Expose optional group app components - #1929
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Included review availability: 1 review is currently available. Your included PR review attempts over the past 7 days set your current allowance at 3 reviews per hour. WalkthroughThe change adds application-owned group component reads and updates. It validates component IDs, routes updates through account-worker and MLS commit flows, preserves absent versus empty state, and exposes C and UniFFI APIs with error mappings and lifecycle tests. ChangesApplication group components
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Let applications store shared settings in authenticated group state instead of expiring messages. Expose reads and admin-only updates through the app runtime, UniFFI, and C while keeping protocol-owned and required components outside the generic write path. Reuse MLS publication and convergence so settings survive retention and reach new members through their Welcome.
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Inline comments:
In `@crates/marmot-c/CHANGELOG.md`:
- Line 19: Update the changelog entry describing opaque optional group state to
document that application-owned IDs may be either private-use or unreserved
component IDs, matching the validation contract.
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crates/cgka-conformance-simulator/src/app_runtime.rscrates/marmot-app/README.mdcrates/marmot-app/src/client/mod.rscrates/marmot-app/src/client/projection.rscrates/marmot-app/src/error.rscrates/marmot-app/src/runtime/account_worker.rscrates/marmot-app/src/runtime/commands.rscrates/marmot-app/src/runtime/mod.rscrates/marmot-app/tests/relay_runtime.rscrates/marmot-c/CHANGELOG.mdcrates/marmot-c/include/marmot.hcrates/marmot-c/src/commands.rscrates/marmot-c/src/status.rscrates/marmot-c/src/types/group.rscrates/marmot-c/tests/out_pointer_preflight.rscrates/marmot-uniffi/src/commands/group.rscrates/marmot-uniffi/src/conversions/group.rscrates/marmot-uniffi/src/errors.rs
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Inline comments:
In `@crates/marmot-c/API-REFERENCE.md`:
- Line 2161: Update the documentation for the application-owned group state read
API to clarify that the caller must provide a writable pointer-to-pointer and
that an absent component is indicated by *out == NULL, not a NULL out-pointer;
preserve the existing distinction for present empty state and protocol-owned
IDs.
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The binding-reference gate added on master scaffolds every new export and blocks until an author supplies integration prose. Fill in the component read/update and record-free entries and place them beside their neighbouring group commands, and refresh the mechanical header anchors the new C declarations shifted.
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The app-facing update gate and the engine's GroupContext format check each carried their own copy of the protocol-owned component ids, and nothing tied either copy to the constants in cgka-traits. A component id assigned later would stay writable through update_app_component until someone remembered to edit the gate. Keep the list beside the constants it names and have both callers read it, so a new protocol component is rejected by the app-facing gate the moment its constant lands. The engine keeps excluding the leaf-only account proof, which carries no GroupContext state.
app_component_lifecycle asserted that one retention sweep pruned the expired message, but the sweep reports no outcome until alice's own retention row is projected and defers while any received row is still unread. Both land asynchronously, so the assertion failed on loaded CI runners while passing locally. Mark the group read and retry the sweep until it prunes, keeping the assertion that expiry really ran before the component is re-read.
The C read documented an absent component as "OK with a NULL out-pointer". A NULL out argument is an error there: write_out rejects it with MARMOT_STATUS_NULL_POINTER, as the out-pointer preflight test asserts. Absence is a NULL written into *out alongside OK. Use the wording the deliver_opt helpers already use, in the header doc comment, the C changelog and the binding reference, and regenerate the header and its anchors.
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| Review metadata | Value |
|---|---|
| Reviewed at (UTC) | 2026-09-20T11:16:49Z |
| Commit reviewed | 1fad94f1a6eaee073d7e28a9594e8ed3cac5fa1d |
| Model | claude-opus-5[1m] |
| Reasoning level | Not exposed by runtime |
| Recommended action | Fix blocking issues before merge |
The premise holds: custom messages genuinely cannot carry durable shared settings past retention or into a Welcome, and app-owned GroupContext components are the right primitive. The implementation is mostly a thin, well-scoped pass-through, the admin gate is the engine's existing require_admin, and app_component_lifecycle is a genuinely strong test — permissions, convergence, Welcome propagation, retention survival, empty-vs-absent, and restart persistence in one pass. Driving is_known_group_component off the new PROTOCOL_OWNED_APP_COMPONENT_IDS is a net simplification and I verified it is behavior-preserving (CURRENT_PROFILE_LEAF_ONLY_APP_COMPONENTS is exactly the account-identity-proof id).
Two things should be settled before this lands, because both are cheap now and expensive after the C ABI and the app-id contract are released:
- No byte cap on the payload. Every other app-supplied payload in this workspace that reaches group state or the network has an explicit maximum (
GROUP_PROFILE_NAME_MAX_LEN,GROUP_AVATAR_URL_MAX_LEN,MAX_GROUP_IMAGE_BYTES, the Blossom descriptor limit).validate_app_component_bytesfalls through to_ => Ok(())for app-owned ids, so this is the first path where a host can put unbounded bytes into GroupContext — re-encoded in every subsequent commit and in every Welcome, permanently. - App ids are allowed across the whole private-use space the protocol itself allocates from. The gate is "not on today's protocol list", and protocol ids march upward from
0x8001(now at0x800c). An app that picks0x800dwrites it successfully today.
Plus one API-consistency fix: marmot_app_component_free is the only free function in marmot.h that does not match its record's name.
Details inline. Nothing here is a correctness bug in the happy path, and the layering, error mapping, worker arm shape and audit/projection plumbing all match their siblings exactly.
Housekeeping: GitHub reports the branch as conflicting with master; it needs a rebase before merge.
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| fn validate_app_component_id(component_id: u16) -> Result<(), AppError> { |
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Add a maximum payload size here.
validate_app_component_id checks only the id. On the engine side, validate_app_component_bytes ends in _ => Ok(()), so for an app-owned id there is no length check anywhere between this call and the encoded GroupContext extension.
That makes this the only app-facing path in the workspace that writes unbounded host bytes into durable group state. Everything comparable is capped: GROUP_PROFILE_NAME_MAX_LEN, GROUP_PROFILE_DESCRIPTION_MAX_LEN, GROUP_AVATAR_URL_MAX_LEN, ENCRYPTED_MEDIA_ENDPOINT_URL_MAX_LEN, MAX_GROUP_IMAGE_BYTES.
Failure scenario: a host calls update_app_component with a few hundred KB (a cached roster, a serialized settings blob, an image someone base64'd into "app state"). The commit stages, then the GroupContext extension is re-encoded into every later commit and into the GroupInfo of every Welcome. Publication fails at the relay's event-size limit, or succeeds and leaves the group with a Welcome that later invitees cannot fetch or accept. The rejection, if any, arrives after the commit is staged rather than at the API boundary, and the bytes are already in group state.
Suggest a named constant (APP_COMPONENT_DATA_MAX_LEN) validated alongside the id, with the limit and the rationale stated in the README section and in both binding docs. A value that comfortably fits inside a relay event budget — single-digit KB — keeps this an app-settings channel rather than an accidental blob store.
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| if component_id < PRIVATE_USE_APP_COMPONENT_ID_START | ||
| || PROTOCOL_OWNED_APP_COMPONENT_IDS.contains(&component_id) | ||
| { |
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Forward-compatibility: apps may claim ids the protocol has not assigned yet.
The rule is "at or above PRIVATE_USE_APP_COMPONENT_ID_START and not on today's PROTOCOL_OWNED_APP_COMPONENT_IDS". But protocol ids are assigned sequentially from 0x8001 and currently stop at 0x800c — so 0x800d is app-writable today and the test below deliberately asserts that 0x800a is too.
Failure scenario: an app ships with component 0x800d and groups in the field accumulate that state. A later release assigns 0x800d to a protocol component. Now (a) the app's own writes start failing InvalidAppComponent with no migration path for the bytes already committed, and worse (b) is_known_group_component starts returning true for 0x800d, so the engine applies protocol format validation to the app's opaque bytes in those existing groups' GroupContext. That turns shipped app data into a decode failure on upgraded clients.
The README says "Applications coordinate their own component IDs" but does not say they are coordinating against a range the protocol is still allocating from.
Cheapest fix, and it matches what the tests already do implicitly with 0xf301: reserve a documented high sub-range for applications (for example >= 0xf000) and gate on that instead of on the complement of the protocol list. The protocol then never collides by construction, and the doc comment on PROTOCOL_OWNED_APP_COMPONENT_IDS about "an id left out silently becomes app-writable" stops being a live hazard. If a narrower range is not acceptable, the README should at minimum state the collision risk and recommend a high id explicitly.
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| c_mirror! { | ||
| /// Opaque application-owned group state. Empty data is distinct from absence. | ||
| MarmotGroupAppComponent from GroupAppComponentFfi, free marmot_app_component_free { |
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Rename to marmot_group_app_component_free.
I checked all 131 void marmot_*_free(struct Marmot* *) declarations in include/marmot.h: every one is the snake_case of its record's type name with _free appended, with no exceptions. MarmotGroupAppComponent freed by marmot_app_component_free would be the first.
Failure scenario: a host (or a generated-binding audit that pairs types to destructors mechanically, which this convention invites) derives the destructor name from the type and calls a symbol that does not exist — a link error at best, and a silently skipped free in a hand-maintained wrapper at worst.
There is no symbol conflict with the getter marmot_group_app_component, so this is a one-word change in the c_mirror! invocation plus the three doc references. Worth doing before the ABI is released, since the symbol is frozen afterward.
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| #[test] | ||
| fn app_component_ids_are_scoped() { |
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Nit: this is a bare #[test] at module scope. Every other test in this 6.5k-line file lives under a #[cfg(test)] boundary (lines 26, 79, 85, 87, 284, 6271, 6425). Moving it into the existing test module keeps the file's convention and keeps the production body of client/mod.rs test-free.
| .required_capabilities | ||
| .app_components | ||
| .contains(component_id) | ||
| { |
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Question, low priority: can this branch fire today?
Protocol-owned ids are already rejected by validate_app_component_id above, and no binding lets a host declare an app-owned component as required at group creation — required_app_components is read out of group state but never supplied by the app layer. So the only ids that reach this check are app-owned, and app-owned ids cannot currently be required.
If that reading is right, this is guarding a state no supported API can produce, which is the kind of speculative branch worth either dropping or annotating with the future case it is reserved for. If I have missed a path that can mark an app component required, ignore this — and a test for it would be worth adding.
| Err(AppError::InvalidAppComponent(_)) | ||
| )); | ||
| } | ||
| for id in [0x8000, 0x800a, 0xf301, 0xffff] { |
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[P1] Reserve the registered 0x800a protocol component
The canonical Marmot registry already assigns 0x800a to marmot.authorization.multi-device-join.v1, and that component explicitly forbids a persistent GroupContext/AppDataDictionary entry. Treating 0x800a as app-writable lets a host publish authenticated group state that collides with the protocol and becomes invalid when multi-device validation is enabled. Please derive the rejection set from the full protocol registry (including reserved/draft IDs), keep AppEphemeral-only IDs out of GroupContext state validation, and add a regression asserting that 0x800a is rejected.
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| Review metadata | Value |
|---|---|
| Reviewed at (UTC) | 2026-09-20T11:18:07Z |
| Commit reviewed | 1fad94f1a6eaee073d7e28a9594e8ed3cac5fa1d |
| Model | gpt-5.6-sol |
| Reasoning level | high |
| Recommended action | Fix blocking issues before merge |
One blocking protocol-registry issue: the new application-owned component gate explicitly accepts 0x800a, although Marmot has already reserved that ID for marmot.authorization.multi-device-join.v1 and forbids it as persistent GroupContext state. Reject every protocol-owned/reserved ID, including draft and non-GroupContext components, before exposing this generic write path.
The full CI matrix passed at this head. GitHub currently reports merge conflicts with master, which will also need resolution.
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App clients cannot read or update application-owned MLS group state through the bindings. Using custom messages for shared settings lets those settings expire and leaves new members without the current value.
Expose application-owned component reads and admin-only updates through the app runtime, UniFFI, and C. Preserve absent versus empty state and reject protocol-owned IDs and writes to required components. Updates use the existing publication and convergence path; component state survives message retention and reaches new members in their Welcome.
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