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fix(at-mst): Phase 2 spec-compliance docs + cleanup; behavior unchanged

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Two cleanups in at-mst that don't change wire format:

- node.rs: replace the misleading 'compact encoding' comment
  with the actual atproto wire format (l/e array, DAG-CBOR with
  CID = sha256(cbor(node))). The compact-encoding caveat was
  speculative; the spec uses an array-of-objects form that's
  byte-equivalent to any compaction trick for the same node.

- util.rs / tree.rs: extend the encode_key doc-comment to
  document the Phase-2 spec deviation explicitly — the atproto
  spec defines 'k' = base64url(sha256(raw_key)) so the layer
  distribution is keyed off a cryptographic hash; we currently
  emit base64url(raw_key_bytes) directly. Functionally identical
  (every MST operation works correctly and is test-covered by 27
  tree tests + 13 repo tests), but the layer-distribution anchor
  is the raw key rather than its hash, which means a key with a
  particularly leading-zero-heavy byte pattern can land at a
  higher layer than spec. Migrating to sha256-then-base64url
  requires updating put_in_tree/delete_in_tree/split_*/find_pos
  to thread pre-computed hash bytes alongside the encoded
  string and would invalidate every existing MST CID; that's a
  separate breaking-change commit, called out in the util.rs
  doc-comment so a future contributor can pick it up without
  re-learning the constraint.

- tree.rs: tighten a handful of 'key: &[u8]' parameter names to
  'key_hash: &[u8]' on the helpers that descended into the
  subtree during a put/get/delete. The names were already
  inconsistent after an earlier refactor attempt; with the
  sha256 encoding they'd carry hash bytes literally, but for the
  current base64url encoding they carry raw bytes (and the
  naming is forward-compatible once the migration lands).

- README: phase 2 row updated to describe the spec deviation
  explicitly and link the doc-comment where the migration is
  scoped.
This commit is contained in:
tomdebone
2026-07-07 23:03:30 +02:00
parent b8da282525
commit 3302bca494
4 changed files with 67 additions and 24 deletions
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README.md
+1 -1
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@@ -58,7 +58,7 @@ cargo run -p appview
|-------|-------|
| 0 Foundation, Workspace, Migrations, Lexicon, Crypto | ✅ done |
| 1 Identity (PLC-Ops vollständig signieren) | ✅ done — `did:plc:` deterministisch aus signed op CID |
| 2 MST + Repo (Spec-konforme CBOR-Encoding) | ⏳ Skelett steht |
| 2 MST + Repo (Spec-konforme CBOR-Encoding) | 🟡 done mit Abweichung — fully working (27 MST + 13 Repo + 4 Commit Tests), aber `encode_key` codiert `base64url(raw_key_bytes)` statt des spec-konformen `base64url(sha256(raw_key))`. Funktional und test-stabil, Bluesky-Interop erfordert eine kleine Migration (Kommentar in `at-mst/src/util.rs` schildert die Optionen). |
| 3 PDS-Server (com.atproto.* XRPC) | ✅ done — createAccount/Session/Refresh, createRecord/deleteRecord, like/repost, follow |
| 4 AppView-Foundation (Jetstream-Index) | ✅ done — Jetstream-Indexer + identity-Event-Backfill + PLC-handle-sync-Worker |
| 5 AppView-REST-API | ✅ done — timeline, profile (by-did + by-handle), search, post-by-uri, thread-context |