你真的瞭解WebSocket嗎？

   老男孩IT教育python教學總監alex一篇文章帶你瞭解WebSocket

 WebSocket協議是基於TCP的一種新的協議。WebSocket最初在HTML5規範中被引用爲TCP鏈接，做爲基於TCP的套接字API的佔位符。它實現了瀏覽器與服務器全雙工(full-duplex)通訊。其本質是保持TCP鏈接，在瀏覽器和服務端經過Socket進行通訊。

 本文將使用Python編寫Socket服務端，一步一步分析請求過程！！！

1. 啓動服務端

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import  socket sock  =  socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,  1 ) sock.bind(( '127.0.0.1' ,  8002 )) sock.listen( 5 ) # 等待用戶鏈接 conn, address  =  sock.accept() ... ... ...

啓動Socket服務器後，等待用戶【鏈接】，而後進行收發數據。

2. 客戶端鏈接

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<script  type = "text/javascript" >      var socket  =  new WebSocket( "ws://127.0.0.1:8002/xxoo" );      ... < / script>

當客戶端向服務端發送鏈接請求時，不只鏈接還會發送【握手】信息，並等待服務端響應，至此鏈接才建立成功！

3. 創建鏈接【握手】

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import  socket   sock  =  socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,  1 ) sock.bind(( '127.0.0.1' ,  8002 )) sock.listen( 5 ) # 獲取客戶端socket對象 conn, address  =  sock.accept() # 獲取客戶端的【握手】信息 data  =  conn.recv( 1024 ) ... ... ... conn.send( '響應【握手】信息' )

請求和響應的【握手】信息須要遵循規則：

• 從請求【握手】信息中提取 Sec-WebSocket-Key

• 利用magic_string 和 Sec-WebSocket-Key 進行hmac1加密，再進行base64加密

• 將加密結果響應給客戶端

注：magic string爲：258EAFA5-E914-47DA-95CA-C5AB0DC85B11

請求【握手】信息爲：

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提取Sec-WebSocket-Key值並加密：

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4.客戶端和服務端收發數據

客戶端和服務端傳輸數據時，須要對數據進行【封包】和【解包】。客戶端的JavaScript類庫已經封裝【封包】和【解包】過程，但Socket服務端須要手動實現。

第一步：獲取客戶端發送的數據【解包】

 基於Python實現解包過程（未實現長內容）

解包詳細過程： 

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The MASK bit simply tells whether the message is encoded. Messages from the client must be masked, so your server should expect this to be 1. (In fact, section 5.1 of the spec says that your server must disconnect from a client if that client sends an unmasked message.) When sending a frame back to the client, do not mask it and do not set the mask bit. We'll explain masking later. Note: You have to mask messages even when using a secure socket.RSV1-3 can be ignored, they are for extensions.

The opcode field defines how to interpret the payload data: 0x0 for continuation, 0x1 for text (which is always encoded in UTF-8), 0x2 for binary, and other so-called "control codes" that will be discussed later. In this version of WebSockets, 0x3 to 0x7 and 0xB to 0xF have no meaning.

The FIN bit tells whether this is the last message in a series. If it's 0, then the server will keep listening for more parts of the message; otherwise, the server should consider the message delivered. More on this later.

Decoding Payload Length

To read the payload data, you must know when to stop reading. That's why the payload length is important to know. Unfortunately, this is somewhat complicated. To read it, follow these steps:

1. Read bits 9-15 (inclusive) and interpret that as an unsigned integer. If it's 125 or less, then that's the length; you're done. If it's 126, go to step 2. If it's 127, go to step 3.

2. Read the next 16 bits and interpret those as an unsigned integer. You're done.

3. Read the next 64 bits and interpret those as an unsigned integer (The most significant bit MUST be 0). You're done.

Reading and Unmasking the Data

If the MASK bit was set (and it should be, for client-to-server messages), read the next 4 octets (32 bits); this is the masking key. Once the payload length and masking key is decoded, you can go ahead and read that number of bytes from the socket. Let's call the data ENCODED, and the key MASK. To get DECODED, loop through the octets (bytes a.k.a. characters for text data) of ENCODED and XOR the octet with the (i modulo 4)th octet of MASK. In pseudo-code (that happens to be valid JavaScript):

 

var DECODED = "";
for (var i = 0; i < ENCODED.length; i++) {
    DECODED[i] = ENCODED[i] ^ MASK[i % 4];
}

 

Now you can figure out what DECODED means depending on your application.

 第二步：向客戶端發送數據【封包】

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5. 基於Python實現簡單示例

a. 基於Python socket實現的WebSocket服務端：

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b. 利用JavaScript類庫實現客戶端

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6. 基於Tornado框架實現Web聊天室

Tornado是一個支持WebSocket的優秀框架，其內部原理正如1~5步驟描述，固然Tornado內部封裝功能更加完整。

如下是基於Tornado實現的聊天室示例：

 app.py

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <title>Python聊天室</title></head><body>
    <div>
        <input type="text" id="txt"/>
        <input type="button" id="btn" value="提交" onclick="sendMsg();"/>
        <input type="button" id="close" value="關閉鏈接" onclick="closeConn();"/>
    </div>
    <div id="container" style="border: 1px solid #dddddd;margin: 20px;min-height: 500px;">

    </div>

    <script src="/static/jquery-2.1.4.min.js"></script>
    <script type="text/javascript">
        $(function () {
            wsUpdater.start();
        });        var wsUpdater = {
            socket: null,
            uid: null,
            start: function() {                var url = "ws://127.0.0.1:8888/chat";
                wsUpdater.socket = new WebSocket(url);
                wsUpdater.socket.onmessage = function(event) {
                    console.log(event);                    if(wsUpdater.uid){
                        wsUpdater.showMessage(event.data);
                    }else{
                        wsUpdater.uid = event.data;
                    }
                }
            },
            showMessage: function(content) {
                $('#container').append(content);
            }
        };        function sendMsg() {            var msg = {
                uid: wsUpdater.uid,
                message: $("#txt").val()
            };
            wsUpdater.socket.send(JSON.stringify(msg));
        }</script></body></html>

示例×××

 

 

參考文獻：https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_servers 

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