Tauri WebSocket plugin can’t listen to messages right after a connection is established.

[yoyo930021]

Describe the bug

I tried porting socket.io to work with Tauri WebSocket and Fetch, but I found that the WebSocket connections were unstable.
After digging into the issue, I discovered that Tauri’s WebSocket JS API currently has a chance of failing to capture the very first message sent by the server right after the connection is established.

The code looks roughly like this:

import RawWebSocket, { CloseFrame } from '@tauri-apps/plugin-websocket'

void RawWebSocket.connect(uri, {
  headers: opts.headers,
}).then((ws) => {
  this.engine = ws
  this.onopen?.()
  this.engine.addListener((message) => {
    console.log('WebSocket message received:', message);
    if (message.type === 'Close') {
      this.onclose?.(message.data)
      return
    }

    if (message.type === 'Ping' || message.type === 'Pong') {
      return
    }

    const data = message.type === 'Binary' ? (() => {
      if (this.binaryType === 'arraybuffer') {
        return new Uint8Array(message.data).buffer
      }
      return new Blob([new Uint8Array(message.data)])
    })() : message.data

    this.onmessage?.({ data })
  })
}).catch(this.onerror);

The problem is that you can only call addListener to listen for incoming messages after the connect call returns and you obtain the WebSocket instance. If the server sends a message during this gap, that message gets lost.

As a result, socket.io cannot complete its handshake properly. This issue is especially easy to reproduce on Windows.

Reproduction

No response

Expected behavior

It should provide a way to listen to messages right from the moment the connection is established.

Full tauri info output

[✔] Environment
    - OS: Windows 10.0.26100 x86_64 (X64)
    ✔ WebView2: 142.0.3595.94
    ✔ MSVC: Visual Studio Community 2022
    ✔ rustc: 1.90.0 (1159e78c4 2025-09-14)
    ✔ cargo: 1.90.0 (840b83a10 2025-07-30)
    ✔ rustup: 1.28.2 (e4f3ad6f8 2025-04-28)
    ✔ Rust toolchain: stable-x86_64-pc-windows-msvc (default)
    - node: 22.20.0
    - npm: 10.9.3

[-] Packages
    - tauri 🦀: 2.8.5, (outdated, latest: 2.9.4)
    - tauri-build 🦀: 2.4.1, (outdated, latest: 2.5.3)
    - wry 🦀: 0.53.3, (outdated, latest: 0.53.5)
    - tao 🦀: 0.34.3, (outdated, latest: 0.34.5)
    - @tauri-apps/api : 2.8.0 (outdated, latest: 2.9.1)
    - @tauri-apps/cli : 2.8.4 (outdated, latest: 2.9.5)

[-] Plugins
    - tauri-plugin-http 🦀: 2.5.2, (outdated, latest: 2.5.4)
    - @tauri-apps/plugin-http : not installed!
    - tauri-plugin-dialog 🦀: 2.4.0, (outdated, latest: 2.4.2)
    - @tauri-apps/plugin-dialog : 2.4.2
    - tauri-plugin-log 🦀: 2.7.1
    - @tauri-apps/plugin-log : 2.7.1
    - tauri-plugin-updater 🦀: 2.9.0
    - @tauri-apps/plugin-updater : 2.9.0
    - tauri-plugin-store 🦀: 2.4.1
    - @tauri-apps/plugin-store : 2.4.1
    - tauri-plugin-fs 🦀: 2.4.2, (outdated, latest: 2.4.4)
    - @tauri-apps/plugin-fs : not installed!
    - tauri-plugin-opener 🦀: 2.5.0, (outdated, latest: 2.5.2)
    - @tauri-apps/plugin-opener : 2.5.0 (outdated, latest: 2.5.2)
    - tauri-plugin-websocket 🦀: 2.4.1
    - @tauri-apps/plugin-websocket : not installed!
    - tauri-plugin-notification 🦀: 2.3.3
    - @tauri-apps/plugin-notification : 2.3.3

[-] App
    - build-type: bundle
    - CSP: unset
    - frontendDist: ../dist
    - devUrl: http://localhost:1420/
    - framework: Vue.js
    - bundler: Vite

Stack trace

Additional context

Maybe we can add listeners to ConnectionConfig?

I can send a PR to this issue if needed.