Websocket implementation principle

 websocket Same as http and https equally , Belong to tcp Based on the application layer protocol ; need Three handshakes, four waves The process of
Generally speaking , What we use http The protocol can only be requested by the client , The server cannot push data directly and actively , This leads to continuous changes on the server ( Such as chat rooms ) The client side is more complex to obtain ( Such as real-time performance and service side pressure ). therefore ,websocket The agreement came into being
   about websocket Agreement for , Both the client and the server can actively push messages , The message content can be either text or binary data . And there is no restriction of homology policy , There is no cross domain problem
  websocket The representation of the agreement ws(ws://xxxx.com); image https equally , If encrypted , The identifier is wxs 
 websocket Handshake
Handshake ： Verify that the server supports websocket agreement
        1） Create connection , The browser connects to the server , Connection created successfully
        2） The browser generates a random string , The browser saves a copy of the random string , Send a copy to the server at the same time （ be based on http The protocol is sent to the server , Will put the string in http The request header is sent to the server ）
        3） After the server receives the random string , Let it follow the magic string （magic string, Globally recognized fixed string ） Splicing , And then through sha1 The algorithm encrypts and then passes base64 After the coding , Generating ciphertext
        4） The server returns the ciphertext to the browser （ The ciphertext cannot be inversely solved ）
        5） The browser also matches the locally stored random string with magic string A ciphertext is obtained by splicing and encrypting
        6） The browser compares the ciphertext sent by the server with the local ciphertext 、 check , If through , It means that both ends use the same magic string, The same encryption method that is used , That is, it can be determined that the server supports websocket agreement , Shake hands with success ; If the verification fails , It means that the server does not support websocket agreement , Handshake failed