MQTT C 客户端库
Eclipse Paho C (opens new window) 与 Eclipse Paho Embedded C (opens new window) 均为 Eclipse Paho 项目下的 C 语言客户端库(MQTT C Client),均为使用 ANSI C 编写的功能齐全的 MQTT 客户端。
Eclipse Paho Embedded C 可以在桌面操作系统上使用,但主要针对 mbed (opens new window),Arduino (opens new window)和 FreeRTOS (opens new window) 等嵌入式环境。
该客户端有同步/异步两种 API ,分别以 MQTTClient 和 MQTTAsync 开头:
- 同步 API 旨在更简单,更有用,某些调用将阻塞直到操作完成为止,使用编程上更加容易;
- 异步 API 中只有一个调用块
API-waitForCompletion
,通过回调进行结果通知,更适用于非主线程的环境。
Paho C 使用示例
MQTT C 语言相关两个客户端库的比较、下载、使用方式等详细说明请移步至项目主页查看,本示例包含 C 语言的 Paho C 连接 EMQX Broker,并进行消息收发完整代码:
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "MQTTClient.h"
#define ADDRESS "tcp://broker.emqx.io:1883"
#define CLIENTID "emqx_test"
#define TOPIC "testtopic/1"
#define PAYLOAD "Hello World!"
#define QOS 1
#define TIMEOUT 10000L
int main(int argc, char* argv[])
{
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_deliveryToken token;
int rc;
MQTTClient_create(&client, ADDRESS, CLIENTID,
MQTTCLIENT_PERSISTENCE_NONE, NULL);
// MQTT 连接参数
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to connect, return code %d\n", rc);
exit(-1);
}
// 发布消息
pubmsg.payload = PAYLOAD;
pubmsg.payloadlen = strlen(PAYLOAD);
pubmsg.qos = QOS;
pubmsg.retained = 0;
MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
printf("Waiting for up to %d seconds for publication of %s\n"
"on topic %s for client with ClientID: %s\n",
(int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);
rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
printf("Message with delivery token %d delivered\n", token);
// 断开连接
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
return rc;
}
Paho C MQTT 5.0 支持
目前 Paho C 已经完整支持 MQTT 5.0。