JavaScript
WebSockets

introduzione

Sintassi

• nuovo WebSocket (url)
• ws.binaryType / * tipo di consegna del messaggio ricevuto: "arraybuffer" o "blob" * /
• ws.close ()
• ws.send (dati)
• ws.onmessage = function (message) {/ * ... * /}
• ws.onopen = function () {/ * ... * /}
• ws.onerror = function () {/ * ... * /}
• ws.onclose = function () {/ * ... * /}

Parametri

Stabilire una connessione web socket

var wsHost = "ws://my-sites-url.com/path/to/web-socket-handler";
var ws = new WebSocket(wsHost);

Lavorare con i messaggi di stringa

var wsHost = "ws://my-sites-url.com/path/to/echo-web-socket-handler";
var ws = new WebSocket(wsHost);
var value = "an example message";

//onmessage : Event Listener - Triggered when we receive message form server
ws.onmessage = function(message) {
    if (message === value) {
        console.log("The echo host sent the correct message.");
    } else {
        console.log("Expected: " + value);
        console.log("Received: " + message);
    }
};

//onopen : Event Listener - event is triggered when websockets readyState changes to open which means now we are ready to send and receives messages from server
ws.onopen = function() {
    //send is used to send the message to server
    ws.send(value);
};

Lavorare con i messaggi binari

var wsHost = "http://my-sites-url.com/path/to/echo-web-socket-handler";
var ws = new WebSocket(wsHost);
var buffer = new ArrayBuffer(5); // 5 byte buffer
var bufferView = new DataView(buffer);

bufferView.setFloat32(0, Math.PI);
bufferView.setUint8(4, 127);

ws.binaryType = 'arraybuffer';

ws.onmessage = function(message) {
    var view = new DataView(message.data);
    console.log('Uint8:', view.getUint8(4), 'Float32:', view.getFloat32(0))
};

ws.onopen = function() {
    ws.send(buffer);
};

Effettuare una connessione web sicura

var sck = "wss://site.com/wss-handler";
var wss = new WebSocket(sck);

Questo usa il wss invece di ws per creare una connessione sicura per il web socket che faccia uso di HTTPS invece di HTTP