feat(tvix/nar-bridge): add nar-bridge-pathinfo command r/6708

This adds an additional nar-bridge-pathinfo command.

It exposes a PathInfoService for a HTTP Binary Cache, ingesting data
into a BlobService/DirectoryService as it goes through the NAR file.

It does this whenever it receives a Get request for a specific output
path, and waits returning with the PathInfo response until it ingested
the data.
It does not do any sort of caching - this means it re-downloads NAR
files again whenever the PathInfo is requested again, so you most likely
do not want to use this currently.

It's one building component as soon as we have store composition (which
we currently don't, so don't use this).

It can be used as an alternative mechanism to ingest data (Blobs and
Directories) of a given store path from a binary cache into tvix-store.

```
❯ nix-build -A third_party.nixpkgs.hello
/nix/store/mdi7lvrn2mx7rfzv3fdq3v5yw8swiks6-hello-2.12.1

❯ nix hash to-sri --type sha1 mdi7lvrn2mx7rfzv3fdq3v5yw8swiks6
sha1-Rs/INeK+7IGbG/u7fHoVNm96Yqs=

❯ out=$(mg build //tvix/nar-bridge)
$out/bin/nar-bridge-pathinfo --log-level debug &
INFO[0000] Starting nar-bridge-pathinfosvc at [::]:8001

❯ mg run //tvix:store -- daemon &
[mg] building target //tvix:store
[mg] running target //tvix:store
  2023-10-03T16:21:57.433739Z  INFO tvix_store: tvix-store listening on [::]:8000
    at src/bin/tvix-store.rs:229

❯ evans --host localhost --port 8001 -r repl
[…]
tvix.store.v1.PathInfoService@localhost:8001> call Get
✔ by_output_hash
by_output_hash (TYPE_BYTES) => Rs/INeK+7IGbG/u7fHoVNm96Yqs=
{
  "narinfo": {
    "narSha256": "sXrPtjqhSoc2u0YfM1HVZThknkSYuRuHdtKCB6wkDFo=",
    "narSize": "226552",
    "referenceNames": [
      "aw2fw9ag10wr9pf0qk4nk5sxi0q0bn56-glibc-2.37-8",
      "mdi7lvrn2mx7rfzv3fdq3v5yw8swiks6-hello-2.12.1"
    ],
    "signatures": [
      {
        "data": "7guDbfaF2Q29HY0c5axhtuacfxN6uxuEqeUfncDiSvMSAWvfHVMppB89ILqV8FE58pEQ04tSbMnRhR3FGPV0AA==",
        "name": "cache.nixos.org-1"
      }
    ]
  },
  "node": {
    "directory": {
      "digest": "xvo6BYbYaDw76IibLu5sr+VZoj9iM0ET2RUuYSYLwKE=",
      "name": "bWRpN2x2cm4ybXg3cmZ6djNmZHEzdjV5dzhzd2lrczYtaGVsbG8tMi4xMi4x",
      "size": 141
    }
  },
  "references": [
    "ptgFMIhdl2nJxMDdlDkITyXuBFc=",
    "Rs/INeK+7IGbG/u7fHoVNm96Yqs="
  ]
}
```

Change-Id: I50167d0ac081c91adf5cf2733bbc4dc0993bd46e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9539
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Reviewed-by: Brian Olsen <me@griff.name>

1 files changed, 3 insertions, 1 deletions

diff --git a/tvix/README.md b/tvix/README.md
index bc154030d8..8fd6eae52b 100644
--- a/tvix/README.md
+++ b/tvix/README.md
@@ -49,7 +49,9 @@ This folder contains the following components:
 * `//tvix/castore` - subtree storage/transfer in a content-addressed fashion
 * `//tvix/cli` - preliminary REPL & CLI implementation for Tvix
 * `//tvix/eval` - an implementation of the Nix programming language
-* `//tvix/nar-bridge` - a HTTP webserver providing a Nix HTTP Binary Cache interface in front of a tvix-store
+* `//tvix/nar-bridge`
+  * `nar-bridge-http`: A HTTP webserver providing a Nix HTTP Binary Cache interface in front of a tvix-store
+  * `nar-bridge-pathinfo`: A gRPC server, exposing a Nix HTTP Binary Cache as a tvix-store PathInfoService
 * `//tvix/nix-compat` - a Rust library for compatibility with C++ Nix, features like encodings and hashing schemes and formats
 * `//tvix/serde` - a Rust library for using the Nix language for app configuration
 * `//tvix/store` - a "filesystem" linking Nix store paths and metadata with the content-addressed layer