Skip to main content

0009. smocket does not mock raw WebSocket

Status: Accepted · 2026-07-28 · #66

TL;DR smocket does not mock the raw WebSocket transport. Raw WebSocket interception is MSW's lane; smocket's lane is socket.io delivery semantics, the routing layer. Scope stays on which sockets receive an event, not the byte transport under it.

Decision​

We do not mock raw WebSocket. smocket reproduces socket.io's delivery and routing layer: which socket receives which event, in which room and namespace, and in what order. It does not intercept the WebSocket frames that a real socket.io connection rides on. Intercepting raw WebSocket, or the HTTP long-poll transport beneath socket.io, is a transport-level concern that MSW already covers, and reproducing it would put smocket in that lane instead of its own.

The two lanes answer different questions. A raw-WebSocket mock answers "what bytes crossed the wire"; smocket answers "given these emits, joins, and broadcasts, which sockets receive what." The socket.io semantics (rooms, broadcast targeting, acks) sit above the transport, and a test that wants those semantics does not want to hand-assemble socket.io's wire protocol on top of a WebSocket fake. Staying at the routing layer is what lets a test read in socket.io's own terms.

Alternatives rejected​

  • Mock raw WebSocket and let callers run real socket.io on top. This reproduces the transport but not the semantics, so every test would still rebuild room and broadcast behaviour by hand, which is the work smocket exists to remove. It also duplicates what MSW already does at that layer.
  • Mock at the transport for fidelity to the wire. The wire format is not what smocket's tests assert on; they assert on delivery. Transport fidelity would add surface without serving the question the project answers.