From 9382ca17e82ab7aca5e35831a2f7c08891f4186a Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@collectd.org>
Date: Fri, 21 Nov 2014 13:17:54 +0100
Subject: [PATCH] mqtt plugin: Let "client ID" default to the hostname.

The MQTT documentation says that this needs to be unique and stable, so
I think the hostname is the best match for this.
---
 src/mqtt.c | 105 +++++++++++++++++++++++++++++++++++--------------------------
 1 file changed, 61 insertions(+), 44 deletions(-)

diff --git a/src/mqtt.c b/src/mqtt.c
index 457d7bd8..3142bf3d 100644
--- a/src/mqtt.c
+++ b/src/mqtt.c
@@ -38,7 +38,6 @@
 #define MQTT_MAX_MESSAGE_SIZE       MQTT_MAX_TOPIC_SIZE + 1024
 #define MQTT_DEFAULT_HOST           "localhost"
 #define MQTT_DEFAULT_PORT           1883
-#define MQTT_DEFAULT_CLIENT_ID      "collectd"
 #define MQTT_DEFAULT_TOPIC_PREFIX   "collectd"
 
 /*
@@ -113,7 +112,7 @@ static void mqtt_free (mqtt_client_conf_t *conf)
  * Functions
  */
 /* must hold conf->lock when calling. */
-static int mqtt_reconnect_broker (mqtt_client_conf_t *conf)
+static int mqtt_reconnect (mqtt_client_conf_t *conf)
 {
     int status;
 
@@ -139,7 +138,64 @@ static int mqtt_reconnect_broker (mqtt_client_conf_t *conf)
             conf->host, conf->port);
 
     return (0);
-} /* mqtt_reconnect_broker */
+} /* mqtt_reconnect */
+
+/* must hold conf->lock when calling. */
+static int mqtt_connect (mqtt_client_conf_t *conf)
+{
+    char const *client_id;
+    int status;
+
+    if (conf->mosq != NULL)
+        return mqtt_reconnect (conf);
+
+    if (conf->client_id)
+        client_id = conf->client_id;
+    else
+        client_id = hostname_g;
+
+    conf->mosq = mosquitto_new (client_id, /* user data = */ conf);
+    if (conf->mosq == NULL)
+    {
+        ERROR ("mqtt plugin: mosquitto_new failed");
+        return (-1);
+    }
+
+    if (conf->username && conf->password)
+    {
+        status = mosquitto_username_pw_set (conf->mosq, conf->username, conf->password);
+        if (status != MOSQ_ERR_SUCCESS)
+        {
+            char errbuf[1024];
+            ERROR ("mqtt plugin: mosquitto_username_pw_set failed: %s",
+                    (status == MOSQ_ERR_ERRNO)
+                    ? sstrerror (errno, errbuf, sizeof (errbuf))
+                    : mosquitto_strerror (status));
+
+            mosquitto_destroy (conf->mosq);
+            conf->mosq = NULL;
+            return (-1);
+        }
+    }
+
+    status = mosquitto_connect (conf->mosq, conf->host, conf->port,
+            /* keepalive = */ 10, /* clean session = */ 1);
+    if (status != MOSQ_ERR_SUCCESS)
+    {
+        char errbuf[1024];
+        ERROR ("mqtt plugin: mosquitto_connect failed: %s",
+                (status == MOSQ_ERR_ERRNO)
+                ? sstrerror (errno, errbuf, sizeof (errbuf))
+                : mosquitto_strerror (status));
+
+        mosquitto_destroy (conf->mosq);
+        conf->mosq = NULL;
+        return (-1);
+    }
+
+    conf->connected = 1;
+    return (0);
+} /* mqtt_connect */
 
 static int publish (mqtt_client_conf_t *conf, char const *topic,
     void const *payload, size_t payload_len)
@@ -148,7 +204,7 @@ static int publish (mqtt_client_conf_t *conf, char const *topic,
 
     pthread_mutex_lock (&conf->lock);
 
-    status = mqtt_reconnect_broker (conf);
+    status = mqtt_connect (conf);
     if (status != 0) {
         pthread_mutex_unlock (&conf->lock);
         ERROR ("mqtt plugin: unable to reconnect to broker");
@@ -278,7 +334,7 @@ static int mqtt_config_broker (oconfig_item_t *ci)
 
     conf->host = strdup (MQTT_DEFAULT_HOST);
     conf->port = MQTT_DEFAULT_PORT;
-    conf->client_id = strdup (MQTT_DEFAULT_CLIENT_ID);
+    conf->client_id = NULL;
     conf->topic_prefix = strdup (MQTT_DEFAULT_TOPIC_PREFIX);
     C_COMPLAIN_INIT (&conf->complaint_cantpublish);
 
@@ -323,49 +379,10 @@ static int mqtt_config_broker (oconfig_item_t *ci)
     memset (&user_data, 0, sizeof (user_data));
     user_data.data = conf;
 
-    conf->mosq = mosquitto_new (conf->client_id, /* user data = */ conf);
-    if (conf->mosq == NULL)
-    {
-        ERROR ("mqtt plugin: mosquitto_new failed");
-        mqtt_free (conf);
-        return (-1);
-    }
-
-    if (conf->username && conf->password)
-    {
-        status = mosquitto_username_pw_set (conf->mosq, conf->username, conf->password);
-        if (status != MOSQ_ERR_SUCCESS)
-        {
-            char errbuf[1024];
-            ERROR ("mqtt plugin: mosquitto_username_pw_set failed: %s",
-                    (status == MOSQ_ERR_ERRNO)
-                    ? sstrerror (errno, errbuf, sizeof (errbuf))
-                    : mosquitto_strerror (status));
-            mqtt_free (conf);
-            return (-1);
-        }
-    }
-
-    status = mosquitto_connect (conf->mosq, conf->host, conf->port,
-            /* keepalive = */ 10, /* clean session = */ 1);
-    if (status != MOSQ_ERR_SUCCESS)
-    {
-        char errbuf[1024];
-        ERROR ("mqtt plugin: mosquitto_connect failed: %s",
-                (status == MOSQ_ERR_ERRNO)
-                ? sstrerror (errno, errbuf, sizeof (errbuf))
-                : mosquitto_strerror (status));
-        mqtt_free (conf);
-        return (-1);
-    }
-
     DEBUG ("mqtt plugin: successfully connected to broker \"%s:%d\"",
         conf->host, conf->port);
 
-    conf->connected = 1;
-
     plugin_register_write ("mqtt", mqtt_write, &user_data);
-
     return (0);
 } /* mqtt_config_broker */
 
-- 
2.11.0