5 files changed, 97 insertions, 3 deletions
diff --git a/tvix/Cargo.lock b/tvix/Cargo.lock
index 913d88b9fc12..106a1e38d0b4 100644
--- a/tvix/Cargo.lock
+++ b/tvix/Cargo.lock
@@ -423,6 +423,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f3ad85c1f65dc7b37604eb0e89748faf0b9653065f2a8ef69f96a687ec1e9279"
 
 [[package]]
+name = "count-write"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ced507ab50aa0123e2c54db8b5f44fdfee04b1c93744d69e924307945fe57a85"
+
+[[package]]
 name = "countme"
 version = "3.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2770,12 +2776,14 @@ dependencies = [
  "anyhow",
  "blake3",
  "clap 4.1.4",
+ "count-write",
  "data-encoding",
  "fastcdc",
  "lazy_static",
  "nix-compat",
  "prost",
  "prost-build",
+ "sha2 0.10.6",
  "sled",
  "tempfile",
  "test-case",
diff --git a/tvix/Cargo.nix b/tvix/Cargo.nix
index 126edecdff17..fc3f945df342 100644
--- a/tvix/Cargo.nix
+++ b/tvix/Cargo.nix
@@ -1246,6 +1246,21 @@ rec {
         ];
 
       };
+      "count-write" = rec {
+        crateName = "count-write";
+        version = "0.1.0";
+        edition = "2018";
+        sha256 = "11bswmgr81s3jagdci1pr6qh9vnz9zsbbf2dqpi260daa2mhgmff";
+        authors = [
+          "SOFe <sofe2038@gmail.com>"
+        ];
+        features = {
+          "futures" = [ "futures-io-preview" ];
+          "futures-io-preview" = [ "dep:futures-io-preview" ];
+          "tokio" = [ "tokio-io" ];
+          "tokio-io" = [ "dep:tokio-io" ];
+        };
+      };
       "countme" = rec {
         crateName = "countme";
         version = "3.0.1";
@@ -8253,6 +8268,10 @@ rec {
             features = [ "derive" "env" ];
           }
           {
+            name = "count-write";
+            packageId = "count-write";
+          }
+          {
             name = "data-encoding";
             packageId = "data-encoding";
           }
@@ -8273,6 +8292,10 @@ rec {
             packageId = "prost";
           }
           {
+            name = "sha2";
+            packageId = "sha2 0.10.6";
+          }
+          {
             name = "sled";
             packageId = "sled";
             features = [ "compression" ];
diff --git a/tvix/store/Cargo.toml b/tvix/store/Cargo.toml
index 769b496235d6..196e986b89ab 100644
--- a/tvix/store/Cargo.toml
+++ b/tvix/store/Cargo.toml
@@ -9,19 +9,21 @@ name = "tvix_store"
 [dependencies]
 anyhow = "1.0.68"
 blake3 = { version = "1.3.1", features = ["rayon", "std"] }
+clap = { version = "4.0", features = ["derive", "env"] }
+count-write = "0.1.0"
 data-encoding = "2.3.3"
+fastcdc = "2.0.0"
 lazy_static = "1.4.0"
-clap = { version = "4.0", features = ["derive", "env"] }
 prost = "0.11.2"
+sha2 = "0.10.6"
 sled = { version = "0.34.7", features = ["compression"] }
 nix-compat = { path = "../nix-compat" }
 thiserror = "1.0.38"
 tokio-stream = "0.1.11"
 tokio = { version = "1.23.0", features = ["rt-multi-thread"] }
 tonic = "0.8.2"
-tracing-subscriber = "0.3.16"
 tracing = "0.1.37"
-fastcdc = "2.0.0"
+tracing-subscriber = "0.3.16"
 
 [dependencies.tonic-reflection]
 optional = true
diff --git a/tvix/store/src/nar/mod.rs b/tvix/store/src/nar/mod.rs
index a3a8677d92a6..d9e0c8143b5a 100644
--- a/tvix/store/src/nar/mod.rs
+++ b/tvix/store/src/nar/mod.rs
@@ -1,8 +1,11 @@
+use crate::proto;
 use data_encoding::BASE64;
 use thiserror::Error;
 
+mod non_caching_calculation_service;
 mod renderer;
 
+pub use non_caching_calculation_service::NonCachingNARCalculationService;
 pub use renderer::NARRenderer;
 
 /// Errors that can encounter while rendering NARs.
@@ -23,3 +26,11 @@ pub enum RenderError {
     #[error("failure using the NAR writer: {0}")]
     NARWriterError(std::io::Error),
 }
+
+/// The base trait for something calculating NARs, and returning their size and sha256.
+pub trait NARCalculationService {
+    fn calculate_nar(
+        &self,
+        root_node: proto::node::Node,
+    ) -> Result<proto::CalculateNarResponse, RenderError>;
+}
diff --git a/tvix/store/src/nar/non_caching_calculation_service.rs b/tvix/store/src/nar/non_caching_calculation_service.rs
new file mode 100644
index 000000000000..880d12636979
--- /dev/null
+++ b/tvix/store/src/nar/non_caching_calculation_service.rs
@@ -0,0 +1,50 @@
+use count_write::CountWrite;
+use sha2::{Digest, Sha256};
+
+use crate::blobservice::BlobService;
+use crate::chunkservice::ChunkService;
+use crate::directoryservice::DirectoryService;
+use crate::proto;
+
+use super::renderer::NARRenderer;
+use super::{NARCalculationService, RenderError};
+
+/// A NAR calculation service which simply renders the whole NAR whenever
+/// we ask for the calculation.
+#[derive(Clone)]
+pub struct NonCachingNARCalculationService<
+    BS: BlobService,
+    CS: ChunkService + Clone,
+    DS: DirectoryService,
+> {
+    nar_renderer: NARRenderer<BS, CS, DS>,
+}
+
+impl<BS: BlobService, CS: ChunkService + Clone, DS: DirectoryService>
+    NonCachingNARCalculationService<BS, CS, DS>
+{
+    pub fn new(blob_service: BS, chunk_service: CS, directory_service: DS) -> Self {
+        Self {
+            nar_renderer: NARRenderer::new(blob_service, chunk_service, directory_service),
+        }
+    }
+}
+
+impl<BS: BlobService, CS: ChunkService + Clone, DS: DirectoryService> NARCalculationService
+    for NonCachingNARCalculationService<BS, CS, DS>
+{
+    fn calculate_nar(
+        &self,
+        root_node: proto::node::Node,
+    ) -> Result<proto::CalculateNarResponse, RenderError> {
+        let h = Sha256::new();
+        let mut cw = CountWrite::from(h);
+
+        self.nar_renderer.write_nar(&mut cw, root_node)?;
+
+        Ok(proto::CalculateNarResponse {
+            nar_size: cw.count() as u32,
+            nar_sha256: cw.into_inner().finalize().to_vec(),
+        })
+    }
+}