Prevent Duplicate Emits When Using Socket.IO Retries

[ayyanar-finstein]

I am using the Socket.IO retry functionality with the following configuration:

const socket = io({
retries: 3,
ackTimeout: 15000
});
When the server acknowledgment is not received within the timeout, the event is retried.
Inside the event listener, I emit another event:

socket.on("my-event", () => {
socket.emit("another-event", params);
});
Due to retries, this listener executes multiple times, causing another-event to be emitted more than once.

My requirement is that another-event should not be emitted multiple times for the same retry attempt.

Could you please suggest the best way to avoid duplicate emits in this case?

[darrachequesne]

Hi!

To prevent duplicates, you can include an ID when sending your event, for example:

function randomId() {
  return Math.random().toString(36).substring(2, 11);
}

socket.emit("my-event", randomId());

And then on the server:

socket.on("my-event", (offset) => {
  // store the offset, either on the socket object itself or in a database
});

You can check the step 8 of the tutorial for a complete example: https://socket.io/docs/v4/tutorial/step-8