mongoose/examples/mqtt-client/main.c

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// Copyright (c) 2020 Cesanta Software Limited
// All rights reserved
//
// Example MQTT client. It performs the following steps:
// 1. Connects to the MQTT server specified by `s_url` variable
// 2. When connected, subscribes to the topic `s_topic`
// 3. Publishes message `hello` to the `s_topic`
// 4. Receives that message back from the subscribed topic and exits
//
// To enable SSL/TLS for this client, build it like this:
// make MBEDTLS_DIR=/path/to/your/mbedtls/installation
#include "mongoose.h"
static const char *s_url = "mqtt://broker.hivemq.com:1883";
static const char *s_topic = "mg/test";
static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
if (ev == MG_EV_ERROR) {
// On error, log error message
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LOG(LL_ERROR, ("%p %s", c->fd, (char *) ev_data));
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} else if (ev == MG_EV_CONNECT) {
// If target URL is SSL/TLS, command client connection to use TLS
if (mg_url_is_ssl(s_url)) {
struct mg_tls_opts opts = {.ca = "ca.pem"};
mg_tls_init(c, &opts);
}
} else if (ev == MG_EV_MQTT_OPEN) {
// MQTT connect is successful
struct mg_str topic = mg_str(s_topic), data = mg_str("hello");
LOG(LL_INFO, ("CONNECTED to %s", s_url));
mg_mqtt_sub(c, &topic, 1);
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LOG(LL_INFO, ("SUBSCRIBED to %.*s", (int) topic.len, topic.ptr));
mg_mqtt_pub(c, &topic, &data, 1, false);
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LOG(LL_INFO, ("PUBSLISHED %.*s -> %.*s", (int) data.len, data.ptr,
(int) topic.len, topic.ptr));
} else if (ev == MG_EV_MQTT_MSG) {
// When we get echo response, print it
struct mg_mqtt_message *mm = (struct mg_mqtt_message *) ev_data;
LOG(LL_INFO, ("RECEIVED %.*s <- %.*s", (int) mm->data.len, mm->data.ptr,
(int) mm->topic.len, mm->topic.ptr));
}
if (ev == MG_EV_ERROR || ev == MG_EV_CLOSE || ev == MG_EV_MQTT_MSG) {
*(bool *) fn_data = true; // Signal that we're done
}
}
int main(void) {
struct mg_mgr mgr; // Event manager
struct mg_mqtt_opts opts; // MQTT connection options
bool done = false; // Event handler flips it to true when done
mg_mgr_init(&mgr); // Initialise event manager
memset(&opts, 0, sizeof(opts)); // Set MQTT options
opts.qos = 1; // Set QoS to 1
opts.will_topic = mg_str(s_topic); // Set last will topic
opts.will_message = mg_str("goodbye"); // And last will message
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mg_mqtt_connect(&mgr, s_url, &opts, fn, &done); // Create client connection
while (done == false) mg_mgr_poll(&mgr, 1000); // Event loop
mg_mgr_free(&mgr); // Finished, cleanup
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return 0;
}