alkgit

Git smart protocol for the alk family: the producer and consumer halves of the git smart protocol as a pure protocol crate, riding alkcall channels on the alk/git ALPN.

The crate serves the wire — V2 upload-pack (advertisement, ls-refs, the negotiation ack loop, the done round's streamed pack) and V0 receive-pack (push advertisement, the bounded packless peek, ingestion through the seam, status reports) — and consumes it (GitSession, the typed fetch/push client). It is a pure protocol crate (ADR-010, the alktty/alktunnels template): no binary, no front doors — the alkhttp git/lfs features and alkssh are family infrastructure (doors.md); a downstream app embeds this crate, brings its own door (alkcall duplex or the smart-http shapes), and supplies the backends. The shipped alkstore + alkblobs composition is the separate alkgit-substrate crate (ADR-025).

The backend seam

Everything the wire layer runs through — five #[async_trait], dyn-compatible traits (ADR-018) every backend implements:

Trait	Contract
GitRegistry	repo id → RepoRecord (ADR-012 §1)
GitRegistryStore	registry writes (put/update/remove; grants ride RepoRecord)
GitRefs	ref listings + apply_updates — the single CAS home (ADR-013 §7)
GitPackGen	pack generation (wants/haves closure) + common_haves (the ack-loop recognition seam, ADR-014 §5)
GitPackIngest	push ingestion, the prepare/apply split (PreparedPush) (ADR-020 §2)

Supporting surface: RepoRecord / Visibility / AccessAction + the repo-id grammar, the error model (RegistryError, StorageError), the budget model (Limits — wall clock, request bodies, refs, negotiation rounds, haves, pack and object sizes, the packless peek window, blocking-pool concurrency — ADR-009), and the wire shapes (RefLine, RefUpdate, RefOutcome, PushOptions).

Serving — the producer half

Sessions take the AuthorizedRepo marker by type (ADR-007 — the resolve→authorize check is unskippable; ACL runs before any protocol byte) and are bounded by Limits throughout:

use std::sync::Arc;
use tokio::sync::Semaphore;

use alkgit::{AuthorizedRepo, AccessAction, Limits, Service, serve_duplex};

// the door resolves + authorizes, then hands the marker on:
let marker = AuthorizedRepo::authorize(record, identity, AccessAction::Read)
    .expect("the check passed");

let pipeline = Arc::new(Semaphore::new(limits.max_concurrent_blocking_tasks));
serve_duplex(
    &marker, stream, Limits::default(), Service::UploadPack,
    refs, packgen, ingest, /* push_options_negotiated */ false, pipeline,
).await?;

On the native transport, GitAdapter fronts the alk/git ALPN directly (it holds the same handles and emits the ADR-016 request-line preamble discipline), and register_openable mounts the channels/git/sub open op for channel-mediated sessions. On the smart-http shapes, serve_stateless_post / serve_stateless_advertisement mount the per-POST entry (one POST = one command invocation) the http door composes — see tests/duplex_serving.rs and tests/stateless_serving.rs for full, working assemblies.

Consuming — the consumer half

GitSession is a typed git client over gix-transport's git-daemon Connection on the alkcall BiStream compat halves (ADR-017):

let mut session = GitSession::connect_direct(
    bistream, "owner/repo", Service::UploadPack, Some("peer.alk.dev"), limits,
)?;

let refs = session.ls_refs(&LsRefsArgs::default()).await?;
let reports = session.fetch(
    vec![FetchRound { wants, haves, done: true }],
    &mut pack_sink,
).await?;

Push rides its own session (Service::ReceivePack, the hand-rolled send-pack — commands, the caller's pack streamed raw, the typed PushReport parsed in both framings).

Status

The protocol core is at its first release; the architecture specs (docs/architecture/) are the authoritative contract — the ADRs and transport.md / backend.md pin every wire shape and trait signature the publish froze. The substrate track (waves 6–10) lands the shipped backend composition in alkgit-substrate.

Documentation

• Architecture docs — the authoritative spec: ADRs, wire formats, and the backend contracts.
• API docs — full crate documentation.
• Changelog

License

MIT OR Apache-2.0