【MQTT】paho.mqtt.cpp 库的介绍、下载、交叉编译、MQTT客户端例子源码

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⏰发布时间⏰：2024-05-13 18:06:13

本文未经允许，不得转发！！！

🎄一、概述
🎄二、paho.mqtt.cpp 库介绍
🎄三、paho.mqtt.cpp 库下载、交叉编译
- ✨3.1 openssl 的下载、交叉编译
- ✨3.2 paho.mqtt.c 交叉编译
- ✨3.3 paho.mqtt.cpp 交叉编译
🎄四、paho.mqtt.cpp库写一个MQTT客户端
- ✨4.1 订阅——async_subscribe.cpp
- ✨4.2 发布——async_publish.cpp
🎄五、总结

在这里插入图片描述

🎄一、概述

前面文章【MQTT】mosquitto 的 “下载、交叉编译、使用” 详细教程，手把手搭建一个MQTT Broker ，介绍了怎样搭建一个MQTT Broker(代理)。MQTT Broker(代理)的搭建很重要，一般很少自己开发一个MQTT Broker，而是搭建好一个开源的MQTT Broker(代理)，然后其他的设备或机器都作为MQTT客户端，让MQTT Broker来转发消息。

关于MQTT协议的，作为编程人员更多的是开发MQTT的客户端，本文介绍的paho.mqtt.cpp就是开发MQTT客户端常用的开源库之一。paho.mqtt.cpp 是 Eclipse Paho 项目的一个开源库。

Eclipse Paho项目提供了以各种编程语言实现的MQTT和MQTT-SN的开源库（主要是客户端）。下面是这个项目的MQTT客户端开源库，想要了解更多Eclipse Paho项目的资料，可以到其官网：https://eclipse.dev/paho/

在这里插入图片描述

🎄二、paho.mqtt.cpp 库介绍

之前介绍的 paho.mqtt.c 库可以在C语言编程中使用，而 paho.mqtt.cpp 库是在C++编程中使用的，它可以使标准C++应用程序（C++11及更高版本）能够连接到 MQTT Broker(代理)、发布消息、订阅主题以及从MQTT Broker(代理)接收消息。

paho.mqtt.cpp 库有如下功能：

Support for MQTT v3.1, v3.1.1, and v5.
Network Transports:
- Standard TCP
- Secure sockets with SSL/TLS
- WebSockets
  - Secure and insecure
  - Proxy support
Message persistence
- User configurable
- Built-in File persistence
- User-defined key/value persistence easy to implement
Automatic Reconnect
Offline Buffering
High Availability
Blocking and non-blocking APIs
Modern C++ interface (C++11 and beyond)

最后，这个库需要依赖于 paho.mqtt.c，所以编译这个库之前需要先编译 paho.mqtt.c 库。

在这里插入图片描述

🎄三、paho.mqtt.cpp 库下载、交叉编译

paho.mqtt.cpp 库需要两个依赖库：openssl、paho.mqtt.c，下面依次介绍怎么编译 openssl、paho.mqtt.c、paho.mqtt.cpp。

✨3.1 openssl 的下载、交叉编译

本文下载的是 openssl-OpenSSL_1_1_1g.tar.gz，
下载地址：https://codeload.github.com/openssl/openssl/tar.gz/refs/tags/OpenSSL_1_1_1g
为什么使用这么旧的版本，因为这个我之前编译过，而且使用没问题。

编译步骤：

1、解压缩
```
tar zxf openssl-OpenSSL_1_1_1g.tar.gz
```
2、进入目录，并配置输出目录和交叉编译器, (linux-generic32表示是32位操作系统,个别文章加了这个选项就不用去掉 -m64，我这里行不通)
```
cd openssl-OpenSSL_1_1_1g/
./config no-asm shared no-async --prefix=`pwd`/ssl_result  --cross-compile-prefix=aarch64-mix210-linux-
```
3、执行下面命令，删除Makefile文件的 -m64，
```
sed -i 's/-m64//' Makefile
```
执行后，可以避免出现这个编译错误：aarch64-mix210-linux-gcc: error: unrecognized command line option '-m64'
4、编译、安装
```
make && make install
```

成功编译后，在openssl-OpenSSL_1_1_1g/目录会生成一个ssl_result目录，可以看到里面生成的库：
在这里插入图片描述

✨3.2 paho.mqtt.c 交叉编译

本文下载的是paho.mqtt.c-1.3.13.tar.gz，下载地址：https://github.com/eclipse/paho.mqtt.c/archive/refs/tags/v1.3.13.tar.gz

编译步骤：

1、解压缩，创建要安装目录paho.mqtt.c_result

tar zxf paho.mqtt.c-1.3.13.tar.gz

mkdir paho.mqtt.c_result/bin -p
mkdir paho.mqtt.c_result/include -p
mkdir paho.mqtt.c_result/lib -p
mkdir paho.mqtt.c_result/share/man/man1 -p

2、进入目录，交叉编译
```
cd paho.mqtt.c-1.3.13/
make  CC=aarch64-mix210-linux-gcc CFLAGS:="-I `pwd`/../ssl_result/include" LDFLAGS:="-L `pwd`/../ssl_result/lib"
```
CFLAGS:=“-I `pwd`/…/ssl_result/include”：指定前面编译的 openssl 的头文件；
LDFLAGS:=“-L `pwd`/…/ssl_result/lib”：指定前面编译的 openssl 的库文件路径；
3、make install，安装编译结果
```
make install prefix=`pwd`/../paho.mqtt.c_result 
```
prefix=`pwd`/…/paho.mqtt.c_result ：指定安装目录路径；

编译完成后，会生成目录，内容如下：
在这里插入图片描述

✨3.3 paho.mqtt.cpp 交叉编译

本文下载的是paho.mqtt.cpp-1.3.2.tar.gz，下载地址：https://github.com/eclipse/paho.mqtt.cpp/archive/refs/tags/v1.3.2.tar.gz

如果你下载的版本跟我的一样或者更新，可以尝试使用下面的脚本进行编译。

编译步骤：

1、保存下面脚本为 paho.mqtt.cpp_install，

#! /bin/sh

# 指定编译结果目录
RESULT_DIR=$(pwd)/result_dir
RESULT_SSL=${RESULT_DIR}/ssl_result
RESULT_MQTT_C=${RESULT_DIR}/paho.mqtt.c_result
RESULT_MQTT_CPP=${RESULT_DIR}/paho.mqtt.cpp_result

# 指定交叉编译工具
CROSSS_COMPILE_TOOL=aarch64-mix210-linux-

# 1、解压缩
tar zxf paho.mqtt.cpp-1.3.2.tar.gz 

# 2、进入目录，
cd paho.mqtt.cpp-1.3.2/

# 3、执行 cmake
mkdir build_arm 
cd build_arm 

# 编译不需要 openssl 的库
cmake ..  -DCMAKE_CXX_COMPILER=${CROSSS_COMPILE_TOOL}g++ \
-DCMAKE_INSTALL_PREFIX=${RESULT_MQTT_CPP} \
-DPAHO_MQTT_C_LIBRARIES=${RESULT_MQTT_C}/lib/libpaho-mqtt3a.so \
-DPAHO_MQTT_C_INCLUDE_DIRS=${RESULT_MQTT_C}/include \
-DPAHO_WITH_SSL=OFF \
-DCMAKE_CXX_FLAGS="-std=gnu++11 -mcpu=cortex-a53"

# 编译带有 openssl 的库
#cmake ..  -DCMAKE_CXX_COMPILER=${CROSSS_COMPILE_TOOL}g++ \
-DCMAKE_INSTALL_PREFIX=${RESULT_MQTT_CPP} \
-DPAHO_MQTT_C_LIBRARIES=${RESULT_MQTT_C}/lib/libpaho-mqtt3a.so \
-DPAHO_MQTT_C_INCLUDE_DIRS=${RESULT_MQTT_C}/include \
-DOPENSSL_SSL_LIBRARY=${RESULT_SSL}/lib/libssl.so  \
-DOPENSSL_INCLUDE_DIR=${RESULT_SSL}/include  \
-DOPENSSL_CRYPTO_LIBRARY=${RESULT_SSL}/lib/libcrypto.so \
-DCMAKE_CXX_FLAGS="-std=gnu++11 -mcpu=cortex-a53"

# 4、编译
make && make install

2、将下载的源码包paho.mqtt.cpp-1.3.2.tar.gz 和上面保存的脚本paho.mqtt.cpp_install 放到同一目录，并且将前面编译好的openssl库、paho.mqtt.c库放在脚本指定的结果目录，我是放到 result_dir 目录，编译目录如下。
3、执行 ./paho.mqtt.cpp_install.sh 编译，编译完成后，在result_dir目录下生成一个名为paho.mqtt.cpp_result的目录，内容如下：

在这里插入图片描述

🎄四、paho.mqtt.cpp库写一个MQTT客户端

下面提供两个使用了 paho.mqtt.cpp库(libpaho-mqttpp3) MQTT客户端的例子。

运行下面代码前，要先搭建一个MQTT Broker，参考上篇文章：【MQTT】mosquitto 的 “下载、交叉编译、使用” 详细教程，手把手搭建一个MQTT Broker

✨4.1 订阅——async_subscribe.cpp

这是使用了 libpaho-mqttpp3.so 进行订阅消息的源码，源码路径在源码的这个路径：paho.mqtt.cpp-1.3.2/src/samples/async_subscribe.cpp，只更改了服务器地址。完整代码如下：

// async_subscribe.cpp
//
// This is a Paho MQTT C++ client, sample application.
//
// This application is an MQTT subscriber using the C++ asynchronous client
// interface, employing callbacks to receive messages and status updates.
//
// The sample demonstrates:
//  - Connecting to an MQTT server/broker.
//  - Subscribing to a topic
//  - Receiving messages through the callback API
//  - Receiving network disconnect updates and attempting manual reconnects.
//  - Using a "clean session" and manually re-subscribing to topics on
//    reconnect.
//

/*******************************************************************************
 * Copyright (c) 2013-2023 Frank Pagliughi <fpagliughi@mindspring.com>
 *
 * 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
 *    http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Frank Pagliughi - initial implementation and documentation
 *******************************************************************************/

#include <iostream>
#include <cstdlib>
#include <string>
#include <cstring>
#include <cctype>
#include <thread>
#include <chrono>
#include "mqtt/async_client.h"

const std::string SERVER_ADDRESS("192.168.3.227:1883");
const std::string CLIENT_ID("paho_cpp_async_subcribe");
const std::string TOPIC("hello");

const int	QOS = 1;
const int	N_RETRY_ATTEMPTS = 5;

/

// Callbacks for the success or failures of requested actions.
// This could be used to initiate further action, but here we just log the
// results to the console.

class action_listener : public virtual mqtt::iaction_listener
{
	std::string name_;

	void on_failure(const mqtt::token& tok) override {
		std::cout << name_ << " failure";
		if (tok.get_message_id() != 0)
			std::cout << " for token: [" << tok.get_message_id() << "]" << std::endl;
		std::cout << std::endl;
	}

	void on_success(const mqtt::token& tok) override {
		std::cout << name_ << " success";
		if (tok.get_message_id() != 0)
			std::cout << " for token: [" << tok.get_message_id() << "]" << std::endl;
		auto top = tok.get_topics();
		if (top && !top->empty())
			std::cout << "\ttoken topic: '" << (*top)[0] << "', ..." << std::endl;
		std::cout << std::endl;
	}

public:
	action_listener(const std::string& name) : name_(name) {}
};

/

/**
 * Local callback & listener class for use with the client connection.
 * This is primarily intended to receive messages, but it will also monitor
 * the connection to the broker. If the connection is lost, it will attempt
 * to restore the connection and re-subscribe to the topic.
 */
class callback : public virtual mqtt::callback,
					public virtual mqtt::iaction_listener

{
	// Counter for the number of connection retries
	int nretry_;
	// The MQTT client
	mqtt::async_client& cli_;
	// Options to use if we need to reconnect
	mqtt::connect_options& connOpts_;
	// An action listener to display the result of actions.
	action_listener subListener_;

	// This deomonstrates manually reconnecting to the broker by calling
	// connect() again. This is a possibility for an application that keeps
	// a copy of it's original connect_options, or if the app wants to
	// reconnect with different options.
	// Another way this can be done manually, if using the same options, is
	// to just call the async_client::reconnect() method.
	void reconnect() {
		std::this_thread::sleep_for(std::chrono::milliseconds(2500));
		try {
			cli_.connect(connOpts_, nullptr, *this);
		}
		catch (const mqtt::exception& exc) {
			std::cerr << "Error: " << exc.what() << std::endl;
			exit(1);
		}
	}

	// Re-connection failure
	void on_failure(const mqtt::token& tok) override {
		std::cout << "Connection attempt failed" << std::endl;
		if (++nretry_ > N_RETRY_ATTEMPTS)
			exit(1);
		reconnect();
	}

	// (Re)connection success
	// Either this or connected() can be used for callbacks.
	void on_success(const mqtt::token& tok) override {}

	// (Re)connection success
	void connected(const std::string& cause) override {
		std::cout << "\nConnection success" << std::endl;
		std::cout << "\nSubscribing to topic '" << TOPIC << "'\n"
			<< "\tfor client " << CLIENT_ID
			<< " using QoS" << QOS << "\n"
			<< "\nPress Q<Enter> to quit\n" << std::endl;

		cli_.subscribe(TOPIC, QOS, nullptr, subListener_);
	}

	// Callback for when the connection is lost.
	// This will initiate the attempt to manually reconnect.
	void connection_lost(const std::string& cause) override {
		std::cout << "\nConnection lost" << std::endl;
		if (!cause.empty())
			std::cout << "\tcause: " << cause << std::endl;

		std::cout << "Reconnecting..." << std::endl;
		nretry_ = 0;
		reconnect();
	}

	// Callback for when a message arrives.
	void message_arrived(mqtt::const_message_ptr msg) override {
		std::cout << "Message arrived" << std::endl;
		std::cout << "\ttopic: '" << msg->get_topic() << "'" << std::endl;
		std::cout << "\tpayload: '" << msg->to_string() << "'\n" << std::endl;
	}

	void delivery_complete(mqtt::delivery_token_ptr token) override {}

public:
	callback(mqtt::async_client& cli, mqtt::connect_options& connOpts)
				: nretry_(0), cli_(cli), connOpts_(connOpts), subListener_("Subscription") {}
};

/

int main(int argc, char* argv[])
{
	// A subscriber often wants the server to remember its messages when its
	// disconnected. In that case, it needs a unique ClientID and a
	// non-clean session.

	mqtt::async_client cli(SERVER_ADDRESS, CLIENT_ID);

	mqtt::connect_options connOpts;
	connOpts.set_clean_session(false);

	// Install the callback(s) before connecting.
	callback cb(cli, connOpts);
	cli.set_callback(cb);

	// Start the connection.
	// When completed, the callback will subscribe to topic.

	try {
		std::cout << "Connecting to the MQTT server..." << std::flush;
		cli.connect(connOpts, nullptr, cb);
	}
	catch (const mqtt::exception& exc) {
		std::cerr << "\nERROR: Unable to connect to MQTT server: '"
			<< SERVER_ADDRESS << "'" << exc << std::endl;
		return 1;
	}

	// Just block till user tells us to quit.

	while (std::tolower(std::cin.get()) != 'q')
		;

	// Disconnect

	try {
		std::cout << "\nDisconnecting from the MQTT server..." << std::flush;
		cli.disconnect()->wait();
		std::cout << "OK" << std::endl;
	}
	catch (const mqtt::exception& exc) {
		std::cerr << exc << std::endl;
		return 1;
	}

 	return 0;
}

交叉编译：

aarch64-mix210-linux-g++ async_subscribe.cpp -I result_dir/paho.mqtt.cpp_result/include/ -I result_dir/paho.mqtt.c_result/include/ -L result_dir/paho.mqtt.cpp_result/lib/ -L result_dir/paho.mqtt.c_result/lib/ -l paho-mqttpp3 -l paho-mqtt3a

在嵌入式板子运行：
在这里插入图片描述

✨4.2 发布——async_publish.cpp

这是使用了 libpaho-mqttpp3.so 进行发布消息的源码，源码路径在源码的这个路径：paho.mqtt.cpp-1.3.2/src/samples/async_publish.cpp，只更改了服务器地址。完整代码如下：

// async_publish.cpp
//
// This is a Paho MQTT C++ client, sample application.
//
// It's an example of how to send messages as an MQTT publisher using the
// C++ asynchronous client interface.
//
// The sample demonstrates:
//  - Connecting to an MQTT server/broker
//  - Publishing messages
//  - Default file persistence
//  - Last will and testament
//  - Using asynchronous tokens
//  - Implementing callbacks and action listeners
//

/*******************************************************************************
 * Copyright (c) 2013-2023 Frank Pagliughi <fpagliughi@mindspring.com>
 *
 * 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
 *    http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Frank Pagliughi - initial implementation and documentation
 *******************************************************************************/

#include <iostream>
#include <cstdlib>
#include <string>
#include <thread>
#include <atomic>
#include <chrono>
#include <cstring>
#include "mqtt/async_client.h"

using namespace std;

const string DFLT_SERVER_ADDRESS	{ "192.168.3.227:1883" };
const string CLIENT_ID				{ "paho_cpp_async_publish" };
const string PERSIST_DIR			{ "./persist" };

const string TOPIC { "hello" };

const char* PAYLOAD1 = "Hello World!";
const char* PAYLOAD2 = "Hi there!";
const char* PAYLOAD3 = "Is anyone listening?";
const char* PAYLOAD4 = "Someone is always listening.";

const char* LWT_PAYLOAD = "Last will and testament.";

const int  QOS = 1;

const auto TIMEOUT = std::chrono::seconds(10);

/

/**
 * A callback class for use with the main MQTT client.
 */
class callback : public virtual mqtt::callback
{
public:
	void connection_lost(const string& cause) override {
		cout << "\nConnection lost" << endl;
		if (!cause.empty())
			cout << "\tcause: " << cause << endl;
	}

	void delivery_complete(mqtt::delivery_token_ptr tok) override {
		cout << "\tDelivery complete for token: "
			<< (tok ? tok->get_message_id() : -1) << endl;
	}
};

/

/**
 * A base action listener.
 */
class action_listener : public virtual mqtt::iaction_listener
{
protected:
	void on_failure(const mqtt::token& tok) override {
		cout << "\tListener failure for token: "
			<< tok.get_message_id() << endl;
	}

	void on_success(const mqtt::token& tok) override {
		cout << "\tListener success for token: "
			<< tok.get_message_id() << endl;
	}
};

/

/**
 * A derived action listener for publish events.
 */
class delivery_action_listener : public action_listener
{
	atomic<bool> done_;

	void on_failure(const mqtt::token& tok) override {
		action_listener::on_failure(tok);
		done_ = true;
	}

	void on_success(const mqtt::token& tok) override {
		action_listener::on_success(tok);
		done_ = true;
	}

public:
	delivery_action_listener() : done_(false) {}
	bool is_done() const { return done_; }
};

/

int main(int argc, char* argv[])
{
	// A client that just publishes normally doesn't need a persistent
	// session or Client ID unless it's using persistence, then the local
	// library requires an ID to identify the persistence files.

	string	address  = (argc > 1) ? string(argv[1]) : DFLT_SERVER_ADDRESS,
			clientID = (argc > 2) ? string(argv[2]) : CLIENT_ID;

	cout << "Initializing for server '" << address << "'..." << endl;
	mqtt::async_client client(address, clientID, PERSIST_DIR);

	callback cb;
	client.set_callback(cb);

	auto connOpts = mqtt::connect_options_builder()
		.clean_session()
		.will(mqtt::message(TOPIC, LWT_PAYLOAD, strlen(LWT_PAYLOAD), QOS, false))
		.finalize();

	cout << "  ...OK" << endl;

	try {
		cout << "\nConnecting..." << endl;
		mqtt::token_ptr conntok = client.connect(connOpts);
		cout << "Waiting for the connection..." << endl;
		conntok->wait();
		cout << "  ...OK" << endl;

		// First use a message pointer.

		cout << "\nSending message..." << endl;
		mqtt::message_ptr pubmsg = mqtt::make_message(TOPIC, PAYLOAD1);
		pubmsg->set_qos(QOS);
		client.publish(pubmsg)->wait_for(TIMEOUT);
		cout << "  ...OK" << endl;

		// Now try with itemized publish.

		cout << "\nSending next message..." << endl;
		mqtt::delivery_token_ptr pubtok;
		pubtok = client.publish(TOPIC, PAYLOAD2, strlen(PAYLOAD2), QOS, false);
		cout << "  ...with token: " << pubtok->get_message_id() << endl;
		cout << "  ...for message with " << pubtok->get_message()->get_payload().size()
			<< " bytes" << endl;
		pubtok->wait_for(TIMEOUT);
		cout << "  ...OK" << endl;

		// Now try with a listener

		cout << "\nSending next message..." << endl;
		action_listener listener;
		pubmsg = mqtt::make_message(TOPIC, PAYLOAD3);
		pubtok = client.publish(pubmsg, nullptr, listener);
		pubtok->wait();
		cout << "  ...OK" << endl;

		// Finally try with a listener, but no token

		cout << "\nSending final message..." << endl;
		delivery_action_listener deliveryListener;
		pubmsg = mqtt::make_message(TOPIC, PAYLOAD4);
		client.publish(pubmsg, nullptr, deliveryListener);

		while (!deliveryListener.is_done()) {
			this_thread::sleep_for(std::chrono::milliseconds(100));
		}
		cout << "OK" << endl;

		// Double check that there are no pending tokens

		auto toks = client.get_pending_delivery_tokens();
		if (!toks.empty())
			cout << "Error: There are pending delivery tokens!" << endl;

		// Disconnect
		cout << "\nDisconnecting..." << endl;
		client.disconnect()->wait();
		cout << "  ...OK" << endl;
	}
	catch (const mqtt::exception& exc) {
		cerr << exc.what() << endl;
		return 1;
	}

 	return 0;
}

交叉编译：

aarch64-mix210-linux-g++ async_publish.cpp -I result_dir/paho.mqtt.cpp_result/include/ -I result_dir/paho.mqtt.c_result/include/ -L result_dir/paho.mqtt.cpp_result/lib/ -L result_dir/paho.mqtt.c_result/lib/ -l paho-mqttpp3 -l paho-mqtt3a -o async_publish

在嵌入式板子的运行结果：
在这里插入图片描述