Using acknoledgment doesn't work with async code

[Sharcoux]

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You want to:

• report a bug
• request a feature

Current behaviour

emitting an event on the server, if the server makes asynchronous treatment before calling ack, null will be retrived to the client before the server could have a chance to response.

Steps to reproduce (if the current behaviour is a bug)

client-side

 socket.emit('event', console.log)

server-side

 socket.on('event', callback => {
    new Promise(resolve => setTimeout(() => resolve('ok'), 1000)).then(callback);
}

Expected behaviour

Log "ok" client side

Current result

Log "null" client side

Setup

• OS: MacOs
• browser: Firefox
• engine.io version: 2.0.4

Other information (e.g. stacktraces, related issues, suggestions how to fix)

I think that the issue is that socket.io probably send back "null" to the client if no listener used the acknoledgment function. I think that the best would be for socket.io to provide an option that would prevent this behaviour in exchange for ensuring that the server will provide an answer, or timeout.

[darrachequesne]

This seems to be fixed in latest versions (both in socket.io@2 and socket.io@3). Please reopen if needed.