Add mosquitto_persistence_location() for plugins.

ChangeLog.txt

@@ -105,6 +105,8 @@ Plugins / plugin interface:
   network loop, to give chance for PUBACK/PUBREC to be sent. Closes #2474.
 - Add MOSQ_EVT_SUBSCRIBE and MOSQ_EVT_UNSUBSCRIBE events that are called when
   subscribe/unsubscribes actually succeed.
+- Add `mosquitto_persistence_location()` for plugins to use to find a valid
+  location for storing persistent data.
 
 Client library:
 - Add MOSQ_OPT_DISABLE_SOCKETPAIR to allow the disabling of the socketpair

include/mosquitto_broker.h

@@ -1148,6 +1148,20 @@ int mosquitto_persist_retain_msg_set(const char *topic, uint64_t store_id);
  */
 int mosquitto_persist_retain_msg_delete(const char *topic);
 
+/* Function: mosquitto_persistence_location
+ *
+ * Returns the `persistence_location` config option, or the contents of the
+ * MOSQUITTO_PERSISTENCE_LOCATION environment variable, if set.
+ *
+ * This location should be used by plugins needing to store persistent data.
+ * Use of sub directories is recommended.
+ *
+ * Returns:
+ *   A valid pointer to the persistence location string
+ *   A NULL pointer if neither the option nor the variable are set
+ */
+const char *mosquitto_persistence_location(void);
+
 #ifdef __cplusplus
 }
 #endif

mosquitto.conf

@@ -485,6 +485,12 @@
 # Default is an empty string (current directory).
 # Set to e.g. /var/lib/mosquitto if running as a proper service on Linux or
 # similar.
+#
+# Can also be defined by setting the MOSQUITTO_PERSISTENCE_LOCATION environment
+# variable prior to running the broker. If both the config file option and the
+# environment variable are set, the environment variable takes precedent.
+#
+# This can also be used by plugins using the mosquitto_persistence_location() function.
 #persistence_location
 
 

src/conf.c

@@ -564,6 +564,14 @@ int config__parse_args(struct mosquitto__config *config, int argc, char *argv[])
 	if(db.verbose){
 		config->log_type = UINT_MAX;
 	}
+
+	if(getenv("MOSQUITTO_PERSISTENCE_LOCATION")){
+		mosquitto__FREE(config->persistence_location);
+		config->persistence_location = mosquitto_strdup(getenv("MOSQUITTO_PERSISTENCE_LOCATION"));
+		if(!config->persistence_location){
+			return MOSQ_ERR_NOMEM;
+		}
+	}
 	return config__check(config);
 }
 

src/linker-macosx.syms

@@ -23,6 +23,7 @@ _mosquitto_kick_client_by_username
 _mosquitto_log_printf
 _mosquitto_log_vprintf
 _mosquitto_malloc
+_mosquitto_persistence_location
 _mosquitto_persist_base_msg_add
 _mosquitto_persist_base_msg_delete
 _mosquitto_persist_client_add

src/linker.syms

@@ -35,6 +35,7 @@
 	mosquitto_persist_client_update;
 	mosquitto_persist_retain_msg_delete;
 	mosquitto_persist_retain_msg_set;
+	mosquitto_persistence_location;
 	mosquitto_plugin_set_info;
 	mosquitto_property_add_binary;
 	mosquitto_property_add_byte;

src/plugin_public.c

@@ -865,3 +865,8 @@ BROKER_EXPORT int mosquitto_broker_node_id_set(uint16_t id)
 		return MOSQ_ERR_SUCCESS;
 	}
 }
+
+BROKER_EXPORT const char *mosquitto_persistence_location(void)
+{
+	return db.config->persistence_location;
+}