File content as of revision 0:1170747a672f:

#include "mbed.h"
#include "WIZnetInterface.h"
#include "MQTTSocket.h"
#include "MQTTClient.h"

DigitalIn BTN(PC_13);
 //W5500接线 mosi,miso,sclk,cs,reset
WIZnetInterface wiz(PA_7,PA_6,PA_5,PB_6,PC_7);
//节点名称任取
#define NODE_NAME "n_12345"
 //接在同一子网下的设备MAC地址必须不同
uint8_t mac_addr[6]={0x50,0x51,0x50,0x00,0x00,0x01};

typedef MQTT::Client<MQTTSocket,Countdown> MClient;
void meta_report(MClient& client, const char* ns, const char* type, 
                    const char* payload = NULL, size_t payload_len = 0, 
                    bool retain = false, MQTT::QoS qos = MQTT::QOS1){
    char topic[64];
    sprintf(topic, "/%s/" NODE_NAME "/%s", ns, type);
    int ret = client.publish(topic, (void*)payload, payload_len, qos, retain);
    printf("client.publish()=%d\r\n",ret);
}
void messageArrived(MQTT::MessageData& md)
{
    MQTT::Message &message = md.message;
    char buf[64];
    int value, len = sizeof(buf)-1;
    if(message.payloadlen < len)
        len = message.payloadlen;
    memcpy(buf, message.payload, len);
    buf[len] = '\0';
    sscanf(buf, "%d", &value);
    printf("received %d\r\n", value);
}
 
int main() {
    int ret;
    wiz.init(mac_addr);
    wiz.connect();
    printf("IP: %s\r\n", wiz.getIPAddress());
    
    MQTTSocket sock;
    MClient client(sock);
    
    ret = sock.connect("tdxls-iot.xicp.net",1883);
    if(ret != 0){
        printf("failed to connect to TCP server\r\n");
        return 1;
    }
    printf("sock.connect()=%d\r\n",ret);
    
    ret = client.connect();
    if(ret != 0){
        printf("MQTT connect failed\r\n");
        return 1;
    }
    printf("client.connect()=%d\r\n",ret);
    
    const char* actuators = "switch,int\n";
    const char* sensors = "analog,mV\n";

    ret = client.subscribe("/control/" NODE_NAME "/switch", MQTT::QOS1, messageArrived);    
    printf("sock.subscribe()=%d\r\n",ret);

    //节点上线消息
    meta_report(client, "events","online");
    //报告所有可接受的控制指令
    meta_report(client, "capability","control", actuators, strlen(actuators), true);
    //报告所有的传感器
    meta_report(client, "capability","values", sensors, strlen(sensors), true);
    
    bool btn = 0;
    while(1){
        bool newBTN = BTN;
        if(newBTN != btn){
            char buf[16];
            int value = newBTN ? 3300 : 0;
            sprintf(buf, "%d mV", value);
            meta_report(client, "values","analog",buf,strlen(buf),true);
            btn = newBTN;
        }else{
            client.yield(100);
        }
    }
}