websocket 数据分析

WebSocket是一种通过单个TCP连接提供全双工通信信道的协议。2011年，IETF将WebSocket协议标准化为RFC 6455，W3C正在对Web IDL中的WebSocket API进行标准化。

WebSocket通信由消息和应用程序代码组成，不需要担心缓冲、解析和重构接收到的数据。例如，如果服务器发送1MB的有效负载，则只有当整个消息在客户端上可用时，才会调用应用程序的onmessage回调。

此外，WebSocket协议不对应用程序有效负载进行任何假设和约束：文本和二进制数据都是公平的游戏。在内部，协议只跟踪两个部分

当浏览器接收到新消息时，它会自动转换为基于文本的数据的DOMString对象，或二进制数据的Blob对象，然后直接传递给应用程序。唯一的其他选项，作为客户端的性能提示和优化，是告诉浏览器将接收到的二进制数据转换为ArrayBuffer而不是Blob：

一旦建立了WebSocket连接，客户端就可以随意发送和接收UTF-8和二进制消息。WebSocket提供双向通信信道，允许通过同一TCP连接在两个方向上传递消息：

Example traffic示例流量

Connection setup连接设置

To establish a WebSocket connection, the client sends a WebSocket handshake request, for which the server returns a WebSocket handshake response, as shown in the example below.为了建立WebSocket连接，客户端发送一个WebSocket握手请求，服务器将为该请求返回一个WebSocket握手响应，如下例所示。

Client request (just like in HTTP, each line ends with \r\n and there must be an extra blank line at the end):客户端请求（就像在HTTP中一样，每一行都以\r\n结尾，并且结尾必须有一个额外的空行）：

GET / HTTP/1.1
Host: 192.168.43.135:12345
Connection: Upgrade
Pragma: no-cache
Cache-Control: no-cache
Upgrade: websocket
Origin: file://
Sec-WebSocket-Version: 13
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36
Accept-Encoding: gzip, deflate, sdch
Accept-Language: zh-CN,zh;q=0.8,en-US;q=0.6,en;q=0.4
Sec-WebSocket-Key: bKdPyn3u98cTfZJSh4TNeQ==
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits 

Server response:服务器响应：

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: 4EaeSCkuOGBy+rjOSJSMV+VMoC0=
WebSocket-Origin: file://
WebSocket-Location: ws://192.168.43.135:12345/ 

Data transmission数据传输

Here is an example of data transmission between a Python WebSocket Server and JavaScript client.下面是Python WebSocket服务器和JavaScript客户端之间的数据传输示例。

An example from server to client:从服务器到客户端的示例：

Frame 7: 79 bytes on wire (632 bits), 79 bytes captured (632 bits)
Ethernet II, Src: Vmware_8a:3d:a7 (00:0c:29:8a:3d:a7), Dst: Vmware_c0:00:08 (00:50:56:c0:00:08)
Internet Protocol Version 4, Src: 192.168.43.135, Dst: 192.168.43.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 50999, Seq: 205, Ack: 510, Len: 25
WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0001 = Opcode: Text (1)
    0... .... = Mask: False
    .001 0111 = Payload length: 23
    Payload
JavaScript Object Notation
Line-based text data
    Welcome, 192.168.43.1 ! 

An example from client to server:从客户端到服务器的示例：

Frame 9: 72 bytes on wire (576 bits), 72 bytes captured (576 bits)
Ethernet II, Src: Vmware_c0:00:08 (00:50:56:c0:00:08), Dst: Vmware_8a:3d:a7 (00:0c:29:8a:3d:a7)
Internet Protocol Version 4, Src: 192.168.43.1, Dst: 192.168.43.135
Transmission Control Protocol, Src Port: 50999, Dst Port: 12345, Seq: 510, Ack: 230, Len: 18
WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0001 = Opcode: Text (1)
    1... .... = Mask: True
    .000 1100 = Payload length: 12
    Masking-Key: e17e8eb9
    Masked payload
    Payload
JavaScript Object Notation
Line-based text data
    test message 

参考文件:
https://hpbn.co/websocket/
https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_servers
https://www.rfc-editor.org/rfc/rfc6455
https://wiki.wireshark.org/WebSocket.md