socket.io: First message never gets sent

For some reason, whenever a new connection is established, the first message I send always seems to go silently ignored. I switched on logging on the Node side, and this is the output:

  engine intercepting request for path "/socket.io/" +14ms
  engine handling "GET" http request "/socket.io/?EIO=3&transport=polling&t=1444437518880-2&sid=DMd9QzeN3O9frdIRAAAA" +0ms
  engine setting new request for existing client +4ms
  engine:polling setting request +0ms
  engine:socket writing a noop packet to polling for fast upgrade +89ms
  engine:polling writing "�6" +1ms
  engine:ws received "5" +41ms
  engine:socket got upgrade packet - upgrading +1ms
Sending bullshit-message 1
  socket.io-parser encoding packet {"type":2,"data":["bullshit-message","Not seen on client"],"nsp":"/"} +0ms
  socket.io-parser encoded {"type":2,"data":["bullshit-message","Not seen on client"],"nsp":"/"} as 2["bullshit-message","Not seen on client"] +1ms
Sending bullshit-message 2
  socket.io:client writing packet {"type":2,"data":["bullshit-message","THIS will be seen on client"],"nsp":"/"} +10s
  socket.io-parser encoding packet {"type":2,"data":["bullshit-message","THIS will be seen on client"],"nsp":"/"} +10s
  socket.io-parser encoded {"type":2,"data":["bullshit-message","THIS will be seen on client"],"nsp":"/"} as 2["bullshit-message","THIS will be seen on client"] +0ms
  engine:socket sending packet "message" (2["bullshit-message","THIS will be seen on client"]) +10s
  engine:socket flushing buffer to transport +0ms
  engine:ws writing "42["bullshit-message","THIS will be seen on client"]" +0ms
Sending Testing 1! to client DMd9QzeN3O9frdIRAAAA
  socket.io:client writing packet {"type":2,"data":["message","Testing 1!"],"nsp":"/"} +5ms
  socket.io-parser encoding packet {"type":2,"data":["message","Testing 1!"],"nsp":"/"} +4ms
  socket.io-parser encoded {"type":2,"data":["message","Testing 1!"],"nsp":"/"} as 2["message","Testing 1!"] +0ms
  engine:socket sending packet "message" (2["message","Testing 1!"]) +4ms
Sending Testing 2! to client DMd9QzeN3O9frdIRAAAA
  socket.io:client writing packet {"type":2,"data":["message","Testing 2!"],"nsp":"/"} +1ms
  socket.io-parser encoding packet {"type":2,"data":["message","Testing 2!"],"nsp":"/"} +1ms
  socket.io-parser encoded {"type":2,"data":["message","Testing 2!"],"nsp":"/"} as 2["message","Testing 2!"] +0ms
  engine:socket sending packet "message" (2["message","Testing 2!"]) +1ms
  engine:socket flushing buffer to transport +2ms
  engine:ws writing "42["message","Testing 1!"]" +0ms
  engine:ws writing "42["message","Testing 2!"]" +0ms
  engine:ws received "2" +15s
  engine:socket packet +1ms
  engine:socket got ping +0ms
  engine:socket sending packet "pong" (undefined) +0ms
  engine:socket flushing buffer to transport +0ms

It seems like the first message (the bullshit-message, as I’ve come to call it in testing) is encoded, but never actually sent off to the client. What is going on here?

On client:

  engine.io-client:socket changing transport and sending upgrade packet +1ms
  socket.io-1.3.7.js:2 engine.io-client:socket setting transport websocket +1ms
  socket.io-1.3.7.js:2 engine.io-client:socket clearing existing transport polling +1ms
  socket.io-1.3.7.js:2 engine.io-client:polling ignoring poll - transport state "paused" +1ms
  socket.io-1.3.7.js:2 engine.io-client:socket socket receive: type "message", data "2["bullshit-message","THIS will be seen on client"]" +10s
  socket.io-1.3.7.js:1 socket.io-parser decoded 2["bullshit-message","THIS will be seen on client"] as %j +9s Object {type: 2, nsp: "/", data: Array[2]}
  socket.io-1.3.7.js:1 socket.io-client:socket emitting event %j +9s ["bullshit-message", "THIS will be seen on client"]
Bullshit data received THIS will be seen on client
  socket.io-1.3.7.js:2 engine.io-client:socket socket receive: type "message", data "2["message","Testing 1!"]" +5ms
  socket.io-1.3.7.js:1 socket.io-parser decoded 2["message","Testing 1!"] as %j +5ms Object {type: 2, nsp: "/", data: Array[2]}
  socket.io-1.3.7.js:1 socket.io-client:socket emitting event %j +5ms ["message", "Testing 1!"]
Data received Testing 1!
  socket.io-1.3.7.js:2 engine.io-client:socket socket receive: type "message", data "2["message","Testing 2!"]" +8ms
  socket.io-1.3.7.js:1 socket.io-parser decoded 2["message","Testing 2!"] as %j +8ms Object {type: 2, nsp: "/", data: Array[2]}
  socket.io-1.3.7.js:1 socket.io-client:socket emitting event %j +8ms ["message", "Testing 2!"]
Data received Testing 2!

About this issue

Original URL
State: closed
Created 9 years ago
Comments: 16 (8 by maintainers)

Most upvoted comments

Digging into this a bit more, I believe something strange is going on with the onopen event. Here is the order of events I’m seeing in the browser:

socket.client-io establishes WebSocket connection to server
socket.client-io fires onopen event
socket.client-io emits my first event (in this case login)
engine.io fires onopen event
engine.io receives ping events from server
engine.io receives first response from server

Why is socket.client-io firing the onopen event before the engine.io has emitted it?

UPDATE: I was able to solve my problem by changing:

import io from 'socket.io-client';

// Instead of
this.socket = new io(BASE_URL);

// I now initialize the Socket.IO client class as:
this.socket = new io(BASE_URL, {transports: ['websocket']});

By default transports seems to be set to ['polling', 'websocket']. I have no idea what polling is or what the transports option does (documentation for this is very hard to find). But it seems to solve my problem. I now consistently see my requests sent and received.

EvHaus on Jan 24, 2016

Any ideas? Same issue

require('log-timestamp');
const   app = require('express')(),
        http = require('http').Server(app),
        io = require('socket.io')(http),
        path = require('path');

app.get('/client', function(req, res) {
    res.sendFile(path.join(__dirname + '/index.html'));
});

http.listen(8080, function(){});
io.on('connection', function (socket) {
    socket.emit('immediate',{'some' : 'data'});  //never received in browser
    setTimeout(() => {
        socket.emit('deferred',{'some' : 'some'}); //always received in browser
    },1500);
});

what i’ve pointed out is that at emmititing ‘immediate’ event the socket.client.Client.conn.socket.upgraded is false, but after 1.5s that is true, and all works just fine

svenez on Apr 5, 2018

Same issue here, please find a fix!

update: rather than applying a timeout, process.nextTick seems a better solution

vinz243 on Apr 16, 2017