Open FastAPI/Quart websocket only when a websocket callback needs it - #3941
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T4rk1n wants to merge 2 commits into
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Open FastAPI/Quart websocket only when a websocket callback needs it#3941T4rk1n wants to merge 2 commits into
T4rk1n wants to merge 2 commits into
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The FastAPI and Quart backends always advertise websocket infrastructure (url/worker_url) in the page config, and the renderer keyed the connect decision on the mere presence of that infra, so every app on these backends opened a socket on page load even with no websocket callbacks. Register the websocket message handlers whenever the infra is present, but only open the socket eagerly when websocket_callbacks=True (config.enabled). Per-callback websocket=True opens it lazily on first dispatch via the existing ensureConnected path; an app with no websocket callbacks never connects. Also guard the visibility reconnect so it never opens a first connection. Add regression tests using a websocket_connect hook as a server-side probe: never-connect (HTTP only), lazy-connect (per-callback), eager-connect (global).
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Closes #3939
Problem
The FastAPI and Quart backends always advertise WebSocket infrastructure (
url/worker_url) in the page config, because they havewebsocket_capability = Trueregardless of whether any WebSocket callback exists. The renderer keyed its "open the socket" decision on the mere presence of that infra, so every app on these backends opened a WebSocket on page load — even apps with no WebSocket callbacks at all.config.websocket.enabled(bool(self._websocket_callbacks)) was already computed but ignored for the connect decision.Repro: a plain
Dash(backend="fastapi")app with only HTTP callbacks opens a socket on load (WebSocket /_dash-ws-callback [accepted]).Fix (renderer only)
Split "register handlers" from "open the socket":
observers/websocketObserver.ts—initializeWebSocketstill registers all message handlers (onSetProps,onGetPropsRequest,onConnected, …) whenever the infra is present, but only opens the socket eagerly whenconfig.websocket.enabledis true. Keeping handlers registered is what lets the lazy path work: a per-callbackwebsocket=Trueopens the socket on first dispatch via the existinghandleWebsocketCallback → workerClient.ensureConnectedpath, and the handlers are already there to route server-pushedset_props/get_props.visibilitychangereconnect withwasDisconnected, so tab focus never opens a first connection for an app that never had one.AppProvider.react.tsx— the effect now registers the observer whenever the infra is available; the enabled/lazy decision lives entirely insideinitializeWebSocket.Resulting behavior
websocket_callbacks=True(global)websocket=TrueTests
tests/websocket/test_ws_lazy_connect.pyadds three regression tests that use awebsocket_connecthook as a precise server-side probe for "did a socket actually open": never-connect (HTTP only), lazy-connect (per-callback), eager-connect (global). Verified they fail on the pre-fix bundle (the never/lazy cases saw a socket open on load) and pass with the fix. Existingtest_ws_basic.py+test_ws_hooks.py(15 tests) still pass.