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老男孩IT教育alex python教學總監教你認識WebSocket
WebSocket協議是基于TCP的一種新的協議。WebSocket最初在HTML5規范中被引用為TCP連接，作為基于TCP的套接字API的占位符。它實現了瀏覽器與服務器全雙工(full-duplex)通信。其本質是保持TCP連接，在瀏覽器和服務端通過Socket進行通信。
本文將使用Python編寫Socket服務端，一步一步分析請求過程！！！
1 2 3 4 5 6 7 8 9 10 | import socketsock = 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)# 等待用戶連接conn, address = sock.accept()......... |
啟動Socket服務器后，等待用戶【連接】，然后進行收發數據。
1 2 3 4 | <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連接請求時，不僅連接還會發送【握手】信息，并等待服務端響應，至此連接才創建成功！
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | import socketsock = 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】信息需要遵循規則：
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為：258EAFA5-E914-47DA-95CA-C5AB0DC85B11
請求【握手】信息為：
提取Sec-WebSocket-Key值并加密：
客戶端和服務端傳輸數據時，需要對數據進行【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服務端需要手動實現。
第一步：獲取客戶端發送的數據【解包】
基于Python實現解包過程（未實現長內容）
解包詳細過程：
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,
0x1for text (which is always encoded in UTF-8),0x2for binary, and other so-called "control codes" that will be discussed later. In this version of WebSockets,0x3to0x7and0xBto0xFhave 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:
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.
Read the next 16 bits and interpret those as an unsigned integer. You're done.
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】
View Code
a. 基于Python socket實現的WebSocket服務端：
b. 利用JavaScript類庫實現客戶端
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，當然Tornado內部封裝功能更加完整。
以下是基于Tornado實現的聊天室示例：
app.py
index.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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