mqtt的C库 paho.mqtt.c 自动重联配置

1、只有异步接口 MQTTAsync中才有，使用起来不是特别方便

2、需要配置参数

 　conn_opts.automaticReconnect = 1;
    conn_opts.minRetryInterval = 2; 
    conn_opts.maxRetryInterval = 365*24*60*60;

3、需要配置函数

if ((rc = MQTTAsync_setConnected(client, client, onReconnected)) != MQTTASYNC_SUCCESS)
 {
  printf("Failed to MQTTAsync_setConnected, return code %d ", rc);
  rc = EXIT_FAILURE;
  goto destroy_exit;
 }

4、连接成功后的回调实现

void onReconnected(void* context, char* cause)
{
 MQTTAsync client = (MQTTAsync)context;
 MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
 int rc;

 printf("Successful reconnection ");

 printf("Subscribing to topic %s for client %s using QoS%d "
           "Press Q<Enter> to quit ", TOPIC, CLIENTID, QOS);
 opts.onSuccess = onSubscribe;
 opts.onFailure = onSubscribeFailure;
 opts.context = client;
 if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
 {
  printf("Failed to start subscribe, return code %d ", rc);
  finished = 1;
 }
 
}

/*******************************************************************************
 * Copyright (c) 2012, 2020 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * and Eclipse Distribution License v1.0 which accompany this distribution. 
 *
 * The Eclipse Public License is available at 
 *   https://www.eclipse.org/legal/epl-2.0/
 * and the Eclipse Distribution License is available at 
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Ian Craggs - initial contribution
 *******************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTAsync.h"

#if !defined(_WIN32)
#include <unistd.h>
#else
#include <windows.h>
#endif

#if defined(_WRS_KERNEL)
#include <OsWrapper.h>
#endif

#define ADDRESS     "tcp://mqtt.eclipse.org:1883"
#define CLIENTID    "ExampleClientSub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int disc_finished = 0;
int subscribed = 0;
int finished = 0;

void connlost(void *context, char *cause)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	int rc;

	printf("
Connection lost
");
	if (cause)
		printf("     cause: %s
", cause);

	printf("Reconnecting
");
	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d
", rc);
		finished = 1;
	}
}


int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message)
{
    printf("Message arrived
");
    printf("     topic: %s
", topicName);
    printf("   message: %.*s
", message->payloadlen, (char*)message->payload);
    MQTTAsync_freeMessage(&message);
    MQTTAsync_free(topicName);
    return 1;
}

void onDisconnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Disconnect failed, rc %d
", response->code);
	disc_finished = 1;
}

void onDisconnect(void* context, MQTTAsync_successData* response)
{
	printf("Successful disconnection
");
	disc_finished = 1;
}

void onSubscribe(void* context, MQTTAsync_successData* response)
{
	printf("Subscribe succeeded
");
	subscribed = 1;
}

void onSubscribeFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Subscribe failed, rc %d
", response->code);
	finished = 1;
}


void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
	printf("Connect failed, rc %d
", response->code);
	finished = 1;
}


void onConnect(void* context, MQTTAsync_successData* response)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	int rc;

	printf("Successful connection
");

	printf("Subscribing to topic %s
for client %s using QoS%d

"
           "Press Q<Enter> to quit

", TOPIC, CLIENTID, QOS);
	opts.onSuccess = onSubscribe;
	opts.onFailure = onSubscribeFailure;
	opts.context = client;
	if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start subscribe, return code %d
", rc);
		finished = 1;
	}
}

void onReconnected(void* context, char* cause)
{
	MQTTAsync client = (MQTTAsync)context;
	MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	int rc;

	printf("Successful reconnection
");

	printf("Subscribing to topic %s
for client %s using QoS%d

"
           "Press Q<Enter> to quit

", TOPIC, CLIENTID, QOS);
	opts.onSuccess = onSubscribe;
	opts.onFailure = onSubscribeFailure;
	opts.context = client;
	if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start subscribe, return code %d
", rc);
		finished = 1;
	}
	
}

int main(int argc, char* argv[])
{
	MQTTAsync client;
	MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
	MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
	int rc;
	int ch;

	if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL))
			!= MQTTASYNC_SUCCESS)
	{
		printf("Failed to create client, return code %d
", rc);
		rc = EXIT_FAILURE;
		goto exit;
	}

	if ((rc = MQTTAsync_setCallbacks(client, client, connlost, msgarrvd, NULL)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to set callbacks, return code %d
", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}
	if ((rc = MQTTAsync_setConnected(client, client, onReconnected)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to MQTTAsync_setConnected, return code %d
", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}
	
	conn_opts.keepAliveInterval = 20;
	conn_opts.cleansession = 1;
	conn_opts.onSuccess = onConnect;
	conn_opts.onFailure = onConnectFailure;
	conn_opts.context = client;
	conn_opts.automaticReconnect = 1;
	conn_opts.minRetryInterval = 2; //seconds
    conn_opts.maxRetryInterval = 365*24*60*60;
	if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start connect, return code %d
", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}

	while (!subscribed && !finished)
		#if defined(_WIN32)
			Sleep(100);
		#else
			usleep(10000L);
		#endif

	if (finished)
		goto exit;

	do 
	{
		ch = getchar();
	} while (ch!='Q' && ch != 'q');

	disc_opts.onSuccess = onDisconnect;
	disc_opts.onFailure = onDisconnectFailure;
	if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS)
	{
		printf("Failed to start disconnect, return code %d
", rc);
		rc = EXIT_FAILURE;
		goto destroy_exit;
	}
 	while (!disc_finished)
 	{
		#if defined(_WIN32)
			Sleep(100);
		#else
			usleep(10000L);
		#endif
 	}

destroy_exit:
	MQTTAsync_destroy(&client);
exit:
 	return rc;
}