0031. Adapters register before admission and may observe whole-socket removal

Status: Accepted · 2026-08-13 · #278 Governed by: 0008, 0010, 0018, 0025

TL;DR Adapter registration is setup-only and each namespace receives a fresh instance. An optional Smocket-only removeSocket(sid) signal follows membership removal, and DelayingAdapter uses it to drain queued delivery in FIFO order.

Decision

Socket.IO constructs one adapter per namespace and removes whole-socket membership through its adapter. Smocket keeps the narrower contract from 0008 and 0025 because a real adapter also owns transport delivery and multi-server behavior that this mock cannot provide. This record adds only the lifecycle needed by stateful Smocket extensions.

io.adapter(factory) must run before the first connection attempt. It prepares a fresh, distinct adapter for the root and every existing static namespace, then installs all of them only after every factory call succeeds. Failure leaves the previous registration unchanged. Future static namespaces and admitted concrete dynamic children each receive another fresh instance. No membership migration or late replacement exists.

The optional removeSocket(sid) method is a whole-socket signal, not Socket.IO's delAll and not an adapter lifecycle event. Cleanup calls del(sid, room) for each room, removes the sid from adapter.sids, then calls removeSocket once while the socket is still in the namespace roster. It next clears the socket's live room Set and removes the roster entry. Rejected and cancelled admission use the same cleanup without connection or disconnect events. Client, server, Manager-wide, and server-close teardown share it.

Calling socket.leave(socket.id) is only a room leave and does not signal removal. DelayingAdapter therefore retains that sid's delay. On actual removal it deletes the delay, detaches the queue, and delivers every queued item synchronously in FIFO order. The already-scheduled head later sees that detached queue and does nothing. A reconnect uses a fresh sid and cannot inherit the removed scheduler state.

This is a narrow follow-up to 0025, not a superseding record. Built-in compatibility observation remains limited to rooms. The shipped Smocket interface still makes sids, socketsIn, scheduling, and removal native extension points without claiming arbitrary Socket.IO Adapter compatibility. The earlier 0018 allowance for delayed delivery after disconnect is superseded only for whole-socket teardown by this required drain.

Alternatives rejected

• Keep cleanup internal. Stateful adapters could not distinguish a disconnect from a room leave and would retain or abandon state.
• Add upstream delAll or lifecycle events. That would broaden compatibility beyond the concrete native need and reopen the surface deferred by 0025.
• Permit late replacement with migration. There is no general way to transfer custom adapter state atomically, while a setup boundary is explicit and deterministic.
• Cancel delayed delivery. Silent cancellation breaks the queued stream and leaves acknowledgement behavior dependent on teardown timing.