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0020. close follows socket.io's socket lifecycle

Status: Accepted · 2026-08-10 · #193 Governed by: 0000

TL;DR Socket.io 4.7 and 4.8 share the close callback and lifecycle but differ in return value; smocket accepts the callback and returns the 4.8 promise. It leaves an armed server-side ack timeout running and removes this server from the origin registry only while it owns the entry.

Decision​

Real socket.io 4.7 and 4.8 close every namespace socket before its listener. The server socket fires disconnecting and then disconnect, both with server shutting down; the client observes transport close. A pending client emitWithAck rejects with socket has been disconnected, and a sent timed client callback receives the same error once. A pending server emitWithAck stays pending. A connection started immediately before close never reaches connection; its client observes connect_error instead, so close cannot resolve and then admit a socket that escaped teardown. Both versions invoke an optional callback when close completes. A later callback receives ERR_SERVER_NOT_RUNNING; in 4.8, the returned promise still resolves. Version 4.7 returns void, while 4.8 returns Promise<void>. Smocket keeps the common callback and returns the 4.8 promise, which adds completion to the older call shape without invalidating it.

An armed server acknowledgement timeout is separate from the connection teardown. Real socket.io leaves its timer running, and its callback still receives operation has timed out after close() resolves. Smocket does the same. Tests that arm one settle it before ending or drive it with fake timers; close() is not a timer reset.

The origin registry has no socket.io counterpart, but leaving a closed server registered would let a later connect(url) attach to an object that has been shut down. close() therefore removes the entry when, and only when, the entry still points to that server. Closing an older server after a replacement was constructed cannot unregister the replacement. A later connect with no replacement follows the existing missing-server behavior in 0005.

Alternatives rejected​

  • Cancel armed acknowledgement timers. Real socket.io does not, and cancellation would need an invented result for callbacks and promises whose timer disappeared.
  • Always delete the origin entry. An old server could remove a newer server registered at the same origin.
  • Leave the closed server registered. A later connection could activate a server after its lifecycle had ended.