STM串口转tcp实现Mqtt客户端

由于现存版本的mqtt代码都是针对嵌入式linux系统的，直接copy过来是不能使用的，必须对其中的动态数组定义顺序等问题进行处理，本例程定义topic最大长度为64，message最大长度为1024。本例程包含3个文件分别是emqtt.h

#ifndef __LIBEMQTT_H__
#define __LIBEMQTT_H__

#include <stdint.h>
#include <string.h>
#ifndef MQTT_CONF_USERNAME_LENGTH
    #define MQTT_CONF_USERNAME_LENGTH 13 // Recommended by MQTT Specification (12 + '\0')
#endif

#ifndef MQTT_CONF_PASSWORD_LENGTH
    #define MQTT_CONF_PASSWORD_LENGTH 13 // Recommended by MQTT Specification (12 + '\0')
#endif

#define MQTT_MSG_CONNECT       1<<4
#define MQTT_MSG_CONNACK       2<<4
#define MQTT_MSG_PUBLISH       3<<4
#define MQTT_MSG_PUBACK        4<<4
#define MQTT_MSG_PUBREC        5<<4
#define MQTT_MSG_PUBREL        6<<4
#define MQTT_MSG_PUBCOMP       7<<4
#define MQTT_MSG_SUBSCRIBE     8<<4
#define MQTT_MSG_SUBACK        9<<4
#define MQTT_MSG_UNSUBSCRIBE  10<<4
#define MQTT_MSG_UNSUBACK     11<<4
#define MQTT_MSG_PINGREQ      12<<4
#define MQTT_MSG_PINGRESP     13<<4
#define MQTT_MSG_DISCONNECT   14<<4


#define MQTTParseMessageType(buffer) ( *buffer & 0xF0 )
#define MQTTParseMessageDuplicate(buffer) ( *buffer & 0x08 )
#define MQTTParseMessageQos(buffer) ( (*buffer & 0x06) >> 1 )
#define MQTTParseMessageRetain(buffer) ( *buffer & 0x01 )




typedef struct {
    // Connection info
    char clientid[50];
    // Auth fields
    char username[MQTT_CONF_USERNAME_LENGTH];
    char password[MQTT_CONF_PASSWORD_LENGTH];
    // Will topic
    uint8_t will_retain;
    uint8_t will_qos;
    uint8_t clean_session;
    // Management fields
    uint16_t seq;
    uint16_t alive;
} mqtt_broker_handle_t;



uint8_t mqtt_num_rem_len_bytes(const uint8_t* buf);
uint16_t mqtt_parse_rem_len(const uint8_t* buf);
uint16_t mqtt_parse_msg_id(const uint8_t* buf);
uint16_t mqtt_parse_pub_topic(const uint8_t* buf, uint8_t* topic);
uint16_t mqtt_parse_pub_topic_ptr(const uint8_t* buf, const uint8_t** topic_ptr);
uint16_t mqtt_parse_publish_msg(const uint8_t* buf, uint8_t* msg);
uint16_t mqtt_parse_pub_msg_ptr(const uint8_t* buf, const uint8_t** msg_ptr);
/** Initialize the information to connect to the broker.
 * @param broker Data structure that contains the connection information with the broker.
 * @param clientid A string that identifies the client id.
 *
 * @note Only has effect before to call mqtt_connect
 */
void mqtt_init(mqtt_broker_handle_t* broker, const char* clientid);
/** Enable the authentication to connect to the broker.
 * @param broker Data structure that contains the connection information with the broker.
 * @param username A string that contains the username.
 * @param password A string that contains the password.
 *
 * @note Only has effect before to call mqtt_connect
 */
void mqtt_init_auth(mqtt_broker_handle_t* broker, const char* username, const char* password);
/** Set the keep alive timer.
 * @param broker Data structure that contains the connection information with the broker.
 * @param alive Keep aliver timer value (in seconds).
 *
 * @note Only has effect before to call mqtt_connect
 */
void mqtt_set_alive(mqtt_broker_handle_t* broker, uint16_t alive);
/** Connect to the broker.
 * @param broker Data structure that contains the connection information with the broker.
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_connect(mqtt_broker_handle_t* broker);
/** Disconnect to the broker.
 * @param broker Data structure that contains the connection information with the broker.
 *
 * @note The socket must also be closed.
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_disconnect(mqtt_broker_handle_t* broker);
/** Publish a message on a topic. This message will be published with 0 Qos level.
 * @param broker Data structure that contains the connection information with the broker.
 * @param topic The topic name.
 * @param msg The message.
 * @param retain Enable or disable the Retain flag (values: 0 or 1).
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_publish(mqtt_broker_handle_t* broker, const char* topic, const char* msg, uint8_t retain);
/** Publish a message on a topic.
 * @param broker Data structure that contains the connection information with the broker.
 * @param topic The topic name.
 * @param msg The message.
 * @param retain Enable or disable the Retain flag (values: 0 or 1).
 * @param qos Quality of Service (values: 0, 1 or 2)
 * @param message_id Variable that will store the Message ID, if the pointer is not NULL.
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_publish_with_qos(mqtt_broker_handle_t* broker, const char* topic, const char* msg, uint8_t retain, uint8_t qos, uint16_t* message_id);
/** Send a PUBREL message. It's used for PUBLISH message with 2 QoS level.
 * @param broker Data structure that contains the connection information with the broker.
 * @param message_id Message ID
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_pubrel(mqtt_broker_handle_t* broker, uint16_t message_id);
/** Subscribe to a topic.
 * @param broker Data structure that contains the connection information with the broker.
 * @param topic The topic name.
 * @param message_id Variable that will store the Message ID, if the pointer is not NULL.
 *
 * @retval  1 On success.
 * @retval  0 On connection error.
 * @retval -1 On IO error.
 */
int mqtt_subscribe(mqtt_broker_handle_t* broker, const char* topic, uint16_t* message_id);
/** Unsubscribe from a topic.
 * @param broker Data structure that contains the connection information with the broker.
 * @param topic The topic name.
 * @param message_id Variable that will store the Message ID, if t