UEC++编写实现MQTT协议

MQTT（Message Queuing Telemetry Transport）是一个轻量级的、基于发布/订阅模式的通讯协议，被广泛应用于物联网等领域。下面是一个使用UEC++编写实现MQTT协议的示例：

#include <iostream>
#include <string>
#include <cstring>
#include <map>
#include <vector>

using namespace std;

// 定义MQTT消息类型
enum MqttMessageType {
  CONNECT = 1,
  CONNACK,
  PUBLISH,
  PUBACK,
  PUBREC,
  PUBREL,
  PUBCOMP,
  SUBSCRIBE,
  SUBACK,
  UNSUBSCRIBE,
  UNSUBACK,
  PINGREQ,
  PINGRESP,
  DISCONNECT
};

// 定义MQTT连接状态
enum MqttConnectStatus {
  CONNECT_ACCEPTED = 0,
  CONNECT_REFUSED_PROTOCOL,
  CONNECT_REFUSED_ID,
  CONNECT_REFUSED_SERVER,
  CONNECT_REFUSED_USER,
  CONNECT_REFUSED_PWD
};

// 定义MQTT消息结构体
struct MqttMessage {
  MqttMessageType type;
  bool dup;
  int qos;
  bool retain;
  int length;
  string topic;
  string payload;
  int packet_id;
  map<string, string> properties;
};

// 定义MQTT连接结构体
struct MqttConnect {
  string protocol_name;
  int protocol_version;
  bool clean_session;
  bool will_flag;
  int will_qos;
  bool will_retain;
  string will_topic;
  string will_message;
  string client_id;
  string username;
  string password;
  map<string, string> properties;
};

// 定义MQTT客户端类
class MqttClient {
public:
  MqttClient(const string& broker_url, int broker_port);
  ~MqttClient();
  bool connect(const MqttConnect& connect);
  bool publish(const MqttMessage& message);
  bool subscribe(const vector<string>& topics);
  bool unsubscribe(const vector<string>& topics);
  void disconnect();
private:
  bool send_message(const MqttMessage& message);
  bool read_message(MqttMessage& message);
  string broker_url_;
  int broker_port_;
  int socket_fd_;
  int packet_id_;
};

// 构造函数
MqttClient::MqttClient(const string& broker_url, int broker_port)
  : broker_url_(broker_url), broker_port_(broker_port), socket_fd_(-1), packet_id_(1) {}

// 析构函数
MqttClient::~MqttClient() {
  disconnect();
}

// 连接到MQTT服务器
bool MqttClient::connect(const MqttConnect& connect) {
  // 建立TCP连接
  socket_fd_ = socket(AF_INET, SOCK_STREAM, 0);
  if (socket_fd_ < 0) {
    cerr << "Failed to create socket." << endl;
    return false;
  }
  struct sockaddr_in broker_addr;
  memset(&broker_addr, 0, sizeof(broker_addr));
  broker_addr.sin_family = AF_INET;
  broker_addr.sin_port = htons(broker_port_);
  broker_addr.sin_addr.s_addr = inet_addr(broker_url_.c_str());
  if (connect(socket_fd_, (struct sockaddr*)&broker_addr, sizeof(broker_addr)) < 0) {
    cerr << "Failed to connect to broker." << endl;
    return false;
  }
  // 发送CONNECT消息
  MqttMessage message;
  message.type = CONNECT;
  message.qos = 0;
  message.properties["protocol_name"] = connect.protocol_name;
  message.properties["protocol_version"] = to_string(connect.protocol_version);
  message.properties["clean_session"] = connect.clean_session ? "1" : "0";
  message.properties["client_id"] = connect.client_id;
  message.properties["will_flag"] = connect.will_flag ? "1" : "0";
  message.properties["will_qos"] = to_string(connect.will_qos);
  message.properties["will_retain"] = connect.will_retain ? "1" : "0";
  message.properties["will_topic"] = connect.will_topic;
  message.properties["will_message"] = connect.will_message;
  message.properties["username"] = connect.username;
  message.properties["password"] = connect.password;
  message.properties.insert(connect.properties.begin(), connect.properties.end());
  if (!send_message(message)) {
    cerr << "Failed to send CONNECT message." << endl;
    return false;
  }
  // 读取CONNACK消息
  MqttMessage connack;
  if (!read_message(connack) || connack.type != CONNACK) {
    cerr << "Failed to receive CONNACK message." << endl;
    return false;
  }
  if (connack.properties["connect_status"] != to_string(CONNECT_ACCEPTED)) {
    cerr << "Connect refused: " << connack.properties["connect_status"] << endl;
    return false;
  }
  return true;
}

// 发布MQTT消息
bool MqttClient::publish(const MqttMessage& message) {
  // 发送PUBLISH消息
  MqttMessage publish_msg = message;
  publish_msg.type = PUBLISH;
  publish_msg.dup = false;
  publish_msg.packet_id = packet_id_++;
  if (!send_message(publish_msg)) {
    cerr << "Failed to send PUBLISH message." << endl;
    return false;
  }
  // 读取PUBACK消息
  if (message.qos == 1) {
    MqttMessage puback;
    if (!read_message(puback) || puback.type != PUBACK || puback.packet_id != publish_msg.packet_id) {
      cerr << "Failed to receive PUBACK message." << endl;
      return false;
    }
  }
  return true;
}

// 订阅MQTT主题
bool MqttClient::subscribe(const vector<string>& topics) {
  // 构造SUBSCRIBE消息
  MqttMessage message;
  message.type = SUBSCRIBE;
  message.qos = 1;
  message.packet_id = packet_id_++;
  for (auto topic : topics) {
    message.properties["topic"] = topic;
    message.properties["qos"] = "1";
  }
  if (!send_message(message)) {
    cerr << "Failed to send SUBSCRIBE message." << endl;
    return false;
  }
  // 读取SUBACK消息
  MqttMessage suback;
  if (!read_message(suback) || suback.type != SUBACK || suback.packet_id != message.packet_id) {
    cerr << "Failed to receive SUBACK message." << endl;
    return false;
  }
  return true;
}

// 取消订阅MQTT主题
bool MqttClient::unsubscribe(const vector<string>& topics) {
  // 构造UNSUBSCRIBE消息
  MqttMessage message;
  message.type = UNSUBSCRIBE;
  message.qos = 1;
  message.packet_id = packet_id_++;
  for (auto topic : topics) {
    message.properties["topic"] = topic;
  }
  if (!send_message(message)) {
    cerr << "Failed to send UNSUBSCRIBE message." << endl;
    return false;
  }
  // 读取UNSUBACK消息
  MqttMessage unsuback;
  if (!read_message(unsuback) || unsuback.type != UNSUBACK || unsuback.packet_id != message.packet_id) {
    cerr << "Failed to receive UNSUBACK message." << endl;
    return false;
  }
  return true;
}

// 断开MQTT连接
void MqttClient::disconnect() {
  if (socket_fd_ >= 0) {
    MqttMessage message;
    message.type = DISCONNECT;
    send_message(message);
    close(socket_fd_);
    socket_fd_ = -1;
  }
}

// 发送MQTT消息
bool MqttClient::send_message(const MqttMessage& message) {
  // 构造消息头
  char header[5];
  int pos = 0;
  header[pos++] = (message.type << 4) | (message.dup << 3) | (message.qos << 1) | message.retain;
  do {
    uint8_t digit = message.length % 128;
    message.length /= 128;
    if (message.length > 0) {
      digit |= 0x80;
    }
    header[pos++] = digit;
  } while (message.length > 0);
  // 发送消息头
  if (write(socket_fd_, header, pos) != pos) {
    return false;
  }
  // 发送消息体
  if (write(socket_fd_, message.topic.c_str(), message.topic.length()) != message.topic.length() ||
      (message.qos > 0 && write(socket_fd_, &message.packet_id, sizeof(message.packet_id)) != sizeof(message.packet_id)) ||
      write(socket_fd_, message.payload.c_str(), message.payload.length()) != message.payload.length()) {
    return false;
  }
  return true;
}

// 读取MQTT消息
bool MqttClient::read_message(MqttMessage& message) {
  // 读取消息头
  char header[5];
  int pos = 0;
  while (pos < 2) {
    int ret = read(socket_fd_, header + pos, 2 - pos);
    if (ret <= 0) {
      return false;
    }
    pos += ret;
  }
  message.type = static_cast<MqttMessageType>((header[0] & 0xf0) >> 4);
  message.dup = (header[0] & 0x08) != 0;
  message.qos = (header[0] & 0x06) >> 1;
  message.retain = (header[0] & 0x01) != 0;
  message.length = 0;
  for (int i = 1; i < pos; ++i) {
    message.length = (message.length << 7) | (header[i] & 0x7f);
    if ((header[i] & 0x80) == 0) {
      break;
    }
  }
  // 读取消息体
  int payload_len = message.length;
  if (message.qos > 0) {
    payload_len -= sizeof(message.packet_id);
  }
  char* payload_buf = new char[payload_len];
  pos = 0;
  while (pos < payload_len) {
    int ret = read(socket_fd_, payload_buf + pos, payload_len - pos);
    if (ret <= 0) {
      delete[] payload_buf;
      return false;
    }
    pos += ret;
  }
  message.topic = string(payload_buf, payload_len);
  if (message.qos > 0) {
    memcpy(&message.packet_id, payload_buf + payload_len, sizeof(message.packet_id));
    message.payload = string(payload_buf + payload_len + sizeof(message.packet_id), message.length - payload_len - sizeof(message.packet_id));
  } else {
    message.payload = string(payload_buf + payload_len, message.length - payload_len);
  }
  delete[] payload_buf;
  return true;
}

int main() {
  MqttConnect connect;
  connect.protocol_name = "MQTT";
  connect.protocol_version = 4;
  connect.clean_session = true;
  connect.client_id = "test_client";
  MqttClient client("localhost", 1883);
  if (client.connect(connect)) {
    MqttMessage message;
    message.qos = 1;
    message.topic = "test_topic";
    message.payload = "hello world";
    client.publish(message);
    client.subscribe({"test_topic"});
    client.unsubscribe({"test_topic"});
    client.disconnect();
  }
  return 0;
}

这段代码实现了MQTT客户端的基本功能，包括连接到MQTT服务器、发布消息、订阅主题和取消订阅主题等。其中，send_message函数用于发送MQTT消息，read_message函数用于读取MQTT消息。MQTT消息的格式和消息头的解析方式参考MQTT协议规范。