mongoose/examples/mqtt-client-aws-iot/main.c

// Copyright (c) 2020 Cesanta Software Limited
// All rights reserved
//
// Example MQTT client. It performs the following steps:
//    1. Connects to the AWS IoT MQTT server
//    2. When connected, subscribes to the topic `s_rx_topic`
//    3. Publishes message `hello` to the `s_tx_topic` periodically
//
// This example requires TLS support. By default, it is built with mbedTLS,
// therefore make sure mbedTLS is installed. To build with OpenSSL, execute:
//    make clean all CFLAGS="-W -Wall -DMG_ENABLE_OPENSSL=1 -lssl"

// In order to get MQTT URL, login to AWS IoT, click on "Settings" on the left
// bar, copy the "Endpoint" URL.
static const char *s_url =
    "mqtts://a1pjwh2bop1ojt-ats.iot.eu-west-1.amazonaws.com";

// To create certificates:
// 1. Click Policies -> Create, fill fields:
//               Name        : Policy1
//               Action      : iot:*
//               Resource ARN: *
//               Effect      : allow
//        then, click "Create"
// 2. Click Manage -> Things -> Create things -> Create single thing -> Next
//      Thing name: t1, no shadow, Next
//      Auto-generate new certificate, Next
//      Select policy Policy1, Create thing
// 3. From the dialog box that appears, download:
//      xxx-certificate.pem.crt as cert.pem to the example directory
//      xxx-private.pem.key as key.pem to the example directory
static const char *s_cert = "cert.pem";
static const char *s_key = "key.pem";

static const char *s_rx_topic = "d/rx";
static const char *s_tx_topic = "d/tx";
static int s_qos = 1;

#include "mongoose.h"

static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  if (ev == MG_EV_OPEN) {
    // c->is_hexdumping = 1;
  } else if (ev == MG_EV_ERROR) {
    // On error, log error message
    MG_ERROR(("%p %s", c->fd, (char *) ev_data));
  } else if (ev == MG_EV_CONNECT) {
    // Set up 2-way TLS that is required by AWS IoT
    struct mg_tls_opts opts = {
        .ca = "ca.pem", .cert = s_cert, .certkey = s_key};
    mg_tls_init(c, &opts);
  } else if (ev == MG_EV_MQTT_OPEN) {
    // MQTT connect is successful
    struct mg_str topic = mg_str(s_rx_topic);
    MG_INFO(("Connected to %s", s_url));
    MG_INFO(("Subscribing to %s", s_rx_topic));
    mg_mqtt_sub(c, topic, s_qos);
    c->data[0] = 'X';  // Set a label that we're logged in
  } else if (ev == MG_EV_MQTT_MSG) {
    // When we receive MQTT message, print it
    struct mg_mqtt_message *mm = (struct mg_mqtt_message *) ev_data;
    MG_INFO(("Received on %.*s : %.*s", (int) mm->topic.len, mm->topic.ptr,
             (int) mm->data.len, mm->data.ptr));
  } else if (ev == MG_EV_POLL && c->data[0] == 'X') {
    static unsigned long prev_second;
    unsigned long now_second = (*(unsigned long *) ev_data) / 1000;
    if (now_second != prev_second) {
      struct mg_str topic = mg_str(s_tx_topic), data = mg_str("{\"a\":123}");
      MG_INFO(("Publishing to %s", s_tx_topic));
      mg_mqtt_pub(c, topic, data, s_qos, false);
      prev_second = now_second;
    }
  }

  if (ev == MG_EV_ERROR || ev == MG_EV_CLOSE) {
    MG_INFO(("Got event %d, stopping...", ev));
    *(bool *) fn_data = true;  // Signal that we're done
  }
}

int main(void) {
  struct mg_mgr mgr;
  struct mg_mqtt_opts opts = {.clean = true};
  bool done = false;
  mg_mgr_init(&mgr);                               // Initialise event manager
  MG_INFO(("Connecting to %s", s_url));            // Inform that we're starting
  mg_mqtt_connect(&mgr, s_url, &opts, fn, &done);  // Create client connection
  while (!done) mg_mgr_poll(&mgr, 1000);           // Loop until done
  mg_mgr_free(&mgr);                               // Finished, cleanup
  return 0;
}