3 files changed, 110 insertions, 3 deletions

diff --git a/src/mqtt.c b/src/mqtt.c
index ce89b0b..32e2ea9 100644
--- a/src/mqtt.c
+++ b/src/mqtt.c
@@ -30,7 +30,9 @@ mqtt_connect(const char *clientid, // NOLINT
                 return NULL;
         }
 
-        mosquitto_message_callback_set(client, callback);
+        if ( callback ) {
+                mosquitto_message_callback_set(client, callback);
+        }
 
         err = mosquitto_connect(client, hostname, port, KEEPALIVE);
         if ( err != MOSQ_ERR_SUCCESS ) {
@@ -45,8 +47,10 @@ mqtt_connect(const char *clientid, // NOLINT
 void
 mqtt_run(struct mosquitto *client, const char *topics[], const volatile bool *quit)
 {
+        int *mid = NULL;
+
         for ( size_t idx = 0; topics[idx] != NULL; ++idx ) {
-                mosquitto_subscribe(client, NULL, topics[idx], 0);
+                mosquitto_subscribe(client, mid, topics[idx], 0);
         }
 
         while ( !*quit ) {
@@ -59,6 +63,10 @@ mqtt_run(struct mosquitto *client, const char *topics[], const volatile bool *qu
                         mosquitto_reconnect(client);
                 }
         }
+
+        for ( size_t idx = 0; topics[idx] != NULL; ++idx ) {
+                mosquitto_unsubscribe(client, mid, topics[idx]);
+        }
 }
 
 void
diff --git a/src/publish.c b/src/publish.c
new file mode 100644
index 0000000..6afc5b4
--- /dev/null
+++ b/src/publish.c
@@ -0,0 +1,99 @@
+// Standard C
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// System
+#include <unistd.h>
+
+// Mosquitto
+#include <mosquitto.h>
+
+// Project
+#include "config.h"
+#include "mqtt.h"
+
+static bool
+streq(const char *lhs, const char *rhs)
+{
+        return strcmp(lhs, rhs) == 0;
+}
+
+static void
+cleanup_app(void)
+{
+        mosquitto_lib_cleanup();
+}
+
+static void
+init_app(void)
+{
+        mosquitto_lib_init();
+        (void) atexit(cleanup_app);
+}
+
+int
+main(void)
+{
+        init_app();
+
+        struct mosquitto *client = mqtt_connect(
+            NULL,
+            USERNAME,
+            PASSWORD,
+            HOSTNAME,
+            PORT,
+            NULL,
+            NULL);
+
+        if ( !client ) {
+                return EXIT_FAILURE;
+        }
+
+        // logic
+        for ( bool quit = false; !quit; ) {
+                printf("> ");
+
+                char command[100] = { 0 }; // NOLINT
+                if ( fgets(command, sizeof command, stdin) == NULL ) {
+                        quit = true;
+                        continue;
+                }
+
+                // remove 'newline' symbol at the end
+                command[strcspn(command, "\n")] = '\0';
+
+                if ( streq(command, "") ) {
+                        ; // do nothing
+                }
+                else if ( streq(command, "quit") ) {
+                        quit = true;
+                }
+                else if ( streq(command, "send") ) {
+                        static const char payload[] = "ich bin ein payload";
+                        static const char topic[] = "testtopic";
+
+                        int err = mosquitto_publish(
+                            client,
+                            NULL,
+                            topic,
+                            sizeof payload,
+                            payload,
+                            0,
+                            false);
+
+                        if ( err ) {
+                                (void) fprintf(stderr, "error on send: %s\n", mosquitto_strerror(err));
+                        }
+                }
+                else {
+                        (void) fprintf(stderr, "unknown command: '%s'\n", command);
+                }
+        }
+
+        mqtt_shutdown(client);
+
+        return EXIT_SUCCESS;
+}
diff --git a/src/subscribe.c b/src/subscribe.c
index 82e7606..e7d5883 100644
--- a/src/subscribe.c
+++ b/src/subscribe.c
@@ -72,7 +72,7 @@ main(void)
                 return EXIT_FAILURE;
         }
 
-        mqtt_run(client, (const char *[]){ TOPIC, NULL }, &terminate);
+        mqtt_run(client, (const char *[]){ TOPIC, "testtopic", NULL }, &terminate);
 
         mqtt_shutdown(client);