From 5731dd8653a7d5e0fa9bb859f79458ba12a2ac15 Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Thu, 5 May 2022 16:17:24 +0100
Subject: [PATCH] Add mosquitto_persistence_location() for plugins.

---
 ChangeLog.txt              |  2 ++
 include/mosquitto_broker.h | 14 ++++++++++++++
 mosquitto.conf             |  6 ++++++
 src/conf.c                 |  8 ++++++++
 src/linker-macosx.syms     |  1 +
 src/linker.syms            |  1 +
 src/plugin_public.c        |  5 +++++
 7 files changed, 37 insertions(+)

diff --git a/ChangeLog.txt b/ChangeLog.txt
index c27f515e..16982b2a 100644
--- a/ChangeLog.txt
+++ b/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
diff --git a/include/mosquitto_broker.h b/include/mosquitto_broker.h
index 69c03a7c..ed1643a8 100644
--- a/include/mosquitto_broker.h
+++ b/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
diff --git a/mosquitto.conf b/mosquitto.conf
index 4e6904b7..49e2265e 100644
--- a/mosquitto.conf
+++ b/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
 
 
diff --git a/src/conf.c b/src/conf.c
index cf2d2339..ac470230 100644
--- a/src/conf.c
+++ b/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);
 }
 
diff --git a/src/linker-macosx.syms b/src/linker-macosx.syms
index 7c4b5ffd..c51c2f9b 100644
--- a/src/linker-macosx.syms
+++ b/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
diff --git a/src/linker.syms b/src/linker.syms
index 700eaf21..57d7c5cb 100644
--- a/src/linker.syms
+++ b/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;
diff --git a/src/plugin_public.c b/src/plugin_public.c
index f10c19a0..0da33858 100644
--- a/src/plugin_public.c
+++ b/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;
+}