Introduction to socket.io learning tutorial in node.js (2)

socket.io provides real-time two-way communication based on events. The following article mainly introduces relevant information about the basic applications of socket.io. It has certain reference and learning value for everyone. Friends who need it can read it together. Take a look.

Preface

Socket.IO supports timely, two-way and event-based communication. It works on every platform, every browser, and every device with the same reliability and speed.

• Real-time analysis: Push data to clients where they will be represented as real-time counters, charts or log clients.

• Real-time communication and chat: It only takes a few lines of code to write a Socket.IO "Hello, World" chat application.

• Binary streaming transmission: Starting from version 1.0, Socket.IO supports any form of binary file transmission, such as: pictures, videos, audio, etc.

• Document merging: Allow multiple users to edit a document at the same time and be able to see the changes made by each user.

Server and client connection

socket.io provides both server and client connections API

The server socket.io must bind an http.Server instance

Bind http.Server

1, Implicit Binding

Implicit binding is performed by passing in the port when instantiating or calling the listen or attach function after instantiation. Socket.io internally instantiates and listens to http.Server

. When instantiating, the incoming port

let io = require('socket.io')(3000)

is directly bound through the listen or attach function. listen is synonymous with attach

let io = require('socket.io') 
io.listen(3000) // io.attach(3000)

2. Display binding

You can manually specify http.Server

Bind when instantiated

let server = require('http').Server(); 
let io = require('socket.io')(server)

server.listen(3000)

Binding through listen or attach

let server = require('http').Server(); 
let io = require('socket.io')()

io.listen(server) // io.attach(server)

server.listen(3000)

can bind http frameworks such as express or koa

express

let app = require('express') 
let server = require('http').Server(app) 
let io = require('socket.io')(server)

app.listen(3000)

koa

let app = require('koa')() 
let server = require('http').Server(app.callback())

let io = require('socket.io')(server)

app.listen(3000)

Listen to the connection status

When the server and client are successfully connected, the server will listen to the connection and connect events (connection and connect are synonymous), and the client The connect event will be monitored. When the connection is disconnected, the server's socket corresponding to the client and the client will both monitor the disconnect event.

Server code

let server = require('http').Server() 
let io = require('socket.io')(server)

server.listen(3000); 
io.on('connection', socket => { 
 console.log('connect')
 socket.on('disconnect', () => {
 console.log('disconnect')
 })
 socket.disconnect()
})

Print after running

connect 
disconnect

Client code

let socket = io('http://localhost:3000') 
socket.on('connect', () => { 
 console.log('connect')
})
socket.on('disconnect', () => { 
 console.log('disconnect')
})

Print after running

connect 
disconnect

Transfer data

Server and client The socket on the client side is an associated EventEmitter object. Events sent by the client socket can be received by the server socket, and events sent by the server socket can also be accepted by the client. Based on this mechanism, two-way communication can be achieved.

Now simulate a situation like this: the client keeps sending random numbers. When the random number is greater than 0.95, the server delays for 1s and then sends a warning and the number of warnings to the client

Server Code

let server = require('http').Server() 
let io = require('socket.io')(server)

server.listen(3000); 
io.on('connection', socket => { 
 socket.on('random', value => {
 console.log(value)
 if (value > 0.95) {
  if (typeof socket.warning === 'undefined') socket.warning = 0
  setTimeout(() => {
  socket.emit('warn', ++socket.warning)
  }, 1000)
 }
 })
})

The socket object can be used to store status information and custom data, such as socket.warning

Client code

let socket = io('http://localhost:3000') 
let interval = setInterval(() => { 
 socket.emit('random', Math.random())
}, 500)
socket.on('warn', count => { 
 console.log('warning count: ' + count)
})
socket.on('disconnect', () => { 
 clearInterval(interval)
})

Transport stream

socket.io can handle streams

Server code

io.on('connection', function (socket) { 
 let stream = ss.createStream()
 ss(socket).emit('script', stream)
 fs.createReadStream(__filename).pipe(stream)
})

Client code

let socket = io('http://localhost:3000') 
ss(socket).on('script', stream => { 
 let buffer = '' 
 stream.on('data', data => {
 buffer += data.toString()
 })
 stream.on('end', () => {
 console.log(buffer)
 })
})

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