Change IPC Channel onmessage Handler Dynamically During Use

[Kynson]

Hi, I was wondering if the setting the onmessage property of Channel to another function is recommended when the rust end is actively sending message to the front end with it? (it works, but not sure if this is safe).

I would like to do this as I have to bind a new handler if the user navigate away from the page and then come back, I would like to ensure the front end still receive updates after the user is back (the channel is globally persisted, so it is always the same Channel passed to the rust end, but I wanted to change the onmessage callback

[vincere-mori]

Reassigning onmessage is safe — Channel calls whatever's currently on onmessage at message time, no captured reference from creation. Swapping mid-stream works.

That said, for the "user leaves and comes back" case I'd keep onmessage stable and dispatch via a registry, because reassigning from a component is fragile (you can drop the new handler if a remount races the reassignment):

import { Channel } from '@tauri-apps/api/core'

class StableChannel<T> {
  channel = new Channel<T>()
  listeners = new Set<(d: T) => void>()
  constructor() {
    this.channel.onmessage = (d) => this.listeners.forEach(l => l(d))
  }
  subscribe(l: (d: T) => void) {
    this.listeners.add(l)
    return () => this.listeners.delete(l)
  }
}

export const updates = new StableChannel<MyUpdate>()

Pass updates.channel to Rust once at startup, components just subscribe/unsubscribe on mount.

[Martzcode]

To add a concrete implementation for the "user navigates away and comes back" use case:

Reassigning onmessage mid-stream is safe — Tauri's Channel calls whatever function is currently assigned at message delivery time, no closure capture from initialization. But when you're in a component framework (React, Vue, Angular), component remounts can race with reassignment, causing you to drop messages during the transition window.

Robust pattern: stable channel + subscriber registry

Keep the Channel alive at the module/service level, and let components subscribe/unsubscribe to it:

TypeScript (framework-agnostic)

import { Channel } from '@tauri-apps/api/core';

class StableChannel<T> {
  readonly channel = new Channel<T>();
  private listeners = new Set<(data: T) => void>();

  constructor() {
    this.channel.onmessage = (data) => {
      this.listeners.forEach(l => l(data));
    };
  }

  subscribe(listener: (data: T) => void): () => void {
    this.listeners.add(listener);
    return () => this.listeners.delete(listener); // returns unsubscribe fn
  }
}

// Singleton, created once and passed to Rust on first use
export const streamChannel = new StableChannel<MyUpdate>();

In your component (React example)

useEffect(() => {
  const unsubscribe = streamChannel.subscribe((data) => {
    setState(data);
  });
  return unsubscribe; // clean unsubscribe on unmount
}, []);

In your component (Angular example)

ngOnInit() {
  this.unsub = streamChannel.subscribe(data => this.data = data);
}
ngOnDestroy() {
  this.unsub?.();
}

This way:

• onmessage is never reassigned — zero race conditions
• Components subscribe/unsubscribe safely
• The Rust loop never stalls or errors during navigation