WebSocket protocol and packet capture

WebSocket protocol

WebSocket is not a new agreement, but to use the HTTP protocol to establish a connection, it aims to establish a two-way communication channel unrestricted between the browser and the server, for example, you can send a message to the server at any time browser

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WebSocket connection must be initiated by the browser, because the request is a standard HTTP protocol requests, the following format:

GET ws://localhost:3000/ws/chat HTTP/1.1
Host: localhost
Upgrade: websocket
Connection: Upgrade
Origin: http://localhost:3000
Sec-WebSocket-Key: client-random-string
Sec-WebSocket-Version: 13

The request and the regular HTTP There are several differences:

1. GET request address is not similar to the / path /, but in ws: // at the beginning of the address;
2. Request header Upgrade: websocket and Connection: Upgrade indicates that the connection is to be converted to WebSocket connection;
3. Sec-WebSocket-Key is used to identify the connection, it is not used to encrypt the data;
4. Sec-WebSocket-Version specifies the WebSocket protocol version

Subsequently, if the server accepts the request, it returns the following responses:

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: server-random-string

The response code 101indicates the current HTTP protocol connection is going to be changed, the changed protocol is Upgrade: websocketspecified WebSocket protocol.

The version number and the sub-agreement parties can understand the data formats, and supports compression and so on. If only the WebSocket API, you do not need to care about these

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Relations HTTP protocol, WebSocket protocol and TCP protocol

      HTTP protocol is built on top of TCP protocol, TCP protocol itself to achieve a full-duplex communication, but the HTTP protocol request - response mechanism to limit the full-duplex communication. After the WebSocket connection is established, in fact, it simply provides: Next, we can not communicate using the HTTP protocol, the data is sent directly to each other now.

      Secure WebSocket connection mechanism and HTTPS similar. First, the browser with wss: // xxx When you create a WebSocket connection, will create a secure connection through HTTPS, then HTTPS connection upgraded to the WebSocket connection, taking the underlying communication is still secure SSL / TLS protocol 

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fiddler crawl WebSocket data

fiddlerDouble-click WebSocket Sessionto view the data connection and received