Add mqtt-server example

examples/mqtt-server/Makefile

@@ -0,0 +1,10 @@
+PROG ?= example
+
+all: $(PROG)
+	$(DEBUGGER) ./$(PROG) $(ARGS)
+
+$(PROG): main.c
+	$(CC) ../../mongoose.c -I../.. -W -Wall -DMG_ENABLE_LINES=1 $(CFLAGS) -o $(PROG) main.c
+
+clean:
+	rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb

examples/mqtt-server/main.c

@@ -0,0 +1,83 @@
+// Copyright (c) 2020 Cesanta Software Limited
+// All rights reserved
+//
+// Example MQTT server. Usage:
+//  1. Start this server, type `make`
+//  2. Install mosquitto MQTT client
+//  3. In one terminal, run:   mosquitto_sub -h localhost -t foo -t bar
+//  4. In another, run:        mosquitto_pub -h localhost -t foo -m hi
+
+#include "mongoose.h"
+
+static const char *s_listen_on = "mqtt://0.0.0.0:1883";
+
+// A list of subscription, held in memory
+struct sub {
+  struct sub *next;
+  struct mg_connection *c;
+  struct mg_str topic;
+  uint8_t qos;
+};
+static struct sub *s_subs = NULL;
+
+// Event handler function
+static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+  if (ev == MG_EV_MQTT_CMD) {
+    struct mg_mqtt_message *mm = (struct mg_mqtt_message *) ev_data;
+    LOG(LL_DEBUG, ("cmd %d qos %d", mm->cmd, mm->qos));
+    switch (mm->cmd) {
+      case MQTT_CMD_CONNECT: {
+        // Client connects. Return success, do not check user/password
+        uint8_t response[] = {0, 0};
+        mg_mqtt_send_header(c, MQTT_CMD_CONNACK, 0, sizeof(response));
+        mg_send(c, response, sizeof(response));
+        break;
+      }
+      case MQTT_CMD_SUBSCRIBE: {
+        // Client subscribes
+        int pos = 4;  // Initial topic offset, where ID ends
+        uint8_t qos;
+        struct mg_str topic;
+        while ((pos = mg_mqtt_next_sub(mm, &topic, &qos, pos)) > 0) {
+          struct sub *sub = calloc(1, sizeof(*sub));
+          sub->c = c;
+          sub->topic = mg_strdup(topic);
+          sub->qos = qos;
+          LIST_ADD_HEAD(struct sub, &s_subs, sub);
+          LOG(LL_INFO,
+              ("SUB %p [%.*s]", c->fd, (int) sub->topic.len, sub->topic.ptr));
+        }
+        break;
+      }
+      case MQTT_CMD_PUBLISH: {
+        // Client published message. Push to all subscribed channels
+        LOG(LL_INFO, ("PUB %p [%.*s] -> [%.*s]", c->fd, (int) mm->data.len,
+                      mm->data.ptr, (int) mm->topic.len, mm->topic.ptr));
+        for (struct sub *sub = s_subs; sub != NULL; sub = sub->next) {
+          if (mg_strcmp(mm->topic, sub->topic) != 0) continue;
+          mg_mqtt_pub(sub->c, &mm->topic, &mm->data);
+        }
+        break;
+      }
+    }
+  } else if (ev == MG_EV_CLOSE) {
+    // Client disconnects. Remove from the subscription list
+    for (struct sub *next, *sub = s_subs; sub != NULL; sub = next) {
+      next = sub->next;
+      if (c != sub->c) continue;
+      LOG(LL_INFO,
+          ("UNSUB %p [%.*s]", c->fd, (int) sub->topic.len, sub->topic.ptr));
+      LIST_DELETE(struct sub, &s_subs, sub);
+    }
+  }
+  (void) fn_data;
+}
+
+int main(void) {
+  struct mg_mgr mgr;                            // Event manager
+  mg_mgr_init(&mgr);                            // Initialise event manager
+  mg_mqtt_listen(&mgr, s_listen_on, fn, NULL);  // Create MQTT listener
+  for (;;) mg_mgr_poll(&mgr, 1000);             // Infinite event loop
+  mg_mgr_free(&mgr);
+  return 0;
+}