上面的例程用ESP32的底层API来写

好的，以下是使用ESP32的底层API来实现发布该主题的例程：

#include <WiFi.h>
#include <PubSubClient.h>

// WiFi网络配置
const char* ssid = "YourSSID";
const char* password = "YourPassword";

// MQTT Broker配置
const char* mqtt_server = "mqtt.yourserver.com";
const int mqtt_port = 1883;
const char* mqtt_username = "YourUsername";
const char* mqtt_password = "YourPassword";

// 设备信息
const char* pid = "YourProductID";
const char* device_name = "YourDeviceName";

WiFiClient espClient;
PubSubClient client(espClient);

void setup_wifi() {
  delay(10);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
}

void connect_mqtt() {
  client.setServer(mqtt_server, mqtt_port);
  while (!client.connected()) {
    if (client.connect(device_name, mqtt_username, mqtt_password)) {
      Serial.println("MQTT connected");
    } else {
      delay(500);
    }
  }
}

void setup() {
  Serial.begin(9600);
  setup_wifi();
  client.setBufferSize(1024);
}

void loop() {
  if (!client.connected()) {
    connect_mqtt();
  }

  // 构造JSON数据
  String json = "{\"id\":\"123\",\"params\":{\"Temperature\":{\"value\":25.3,\"time\":1592345678},\"Humidity\":{\"value\":60.5,\"time\":1592345678}},\"method\":\"thing.event.property.post\"}";

  // 发布主题
  char topic[64];
  snprintf(topic, 64, "$sys/%s/%s/thing/property/post", pid, device_name);
  
  // 建立TCP连接
  IPAddress mqtt_ip;
  WiFi.hostByName(mqtt_server, mqtt_ip);
  int mqtt_port = 1883;
  int timeout = 5000;
  int max_retries = 5;
  for (int retries = 0; retries < max_retries; retries++) {
    if (espClient.connect(mqtt_ip, mqtt_port, timeout)) {
      break;
    } else {
      delay(1000);
    }
  }
  
  // 发送MQTT连接请求
  const char* mqtt_connect = "\x10\x12\x00\x04MQTT\x04\x02\x00\x0a\x00\x1e";
  espClient.write((uint8_t*)mqtt_connect, sizeof(mqtt_connect) - 1);
  
  // 等待MQTT连接确认
  uint8_t mqtt_recv[4];
  int mqtt_recv_len = 0;
  while (mqtt_recv_len < 4) {
    mqtt_recv_len += espClient.read(mqtt_recv + mqtt_recv_len, 4 - mqtt_recv_len);
  }
  
  // 发送MQTT发布消息
  int payload_len = json.length();
  uint8_t mqtt_publish[128];
  int mqtt_publish_len = 0;
  mqtt_publish[mqtt_publish_len++] = 0x30; // MQTT PUBLISH消息头
  mqtt_publish[mqtt_publish_len++] = 2 + strlen(topic) + 2 + payload_len; // MQTT PUBLISH消息长度
  mqtt_publish[mqtt_publish_len++] = 0x00; // MQTT PUBLISH消息主题长度
  mqtt_publish[mqtt_publish_len++] = strlen(topic); // MQTT PUBLISH消息主题长度
  memcpy(mqtt_publish + mqtt_publish_len, topic, strlen(topic)); // MQTT PUBLISH消息主题
  mqtt_publish_len += strlen(topic);
  mqtt_publish[mqtt_publish_len++] = 0x00; // MQTT PUBLISH消息ID
  mqtt_publish[mqtt_publish_len++] = 0x01; // MQTT PUBLISH消息ID
  memcpy(mqtt_publish + mqtt_publish_len, json.c_str(), payload_len); // MQTT PUBLISH消息负载
  mqtt_publish_len += payload_len;
  espClient.write(mqtt_publish, mqtt_publish_len);
  
  // 断开TCP连接
  espClient.stop();
  
  delay(3000);
}

上述例程中，使用`WiFi.hostByName()`函数获取MQTT Broker的IP地址，并使用ESP32底层API发送MQTT连接请求和MQTT发布消息。根据MQTT协议，需要先发送MQTT连接请求，等待MQTT连接确认后再发送MQTT发布消息。在发送MQTT发布消息时，需要构造MQTT PUBLISH消息的消息头和消息体，并使用`espClient.write()`函数发送消息。

请注意，上述例程仅提供参考。实际应用中，需要根据具体需求进行修改和优化。