gprs模块用TCP实现MQTT协议（基于SIM900A）

mqtt部分：

int strlen(char *str)
{
    int len = 0;
    while (*str != '\0') {
        len++;
        str++;
    }
    return len;
}

// **********************************
// *                                *
// * 根据主机地址和端口号连接服务器 *
// *                                *
// **********************************


void tcp_connect(char *host,int port)
{
   uart_send_str("AT\r\n");
   uart_send_str("AT+CPIN? \r\n");
   seelp(500);
   uart_send_str("AT+CREG? \r\n");
   seelp(500);
   uart_send_str("AT+CGATT? \r\n");
   seelp(500);
   uart_send_str("AT+CSTT=\"CMNET\" \r\n");
   seelp(500);
   uart_send_str("AT+CIICR \r\n");
   seelp(1500);
   uart_send_str("AT+CIFSR \r\n");
   seelp(1000);
   uart_send_str("AT+CIPSTART=\"TCP\"\,\"23.106.139.167\"\,\"1883\" \r\n"); //连接TCP Server  8081 1883
}


// *************************
// *                       *
// *  构建MQTT连接包       *
// *                       *
// *************************

int baseIndex;
int mqtt_connect_message(unsigned char *mqtt_message,char *client_id,char *username,char *password)
{ 
    char i = 0;  
    char client_id_length = strlen(client_id);  
    int username_length = strlen(username);  
    int password_length = strlen(password);  
    int packetLen = 12 + 2 + client_id_length + 2 + username_length + 2 + password_length;  
      
    mqtt_message[0] = 16;                      // MQTT Message Type CONNECT  
    mqtt_message[1] = packetLen%256;  
    baseIndex = 2;  
    if( packetLen >127 ){//  
        mqtt_message[2] = 1;//packetLen/127;  
        baseIndex = 3;  
    }  
      
      
    mqtt_message[baseIndex] = 0;                       // Protocol Name Length MSB  
    mqtt_message[baseIndex+1] = 6;                       // Protocol Name Length LSB  
    mqtt_message[baseIndex+2] = 77;                      // ASCII Code for M  
    mqtt_message[baseIndex+3] = 81;                      // ASCII Code for Q  
    mqtt_message[baseIndex+4] = 73;                      // ASCII Code for I  
    mqtt_message[baseIndex+5] = 115;                     // ASCII Code for s  
    mqtt_message[baseIndex+6] = 100;                     // ASCII Code for d  
    mqtt_message[baseIndex+7] = 112;                     // ASCII Code for p  
    mqtt_message[baseIndex+8] = 3;                      // MQTT Protocol version = 3  
    mqtt_message[baseIndex+9] = 194;                   // conn flags  
    mqtt_message[baseIndex+10] = 0;                      // Keep-alive Time Length MSB  
    mqtt_message[baseIndex+11] = 60;                     // Keep-alive Time Length LSB  
      
    mqtt_message[baseIndex+12] = 0;                      // Client ID length MSB  
    mqtt_message[baseIndex+13] = client_id_length;       // Client ID length LSB  
      
    baseIndex += 14;  
    // Client ID  
    for(i = 0; i < client_id_length; i++){  
        mqtt_message[baseIndex + i] = client_id[i];  
    }  
      
    baseIndex = baseIndex+client_id_length;  
      
    //username  
    mqtt_message[baseIndex] = 0;                      //username length MSB  
    mqtt_message[baseIndex+1] = username_length;       //username length LSB  
    baseIndex = baseIndex+2;  
    for(i = 0; i < username_length ; i++){  
        mqtt_message[baseIndex + i] = username[i];  
    }  
      
    baseIndex = baseIndex + username_length;  
      
    //password  
    mqtt_message[baseIndex] = 0;                      //password length MSB  
    mqtt_message[baseIndex+1] = password_length;       //password length LSB  
    baseIndex = baseIndex + 2;  
    for(i = 0; i < password_length ; i++){  
        mqtt_message[baseIndex + i] = password[i];  
    }  
      
    baseIndex += password_length;  
  
    return baseIndex;  
}


int mqtt_publish_message(unsigned char *mqtt_message, char * topic, char * message) {  
      
    //mqtt_message = 0;  
      
    unsigned char i = 0;  
    unsigned char topic_length = strlen(topic);  
    unsigned char message_length = strlen(message);  
      
    mqtt_message[0] = 48;                                  // MQTT Message Type CONNECT  
    mqtt_message[1] = 2 + topic_length + message_length;   // Remaining length  
    mqtt_message[2] = 0;                                   // MQTT Message Type CONNECT  
    mqtt_message[3] = topic_length;                        // MQTT Message Type CONNECT  
      
    // Topic  
    for(i = 0; i < topic_length; i++){  
        mqtt_message[4 + i] = topic[i];  
    }  
      
    // Message  
    for(i = 0; i < message_length; i++){  
        mqtt_message[4 + topic_length + i] = message[i];  
    }  
      
    return 4 + topic_length + message_length;  
}  


int subindex = 0;
int mqtt_subscribe_message(unsigned char *mqtt_message,unsigned char *topic)  
{  
    unsigned char topic_len = strlen(topic);  
    mqtt_message[0] = 130;  
    mqtt_message[1] = topic_len+5;  
    mqtt_message[2] = 0;  
    mqtt_message[3] = 1;  
    mqtt_message[4] = 0;  
    mqtt_message[5] = topic_len;  

    for (subindex=0; subindex