21 lines
772 B
Markdown
21 lines
772 B
Markdown
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# ADR 0002: In-memory WebSocket hub
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- Status: accepted
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- Date: 2026-09
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## Context
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Realtime delivery (messages, typing, presence, read receipts) must reach
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connected clients immediately. Options: external broker (Redis pub/sub,
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NATS), Postgres LISTEN/NOTIFY, or an in-process hub.
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## Decision
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Use an in-process hub: `map[userID] -> connections` plus
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`map[conversationID] -> subscribers`, guarded by a mutex. Membership and
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read-state are resolved through a `MembershipProvider` interface implemented
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by the store.
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## Consequences
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- Sub-millisecond fan-out, no extra moving parts.
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- Presence checks (`IsOnline`) are lock-free reads used by the push notifier.
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- Multi-node scaling would require a broker; the hub's publish methods are
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the seam where that would plug in.
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