ESA2GJK1DH1K基础篇: 来吧! 彻底了解一下MQTT

/**
* @brief  连接服务器的打包函数
* @param  
* @retval 
* @example 
**/
int ConnectMqtt(char *ClientID,char *Username,char *Password)
{
    int ClientIDLen = strlen(ClientID);
    int UsernameLen    = strlen(Username);
    int PasswordLen = strlen(Password);
    int DataLen = 0;
    int Index = 2;
    int i = 0;
    DataLen = 12 + 2+2+ClientIDLen+UsernameLen+PasswordLen;
    MqttSendData[0] = 0x10;                //MQTT Message Type CONNECT
    MqttSendData[1] = DataLen;    //剩余长度(不包括固定头部)
    MqttSendData[Index++] = 0;        // Protocol Name Length MSB    
    MqttSendData[Index++] = 4;        // Protocol Name Length LSB    
    MqttSendData[Index++] = 'M';        // ASCII Code for M    
    MqttSendData[Index++] = 'Q';        // ASCII Code for Q    
    MqttSendData[Index++] = 'T';        // ASCII Code for T    
    MqttSendData[Index++] = 'T';        // ASCII Code for T    
    MqttSendData[Index++] = 4;        // MQTT Protocol version = 4    
    MqttSendData[Index++] = 0xc2;        // conn flags 
    MqttSendData[Index++] = 0;        // Keep-alive Time Length MSB    
    MqttSendData[Index++] = 60;        // Keep-alive Time Length LSB  60S心跳包  
    MqttSendData[Index++] = (0xff00&ClientIDLen)>>8;// Client ID length MSB    
    MqttSendData[Index++] = 0xff&ClientIDLen;    // Client ID length LSB  

    for(i = 0; i < ClientIDLen; i++)
    {
        MqttSendData[Index + i] = ClientID[i];          
    }
    Index = Index + ClientIDLen;
    
    if(UsernameLen > 0)
    {   
        MqttSendData[Index++] = (0xff00&UsernameLen)>>8;//username length MSB    
        MqttSendData[Index++] = 0xff&UsernameLen;    //username length LSB    
        for(i = 0; i < UsernameLen ; i++)
        {
            MqttSendData[Index + i] = Username[i];    
        }
        Index = Index + UsernameLen;
    }
    
    if(PasswordLen > 0)
    {    
        MqttSendData[Index++] = (0xff00&PasswordLen)>>8;//password length MSB    
        MqttSendData[Index++] = 0xff&PasswordLen;    //password length LSB    
        for(i = 0; i < PasswordLen ; i++)
        {
            MqttSendData[Index + i] = Password[i];    
        }
        Index = Index + PasswordLen; 
    }    
    return Index;
}

/**
* @brief  MQTT订阅/取消订阅数据打包函数
* @param  SendData 
* @param  topic                主题 
* @param  qos         消息等级 
* @param  whether     订阅/取消订阅请求包
* @retval 
* @example 
**/
int MqttSubscribeTopic(char *topic,u8 qos,u8 whether)
{    
    int topiclen = strlen(topic);
    int i=0,index = 0;
  
    if(whether)
        MqttSendData[index++] = 0x82;                        //0x82 //消息类型和标志 SUBSCRIBE 订阅
    else
        MqttSendData[index++] = 0xA2;                        //0xA2 取消订阅
    MqttSendData[index++] = topiclen + 5;                //剩余长度(不包括固定头部)
    MqttSendData[index++] = 0;                          //消息标识符,高位
    MqttSendData[index++] = 0x01;                    //消息标识符,低位
    MqttSendData[index++] = (0xff00&topiclen)>>8;    //主题长度(高位在前,低位在后)
    MqttSendData[index++] = 0xff&topiclen;              //主题长度 
    
    for (i = 0;i < topiclen; i++)
    {
        MqttSendData[index + i] = topic[i];
    }
    index = index + topiclen;
    
    if(whether)
    {
        MqttSendData[index] = qos;//QoS级别
        index++;
    }
    return index;
}

/**
* @brief  MQTT发布数据打包函数
* @param  mqtt_message 
* @param  topic                主题 
* @param  qos         消息等级 
* @retval 
* @example 
**/
int MqttPublishData(char * topic, char * message, u8 qos)
{  
    int topic_length = strlen(topic);    
    int message_length = strlen(message);  
    int i,index=0;    
    static u16 id=0;
    
    MqttSendData[index++] = 0x30;    // MQTT Message Type PUBLISH  

  
    if(qos)
        MqttSendData[index++] = 2 + topic_length + 2 + message_length;//数据长度
    else
        MqttSendData[index++] = 2 + topic_length + message_length;   // Remaining length  

  
    MqttSendData[index++] = (0xff00&topic_length)>>8;//主题长度
    MqttSendData[index++] = 0xff&topic_length;
         
    for(i = 0; i < topic_length; i++)
    {
        MqttSendData[index + i] = topic[i];//拷贝主题
    }
    index += topic_length;
        
    if(qos)
    {
        MqttSendData[index++] = (0xff00&id)>>8;
        MqttSendData[index++] = 0xff&id;
        id++;
    }
  
    for(i = 0; i < message_length; i++)
    {
        MqttSendData[index + i] = message[i];//拷贝数据
    }
    index += message_length;
        
    return index;
}