Eclipse Paho：MQTT Client C的使用

https://www.eclipse.org/paho/downloads.php

eclipse/paho.mqtt.c庫（使用v1.3.0）的下載下傳位址是：

https://github.com/eclipse/paho.mqtt.c/tree/v1.3.0

1、paho.mqtt.c-1.3.0\CMakeLists.txt，使能PAHO_BUILD_STATIC 和PAHO_BUILD_SAMPLES

## build options

SET(PAHO_WITH_SSL FALSE CACHE BOOL "Flag that defines whether to build ssl-enabled binaries too. ")

SET(PAHO_BUILD_STATIC TRUE CACHE BOOL "Build static library") #firecat modify

SET(PAHO_BUILD_DOCUMENTATION FALSE CACHE BOOL "Create and install the HTML based API documentation (requires Doxygen)")

SET(PAHO_BUILD_SAMPLES TRUE CACHE BOOL "Build sample programs") #firecat modify

SET(PAHO_BUILD_DEB_PACKAGE FALSE CACHE BOOL "Build debian package")

SET(PAHO_ENABLE_TESTING TRUE CACHE BOOL "Build tests and run")

SET(PAHO_ENABLE_CPACK TRUE CACHE BOOL "Enable CPack")

2、paho.mqtt.c-1.3.0\src\samples\CMakeLists.txt

#*******************************************************************************
#  Copyright (c) 2015, 2017 logi.cals GmbH and others
#
#  All rights reserved. This program and the accompanying materials
#  are made available under the terms of the Eclipse Public License v1.0
#  and Eclipse Distribution License v1.0 which accompany this distribution.
#
#  The Eclipse Public License is available at
#     http://www.eclipse.org/legal/epl-v10.html
#  and the Eclipse Distribution License is available at
#    http://www.eclipse.org/org/documents/edl-v10.php.
#
#  Contributors:
#     Rainer Poisel - initial version
#     Ian Craggs - update sample names
#*******************************************************************************/
 
# Note: on OS X you should install XCode and the associated command-line tools
 
## compilation/linkage settings
INCLUDE_DIRECTORIES(
    .
    ${CMAKE_SOURCE_DIR}/src
    ${CMAKE_BINARY_DIR}
    )
 
IF (WIN32)
    ADD_DEFINITIONS(/DCMAKE_BUILD /D_CRT_SECURE_NO_DEPRECATE)
ENDIF()
 
# sample files c
#ADD_EXECUTABLE(paho_c_pub paho_c_pub.c pubsub_opts.c) #firecat
#ADD_EXECUTABLE(paho_c_sub paho_c_sub.c pubsub_opts.c)
#ADD_EXECUTABLE(paho_cs_pub paho_cs_pub.c pubsub_opts.c)
#ADD_EXECUTABLE(paho_cs_sub paho_cs_sub.c pubsub_opts.c)
 
#TARGET_LINK_LIBRARIES(paho_c_pub paho-mqtt3as)
#TARGET_LINK_LIBRARIES(paho_c_sub paho-mqtt3as)
#TARGET_LINK_LIBRARIES(paho_cs_pub paho-mqtt3cs)
#TARGET_LINK_LIBRARIES(paho_cs_sub paho-mqtt3cs)
 
ADD_EXECUTABLE(MQTTAsync_subscribe MQTTAsync_subscribe.c)
ADD_EXECUTABLE(MQTTAsync_publish MQTTAsync_publish.c)
ADD_EXECUTABLE(MQTTClient_subscribe MQTTClient_subscribe.c)
ADD_EXECUTABLE(MQTTClient_publish MQTTClient_publish.c)
ADD_EXECUTABLE(MQTTClient_publish_async MQTTClient_publish_async.c)
 
TARGET_LINK_LIBRARIES(MQTTAsync_subscribe paho-mqtt3a)
TARGET_LINK_LIBRARIES(MQTTAsync_publish paho-mqtt3a)
TARGET_LINK_LIBRARIES(MQTTClient_subscribe paho-mqtt3c)
TARGET_LINK_LIBRARIES(MQTTClient_publish paho-mqtt3c)
TARGET_LINK_LIBRARIES(MQTTClient_publish_async paho-mqtt3c)
 
#INSTALL(TARGETS paho_c_sub #firecat
#                paho_c_pub
#                paho_cs_sub
#                paho_cs_pub
#                MQTTAsync_subscribe
#                MQTTAsync_publish
#                MQTTClient_subscribe
#                MQTTClient_publish
#                MQTTClient_publish_async
 
#    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
#    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})

      

3、使用cmake release編譯，生成以下的動态庫和靜态庫檔案：

The Paho C client comprises four shared libraries:

libmqttv3a.so - asynchronous

libmqttv3as.so - asynchronous with SSL

libmqttv3c.so - "classic" / synchronous

libmqttv3cs.so - "classic" / synchronous with SSL

Optionally, using the CMake build, you can build static versions of those libraries.

libpaho-mqtt3a.so

libpaho-mqtt3a.so.1

libpaho-mqtt3a.so.1.3.0

libpaho-mqtt3a-static.a

libpaho-mqtt3c.so

libpaho-mqtt3c.so.1

libpaho-mqtt3c.so.1.3.0

libpaho-mqtt3c-static.a

把它們一起拷貝到路徑：/usr/local/lib/

此時需要在/etc/ld.so.conf中加入庫檔案所在的目錄:/usr/local/lib/

然後在終端執行指令，使之生效:

[root@localhost etc]# ldconfig

注意，/usr/local/lib/每次有庫檔案更新，都需要終端重新運作一次ldconfig這條指令。

4、使用案例

/*******************************************************************************
 * Copyright (c) 2012, 2017 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *   http://www.eclipse.org/legal/epl-v10.html
 * 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 "MQTTClient.h"
 
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <sys/resource.h>    /*setrlimit */
#include <fcntl.h> //daemonize
 
#define ADDRESS     "tcp://192.168.83.128:1883"
#define CLIENTID    "id001"
#define TOPIC       "keepalived"
#define PAYLOAD     "Hello World!"
#define QOS         0
#define USERNAME    "inTerm"
#define PASSWORD    "in2018"
 
static int run = 1;
 
volatile MQTTClient_deliveryToken deliveredtoken;
 
void daemonize(void) { //come from /redis/server.c/daemonize()
    int fd;
 
    if (fork() != 0) exit(0); /* parent exits */
    setsid(); /* create a new session */
 
    /* Every output goes to /dev/null. If Redis is daemonized but
     * the 'logfile' is set to 'stdout' in the configuration file
     * it will not log at all. */
    if ((fd = open("/dev/null", O_RDWR, 0)) != -1) {
        dup2(fd, STDIN_FILENO);
        dup2(fd, STDOUT_FILENO);
        dup2(fd, STDERR_FILENO);
        if (fd > STDERR_FILENO) close(fd);
    }
}
 
void signal_exit_func(int signo)
{
    run = 0;
    printf("exit signo is %d\n", signo);
}
 
void signal_exit_handler()
{
    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = signal_exit_func;
    sigaction(SIGINT, &sa, NULL);//當按下ctrl+c時，它的效果就是發送SIGINT信号
    sigaction(SIGTERM, &sa, NULL);//kill pid
    sigaction(SIGQUIT, &sa, NULL);//ctrl+\代表退出SIGQUIT
 
    //SIGSTOP和SIGKILL信号是不可捕獲的,是以下面兩句話寫了等于沒有寫
    sigaction(SIGKILL, &sa, NULL);//kill -9 pid
    sigaction(SIGSTOP, &sa, NULL);//ctrl+z代表停止
 
    //#define    SIGTERM        15
    //#define    SIGKILL        9
    //kill和kill -9，兩個指令在linux中都有殺死程序的效果，然而兩指令的執行過程卻大有不同，在程式中如果用錯了，可能會造成莫名其妙的現象。
    //執行kill pid指令，系統會發送一個SIGTERM信号給對應的程式。
    //執行kill -9 pid指令，系統給對應程式發送的信号是SIGKILL，即exit。exit信号不會被系統阻塞，是以kill -9能順利殺掉程序。
}
 
void delivered(void *context, MQTTClient_deliveryToken dt)
{
    printf("Message with token value %d delivery confirmed\n", dt);
    deliveredtoken = dt;
}
 
int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
    int i;
    char* payloadptr;
 
    printf("Message arrived\n");
    printf("     topic: %s\n", topicName);
    printf("   message: ");
 
    payloadptr = message->payload;
    for(i=0; i<message->payloadlen; i++)
    {
        putchar(*payloadptr++);
    }
    putchar('\n');
    MQTTClient_freeMessage(&message);
    MQTTClient_free(topicName);
    return 1;
}
 
void connlost(void *context, char *cause)//心跳時間達到，如果沒有收到伺服器的reponse，用戶端的socket會自動關閉
{
    printf("\nConnection lost\n");
    printf("     cause: %s\n", cause);
    exit(EXIT_FAILURE); //firecat
}
 
//./MQTTClient_firecat "tcp://192.168.83.128:1883" "id001"
int main(int argc, char* argv[])
{
    int background = 1;//firecat add
    if (background)
    {
        daemonize();
    }
 
    //signal(SIGHUP, SIG_IGN); //開啟的話，就捕獲不到終端視窗關閉的信号了。即視窗關閉，程序仍然進行。
    signal(SIGPIPE, SIG_IGN);
 
    char *serverURI;
    char *clientId;
    if (argc == 1)
    {
        serverURI = ADDRESS;
        clientId = CLIENTID;
    }
    else if (argc == 3)
    {
        serverURI = argv[1];
        clientId = argv[2];
    }
    else
    {
        printf("argc error\n");
        exit(EXIT_FAILURE);
    }
 
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    int rc;
    int ch;
 
    MQTTClient_create(&client, serverURI, clientId,
                      MQTTCLIENT_PERSISTENCE_NONE, NULL);
    conn_opts.keepAliveInterval = 60;
    conn_opts.cleansession = 1;
    conn_opts.MQTTVersion = MQTTVERSION_3_1_1;
    conn_opts.username = USERNAME;
    conn_opts.password = PASSWORD;
 
    MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);
 
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }
    printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
           "Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
    MQTTClient_subscribe(client, TOPIC, QOS);
 
    if (background)
    {
        while (run)
        {
            sleep(1);
        }
    }
    else
    {
        do
        {
            ch = getchar();
        } while(ch!='Q' && ch != 'q');
    }
 
    MQTTClient_unsubscribe(client, TOPIC);
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}