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Principles of websocket + probuf

2020-11-07 20:19:21 Support

1、WebSocket  

  WebSocket, Everybody knows , Since the name contains Socket, So and Socket There must be little difference , Yes , You're not mistaken , There's no big difference .

   In network programming , Our general agreement is based on TCP/IP,WebSocket No exception . and HTTP equally , He also has his own head and specific data .

Let's see .

This is a ,websocket Initiated connection , First one http Request , Tell the server , I want to send WebSocket The connection of , The server , Return to a paragraph ok. You can continue to use this connection later , Carry out basic WebSocket Request the .

Actually ,WebSocket And ordinary Socket There's no difference , All are send,receive, Sending and receiving data , It's just that the data format needs special treatment . Let's explain .

WebSocket The data format sent by ( Receiving and sending are the same ):

   Let's have a web map :

   Here's an online post : Explain it. :

  • FIN, To specify Frame Is it a Message In the end Frame( I said one before Message There may be more Frame form )
  • RSV1-3, must yes 0, Unless an extension defines the meaning of a nonzero value .
  • Opcode, This is more important , The following values are defined by the protocol
    • %x0 denotes a continuation frame

    • %x1 It means a text frame

    • %x2 It means a binary frame

    • %x3-7 are reserved for further non-control frames

    • %x8 Indicates that the connection is closed

    • %x9 Express ping ( Heart rate detection is related to , The back can speak )

    • %xA Express pong ( Heart rate detection is related to , The back can speak )

    • %xB-F are reserved for further control frames

  • Mask, This is to indicate “payload data” Whether the mask is calculated . This and the following Masking-key of ( If =0, There is no need to calculate the result : The result is clear , If it is =1,name With the next four bytes of masking-key, To handle decoding operations . Byte XOR by bit , Four at a time .)

      if(mask == 1){ 

       byte[] payload = xxxx; // It is assumed here that

            byte[] mask_key = new byte[4];// It is assumed here that

            for(int i=0;i<payload.Count;i++){

                   payload[i] = (byte)(payload[i] ^ mask_key[i%4]);

            }

            // So you can decode the plaintext

      }else{

            // In the case of plaintext ,2 After the byte or 4 byte ,12 After the byte is the specific data ,( The truth , According to the specific data ).

    }

  • Payload len, The total length of the data , There are three situations [<126,>126 && <= 65535,> 65535], These three situations , It's not the same , The first one is , Default footprint ( It itself ),( The following bytes are data or masking-key(mask by 1 Only then masking-key))
  • Masking-key, Encryption function
  • Payload data, The data that the frame really wants to send , It can be any length , But although theoretically there is no limit to the size of the frame , But you can't send too much data , Otherwise, it will lead to the inability to Efficient use of network bandwidth , As mentioned above Websocket Provide slicing .
  Is it right? , It's over in an instant , you 're right , It's almost the same here . If you want to encrypt your own data ,mask It can be written as a value or randomly , Anyway, it's all 4 It's just a byte .
  

  2、Probuf

   Our network often encodes and transmits data , In general, some of the ways we use back content original text ,xml,json, And there's what we're all about probuf 了 .

   What are the benefits of this coding , It greatly reduces the consumption of network bandwidth , At the same time, it reduces the time consumption of data analysis .

Let's have another wave of network graphics , The arrangement of data .

   chart 1:

   obvious , You can see it here ,Tag Take a place ,length Take a place , General situation , If it's long data ,namelength It may take up more than one byte . according to length The first decision of .(length Also the first one is to identify whether the second direct join calculation is needed , One analogy , Here's an explanation :

Varint: A kind of , Put the first place , As a condition of judgment , Come on length The way the calculation is done .

  0-0111 1111, A byte can represent a range : [0,0x7f] Size ,

      1000 0000 - 0000 0001 ----- 1111 1111 - 0111 1111 , Two bytes can represent the range :[1<<7, 0x7f<<7 + 0x7f]
      1000 0000 - 0000 0000 - 0000 0001 ----- 1111 1111 - 1111 1111 - 0111 1111 , Three bytes can represent the range :[1 << 7 * 2,  0x7f<<7 <<7 + 0x7f<<7 + 0x7f]

   So generally speaking , You just need a small number of direct mail to process most of the data .

   So was born probuf Description or parsing file of :( Have a chestnut )

message DownStreamMessages {
    repeated DownStreamMessage list = 1;
    required int64 syncTime = 2;
    optional bool finished = 3;
}

message DownStreamMessage {
required string fromUserId = 1;
required ChannelType type = 2;
optional string groupId = 3;
required string classname = 4;
required bytes content = 5;
required int64 dataTime = 6;
required int64 status = 7;
optional int64 extra = 8;
optional string msgId = 9;
optional int32 direction = 10;
optional int32 plantform =11;
optional int32 isRemoved = 12;
optional string source = 13;
optional int64 clientUniqueId = 14;
optional string extraContent = 15;
}

enum ChannelType {
PERSON = 1;
PERSONS = 2;
GROUP = 3;
TEMPGROUP = 4;
CUSTOMERSERVICE = 5;
NOTIFY = 6;
MC=7;
MP=8;
}

There are several key words to deal with :(bool and enum They are all treated as integers ), After field   = 1;  = 2 On the surface filed_number. value .

  required  It's usually necessary

       optional Not a must

       repeated Repetitive , A representation set .

        

   Here is a picture of the net :

      

                    Encoding data length .

                     

   The figure above shows the data The arrangement is regular , The data is compact .

   In particular repeat The situation of ,repeat hinder length It refers to the number of bytes needed to read this . Not the number of repetitions .

 

        Reference resources :https://juejin.im/post/6844903582290935822

   Reference resources :https://blog.csdn.net/carson_ho/article/details/70568606

   Reference resources :https://blog.csdn.net/JMW1407/article/details/107197938/

 

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