From 7eb25df5269022a31586c52bc136e854c76f6ed0 Mon Sep 17 00:00:00 2001
From: Henning Fleddermann <henning.fleddermann@grandcentrix.net>
Date: Tue, 8 Feb 2022 01:48:32 +0100
Subject: [PATCH] net: lib: lwm2m: add lwm2m_engine_is_observed function

add helper function to check wether a specific lwm2m
path is observed

Signed-off-by: Henning Fleddermann <henning.fleddermann@grandcentrix.net>
---
 include/net/lwm2m.h                 | 13 +++++++++++++
 subsys/net/lib/lwm2m/lwm2m_engine.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/net/lwm2m.h b/include/net/lwm2m.h
index d174589f77b..7b362be16d9 100644
--- a/include/net/lwm2m.h
+++ b/include/net/lwm2m.h
@@ -1062,6 +1062,19 @@ int lwm2m_engine_update_service_period(k_work_handler_t service, uint32_t period
  */
 int lwm2m_update_device_service_period(uint32_t period_ms);
 
+/**
+ * @brief Check whether a path is observed
+ *
+ * @param[in] pathstr LwM2M path string to check, e.g. "3/0/1"
+ *
+ * @return true when there exists an observation of the same level
+ *         or lower as the given path, false if it doesn't or path is not a
+ *         valid LwM2M-path.
+ *         E.g. true if path refers to a resource and the parent object has an
+ *         observation, false for the inverse.
+ */
+bool lwm2m_engine_path_is_observed(const char *pathstr);
+
 /**
  * @brief Start the LwM2M engine
  *
diff --git a/subsys/net/lib/lwm2m/lwm2m_engine.c b/subsys/net/lib/lwm2m/lwm2m_engine.c
index f01afa4b0dc..0f004ade750 100644
--- a/subsys/net/lib/lwm2m/lwm2m_engine.c
+++ b/subsys/net/lib/lwm2m/lwm2m_engine.c
@@ -2105,6 +2105,35 @@ int lwm2m_engine_delete_res_inst(const char *pathstr)
 	return 0;
 }
 
+bool lwm2m_engine_path_is_observed(const char *pathstr)
+{
+	struct observe_node *obs;
+	struct lwm2m_obj_path path;
+	int ret;
+	int i;
+
+	ret = string_to_path(pathstr, &path, '/');
+	if (ret < 0) {
+		return false;
+	}
+
+	for (i = 0; i < sock_nfds; ++i) {
+		SYS_SLIST_FOR_EACH_CONTAINER(&sock_ctx[i]->observer, obs, node) {
+			if (obs->path.level <= path.level &&
+			    (obs->path.obj_id == path.obj_id &&
+			     (obs->path.level < LWM2M_PATH_LEVEL_OBJECT_INST ||
+			      (obs->path.obj_inst_id == path.obj_inst_id &&
+			       (obs->path.level < LWM2M_PATH_LEVEL_RESOURCE ||
+				(obs->path.res_id == path.res_id &&
+				 (obs->path.level < LWM2M_PATH_LEVEL_RESOURCE_INST ||
+				  obs->path.res_inst_id == path.res_inst_id))))))) {
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
 int lwm2m_engine_register_read_callback(const char *pathstr,
 					lwm2m_engine_get_data_cb_t cb)
 {