net: lwm2m: Add LwM2M 1.1 discovery support

LwM2M adds Resource Instance reporting in Discovery response, along with
attributes assinged at the Resource Instance level.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

subsys/net/lib/lwm2m/lwm2m_engine.c

@@ -3399,6 +3399,54 @@ move_forward:
 	return ret;
 }
 
+static int lwm2m_discover_add_res(struct lwm2m_message *msg,
+				  struct lwm2m_engine_obj_inst *obj_inst,
+				  struct lwm2m_engine_res *res)
+{
+	int ret;
+	struct lwm2m_obj_path path = {
+		.obj_id = obj_inst->obj->obj_id,
+		.obj_inst_id = obj_inst->obj_inst_id,
+		.res_id = res->res_id,
+		.level = LWM2M_PATH_LEVEL_RESOURCE,
+	};
+
+	ret = engine_put_corelink(&msg->out, &path);
+	if (ret < 0) {
+		return ret;
+	}
+
+	/* Report resource instances, if applicable. */
+	if (IS_ENABLED(CONFIG_LWM2M_VERSION_1_1) &&
+	    msg->path.level == LWM2M_PATH_LEVEL_RESOURCE &&
+	    res->multi_res_inst) {
+		for (int i = 0; i < res->res_inst_count; i++) {
+			struct lwm2m_engine_res_inst *res_inst =
+						&res->res_instances[i];
+
+			if (res_inst->res_inst_id ==
+				RES_INSTANCE_NOT_CREATED) {
+				continue;
+			}
+
+			path = (struct lwm2m_obj_path){
+				.obj_id = obj_inst->obj->obj_id,
+				.obj_inst_id = obj_inst->obj_inst_id,
+				.res_id = res->res_id,
+				.res_inst_id = res_inst->res_inst_id,
+				.level = LWM2M_PATH_LEVEL_RESOURCE_INST,
+			};
+
+			ret = engine_put_corelink(&msg->out, &path);
+			if (ret < 0) {
+				return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
 int lwm2m_discover_handler(struct lwm2m_message *msg, bool is_bootstrap)
 {
 	struct lwm2m_engine_obj *obj;
@@ -3515,14 +3563,8 @@ int lwm2m_discover_handler(struct lwm2m_message *msg, bool is_bootstrap)
 					continue;
 				}
 
-				struct lwm2m_obj_path path = {
+				ret = lwm2m_discover_add_res(msg, obj_inst,
-					.obj_id = obj_inst->obj->obj_id,
+							     &obj_inst->resources[i]);
-					.obj_inst_id = obj_inst->obj_inst_id,
-					.res_id = obj_inst->resources[i].res_id,
-					.level = LWM2M_PATH_LEVEL_RESOURCE,
-				};
-
-				ret = engine_put_corelink(&msg->out, &path);
 				if (ret < 0) {
 					return ret;
 				}
@@ -3646,6 +3688,24 @@ struct lwm2m_engine_res *lwm2m_engine_get_res(
 	return res;
 }
 
+struct lwm2m_engine_res_inst *lwm2m_engine_get_res_inst(
+					const struct lwm2m_obj_path *path)
+{
+	struct lwm2m_engine_res_inst *res_inst = NULL;
+	int ret;
+
+	if (path->level != LWM2M_PATH_LEVEL_RESOURCE_INST) {
+		return NULL;
+	}
+
+	ret = path_to_objs(path, NULL, NULL, NULL, &res_inst);
+	if (ret < 0) {
+		return NULL;
+	}
+
+	return res_inst;
+}
+
 bool lwm2m_engine_shall_report_obj_version(const struct lwm2m_engine_obj *obj)
 {
 	if (obj->is_core) {

subsys/net/lib/lwm2m/lwm2m_engine.h

@@ -87,6 +87,8 @@ struct lwm2m_engine_obj_inst *lwm2m_engine_get_obj_inst(
 					const struct lwm2m_obj_path *path);
 struct lwm2m_engine_res *lwm2m_engine_get_res(
 					const struct lwm2m_obj_path *path);
+struct lwm2m_engine_res_inst *lwm2m_engine_get_res_inst(
+					const struct lwm2m_obj_path *path);
 
 bool lwm2m_engine_shall_report_obj_version(const struct lwm2m_engine_obj *obj);
 

subsys/net/lib/lwm2m/lwm2m_rw_link_format.c

@@ -436,6 +436,55 @@ static int put_res_corelink(struct lwm2m_output_context *out,
 	return len;
 }
 
+static int put_res_inst_corelink(struct lwm2m_output_context *out,
+				 const struct lwm2m_obj_path *path,
+				 struct link_format_out_formatter_data *fd)
+{
+	char obj_buf[CORELINK_BUF_SIZE];
+	int len = 0;
+	int ret;
+
+	if (fd->mode != LINK_FORMAT_MODE_DISCOVERY) {
+		/* Report resources instances only in device management
+		 * discovery.
+		 */
+		return 0;
+	}
+
+	ret = snprintk(obj_buf, sizeof(obj_buf), "</%u/%u/%u/%u>", path->obj_id,
+		       path->obj_inst_id, path->res_id, path->res_inst_id);
+	if (ret < 0 || ret >= sizeof(obj_buf)) {
+		return -ENOMEM;
+	}
+
+	len += ret;
+
+	ret = buf_append(CPKT_BUF_WRITE(out->out_cpkt), obj_buf, len);
+	if (ret < 0) {
+		return ret;
+	}
+
+	/* Report resource instance attrs only when resource was specified. */
+	if (fd->request_level == LWM2M_PATH_LEVEL_RESOURCE) {
+		struct lwm2m_engine_res_inst *res_inst =
+					lwm2m_engine_get_res_inst(path);
+
+		if (res_inst == NULL) {
+			return -EINVAL;
+		}
+
+		ret = put_corelink_attributes(out, res_inst, obj_buf,
+					      sizeof(obj_buf));
+		if (ret < 0) {
+			return ret;
+		}
+
+		len += ret;
+	}
+
+	return len;
+}
+
 static int put_corelink(struct lwm2m_output_context *out,
 			const struct lwm2m_obj_path *path)
 {
@@ -487,6 +536,19 @@ static int put_corelink(struct lwm2m_output_context *out,
 		len += ret;
 		break;
 
+	case LWM2M_PATH_LEVEL_RESOURCE_INST:
+		if (IS_ENABLED(CONFIG_LWM2M_VERSION_1_1)) {
+			ret = put_res_inst_corelink(out, path, fd);
+			if (ret < 0) {
+				return ret;
+			}
+
+			len += ret;
+			break;
+		}
+
+		__fallthrough;
+
 	default:
 		LOG_ERR("Invalid corelink path level: %d", path->level);
 		return -EINVAL;