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標題: MQTT底層封包協(xié)議 [打印本頁]
作者: supper戰(zhàn)    時間: 2020-6-26 15:31
標題: MQTT底層封包協(xié)議
MQTT（Message Queuing Telemetry Transport，消息隊列遙測傳輸協(xié)議），是一種基于發(fā)布/訂閱（publish/subscribe）模式的"輕量級"通訊協(xié)議，該協(xié)議構(gòu)建于TCP/IP協(xié)議上，由IBM在1999年發(fā)布。MQTT最大優(yōu)點在于，可以以極少的代碼和有限的帶寬，為連接遠程設(shè)備提供實時可靠的消息服務(wù)。作為一種低開銷、低帶寬占用的即時通訊協(xié)議，使其在物聯(lián)網(wǎng)、小型設(shè)備、移動應(yīng)用等方面有較廣泛的應(yīng)用。
在基于C的封包底層上有許多比較精妙的地方，可以參考看一看
  1. /**
  2.   ******************************************************************************
  3.   * @version V1.0.0
  4.   * @date    2019/12/15
  5.   * @brief   
  6.   ******************************************************************************
  7.        
  8.   ******************************************************************************
  9.   */

  11. #define MQTTCLIENT_C_//如果沒有定義

  13. #include "mqtt_msg.h"
  14. #include "string.h"
  15. #include "stm32f10x.h"


  18. #define MQTT_MAX_FIXED_HEADER_SIZE 3

  20. uint16_t mqtt_message_id = 0;

  22. enum mqtt_connect_flag
  23. {
  24.   MQTT_CONNECT_FLAG_USERNAME = 1 << 7,
  25.   MQTT_CONNECT_FLAG_PASSWORD = 1 << 6,
  26.   MQTT_CONNECT_FLAG_WILL_RETAIN = 1 << 5,
  27.   MQTT_CONNECT_FLAG_WILL = 1 << 2,
  28.   MQTT_CONNECT_FLAG_CLEAN_SESSION = 1 << 1
  29. };
  30. //__attribute((__packed__))
  31. struct  mqtt_connect_variable_header
  32. {
  33.   uint8_t lengthMsb;
  34.   uint8_t lengthLsb;
  35.   uint8_t magic[4];
  36.   uint8_t version;
  37.   uint8_t flags;
  38.   uint8_t keepaliveMsb;
  39.   uint8_t keepaliveLsb;
  40. };


  43. int mqtt_get_type(char* buffer) { return (buffer[0] & 0xf0) >> 4; }
  44. int mqtt_get_connect_ret_code(char* buffer) { return (buffer[3]); }
  45. int mqtt_get_qos(char* buffer) { return (buffer[0] & 0x06) >> 1; }


  48. int append_string(int *length, char* buffer,int buffer_length, char* string, int len)
  49. {
  50.   if((*length) + len + 2 > buffer_length)//加上 ClientID 和 記錄 ClientID個數(shù)(兩位) 以后超出了數(shù)組
  51.     return -1;

  53.   buffer[(*length)++] = len >> 8;
  54.   buffer[(*length)++] = len & 0xff;
  55.   c_memcpy(buffer + (*length), string, len);
  56.   (*length) += len;
  57.   return len + 2;
  58. }



  62. uint16_t append_message_id(int *length, char* buffer,int buffer_length, uint16_t message_id)
  63. {
  64.   // If message_id is zero then we should assign one, otherwise
  65.   // we'll use the one supplied by the caller
  66.   while(message_id == 0)
  67.     message_id = ++mqtt_message_id;

  69.   if((*length) + 2 > buffer_length)
  70.     return 0;

  72.   buffer[(*length)++] = message_id >> 8;
  73.   buffer[(*length)++] = message_id & 0xff;
  74.        
  75.   return message_id;
  76. }


  79. int fini_message(char **data_ptr,int        length,char* buffer, int type, int dup, int qos, int retain)
  80. {
  81.   int remaining_length = length - MQTT_MAX_FIXED_HEADER_SIZE;
  82.        
  83.   if(remaining_length > 127)
  84.   {
  85.     buffer[0] = ((type & 0x0f) << 4) | ((dup & 1) << 3) | ((qos & 3) << 1) | (retain & 1);
  86.     buffer[1] = 0x80 | (remaining_length % 128);
  87.     buffer[2] = remaining_length / 128;
  88.     length = remaining_length + 3;
  89.     *data_ptr = buffer;
  90.   }
  91.   else
  92.   {
  93.     buffer[1] = ((type & 0x0f) << 4) | ((dup & 1) << 3) | ((qos & 3) << 1) | (retain & 1);
  94.     buffer[2] = remaining_length;
  95.     length = remaining_length + 2;
  96.     *data_ptr = buffer + 1;
  97.   }

  99.   return length;
  100. }



  104. uint16_t mqtt_get_id(char* buffer, uint16_t length)
  105. {
  106.   if(length < 1)
  107.     return 0;
  108.        
  109.   switch(mqtt_get_type(buffer))
  110.   {
  111.     case MQTT_MSG_TYPE_PUBLISH:
  112.     {
  113.       int i;
  114.       int topiclen;

  116.       for(i = 1; i < length; ++i)
  117.       {
  118.         if((buffer[i] & 0x80) == 0)
  119.         {
  120.           ++i;
  121.           break;
  122.         }
  123.       }

  125.       if(i + 2 >= length)
  126.         return 0;
  127.       topiclen = buffer[i++] << 8;
  128.       topiclen |= buffer[i++];

  130.       if(i + topiclen >= length)
  131.         return 0;
  132.       i += topiclen;

  134.       if(mqtt_get_qos(buffer) > 0)
  135.       {
  136.         if(i + 2 >= length)
  137.           return 0;
  138.         //i += 2;
  139.       } else {
  140.               return 0;
  141.       }
  142.       return (buffer[i] << 8) | buffer[i + 1];
  143.     }
  144.     case MQTT_MSG_TYPE_PUBACK:
  145.     case MQTT_MSG_TYPE_PUBREC:
  146.     case MQTT_MSG_TYPE_PUBREL:
  147.     case MQTT_MSG_TYPE_PUBCOMP:
  148.     case MQTT_MSG_TYPE_SUBACK:
  149.     case MQTT_MSG_TYPE_UNSUBACK:
  150.     case MQTT_MSG_TYPE_SUBSCRIBE:
  151.     {
  152.       // This requires the remaining length to be encoded in 1 byte,
  153.       // which it should be.
  154.       if(length >= 4 && (buffer[1] & 0x80) == 0)
  155.         return (buffer[2] << 8) | buffer[3];
  156.       else
  157.         return 0;
  158.     }

  160.     default:
  161.       return 0;
  162.   }
  163. }






  170. /**
  171. * @brief   打包連接MQTT指令
  172. * @param   info     MQTT信息
  173. * @param   data_ptr 打包的數(shù)據(jù)首地址
  174. * @param   buffer   打包進的數(shù)組
  175. * @param   buffer_length 數(shù)組長度
  176. * @retval  數(shù)據(jù)長度
  177. * @warning None
  178. * @example
  179. **/
  180. int mqtt_msg_connect(mqtt_connect_info_t* info,char **data_ptr,char* buffer,int buffer_length)
  181. {
  182.         int length;
  183.   struct mqtt_connect_variable_header* variable_header;
  184.        
  185.         mqtt_message_id = 0;
  186.        
  187.         length = MQTT_MAX_FIXED_HEADER_SIZE;//頭.連接類型1位,數(shù)據(jù)個數(shù)2位(如果大于127就需要兩位)
  188.        
  189.   if(length + sizeof(*variable_header) > buffer_length)//數(shù)組不夠存儲的
  190.     return 0;
  191.        
  192.   variable_header = (void*)(buffer + length);//把數(shù)組分給這個結(jié)構(gòu)體里面的變量
  193.   length += sizeof(*variable_header);//存儲完 連接類型,整個數(shù)據(jù)個數(shù),版本號個數(shù),版本號,等
  194.        
  195.   variable_header->lengthMsb = 0;//版本名稱個數(shù)高位
  196.   variable_header->lengthLsb = 4;//版本名稱個數(shù)低位
  197.   c_memcpy(variable_header->magic, "MQTT", 4);//版本名稱MQTT
  198.   variable_header->version = 4;//版本號
  199.   variable_header->flags = 0;//先清零
  200.   variable_header->keepaliveMsb = info->keepalive >> 8;//心跳包時間
  201.   variable_header->keepaliveLsb = info->keepalive & 0xff;//心跳包時間

  203.   if(info->clean_session)//清除連接信息
  204.     variable_header->flags |= MQTT_CONNECT_FLAG_CLEAN_SESSION;

  206.   if(info->client_id != NULL && info->client_id[0] != '\0')//client_id
  207.   {
  208.     if(append_string(&length,buffer,buffer_length, info->client_id, c_strlen(info->client_id)) < 0)//拷貝
  209.       return -1;//數(shù)組不夠用呀...
  210.   }
  211.   else
  212.     return -2;//沒有設(shè)置client_id

  214.   if(info->will_topic != NULL && info->will_topic[0] != '\0')//遺囑
  215.   {
  216.     if(append_string(&length,buffer,buffer_length , info->will_topic, c_strlen(info->will_topic)) < 0)//遺囑的主題
  217.       return -3;

  219.     if(append_string(&length,buffer,buffer_length , info->will_message, c_strlen(info->will_message)) < 0)//遺囑的消息
  220.       return -4;

  222.     variable_header->flags |= MQTT_CONNECT_FLAG_WILL;//需要遺囑
  223.     if(info->will_retain)//遺囑是夠需要服務(wù)器保留
  224.       variable_header->flags |= MQTT_CONNECT_FLAG_WILL_RETAIN;//保留遺囑
  225.     variable_header->flags |= (info->will_qos & 3) << 3;//遺囑消息等級
  226.   }

  228.   if(info->username != NULL && info->username[0] != '\0')//username
  229.   {
  230.     if(append_string(&length,buffer,buffer_length, info->username, c_strlen(info->username)) < 0)//拷貝用戶名
  231.       return -5;

  233.     variable_header->flags |= MQTT_CONNECT_FLAG_USERNAME;//有用戶名
  234.   }
  235.        
  236.   if(info->password != NULL && info->password[0] != '\0')//password
  237.   {
  238.     if(append_string(&length,buffer,buffer_length, info->password, c_strlen(info->password)) < 0)
  239.       return -6;

  241.     variable_header->flags |= MQTT_CONNECT_FLAG_PASSWORD;//有密碼
  242.   }

  244.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_CONNECT, 0, 0, 0);//最終組合連接MQTT的指令
  245. }


  248. /**
  249. * @brief  判斷是否連接上MQTT
  250. * @param  服務(wù)器返回的數(shù)據(jù)
  251. * @param  
  252. * @retval 0 連接成功
  253. * @example
  254. **/
  255. int  mqtt_msg_connect_ack(char *buff)
  256. {
  257.         if(mqtt_get_type(buff) == MQTT_MSG_TYPE_CONNACK)
  258.         {
  259.                 return mqtt_get_connect_ret_code(buff);
  260.         }
  261.         return -1;
  262. }


  265. /**
  266. * @brief   斷開連接
  267. * @param   data_ptr 打包的數(shù)據(jù)首地址
  268. * @param   buffer   打包進的數(shù)組
  269. * @param   buffer_length 數(shù)組長度
  270. * @retval  數(shù)據(jù)長度
  271. * @warning None
  272. * @example
  273. **/
  274. int mqtt_msg_disconnect(char **data_ptr,char* buffer,int buffer_length)
  275. {
  276.         int length;
  277.         length = MQTT_MAX_FIXED_HEADER_SIZE;
  278.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_DISCONNECT, 0, 0, 0);
  279. }



  283. /**
  284. * @brief   訂閱主題
  285. * @param   topic   訂閱的主題
  286. * @param   qos     消息等級
  287. * @param   data_ptr 打包的數(shù)據(jù)首地址
  288. * @param   buffer   打包進的數(shù)組
  289. * @param   buffer_length 數(shù)組長度
  290. * @retval  數(shù)據(jù)長度
  291. * @warning None
  292. * @example
  293. **/
  294. int mqtt_msg_subscribe_topic(char* topic, int qos,char **data_ptr,char* buffer,int buffer_length)
  295. {
  296.         int length;
  297.         length = MQTT_MAX_FIXED_HEADER_SIZE;
  298.        
  299.         if(topic == NULL || topic[0] == '\0')
  300.                 return -1;
  301.        
  302.         if((mqtt_message_id = append_message_id(&length, buffer, buffer_length, 0)) == 0)
  303.                 return -2;
  304.        
  305.         if(append_string(&length, buffer, buffer_length, topic, c_strlen(topic)) < 0)
  306.                 return -3;
  307.        
  308.         if(length + 1 > buffer_length)
  309.     return -4;
  310.   buffer[length++] = qos;
  311.        
  312.         return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_SUBSCRIBE, 0, 1, 0);
  313. }



  317. /**
  318. * @brief  判斷是否成功訂閱
  319. * @param  buffer  服務(wù)器返回的數(shù)據(jù)
  320. * @param  length  服務(wù)器返回的數(shù)據(jù)長度
  321. * @retval 0:成功  1:失敗
  322. * @example
  323. **/
  324. int mqtt_msg_subscribe_ack(char* buffer, uint16_t length)
  325. {
  326.         if(mqtt_get_type(buffer) == MQTT_MSG_TYPE_SUBACK)
  327.         {
  328.                 if(mqtt_get_id(buffer,length) == mqtt_message_id)
  329.                 {
  330.                         return 0;
  331.                 }
  332.                 else
  333.                 {
  334.                         return 1;
  335.                 }
  336.         }
  337.         else
  338.         {
  339.                 return 1;
  340.         }
  341. }


  344. /**
  345. * @brief   發(fā)布消息
  346. * @param   topic    主題
  347. * @param   data     消息
  348. * @param   data_length 消息長度
  349. * @param   qos      消息等級
  350. * @param   retain   是否需要保留消息
  351. * @param   data_ptr 打包的數(shù)據(jù)首地址
  352. * @param   buffer   打包進的數(shù)組
  353. * @param   buffer_length 數(shù)組長度
  354. * @retval  數(shù)據(jù)長度
  355. * @warning None
  356. * @example
  357. **/
  358. int mqtt_msg_publish(char* topic, char* date, int data_length, int qos, int retain, char **data_ptr,char* buffer,int buffer_length)
  359. {
  360.         int length;
  361.         length = MQTT_MAX_FIXED_HEADER_SIZE;

  363.   if(topic == NULL || topic[0] == '\0')
  364.     return -1;

  366.   if(append_string(&length, buffer, buffer_length, topic, strlen(topic)) < 0)
  367.     return -2;

  369.   if(qos > 0)
  370.   {
  371.     if((mqtt_message_id = append_message_id(&length, buffer, buffer_length,  0)) == 0)
  372.       return -3;
  373.   }
  374.   else
  375.     mqtt_message_id = 0;

  377.   if(length + data_length > buffer_length)
  378.     return -4;
  379.   memcpy(buffer + length, date, data_length);
  380.   length += data_length;

  382.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PUBLISH, 0, qos, retain);
  383. }



  387. int mqtt_msg_puback(uint16_t message_id,char **data_ptr,char* buffer,int buffer_length)
  388. {
  389.         int length;
  390.   length = MQTT_MAX_FIXED_HEADER_SIZE;
  391.   if(append_message_id(&length, buffer, buffer_length,message_id) == 0)
  392.     return -1;
  393.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PUBACK, 0, 0, 0);
  394. }


  397. int mqtt_msg_pubrec(uint16_t message_id,char **data_ptr,char* buffer,int buffer_length)
  398. {
  399.         int length;
  400.   length = MQTT_MAX_FIXED_HEADER_SIZE;
  401.   if(append_message_id(&length, buffer, buffer_length,message_id) == 0)
  402.     return -1;
  403.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PUBREC, 0, 0, 0);
  404. }


  407. int mqtt_msg_pubrel(uint16_t message_id,char **data_ptr,char* buffer,int buffer_length)
  408. {
  409.         int length;
  410.   length = MQTT_MAX_FIXED_HEADER_SIZE;
  411.        
  412.   if(append_message_id(&length, buffer, buffer_length,message_id) == 0)
  413.     return -1;
  414.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PUBREL, 0, 1, 0);
  415. }


  418. int mqtt_msg_pubcomp(uint16_t message_id,char **data_ptr,char* buffer,int buffer_length)
  419. {
  420.         int length;
  421.   length = MQTT_MAX_FIXED_HEADER_SIZE;
  422.   if(append_message_id(&length, buffer, buffer_length,message_id) == 0)
  423.     return -1;
  424.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PUBCOMP, 0, 0, 0);
  425. }


  428. const char* mqtt_get_publish_topic(char* buffer, uint16_t* length)
  429. {
  430.   int i;
  431.   int totlen = 0;
  432.   int topiclen;

  434.   for(i = 1; i < *length; ++i)
  435.   {
  436.     totlen += (buffer[i] & 0x7f) << (7 * (i -1));
  437.     if((buffer[i] & 0x80) == 0)
  438.     {
  439.       ++i;
  440.       break;
  441.     }
  442.   }
  443.   totlen += i;

  445.   if(i + 2 >= *length)
  446.     return NULL;
  447.   topiclen = buffer[i++] << 8;
  448.   topiclen |= buffer[i++];

  450.   if(i + topiclen > *length)
  451.     return NULL;

  453.   *length = topiclen;
  454.   return (const char*)(buffer + i);
  455. }


  458. const char* mqtt_get_publish_data(char* buffer, uint16_t* length)
  459. {
  460.   int i;
  461.   int totlen = 0;
  462.   int topiclen;
  463.   int blength = *length;
  464.   *length = 0;

  466.   for(i = 1; i < blength; ++i)
  467.   {
  468.     totlen += (buffer[i] & 0x7f) << (7 * (i - 1));
  469.     if((buffer[i] & 0x80) == 0)
  470.     {
  471.       ++i;
  472.       break;
  473.     }
  474.   }
  475.   totlen += i;

  477.   if(i + 2 >= blength)
  478.     return NULL;
  479.   topiclen = buffer[i++] << 8;
  480.   topiclen |= buffer[i++];

  482.   if(i + topiclen >= blength)
  483.     return NULL;

  485.   i += topiclen;

  487.   if(mqtt_get_qos(buffer) > 0)
  488.   {
  489.     if(i + 2 >= blength)
  490.       return NULL;
  491.     i += 2;
  492.   }

  494.   if(totlen < i)
  495.     return NULL;

  497.   if(totlen <= blength)
  498.     *length = totlen - i;
  499.   else
  500.     *length = blength - i;
  501.   return (const char*)(buffer + i);
  502. }

  504. /**
  505. * @brief   打包服務(wù)器返回的心跳包數(shù)據(jù)(用不到)
  506. * @param   data_ptr 打包的數(shù)據(jù)首地址
  507. * @param   buffer   打包進的數(shù)組
  508. * @param   buffer_length 數(shù)組長度
  509. * @retval  數(shù)據(jù)長度
  510. * @warning None
  511. * @example
  512. **/
  513. int mqtt_msg_pingresp(char **data_ptr,char* buffer,int buffer_length)
  514. {
  515.         int length;
  516.         length = MQTT_MAX_FIXED_HEADER_SIZE;       
  517.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PINGRESP, 0, 0, 0);
  518. }

  520. /**
  521. * @brief   獲取發(fā)送給服務(wù)器的心跳包數(shù)據(jù)
  522. * @param   data_ptr 打包的數(shù)據(jù)首地址
  523. * @param   buffer   打包進的數(shù)組
  524. * @param   buffer_length 數(shù)組長度
  525. * @retval  數(shù)據(jù)長度
  526. * @warning None
  527. * @example
  528. **/
  529. int mqtt_msg_pingreq(char **data_ptr,char* buffer,int buffer_length)
  530. {
  531.         int length;
  532.         length = MQTT_MAX_FIXED_HEADER_SIZE;       
  533.   return fini_message(data_ptr,length, buffer, MQTT_MSG_TYPE_PINGREQ, 0, 0, 0);
  534. }


復制代碼



MQTT封包解包底層(C語言).zip

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作者: hsl32    時間: 2020-7-7 13:00
資料不錯，下來看看。如果來個教程就完美了。



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