socketio / socketio/socket.io

last message processed after the disconnect callback

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needs investigation
Dominant language
TypeScript
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Description

Describe the bug
Sometimes I noticed that the last message I sent right before terminating my app is processed by my event listener socket.on("event", () => {}) after the disconnect callback has been called socket.on("disconnect", () => {}).
This does not always happen: in my case I was able to reproduce it on my mac M1 but not on my raspberry pi.

This is a weird issue and I don't know how to reproduce it. But I am wondering if this is a know issue or if others faced the same behavior.

Expected behavior
I would expect the disconnect callback to be always call after the last message.

Versions:

  • "socket.io-client": "^4.4.1"
  • "socket.io": "^4.4.1"

Platform:

  • Device: Macbook air M1
  • OS: Macos

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the socket.on("event") and socket.on("disconnect") callbacks described in the report, using socket.io-client and socket.io 4.4.1. Try to create a minimal reproduction on macOS and compare its event ordering with the Raspberry Pi case. Done means determining whether disconnect ordering is guaranteed and, if it is a bug, identifying a reproducible regression case.

Written by the indexing model from the issue text.

Assessment

Tech stack
nodejs, typescript
Domain
backend, networking
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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