Add examples/mqtt-client-aws-iot

examples/mqtt-client-aws-iot/Makefile

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+PROG ?= example
+CFLAGS ?= -W -Wall -O2 -DMG_ENABLE_MBEDTLS=1 -lmbedtls -lmbedcrypto -lmbedx509
+
+all: $(PROG)
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): main.c
+	$(CC) main.c ../../mongoose.c -I../.. $(CFLAGS) -o $(PROG)
+
+clean:
+	rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb

examples/mqtt-client-aws-iot/ca.pem

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+../../test/data/ca.pem

examples/mqtt-client-aws-iot/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 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
+    LOG(LL_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);
+    LOG(LL_INFO, ("Connected to %s", s_url));
+    LOG(LL_INFO, ("Subscribing to %s", s_rx_topic));
+    mg_mqtt_sub(c, &topic, s_qos);
+    c->label[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;
+    LOG(LL_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->label[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}");
+      LOG(LL_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) {
+    LOG(LL_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 = {.qos = s_qos};
+  bool done = false;
+  mg_mgr_init(&mgr);                               // Initialise event manager
+  LOG(LL_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;
+}