The black-box monitor tests showed socketv1_controller.go and
socketv2_controller.go were near-identical: same constants (identical
values), upgrader, read/write pumps, Close, and handler bodies, differing
only in the event payload shape and v1 dropping deletions.
Extract the shared machinery into socket_controller.go:
- msgListener[T] generic listener with toStored/toDeleted payload
transforms; a nil toDeleted preserves the socketv1 behavior of ignoring
deletions
- socketReadPump / socketWritePump free functions (WriteJSON is
payload-type agnostic)
- serveMonitor shared handler body (upgrade, gauge tracking, listener
registration, pump wiring)
The version files shrink to their listener constructors and the four
exported handlers, whose signatures are unchanged. v1 payloads are now
shaped at enqueue time rather than write time; the JSON on the wire is
identical, pinned by the commit-1 tests, which pass unmodified.
Adds direct unit tests for the extracted listener logic: watches()
filtering, Receive/Delete filtering + payload shaping, nil-toDeleted
deletion dropping, and sequential Close idempotency.
James Hillyerd