So far I have only seen examples where an application in Node.js has been setup as a server for websockets. Usually the client is browser-based, and I have yet to see an example of a Node.js client.
How come there are so few examples on Node.js websocket clients? Alternatively, what other options are there for client-server communication?
Node. js can maintain many hundreds of WebSockets connections simultaneously. WebSockets on the server can become complicated as the connection upgrade from HTTP to WebSockets requires handling. This is why developers commonly use a library to manage this for them.
js modules from JavaScript running in the browser has many advantages because it allows you to use Node. js modules for client-side JavaScript applications without having to use a server with Node. js just to implement functionality that is already available as a Node. js module that is available via an npm package.
The theoretical limit is 65k connections per IP address but the actual limit is often more like 20k, so we use multiple addresses to connect 20k to each (50 * 20k = 1 mil).
There actually are many different examples.
I used the websockets package for example
https://www.npmjs.com/package/websocket
This code demonstrates a client in Node.js, not in the browser
#!/usr/bin/env node
var WebSocketClient = require('websocket').client;
var client = new WebSocketClient();
client.on('connectFailed', function(error) {
console.log('Connect Error: ' + error.toString());
});
client.on('connect', function(connection) {
console.log('WebSocket Client Connected');
connection.on('error', function(error) {
console.log("Connection Error: " + error.toString());
});
connection.on('close', function() {
console.log('echo-protocol Connection Closed');
});
connection.on('message', function(message) {
if (message.type === 'utf8') {
console.log("Received: '" + message.utf8Data + "'");
}
});
function sendNumber() {
if (connection.connected) {
var number = Math.round(Math.random() * 0xFFFFFF);
connection.sendUTF(number.toString());
setTimeout(sendNumber, 1000);
}
}
sendNumber();
});
client.connect('ws://localhost:8080/', 'echo-protocol');
It's pretty easy, if you need further help, tell us!
You can use W3C Websocket API for applications running on both Node and browsers (via the W3CWebSocket class).
https://websockets.spec.whatwg.org
npm install websocket
Server Example
Here's a short example showing a server that echos back anything sent to it, whether utf-8 or binary.
#!/usr/bin/env node
var WebSocketServer = require('websocket').server;
var http = require('http');
var server = http.createServer(function(request, response) {
console.log((new Date()) + ' Received request for ' + request.url);
response.writeHead(404);
response.end();
});
server.listen(8080, function() {
console.log((new Date()) + ' Server is listening on port 8080');
});
wsServer = new WebSocketServer({
httpServer: server,
// You should not use autoAcceptConnections for production
// applications, as it defeats all standard cross-origin protection
// facilities built into the protocol and the browser. You should
// *always* verify the connection's origin and decide whether or not
// to accept it.
autoAcceptConnections: false
});
function originIsAllowed(origin) {
// put logic here to detect whether the specified origin is allowed.
return true;
}
wsServer.on('request', function(request) {
if (!originIsAllowed(request.origin)) {
// Make sure we only accept requests from an allowed origin
request.reject();
console.log((new Date()) + ' Connection from origin ' + request.origin + ' rejected.');
return;
}
var connection = request.accept('echo-protocol', request.origin);
console.log((new Date()) + ' Connection accepted.');
connection.on('message', function(message) {
if (message.type === 'utf8') {
console.log('Received Message: ' + message.utf8Data);
connection.sendUTF(message.utf8Data);
}
else if (message.type === 'binary') {
console.log('Received Binary Message of ' + message.binaryData.length + ' bytes');
connection.sendBytes(message.binaryData);
}
});
connection.on('close', function(reasonCode, description) {
console.log((new Date()) + ' Peer ' + connection.remoteAddress + ' disconnected.');
});
});
Client Example
This is a simple example client that will print out any utf-8 messages it receives on the console, and periodically sends a random number.
This code demonstrates a client in Node.js, not in the browser
var W3CWebSocket = require('websocket').w3cwebsocket;
var client = new W3CWebSocket('ws://localhost:8080/', 'echo-protocol');
client.onerror = function() {
console.log('Connection Error');
};
client.onopen = function() {
console.log('WebSocket Client Connected');
function sendNumber() {
if (client.readyState === client.OPEN) {
var number = Math.round(Math.random() * 0xFFFFFF);
client.send(number.toString());
setTimeout(sendNumber, 1000);
}
}
sendNumber();
};
client.onclose = function() {
console.log('echo-protocol Client Closed');
};
client.onmessage = function(e) {
if (typeof e.data === 'string') {
console.log("Received: '" + e.data + "'");
}
};
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