glm-5.3-flash
e76f91f6d7
- ADR-013: V0-framed push machine grounded in real git 2.43.0 captures
(file://, git://, smart-http mock, raw stdio into real receive-pack):
V0-shaped ref advertisement (caps on first ref line, capabilities^{}
sentinel only for empty repos), served capability set, shallow requests
rejected for v1, thin packs accepted with server-odb bases (no
capability involved; push.thin default), ingestion bound to
Bundle::write_to_directory_eagerly + gix-fsck + one gix-ref transaction
per push (.keep-guarded), unpack-first CAS timing with observed
upstream order, band-1 pkt-line-framed status report, http framing
(probe/Content-Length/chunked), v1 update policy (CAS only; deletes
and force-push allowed)
- docs/research/push-captures.md: the normative push wire record
- transport.md/backend.md/doors.md: receive-pack sections rewritten to
the decided shapes; backend.md ingestion composition bound; stale
OQ-04 references resolved
- ADR-003 amended: V2-only governs fetch; push is V0-framed by upstream
design (fixes the V2-only contradiction found in review)
- ADR-009 amended: haves default reconciled with the client's stateless
ceiling (16384); blocking-pipeline budget covers generation+ingestion
- OQ-04 resolved; tracker task closed; CAS-fail-fast optimization
tracked (tasks/architecture/oq-13-cas-failfast.md)
- research index: poc findings + capture docs listed
Verification: cargo test / clippy -D warnings / fmt --check / doc pass
82 lines
3.9 KiB
Markdown
82 lines
3.9 KiB
Markdown
# ADR-003: Protocol V2-first with honest capability advertisement
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## Status
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Accepted
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## Context
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The git smart protocol has three versions in the wild: V0 (the original),
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V1 (capability line prefixed), and V2 (command-based, default since git
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2.18+). POC-1 and POC-2 validated the full V2 fetch path against real git
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2.43 end-to-end (advertisement, ls-refs, fetch with sideband packs) over
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both duplex and http substrates. V0/V1 stateless-http is a different
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framing (per-round POSTs, stateless ack re-derivation).
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The research inventory (`git-protocol.md` §"Open items") left the V0/V1
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question open: support V0/V1 on http? On ssh? Which first?
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Decision drivers:
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- Our deployment anchor (vision §"Primary deployment target") is modern
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git clients over http and ssh; every git client from the last six years
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speaks V2.
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- Honest capability advertisement (vision principle 5) is easiest to keep
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honest with fewer served shapes.
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- V0/V1 stateless-http needs multi-round negotiation state re-derivation —
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meaningful complexity for a client population that is effectively
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extinct.
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## Decision
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**Serve protocol V2 first.** alkgit v1 serves V2 on both doors:
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- Advertisement is once-per-session (duplex) / per-request-set (http),
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exactly as observed in POC-1 (re-advertising between commands hangs real
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git).
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- Advertised capabilities are exactly what we serve: `ls-refs=unborn`,
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`fetch=wait-for-done` (the full-closure pack on `done` policy
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validated in POC-1/2; the multi-round ack loop, ADR-014, needs no
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capability change — the acknowledgments section is grammar, not
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capability), `object-format=sha1` (+ sha256 under the feature flag, if and
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when tested — OQ-05). Nothing unimplemented is advertised
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(shallow, filter, packfile-uris, object-info, server-option are
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*declined by omission*; POC-1 confirmed real git accepts this).
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On the push side, `git-upload-archive` is not served at all — ssh
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exec requests for it get a fixed refusal (doors.md; ADR-008's
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never-execute rule).
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- HTTP requests protocol V2 only; ssh requests protocol V2 only (see
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below).
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**V0/V1 policy: decided now as V2-only for v1 — fetch only.** Both doors
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(http and ssh) speak V2 for *fetch*; clients that cannot speak V2 get a
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clear pkt-line error. Reversal is wire-visible (the advertised version set is a wire
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format), so treat this as effectively one-way once published — the
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decision is still made now, and revisiting it needs a new ADR plus a
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deprecation window for clients. The motivation stands: a concrete consumer
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needing V0/V1 (e.g. very old CI images) has not been identified.
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**Receive-pack is exempt**: the push path is V0-framed by upstream design
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on every client generation (no version negotiation exists on push at
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all — ADR-013 §1), so the V2-only rule never touches `git push`. The
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V0/V1 decline applies to the fetch path only.
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Sequencing note: the v1 fetch policy that ships first is full-closure-on-`done` (POC-validated).
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Multi-round V2 negotiation (haves/acks without `done`) is in v1's *scope*
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but lands after the done-path works end-to-end; its ack loop is now
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decided (ADR-014) and needs no capability-advertisement change.
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## Consequences
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- Smallest honest surface; POC-validated shapes only.
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- Old-client support is declined explicitly (error, not silence).
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- The POC's observed `done`-path shape (no acknowledgments section, no
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`ready`, response ends at flush) is our normative wire behavior, not the
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docs' grammar — `git-protocol.md` §V2 records this.
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- If V0/V1 is ever added, the state machines in transport must be
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re-shaped around a version-dispatch at session start (single point, by
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design — see ADR-005).
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## References
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- `docs/research/git-protocol.md` §"Protocol surface inventory", §"Negotiation policy"
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- `docs/research/poc-1-findings.md` (advertisement-once, capability declination), POC-3 (http V2 framing)
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- ADR-005 (substrate types), ADR-007 (ACL before advertisement)
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- transport.md, doors.md |