WebSocket協議探究（三）：MQTT子協議

時間 2019-11-18

標籤 websocket 協議探究 mqtt 简体版

原文原文鏈接

一複習和目標

1 複習

Nodejs實現WebSocket服務器
Netty實現WebSocket服務器(附帶了源碼分析)
Js api實現WebSocket客戶端

注：Nodejs使用的Socket.io模塊實現，Netty自己對WebSocket有必定的支持，因此這兩種實現都相對容易理解，你們本身可使用本身喜歡的語言實現(參考Nodejs版本，即不須要考慮過多的狀況)。html

2 目標

使用WebSocket協議進行發送Mqtt消息
即Mqtt協議做爲WebSocket協議的子協議進行通訊

注1：WebSocket協議內容很少，可是遠遠不止這麼少。可是學習不要完美主義(即學到同樣東西就想着一開始就把這樣東西學透)，學習要帶着目的性。好比：我就是想弄懂爲何前端須要使用WebSocket協議才能發送Mqtt消息？WebSocket爲何須要HTTP協議來進行協議升級協商？HTTP協議爲何基於TCP協議？TCP協議是全雙工的爲何HTTP協議不能全雙工？等等......前端

注2：協議目前學習了MQTT、TCP、HTTP和WebSocket，並非如今學完了，之後就能夠再也不去學習這些，而是說對於如今的學習目的已經達到了，不須要再花費過多的精力罷了。web

二 WireShark抓包

1 WebSocket鏈接

請求升級協議：HTTP -> WebSocket(mqtt)

# 省略無關頭部
Hypertext Transfer Protocol
    GET /mqtt HTTP/1.1\r\n
    Host: 103.61.37.192:8083\r\n
    Sec-WebSocket-Version: 13\r\n
    Sec-WebSocket-Protocol: mqtt\r\n # 子協議爲mqtt
    Sec-WebSocket-Extensions: permessage-deflate\r\n
    Sec-WebSocket-Key: npQCPFw1Pc5G9vqjJyi90w==\r\n
    Connection: keep-alive, Upgrade\r\n
    Upgrade: websocket\r\n
    \r\n

響應成功

# 省略無關頭部
Hypertext Transfer Protocol
    HTTP/1.1 101 Switching Protocols\r\n
    Connection: Upgrade\r\n
    Content-Length: 0\r\n
    Sec-Websocket-Accept: biw/vsujgvKx8B0bfoDnjuxHMgA=\r\n
    Sec-Websocket-Protocol: mqtt\r\n # 確認子協議爲mqtt
    Upgrade: websocket\r\n
    \r\n

2 MQTT創建鏈接

客戶端 -> 服務器：CONNECT
- 原本MQTT TCP鏈接能夠經過分段或一次傳輸完成的WebSocket則分紅了13次發送

# 發送了13個幀
192.168.1.46    103.61.37.192   WebSocket   WebSocket Binary [FIN] [MASKED]
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    1... .... = Mask: True
    .000 0001 = Payload length: 1
    Masking-Key: 0c3cb539
    Masked payload
        1C  
        
# 幀序號    數據                                                           
# 1        Data: 10  -> Header Flags:Connect 
# 2        Data: 58  -> Msg Len:88
# 3        Data: 0004 -> Protocol Name Length: 4 
# 4        Data: 4d515454 -> Protocol Name: MQTT
# 5        Data: 04 -> Version：v3.1.1
# 6        Data: c2 
#            1... .... = User Name Flag: Set # 用戶名
#            .1.. .... = Password Flag: Set # 密碼
#            ..0. .... = Will Retain: Not Set # 遺囑保留
#            ...0 0... = Qos Level: 0
#            .... .0.. = Will Flag: Not Set # 遺囑
#            .... ..1. = Clean Session Flag: Set # 清除會話
#            .... ...0 = (Reserverd): Not Set # 固定爲0
# 7        Data: 003c -> Keep Alive: 60秒
# 8        Data: 0011 -> Client ID Length: 17
# 9        Data: 6d 71 74 74 6a 73 5f 39 38 33 37 66 65 30 62 61 38 -> ClientId
# 10       Data: 000b -> Username Length
# 11       Data: 64656c696768742f776562 -> Username
# 12       Data: 002c -> Password Length
# 13       Data: 45396a4d58416c35523939596b48756350506c3377545468... -> Password

服務器 -> 客戶端：CONNACK

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    0... .... = Mask: False
    .000 0100 = Payload length: 4
    Data (4 bytes)
        Data: 20 02 00 00
# 20 -> Header Flags:CONNACK
# 02 -> Msg Len：2
# 00 -> Acknowledge Flags: 0x00 # 鏈接確認標誌
# 00 -> Return Code: Connection Accepted (0) # 鏈接返回碼

3 MQTT的PINGREQ和PINGRESP

客戶端 -> 服務器：PINGREQ

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    1... .... = Mask: True
    .000 0010 = Payload length: 2
    Masking-Key: 0657364e
    Data (2 bytes)
        Data: c000 

# C0 -> Header Flags: 0xC0 (Ping Request)
# 00 -> Msg Len: 0

服務器 -> 客戶端：PINGRESP

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    0... .... = Mask: False
    .000 0010 = Payload length: 2
    Data (2 bytes)
        Data: d000

# D0 -> Header Flags: 0xD0 (Ping Response)  
# 00 -> Msg Len: 0

4 MQTT的SUBSCRIBE和SUBACK

客戶端 -> 服務器：SUBSCRIBE

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    1... .... = Mask: True
    .000 0001 = Payload length: 1
    Masking-Key: d0f56152
    Data (1 byte)
        Data: 82
        
# 幀序號    數據                                                          
# 1        Data: 82  -> Header Flags: Subscribe Request
# 2        Data: 0b  -> Msg Len:11
# 3        Data: a5b2 -> Message Identifier: a5b2
# 4        Data: 0006 ->  Topic Length: 6
# 5        Data: 2f 57 6f 72 6c 64 -> Topic:/World
# 6        Data: 00 -> Requested QoS:0

服務器 -> 客戶端：SUBACK

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    0... .... = Mask: False
    .000 0101 = Payload length: 5
    Data (5 bytes)
        Data: 9003a5b200

# 90 ->  Header Flags: Subscribe Ack
# 03 -> Msg Len: 3 
# a5b2 -> Message Identifier:a5b2
# 00 -> 成功

5 MQTT的PUBLISH(Qos0)

# 幀序號    數據                                                          
# 1        Data: 30 -> Header Flags: Publish Message
# 2        Data: 0d ->  Msg Len: 13 
# 3        Data: 0006 -> Topic Length:6
# 4        Data: 2f 57 6f 72 6c 64 ->  Topic:/World
# 5        Data: 68 65 6c 6c 6f -> Message:hello

6 MQTT的DISCONNECT

WebSocket
    1... .... = Fin: True
    .000 .... = Reserved: 0x0
    .... 0010 = Opcode: Binary (2)
    1... .... = Mask: True
    .000 0010 = Payload length: 2
    Masking-Key: d70088a5
    Data (5 bytes)
        Data: e000

# e0 -> Header Flags: Disconnect
# 00 -> Msg Len: 0

注1：MQTT報文格式請參考MQTT協議探究(一) MQTT協議探究（二）shell

注2：MQTT其餘報文就不作貼出來了，請自行測試。api

注3：協議的學習基本完成，後面結合Netty來加深對協議的複習和補充。服務器