39 lines
2.1 KiB
Markdown
39 lines
2.1 KiB
Markdown
# 1:1 Channel Design (MVP)
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## Goals
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- First-class 1:1 channels (DMs) atop NodeService.
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- Authz on enqueue/fetch per channel, not just recipient key.
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- Privacy: MLS-encrypted payloads; metadata limited to channel ID + participants.
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- Retention: 7d message retention; keypackages expire after 24h (configurable later).
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- Compatibility: additive schema change with version tagging; N-1 clients can interop if they ignore new fields.
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## Schema changes (Cap'n Proto)
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- Add `channelId :Data` (UUID/16B) to enqueue/fetch/fetchWait requests.
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- Add `version :UInt16` to NodeService messages (reject unknown > current).
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- Keep `recipientKey` for routing; server authz uses `(channelId, caller identity)`.
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## AuthZ model
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- Channel membership: exactly two identities (A,B). Server stores membership map `{channelId -> {a_key, b_key}}`.
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- Enqueue allowed if caller identity ∈ channel members; fetch/fetchWait allowed only for caller identity.
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- Rate limits applied per channel and per identity (50 r/s per IP/identity, 5 MB max payload).
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## Storage model
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- New table/map: `channels` with `channelId`, `member_keys[2]`, `created_at`.
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- Deliveries keyed by `(channelId, recipient_key)`; queues retain per recipient, per channel.
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- Messages carry `received_at` timestamp; TTL eviction at fetch time and background sweep.
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## Flows
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- Create channel: caller provides peer identity; server generates channelId, stores membership, returns channelId.
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- Send: client includes channelId + recipientKey; server authz + size/TTL checks; enqueue.
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- Receive: fetch/fetchWait drains messages for `(channelId, caller_key)`; applies TTL, returns non-expired.
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## Backward compatibility
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- Old clients without channelId: server treats channelId=nil as legacy mode (current behavior) for interim.
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- Version field allows rejecting future schema changes cleanly.
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## Open items
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- Persistence backend: extend FileBackedStore or move to proper DB for channels + TTL metadata.
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- API surface: add `createChannel(channelMembers)` RPC or reuse auth service.
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- Client UX: map peer identity → channelId discovery; cache channelId in state file.
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- Auditing: log channel create, authz failures, send/recv events with redaction.
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