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🔒️ Only accept presence for the doc on its channel - #752
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coverage: 97.949% (+0.03%) from 97.916% — check-doc-presence-channel into main |
This was referenced Oct 6, 2026
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🟡 Changes recommended
Mismatched presence errors can bypass the client filter and reach another local presence with the same ID.
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What changed in this PR
Hardens document presence channel validation and documents presence access-control responsibilities.
Changes:
- Validates document presence channels server-side and filters mismatched client updates.
- Adds security regression tests.
- Documents middleware-based access control and presence ID ownership.
| File | Description |
|---|---|
lib/agent.js |
Validates document presence channels. |
lib/client/presence/doc-presence.js |
Filters updates for other documents. |
test/client/presence/doc-presence.js |
Tests channel validation and filtering. |
docs/presence.md |
Adds access-control guidance. |
docs/middleware/actions.md |
Adds presence permission warnings. |
docs/api/presence.md |
Documents presence ID ownership. |
docs/api/backend.md |
Documents presence error-forwarding configuration. |
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Fixes #738 At the moment, the server checks read access against a presence's `c` and `d`, but broadcasts it on its `ch`: 1. Deny `docs/secret` in `readSnapshots` 2. Send presence on `docs.secret` with the `c`/`d` of a readable doc 3. `docs/secret` subscribers apply it This change rejects doc presence whose `c` and `d` don't match its channel, and `DocPresence` ignores presence for any other doc, which also covers untyped presence and dotted-name channel collisions. Forwarded `sendPresence` errors no longer reach a local presence with the same ID either: unlike replies to the client's own submissions, they carry no `pv`. Subscribing, write access and presence ID ownership are left to middleware, which the new "Access control" docs cover. The server check only holds once every instance is upgraded, and the client filter only protects upgraded clients. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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Fixes #735 At the moment, the server relays a doc presence whose `v` is ahead of the doc unchanged, which lets one client make every subscriber fetch: 1. Submit presence with `v: 1e9` to a doc with 20 subscribers 2. Each subscriber calls `doc.fetch()`, since `v > doc.version` 3. The presence stays pending, so every later op fetches again This change has the `Agent` pass its tracked doc version through to the presence transform, which reads ops from the lower of that and `v`. The tracker can lag the database but never lead it, so a `v` past the last op read is ahead of the doc. Ops in that lag may have been deleted, though, so we check the snapshot version before rejecting. Doc presence must now carry an integer `v`, and so must ops that send one. A rejected presence restores the `Agent`'s previously cached request, so the leave it replays on disconnect isn't rejected too. Presence sent without `c`/`d` skips all of this, since the server can't tell it from generic presence, but clients ignore it since #752. We deliberately don't bound presence that is far *behind*: a `fetch` with `v: 0` already makes the server read the whole op history. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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October 15, 2026 14:07
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Fixes #738
At the moment, the server checks read access against a presence's
candd, but broadcasts it on itsch:docs/secretinreadSnapshotsdocs.secretwith thec/dof a readable docdocs/secretsubscribers apply itThis change rejects doc presence whose
candddon't match its channel, andDocPresenceignores presence for any other doc, which also covers untyped presence and dotted-name channel collisions. ForwardedsendPresenceerrors no longer reach a local presence with the same ID either: unlike replies to the client's own submissions, they carry nopv. Subscribing, write access and presence ID ownership are left to middleware, which the new "Access control" docs cover.The server check only holds once every instance is upgraded, and the client filter only protects upgraded clients.
🤖 Generated with Claude Code
Co-Authored-By: Claude noreply@anthropic.com