+}
+
+/// Process an intermediate node in the structure.
+/// This consumes the node.
+#[async_recursion]
+async fn walk_node<BS, DS>(
+    nar_node: nar_writer::Node<'async_recursion, '_>,
+    proto_node: &castorepb::node::Node,
+    blob_service: BS,
+    directory_service: DS,
+) -> Result<(BS, DS), RenderError>
+where
+    BS: AsRef<dyn BlobService> + Send,
+    DS: AsRef<dyn DirectoryService> + Send,
+{
+    match proto_node {
+        castorepb::node::Node::Symlink(proto_symlink_node) => {
+            nar_node
+                .symlink(&proto_symlink_node.target)
+                .await
+                .map_err(RenderError::NARWriterError)?;
+        }
+        castorepb::node::Node::File(proto_file_node) => {
+            let digest_len = proto_file_node.digest.len();
+            let digest = proto_file_node.digest.clone().try_into().map_err(|_| {
+                RenderError::StoreError(io::Error::new(
+                    io::ErrorKind::Other,
+                    format!("invalid digest len {} in file node", digest_len),
+                ))
+            })?;
+
+            let blob_reader = match blob_service
+                .as_ref()
+                .open_read(&digest)
+                .await
+                .map_err(RenderError::StoreError)?
+            {
+                Some(blob_reader) => Ok(BufReader::new(blob_reader)),
+                None => Err(RenderError::NARWriterError(io::Error::new(
+                    io::ErrorKind::NotFound,
+                    format!("blob with digest {} not found", &digest),
+                ))),
+            }?;
+
+            nar_node
+                .file(
+                    proto_file_node.executable,
+                    proto_file_node.size,
+                    &mut blob_reader.compat(),
+                )
+                .await
+                .map_err(RenderError::NARWriterError)?;
+        }
+        castorepb::node::Node::Directory(proto_directory_node) => {
+            let digest_len = proto_directory_node.digest.len();
+            let digest = proto_directory_node
+                .digest
+                .clone()
+                .try_into()
+                .map_err(|_| {
+                    RenderError::StoreError(io::Error::new(
+                        io::ErrorKind::InvalidData,
+                        format!("invalid digest len {} in directory node", digest_len),
+                    ))
+                })?;
+
+            // look it up with the directory service
+            match directory_service
+                .as_ref()
+                .get(&digest)
+                .await
+                .map_err(|e| RenderError::StoreError(e.into()))?
+            {
+                // if it's None, that's an error!
+                None => Err(RenderError::DirectoryNotFound(
+                    digest,
+                    proto_directory_node.name.clone(),
+                ))?,
+                Some(proto_directory) => {
+                    // start a directory node
+                    let mut nar_node_directory = nar_node
+                        .directory()
+                        .await
+                        .map_err(RenderError::NARWriterError)?;
+
+                    // We put blob_service, directory_service back here whenever we come up from
+                    // the recursion.
+                    let mut blob_service = blob_service;
+                    let mut directory_service = directory_service;
+
+                    // for each node in the directory, create a new entry with its name,
+                    // and then recurse on that entry.
+                    for proto_node in proto_directory.nodes() {
+                        let child_node = nar_node_directory
+                            .entry(proto_node.get_name())
+                            .await
+                            .map_err(RenderError::NARWriterError)?;
+
+                        (blob_service, directory_service) =
+                            walk_node(child_node, &proto_node, blob_service, directory_service)
+                                .await?;
+                    }
+
+                    // close the directory
+                    nar_node_directory
+                        .close()
+                        .await
+                        .map_err(RenderError::NARWriterError)?;
+
+                    return Ok((blob_service, directory_service));
+                }
+            }
+        }
+    }
+
+    Ok((blob_service, directory_service))
+}
diff --git a/tvix/store/src/pathinfoservice/from_addr.rs b/tvix/store/src/pathinfoservice/from_addr.rs
new file mode 100644
index 000000000000..5113b19c1535
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/from_addr.rs
@@ -0,0 +1,187 @@
+use crate::proto::path_info_service_client::PathInfoServiceClient;
+
+use super::{
+    GRPCPathInfoService, MemoryPathInfoService, NixHTTPPathInfoService, PathInfoService,
+    SledPathInfoService,
+};
+
+use nix_compat::narinfo;
+use std::sync::Arc;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService, Error};
+use url::Url;
+
+/// Constructs a new instance of a [PathInfoService] from an URI.
+///
+/// The following URIs are supported:
+/// - `memory:`
+///   Uses a in-memory implementation.
+/// - `sled:`
+///   Uses a in-memory sled implementation.
+/// - `sled:///absolute/path/to/somewhere`
+///   Uses sled, using a path on the disk for persistency. Can be only opened
+///   from one process at the same time.
+/// - `nix+https://cache.nixos.org?trusted-public-keys=cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=`
+///   Exposes the Nix binary cache as a PathInfoService, ingesting NARs into the
+///   {Blob,Directory}Service. You almost certainly want to use this with some cache.
+///   The `trusted-public-keys` URL parameter can be provided, which will then
+///   enable signature verification.
+/// - `grpc+unix:///absolute/path/to/somewhere`
+///   Connects to a local tvix-store gRPC service via Unix socket.
+/// - `grpc+http://host:port`, `grpc+https://host:port`
+///    Connects to a (remote) tvix-store gRPC service.
+///
+/// As the [PathInfoService] needs to talk to [BlobService] and [DirectoryService],
+/// these also need to be passed in.
+pub async fn from_addr(
+    uri: &str,
+    blob_service: Arc<dyn BlobService>,
+    directory_service: Arc<dyn DirectoryService>,
+) -> Result<Box<dyn PathInfoService>, Error> {
+    let url =
+        Url::parse(uri).map_err(|e| Error::StorageError(format!("unable to parse url: {}", e)))?;
+
+    Ok(if url.scheme() == "memory" {
+        // memory doesn't support host or path in the URL.
+        if url.has_host() || !url.path().is_empty() {
+            return Err(Error::StorageError("invalid url".to_string()));
+        }
+        Box::new(MemoryPathInfoService::new(blob_service, directory_service))
+    } else if url.scheme() == "sled" {
+        // sled doesn't support host, and a path can be provided (otherwise
+        // it'll live in memory only).
+        if url.has_host() {
+            return Err(Error::StorageError("no host allowed".to_string()));
+        }
+
+        if url.path() == "/" {
+            return Err(Error::StorageError(
+                "cowardly refusing to open / with sled".to_string(),
+            ));
+        }
+
+        // TODO: expose other parameters as URL parameters?
+
+        if url.path().is_empty() {
+            return Ok(Box::new(
+                SledPathInfoService::new_temporary(blob_service, directory_service)
+                    .map_err(|e| Error::StorageError(e.to_string()))?,
+            ));
+        }
+        return Ok(Box::new(
+            SledPathInfoService::new(url.path(), blob_service, directory_service)
+                .map_err(|e| Error::StorageError(e.to_string()))?,
+        ));
+    } else if url.scheme() == "nix+http" || url.scheme() == "nix+https" {
+        // Stringify the URL and remove the nix+ prefix.
+        // We can't use `url.set_scheme(rest)`, as it disallows
+        // setting something http(s) that previously wasn't.
+        let new_url = Url::parse(url.to_string().strip_prefix("nix+").unwrap()).unwrap();
+
+        let mut nix_http_path_info_service =
+            NixHTTPPathInfoService::new(new_url, blob_service, directory_service);
+
+        let pairs = &url.query_pairs();
+        for (k, v) in pairs.into_iter() {
+            if k == "trusted-public-keys" {
+                let pubkey_strs: Vec<_> = v.split_ascii_whitespace().collect();
+
+                let mut pubkeys: Vec<narinfo::PubKey> = Vec::with_capacity(pubkey_strs.len());
+                for pubkey_str in pubkey_strs {
+                    pubkeys
+                        .push(narinfo::PubKey::parse(pubkey_str).map_err(|e| {
+                            Error::StorageError(format!("invalid public key: {e}"))
+                        })?);
+                }
+
+                nix_http_path_info_service.set_public_keys(pubkeys);
+            }
+        }
+
+        Box::new(nix_http_path_info_service)
+    } else if url.scheme().starts_with("grpc+") {
+        // schemes starting with grpc+ go to the GRPCPathInfoService.
+        //   That's normally grpc+unix for unix sockets, and grpc+http(s) for the HTTP counterparts.
+        // - In the case of unix sockets, there must be a path, but may not be a host.
+        // - In the case of non-unix sockets, there must be a host, but no path.
+        // Constructing the channel is handled by tvix_castore::channel::from_url.
+        let client = PathInfoServiceClient::new(tvix_castore::tonic::channel_from_url(&url).await?);
+        Box::new(GRPCPathInfoService::from_client(client))
+    } else {
+        Err(Error::StorageError(format!(
+            "unknown scheme: {}",
+            url.scheme()
+        )))?
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::from_addr;
+    use lazy_static::lazy_static;
+    use tempfile::TempDir;
+    use test_case::test_case;
+    use tvix_castore::utils::{gen_blob_service, gen_directory_service};
+
+    lazy_static! {
+        static ref TMPDIR_SLED_1: TempDir = TempDir::new().unwrap();
+        static ref TMPDIR_SLED_2: TempDir = TempDir::new().unwrap();
+    }
+
+    // the gRPC tests below don't fail, because we connect lazily.
+
+    /// This uses a unsupported scheme.
+    #[test_case("http://foo.example/test", false; "unsupported scheme")]
+    /// This configures sled in temporary mode.
+    #[test_case("sled://", true; "sled valid temporary")]
+    /// This configures sled with /, which should fail.
+    #[test_case("sled:///", false; "sled invalid root")]
+    /// This configures sled with a host, not path, which should fail.
+    #[test_case("sled://foo.example", false; "sled invalid host")]
+    /// This configures sled with a valid path path, which should succeed.
+    #[test_case(&format!("sled://{}", &TMPDIR_SLED_1.path().to_str().unwrap()), true; "sled valid path")]
+    /// This configures sled with a host, and a valid path path, which should fail.
+    #[test_case(&format!("sled://foo.example{}", &TMPDIR_SLED_2.path().to_str().unwrap()), false; "sled invalid host with valid path")]
+    /// This correctly sets the scheme, and doesn't set a path.
+    #[test_case("memory://", true; "memory valid")]
+    /// This sets a memory url host to `foo`
+    #[test_case("memory://foo", false; "memory invalid host")]
+    /// This sets a memory url path to "/", which is invalid.
+    #[test_case("memory:///", false; "memory invalid root path")]
+    /// This sets a memory url path to "/foo", which is invalid.
+    #[test_case("memory:///foo", false; "memory invalid root path foo")]
+    /// Correct Scheme for the cache.nixos.org binary cache.
+    #[test_case("nix+https://cache.nixos.org", true; "correct nix+https")]
+    /// Correct Scheme for the cache.nixos.org binary cache (HTTP URL).
+    #[test_case("nix+http://cache.nixos.org", true; "correct nix+http")]
+    /// Correct Scheme for Nix HTTP Binary cache, with a subpath.
+    #[test_case("nix+http://192.0.2.1/foo", true; "correct nix http with subpath")]
+    /// Correct Scheme for Nix HTTP Binary cache, with a subpath and port.
+    #[test_case("nix+http://[::1]:8080/foo", true; "correct nix http with subpath and port")]
+    /// Correct Scheme for the cache.nixos.org binary cache, and correct trusted public key set
+    #[test_case("nix+https://cache.nixos.org?trusted-public-keys=cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=", true; "correct nix+https with trusted-public-key")]
+    /// Correct Scheme for the cache.nixos.org binary cache, and two correct trusted public keys set
+    #[test_case("nix+https://cache.nixos.org?trusted-public-keys=cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=%20foo:jp4fCEx9tBEId/L0ZsVJ26k0wC0fu7vJqLjjIGFkup8=", true; "correct nix+https with two trusted-public-key")]
+    /// Correct scheme to connect to a unix socket.
+    #[test_case("grpc+unix:///path/to/somewhere", true; "grpc valid unix socket")]
+    /// Correct scheme for unix socket, but setting a host too, which is invalid.
+    #[test_case("grpc+unix://host.example/path/to/somewhere", false; "grpc invalid unix socket and host")]
+    /// Correct scheme to connect to localhost, with port 12345
+    #[test_case("grpc+http://[::1]:12345", true; "grpc valid IPv6 localhost port 12345")]
+    /// Correct scheme to connect to localhost over http, without specifying a port.
+    #[test_case("grpc+http://localhost", true; "grpc valid http host without port")]
+    /// Correct scheme to connect to localhost over http, without specifying a port.
+    #[test_case("grpc+https://localhost", true; "grpc valid https host without port")]
+    /// Correct scheme to connect to localhost over http, but with additional path, which is invalid.
+    #[test_case("grpc+http://localhost/some-path", false; "grpc valid invalid host and path")]
+    #[tokio::test]
+    async fn test_from_addr_tokio(uri_str: &str, is_ok: bool) {
+        let resp = from_addr(
+            uri_str,
+            gen_blob_service().into(),
+            gen_directory_service().into(),
+        )
+        .await;
+
+        assert_eq!(resp.is_ok(), is_ok);
+    }
+}
diff --git a/tvix/store/src/pathinfoservice/fs/mod.rs b/tvix/store/src/pathinfoservice/fs/mod.rs
new file mode 100644
index 000000000000..45d59fd0bcb8
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/fs/mod.rs
@@ -0,0 +1,79 @@
+use futures::stream::BoxStream;
+use futures::StreamExt;
+use tonic::async_trait;
+use tvix_castore::fs::{RootNodes, TvixStoreFs};
+use tvix_castore::proto as castorepb;
+use tvix_castore::Error;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService};
+
+use super::PathInfoService;
+
+/// Helper to construct a [TvixStoreFs] from a [BlobService], [DirectoryService]
+/// and [PathInfoService].
+/// This avoids users to have to interact with the wrapper struct directly, as
+/// it leaks into the type signature of TvixStoreFS.
+pub fn make_fs<BS, DS, PS>(
+    blob_service: BS,
+    directory_service: DS,
+    path_info_service: PS,
+    list_root: bool,
+) -> TvixStoreFs<BS, DS, RootNodesWrapper<PS>>
+where
+    BS: AsRef<dyn BlobService> + Send + Clone + 'static,
+    DS: AsRef<dyn DirectoryService> + Send + Clone + 'static,
+    PS: AsRef<dyn PathInfoService> + Send + Sync + Clone + 'static,
+{
+    TvixStoreFs::new(
+        blob_service,
+        directory_service,
+        RootNodesWrapper(path_info_service),
+        list_root,
+    )
+}
+
+/// Wrapper to satisfy Rust's orphan rules for trait implementations, as
+/// RootNodes is coming from the [tvix-castore] crate.
+#[doc(hidden)]
+#[derive(Clone, Debug)]
+pub struct RootNodesWrapper<T>(pub(crate) T);
+
+/// Implements root node lookup for any [PathInfoService]. This represents a flat
+/// directory structure like /nix/store where each entry in the root filesystem
+/// directory corresponds to a CA node.
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+#[async_trait]
+impl<T> RootNodes for RootNodesWrapper<T>
+where
+    T: AsRef<dyn PathInfoService> + Send + Sync,
+{
+    async fn get_by_basename(&self, name: &[u8]) -> Result<Option<castorepb::node::Node>, Error> {
+        let Ok(store_path) = nix_compat::store_path::StorePath::from_bytes(name) else {
+            return Ok(None);
+        };
+
+        Ok(self
+            .0
+            .as_ref()
+            .get(*store_path.digest())
+            .await?
+            .map(|path_info| {
+                path_info
+                    .node
+                    .expect("missing root node")
+                    .node
+                    .expect("empty node")
+            }))
+    }
+
+    fn list(&self) -> BoxStream<Result<castorepb::node::Node, Error>> {
+        Box::pin(self.0.as_ref().list().map(|result| {
+            result.map(|path_info| {
+                path_info
+                    .node
+                    .expect("missing root node")
+                    .node
+                    .expect("empty node")
+            })
+        }))
+    }
+}
diff --git a/tvix/store/src/pathinfoservice/grpc.rs b/tvix/store/src/pathinfoservice/grpc.rs
new file mode 100644
index 000000000000..4e15a5bb0b5b
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/grpc.rs
@@ -0,0 +1,204 @@
+use super::PathInfoService;
+use crate::proto::{self, ListPathInfoRequest, PathInfo};
+use async_stream::try_stream;
+use futures::stream::BoxStream;
+use tonic::{async_trait, transport::Channel, Code};
+use tvix_castore::{proto as castorepb, Error};
+
+/// Connects to a (remote) tvix-store PathInfoService over gRPC.
+#[derive(Clone)]
+pub struct GRPCPathInfoService {
+    /// The internal reference to a gRPC client.
+    /// Cloning it is cheap, and it internally handles concurrent requests.
+    grpc_client: proto::path_info_service_client::PathInfoServiceClient<Channel>,
+}
+
+impl GRPCPathInfoService {
+    /// construct a [GRPCPathInfoService] from a [proto::path_info_service_client::PathInfoServiceClient].
+    /// panics if called outside the context of a tokio runtime.
+    pub fn from_client(
+        grpc_client: proto::path_info_service_client::PathInfoServiceClient<Channel>,
+    ) -> Self {
+        Self { grpc_client }
+    }
+}
+
+#[async_trait]
+impl PathInfoService for GRPCPathInfoService {
+    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
+        let path_info = self
+            .grpc_client
+            .clone()
+            .get(proto::GetPathInfoRequest {
+                by_what: Some(proto::get_path_info_request::ByWhat::ByOutputHash(
+                    digest.to_vec().into(),
+                )),
+            })
+            .await;
+
+        match path_info {
+            Ok(path_info) => {
+                let path_info = path_info.into_inner();
+
+                path_info
+                    .validate()
+                    .map_err(|e| Error::StorageError(format!("invalid pathinfo: {}", e)))?;
+
+                Ok(Some(path_info))
+            }
+            Err(e) if e.code() == Code::NotFound => Ok(None),
+            Err(e) => Err(Error::StorageError(e.to_string())),
+        }
+    }
+
+    async fn put(&self, path_info: PathInfo) -> Result<PathInfo, Error> {
+        let path_info = self
+            .grpc_client
+            .clone()
+            .put(path_info)
+            .await
+            .map_err(|e| Error::StorageError(e.to_string()))?
+            .into_inner();
+
+        Ok(path_info)
+    }
+
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), Error> {
+        let path_info = self
+            .grpc_client
+            .clone()
+            .calculate_nar(castorepb::Node {
+                node: Some(root_node.clone()),
+            })
+            .await
+            .map_err(|e| Error::StorageError(e.to_string()))?
+            .into_inner();
+
+        let nar_sha256: [u8; 32] = path_info
+            .nar_sha256
+            .to_vec()
+            .try_into()
+            .map_err(|_e| Error::StorageError("invalid digest length".to_string()))?;
+
+        Ok((path_info.nar_size, nar_sha256))
+    }
+
+    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
+        let mut grpc_client = self.grpc_client.clone();
+
+        let stream = try_stream! {
+            let resp = grpc_client.list(ListPathInfoRequest::default()).await;
+
+            let mut stream = resp.map_err(|e| Error::StorageError(e.to_string()))?.into_inner();
+
+            loop {
+                match stream.message().await {
+                    Ok(o) => match o {
+                        Some(pathinfo) => {
+                            // validate the pathinfo
+                            if let Err(e) = pathinfo.validate() {
+                                Err(Error::StorageError(format!(
+                                    "pathinfo {:?} failed validation: {}",
+                                    pathinfo, e
+                                )))?;
+                            }
+                            yield pathinfo
+                        }
+                        None => {
+                            return;
+                        },
+                    },
+                    Err(e) => Err(Error::StorageError(e.to_string()))?,
+                }
+            }
+        };
+
+        Box::pin(stream)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use tempfile::TempDir;
+    use tokio::net::UnixListener;
+    use tokio_retry::strategy::ExponentialBackoff;
+    use tokio_retry::Retry;
+    use tokio_stream::wrappers::UnixListenerStream;
+
+    use crate::pathinfoservice::MemoryPathInfoService;
+    use crate::proto::path_info_service_client::PathInfoServiceClient;
+    use crate::proto::GRPCPathInfoServiceWrapper;
+    use crate::tests::fixtures;
+    use crate::tests::utils::gen_blob_service;
+    use crate::tests::utils::gen_directory_service;
+
+    use super::GRPCPathInfoService;
+    use super::PathInfoService;
+
+    /// This ensures connecting via gRPC works as expected.
+    #[tokio::test]
+    async fn test_valid_unix_path_ping_pong() {
+        let tmpdir = TempDir::new().unwrap();
+        let socket_path = tmpdir.path().join("daemon");
+
+        let path_clone = socket_path.clone();
+
+        // Spin up a server
+        tokio::spawn(async {
+            let uds = UnixListener::bind(path_clone).unwrap();
+            let uds_stream = UnixListenerStream::new(uds);
+
+            // spin up a new server
+            let mut server = tonic::transport::Server::builder();
+            let router = server.add_service(
+                crate::proto::path_info_service_server::PathInfoServiceServer::new(
+                    GRPCPathInfoServiceWrapper::new(Box::new(MemoryPathInfoService::new(
+                        gen_blob_service(),
+                        gen_directory_service(),
+                    ))
+                        as Box<dyn PathInfoService>),
+                ),
+            );
+            router.serve_with_incoming(uds_stream).await
+        });
+
+        // wait for the socket to be created
+        Retry::spawn(
+            ExponentialBackoff::from_millis(20).max_delay(Duration::from_secs(10)),
+            || async {
+                if socket_path.exists() {
+                    Ok(())
+                } else {
+                    Err(())
+                }
+            },
+        )
+        .await
+        .expect("failed to wait for socket");
+
+        // prepare a client
+        let grpc_client = {
+            let url = url::Url::parse(&format!("grpc+unix://{}", socket_path.display()))
+                .expect("must parse");
+            let client = PathInfoServiceClient::new(
+                tvix_castore::tonic::channel_from_url(&url)
+                    .await
+                    .expect("must succeed"),
+            );
+
+            GRPCPathInfoService::from_client(client)
+        };
+
+        let path_info = grpc_client
+            .get(fixtures::DUMMY_OUTPUT_HASH.to_vec().try_into().unwrap())
+            .await
+            .expect("must not be error");
+
+        assert!(path_info.is_none());
+    }
+}
diff --git a/tvix/store/src/pathinfoservice/memory.rs b/tvix/store/src/pathinfoservice/memory.rs
new file mode 100644
index 000000000000..f8435dbbf809
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/memory.rs
@@ -0,0 +1,84 @@
+use super::PathInfoService;
+use crate::{nar::calculate_size_and_sha256, proto::PathInfo};
+use futures::stream::{iter, BoxStream};
+use std::{
+    collections::HashMap,
+    sync::{Arc, RwLock},
+};
+use tonic::async_trait;
+use tvix_castore::proto as castorepb;
+use tvix_castore::Error;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService};
+
+pub struct MemoryPathInfoService<BS, DS> {
+    db: Arc<RwLock<HashMap<[u8; 20], PathInfo>>>,
+
+    blob_service: BS,
+    directory_service: DS,
+}
+
+impl<BS, DS> MemoryPathInfoService<BS, DS> {
+    pub fn new(blob_service: BS, directory_service: DS) -> Self {
+        Self {
+            db: Default::default(),
+            blob_service,
+            directory_service,
+        }
+    }
+}
+
+#[async_trait]
+impl<BS, DS> PathInfoService for MemoryPathInfoService<BS, DS>
+where
+    BS: AsRef<dyn BlobService> + Send + Sync,
+    DS: AsRef<dyn DirectoryService> + Send + Sync,
+{
+    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
+        let db = self.db.read().unwrap();
+
+        match db.get(&digest) {
+            None => Ok(None),
+            Some(path_info) => Ok(Some(path_info.clone())),
+        }
+    }
+
+    async fn put(&self, path_info: PathInfo) -> Result<PathInfo, Error> {
+        // Call validate on the received PathInfo message.
+        match path_info.validate() {
+            Err(e) => Err(Error::InvalidRequest(format!(
+                "failed to validate PathInfo: {}",
+                e
+            ))),
+
+            // In case the PathInfo is valid, and we were able to extract a NixPath, store it in the database.
+            // This overwrites existing PathInfo objects.
+            Ok(nix_path) => {
+                let mut db = self.db.write().unwrap();
+                db.insert(*nix_path.digest(), path_info.clone());
+
+                Ok(path_info)
+            }
+        }
+    }
+
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), Error> {
+        calculate_size_and_sha256(root_node, &self.blob_service, &self.directory_service)
+            .await
+            .map_err(|e| Error::StorageError(e.to_string()))
+    }
+
+    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
+        let db = self.db.read().unwrap();
+
+        // Copy all elements into a list.
+        // This is a bit ugly, because we can't have db escape the lifetime
+        // of this function, but elements need to be returned owned anyways, and this in-
+        // memory impl is only for testing purposes anyways.
+        let items: Vec<_> = db.iter().map(|(_k, v)| Ok(v.clone())).collect();
+
+        Box::pin(iter(items))
+    }
+}
diff --git a/tvix/store/src/pathinfoservice/mod.rs b/tvix/store/src/pathinfoservice/mod.rs
new file mode 100644
index 000000000000..55ada92b7e88
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/mod.rs
@@ -0,0 +1,52 @@
+mod from_addr;
+mod grpc;
+mod memory;
+mod nix_http;
+mod sled;
+
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+mod fs;
+
+use futures::stream::BoxStream;
+use tonic::async_trait;
+use tvix_castore::proto as castorepb;
+use tvix_castore::Error;
+
+use crate::proto::PathInfo;
+
+pub use self::from_addr::from_addr;
+pub use self::grpc::GRPCPathInfoService;
+pub use self::memory::MemoryPathInfoService;
+pub use self::nix_http::NixHTTPPathInfoService;
+pub use self::sled::SledPathInfoService;
+
+#[cfg(any(feature = "fuse", feature = "virtiofs"))]
+pub use self::fs::make_fs;
+
+/// The base trait all PathInfo services need to implement.
+#[async_trait]
+pub trait PathInfoService: Send + Sync {
+    /// Retrieve a PathInfo message by the output digest.
+    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error>;
+
+    /// Store a PathInfo message. Implementations MUST call validate and reject
+    /// invalid messages.
+    async fn put(&self, path_info: PathInfo) -> Result<PathInfo, Error>;
+
+    /// Return the nar size and nar sha256 digest for a given root node.
+    /// This can be used to calculate NAR-based output paths,
+    /// and implementations are encouraged to cache it.
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), Error>;
+
+    /// Iterate over all PathInfo objects in the store.
+    /// Implementations can decide to disallow listing.
+    ///
+    /// This returns a pinned, boxed stream. The pinning allows for it to be polled easily,
+    /// and the box allows different underlying stream implementations to be returned since
+    /// Rust doesn't support this as a generic in traits yet. This is the same thing that
+    /// [async_trait] generates, but for streams instead of futures.
+    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>>;
+}
diff --git a/tvix/store/src/pathinfoservice/nix_http.rs b/tvix/store/src/pathinfoservice/nix_http.rs
new file mode 100644
index 000000000000..7b4130fcae27
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/nix_http.rs
@@ -0,0 +1,312 @@
+use std::io::{self, BufRead, Read, Write};
+
+use data_encoding::BASE64;
+use futures::{stream::BoxStream, TryStreamExt};
+use nix_compat::{
+    narinfo::{self, NarInfo},
+    nixbase32,
+};
+use reqwest::StatusCode;
+use sha2::{digest::FixedOutput, Digest, Sha256};
+use tonic::async_trait;
+use tracing::{debug, instrument, warn};
+use tvix_castore::{
+    blobservice::BlobService, directoryservice::DirectoryService, proto as castorepb, Error,
+};
+
+use crate::proto::PathInfo;
+
+use super::PathInfoService;
+
+/// NixHTTPPathInfoService acts as a bridge in between the Nix HTTP Binary cache
+/// protocol provided by Nix binary caches such as cache.nixos.org, and the Tvix
+/// Store Model.
+/// It implements the [PathInfoService] trait in an interesting way:
+/// Every [PathInfoService::get] fetches the .narinfo and referred NAR file,
+/// inserting components into a [BlobService] and [DirectoryService], then
+/// returning a [PathInfo] struct with the root.
+///
+/// Due to this being quite a costly operation, clients are expected to layer
+/// this service with store composition, so they're only ingested once.
+///
+/// The client is expected to be (indirectly) using the same [BlobService] and
+/// [DirectoryService], so able to fetch referred Directories and Blobs.
+/// [PathInfoService::put] and [PathInfoService::calculate_nar] are not
+/// implemented and return an error if called.
+/// TODO: what about reading from nix-cache-info?
+pub struct NixHTTPPathInfoService<BS, DS> {
+    base_url: url::Url,
+    http_client: reqwest::Client,
+
+    blob_service: BS,
+    directory_service: DS,
+
+    /// An optional list of [narinfo::PubKey].
+    /// If set, the .narinfo files received need to have correct signature by at least one of these.
+    public_keys: Option<Vec<narinfo::PubKey>>,
+}
+
+impl<BS, DS> NixHTTPPathInfoService<BS, DS> {
+    pub fn new(base_url: url::Url, blob_service: BS, directory_service: DS) -> Self {
+        Self {
+            base_url,
+            http_client: reqwest::Client::new(),
+            blob_service,
+            directory_service,
+
+            public_keys: None,
+        }
+    }
+
+    /// Configures [Self] to validate NARInfo fingerprints with the public keys passed.
+    pub fn set_public_keys(&mut self, public_keys: Vec<narinfo::PubKey>) {
+        self.public_keys = Some(public_keys);
+    }
+}
+
+#[async_trait]
+impl<BS, DS> PathInfoService for NixHTTPPathInfoService<BS, DS>
+where
+    BS: AsRef<dyn BlobService> + Send + Sync + Clone + 'static,
+    DS: AsRef<dyn DirectoryService> + Send + Sync + Clone + 'static,
+{
+    #[instrument(skip_all, err, fields(path.digest=BASE64.encode(&digest)))]
+    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
+        let narinfo_url = self
+            .base_url
+            .join(&format!("{}.narinfo", nixbase32::encode(&digest)))
+            .map_err(|e| {
+                warn!(e = %e, "unable to join URL");
+                io::Error::new(io::ErrorKind::InvalidInput, "unable to join url")
+            })?;
+
+        debug!(narinfo_url= %narinfo_url, "constructed NARInfo url");
+
+        let resp = self
+            .http_client
+            .get(narinfo_url)
+            .send()
+            .await
+            .map_err(|e| {
+                warn!(e=%e,"unable to send NARInfo request");
+                io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    "unable to send NARInfo request",
+                )
+            })?;
+
+        // In the case of a 404, return a NotFound.
+        // We also return a NotFound in case of a 403 - this is to match the behaviour as Nix,
+        // when querying nix-cache.s3.amazonaws.com directly, rather than cache.nixos.org.
+        if resp.status() == StatusCode::NOT_FOUND || resp.status() == StatusCode::FORBIDDEN {
+            return Ok(None);
+        }
+
+        let narinfo_str = resp.text().await.map_err(|e| {
+            warn!(e=%e,"unable to decode response as string");
+            io::Error::new(
+                io::ErrorKind::InvalidData,
+                "unable to decode response as string",
+            )
+        })?;
+
+        // parse the received narinfo
+        let narinfo = NarInfo::parse(&narinfo_str).map_err(|e| {
+            warn!(e=%e,"unable to parse response as NarInfo");
+            io::Error::new(
+                io::ErrorKind::InvalidData,
+                "unable to parse response as NarInfo",
+            )
+        })?;
+
+        // if [self.public_keys] is set, ensure there's at least one valid signature.
+        if let Some(public_keys) = &self.public_keys {
+            let fingerprint = narinfo.fingerprint();
+
+            if !public_keys.iter().any(|pubkey| {
+                narinfo
+                    .signatures
+                    .iter()
+                    .any(|sig| pubkey.verify(&fingerprint, sig))
+            }) {
+                warn!("no valid signature found");
+                Err(io::Error::new(
+                    io::ErrorKind::InvalidData,
+                    "no valid signature found",
+                ))?;
+            }
+        }
+
+        // Convert to a (sparse) PathInfo. We still need to populate the node field,
+        // and for this we need to download the NAR file.
+        // FUTUREWORK: Keep some database around mapping from narsha256 to
+        // (unnamed) rootnode, so we can use that (and the name from the
+        // StorePath) and avoid downloading the same NAR a second time.
+        let pathinfo: PathInfo = (&narinfo).into();
+
+        // create a request for the NAR file itself.
+        let nar_url = self.base_url.join(narinfo.url).map_err(|e| {
+            warn!(e = %e, "unable to join URL");
+            io::Error::new(io::ErrorKind::InvalidInput, "unable to join url")
+        })?;
+        debug!(nar_url= %nar_url, "constructed NAR url");
+
+        let resp = self
+            .http_client
+            .get(nar_url.clone())
+            .send()
+            .await
+            .map_err(|e| {
+                warn!(e=%e,"unable to send NAR request");
+                io::Error::new(io::ErrorKind::InvalidInput, "unable to send NAR request")
+            })?;
+
+        // if the request is not successful, return an error.
+        if !resp.status().is_success() {
+            return Err(Error::StorageError(format!(
+                "unable to retrieve NAR at {}, status {}",
+                nar_url,
+                resp.status()
+            )));
+        }
+
+        // get an AsyncRead of the response body.
+        let async_r = tokio_util::io::StreamReader::new(resp.bytes_stream().map_err(|e| {
+            let e = e.without_url();
+            warn!(e=%e, "failed to get response body");
+            io::Error::new(io::ErrorKind::BrokenPipe, e.to_string())
+        }));
+        let sync_r = tokio_util::io::SyncIoBridge::new(async_r);
+
+        // handle decompression, by wrapping the reader.
+        let sync_r: Box<dyn BufRead + Send> = match narinfo.compression {
+            Some("none") => Box::new(sync_r),
+            Some("xz") => Box::new(io::BufReader::new(xz2::read::XzDecoder::new(sync_r))),
+            Some(comp) => {
+                return Err(Error::InvalidRequest(
+                    format!("unsupported compression: {}", comp).to_string(),
+                ))
+            }
+            None => {
+                return Err(Error::InvalidRequest(
+                    "unsupported compression: bzip2".to_string(),
+                ))
+            }
+        };
+
+        let res = tokio::task::spawn_blocking({
+            let blob_service = self.blob_service.clone();
+            let directory_service = self.directory_service.clone();
+            move || -> io::Result<_> {
+                // Wrap the reader once more, so we can calculate NarSize and NarHash
+                let mut sync_r = io::BufReader::new(NarReader::from(sync_r));
+                let root_node = crate::nar::read_nar(&mut sync_r, blob_service, directory_service)?;
+
+                let (_, nar_hash, nar_size) = sync_r.into_inner().into_inner();
+
+                Ok((root_node, nar_hash, nar_size))
+            }
+        })
+        .await
+        .unwrap();
+
+        match res {
+            Ok((root_node, nar_hash, nar_size)) => {
+                // ensure the ingested narhash and narsize do actually match.
+                if narinfo.nar_size != nar_size {
+                    warn!(
+                        narinfo.nar_size = narinfo.nar_size,
+                        http.nar_size = nar_size,
+                        "NARSize mismatch"
+                    );
+                    Err(io::Error::new(
+                        io::ErrorKind::InvalidData,
+                        "NarSize mismatch".to_string(),
+                    ))?;
+                } else if narinfo.nar_hash != nar_hash {
+                    warn!(
+                        narinfo.nar_hash = BASE64.encode(&narinfo.nar_hash),
+                        http.nar_hash = BASE64.encode(&nar_hash),
+                        "NarHash mismatch"
+                    );
+                    Err(io::Error::new(
+                        io::ErrorKind::InvalidData,
+                        "NarHash mismatch".to_string(),
+                    ))?;
+                }
+
+                Ok(Some(PathInfo {
+                    node: Some(castorepb::Node {
+                        // set the name of the root node to the digest-name of the store path.
+                        node: Some(
+                            root_node.rename(narinfo.store_path.to_string().to_owned().into()),
+                        ),
+                    }),
+                    references: pathinfo.references,
+                    narinfo: pathinfo.narinfo,
+                }))
+            }
+            Err(e) => Err(e.into()),
+        }
+    }
+
+    #[instrument(skip_all, fields(path_info=?_path_info))]
+    async fn put(&self, _path_info: PathInfo) -> Result<PathInfo, Error> {
+        Err(Error::InvalidRequest(
+            "put not supported for this backend".to_string(),
+        ))
+    }
+
+    #[instrument(skip_all, fields(root_node=?root_node))]
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), Error> {
+        Err(Error::InvalidRequest(
+            "calculate_nar not supported for this backend".to_string(),
+        ))
+    }
+
+    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
+        Box::pin(futures::stream::once(async {
+            Err(Error::InvalidRequest(
+                "list not supported for this backend".to_string(),
+            ))
+        }))
+    }
+}
+
+/// Small helper reader implementing [std::io::Read].
+/// It can be used to wrap another reader, counts the number of bytes read
+/// and the sha256 digest of the contents.
+struct NarReader<R: Read> {
+    r: R,
+
+    sha256: sha2::Sha256,
+    bytes_read: u64,
+}
+
+impl<R: Read> NarReader<R> {
+    pub fn from(inner: R) -> Self {
+        Self {
+            r: inner,
+            sha256: Sha256::new(),
+            bytes_read: 0,
+        }
+    }
+
+    /// Returns the (remaining) inner reader, the sha256 digest and the number of bytes read.
+    pub fn into_inner(self) -> (R, [u8; 32], u64) {
+        (self.r, self.sha256.finalize_fixed().into(), self.bytes_read)
+    }
+}
+
+impl<R: Read> Read for NarReader<R> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.r.read(buf).map(|n| {
+            self.bytes_read += n as u64;
+            self.sha256.write_all(&buf[..n]).unwrap();
+            n
+        })
+    }
+}
diff --git a/tvix/store/src/pathinfoservice/sled.rs b/tvix/store/src/pathinfoservice/sled.rs
new file mode 100644
index 000000000000..7b6d7fd7abcd
--- /dev/null
+++ b/tvix/store/src/pathinfoservice/sled.rs
@@ -0,0 +1,140 @@
+use super::PathInfoService;
+use crate::nar::calculate_size_and_sha256;
+use crate::proto::PathInfo;
+use futures::stream::iter;
+use futures::stream::BoxStream;
+use prost::Message;
+use std::path::Path;
+use tonic::async_trait;
+use tracing::warn;
+use tvix_castore::proto as castorepb;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService, Error};
+
+/// SledPathInfoService stores PathInfo in a [sled](https://github.com/spacejam/sled).
+///
+/// The PathInfo messages are stored as encoded protos, and keyed by their output hash,
+/// as that's currently the only request type available.
+pub struct SledPathInfoService<BS, DS> {
+    db: sled::Db,
+
+    blob_service: BS,
+    directory_service: DS,
+}
+
+impl<BS, DS> SledPathInfoService<BS, DS> {
+    pub fn new<P: AsRef<Path>>(
+        p: P,
+        blob_service: BS,
+        directory_service: DS,
+    ) -> Result<Self, sled::Error> {
+        let config = sled::Config::default()
+            .use_compression(false) // is a required parameter
+            .path(p);
+        let db = config.open()?;
+
+        Ok(Self {
+            db,
+            blob_service,
+            directory_service,
+        })
+    }
+
+    pub fn new_temporary(blob_service: BS, directory_service: DS) -> Result<Self, sled::Error> {
+        let config = sled::Config::default().temporary(true);
+        let db = config.open()?;
+
+        Ok(Self {
+            db,
+            blob_service,
+            directory_service,
+        })
+    }
+}
+
+#[async_trait]
+impl<BS, DS> PathInfoService for SledPathInfoService<BS, DS>
+where
+    BS: AsRef<dyn BlobService> + Send + Sync,
+    DS: AsRef<dyn DirectoryService> + Send + Sync,
+{
+    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
+        match self.db.get(digest) {
+            Ok(None) => Ok(None),
+            Ok(Some(data)) => match PathInfo::decode(&*data) {
+                Ok(path_info) => Ok(Some(path_info)),
+                Err(e) => {
+                    warn!("failed to decode stored PathInfo: {}", e);
+                    Err(Error::StorageError(format!(
+                        "failed to decode stored PathInfo: {}",
+                        e
+                    )))
+                }
+            },
+            Err(e) => {
+                warn!("failed to retrieve PathInfo: {}", e);
+                Err(Error::StorageError(format!(
+                    "failed to retrieve PathInfo: {}",
+                    e
+                )))
+            }
+        }
+    }
+
+    async fn put(&self, path_info: PathInfo) -> Result<PathInfo, Error> {
+        // Call validate on the received PathInfo message.
+        match path_info.validate() {
+            Err(e) => Err(Error::InvalidRequest(format!(
+                "failed to validate PathInfo: {}",
+                e
+            ))),
+            // In case the PathInfo is valid, and we were able to extract a NixPath, store it in the database.
+            // This overwrites existing PathInfo objects.
+            Ok(nix_path) => match self
+                .db
+                .insert(*nix_path.digest(), path_info.encode_to_vec())
+            {
+                Ok(_) => Ok(path_info),
+                Err(e) => {
+                    warn!("failed to insert PathInfo: {}", e);
+                    Err(Error::StorageError(format! {
+                        "failed to insert PathInfo: {}", e
+                    }))
+                }
+            },
+        }
+    }
+
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), Error> {
+        calculate_size_and_sha256(root_node, &self.blob_service, &self.directory_service)
+            .await
+            .map_err(|e| Error::StorageError(e.to_string()))
+    }
+
+    fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
+        Box::pin(iter(self.db.iter().values().map(|v| match v {
+            Ok(data) => {
+                // we retrieved some bytes
+                match PathInfo::decode(&*data) {
+                    Ok(path_info) => Ok(path_info),
+                    Err(e) => {
+                        warn!("failed to decode stored PathInfo: {}", e);
+                        Err(Error::StorageError(format!(
+                            "failed to decode stored PathInfo: {}",
+                            e
+                        )))
+                    }
+                }
+            }
+            Err(e) => {
+                warn!("failed to retrieve PathInfo: {}", e);
+                Err(Error::StorageError(format!(
+                    "failed to retrieve PathInfo: {}",
+                    e
+                )))
+            }
+        })))
+    }
+}
diff --git a/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs b/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs
new file mode 100644
index 000000000000..a5c5776cd4ef
--- /dev/null
+++ b/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs
@@ -0,0 +1,116 @@
+use crate::nar::RenderError;
+use crate::pathinfoservice::PathInfoService;
+use crate::proto;
+use futures::{stream::BoxStream, TryStreamExt};
+use std::ops::Deref;
+use tonic::{async_trait, Request, Response, Result, Status};
+use tracing::{instrument, warn};
+use tvix_castore::proto as castorepb;
+
+pub struct GRPCPathInfoServiceWrapper<PS> {
+    inner: PS,
+    // FUTUREWORK: allow exposing without allowing listing
+}
+
+impl<PS> GRPCPathInfoServiceWrapper<PS> {
+    pub fn new(path_info_service: PS) -> Self {
+        Self {
+            inner: path_info_service,
+        }
+    }
+}
+
+#[async_trait]
+impl<PS> proto::path_info_service_server::PathInfoService for GRPCPathInfoServiceWrapper<PS>
+where
+    PS: Deref<Target = dyn PathInfoService> + Send + Sync + 'static,
+{
+    type ListStream = BoxStream<'static, tonic::Result<proto::PathInfo, Status>>;
+
+    #[instrument(skip(self))]
+    async fn get(
+        &self,
+        request: Request<proto::GetPathInfoRequest>,
+    ) -> Result<Response<proto::PathInfo>> {
+        match request.into_inner().by_what {
+            None => Err(Status::unimplemented("by_what needs to be specified")),
+            Some(proto::get_path_info_request::ByWhat::ByOutputHash(output_digest)) => {
+                let digest: [u8; 20] = output_digest
+                    .to_vec()
+                    .try_into()
+                    .map_err(|_e| Status::invalid_argument("invalid output digest length"))?;
+                match self.inner.get(digest).await {
+                    Ok(None) => Err(Status::not_found("PathInfo not found")),
+                    Ok(Some(path_info)) => Ok(Response::new(path_info)),
+                    Err(e) => {
+                        warn!("failed to retrieve PathInfo: {}", e);
+                        Err(e.into())
+                    }
+                }
+            }
+        }
+    }
+
+    #[instrument(skip(self))]
+    async fn put(&self, request: Request<proto::PathInfo>) -> Result<Response<proto::PathInfo>> {
+        let path_info = request.into_inner();
+
+        // Store the PathInfo in the client. Clients MUST validate the data
+        // they receive, so we don't validate additionally here.
+        match self.inner.put(path_info).await {
+            Ok(path_info_new) => Ok(Response::new(path_info_new)),
+            Err(e) => {
+                warn!("failed to insert PathInfo: {}", e);
+                Err(e.into())
+            }
+        }
+    }
+
+    #[instrument(skip(self))]
+    async fn calculate_nar(
+        &self,
+        request: Request<castorepb::Node>,
+    ) -> Result<Response<proto::CalculateNarResponse>> {
+        match request.into_inner().node {
+            None => Err(Status::invalid_argument("no root node sent")),
+            Some(root_node) => {
+                let (nar_size, nar_sha256) = self
+                    .inner
+                    .calculate_nar(&root_node)
+                    .await
+                    .expect("error during nar calculation"); // TODO: handle error
+
+                Ok(Response::new(proto::CalculateNarResponse {
+                    nar_size,
+                    nar_sha256: nar_sha256.to_vec().into(),
+                }))
+            }
+        }
+    }
+
+    #[instrument(skip(self))]
+    async fn list(
+        &self,
+        _request: Request<proto::ListPathInfoRequest>,
+    ) -> Result<Response<Self::ListStream>, Status> {
+        let stream = Box::pin(
+            self.inner
+                .list()
+                .map_err(|e| Status::internal(e.to_string())),
+        );
+
+        Ok(Response::new(Box::pin(stream)))
+    }
+}
+
+impl From<RenderError> for tonic::Status {
+    fn from(value: RenderError) -> Self {
+        match value {
+            RenderError::BlobNotFound(_, _) => Self::not_found(value.to_string()),
+            RenderError::DirectoryNotFound(_, _) => Self::not_found(value.to_string()),
+            RenderError::NARWriterError(_) => Self::internal(value.to_string()),
+            RenderError::StoreError(_) => Self::internal(value.to_string()),
+            RenderError::UnexpectedBlobMeta(_, _, _, _) => Self::internal(value.to_string()),
+        }
+    }
+}
diff --git a/tvix/store/src/proto/mod.rs b/tvix/store/src/proto/mod.rs
new file mode 100644
index 000000000000..665da8c6c58f
--- /dev/null
+++ b/tvix/store/src/proto/mod.rs
@@ -0,0 +1,368 @@
+#![allow(clippy::derive_partial_eq_without_eq, non_snake_case)]
+use bytes::Bytes;
+use data_encoding::BASE64;
+// https://github.com/hyperium/tonic/issues/1056
+use nix_compat::{
+    narinfo::Flags,
+    nixhash::{CAHash, NixHash},
+    store_path::{self, StorePathRef},
+};
+use thiserror::Error;
+use tvix_castore::proto::{self as castorepb, NamedNode, ValidateNodeError};
+
+mod grpc_pathinfoservice_wrapper;
+
+pub use grpc_pathinfoservice_wrapper::GRPCPathInfoServiceWrapper;
+
+tonic::include_proto!("tvix.store.v1");
+
+#[cfg(feature = "tonic-reflection")]
+/// Compiled file descriptors for implementing [gRPC
+/// reflection](https://github.com/grpc/grpc/blob/master/doc/server-reflection.md) with e.g.
+/// [`tonic_reflection`](https://docs.rs/tonic-reflection).
+pub const FILE_DESCRIPTOR_SET: &[u8] = tonic::include_file_descriptor_set!("tvix.store.v1");
+
+#[cfg(test)]
+mod tests;
+
+/// Errors that can occur during the validation of PathInfo messages.
+#[derive(Debug, Error, PartialEq)]
+pub enum ValidatePathInfoError {
+    /// Invalid length of a reference
+    #[error("Invalid length of digest at position {}, expected {}, got {}", .0, store_path::DIGEST_SIZE, .1)]
+    InvalidReferenceDigestLen(usize, usize),
+
+    /// No node present
+    #[error("No node present")]
+    NoNodePresent,
+
+    /// Node fails validation
+    #[error("Invalid root node: {:?}", .0.to_string())]
+    InvalidRootNode(ValidateNodeError),
+
+    /// Invalid node name encountered. Root nodes in PathInfos have more strict name requirements
+    #[error("Failed to parse {0:?} as StorePath: {1}")]
+    InvalidNodeName(Vec<u8>, store_path::Error),
+
+    /// The digest in narinfo.nar_sha256 has an invalid len.
+    #[error("Invalid narinfo.nar_sha256 length: expected {}, got {}", 32, .0)]
+    InvalidNarSha256DigestLen(usize),
+
+    /// The number of references in the narinfo.reference_names field does not match
+    /// the number of references in the .references field.
+    #[error("Inconsistent Number of References: {0} (references) vs {1} (narinfo)")]
+    InconsistentNumberOfReferences(usize, usize),
+
+    /// A string in narinfo.reference_names does not parse to a [store_path::StorePath].
+    #[error("Invalid reference_name at position {0}: {1}")]
+    InvalidNarinfoReferenceName(usize, String),
+
+    /// The digest in the parsed `.narinfo.reference_names[i]` does not match
+    /// the one in `.references[i]`.`
+    #[error("digest in reference_name at position {} does not match digest in PathInfo, expected {}, got {}", .0, BASE64.encode(.1), BASE64.encode(.2))]
+    InconsistentNarinfoReferenceNameDigest(
+        usize,
+        [u8; store_path::DIGEST_SIZE],
+        [u8; store_path::DIGEST_SIZE],
+    ),
+
+    /// The deriver field is invalid.
+    #[error("deriver field is invalid: {0}")]
+    InvalidDeriverField(store_path::Error),
+}
+
+/// Parses a root node name.
+///
+/// On success, this returns the parsed [store_path::StorePath].
+/// On error, it returns an error generated from the supplied constructor.
+fn parse_node_name_root<E>(
+    name: &[u8],
+    err: fn(Vec<u8>, store_path::Error) -> E,
+) -> Result<store_path::StorePath, E> {
+    match store_path::StorePath::from_bytes(name) {
+        Ok(np) => Ok(np),
+        Err(e) => Err(err(name.to_vec(), e)),
+    }
+}
+
+impl PathInfo {
+    /// validate performs some checks on the PathInfo struct,
+    /// Returning either a [store_path::StorePath] of the root node, or a
+    /// [ValidatePathInfoError].
+    pub fn validate(&self) -> Result<store_path::StorePath, ValidatePathInfoError> {
+        // ensure the references have the right number of bytes.
+        for (i, reference) in self.references.iter().enumerate() {
+            if reference.len() != store_path::DIGEST_SIZE {
+                return Err(ValidatePathInfoError::InvalidReferenceDigestLen(
+                    i,
+                    reference.len(),
+                ));
+            }
+        }
+
+        // If there is a narinfo field populated…
+        if let Some(narinfo) = &self.narinfo {
+            // ensure the nar_sha256 digest has the correct length.
+            if narinfo.nar_sha256.len() != 32 {
+                return Err(ValidatePathInfoError::InvalidNarSha256DigestLen(
+                    narinfo.nar_sha256.len(),
+                ));
+            }
+
+            // ensure the number of references there matches PathInfo.references count.
+            if narinfo.reference_names.len() != self.references.len() {
+                return Err(ValidatePathInfoError::InconsistentNumberOfReferences(
+                    self.references.len(),
+                    narinfo.reference_names.len(),
+                ));
+            }
+
+            // parse references in reference_names.
+            for (i, reference_name_str) in narinfo.reference_names.iter().enumerate() {
+                // ensure thy parse as (non-absolute) store path
+                let reference_names_store_path = store_path::StorePath::from_bytes(
+                    reference_name_str.as_bytes(),
+                )
+                .map_err(|_| {
+                    ValidatePathInfoError::InvalidNarinfoReferenceName(
+                        i,
+                        reference_name_str.to_owned(),
+                    )
+                })?;
+
+                // ensure their digest matches the one at self.references[i].
+                {
+                    // This is safe, because we ensured the proper length earlier already.
+                    let reference_digest = self.references[i].to_vec().try_into().unwrap();
+
+                    if reference_names_store_path.digest() != &reference_digest {
+                        return Err(
+                            ValidatePathInfoError::InconsistentNarinfoReferenceNameDigest(
+                                i,
+                                reference_digest,
+                                *reference_names_store_path.digest(),
+                            ),
+                        );
+                    }
+                }
+
+                // If the Deriver field is populated, ensure it parses to a
+                // [store_path::StorePath].
+                // We can't check for it to *not* end with .drv, as the .drv files produced by
+                // recursive Nix end with multiple .drv suffixes, and only one is popped when
+                // converting to this field.
+                if let Some(deriver) = &narinfo.deriver {
+                    store_path::StorePathRef::from_name_and_digest(&deriver.name, &deriver.digest)
+                        .map_err(ValidatePathInfoError::InvalidDeriverField)?
+                        .to_owned();
+                }
+            }
+        }
+
+        // Ensure there is a (root) node present, and it properly parses to a [store_path::StorePath].
+        let root_nix_path = match &self.node {
+            None | Some(castorepb::Node { node: None }) => {
+                Err(ValidatePathInfoError::NoNodePresent)?
+            }
+            Some(castorepb::Node { node: Some(node) }) => {
+                node.validate()
+                    .map_err(ValidatePathInfoError::InvalidRootNode)?;
+                // parse the name of the node itself and return
+                parse_node_name_root(node.get_name(), ValidatePathInfoError::InvalidNodeName)?
+            }
+        };
+
+        // return the root nix path
+        Ok(root_nix_path)
+    }
+
+    /// With self and a given StorePathRef, this reconstructs a
+    /// [nix_compat::narinfo::NarInfo<'_>].
+    /// It can be used to validate Signatures, or get back a (sparse) NarInfo
+    /// struct to prepare writing it out.
+    ///
+    /// This doesn't allocate any new data.
+    ///
+    /// Keep in mind this is not able to reconstruct all data present in the
+    /// NarInfo<'_>, as some of it is not stored at all:
+    /// - the `system`, `file_hash` and `file_size` fields are set to `None`.
+    /// - the URL is set to an empty string.
+    /// - Compression is set to "none"
+    ///
+    /// If you want to render it out to a string and be able to parse it back
+    /// in, at least URL *must* be set again.
+    pub fn as_narinfo<'a>(
+        &'a self,
+        store_path: store_path::StorePathRef<'a>,
+    ) -> Option<nix_compat::narinfo::NarInfo<'_>> {
+        let narinfo = &self.narinfo.as_ref()?;
+
+        Some(nix_compat::narinfo::NarInfo {
+            flags: Flags::empty(),
+            store_path,
+            nar_hash: narinfo.nar_sha256.to_vec().try_into().unwrap(),
+            nar_size: narinfo.nar_size,
+            references: narinfo
+                .reference_names
+                .iter()
+                .map(|ref_name| {
+                    // This shouldn't pass validation
+                    StorePathRef::from_bytes(ref_name.as_bytes()).expect("invalid reference")
+                })
+                .collect(),
+            signatures: narinfo
+                .signatures
+                .iter()
+                .map(|sig| {
+                    nix_compat::narinfo::Signature::new(
+                        &sig.name,
+                        // This shouldn't pass validation
+                        sig.data[..].try_into().expect("invalid signature len"),
+                    )
+                })
+                .collect(),
+            ca: narinfo
+                .ca
+                .as_ref()
+                .map(|ca| ca.try_into().expect("invalid ca")),
+            system: None,
+            deriver: narinfo.deriver.as_ref().map(|deriver| {
+                StorePathRef::from_name_and_digest(&deriver.name, &deriver.digest)
+                    .expect("invalid deriver")
+            }),
+            url: "",
+            compression: Some("none"),
+            file_hash: None,
+            file_size: None,
+        })
+    }
+}
+
+/// Errors that can occur when converting from a [nar_info::Ca] to a (stricter)
+/// [nix_compat::nixhash::CAHash].
+#[derive(Debug, Error, PartialEq)]
+pub enum ConvertCAError {
+    /// Invalid length of a reference
+    #[error("Invalid digest length '{0}' for type {1}")]
+    InvalidReferenceDigestLen(usize, &'static str),
+    /// Unknown Hash type
+    #[error("Unknown hash type: {0}")]
+    UnknownHashType(i32),
+}
+
+impl TryFrom<&nar_info::Ca> for nix_compat::nixhash::CAHash {
+    type Error = ConvertCAError;
+
+    fn try_from(value: &nar_info::Ca) -> Result<Self, Self::Error> {
+        Ok(match value.r#type {
+            typ if typ == nar_info::ca::Hash::FlatMd5 as i32 => {
+                Self::Flat(NixHash::Md5(value.digest[..].try_into().map_err(|_| {
+                    ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "FlatMd5")
+                })?))
+            }
+            typ if typ == nar_info::ca::Hash::FlatSha1 as i32 => {
+                Self::Flat(NixHash::Sha1(value.digest[..].try_into().map_err(
+                    |_| ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "FlatSha1"),
+                )?))
+            }
+            typ if typ == nar_info::ca::Hash::FlatSha256 as i32 => {
+                Self::Flat(NixHash::Sha256(value.digest[..].try_into().map_err(
+                    |_| ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "FlatSha256"),
+                )?))
+            }
+            typ if typ == nar_info::ca::Hash::FlatSha512 as i32 => Self::Flat(NixHash::Sha512(
+                Box::new(value.digest[..].try_into().map_err(|_| {
+                    ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "FlatSha512")
+                })?),
+            )),
+            typ if typ == nar_info::ca::Hash::NarMd5 as i32 => {
+                Self::Nar(NixHash::Md5(value.digest[..].try_into().map_err(|_| {
+                    ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "NarMd5")
+                })?))
+            }
+            typ if typ == nar_info::ca::Hash::NarSha1 as i32 => {
+                Self::Nar(NixHash::Sha1(value.digest[..].try_into().map_err(
+                    |_| ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "NarSha1"),
+                )?))
+            }
+            typ if typ == nar_info::ca::Hash::NarSha256 as i32 => {
+                Self::Nar(NixHash::Sha256(value.digest[..].try_into().map_err(
+                    |_| ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "NarSha256"),
+                )?))
+            }
+            typ if typ == nar_info::ca::Hash::NarSha512 as i32 => Self::Nar(NixHash::Sha512(
+                Box::new(value.digest[..].try_into().map_err(|_| {
+                    ConvertCAError::InvalidReferenceDigestLen(value.digest.len(), "NarSha512")
+                })?),
+            )),
+            typ => return Err(ConvertCAError::UnknownHashType(typ)),
+        })
+    }
+}
+
+impl From<&nix_compat::nixhash::CAHash> for nar_info::Ca {
+    fn from(value: &nix_compat::nixhash::CAHash) -> Self {
+        nar_info::Ca {
+            r#type: match value {
+                CAHash::Flat(NixHash::Md5(_)) => nar_info::ca::Hash::FlatMd5.into(),
+                CAHash::Flat(NixHash::Sha1(_)) => nar_info::ca::Hash::FlatSha1.into(),
+                CAHash::Flat(NixHash::Sha256(_)) => nar_info::ca::Hash::FlatSha256.into(),
+                CAHash::Flat(NixHash::Sha512(_)) => nar_info::ca::Hash::FlatSha512.into(),
+                CAHash::Nar(NixHash::Md5(_)) => nar_info::ca::Hash::NarMd5.into(),
+                CAHash::Nar(NixHash::Sha1(_)) => nar_info::ca::Hash::NarSha1.into(),
+                CAHash::Nar(NixHash::Sha256(_)) => nar_info::ca::Hash::NarSha256.into(),
+                CAHash::Nar(NixHash::Sha512(_)) => nar_info::ca::Hash::NarSha512.into(),
+                CAHash::Text(_) => nar_info::ca::Hash::TextSha256.into(),
+            },
+            digest: match value {
+                CAHash::Flat(ref nixhash) | CAHash::Nar(ref nixhash) => {
+                    nixhash.digest_as_bytes().to_vec().into()
+                }
+                CAHash::Text(digest) => digest.to_vec().into(),
+            },
+        }
+    }
+}
+
+impl From<&nix_compat::narinfo::NarInfo<'_>> for NarInfo {
+    /// Converts from a NarInfo (returned from the NARInfo parser) to the proto-
+    /// level NarInfo struct.
+    fn from(value: &nix_compat::narinfo::NarInfo<'_>) -> Self {
+        let signatures = value
+            .signatures
+            .iter()
+            .map(|sig| nar_info::Signature {
+                name: sig.name().to_string(),
+                data: Bytes::copy_from_slice(sig.bytes()),
+            })
+            .collect();
+
+        NarInfo {
+            nar_size: value.nar_size,
+            nar_sha256: Bytes::copy_from_slice(&value.nar_hash),
+            signatures,
+            reference_names: value.references.iter().map(|r| r.to_string()).collect(),
+            deriver: value.deriver.as_ref().map(|sp| StorePath {
+                name: sp.name().to_owned(),
+                digest: Bytes::copy_from_slice(sp.digest()),
+            }),
+            ca: value.ca.as_ref().map(|ca| ca.into()),
+        }
+    }
+}
+
+impl From<&nix_compat::narinfo::NarInfo<'_>> for PathInfo {
+    /// Converts from a NarInfo (returned from the NARInfo parser) to a PathInfo
+    /// struct with the node set to None.
+    fn from(value: &nix_compat::narinfo::NarInfo<'_>) -> Self {
+        Self {
+            node: None,
+            references: value
+                .references
+                .iter()
+                .map(|x| Bytes::copy_from_slice(x.digest()))
+                .collect(),
+            narinfo: Some(value.into()),
+        }
+    }
+}
diff --git a/tvix/store/src/proto/tests/grpc_pathinfoservice.rs b/tvix/store/src/proto/tests/grpc_pathinfoservice.rs
new file mode 100644
index 000000000000..8016b9901d96
--- /dev/null
+++ b/tvix/store/src/proto/tests/grpc_pathinfoservice.rs
@@ -0,0 +1,74 @@
+use crate::proto::get_path_info_request::ByWhat::ByOutputHash;
+use crate::proto::path_info_service_server::PathInfoService as GRPCPathInfoService;
+use crate::proto::GRPCPathInfoServiceWrapper;
+use crate::proto::GetPathInfoRequest;
+use crate::proto::PathInfo;
+use crate::tests::fixtures::DUMMY_OUTPUT_HASH;
+use crate::tests::utils::gen_blob_service;
+use crate::tests::utils::gen_directory_service;
+use crate::tests::utils::gen_pathinfo_service;
+use futures::stream::BoxStream;
+use std::sync::Arc;
+use tonic::Request;
+use tvix_castore::proto as castorepb;
+
+/// generates a GRPCPathInfoService out of blob, directory and pathinfo services.
+///
+/// We only interact with it via the PathInfo GRPC interface.
+/// It uses the NonCachingNARCalculationService NARCalculationService to
+/// calculate NARs.
+fn gen_grpc_service(
+) -> Arc<dyn GRPCPathInfoService<ListStream = BoxStream<'static, Result<PathInfo, tonic::Status>>>>
+{
+    let blob_service = gen_blob_service();
+    let directory_service = gen_directory_service();
+    Arc::new(GRPCPathInfoServiceWrapper::new(gen_pathinfo_service(
+        blob_service,
+        directory_service,
+    )))
+}
+
+/// Trying to get a non-existent PathInfo should return a not found error.
+#[tokio::test]
+async fn not_found() {
+    let service = gen_grpc_service();
+
+    let resp = service
+        .get(Request::new(GetPathInfoRequest {
+            by_what: Some(ByOutputHash(DUMMY_OUTPUT_HASH.clone())),
+        }))
+        .await;
+
+    let resp = resp.expect_err("must fail");
+    assert_eq!(resp.code(), tonic::Code::NotFound);
+}
+
+/// Put a PathInfo into the store, get it back.
+#[tokio::test]
+async fn put_get() {
+    let service = gen_grpc_service();
+
+    let path_info = PathInfo {
+        node: Some(castorepb::Node {
+            node: Some(castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+                name: "00000000000000000000000000000000-foo".into(),
+                target: "doesntmatter".into(),
+            })),
+        }),
+        ..Default::default()
+    };
+
+    let resp = service.put(Request::new(path_info.clone())).await;
+
+    assert!(resp.is_ok());
+    assert_eq!(resp.expect("must succeed").into_inner(), path_info);
+
+    let resp = service
+        .get(Request::new(GetPathInfoRequest {
+            by_what: Some(ByOutputHash(DUMMY_OUTPUT_HASH.clone())),
+        }))
+        .await;
+
+    assert!(resp.is_ok());
+    assert_eq!(resp.expect("must succeed").into_inner(), path_info);
+}
diff --git a/tvix/store/src/proto/tests/mod.rs b/tvix/store/src/proto/tests/mod.rs
new file mode 100644
index 000000000000..bff885624380
--- /dev/null
+++ b/tvix/store/src/proto/tests/mod.rs
@@ -0,0 +1,2 @@
+mod grpc_pathinfoservice;
+mod pathinfo;
diff --git a/tvix/store/src/proto/tests/pathinfo.rs b/tvix/store/src/proto/tests/pathinfo.rs
new file mode 100644
index 000000000000..7c1b69c2a376
--- /dev/null
+++ b/tvix/store/src/proto/tests/pathinfo.rs
@@ -0,0 +1,448 @@
+use crate::proto::{nar_info::Signature, NarInfo, PathInfo, ValidatePathInfoError};
+use crate::tests::fixtures::*;
+use bytes::Bytes;
+use data_encoding::BASE64;
+use nix_compat::nixbase32;
+use nix_compat::store_path::{self, StorePath, StorePathRef};
+use std::str::FromStr;
+use test_case::test_case;
+use tvix_castore::proto as castorepb;
+
+#[test_case(
+    None,
+    Err(ValidatePathInfoError::NoNodePresent) ;
+    "No node"
+)]
+#[test_case(
+    Some(castorepb::Node { node: None }),
+    Err(ValidatePathInfoError::NoNodePresent);
+    "No node 2"
+)]
+fn validate_no_node(
+    t_node: Option<castorepb::Node>,
+    t_result: Result<StorePath, ValidatePathInfoError>,
+) {
+    // construct the PathInfo object
+    let p = PathInfo {
+        node: t_node,
+        ..Default::default()
+    };
+    assert_eq!(t_result, p.validate());
+}
+
+#[test_case(
+    castorepb::DirectoryNode {
+        name: DUMMY_NAME.into(),
+        digest: DUMMY_DIGEST.clone().into(),
+        size: 0,
+    },
+    Ok(StorePath::from_str(DUMMY_NAME).expect("must succeed"));
+    "ok"
+)]
+#[test_case(
+    castorepb::DirectoryNode {
+        name: DUMMY_NAME.into(),
+        digest: Bytes::new(),
+        size: 0,
+    },
+    Err(ValidatePathInfoError::InvalidRootNode(castorepb::ValidateNodeError::InvalidDigestLen(0)));
+    "invalid digest length"
+)]
+#[test_case(
+    castorepb::DirectoryNode {
+        name: "invalid".into(),
+        digest: DUMMY_DIGEST.clone().into(),
+        size: 0,
+    },
+    Err(ValidatePathInfoError::InvalidNodeName(
+        "invalid".into(),
+        store_path::Error::InvalidLength
+    ));
+    "invalid node name"
+)]
+fn validate_directory(
+    t_directory_node: castorepb::DirectoryNode,
+    t_result: Result<StorePath, ValidatePathInfoError>,
+) {
+    // construct the PathInfo object
+    let p = PathInfo {
+        node: Some(castorepb::Node {
+            node: Some(castorepb::node::Node::Directory(t_directory_node)),
+        }),
+        ..Default::default()
+    };
+    assert_eq!(t_result, p.validate());
+}
+
+#[test_case(
+    castorepb::FileNode {
+        name: DUMMY_NAME.into(),
+        digest: DUMMY_DIGEST.clone().into(),
+        size: 0,
+        executable: false,
+    },
+    Ok(StorePath::from_str(DUMMY_NAME).expect("must succeed"));
+    "ok"
+)]
+#[test_case(
+    castorepb::FileNode {
+        name: DUMMY_NAME.into(),
+        digest: Bytes::new(),
+        ..Default::default()
+    },
+    Err(ValidatePathInfoError::InvalidRootNode(castorepb::ValidateNodeError::InvalidDigestLen(0)));
+    "invalid digest length"
+)]
+#[test_case(
+    castorepb::FileNode {
+        name: "invalid".into(),
+        digest: DUMMY_DIGEST.clone().into(),
+        ..Default::default()
+    },
+    Err(ValidatePathInfoError::InvalidNodeName(
+        "invalid".into(),
+        store_path::Error::InvalidLength
+    ));
+    "invalid node name"
+)]
+fn validate_file(
+    t_file_node: castorepb::FileNode,
+    t_result: Result<StorePath, ValidatePathInfoError>,
+) {
+    // construct the PathInfo object
+    let p = PathInfo {
+        node: Some(castorepb::Node {
+            node: Some(castorepb::node::Node::File(t_file_node)),
+        }),
+        ..Default::default()
+    };
+    assert_eq!(t_result, p.validate());
+}
+
+#[test_case(
+    castorepb::SymlinkNode {
+        name: DUMMY_NAME.into(),
+        target: "foo".into(),
+    },
+    Ok(StorePath::from_str(DUMMY_NAME).expect("must succeed"));
+    "ok"
+)]
+#[test_case(
+    castorepb::SymlinkNode {
+        name: "invalid".into(),
+        target: "foo".into(),
+    },
+    Err(ValidatePathInfoError::InvalidNodeName(
+        "invalid".into(),
+        store_path::Error::InvalidLength
+    ));
+    "invalid node name"
+)]
+fn validate_symlink(
+    t_symlink_node: castorepb::SymlinkNode,
+    t_result: Result<StorePath, ValidatePathInfoError>,
+) {
+    // construct the PathInfo object
+    let p = PathInfo {
+        node: Some(castorepb::Node {
+            node: Some(castorepb::node::Node::Symlink(t_symlink_node)),
+        }),
+        ..Default::default()
+    };
+    assert_eq!(t_result, p.validate());
+}
+
+/// Ensure parsing a correct PathInfo without narinfo populated succeeds.
+#[test]
+fn validate_references_without_narinfo_ok() {
+    assert!(PATH_INFO_WITHOUT_NARINFO.validate().is_ok());
+}
+
+/// Ensure parsing a correct PathInfo with narinfo populated succeeds.
+#[test]
+fn validate_references_with_narinfo_ok() {
+    assert!(PATH_INFO_WITH_NARINFO.validate().is_ok());
+}
+
+/// Create a PathInfo with a wrong digest length in narinfo.nar_sha256, and
+/// ensure validation fails.
+#[test]
+fn validate_wrong_nar_sha256() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+    path_info.narinfo.as_mut().unwrap().nar_sha256 = vec![0xbe, 0xef].into();
+
+    match path_info.validate().expect_err("must_fail") {
+        ValidatePathInfoError::InvalidNarSha256DigestLen(2) => {}
+        e => panic!("unexpected error: {:?}", e),
+    };
+}
+
+/// Create a PathInfo with a wrong count of narinfo.reference_names,
+/// and ensure validation fails.
+#[test]
+fn validate_inconsistent_num_refs_fail() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+    path_info.narinfo.as_mut().unwrap().reference_names = vec![];
+
+    match path_info.validate().expect_err("must_fail") {
+        ValidatePathInfoError::InconsistentNumberOfReferences(1, 0) => {}
+        e => panic!("unexpected error: {:?}", e),
+    };
+}
+
+/// Create a PathInfo with a wrong digest length in references.
+#[test]
+fn validate_invalid_reference_digest_len() {
+    let mut path_info = PATH_INFO_WITHOUT_NARINFO.clone();
+    path_info.references.push(vec![0xff, 0xff].into());
+
+    match path_info.validate().expect_err("must fail") {
+        ValidatePathInfoError::InvalidReferenceDigestLen(
+            1, // position
+            2, // unexpected digest len
+        ) => {}
+        e => panic!("unexpected error: {:?}", e),
+    };
+}
+
+/// Create a PathInfo with a narinfo.reference_name[1] that is no valid store path.
+#[test]
+fn validate_invalid_narinfo_reference_name() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+
+    // This is invalid, as the store prefix is not part of reference_names.
+    path_info.narinfo.as_mut().unwrap().reference_names[0] =
+        "/nix/store/00000000000000000000000000000000-dummy".to_string();
+
+    match path_info.validate().expect_err("must fail") {
+        ValidatePathInfoError::InvalidNarinfoReferenceName(0, reference_name) => {
+            assert_eq!(
+                "/nix/store/00000000000000000000000000000000-dummy",
+                reference_name
+            );
+        }
+        e => panic!("unexpected error: {:?}", e),
+    }
+}
+
+/// Create a PathInfo with a narinfo.reference_name[0] that doesn't match references[0].
+#[test]
+fn validate_inconsistent_narinfo_reference_name_digest() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+
+    // mutate the first reference, they were all zeroes before
+    path_info.references[0] = vec![0xff; store_path::DIGEST_SIZE].into();
+
+    match path_info.validate().expect_err("must fail") {
+        ValidatePathInfoError::InconsistentNarinfoReferenceNameDigest(0, e_expected, e_actual) => {
+            assert_eq!(path_info.references[0][..], e_expected);
+            assert_eq!(DUMMY_OUTPUT_HASH[..], e_actual);
+        }
+        e => panic!("unexpected error: {:?}", e),
+    }
+}
+
+/// Create a node with an empty symlink target, and ensure it fails validation.
+#[test]
+fn validate_symlink_empty_target_invalid() {
+    let node = castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+        name: "foo".into(),
+        target: "".into(),
+    });
+
+    node.validate().expect_err("must fail validation");
+}
+
+/// Create a node with a symlink target including null bytes, and ensure it
+/// fails validation.
+#[test]
+fn validate_symlink_target_null_byte_invalid() {
+    let node = castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+        name: "foo".into(),
+        target: "foo\0".into(),
+    });
+
+    node.validate().expect_err("must fail validation");
+}
+
+/// Create a PathInfo with a correct deriver field and ensure it succeeds.
+#[test]
+fn validate_valid_deriver() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+
+    // add a valid deriver
+    let narinfo = path_info.narinfo.as_mut().unwrap();
+    narinfo.deriver = Some(crate::proto::StorePath {
+        name: "foo".to_string(),
+        digest: DUMMY_OUTPUT_HASH.clone(),
+    });
+
+    path_info.validate().expect("must validate");
+}
+
+/// Create a PathInfo with a broken deriver field and ensure it fails.
+#[test]
+fn validate_invalid_deriver() {
+    let mut path_info = PATH_INFO_WITH_NARINFO.clone();
+
+    // add a broken deriver (invalid digest)
+    let narinfo = path_info.narinfo.as_mut().unwrap();
+    narinfo.deriver = Some(crate::proto::StorePath {
+        name: "foo".to_string(),
+        digest: vec![].into(),
+    });
+
+    match path_info.validate().expect_err("must fail validation") {
+        ValidatePathInfoError::InvalidDeriverField(_) => {}
+        e => panic!("unexpected error: {:?}", e),
+    }
+}
+
+#[test]
+fn from_nixcompat_narinfo() {
+    let narinfo_parsed = nix_compat::narinfo::NarInfo::parse(
+        r#"StorePath: /nix/store/s66mzxpvicwk07gjbjfw9izjfa797vsw-hello-2.12.1
+URL: nar/1nhgq6wcggx0plpy4991h3ginj6hipsdslv4fd4zml1n707j26yq.nar.xz
+Compression: xz
+FileHash: sha256:1nhgq6wcggx0plpy4991h3ginj6hipsdslv4fd4zml1n707j26yq
+FileSize: 50088
+NarHash: sha256:0yzhigwjl6bws649vcs2asa4lbs8hg93hyix187gc7s7a74w5h80
+NarSize: 226488
+References: 3n58xw4373jp0ljirf06d8077j15pc4j-glibc-2.37-8 s66mzxpvicwk07gjbjfw9izjfa797vsw-hello-2.12.1
+Deriver: ib3sh3pcz10wsmavxvkdbayhqivbghlq-hello-2.12.1.drv
+Sig: cache.nixos.org-1:8ijECciSFzWHwwGVOIVYdp2fOIOJAfmzGHPQVwpktfTQJF6kMPPDre7UtFw3o+VqenC5P8RikKOAAfN7CvPEAg=="#).expect("must parse");
+
+    assert_eq!(
+        PathInfo {
+            node: None,
+            references: vec![
+                Bytes::copy_from_slice(&nixbase32::decode_fixed::<20>("3n58xw4373jp0ljirf06d8077j15pc4j").unwrap()),
+                Bytes::copy_from_slice(&nixbase32::decode_fixed::<20>("s66mzxpvicwk07gjbjfw9izjfa797vsw").unwrap()),
+            ],
+            narinfo: Some(
+                NarInfo {
+                    nar_size: 226488,
+                    nar_sha256: Bytes::copy_from_slice(
+                        &nixbase32::decode_fixed::<32>("0yzhigwjl6bws649vcs2asa4lbs8hg93hyix187gc7s7a74w5h80".as_bytes())
+                            .unwrap()
+                    ),
+                    signatures: vec![Signature {
+                        name: "cache.nixos.org-1".to_string(),
+                        data: BASE64.decode("8ijECciSFzWHwwGVOIVYdp2fOIOJAfmzGHPQVwpktfTQJF6kMPPDre7UtFw3o+VqenC5P8RikKOAAfN7CvPEAg==".as_bytes()).unwrap().into(),
+                    }],
+                    reference_names: vec![
+                        "3n58xw4373jp0ljirf06d8077j15pc4j-glibc-2.37-8".to_string(),
+                        "s66mzxpvicwk07gjbjfw9izjfa797vsw-hello-2.12.1".to_string()
+                    ],
+                    deriver: Some(crate::proto::StorePath {
+                        digest: Bytes::copy_from_slice(&nixbase32::decode_fixed::<20>("ib3sh3pcz10wsmavxvkdbayhqivbghlq").unwrap()),
+                        name: "hello-2.12.1".to_string(),
+                     }),
+                    ca: None,
+                }
+            )
+        },
+        (&narinfo_parsed).into(),
+    );
+}
+
+#[test]
+fn from_nixcompat_narinfo_fod() {
+    let narinfo_parsed = nix_compat::narinfo::NarInfo::parse(
+        r#"StorePath: /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
+URL: nar/1zjrhzhaizsrlsvdkqfl073vivmxcqnzkff4s50i0cdf541ary1r.nar.xz
+Compression: xz
+FileHash: sha256:1zjrhzhaizsrlsvdkqfl073vivmxcqnzkff4s50i0cdf541ary1r
+FileSize: 1033524
+NarHash: sha256:1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh
+NarSize: 1033416
+References: 
+Deriver: dyivpmlaq2km6c11i0s6bi6mbsx0ylqf-hello-2.12.1.tar.gz.drv
+Sig: cache.nixos.org-1:ywnIG629nQZQhEr6/HLDrLT/mUEp5J1LC6NmWSlJRWL/nM7oGItJQUYWGLvYGhSQvHrhIuvMpjNmBNh/WWqCDg==
+CA: fixed:sha256:086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"#
+    ).expect("must parse");
+
+    assert_eq!(
+        PathInfo {
+            node: None,
+            references: vec![],
+            narinfo: Some(
+                NarInfo {
+                    nar_size: 1033416,
+                    nar_sha256: Bytes::copy_from_slice(
+                        &nixbase32::decode_fixed::<32>(
+                            "1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh"
+                        )
+                        .unwrap()
+                    ),
+                    signatures: vec![Signature {
+                        name: "cache.nixos.org-1".to_string(),
+                        data: BASE64
+                            .decode("ywnIG629nQZQhEr6/HLDrLT/mUEp5J1LC6NmWSlJRWL/nM7oGItJQUYWGLvYGhSQvHrhIuvMpjNmBNh/WWqCDg==".as_bytes())
+                            .unwrap()
+                            .into(),
+                    }],
+                    reference_names: vec![],
+                    deriver: Some(crate::proto::StorePath {
+                        digest: Bytes::copy_from_slice(
+                            &nixbase32::decode_fixed::<20>("dyivpmlaq2km6c11i0s6bi6mbsx0ylqf").unwrap()
+                        ),
+                        name: "hello-2.12.1.tar.gz".to_string(),
+                    }),
+                    ca: Some(crate::proto::nar_info::Ca {
+                        r#type: crate::proto::nar_info::ca::Hash::FlatSha256.into(),
+                        digest: Bytes::copy_from_slice(
+                            &nixbase32::decode_fixed::<32>(
+                                "086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"
+                            )
+                            .unwrap()
+                        )
+                    }),
+                }
+            ),
+        },
+        (&narinfo_parsed).into()
+    );
+}
+
+/// Exercise .as_narinfo() on a PathInfo and ensure important fields are preserved..
+#[test]
+fn as_narinfo() {
+    let narinfo_parsed = nix_compat::narinfo::NarInfo::parse(
+        r#"StorePath: /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
+URL: nar/1zjrhzhaizsrlsvdkqfl073vivmxcqnzkff4s50i0cdf541ary1r.nar.xz
+Compression: xz
+FileHash: sha256:1zjrhzhaizsrlsvdkqfl073vivmxcqnzkff4s50i0cdf541ary1r
+FileSize: 1033524
+NarHash: sha256:1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh
+NarSize: 1033416
+References: 
+Deriver: dyivpmlaq2km6c11i0s6bi6mbsx0ylqf-hello-2.12.1.tar.gz.drv
+Sig: cache.nixos.org-1:ywnIG629nQZQhEr6/HLDrLT/mUEp5J1LC6NmWSlJRWL/nM7oGItJQUYWGLvYGhSQvHrhIuvMpjNmBNh/WWqCDg==
+CA: fixed:sha256:086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"#
+    ).expect("must parse");
+
+    let path_info: PathInfo = (&narinfo_parsed).into();
+
+    let mut narinfo_returned = path_info
+        .as_narinfo(
+            StorePathRef::from_bytes(b"pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz")
+                .expect("invalid storepath"),
+        )
+        .expect("must be some");
+    narinfo_returned.url = "some.nar";
+
+    assert_eq!(
+        r#"StorePath: /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
+URL: some.nar
+Compression: none
+NarHash: sha256:1lvqpbk2k1sb39z8jfxixf7p7v8sj4z6mmpa44nnmff3w1y6h8lh
+NarSize: 1033416
+References: 
+Deriver: dyivpmlaq2km6c11i0s6bi6mbsx0ylqf-hello-2.12.1.tar.gz.drv
+Sig: cache.nixos.org-1:ywnIG629nQZQhEr6/HLDrLT/mUEp5J1LC6NmWSlJRWL/nM7oGItJQUYWGLvYGhSQvHrhIuvMpjNmBNh/WWqCDg==
+CA: fixed:sha256:086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd
+"#,
+        narinfo_returned.to_string(),
+    );
+}
diff --git a/tvix/store/src/tests/fixtures.rs b/tvix/store/src/tests/fixtures.rs
new file mode 100644
index 000000000000..7c72d71c6d1e
--- /dev/null
+++ b/tvix/store/src/tests/fixtures.rs
@@ -0,0 +1,125 @@
+use lazy_static::lazy_static;
+pub use tvix_castore::fixtures::*;
+use tvix_castore::proto as castorepb;
+
+use crate::proto::{nar_info::ca, nar_info::Ca, NarInfo, PathInfo};
+
+pub const DUMMY_NAME: &str = "00000000000000000000000000000000-dummy";
+
+lazy_static! {
+    // output hash
+    pub static ref DUMMY_OUTPUT_HASH: bytes::Bytes = vec![0; 20].into();
+
+    /// The NAR representation of a symlink pointing to `/nix/store/somewhereelse`
+    pub static ref NAR_CONTENTS_SYMLINK: Vec<u8> = vec![
+        13, 0, 0, 0, 0, 0, 0, 0, b'n', b'i', b'x', b'-', b'a', b'r', b'c', b'h', b'i', b'v', b'e', b'-', b'1', 0,
+        0, 0, // "nix-archive-1"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        7, 0, 0, 0, 0, 0, 0, 0, b's', b'y', b'm', b'l', b'i', b'n', b'k', 0, // "symlink"
+        6, 0, 0, 0, 0, 0, 0, 0, b't', b'a', b'r', b'g', b'e', b't', 0, 0, // target
+        24, 0, 0, 0, 0, 0, 0, 0, b'/', b'n', b'i', b'x', b'/', b's', b't', b'o', b'r', b'e', b'/', b's', b'o',
+        b'm', b'e', b'w', b'h', b'e', b'r', b'e', b'e', b'l', b's',
+        b'e', // "/nix/store/somewhereelse"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0 // ")"
+    ];
+
+    /// The NAR representation of a regular file with the contents "Hello World!"
+    pub static ref NAR_CONTENTS_HELLOWORLD: Vec<u8> = vec![
+        13, 0, 0, 0, 0, 0, 0, 0, b'n', b'i', b'x', b'-', b'a', b'r', b'c', b'h', b'i', b'v', b'e', b'-', b'1', 0,
+        0, 0, // "nix-archive-1"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        7, 0, 0, 0, 0, 0, 0, 0, b'r', b'e', b'g', b'u', b'l', b'a', b'r', 0, // "regular"
+        8, 0, 0, 0, 0, 0, 0, 0, b'c', b'o', b'n', b't', b'e', b'n', b't', b's', // "contents"
+        12, 0, 0, 0, 0, 0, 0, 0, b'H', b'e', b'l', b'l', b'o', b' ', b'W', b'o', b'r', b'l', b'd', b'!', 0, 0,
+        0, 0, // "Hello World!"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0 // ")"
+    ];
+
+    /// The NAR representation of a more complicated directory structure.
+    pub static ref NAR_CONTENTS_COMPLICATED: Vec<u8> = vec![
+        13, 0, 0, 0, 0, 0, 0, 0, b'n', b'i', b'x', b'-', b'a', b'r', b'c', b'h', b'i', b'v', b'e', b'-', b'1', 0,
+        0, 0, // "nix-archive-1"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        9, 0, 0, 0, 0, 0, 0, 0, b'd', b'i', b'r', b'e', b'c', b't', b'o', b'r', b'y', 0, 0, 0, 0, 0, 0, 0, // "directory"
+        5, 0, 0, 0, 0, 0, 0, 0, b'e', b'n', b't', b'r', b'y', 0, 0, 0, // "entry"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'a', b'm', b'e', 0, 0, 0, 0, // "name"
+        5, 0, 0, 0, 0, 0, 0, 0, b'.', b'k', b'e', b'e', b'p', 0, 0, 0, // ".keep"
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'o', b'd', b'e', 0, 0, 0, 0, // "node"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        7, 0, 0, 0, 0, 0, 0, 0, b'r', b'e', b'g', b'u', b'l', b'a', b'r', 0, // "regular"
+        8, 0, 0, 0, 0, 0, 0, 0, b'c', b'o', b'n', b't', b'e', b'n', b't', b's', // "contents"
+        0, 0, 0, 0, 0, 0, 0, 0, // ""
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        5, 0, 0, 0, 0, 0, 0, 0, b'e', b'n', b't', b'r', b'y', 0, 0, 0, // "entry"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'a', b'm', b'e', 0, 0, 0, 0, // "name"
+        2, 0, 0, 0, 0, 0, 0, 0, b'a', b'a', 0, 0, 0, 0, 0, 0, // "aa"
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'o', b'd', b'e', 0, 0, 0, 0, // "node"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        7, 0, 0, 0, 0, 0, 0, 0, b's', b'y', b'm', b'l', b'i', b'n', b'k', 0, // "symlink"
+        6, 0, 0, 0, 0, 0, 0, 0, b't', b'a', b'r', b'g', b'e', b't', 0, 0, // target
+        24, 0, 0, 0, 0, 0, 0, 0, b'/', b'n', b'i', b'x', b'/', b's', b't', b'o', b'r', b'e', b'/', b's', b'o',
+        b'm', b'e', b'w', b'h', b'e', b'r', b'e', b'e', b'l', b's',
+        b'e', // "/nix/store/somewhereelse"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        5, 0, 0, 0, 0, 0, 0, 0, b'e', b'n', b't', b'r', b'y', 0, 0, 0, // "entry"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'a', b'm', b'e', 0, 0, 0, 0, // "name"
+        4, 0, 0, 0, 0, 0, 0, 0, b'k', b'e', b'e', b'p', 0, 0, 0, 0, // "keep"
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'o', b'd', b'e', 0, 0, 0, 0, // "node"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        9, 0, 0, 0, 0, 0, 0, 0, b'd', b'i', b'r', b'e', b'c', b't', b'o', b'r', b'y', 0, 0, 0, 0, 0, 0, 0, // "directory"
+        5, 0, 0, 0, 0, 0, 0, 0, b'e', b'n', b't', b'r', b'y', 0, 0, 0, // "entry"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b'n', b'a', b'm', b'e', 0, 0, 0, 0, // "name"
+        5, 0, 0, 0, 0, 0, 0, 0, 46, 107, 101, 101, 112, 0, 0, 0, // ".keep"
+        4, 0, 0, 0, 0, 0, 0, 0, 110, 111, 100, 101, 0, 0, 0, 0, // "node"
+        1, 0, 0, 0, 0, 0, 0, 0, b'(', 0, 0, 0, 0, 0, 0, 0, // "("
+        4, 0, 0, 0, 0, 0, 0, 0, b't', b'y', b'p', b'e', 0, 0, 0, 0, // "type"
+        7, 0, 0, 0, 0, 0, 0, 0, b'r', b'e', b'g', b'u', b'l', b'a', b'r', 0, // "regular"
+        8, 0, 0, 0, 0, 0, 0, 0, b'c', b'o', b'n', b't', b'e', b'n', b't', b's', // "contents"
+        0, 0, 0, 0, 0, 0, 0, 0, // ""
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+        1, 0, 0, 0, 0, 0, 0, 0, b')', 0, 0, 0, 0, 0, 0, 0, // ")"
+    ];
+
+    /// A PathInfo message without .narinfo populated.
+    pub static ref PATH_INFO_WITHOUT_NARINFO : PathInfo = PathInfo {
+        node: Some(castorepb::Node {
+            node: Some(castorepb::node::Node::Directory(castorepb::DirectoryNode {
+                name: DUMMY_NAME.into(),
+                digest: DUMMY_DIGEST.clone().into(),
+                size: 0,
+            })),
+        }),
+        references: vec![DUMMY_OUTPUT_HASH.clone()],
+        narinfo: None,
+    };
+
+    /// A PathInfo message with .narinfo populated.
+    /// The references in `narinfo.reference_names` aligns with what's in
+    /// `references`.
+    pub static ref PATH_INFO_WITH_NARINFO : PathInfo = PathInfo {
+        narinfo: Some(NarInfo {
+            nar_size: 0,
+            nar_sha256: DUMMY_DIGEST.clone().into(),
+            signatures: vec![],
+            reference_names: vec![DUMMY_NAME.to_string()],
+            deriver: None,
+            ca: Some(Ca { r#type: ca::Hash::NarSha256.into(), digest:  DUMMY_DIGEST.clone().into() })
+        }),
+      ..PATH_INFO_WITHOUT_NARINFO.clone()
+    };
+}
diff --git a/tvix/store/src/tests/mod.rs b/tvix/store/src/tests/mod.rs
new file mode 100644
index 000000000000..daea048deddf
--- /dev/null
+++ b/tvix/store/src/tests/mod.rs
@@ -0,0 +1,3 @@
+pub mod fixtures;
+mod nar_renderer;
+pub mod utils;
diff --git a/tvix/store/src/tests/nar_renderer.rs b/tvix/store/src/tests/nar_renderer.rs
new file mode 100644
index 000000000000..65059fe9c025
--- /dev/null
+++ b/tvix/store/src/tests/nar_renderer.rs
@@ -0,0 +1,231 @@
+use crate::nar::calculate_size_and_sha256;
+use crate::nar::write_nar;
+use crate::tests::fixtures::*;
+use crate::tests::utils::*;
+use sha2::{Digest, Sha256};
+use std::io;
+use std::sync::Arc;
+use tokio::io::sink;
+use tvix_castore::blobservice::BlobService;
+use tvix_castore::directoryservice::DirectoryService;
+use tvix_castore::proto as castorepb;
+
+#[tokio::test]
+async fn single_symlink() {
+    let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+    let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+    let mut buf: Vec<u8> = vec![];
+
+    write_nar(
+        &mut buf,
+        &castorepb::node::Node::Symlink(castorepb::SymlinkNode {
+            name: "doesntmatter".into(),
+            target: "/nix/store/somewhereelse".into(),
+        }),
+        // don't put anything in the stores, as we don't actually do any requests.
+        blob_service,
+        directory_service,
+    )
+    .await
+    .expect("must succeed");
+
+    assert_eq!(buf, NAR_CONTENTS_SYMLINK.to_vec());
+}
+
+/// Make sure the NARRenderer fails if a referred blob doesn't exist.
+#[tokio::test]
+async fn single_file_missing_blob() {
+    let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+    let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+
+    let e = write_nar(
+        sink(),
+        &castorepb::node::Node::File(castorepb::FileNode {
+            name: "doesntmatter".into(),
+            digest: HELLOWORLD_BLOB_DIGEST.clone().into(),
+            size: HELLOWORLD_BLOB_CONTENTS.len() as u64,
+            executable: false,
+        }),
+        // the blobservice is empty intentionally, to provoke the error.
+        blob_service,
+        directory_service,
+    )
+    .await
+    .expect_err("must fail");
+
+    match e {
+        crate::nar::RenderError::NARWriterError(e) => {
+            assert_eq!(io::ErrorKind::NotFound, e.kind());
+        }
+        _ => panic!("unexpected error: {:?}", e),
+    }
+}
+
+/// Make sure the NAR Renderer fails if the returned blob meta has another size
+/// than specified in the proto node.
+#[tokio::test]
+async fn single_file_wrong_blob_size() {
+    let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+
+    // insert blob into the store
+    let mut writer = blob_service.open_write().await;
+    tokio::io::copy(
+        &mut io::Cursor::new(HELLOWORLD_BLOB_CONTENTS.to_vec()),
+        &mut writer,
+    )
+    .await
+    .unwrap();
+    assert_eq!(
+        HELLOWORLD_BLOB_DIGEST.clone(),
+        writer.close().await.unwrap()
+    );
+
+    let bs = blob_service.clone();
+    // Test with a root FileNode of a too big size
+    {
+        let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+        let e = write_nar(
+            sink(),
+            &castorepb::node::Node::File(castorepb::FileNode {
+                name: "doesntmatter".into(),
+                digest: HELLOWORLD_BLOB_DIGEST.clone().into(),
+                size: 42, // <- note the wrong size here!
+                executable: false,
+            }),
+            bs,
+            directory_service,
+        )
+        .await
+        .expect_err("must fail");
+
+        match e {
+            crate::nar::RenderError::NARWriterError(e) => {
+                assert_eq!(io::ErrorKind::UnexpectedEof, e.kind());
+            }
+            _ => panic!("unexpected error: {:?}", e),
+        }
+    }
+
+    let bs = blob_service.clone();
+    // Test with a root FileNode of a too small size
+    {
+        let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+        let e = write_nar(
+            sink(),
+            &castorepb::node::Node::File(castorepb::FileNode {
+                name: "doesntmatter".into(),
+                digest: HELLOWORLD_BLOB_DIGEST.clone().into(),
+                size: 2, // <- note the wrong size here!
+                executable: false,
+            }),
+            bs,
+            directory_service,
+        )
+        .await
+        .expect_err("must fail");
+
+        match e {
+            crate::nar::RenderError::NARWriterError(e) => {
+                assert_eq!(io::ErrorKind::InvalidInput, e.kind());
+            }
+            _ => panic!("unexpected error: {:?}", e),
+        }
+    }
+}
+
+#[tokio::test]
+async fn single_file() {
+    let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+    let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+
+    // insert blob into the store
+    let mut writer = blob_service.open_write().await;
+    tokio::io::copy(&mut io::Cursor::new(HELLOWORLD_BLOB_CONTENTS), &mut writer)
+        .await
+        .unwrap();
+
+    assert_eq!(
+        HELLOWORLD_BLOB_DIGEST.clone(),
+        writer.close().await.unwrap()
+    );
+
+    let mut buf: Vec<u8> = vec![];
+
+    write_nar(
+        &mut buf,
+        &castorepb::node::Node::File(castorepb::FileNode {
+            name: "doesntmatter".into(),
+            digest: HELLOWORLD_BLOB_DIGEST.clone().into(),
+            size: HELLOWORLD_BLOB_CONTENTS.len() as u64,
+            executable: false,
+        }),
+        blob_service,
+        directory_service,
+    )
+    .await
+    .expect("must succeed");
+
+    assert_eq!(buf, NAR_CONTENTS_HELLOWORLD.to_vec());
+}
+
+#[tokio::test]
+async fn test_complicated() {
+    let blob_service: Arc<dyn BlobService> = gen_blob_service().into();
+    let directory_service: Arc<dyn DirectoryService> = gen_directory_service().into();
+
+    // put all data into the stores.
+    // insert blob into the store
+    let mut writer = blob_service.open_write().await;
+    tokio::io::copy(&mut io::Cursor::new(EMPTY_BLOB_CONTENTS), &mut writer)
+        .await
+        .unwrap();
+    assert_eq!(EMPTY_BLOB_DIGEST.clone(), writer.close().await.unwrap());
+
+    directory_service
+        .put(DIRECTORY_WITH_KEEP.clone())
+        .await
+        .unwrap();
+    directory_service
+        .put(DIRECTORY_COMPLICATED.clone())
+        .await
+        .unwrap();
+
+    let mut buf: Vec<u8> = vec![];
+
+    let bs = blob_service.clone();
+    let ds = directory_service.clone();
+
+    write_nar(
+        &mut buf,
+        &castorepb::node::Node::Directory(castorepb::DirectoryNode {
+            name: "doesntmatter".into(),
+            digest: DIRECTORY_COMPLICATED.digest().into(),
+            size: DIRECTORY_COMPLICATED.size(),
+        }),
+        bs,
+        ds,
+    )
+    .await
+    .expect("must succeed");
+
+    assert_eq!(buf, NAR_CONTENTS_COMPLICATED.to_vec());
+
+    // ensure calculate_nar does return the correct sha256 digest and sum.
+    let bs = blob_service.clone();
+    let ds = directory_service.clone();
+    let (nar_size, nar_digest) = calculate_size_and_sha256(
+        &castorepb::node::Node::Directory(castorepb::DirectoryNode {
+            name: "doesntmatter".into(),
+            digest: DIRECTORY_COMPLICATED.digest().into(),
+            size: DIRECTORY_COMPLICATED.size(),
+        }),
+        bs,
+        ds,
+    )
+    .await
+    .expect("must succeed");
+
+    assert_eq!(NAR_CONTENTS_COMPLICATED.len() as u64, nar_size);
+    let d = Sha256::digest(NAR_CONTENTS_COMPLICATED.clone());
+    assert_eq!(d.as_slice(), nar_digest);
+}
diff --git a/tvix/store/src/tests/utils.rs b/tvix/store/src/tests/utils.rs
new file mode 100644
index 000000000000..040b7ee7f51f
--- /dev/null
+++ b/tvix/store/src/tests/utils.rs
@@ -0,0 +1,16 @@
+use crate::pathinfoservice::{MemoryPathInfoService, PathInfoService};
+use std::sync::Arc;
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService};
+
+pub use tvix_castore::utils::*;
+
+pub fn gen_pathinfo_service<BS, DS>(
+    blob_service: BS,
+    directory_service: DS,
+) -> Arc<dyn PathInfoService>
+where
+    BS: AsRef<dyn BlobService> + Send + Sync + 'static,
+    DS: AsRef<dyn DirectoryService> + Send + Sync + 'static,
+{
+    Arc::new(MemoryPathInfoService::new(blob_service, directory_service))
+}
diff --git a/tvix/store/src/utils.rs b/tvix/store/src/utils.rs
new file mode 100644
index 000000000000..041a9e683d59
--- /dev/null
+++ b/tvix/store/src/utils.rs
@@ -0,0 +1,35 @@
+use std::sync::Arc;
+
+use tvix_castore::{
+    blobservice::{self, BlobService},
+    directoryservice::{self, DirectoryService},
+};
+
+use crate::pathinfoservice::{self, PathInfoService};
+
+/// Construct the three store handles from their addrs.
+pub async fn construct_services(
+    blob_service_addr: impl AsRef<str>,
+    directory_service_addr: impl AsRef<str>,
+    path_info_service_addr: impl AsRef<str>,
+) -> std::io::Result<(
+    Arc<dyn BlobService>,
+    Arc<dyn DirectoryService>,
+    Box<dyn PathInfoService>,
+)> {
+    let blob_service: Arc<dyn BlobService> = blobservice::from_addr(blob_service_addr.as_ref())
+        .await?
+        .into();
+    let directory_service: Arc<dyn DirectoryService> =
+        directoryservice::from_addr(directory_service_addr.as_ref())
+            .await?
+            .into();
+    let path_info_service = pathinfoservice::from_addr(
+        path_info_service_addr.as_ref(),
+        blob_service.clone(),
+        directory_service.clone(),
+    )
+    .await?;
+
+    Ok((blob_service, directory_service, path_info_service))
+}