I have the following code:
express = require('express');
app = express();
http = require('http').createServer(app);
io = require('socket.io')(http);
app.use(express.static(__dirname + '/'));
http.listen(80);
I know it creates a server that clients can connect to and it works. But I don't know what exactly happens. Can you explain in detail?
Also, why things don't work when I forget about Express.js and just use this line:
io = require('socket.io').listen(80);
It appears to listen for connections. However, inside the browser when I go to http://localhost/, nothing happens. My guess is that I don't specify the directory for my app like that:
app.use(express.static(__dirname + '/'));
Is that why I need Express? To specify the directory?
At the client, I use:
socket = io('http://localhost/'); // this
socket = io(); // or this
None of them work with the single line code at the server-side.
Also, why do I need an HTTP server when Socket.IO uses the WebSocket protocol?
When your browser goes to http://localhost/, you need a web server that's going to respond back to the browser with a web page. That's what Express and the express.static() lines were doing. When you remove those, you do indeed have a server listening for webSocket connections on a specific path, but you don't have anything serving web pages. So, when the browser goes to http://localhost/, there's nothing responding back with a plain web page.
Also, why do I need an HTTP server when Socket.IO uses the WebSocket
protocol?
All socket.io connections start with an HTTP request. socket.io is based on the webSocket protocol and all webSocket connections are initiated with an HTTP request. So, to accept a socket.io connection, you need a web server that responds to an HTTP request and you then need a web server that is smart enough to recognize a request for a webSocket connection so it can "upgrade" the protocol from HTTP to webSocket.
For a well written overview of how a webSocket connection is established, see this overview on MDN.
The socket.io infrastructure then runs on top of that webSocket once it is connected.
I know it creates a server that clients can connect to and it works.
But I don't know what exactly happens. Can you explain in detail?
Here's a line-by-line explanation of your code:
express = require('express');
This loads the Express library.
app = express();
This creates an Express app object which can be used as a webServer request handler.
http = require('http').createServer(app);
This creates a web server and passes it the Express app object as the webServer request handler.
io = require('socket.io')(http);
This hooks socket.io into your web server as another request handler so it can see any incoming http requests that are actually the first stage of starting a webSocket/socket.io connection.
app.use(express.static(__dirname + '/'));
This tells Express that if any request is made for a web page that it should look in the __dirname for a file that matches the requested path. If found, it should return that path.
http.listen(80);
This starts the web server listening on port 80.
None of them work with the single line code at the server-side.
Both of those lines of code to create a socket.io connection will work when used properly. You don't say how this code is being run. If you're trying to run this code from a web page that the browser loads from http://localhost/, then I've already explained why that web page won't load if you don't start Express. If you're trying to run those lines of code from a web page loaded some other way, then you're probably having a same-origin security issue were the browser by default won't let you access a domain that is different than the one the web page came from.
You need the express http server to deliver the socket client to the browser.
Express server starts on port 80
Browser connects to express on port 80, the socket.io server component delivers socket client javascript to the browser (http://localhost:80/socket.io/socket.io.js)
Socket client (running in browser) can then connect to socket.io server
Related
I'm using Socket.IO to run a WebSocket server locally in NodeJS using the following code:
import express = require('express');
const path = require('path');
import http = require('http');
import { Socket } from 'socket.io';
const app = express();
const server = http.createServer(app);
const socketio = require('socket.io')(server);
app.get('/', (req, res) => {
res.send("Node Server is running");
});
server.listen(3000, function () {
console.log('Example app listening on port 3000!');
});
socketio.on("connection", (socket: Socket) => {
console.log(`connect ${socket.id}`);
console.log(`connect ${socket.handshake.url}`);
socket.on("disconnect", () => {
console.log(`disconnect ${socket.id}`);
});
});
Using a tool like Firecamp, I try to establish a connection on ws://localhost:3000, but to no avail. I eventually use the Socket.IO client to connect from a simple web page by running let socket = io(). It seems the only reason this works is because that call connects to the host serving the page by default, as stated here. Running console.log(socket) and looking at the output, I eventually find that the URL inside the engine field is ws://localhost:3000/socket.io/?EIO=4&transport=websocket&sid=qerg3iHm3IKMOjdNAAAA.
My question is why is the URL so complicated rather than simply ws://localhost:3000? And is there no easier way to get the URL instead of having to access it through dev tools?
A socket.io server does not accept generic webSocket connections. It only accepts socket.io connections as socket.io goes through an extra layer of preparation stuff (over http) before establishing the actual webSocket connection. It then also adds a layer on top of the regular webSocket packet format to support some of its features (such as message names).
When using a socket client to connect to a socket.io server in the default configuration, socket.io first makes a few regular http requests to the socket.io server and with those http requests it sends a few parameters. In your URL:
ws://localhost:3000/socket.io/?EIO=4&transport=websocket&sid=qerg3iHm3IKMOjdNAAAA
The path:
/socket.io/
Is the path that the socket.io server is looking for requests on as destined for the socket.io server. Since this is a unique path and not generally used by other requests, this allows you to share an http server between socket.io and other http requests. In fact, this is a common way to deploy a socket.io server (hooking into an http server that you are already using for http requests).
In fact, the path /socket.io/socket.io.js is also served by the socket.io server and that will return the client-side socket.io.js file. So, clients often use this in their HTML files:
<script src="/socket.io/socket.io.js"></script>
as a means of getting the socket.io client code. Again you see the use of the path prefix /socket.io on all socket.io related URLs.
In your original URL, you can see parameters for:
EIO=4 // engine.io protocol version
transport=websocket // desired transport once both sides agree
sid=qerg3iHm3IKMOjdNAAAA // client identifier so the server knows which client this
// is before the actual webSocket connection is established
Once both sides agree that the connection looks OK, then the client will make a webSocket connection to the server. In cases where webSocket connections are blocked (by network equipment that doesn't support them or blocks them), then socket.io will use a form of http polling where it repeatedly "polls" the server asking for any more data and it will attempt to simulate a continuous connection. The client configuration can avoid this http polling and go straight to a webSocket connection if you want, but you would give up the fallback behavior in case continuous webSocket connections are blocked.
And is there no easier way to get the URL instead of having to access it through dev tools?
Not really. This URL is not something you have to know at all. The socket.io client will construct this URL for you. You just specify http://localhost:3000 as the URL you want to connect to and the socket.io client will add the other parameters to it.
I am looking to implement real-time updates in my application that has a node.js backend. I want to use socket.io for this and I understand the library that needs to be implemented. However, I already have a node.js server running:
app.listen(process.env.PORT, () => {
console.log("Server is up and running")
})
The question is fairly simple: is it possible to use the same server with the same port to listen for socket.io connections, or should I run this entirely on a different server or just open another port for this? Because what I often see in the examples is that it listens to http. See below.
What I usually see (this example comes from this post)
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
http.listen(3000, function () {
console.log('listening on *:3000');
});
Now, if I would use the same server and port, how could I also listen for incoming socket.io requests or emit to its clients? Can I just keep listening with app.listen and will it also connect to socket.io?
In short yes, the socket connection starts as an http request on the same address and port.
The WebSocket protocol was designed to work well with the existing Web
infrastructure. As part of this design principle, the protocol
specification defines that the WebSocket connection starts its life as
an HTTP connection, guaranteeing full backwards compatibility with the
pre-WebSocket world. The protocol switch from HTTP to WebSocket is
referred to as a the WebSocket handshake.
At this point the HTTP connection breaks down and is replaced by the
WebSocket connection over the same underlying TCP/IP connection. The
WebSocket connection uses the same ports as HTTP (80) and HTTPS (443),
by default.
https://websocket.org/aboutwebsocket.html
I need to create a small authentication layer on top of a 3rd party web-socket based chat application. I have a simple API (get) that can validate api tokens from requests. What I want to do is essentially validate their token (which I know how to do) then proxy the websocket connection to the actual chat server.
I've been looking for solutions and this thread seems to give some pointers in the right direction however I can't get any of the solutions to work.
var http = require('http'),
WebSocket = require('faye-websocket'),
conf = require('./conf.json');
var server = http.createServer();
server.on('upgrade', function(request, socket, body) {
console.log('upgrade fired');
var frontend = new WebSocket(request, socket, body),
backend = new WebSocket.Client('ws://echo.websocket.org');
frontend.pipe(backend).pipe(frontend);
});
server.on('connection', function(socket) {
console.log('connection')
backend = new WebSocket.Client('ws://echo.websocket.org');
console.log(backend);
socket.pipe(backend).pipe(socket);
})
server.listen(conf.port);
console.log('Listening on '+port.conf);
The connection event is fired, however the upgrade event which is supposed to be fired on a ws connection never is.
The goal is to first authenticate a api key to an external server, then open a proxy to the chat websocket all through a request to this node server via a websocket connection. I'll most likely pass the api key as a get parameter for simplicity. I also looked at this package and attempted using it however it didn't work as well.
The issue ended up being with nginx. I forgot I was proxying requests through the reverse proxy and by default nginx does not support the ws:// connection so it drops it.
I am trying to build a command-line chat room using Node.js and Socket.io.
This is my server-side code so far, I have tried this with both http initialisations (with express, like on the official website's tutorial, and without it):
#app = require('express')()
#http = require('http').Server(app)
http = require('http').createServer()
io = require('socket.io')(http)
io.sockets.on 'connect', (socket) ->
console.log 'a user connected'
http.listen 3000, () ->
console.log 'listening on *:3000'
I start this with nodejs server.js, the "Listening on" is showing up.
If I run lsof -i tcp:3000, the server.js process shows up.
However, when I start this client-side code:
socket = require('socket.io-client')('localhost:3000', {})
socket.on 'connect', (socket) ->
console.log "Connected"
No luck... When I run nodejs client.js, neither "connect" events, from server nor client, are fired!
My questions are :
- What am I doing wrong?
- Is it necessary to start a HTTP server to use it? Sockets are on the transport layer, right? So in theory I don't need a HTTP protocol to trade messages.
If this is a server to server connection and you're only making a socket.io connection (not also setting it up for regular HTTP connections), then this code shows the simple way for just a socket.io connection:
Listening socket.io-only server
// Load the library and initialize a server on port 3000
// This will create an underlying HTTP server, start it and bind socket.io to it
const io = require('socket.io')(3000);
// listen for incoming client connections and log connect and disconnect events
io.on('connection', function (socket) {
console.log("socket.io connect: ", socket.id);
socket.on('disconnect', function() {
console.log("socket.io disconnect: ", socket.id);
});
});
Node.js socket.io client - connects to another socket.io server
// load the client-side library
const io = require('socket.io-client');
// connect to a server and port
const socket = io('http://localhost:3000');
// listen for successful connection to the server
socket.on('connect', function() {
console.log("socket.io connection: ", socket.id);
});
This code works on my computer. I can run two separate node.js apps on the same host and they can talk to one another and both see the connect and disconnect events.
Some Explaining
The socket.io protocol is initiated by making an HTTP connection to an HTTP server. So, anytime you have a socket.io connection, there is an HTTP server listening somewhere. That HTTP connection is initially sent with some special headers that indicate to the server that this is a request to "upgrade" to the webSocket protocol and some additional security info is included.
This is pretty great reference on how a webSocket connection is initially established. It will show you step by step what happens.
Once both sides agree on the "upgrade" in protocol, then the protocol is switched to webSocket (socket.io is then an additional protocol layer on top of the base webSocket protocol, but the connection is all established at the HTTP/webSocket level). Once the upgrade is agreed upon, the exact same TCP connection that was originally the incoming HTTP connection is repurposed and becomes the webSocket/socket.io connection.
With the socket.io server-side library, you can either create the HTTP server yourself and then pass that to socket.io or you can have socket.io just create one for you. If you're only using socket.io on this server and not also sharing using http server for regular http requests, then you can go either way. The minimal code example above, just lets socket.io create the http server for you transparently and then socket.io binds to it. If you are also fielding regular web requests from the http server, then you would typically create the http server first and then pass it to socket.io so socket.io could bind to the http server you already have.
Then, keep in mind that socket.io is using the webSocket transport. It's just some additional packet structure on top of the webSocket transport. It would akin to agreeing to send JSON across an HTTP connection. HTTP is the host transport and underlying data format. Both sides then agree to format some data in JSON format and send it across HTTP. The socket.io message format sits on top of webSocket in that way.
Your Questions
Is it necessary to start a HTTP server to use it?
Yes, an HTTP server must exist somewhere because all socket.io connections start with an HTTP request to an HTTP server.
Sockets are on the transport layer, right?
The initial connection protocol stack works like this:
TCP <- HTTP protocol
Then, after the protocol upgrade:
TCP <- webSocket <- socket.io
So after the protocol upgrade from HTTP to the webSocket transport, you then have socket.io packet format sitting on top of the webSocket format sitting on top of TCP.
So in theory I don't need a HTTP protocol to trade messages.
No, that is not correct. All connections are initially established with HTTP. Once the upgrade happens to the webSocket transport, HTTP is no longer used.
It's pretty easy to configure a http server (using express) and a socket server (socket.io) assigned to it:
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
How can I run http server and socket server in two different node.js instances?
My idea is to leverage the performance this way, releasing the http node instance from the responsibility of also sending notifications back to the clients.
In a regular Socket.IO + Express app, Socket.IO intercepts requests starting with /socket.io/.
You may set Nginx (or any other webserver that supports proxying) listening 80 port, and make it proxy to Socket.IO process if request starts with /socket.io/, and to Express process otherwise.
Edit: To set up Socket.IO in separate process you may use the following code:
var io = require('socket.io')();
io.on('connection', function(socket){
//here you can emit and listen messages
});
io.listen(3000);