Type error when using socket.timeout.emitWithAck

[GStarP]

Describe the bug
When using socket.timeout.emitWithAck, even if you set EmitEvents correctly, the return type will be a wrong any.

To Reproduce

no need for server participation.

Server

Socket.IO client version: 4.7.4

Client

import type { Socket } from 'socket.io-client'

type MySocket = Socket<DefaultEventsMap, EmitEvents>
type DefaultEventsMap = {
  [event: string]: (...args: any[]) => void
}
type EmitEvents = {
  hello: (cb: (val: number) => void) => void
}

const socket = {} as MySocket
const r1 = socket.emitWithAck('hello') // Promise<number>
const r2 = socket.timeout(1000).emitWithAck('hello') // Promise<any>

Expected behavior
r2 should also be inferred as Promise<number>.

Platform:

• Typescript version: 5.3.3

Additional context

The return type of emitWithAck is from Promise<FirstArg<Last<EventParams<EmitEvents, Ev>>>>, which picks the first argument of cb. However, timeout uses DecorateAcknowledgements then PrependTimeoutError, which prepend a Error type param to cb, so this FirstArg will focus on the error instead of the real return value.

Maybe replace FirstArg with a type LastArg<T> = T extends (...args: infer Args) => any ? Args extends [] ? never : Args extends [...infer _, infer Last] ? Last : never : never; will solve this issue? I'm not so familiar with the js logic, so just a hypothesis.

By the way, I have found the same problem in #4813 , it can be solved by using socket options ackTimeout in the client side (I have already adopted this solution). But I think it's better if this problem can be solved completely.

[darrachequesne]

You are right, we need to apply the same changes on the client side: #4817

[GStarP]

Oh sorry, I should post this issue in the client side repo.

Thanks for answering, I will close this issue and look forward to the new version client.

[DudaGod]

You are right, we need to apply the same changes on the client side: #4817

Hello. Do I understand correctly that this is not supported on the client yet? When can I expect a new version?

Thanks.

[MiloWang2048]

I can reproduce this error with socket.io version 4.7.5, on server side, with or without timeout() call.

await targetUserSocket.emitWithAck("PrivateMessage", content);

Argument of type 'string' is not assignable to parameter of type 'never'.ts(2345)

But socket.emit() works just fine.