It's possible to implement socket.io with ack, and if the server did not receive the ack, the server try again to emit the event? - sockets

Question

It's possible to implement socket.io with ack , and if the server did not receive the ack, the server try again to emit the event?

Answer 1

socket.io uses TCP as the underlying transport which is a "reliable" transport. TCP will retry on it's own. The packet will be delivered unless the connection is permanently down. If the connection is down, what you really need is for the client to reconnect (which it will do eventually if the connection is actually down).
You can use socket.io's ACK feature and implement your own timeout to retry, but I don't think it will really buy you much because if the connection is working, then TCP will deliver it for you as soon as the connection allows. If TCP can't deliver it for you, then you really need to client to establish a new connection (which it will do eventually) and then when the new connection comes in is when you need to retransmit.
If you wanted to try your own retry, you could do it like this:
function delay(t) {
return new Promise(function(resolve) {
setTimeout(resolve, t);
});
}
function send(socket, msg, data, maxRetries, retryTime) {
maxRetries = maxRetries || 5;
retryTime = retryTime || 30 * 1000;
return write(socket, msg, data).catch(function() {
--maxRetries;
if (maxRetries >= 0) {
return delay(retryTime).write(socket, msg, data);
} else {
throw new Error("socket.io write failed after maxRetries")
}
});
function write(socket, msg, data) {
return new Promise(function(resolve, reject) {
let timer = setTimeout(reject, retryTime);
socket.emit(msg, data, function() {
clearTimeout(timer);
resolve();
});
});
}
}
And, the listener on the client for the message you are sending would have to reply appropriately to the ACK.
// client side
io.on('someMsg', function(data, fn) {
// process data here
console.log(data);
// call ACK function to send ack back
fn();
});