xref: /Zephyr-latest/subsys/net/lib/lwm2m/lwm2m_message_handling.c

/*
 * Copyright (c) 2017 Linaro Limited
 * Copyright (c) 2018-2019 Foundries.io
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/*
 * Uses some original concepts by:
 *         Joakim Eriksson <joakime@sics.se>
 *         Niclas Finne <nfi@sics.se>
 *         Joel Hoglund <joel@sics.se>
 */

#define LOG_MODULE_NAME net_lwm2m_message_handling
#define LOG_LEVEL	CONFIG_LWM2M_LOG_LEVEL

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(LOG_MODULE_NAME);

#include <ctype.h>
#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <zephyr/init.h>
#include <zephyr/net/http/parser_url.h>
#include <zephyr/net/lwm2m.h>
#include <zephyr/net/lwm2m_path.h>
#include <zephyr/net/net_ip.h>
#include <zephyr/net/socket.h>
#include <zephyr/sys/printk.h>
#include <zephyr/types.h>
#include <zephyr/sys/hash_function.h>

#if defined(CONFIG_LWM2M_DTLS_SUPPORT)
#include <zephyr/net/tls_credentials.h>
#endif
#if defined(CONFIG_DNS_RESOLVER)
#include <zephyr/net/dns_resolve.h>
#endif

#include "lwm2m_engine.h"
#include "lwm2m_object.h"
#include "lwm2m_obj_access_control.h"
#include "lwm2m_obj_server.h"
#include "lwm2m_obj_gateway.h"
#include "lwm2m_rw_link_format.h"
#include "lwm2m_rw_oma_tlv.h"
#include "lwm2m_rw_plain_text.h"
#include "lwm2m_rw_opaque.h"
#include "lwm2m_util.h"
#include "lwm2m_rd_client.h"
#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
#include "lwm2m_rw_senml_json.h"
#endif
#ifdef CONFIG_LWM2M_RW_JSON_SUPPORT
#include "lwm2m_rw_json.h"
#endif
#ifdef CONFIG_LWM2M_RW_CBOR_SUPPORT
#include "lwm2m_rw_cbor.h"
#endif
#ifdef CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT
#include "lwm2m_rw_senml_cbor.h"
#endif

/* TODO: figure out what's correct value */
#define TIMEOUT_BLOCKWISE_TRANSFER_MS (MSEC_PER_SEC * 30)

#define LWM2M_DP_CLIENT_URI "dp"

#define OUTPUT_CONTEXT_IN_USE_MARK (enum coap_block_size)(-1)

#ifdef CONFIG_ZTEST
#define STATIC
#else
#define STATIC static
#endif

/* Resources */

/* Shared set of in-flight LwM2M messages */
static struct lwm2m_message messages[CONFIG_LWM2M_ENGINE_MAX_MESSAGES];
static struct lwm2m_block_context block1_contexts[NUM_BLOCK1_CONTEXT];
static struct lwm2m_message *ongoing_block2_tx;

#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
/* we need 1 more buffer as the payload is encoded in that buffer first even if
 * block transfer is not required for the message.
 */
#define ENCODE_BUFFER_POOL_SIZE (CONFIG_LWM2M_NUM_OUTPUT_BLOCK_CONTEXT + 1)
/* buffers for serializing big message bodies */
K_MEM_SLAB_DEFINE_STATIC(body_encode_buffer_slab, CONFIG_LWM2M_COAP_ENCODE_BUFFER_SIZE,
			 ENCODE_BUFFER_POOL_SIZE, 4);
#endif

/* External resources */
sys_slist_t *lwm2m_engine_obj_list(void);

sys_slist_t *lwm2m_engine_obj_inst_list(void);

static int handle_request(struct coap_packet *request, struct lwm2m_message *msg);
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
STATIC int build_msg_block_for_send(struct lwm2m_message *msg, uint16_t block_num,
				    enum coap_block_size block_size);
struct coap_block_context *lwm2m_output_block_context(void);
#endif

/* block-wise transfer functions */

enum coap_block_size lwm2m_default_block_size(void)
{
	return coap_bytes_to_block_size(CONFIG_LWM2M_COAP_BLOCK_SIZE);
}

void lwm2m_clear_block_contexts(void)
{
	lwm2m_engine_lock();
	(void)memset(block1_contexts, 0, sizeof(block1_contexts));
	lwm2m_engine_unlock();
}

static int init_block_ctx(const struct lwm2m_obj_path *path, struct lwm2m_block_context **ctx)
{
	int i;
	int64_t timestamp;

	if (!path) {
		LOG_ERR("Null block ctx path");
		return -EFAULT;
	}

	lwm2m_engine_lock();

	*ctx = NULL;
	timestamp = k_uptime_get();
	for (i = 0; i < NUM_BLOCK1_CONTEXT; i++) {
		if (block1_contexts[i].path.level == 0U) {
			*ctx = &block1_contexts[i];
			break;
		}

		if (timestamp - block1_contexts[i].timestamp >
		    TIMEOUT_BLOCKWISE_TRANSFER_MS) {
			*ctx = &block1_contexts[i];
			/* TODO: notify application for block
			 * transfer timeout
			 */
			break;
		}
	}

	if (*ctx == NULL) {
		lwm2m_engine_unlock();
		LOG_ERR("Cannot find free block context");
		return -ENOMEM;
	}

	memcpy(&(*ctx)->path, path, sizeof(struct lwm2m_obj_path));
	coap_block_transfer_init(&(*ctx)->ctx, lwm2m_default_block_size(), 0);
	(*ctx)->timestamp = timestamp;
	(*ctx)->expected = 0;
	(*ctx)->last_block = false;
	memset(&(*ctx)->opaque, 0, sizeof((*ctx)->opaque));

	lwm2m_engine_unlock();

	return 0;
}

static int get_block_ctx(const struct lwm2m_obj_path *path, struct lwm2m_block_context **ctx)
{
	int i;

	if (!path) {
		LOG_ERR("Null block ctx path");
		return -EFAULT;
	}

	*ctx = NULL;

	lwm2m_engine_lock();

	for (i = 0; i < NUM_BLOCK1_CONTEXT; i++) {
		if (lwm2m_obj_path_equal(path, &block1_contexts[i].path)) {
			*ctx = &block1_contexts[i];
			/* refresh timestamp */
			(*ctx)->timestamp = k_uptime_get();
			break;
		}
	}

	lwm2m_engine_unlock();

	if (*ctx == NULL) {
		return -ENOENT;
	}

	return 0;
}

static void free_block_ctx(struct lwm2m_block_context *ctx)
{
	if (ctx == NULL) {
		return;
	}

	lwm2m_engine_lock();
	memset(&ctx->path, 0, sizeof(struct lwm2m_obj_path));
	lwm2m_engine_unlock();
}

#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
STATIC int request_output_block_ctx(struct coap_block_context **ctx)
{
	int ret = -ENOMEM;
	int i;

	*ctx = NULL;

	lwm2m_engine_lock();
	for (i = 0; i < NUM_OUTPUT_BLOCK_CONTEXT; i++) {
		if (lwm2m_output_block_context()[i].block_size == 0) {
			*ctx = &lwm2m_output_block_context()[i];
			(*ctx)->block_size = OUTPUT_CONTEXT_IN_USE_MARK;
			ret = 0;
			break;
		}
	}
	lwm2m_engine_unlock();

	return ret;
}

STATIC void release_output_block_ctx(struct coap_block_context **ctx)
{
	int i;

	if (ctx == NULL) {
		return;
	}

	lwm2m_engine_lock();
	for (i = 0; i < NUM_OUTPUT_BLOCK_CONTEXT; i++) {
		if (&lwm2m_output_block_context()[i] == *ctx) {
			lwm2m_output_block_context()[i].block_size = 0;
			*ctx = NULL;
		}
	}
	lwm2m_engine_unlock();
}


static inline void log_buffer_usage(void)
{
#if defined(CONFIG_LWM2M_LOG_ENCODE_BUFFER_ALLOCATIONS)
	LOG_PRINTK("body_encode_buffer_slab: free: %u, allocated: %u, max. allocated: %u\n",
		 k_mem_slab_num_free_get(&body_encode_buffer_slab),
		 k_mem_slab_num_used_get(&body_encode_buffer_slab),
		 k_mem_slab_max_used_get(&body_encode_buffer_slab));
#endif
}

static inline int request_body_encode_buffer(uint8_t **buffer)
{
	int r;

	r = k_mem_slab_alloc(&body_encode_buffer_slab, (void **)buffer, K_NO_WAIT);
	log_buffer_usage();
	return r;
}

static inline void release_body_encode_buffer(uint8_t **buffer)
{
	if (buffer && *buffer) {
		k_mem_slab_free(&body_encode_buffer_slab, (void *)*buffer);
		log_buffer_usage();
	}
}

STATIC int build_msg_block_for_send(struct lwm2m_message *msg, uint16_t block_num,
				    enum coap_block_size block_size)
{
	int ret;
	uint16_t payload_size;
	const uint16_t block_size_bytes = coap_block_size_to_bytes(block_size);
	uint16_t complete_payload_len;
	const uint8_t *complete_payload =
		coap_packet_get_payload(&msg->body_encode_buffer, &complete_payload_len);
	uint8_t token[COAP_TOKEN_MAX_LEN];
	uint8_t tkl;

	NET_ASSERT(msg->msg_data == msg->cpkt.data,
		   "big data buffer should not be in use for writing message");

	if (block_num * block_size_bytes >= complete_payload_len) {
		return -EINVAL;
	}

	if (block_num == 0) {
		/* Copy the header only for first block.
		 * For following blocks a new one is generated.
		 */
		ret = buf_append(CPKT_BUF_WRITE(&msg->cpkt), msg->body_encode_buffer.data,
				 msg->body_encode_buffer.hdr_len);
		if (ret < 0) {
			return ret;
		}
		msg->cpkt.hdr_len = msg->body_encode_buffer.hdr_len;
	} else {
		/* Keep user data between blocks */
		void *user_data = msg->reply ? msg->reply->user_data : NULL;

		/* reuse message for next block. Copy token from the new query to allow
		 * CoAP clients to use new token for every query of ongoing transaction
		 */
		lwm2m_reset_message(msg, false);
		if (msg->type == COAP_TYPE_ACK) {
			msg->mid = coap_header_get_id(msg->in.in_cpkt);
			tkl = coap_header_get_token(msg->in.in_cpkt, token);
		} else {
			msg->mid = coap_next_id();
			tkl = LWM2M_MSG_TOKEN_GENERATE_NEW;
		}
		msg->token = token;
		msg->tkl = tkl;
		ret = lwm2m_init_message(msg);
		if (ret < 0) {
			lwm2m_reset_message(msg, true);
			LOG_ERR("Unable to init lwm2m message for next block!");
			return ret;
		}
		if (msg->reply) {
			msg->reply->user_data = user_data;
		}
	}

	/* copy the options */
	ret = buf_append(CPKT_BUF_WRITE(&msg->cpkt),
			 msg->body_encode_buffer.data + msg->body_encode_buffer.hdr_len,
			 msg->body_encode_buffer.opt_len);
	if (ret < 0) {
		return ret;
	}
	msg->cpkt.opt_len = msg->body_encode_buffer.opt_len;

	msg->cpkt.delta = msg->body_encode_buffer.delta;

	if (block_num == 0) {
		ret = request_output_block_ctx(&msg->out.block_ctx);
		if (ret < 0) {
			LOG_ERR("coap packet init error: no output block context available");
			return ret;
		}
		ret = coap_block_transfer_init(msg->out.block_ctx, block_size,
					       complete_payload_len);
		if (ret < 0) {
			return ret;
		}
		if (msg->type == COAP_TYPE_ACK) {
			ongoing_block2_tx = msg;
		}
		msg->block_send = true;
	} else {
		/*  update block context */
		msg->out.block_ctx->current = block_num * block_size_bytes;
		msg->out.block_ctx->block_size = block_size;
	}

	ret = coap_append_descriptive_block_option(&msg->cpkt, msg->out.block_ctx);
	if (ret < 0) {
		return ret;
	}

	ret = coap_packet_append_payload_marker(&msg->cpkt);
	if (ret < 0) {
		return ret;
	}

	payload_size = MIN(complete_payload_len - block_num * block_size_bytes, block_size_bytes);
	ret = buf_append(CPKT_BUF_WRITE(&msg->cpkt),
			 complete_payload + (block_num * block_size_bytes), payload_size);
	if (ret < 0) {
		return ret;
	}

	return 0;
}

STATIC int prepare_msg_for_send(struct lwm2m_message *msg)
{
	int ret;
	uint16_t len;
	const uint8_t *payload;

	/* save the big buffer for later use (splitting blocks) */
	msg->body_encode_buffer = msg->cpkt;

	/* set the default (small) buffer for sending blocks */
	msg->cpkt.data = msg->msg_data;
	msg->cpkt.offset = 0;
	msg->cpkt.max_len = MAX_PACKET_SIZE;

	payload = coap_packet_get_payload(&msg->body_encode_buffer, &len);
	if (len <= CONFIG_LWM2M_COAP_MAX_MSG_SIZE) {

		/* copy the packet */
		ret = buf_append(CPKT_BUF_WRITE(&msg->cpkt), msg->body_encode_buffer.data,
				 msg->body_encode_buffer.offset);
		if (ret != 0) {
			return ret;
		}

		msg->cpkt.hdr_len = msg->body_encode_buffer.hdr_len;
		msg->cpkt.opt_len = msg->body_encode_buffer.opt_len;

		/* clear big buffer */
		release_body_encode_buffer(&msg->body_encode_buffer.data);
		msg->body_encode_buffer.data = NULL;

		NET_ASSERT(msg->out.block_ctx == NULL, "Expecting to have no context to release");
	} else {
		/* Before splitting the content, append Etag option to protect the integrity of
		 * the payload.
		 */
		if (IS_ENABLED(CONFIG_SYS_HASH_FUNC32)) {
			uint32_t hash = sys_hash32(payload, len);

			coap_packet_append_option(&msg->body_encode_buffer, COAP_OPTION_ETAG,
						  (const uint8_t *)&hash, sizeof(hash));
		}

		ret = build_msg_block_for_send(msg, 0, lwm2m_default_block_size());
		if (ret != 0) {
			return ret;
		}
	}

	return 0;
}

#endif

void lwm2m_engine_context_close(struct lwm2m_ctx *client_ctx)
{
	struct lwm2m_message *msg;
	sys_snode_t *obs_node;
	struct observe_node *obs;
	size_t i;

	lwm2m_client_lock(client_ctx);

	/* Remove observes for this context */
	while (!sys_slist_is_empty(&client_ctx->observer)) {
		obs_node = sys_slist_get_not_empty(&client_ctx->observer);
		obs = SYS_SLIST_CONTAINER(obs_node, obs, node);
		remove_observer_from_list(client_ctx, NULL, obs);
	}

	for (i = 0, msg = messages; i < ARRAY_SIZE(messages); i++, msg++) {
		if (msg->ctx == client_ctx) {
			if (msg->send_status_cb) {
				msg->send_status_cb(LWM2M_SEND_STATUS_FAILURE);
			}
			lwm2m_reset_message(msg, true);
		}
	}

	coap_pendings_clear(client_ctx->pendings, ARRAY_SIZE(client_ctx->pendings));
	coap_replies_clear(client_ctx->replies, ARRAY_SIZE(client_ctx->replies));

	client_ctx->connection_suspended = false;
#if defined(CONFIG_LWM2M_QUEUE_MODE_ENABLED)
	client_ctx->buffer_client_messages = true;
#endif
	lwm2m_client_unlock(client_ctx);
}

void lwm2m_engine_context_init(struct lwm2m_ctx *client_ctx)
{
	sys_slist_init(&client_ctx->pending_sends);
	sys_slist_init(&client_ctx->observer);
	client_ctx->connection_suspended = false;
#if defined(CONFIG_LWM2M_QUEUE_MODE_ENABLED)
	client_ctx->buffer_client_messages = true;
	sys_slist_init(&client_ctx->queued_messages);
#endif
	k_mutex_init(&client_ctx->lock);
}
/* utility functions */

int coap_options_to_path(struct coap_option *opt, int options_count,
				struct lwm2m_obj_path *path)
{
	uint16_t len,
		*id[4] = {&path->obj_id, &path->obj_inst_id, &path->res_id, &path->res_inst_id};

	path->level = options_count;

	for (int i = 0; i < options_count; i++) {
		*id[i] = lwm2m_atou16(opt[i].value, opt[i].len, &len);
		if (len == 0U || opt[i].len != len) {
			path->level = i;
			break;
		}
	}

	return options_count == path->level ? 0 : -EINVAL;
}

struct lwm2m_message *find_msg(struct coap_pending *pending, struct coap_reply *reply)
{
	size_t i;
	struct lwm2m_message *msg;

	if (!pending && !reply) {
		return NULL;
	}

	msg = lwm2m_get_ongoing_rd_msg();
	if (msg) {
		if (pending != NULL && msg->pending == pending) {
			return msg;
		}

		if (reply != NULL && msg->reply == reply) {
			return msg;
		}
	}

	for (i = 0; i < CONFIG_LWM2M_ENGINE_MAX_MESSAGES; i++) {
		if (pending != NULL && messages[i].ctx && messages[i].pending == pending) {
			return &messages[i];
		}

		if (reply != NULL && messages[i].ctx && messages[i].reply == reply) {
			return &messages[i];
		}
	}

	return NULL;
}

struct lwm2m_message *lwm2m_get_message(struct lwm2m_ctx *client_ctx)
{
	struct lwm2m_message *msg = NULL;
	size_t i;

	lwm2m_engine_lock();

	for (i = 0; i < CONFIG_LWM2M_ENGINE_MAX_MESSAGES; i++) {
		if (!messages[i].ctx) {
			messages[i].ctx = client_ctx;
			msg = &messages[i];
			break;
		}
	}

	lwm2m_engine_unlock();

	return msg;
}

void lm2m_message_clear_allocations(struct lwm2m_message *msg)
{
	if (msg->pending) {
		coap_pending_clear(msg->pending);
		msg->pending = NULL;
	}

	if (msg->reply) {
		/* make sure we want to clear the reply */
		coap_reply_clear(msg->reply);
		msg->reply = NULL;
	}
}

void lwm2m_reset_message(struct lwm2m_message *msg, bool release)
{
	if (!msg) {
		return;
	}

	lm2m_message_clear_allocations(msg);

	if (msg->ctx) {
		lwm2m_client_lock(msg->ctx);
		sys_slist_find_and_remove(&msg->ctx->pending_sends, &msg->node);
#if defined(CONFIG_LWM2M_QUEUE_MODE_ENABLED)
		sys_slist_find_and_remove(&msg->ctx->queued_messages, &msg->node);
#endif
		lwm2m_client_unlock(msg->ctx);
	}

	if (release) {
		lwm2m_engine_lock();
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
		release_output_block_ctx(&msg->out.block_ctx);
		release_body_encode_buffer(&msg->body_encode_buffer.data);
#endif
		(void)memset(msg, 0, sizeof(*msg));
		lwm2m_engine_unlock();
	} else {
		msg->message_timeout_cb = NULL;
		(void)memset(&msg->cpkt, 0, sizeof(msg->cpkt));
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
		msg->cache_info = NULL;
#endif
	}
}

int lwm2m_init_message(struct lwm2m_message *msg)
{
	uint8_t tokenlen = 0U;
	uint8_t *token = NULL;
	uint8_t *body_data;
	uint16_t body_data_max_len;
	int r = 0;

	if (!msg || !msg->ctx) {
		LOG_ERR("LwM2M message is invalid.");
		return -EINVAL;
	}

	if (msg->tkl == LWM2M_MSG_TOKEN_GENERATE_NEW) {
		tokenlen = 8U;
		token = coap_next_token();
	} else if (msg->token && msg->tkl != 0) {
		tokenlen = msg->tkl;
		token = msg->token;
	}

	lm2m_message_clear_allocations(msg);
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	msg->cache_info = NULL;
#endif
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
	if (msg->body_encode_buffer.data == NULL) {
		/* Get new big buffer for serializing the message */
		r = request_body_encode_buffer(&body_data);
		if (r < 0) {
			LOG_ERR("coap packet init error: no msg buffer available");
			goto cleanup;
		}
		/*  in case of failure the buffer is released with this pointer */
		msg->body_encode_buffer.data = body_data;
		body_data_max_len = CONFIG_LWM2M_COAP_ENCODE_BUFFER_SIZE;
	} else {
		/* We have already a big buffer. The message is reused for each block. */
		body_data = msg->msg_data;
		body_data_max_len = sizeof(msg->msg_data);
	}
#else
	body_data = msg->msg_data;
	body_data_max_len = sizeof(msg->msg_data);
#endif
	r = coap_packet_init(&msg->cpkt, body_data, body_data_max_len, COAP_VERSION_1, msg->type,
			     tokenlen, token, msg->code, msg->mid);
	if (r < 0) {
		LOG_ERR("coap packet init error (err:%d)", r);
		goto cleanup;
	}

	/* only TYPE_CON messages need pending tracking / reply handling */
	if (msg->type != COAP_TYPE_CON) {
		return 0;
	}

	lwm2m_client_lock(msg->ctx);

	msg->pending = coap_pending_next_unused(msg->ctx->pendings, ARRAY_SIZE(msg->ctx->pendings));
	if (!msg->pending) {
		LOG_ERR("Unable to find a free pending to track "
			"retransmissions.");
		r = -ENOMEM;
		goto cleanup_unlock;
	}

	r = coap_pending_init(msg->pending, &msg->cpkt, &msg->ctx->remote_addr, NULL);
	if (r < 0) {
		LOG_ERR("Unable to initialize a pending "
			"retransmission (err:%d).",
			r);
		goto cleanup_unlock;
	}

	if (msg->reply_cb) {
		msg->reply =
			coap_reply_next_unused(msg->ctx->replies, ARRAY_SIZE(msg->ctx->replies));
		if (!msg->reply) {
			LOG_ERR("No resources for waiting for replies.");
			r = -ENOMEM;
			goto cleanup_unlock;
		}

		coap_reply_clear(msg->reply);
		coap_reply_init(msg->reply, &msg->cpkt);
		msg->reply->reply = msg->reply_cb;
	}

	lwm2m_client_unlock(msg->ctx);

	return 0;

cleanup_unlock:
	lwm2m_client_unlock(msg->ctx);
cleanup:
	lwm2m_reset_message(msg, true);

	return r;
}

int lwm2m_send_message_async(struct lwm2m_message *msg)
{
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)

	/* check if body encode buffer is in use => packet is not yet prepared for send */
	if (msg->body_encode_buffer.data == msg->cpkt.data) {
		int ret = prepare_msg_for_send(msg);

		if (ret) {
			lwm2m_reset_message(msg, true);
			return ret;
		}
	}
#endif
	if (IS_ENABLED(CONFIG_LWM2M_QUEUE_MODE_ENABLED)) {
		int ret = lwm2m_rd_client_connection_resume(msg->ctx);

		if (ret && ret != -EPERM) {
			lwm2m_reset_message(msg, true);
			return ret;
		}
	}

	lwm2m_client_lock(msg->ctx);
	sys_slist_append(&msg->ctx->pending_sends, &msg->node);
	lwm2m_client_unlock(msg->ctx);

	if (IS_ENABLED(CONFIG_LWM2M_QUEUE_MODE_ENABLED)) {
		engine_update_tx_time();
	}
	lwm2m_engine_wake_up();
	return 0;
}

int lwm2m_information_interface_send(struct lwm2m_message *msg)
{
#if defined(CONFIG_LWM2M_QUEUE_MODE_ENABLED)
	int ret;

	ret = lwm2m_rd_client_connection_resume(msg->ctx);
	if (ret) {
		lwm2m_reset_message(msg, true);
		return ret;
	}

	if (IS_ENABLED(CONFIG_LWM2M_QUEUE_MODE_NO_MSG_BUFFERING)) {
		lwm2m_client_lock(msg->ctx);
		sys_slist_append(&msg->ctx->pending_sends, &msg->node);
		lwm2m_client_unlock(msg->ctx);
		lwm2m_engine_wake_up();
		lwm2m_engine_connection_resume(msg->ctx);
		return 0;
	}

	if (msg->ctx->buffer_client_messages) {
		lwm2m_client_lock(msg->ctx);
		sys_slist_append(&msg->ctx->queued_messages, &msg->node);
		lwm2m_client_unlock(msg->ctx);
		lwm2m_engine_wake_up();
		return 0;
	}
#endif

	return lwm2m_send_message_async(msg);
}

int lwm2m_send_empty_ack(struct lwm2m_ctx *client_ctx, uint16_t mid)
{
	struct lwm2m_message *msg;
	int ret;

	msg = lwm2m_get_message(client_ctx);
	if (!msg) {
		LOG_ERR("Unable to get a lwm2m message!");
		return -ENOMEM;
	}

	msg->type = COAP_TYPE_ACK;
	msg->code = COAP_CODE_EMPTY;
	msg->mid = mid;

	ret = lwm2m_init_message(msg);
	if (ret) {
		goto cleanup;
	}

	ret = zsock_send(client_ctx->sock_fd, msg->cpkt.data, msg->cpkt.offset, 0);

	if (ret < 0) {
		LOG_ERR("Failed to send packet, err %d", errno);
		ret = -errno;
	}

cleanup:
	lwm2m_reset_message(msg, true);
	return ret;
}

void lwm2m_acknowledge(struct lwm2m_ctx *client_ctx)
{
	struct lwm2m_message *request;

	if (client_ctx == NULL || client_ctx->processed_req == NULL) {
		return;
	}

	request = (struct lwm2m_message *)client_ctx->processed_req;

	if (request->acknowledged) {
		return;
	}

	if (lwm2m_send_empty_ack(client_ctx, request->mid) < 0) {
		return;
	}

	request->acknowledged = true;
}

int lwm2m_register_payload_handler(struct lwm2m_message *msg)
{
	struct lwm2m_engine_obj *obj;
	struct lwm2m_engine_obj_inst *obj_inst;
	int ret;
	sys_slist_t *engine_obj_list = lwm2m_engine_obj_list();
	sys_slist_t *engine_obj_inst_list = lwm2m_engine_obj_inst_list();

	ret = engine_put_begin(&msg->out, NULL);
	if (ret < 0) {
		return ret;
	}

	SYS_SLIST_FOR_EACH_CONTAINER(engine_obj_list, obj, node) {
		/* Security obj MUST NOT be part of registration message */
		if (obj->obj_id == LWM2M_OBJECT_SECURITY_ID) {
			continue;
		}

		/* Only report <OBJ_ID> when no instance available or it's
		 * needed to report object version.
		 */
		if (obj->instance_count == 0U || lwm2m_engine_shall_report_obj_version(obj)) {
			ret = engine_put_corelink(&msg->out, &LWM2M_OBJ(obj->obj_id));
			if (ret < 0) {
				return ret;
			}

			if (obj->instance_count == 0U) {
				continue;
			}
		}

		SYS_SLIST_FOR_EACH_CONTAINER(engine_obj_inst_list, obj_inst, node) {
			if (obj_inst->obj->obj_id == obj->obj_id) {
				ret = engine_put_corelink(
					&msg->out,
					&LWM2M_OBJ(obj_inst->obj->obj_id, obj_inst->obj_inst_id));
				if (ret < 0) {
					return ret;
				}
			}
		}
	}

	return 0;
}

static int select_writer(struct lwm2m_output_context *out, uint16_t accept)
{
	switch (accept) {

	case LWM2M_FORMAT_APP_LINK_FORMAT:
		out->writer = &link_format_writer;
		break;

	case LWM2M_FORMAT_APP_OCTET_STREAM:
		out->writer = &opaque_writer;
		break;

	case LWM2M_FORMAT_PLAIN_TEXT:
	case LWM2M_FORMAT_OMA_PLAIN_TEXT:
		out->writer = &plain_text_writer;
		break;

#ifdef CONFIG_LWM2M_RW_OMA_TLV_SUPPORT
	case LWM2M_FORMAT_OMA_TLV:
	case LWM2M_FORMAT_OMA_OLD_TLV:
		out->writer = &oma_tlv_writer;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_JSON_SUPPORT
	case LWM2M_FORMAT_OMA_JSON:
	case LWM2M_FORMAT_OMA_OLD_JSON:
		out->writer = &json_writer;
		break;
#endif

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		out->writer = &senml_json_writer;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_CBOR:
		out->writer = &cbor_writer;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_SENML_CBOR:
		out->writer = &senml_cbor_writer;
		break;
#endif

	default:
		LOG_WRN("Unknown content type %u", accept);
		return -ECANCELED;
	}

	return 0;
}

static int select_reader(struct lwm2m_input_context *in, uint16_t format)
{
	switch (format) {

	case LWM2M_FORMAT_APP_OCTET_STREAM:
		in->reader = &opaque_reader;
		break;

	case LWM2M_FORMAT_PLAIN_TEXT:
	case LWM2M_FORMAT_OMA_PLAIN_TEXT:
		in->reader = &plain_text_reader;
		break;

#ifdef CONFIG_LWM2M_RW_OMA_TLV_SUPPORT
	case LWM2M_FORMAT_OMA_TLV:
	case LWM2M_FORMAT_OMA_OLD_TLV:
		in->reader = &oma_tlv_reader;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_JSON_SUPPORT
	case LWM2M_FORMAT_OMA_JSON:
	case LWM2M_FORMAT_OMA_OLD_JSON:
		in->reader = &json_reader;
		break;
#endif

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		in->reader = &senml_json_reader;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_CBOR:
		in->reader = &cbor_reader;
		break;
#endif

#ifdef CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_SENML_CBOR:
		in->reader = &senml_cbor_reader;
		break;
#endif
	default:
		LOG_WRN("Unknown content type %u", format);
		return -ENOMSG;
	}

	return 0;
}

/* generic data handlers */
static int lwm2m_write_handler_opaque(struct lwm2m_engine_obj_inst *obj_inst,
				      struct lwm2m_engine_res *res,
				      struct lwm2m_engine_res_inst *res_inst,
				      struct lwm2m_message *msg, void *data_ptr, size_t data_len)
{
	int len = 1;
	bool last_pkt_block = false;
	int ret = 0;
	bool last_block = true;
	struct lwm2m_opaque_context opaque_ctx = {0};
	void *write_buf;
	size_t write_buf_len;
	int written = 0;

	if (msg->in.block_ctx != NULL) {
		last_block = msg->in.block_ctx->last_block;

		/* Restore the opaque context from the block context, if used. */
		opaque_ctx = msg->in.block_ctx->opaque;
	}

#if CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0
	/* In case validation callback is present, write data to the temporary
	 * buffer first, for validation. Otherwise, write to the data buffer
	 * directly.
	 */
	if (res->validate_cb) {
		write_buf = msg->ctx->validate_buf;
		write_buf_len = sizeof(msg->ctx->validate_buf);
	} else
#endif /* CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0 */
	{
		write_buf = data_ptr;
		write_buf_len = data_len;
	}

	while (!last_pkt_block && len > 0) {
		len = engine_get_opaque(&msg->in, write_buf, MIN(data_len, write_buf_len),
					&opaque_ctx, &last_pkt_block);
		if (len <= 0) {
			break;
		}

#if CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0
		if (res->validate_cb) {
			ret = res->validate_cb(obj_inst->obj_inst_id, res->res_id,
					       res_inst->res_inst_id, write_buf, len,
					       last_pkt_block && last_block, opaque_ctx.len,
					       opaque_ctx.offset);
			if (ret < 0) {
				/* -EEXIST will generate Bad Request LWM2M response. */
				return -EEXIST;
			}

			memcpy(data_ptr, write_buf, len);
		}
#endif /* CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0 */

		if (res->post_write_cb) {
			ret = res->post_write_cb(
				obj_inst->obj_inst_id, res->res_id, res_inst->res_inst_id, data_ptr,
				len, last_pkt_block && last_block, opaque_ctx.len,
				opaque_ctx.offset);
			if (ret < 0) {
				return ret;
			}
		}
		if (msg->in.block_ctx && !last_pkt_block) {
			msg->in.block_ctx->ctx.current += len;
		}
		opaque_ctx.offset += len;
		written += len;
	}

	if (msg->in.block_ctx != NULL) {
		msg->in.block_ctx->opaque = opaque_ctx;
	}

	return (len < 0 ? len : written);
}
/* This function is exposed for the content format writers */
int lwm2m_write_handler(struct lwm2m_engine_obj_inst *obj_inst, struct lwm2m_engine_res *res,
			struct lwm2m_engine_res_inst *res_inst,
			struct lwm2m_engine_obj_field *obj_field, struct lwm2m_message *msg)
{
	void *data_ptr = NULL;
	size_t data_len = 0;
	size_t len = 0;
	size_t total_size = 0;
	int64_t temp64 = 0;
	int32_t temp32 = 0;
	time_t temp_time = 0;
	int ret = 0;
	bool last_block = true;
	void *write_buf;
	size_t write_buf_len;
	size_t offset = 0;

	if (!obj_inst || !res || !res_inst || !obj_field || !msg) {
		return -EINVAL;
	}

	if (LWM2M_HAS_RES_FLAG(res_inst, LWM2M_RES_DATA_FLAG_RO)) {
		return -EACCES;
	}

	/* setup initial data elements */
	data_ptr = res_inst->data_ptr;
	data_len = res_inst->max_data_len;

	/* allow user to override data elements via callback */
	if (res->pre_write_cb) {
		data_ptr = res->pre_write_cb(obj_inst->obj_inst_id, res->res_id,
					     res_inst->res_inst_id, &data_len);
	}

	if (msg->in.block_ctx != NULL) {
		/* Get block_ctx for total_size (might be zero) */
		total_size = msg->in.block_ctx->ctx.total_size;
		offset = msg->in.block_ctx->opaque.offset;

		LOG_DBG("BLOCK1: total:%zu current:%zu"
			" last:%u",
			msg->in.block_ctx->ctx.total_size, msg->in.block_ctx->ctx.current,
			msg->in.block_ctx->last_block);
	}

	/* Only when post_write callback is set, we allow larger content than our
	 * buffer sizes. The post-write callback handles assembling of the data
	 */
	if (!res->post_write_cb) {
		if ((offset > 0 && offset >= data_len) || total_size > data_len) {
			return -ENOMEM;
		}
		data_len -= offset;
		data_ptr = (uint8_t *)data_ptr + offset;
	}

#if CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0
	/* In case validation callback is present, write data to the temporary
	 * buffer first, for validation. Otherwise, write to the data buffer
	 * directly.
	 */
	if (res->validate_cb) {
		write_buf = msg->ctx->validate_buf;
		write_buf_len = sizeof(msg->ctx->validate_buf);
	} else
#endif /* CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0 */
	{
		write_buf = data_ptr;
		write_buf_len = data_len;
	}

	if (data_ptr && data_len > 0) {
		switch (obj_field->data_type) {

		case LWM2M_RES_TYPE_OPAQUE:
			ret = lwm2m_write_handler_opaque(obj_inst, res, res_inst, msg, data_ptr,
							 data_len);
			len = ret;
			break;

		case LWM2M_RES_TYPE_STRING:
			ret = engine_get_string(&msg->in, write_buf, write_buf_len);
			if (ret < 0) {
				break;
			}

			len = strlen((char *)write_buf) + 1;
			break;

		case LWM2M_RES_TYPE_TIME:
			ret = engine_get_time(&msg->in, &temp_time);
			if (ret < 0) {
				break;
			}

			if (data_len == sizeof(time_t)) {
				*(time_t *)write_buf = temp_time;
				len = sizeof(time_t);
			} else if (data_len == sizeof(uint32_t)) {
				*(uint32_t *)write_buf = (uint32_t)temp_time;
				len = sizeof(uint32_t);
			} else {
				LOG_ERR("Time resource buf len not supported %zu", data_len);
				ret = -EINVAL;
			}

			break;

		case LWM2M_RES_TYPE_U32:
			ret = engine_get_s64(&msg->in, &temp64);
			if (ret < 0) {
				break;
			}

			*(uint32_t *)write_buf = temp64;
			len = 4;
			break;

		case LWM2M_RES_TYPE_U16:
			ret = engine_get_s32(&msg->in, &temp32);
			if (ret < 0) {
				break;
			}

			*(uint16_t *)write_buf = temp32;
			len = 2;
			break;

		case LWM2M_RES_TYPE_U8:
			ret = engine_get_s32(&msg->in, &temp32);
			if (ret < 0) {
				break;
			}

			*(uint8_t *)write_buf = temp32;
			len = 1;
			break;

		case LWM2M_RES_TYPE_S64:
			ret = engine_get_s64(&msg->in, (int64_t *)write_buf);
			len = 8;
			break;

		case LWM2M_RES_TYPE_S32:
			ret = engine_get_s32(&msg->in, (int32_t *)write_buf);
			len = 4;
			break;

		case LWM2M_RES_TYPE_S16:
			ret = engine_get_s32(&msg->in, &temp32);
			if (ret < 0) {
				break;
			}

			*(int16_t *)write_buf = temp32;
			len = 2;
			break;

		case LWM2M_RES_TYPE_S8:
			ret = engine_get_s32(&msg->in, &temp32);
			if (ret < 0) {
				break;
			}

			*(int8_t *)write_buf = temp32;
			len = 1;
			break;

		case LWM2M_RES_TYPE_BOOL:
			ret = engine_get_bool(&msg->in, (bool *)write_buf);
			len = 1;
			break;

		case LWM2M_RES_TYPE_FLOAT:
			ret = engine_get_float(&msg->in, (double *)write_buf);
			len = sizeof(double);
			break;

		case LWM2M_RES_TYPE_OBJLNK:
			ret = engine_get_objlnk(&msg->in, (struct lwm2m_objlnk *)write_buf);
			len = sizeof(struct lwm2m_objlnk);
			break;

		default:
			LOG_ERR("unknown obj data_type %d", obj_field->data_type);
			return -EINVAL;
		}

		if (ret < 0) {
			return ret;
		}
	} else {
		return -ENOENT;
	}

	if (obj_field->data_type != LWM2M_RES_TYPE_OPAQUE) {

#if CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0
		if (res->validate_cb) {
			ret = res->validate_cb(obj_inst->obj_inst_id, res->res_id,
					       res_inst->res_inst_id, write_buf, len, last_block,
					       total_size, offset);
			if (ret < 0) {
				/* -EEXIST will generate Bad Request LWM2M response. */
				return -EEXIST;
			}

			if (len > data_len) {
				LOG_ERR("Received data won't fit into provided "
					"buffer");
				return -ENOMEM;
			}

			if (obj_field->data_type == LWM2M_RES_TYPE_STRING) {
				strncpy(data_ptr, write_buf, data_len);
			} else {
				memcpy(data_ptr, write_buf, len);
			}
		}
#endif /* CONFIG_LWM2M_ENGINE_VALIDATION_BUFFER_SIZE > 0 */

		if (res->post_write_cb) {
			ret = res->post_write_cb(obj_inst->obj_inst_id, res->res_id,
						 res_inst->res_inst_id, data_ptr, len, last_block,
						 total_size, offset);
		}
	}

	if (!res->post_write_cb) {
		len += offset;
	}

	res_inst->data_len = len;

	if (LWM2M_HAS_PERM(obj_field, LWM2M_PERM_R)) {
		lwm2m_notify_observer_path(&msg->path);
	}

	return ret;
}

static int lwm2m_read_resource_data(struct lwm2m_message *msg, void *data_ptr, size_t data_len,
			       uint8_t data_type)
{
	int ret;

	switch (data_type) {

	case LWM2M_RES_TYPE_OPAQUE:
		ret = engine_put_opaque(&msg->out, &msg->path, (uint8_t *)data_ptr, data_len);
		break;

	case LWM2M_RES_TYPE_STRING:
		if (data_len) {
			data_len -= 1; /* Remove the '\0' */
		}
		ret = engine_put_string(&msg->out, &msg->path, (uint8_t *)data_ptr, data_len);
		break;

	case LWM2M_RES_TYPE_U32:
		ret = engine_put_s64(&msg->out, &msg->path, (int64_t) *(uint32_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_U16:
		ret = engine_put_s32(&msg->out, &msg->path, (int32_t) *(uint16_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_U8:
		ret = engine_put_s16(&msg->out, &msg->path, (int16_t) *(uint8_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_S64:
		ret = engine_put_s64(&msg->out, &msg->path, *(int64_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_S32:
		ret = engine_put_s32(&msg->out, &msg->path, *(int32_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_S16:
		ret = engine_put_s16(&msg->out, &msg->path, *(int16_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_S8:
		ret = engine_put_s8(&msg->out, &msg->path, *(int8_t *)data_ptr);
		break;

	case LWM2M_RES_TYPE_TIME:
		if (data_len == sizeof(time_t)) {
			ret = engine_put_time(&msg->out, &msg->path, *(time_t *)data_ptr);
		} else if (data_len == sizeof(uint32_t)) {
			ret = engine_put_time(&msg->out, &msg->path,
					      (time_t) *((uint32_t *)data_ptr));
		} else {
			LOG_ERR("Resource time length not supported %zu", data_len);
			ret = -EINVAL;
		}

		break;

	case LWM2M_RES_TYPE_BOOL:
		ret = engine_put_bool(&msg->out, &msg->path, *(bool *)data_ptr);
		break;

	case LWM2M_RES_TYPE_FLOAT:
		ret = engine_put_float(&msg->out, &msg->path, (double *)data_ptr);
		break;

	case LWM2M_RES_TYPE_OBJLNK:
		ret = engine_put_objlnk(&msg->out, &msg->path, (struct lwm2m_objlnk *)data_ptr);
		break;

	default:
		LOG_ERR("unknown obj data_type %d", data_type);
		ret = -EINVAL;
	}

	return ret;
}

static int lwm2m_read_cached_data(struct lwm2m_message *msg,
				  struct lwm2m_time_series_resource *cached_data, uint8_t data_type)
{
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	int ret;
	struct lwm2m_time_series_elem buf;
	struct lwm2m_cache_read_entry *read_info;
	size_t  length = lwm2m_cache_size(cached_data);

	LOG_DBG("Read cached data size %u", length);

	if (msg->cache_info) {
		read_info = &msg->cache_info->read_info[msg->cache_info->entry_size];
		/* Store original timeseries ring buffer get states for failure handling */
		read_info->cache_data = cached_data;
		read_info->original_rb_get = cached_data->rb.get;
		msg->cache_info->entry_size++;
		if (msg->cache_info->entry_limit) {
			length = MIN(length, msg->cache_info->entry_limit);
			LOG_DBG("Limited number of read %d", length);
		}
	}

	for (size_t i = 0; i < length; i++) {

		if (!lwm2m_cache_read(cached_data, &buf)) {
			LOG_ERR("Read operation fail");
			return -ENOMEM;
		}

		ret = engine_put_timestamp(&msg->out, buf.t);
		if (ret) {
			return ret;
		}

		switch (data_type) {

		case LWM2M_RES_TYPE_U32:
			ret = engine_put_s64(&msg->out, &msg->path, (int64_t)buf.u32);
			break;

		case LWM2M_RES_TYPE_U16:
			ret = engine_put_s32(&msg->out, &msg->path, (int32_t)buf.u16);
			break;

		case LWM2M_RES_TYPE_U8:
			ret = engine_put_s16(&msg->out, &msg->path, (int16_t)buf.u8);
			break;

		case LWM2M_RES_TYPE_S64:
			ret = engine_put_s64(&msg->out, &msg->path, buf.i64);
			break;

		case LWM2M_RES_TYPE_S32:
			ret = engine_put_s32(&msg->out, &msg->path, buf.i32);
			break;

		case LWM2M_RES_TYPE_S16:
			ret = engine_put_s16(&msg->out, &msg->path, buf.i16);
			break;

		case LWM2M_RES_TYPE_S8:
			ret = engine_put_s8(&msg->out, &msg->path, buf.i8);
			break;

		case LWM2M_RES_TYPE_BOOL:
			ret = engine_put_bool(&msg->out, &msg->path, buf.b);
			break;

		case LWM2M_RES_TYPE_TIME:
			ret = engine_put_time(&msg->out, &msg->path, buf.time);
			break;

		default:
			ret = engine_put_float(&msg->out, &msg->path, &buf.f);
			break;

		}

		/* Validate that we really read some data */
		if (ret < 0) {
			LOG_ERR("Read operation fail");
			return -ENOMEM;
		}
	}

	return 0;
#else
	return -ENOTSUP;
#endif
}

static bool lwm2m_accept_timeseries_read(struct lwm2m_message *msg,
					 struct lwm2m_time_series_resource *cached_data)
{
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	if (cached_data && msg->cache_info && lwm2m_cache_size(cached_data) &&
	    msg->out.writer->put_data_timestamp) {
		return true;
	}
#endif
	return false;
}

static int lwm2m_read_handler(struct lwm2m_engine_obj_inst *obj_inst, struct lwm2m_engine_res *res,
			      struct lwm2m_engine_obj_field *obj_field, struct lwm2m_message *msg)
{
	int i, loop_max = 1, found_values = 0;
	uint16_t res_inst_id_tmp = 0U;
	void *data_ptr = NULL;
	struct lwm2m_time_series_resource *cached_data = NULL;
	size_t data_len = 0;
	struct lwm2m_obj_path temp_path;
	int ret = 0;

	if (!obj_inst || !res || !obj_field || !msg) {
		return -EINVAL;
	}
	temp_path.obj_id = obj_inst->obj->obj_id;

	temp_path.obj_inst_id = obj_inst->obj_inst_id;
	temp_path.res_id = obj_field->res_id;
	temp_path.level = LWM2M_PATH_LEVEL_RESOURCE;

	loop_max = res->res_inst_count;
	if (res->multi_res_inst) {
		/* search for valid resource instances */
		for (i = 0; i < loop_max; i++) {
			if (res->res_instances[i].res_inst_id != RES_INSTANCE_NOT_CREATED) {
				found_values = 1;
				break;
			}
		}

		if (!found_values) {
			return -ENOENT;
		}

		ret = engine_put_begin_ri(&msg->out, &msg->path);
		if (ret < 0) {
			return ret;
		}

		res_inst_id_tmp = msg->path.res_inst_id;
	}

	for (i = 0; i < loop_max; i++) {
		if (res->res_instances[i].res_inst_id == RES_INSTANCE_NOT_CREATED) {
			continue;
		}

		if (IS_ENABLED(CONFIG_LWM2M_VERSION_1_1) &&
		    msg->path.level == LWM2M_PATH_LEVEL_RESOURCE_INST &&
		    msg->path.res_inst_id != res->res_instances[i].res_inst_id) {
			continue;
		}

		if (res->res_inst_count > 1) {
			msg->path.res_inst_id = res->res_instances[i].res_inst_id;
		}
		if (res->multi_res_inst) {
			temp_path.res_inst_id = res->res_instances[i].res_inst_id;
			temp_path.level = LWM2M_PATH_LEVEL_RESOURCE_INST;
		}

		cached_data = lwm2m_cache_entry_get_by_object(&temp_path);

		if (lwm2m_accept_timeseries_read(msg, cached_data)) {
			/* Content Format Writer have to support timestamp write */
			ret = lwm2m_read_cached_data(msg, cached_data, obj_field->data_type);
		} else {
			/* setup initial data elements */
			data_ptr = res->res_instances[i].data_ptr;
			data_len = res->res_instances[i].data_len;

			/* allow user to override data elements via callback */
			if (res->read_cb) {
				data_ptr =
					res->read_cb(obj_inst->obj_inst_id, res->res_id,
						     res->res_instances[i].res_inst_id, &data_len);
			}

			if (!data_ptr && data_len) {
				return -ENOENT;
			}

			if (!data_len) {
				if (obj_field->data_type != LWM2M_RES_TYPE_OPAQUE &&
				    obj_field->data_type != LWM2M_RES_TYPE_STRING) {
					return -ENOENT;
				}
				/* Only opaque and string types can be empty, and when
				 * empty, we should not give pointer to potentially uninitialized
				 * data to a content formatter. Give pointer to empty string
				 * instead.
				 */
				data_ptr = "";
			}
			ret = lwm2m_read_resource_data(msg, data_ptr, data_len,
						       obj_field->data_type);
		}

		/* Validate that we really read some data */
		if (ret < 0) {
			LOG_ERR("Read operation fail");
			return -ENOMEM;
		}
	}

	if (res->multi_res_inst) {
		ret = engine_put_end_ri(&msg->out, &msg->path);
		if (ret < 0) {
			return ret;
		}

		msg->path.res_inst_id = res_inst_id_tmp;
	}

	return 0;
}

static int lwm2m_delete_handler(struct lwm2m_message *msg)
{
	int ret;

	if (!msg) {
		return -EINVAL;
	}

	/* Device management interface is not allowed to delete Security and
	 * Device objects instances.
	 */
	if (msg->path.obj_id == LWM2M_OBJECT_SECURITY_ID ||
	    msg->path.obj_id == LWM2M_OBJECT_DEVICE_ID) {
		return -EPERM;
	}

	ret = lwm2m_delete_obj_inst(msg->path.obj_id, msg->path.obj_inst_id);
	if (ret < 0) {
		return ret;
	}

	if (!msg->ctx->bootstrap_mode) {
		engine_trigger_update(true);
	}

	return 0;
}

static int do_read_op(struct lwm2m_message *msg, uint16_t content_format)
{
	switch (content_format) {

	case LWM2M_FORMAT_APP_OCTET_STREAM:
		return do_read_op_opaque(msg, content_format);

	case LWM2M_FORMAT_PLAIN_TEXT:
	case LWM2M_FORMAT_OMA_PLAIN_TEXT:
		return do_read_op_plain_text(msg, content_format);

#if defined(CONFIG_LWM2M_RW_OMA_TLV_SUPPORT)
	case LWM2M_FORMAT_OMA_TLV:
	case LWM2M_FORMAT_OMA_OLD_TLV:
		return do_read_op_tlv(msg, content_format);
#endif

#if defined(CONFIG_LWM2M_RW_JSON_SUPPORT)
	case LWM2M_FORMAT_OMA_JSON:
	case LWM2M_FORMAT_OMA_OLD_JSON:
		return do_read_op_json(msg, content_format);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		return do_read_op_senml_json(msg);
#endif

#if defined(CONFIG_LWM2M_RW_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_CBOR:
		return do_read_op_cbor(msg);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_SENML_CBOR:
		return do_read_op_senml_cbor(msg);
#endif

	default:
		LOG_ERR("Unsupported content-format: %u", content_format);
		return -ENOMSG;
	}
}

static int do_composite_read_op(struct lwm2m_message *msg, uint16_t content_format)
{
	switch (content_format) {

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		return do_composite_read_op_senml_json(msg);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_SENML_CBOR:
		return do_composite_read_op_senml_cbor(msg);
#endif

	default:
		LOG_ERR("Unsupported content-format: %u", content_format);
		return -ENOMSG;
	}
}

static int lwm2m_perform_read_object_instance(struct lwm2m_message *msg,
					      struct lwm2m_engine_obj_inst *obj_inst,
					      uint8_t *num_read)
{
	struct lwm2m_engine_res *res = NULL;
	struct lwm2m_engine_obj_field *obj_field;
	int ret = 0;

	while (obj_inst) {
		if (!obj_inst->resources || obj_inst->resource_count == 0U) {
			goto move_forward;
		}

		/* update the obj_inst_id as we move through the instances */
		msg->path.obj_inst_id = obj_inst->obj_inst_id;

		ret = engine_put_begin_oi(&msg->out, &msg->path);
		if (ret < 0) {
			return ret;
		}

		for (int index = 0; index < obj_inst->resource_count; index++) {
			if (msg->path.level > LWM2M_PATH_LEVEL_OBJECT_INST &&
			    msg->path.res_id != obj_inst->resources[index].res_id) {
				continue;
			}

			res = &obj_inst->resources[index];
			msg->path.res_id = res->res_id;
			obj_field = lwm2m_get_engine_obj_field(obj_inst->obj, res->res_id);
			if (!obj_field) {
				ret = -ENOENT;
			} else if (!LWM2M_HAS_PERM(obj_field, LWM2M_PERM_R)) {
				ret = -EPERM;
			} else {
				/* start resource formatting */
				ret = engine_put_begin_r(&msg->out, &msg->path);
				if (ret < 0) {
					return ret;
				}

				/* perform read operation on this resource */
				ret = lwm2m_read_handler(obj_inst, res, obj_field, msg);
				if (ret == -ENOMEM) {
					/* No point continuing if there's no
					 * memory left in a message.
					 */
					return ret;
				} else if (ret < 0) {
					/* ignore errors unless single read */
					if (msg->path.level > LWM2M_PATH_LEVEL_OBJECT_INST &&
					    !LWM2M_HAS_PERM(obj_field, BIT(LWM2M_FLAG_OPTIONAL))) {
						LOG_ERR("READ OP: %d", ret);
					}
				} else {
					*num_read += 1U;
				}

				/* end resource formatting */
				ret = engine_put_end_r(&msg->out, &msg->path);
				if (ret < 0) {
					return ret;
				}
			}

			/* on single read break if errors */
			if (ret < 0 && msg->path.level > LWM2M_PATH_LEVEL_OBJECT_INST) {
				break;
			}
		}

move_forward:
		ret = engine_put_end_oi(&msg->out, &msg->path);
		if (ret < 0) {
			return ret;
		}

		if (msg->path.level <= LWM2M_PATH_LEVEL_OBJECT) {
			/* advance to the next object instance */
			obj_inst = next_engine_obj_inst(msg->path.obj_id, obj_inst->obj_inst_id);
		} else {
			obj_inst = NULL;
		}
	}

	return ret;
}

int lwm2m_perform_read_op(struct lwm2m_message *msg, uint16_t content_format)
{
	struct lwm2m_engine_obj_inst *obj_inst = NULL;
	struct lwm2m_obj_path temp_path;
	int ret = 0;
	uint8_t num_read = 0U;

	if (msg->path.level >= LWM2M_PATH_LEVEL_OBJECT_INST) {
		obj_inst = get_engine_obj_inst(msg->path.obj_id, msg->path.obj_inst_id);
		if (!obj_inst) {
			/* When Object instance is indicated error have to be reported */
			return -ENOENT;
		}
	} else if (msg->path.level == LWM2M_PATH_LEVEL_OBJECT) {
		/* find first obj_inst with path's obj_id.
		 * Path level 1 can accept NULL. It define empty payload to response.
		 */
		obj_inst = next_engine_obj_inst(msg->path.obj_id, -1);
	}

	/* set output content-format */
	ret = coap_append_option_int(msg->out.out_cpkt, COAP_OPTION_CONTENT_FORMAT, content_format);
	if (ret < 0) {
		LOG_ERR("Error setting response content-format: %d", ret);
		return ret;
	}

	ret = coap_packet_append_payload_marker(msg->out.out_cpkt);
	if (ret < 0) {
		LOG_ERR("Error appending payload marker: %d", ret);
		return ret;
	}

	/* store original path values so we can change them during processing */
	memcpy(&temp_path, &msg->path, sizeof(temp_path));

	if (engine_put_begin(&msg->out, &msg->path) < 0) {
		return -ENOMEM;
	}

	ret = lwm2m_perform_read_object_instance(msg, obj_inst, &num_read);
	if (ret < 0) {
		return ret;
	}

	if (engine_put_end(&msg->out, &msg->path) < 0) {
		return -ENOMEM;
	}

	/* restore original path values */
	memcpy(&msg->path, &temp_path, sizeof(temp_path));

	/* did not read anything even if we should have - on single item */
	if (ret == 0 && num_read == 0U) {
		if (msg->path.level == LWM2M_PATH_LEVEL_RESOURCE) {
			return -ENOENT;
		}

		if (IS_ENABLED(CONFIG_LWM2M_VERSION_1_1) &&
		    msg->path.level == LWM2M_PATH_LEVEL_RESOURCE_INST) {
			return -ENOENT;
		}
	}

	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;

	ret = engine_put_corelink(
		&msg->out, &LWM2M_OBJ(obj_inst->obj->obj_id, obj_inst->obj_inst_id, res->res_id));
	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;
			}

			ret = engine_put_corelink(
				&msg->out, &LWM2M_OBJ(obj_inst->obj->obj_id, obj_inst->obj_inst_id,
						      res->res_id, res_inst->res_inst_id));
			if (ret < 0) {
				return ret;
			}
		}
	}

	return 0;
}

int lwm2m_discover_handler(struct lwm2m_message *msg, bool is_bootstrap)
{
	struct lwm2m_engine_obj *obj;
	struct lwm2m_engine_obj_inst *obj_inst;
	int ret;
	bool reported = false;
	sys_slist_t *engine_obj_list = lwm2m_engine_obj_list();
	sys_slist_t *engine_obj_inst_list = lwm2m_engine_obj_inst_list();

	/* Object ID is required in Device Management Discovery (5.4.2). */
	if (!is_bootstrap && (msg->path.level == LWM2M_PATH_LEVEL_NONE ||
			      msg->path.obj_id == LWM2M_OBJECT_SECURITY_ID)) {
		return -EPERM;
	}

	/* Bootstrap discovery allows to specify at most Object ID. */
	if (is_bootstrap && msg->path.level > LWM2M_PATH_LEVEL_OBJECT) {
		return -EPERM;
	}

	/* set output content-format */
	ret = coap_append_option_int(msg->out.out_cpkt, COAP_OPTION_CONTENT_FORMAT,
				     LWM2M_FORMAT_APP_LINK_FORMAT);
	if (ret < 0) {
		LOG_ERR("Error setting response content-format: %d", ret);
		return ret;
	}

	ret = coap_packet_append_payload_marker(msg->out.out_cpkt);
	if (ret < 0) {
		return ret;
	}

	/*
	 * Add required prefix for bootstrap discovery (5.2.7.3).
	 * For device management discovery, `engine_put_begin()` adds nothing.
	 */
	ret = engine_put_begin(&msg->out, &msg->path);
	if (ret < 0) {
		return ret;
	}

	SYS_SLIST_FOR_EACH_CONTAINER(engine_obj_list, obj, node) {
		/* Skip unrelated objects */
		if (msg->path.level > 0 && msg->path.obj_id != obj->obj_id) {
			continue;
		}

		/* For bootstrap discover, only report object ID when no
		 * instance is available or it's needed to report object
		 * version.
		 * For device management discovery, only report object ID with
		 * attributes if object ID (alone) was provided.
		 */
		if ((is_bootstrap &&
		     (obj->instance_count == 0U || lwm2m_engine_shall_report_obj_version(obj))) ||
		    (!is_bootstrap && msg->path.level == LWM2M_PATH_LEVEL_OBJECT)) {
			ret = engine_put_corelink(&msg->out, &LWM2M_OBJ(obj->obj_id));
			if (ret < 0) {
				return ret;
			}

			reported = true;

			if (obj->instance_count == 0U) {
				continue;
			}
		}

		SYS_SLIST_FOR_EACH_CONTAINER(engine_obj_inst_list, obj_inst, node) {
			if (obj_inst->obj->obj_id != obj->obj_id) {
				continue;
			}

			/* Skip unrelated object instance. */
			if (msg->path.level > LWM2M_PATH_LEVEL_OBJECT &&
			    msg->path.obj_inst_id != obj_inst->obj_inst_id) {
				continue;
			}

			/* Report object instances only if no Resource ID is
			 * provided.
			 */
			if (msg->path.level <= LWM2M_PATH_LEVEL_OBJECT_INST) {
				ret = engine_put_corelink(
					&msg->out,
					&LWM2M_OBJ(obj_inst->obj->obj_id, obj_inst->obj_inst_id));
				if (ret < 0) {
					return ret;
				}

				reported = true;
			}

			/* Do not report resources in bootstrap discovery. */
			if (is_bootstrap) {
				continue;
			}

			for (int i = 0; i < obj_inst->resource_count; i++) {
				/* Skip unrelated resources. */
				if (msg->path.level == LWM2M_PATH_LEVEL_RESOURCE &&
				    msg->path.res_id != obj_inst->resources[i].res_id) {
					continue;
				}

				ret = lwm2m_discover_add_res(msg, obj_inst,
							     &obj_inst->resources[i]);
				if (ret < 0) {
					return ret;
				}

				reported = true;
			}
		}
	}

	return reported ? 0 : -ENOENT;
}

static int do_discover_op(struct lwm2m_message *msg, uint16_t content_format)
{
	switch (content_format) {
	case LWM2M_FORMAT_APP_LINK_FORMAT:
		return do_discover_op_link_format(msg, msg->ctx->bootstrap_mode);

	default:
		LOG_ERR("Unsupported format: %u", content_format);
		return -ENOMSG;
	}
}

static int do_write_op(struct lwm2m_message *msg, uint16_t format)
{
	int r;

	switch (format) {

	case LWM2M_FORMAT_APP_OCTET_STREAM:
		r = do_write_op_opaque(msg);
		break;

	case LWM2M_FORMAT_PLAIN_TEXT:
	case LWM2M_FORMAT_OMA_PLAIN_TEXT:
		r = do_write_op_plain_text(msg);
		break;

#ifdef CONFIG_LWM2M_RW_OMA_TLV_SUPPORT
	case LWM2M_FORMAT_OMA_TLV:
	case LWM2M_FORMAT_OMA_OLD_TLV:
		r = do_write_op_tlv(msg);
		break;
#endif

#ifdef CONFIG_LWM2M_RW_JSON_SUPPORT
	case LWM2M_FORMAT_OMA_JSON:
	case LWM2M_FORMAT_OMA_OLD_JSON:
		r = do_write_op_json(msg);
		break;
#endif

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		r = do_write_op_senml_json(msg);
		break;
#endif

#ifdef CONFIG_LWM2M_RW_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_CBOR:
		r = do_write_op_cbor(msg);
		break;
#endif

#ifdef CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT
	case LWM2M_FORMAT_APP_SENML_CBOR:
		r = do_write_op_senml_cbor(msg);
		break;
#endif

	default:
		LOG_ERR("Unsupported format: %u", format);
		r = -ENOMSG;
		break;
	}

	return r;
}

static int parse_write_op(struct lwm2m_message *msg, uint16_t format)
{
	int block_opt, block_num;
	struct lwm2m_block_context *block_ctx = NULL;
	enum coap_block_size block_size;
	bool last_block = false;
	int r;
	uint16_t payload_len = 0U;
	const uint8_t *payload_start;

	/* setup incoming data */
	payload_start = coap_packet_get_payload(msg->in.in_cpkt, &payload_len);
	if (payload_len > 0) {
		msg->in.offset = payload_start - msg->in.in_cpkt->data;
	} else {
		msg->in.offset = msg->in.in_cpkt->offset;
	}

	/* Check for block transfer */
	block_opt = coap_get_option_int(msg->in.in_cpkt, COAP_OPTION_BLOCK1);
	if (block_opt > 0) {
		last_block = !GET_MORE(block_opt);

		/* RFC7252: 4.6. Message Size */
		block_size = GET_BLOCK_SIZE(block_opt);
		if (!last_block && coap_block_size_to_bytes(block_size) > payload_len) {
			LOG_DBG("Trailing payload is discarded!");
			return -EFBIG;
		}

		block_num = GET_BLOCK_NUM(block_opt);

		/*
		 * RFC7959: 2.5. Using the Block1 Option
		 * If we've received first block, replace old context (if any) with a new one.
		 */
		r = get_block_ctx(&msg->path, &block_ctx);
		if (block_num == 0) {
			/* free block context for previous incomplete transfer */
			free_block_ctx(block_ctx);

			r = init_block_ctx(&msg->path, &block_ctx);
			/* If we have already parsed the packet, we can handle the block size
			 * given by the server.
			 */
			block_ctx->ctx.block_size = block_size;
		}

		if (r < 0) {
			LOG_ERR("Cannot find block context");
			return r;
		}

		msg->in.block_ctx = block_ctx;

		if (block_num < block_ctx->expected) {
			LOG_WRN("Block already handled %d, expected %d", block_num,
				block_ctx->expected);
			(void)coap_header_set_code(msg->out.out_cpkt, COAP_RESPONSE_CODE_CONTINUE);
			/* Respond with the original Block1 header, original Ack might have been
			 * lost, and this is a retry. We don't know the original response, but
			 * since it is handled, just assume we can continue.
			 */
			(void)coap_append_option_int(msg->out.out_cpkt, COAP_OPTION_BLOCK1,
						     block_opt);
			return 0;
		}
		if (block_num > block_ctx->expected) {
			LOG_WRN("Block out of order %d, expected %d", block_num,
				block_ctx->expected);
			r = -EFAULT;
			return r;
		}
		r = coap_update_from_block(msg->in.in_cpkt, &block_ctx->ctx);
		if (r < 0) {
			LOG_ERR("Error from block update: %d", r);
			return r;
		}

		block_ctx->last_block = last_block;
		block_ctx->expected++;
	}

	r = do_write_op(msg, format);

	/* Handle blockwise 1 (Part 2): Append BLOCK1 option / free context */
	if (block_ctx) {
		if (r >= 0) {
			/* Add block1 option to response.
			 * As RFC7959 Section-2.3, More flag is off, because we have already
			 * written the data.
			 */
			r = coap_append_block1_option(msg->out.out_cpkt, &block_ctx->ctx);
			if (r < 0) {
				/* report as internal server error */
				LOG_DBG("Fail adding block1 option: %d", r);
				r = -EINVAL;
			}
			if (!last_block) {
				r = coap_header_set_code(msg->out.out_cpkt,
							 COAP_RESPONSE_CODE_CONTINUE);
				if (r < 0) {
					LOG_DBG("Failed to modify response code");
					r = -EINVAL;
				}
			}
		}
		if (r < 0 || last_block) {
			/* Free context when finished or when there is error */
			free_block_ctx(block_ctx);
		}
	}

	return r;
}

static int do_composite_write_op(struct lwm2m_message *msg, uint16_t format)
{
	uint16_t payload_len = 0U;
	const uint8_t *payload_start;

	/* setup incoming data */
	payload_start = coap_packet_get_payload(msg->in.in_cpkt, &payload_len);
	if (payload_len > 0) {
		msg->in.offset = payload_start - msg->in.in_cpkt->data;
	} else {
		msg->in.offset = msg->in.in_cpkt->offset;
	}

	if (coap_get_option_int(msg->in.in_cpkt, COAP_OPTION_BLOCK1) >= 0) {
		return -ENOTSUP;
	}

	switch (format) {
#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		return do_write_op_senml_json(msg);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_SENML_CBOR:
		return do_write_op_senml_cbor(msg);
#endif

	default:
		LOG_ERR("Unsupported format: %u", format);
		return -ENOMSG;
	}
}

static bool lwm2m_engine_path_included(uint8_t code, bool bootstrap_mode)
{
	switch (code & COAP_REQUEST_MASK) {
#if defined(CONFIG_LWM2M_RD_CLIENT_SUPPORT_BOOTSTRAP)
	case COAP_METHOD_DELETE:
	case COAP_METHOD_GET:
		if (bootstrap_mode) {
			return false;
		}
		break;
#endif
	case COAP_METHOD_FETCH:
	/* Composite Read operation */
	case COAP_METHOD_IPATCH:
		/* Composite write operation */
		return false;
	default:
		break;
	}
	return true;
}

static int lwm2m_engine_default_content_format(uint16_t *accept_format)
{
	if (IS_ENABLED(CONFIG_LWM2M_VERSION_1_1)) {
		/* Select content format use SenML CBOR when it possible */
		if (IS_ENABLED(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)) {
			LOG_DBG("No accept option given. Assume SenML CBOR.");
			*accept_format = LWM2M_FORMAT_APP_SENML_CBOR;
		} else if (IS_ENABLED(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)) {
			LOG_DBG("No accept option given. Assume SenML Json.");
			*accept_format = LWM2M_FORMAT_APP_SEML_JSON;
		} else if (IS_ENABLED(CONFIG_LWM2M_RW_CBOR_SUPPORT)) {
			LOG_DBG("No accept option given. Assume CBOR.");
			*accept_format = LWM2M_FORMAT_APP_CBOR;
		} else if (IS_ENABLED(CONFIG_LWM2M_RW_OMA_TLV_SUPPORT)) {
			LOG_DBG("No accept option given. Assume OMA TLV.");
			*accept_format = LWM2M_FORMAT_OMA_TLV;
		} else {
			LOG_ERR("CBOR, SenML CBOR, SenML JSON or OMA TLV is not supported");
			return -ENOTSUP;
		}
	} else if (IS_ENABLED(CONFIG_LWM2M_RW_OMA_TLV_SUPPORT)) {
		LOG_DBG("No accept option given. Assume OMA TLV.");
		*accept_format = LWM2M_FORMAT_OMA_TLV;
	} else {
		LOG_ERR("No default content format is set");
		return -ENOTSUP;
	}

	return 0;
}

static int lwm2m_exec_handler(struct lwm2m_message *msg)
{
	struct lwm2m_engine_obj_inst *obj_inst;
	struct lwm2m_engine_res *res = NULL;
	int ret;
	uint8_t *args;
	uint16_t args_len;

	if (!msg) {
		return -EINVAL;
	}

	ret = path_to_objs(&msg->path, &obj_inst, NULL, &res, NULL);
	if (ret < 0) {
		return ret;
	}

	args = (uint8_t *)coap_packet_get_payload(msg->in.in_cpkt, &args_len);

	if (res->execute_cb) {
		return res->execute_cb(obj_inst->obj_inst_id, args, args_len);
	}

	/* TODO: something else to handle for execute? */
	return -ENOENT;
}

static int handle_request(struct coap_packet *request, struct lwm2m_message *msg)
{
	int r;
	uint8_t code;
	struct coap_option options[4];
	struct lwm2m_engine_obj *obj = NULL;
	uint8_t token[8];
	uint8_t tkl = 0U;
	uint16_t format = LWM2M_FORMAT_NONE, accept;
	int observe = -1; /* default to -1, 0 = ENABLE, 1 = DISABLE */

	/* set CoAP request / message */
	msg->in.in_cpkt = request;
	msg->out.out_cpkt = &msg->cpkt;

	/* set default reader/writer */
	msg->in.reader = &plain_text_reader;
	msg->out.writer = &plain_text_writer;

	code = coap_header_get_code(msg->in.in_cpkt);

	/* setup response token */
	tkl = coap_header_get_token(msg->in.in_cpkt, token);
	if (tkl) {
		msg->tkl = tkl;
		msg->token = token;
	}

	if (IS_ENABLED(CONFIG_LWM2M_GATEWAY_OBJ_SUPPORT)) {
		r = lwm2m_gw_handle_req(msg);
		if (r == 0) {
			return 0;
		} else if (r != -ENOENT) {
			goto error;
		}
	}

	/* parse the URL path into components */
	r = coap_find_options(msg->in.in_cpkt, COAP_OPTION_URI_PATH, options, ARRAY_SIZE(options));
	if (r < 0) {
		goto error;
	}

	/* Treat empty URI path option as is there were no option - this will be
	 * represented as a level "zero" in the path structure.
	 */
	if (r == 1 && options[0].len == 0) {
		r = 0;
	}

	if (r == 0 && lwm2m_engine_path_included(code, msg->ctx->bootstrap_mode)) {
		/* No URI path or empty URI path option - allowed only during
		 * bootstrap or CoAP Fetch or iPATCH.
		 */

		r = -EPERM;
		goto error;
	}

#if defined(CONFIG_LWM2M_RD_CLIENT_SUPPORT_BOOTSTRAP)
	/* check for bootstrap-finish */
	if ((code & COAP_REQUEST_MASK) == COAP_METHOD_POST && r == 1 &&
	    strncmp(options[0].value, "bs", options[0].len) == 0) {
		engine_bootstrap_finish();

		msg->code = COAP_RESPONSE_CODE_CHANGED;

		r = lwm2m_init_message(msg);
		if (r < 0) {
			goto error;
		}

		return 0;
	}
#endif

	r = coap_options_to_path(options, r, &msg->path);
	if (r < 0) {
		r = -ENOENT;
		goto error;
	}

	/* read Content Format / setup in.reader */
	r = coap_find_options(msg->in.in_cpkt, COAP_OPTION_CONTENT_FORMAT, options, 1);
	if (r > 0) {
		format = coap_option_value_to_int(&options[0]);
		r = select_reader(&msg->in, format);
		if (r < 0) {
			goto error;
		}
	}

	/* read Accept / setup out.writer */
	r = coap_find_options(msg->in.in_cpkt, COAP_OPTION_ACCEPT, options, 1);
	if (r > 0) {
		accept = coap_option_value_to_int(&options[0]);
	} else {
		/* Select Default based LWM2M_VERSION */
		r = lwm2m_engine_default_content_format(&accept);
		if (r) {
			goto error;
		}
	}

	r = select_writer(&msg->out, accept);
	if (r < 0) {
		goto error;
	}

	/* Do Only Object find if path have been parsed */
	if (lwm2m_engine_path_included(code, msg->ctx->bootstrap_mode)) {
		if (!(msg->ctx->bootstrap_mode && msg->path.level == LWM2M_PATH_LEVEL_NONE)) {
			/* find registered obj */
			obj = get_engine_obj(msg->path.obj_id);
			if (!obj) {
				/* No matching object found - ignore request */
				r = -ENOENT;
				goto error;
			}
		}
	}

	/* set the operation */
	switch (code & COAP_REQUEST_MASK) {

	case COAP_METHOD_GET:
		/*
		 * LwM2M V1_0_1-20170704-A, table 25,
		 * Discover: CoAP GET + accept=LWM2M_FORMAT_APP_LINK_FORMAT
		 */
		if (accept == LWM2M_FORMAT_APP_LINK_FORMAT) {
			msg->operation = LWM2M_OP_DISCOVER;
			accept = LWM2M_FORMAT_APP_LINK_FORMAT;
		} else {
			msg->operation = LWM2M_OP_READ;
		}

		/* check for observe */
		observe = coap_get_option_int(msg->in.in_cpkt, COAP_OPTION_OBSERVE);
		msg->code = COAP_RESPONSE_CODE_CONTENT;
		break;

	case COAP_METHOD_FETCH:
		msg->operation = LWM2M_OP_READ;
		/* check for observe */
		observe = coap_get_option_int(msg->in.in_cpkt, COAP_OPTION_OBSERVE);
		msg->code = COAP_RESPONSE_CODE_CONTENT;
		break;

	case COAP_METHOD_IPATCH:
		msg->operation = LWM2M_OP_WRITE;
		msg->code = COAP_RESPONSE_CODE_CHANGED;
		break;

	case COAP_METHOD_POST:
		if (msg->path.level == 1U) {
			/* create an object instance */
			msg->operation = LWM2M_OP_CREATE;
			msg->code = COAP_RESPONSE_CODE_CREATED;
		} else if (msg->path.level == 2U) {
			/* write values to an object instance */
			msg->operation = LWM2M_OP_WRITE;
			msg->code = COAP_RESPONSE_CODE_CHANGED;
		} else {
			msg->operation = LWM2M_OP_EXECUTE;
			msg->code = COAP_RESPONSE_CODE_CHANGED;
		}

		break;

	case COAP_METHOD_PUT:
		/* write attributes if content-format is absent */
		if (format == LWM2M_FORMAT_NONE) {
			msg->operation = LWM2M_OP_WRITE_ATTR;
		} else {
			msg->operation = LWM2M_OP_WRITE;
		}

		msg->code = COAP_RESPONSE_CODE_CHANGED;
		break;

	case COAP_METHOD_DELETE:
		msg->operation = LWM2M_OP_DELETE;
		msg->code = COAP_RESPONSE_CODE_DELETED;
		break;

	default:
		break;
	}

	/* render CoAP packet header */
	r = lwm2m_init_message(msg);
	if (r < 0) {
		goto error;
	}

#if defined(CONFIG_LWM2M_ACCESS_CONTROL_ENABLE)
	r = access_control_check_access(msg->path.obj_id, msg->path.obj_inst_id,
					msg->ctx->srv_obj_inst, msg->operation,
					msg->ctx->bootstrap_mode);
	if (r < 0) {
		LOG_ERR("Access denied - Server obj %u does not have proper access to "
			"resource",
			msg->ctx->srv_obj_inst);
		goto error;
	}
#endif
	if (msg->path.level > LWM2M_PATH_LEVEL_NONE &&
	    msg->path.obj_id == LWM2M_OBJECT_SECURITY_ID && !msg->ctx->bootstrap_mode) {
		r = -EACCES;
		goto error;
	}

	switch (msg->operation) {

	case LWM2M_OP_READ:
		if (observe >= 0) {
			/* Validate That Token is valid for Observation */
			if (!msg->token) {
				LOG_ERR("OBSERVE request missing token");
				r = -EINVAL;
				goto error;
			}

			if ((code & COAP_REQUEST_MASK) == COAP_METHOD_GET) {
				/* Normal Observation Request or Cancel */
				r = lwm2m_engine_observation_handler(msg, observe, accept,
									false);
				if (r < 0) {
					goto error;
				}

				r = do_read_op(msg, accept);
			} else {
				/* Composite Observation request & cancel handler */
				r = lwm2m_engine_observation_handler(msg, observe, accept,
									true);
				if (r < 0) {
					goto error;
				}
			}
		} else {
			if ((code & COAP_REQUEST_MASK) == COAP_METHOD_GET) {
				r = do_read_op(msg, accept);
			} else {
				r = do_composite_read_op(msg, accept);
			}
		}
		break;

	case LWM2M_OP_DISCOVER:
		r = do_discover_op(msg, accept);
		break;

	case LWM2M_OP_WRITE:
	case LWM2M_OP_CREATE:
		if ((code & COAP_REQUEST_MASK) == COAP_METHOD_IPATCH) {
			/* iPATCH is for Composite purpose */
			r = do_composite_write_op(msg, format);
		} else {
			/* Single resource write Operation */
			r = parse_write_op(msg, format);
		}
#if defined(CONFIG_LWM2M_ACCESS_CONTROL_ENABLE)
		if (msg->operation == LWM2M_OP_CREATE && r >= 0) {
			access_control_add(msg->path.obj_id, msg->path.obj_inst_id,
						msg->ctx->srv_obj_inst);
		}
#endif
		break;

	case LWM2M_OP_WRITE_ATTR:
		r = lwm2m_write_attr_handler(obj, msg);
		break;

	case LWM2M_OP_EXECUTE:
		r = lwm2m_exec_handler(msg);
		break;

	case LWM2M_OP_DELETE:
#if defined(CONFIG_LWM2M_RD_CLIENT_SUPPORT_BOOTSTRAP)
		if (msg->ctx->bootstrap_mode) {
			r = bootstrap_delete(msg);
			break;
		}
#endif
		r = lwm2m_delete_handler(msg);
		break;

	default:
		LOG_ERR("Unknown operation: %u", msg->operation);
		r = -EINVAL;
	}

	if (r < 0) {
		goto error;
	}

	return 0;

error:
	lwm2m_reset_message(msg, false);
	if (r == -ENOENT) {
		msg->code = COAP_RESPONSE_CODE_NOT_FOUND;
	} else if (r == -EPERM) {
		msg->code = COAP_RESPONSE_CODE_NOT_ALLOWED;
	} else if (r == -EEXIST) {
		msg->code = COAP_RESPONSE_CODE_BAD_REQUEST;
	} else if (r == -EFAULT) {
		msg->code = COAP_RESPONSE_CODE_INCOMPLETE;
	} else if (r == -EFBIG) {
		msg->code = COAP_RESPONSE_CODE_REQUEST_TOO_LARGE;
	} else if (r == -ENOTSUP) {
		msg->code = COAP_RESPONSE_CODE_NOT_IMPLEMENTED;
	} else if (r == -ENOMSG) {
		msg->code = COAP_RESPONSE_CODE_UNSUPPORTED_CONTENT_FORMAT;
	} else if (r == -EACCES) {
		msg->code = COAP_RESPONSE_CODE_UNAUTHORIZED;
	} else if (r == -ECANCELED) {
		msg->code = COAP_RESPONSE_CODE_NOT_ACCEPTABLE;
	} else {
		/* Failed to handle the request */
		msg->code = COAP_RESPONSE_CODE_INTERNAL_ERROR;
	}

	r = lwm2m_init_message(msg);
	if (r < 0) {
		LOG_ERR("Error recreating message: %d", r);
	}

	return 0;
}

static int lwm2m_response_promote_to_con(struct lwm2m_message *msg)
{
	int ret;

	msg->type = COAP_TYPE_CON;
	msg->mid = coap_next_id();

	/* Since the response CoAP packet is already generated at this point,
	 * tweak the specific fields manually:
	 * - CoAP message type (byte 0, bits 2 and 3)
	 * - CoAP message id (bytes 2 and 3)
	 */
	msg->cpkt.data[0] &= ~(0x3 << 4);
	msg->cpkt.data[0] |= (msg->type & 0x3) << 4;
	msg->cpkt.data[2] = msg->mid >> 8;
	msg->cpkt.data[3] = (uint8_t)msg->mid;

	if (msg->pending) {
		coap_pending_clear(msg->pending);
	}

	lwm2m_client_lock(msg->ctx);

	/* Add the packet to the pending list. */
	msg->pending = coap_pending_next_unused(msg->ctx->pendings, ARRAY_SIZE(msg->ctx->pendings));
	if (!msg->pending) {
		LOG_ERR("Unable to find a free pending to track "
			"retransmissions.");
		lwm2m_client_unlock(msg->ctx);
		return -ENOMEM;
	}

	ret = coap_pending_init(msg->pending, &msg->cpkt, &msg->ctx->remote_addr, NULL);
	if (ret < 0) {
		LOG_ERR("Unable to initialize a pending "
			"retransmission (err:%d).",
			ret);
	}

	lwm2m_client_unlock(msg->ctx);

	return ret;
}

static struct lwm2m_message *find_ongoing_block2_tx(void)
{
	/* TODO: I could try to check if there is Request-Tags attached, and then match queries
	 * for those, but currently popular LwM2M servers don't attach those tags, so in reality
	 * I have no way of properly matching query with BLOCK2 option to a previous query.
	 * Therefore we can only support one ongoing BLOCK2 transfer and assume all BLOCK2 requests
	 * are part of currently ongoing one.
	 */
	return ongoing_block2_tx;
}

static void clear_ongoing_block2_tx(void)
{
	if (ongoing_block2_tx) {
		LOG_DBG("clear");
		lwm2m_reset_message(ongoing_block2_tx, true);
		ongoing_block2_tx = NULL;
	}
}

static void handle_ongoing_block2_tx(struct lwm2m_message *msg, struct coap_packet *cpkt)
{
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
	int r;
	bool more;
	uint32_t block;
	enum coap_block_size block_size;

	r = coap_get_block2_option(cpkt, &more, &block);
	if (r < 0) {
		LOG_ERR("Failed to parse BLOCK2");
		return;
	}

	block_size = coap_bytes_to_block_size(r);
	msg->in.in_cpkt = cpkt;

	r = build_msg_block_for_send(msg, block, block_size);
	if (r < 0) {
		clear_ongoing_block2_tx();
		LOG_ERR("Unable to build next block of lwm2m message! r=%d", r);
		return;
	}

	r = lwm2m_send_message_async(msg);
	if (r < 0) {
		clear_ongoing_block2_tx();
		LOG_ERR("Unable to send next block of lwm2m message!");
		return;
	}
#endif
}

void lwm2m_udp_receive(struct lwm2m_ctx *client_ctx, uint8_t *buf, uint16_t buf_len,
		       struct sockaddr *from_addr)
{
	struct lwm2m_message *msg = NULL;
	struct coap_pending *pending;
	struct coap_reply *reply;
	struct coap_packet response;
	int r;
#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
	bool more_blocks = false;
	uint32_t block_num;
	uint32_t last_block_num;
#endif
	bool has_block2;

	r = coap_packet_parse(&response, buf, buf_len, NULL, 0);
	if (r < 0) {
		LOG_ERR("Invalid data received (err:%d)", r);
		return;
	}

	has_block2 = coap_get_option_int(&response, COAP_OPTION_BLOCK2) > 0 ? true : false;

	lwm2m_client_lock(client_ctx);

	pending = coap_pending_received(&response, client_ctx->pendings,
					ARRAY_SIZE(client_ctx->pendings));
	if (pending && coap_header_get_type(&response) == COAP_TYPE_ACK) {
		msg = find_msg(pending, NULL);
		if (msg == NULL) {
			LOG_DBG("Orphaned pending %p.", pending);
			coap_pending_clear(pending);
			goto client_unlock;
		}

		msg->acknowledged = true;

		if (msg->reply == NULL) {
			/* No response expected, release the message. */
			lwm2m_reset_message(msg, true);
			goto client_unlock;
		}

		bool is_empty = coap_header_get_code(&response) == COAP_CODE_EMPTY;
		bool was_request = coap_packet_is_request(&msg->cpkt);

		/* If the original message was a request and an empty
		 * ACK was received, expect separate response later.
		 */
		if (was_request && is_empty) {
			LOG_DBG("Empty ACK, expect separate response.");
			goto client_unlock;
		}

		/* If the original message was a response (like a Notify) and
		 * empty Ack is received, handle that as a response.
		 */
		if (!was_request && is_empty) {
			msg->reply->reply(&response, msg->reply, from_addr);
			lwm2m_reset_message(msg, true);
			goto client_unlock;
		}
	}

	reply = coap_response_received(&response, from_addr, client_ctx->replies,
				       ARRAY_SIZE(client_ctx->replies));
	if (reply) {
		msg = find_msg(NULL, reply);

		if (coap_header_get_type(&response) == COAP_TYPE_CON) {
			r = lwm2m_send_empty_ack(client_ctx, coap_header_get_id(&response));
			if (r < 0) {
				LOG_ERR("Error transmitting ACK");
			}
		}

#if defined(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)
		if (coap_header_get_code(&response) == COAP_RESPONSE_CODE_CONTINUE) {

			r = coap_get_block1_option(&response, &more_blocks, &block_num);
			if (r < 0) {
				LOG_ERR("Missing block1 option in response with continue");
				goto client_unlock;
			}

			enum coap_block_size block_size = coap_bytes_to_block_size(r);

			if (r != CONFIG_LWM2M_COAP_BLOCK_SIZE) {
				LOG_WRN("Server requests different block size: ignore");
			}

			if (!more_blocks) {
				lwm2m_reset_message(msg, true);
				LOG_ERR("Missing more flag in response with continue");
				goto client_unlock;
			}

			last_block_num = msg->out.block_ctx->current /
					 coap_block_size_to_bytes(block_size);
			if (last_block_num > block_num) {
				LOG_INF("Block already sent: ignore");
				goto client_unlock;
			} else if (last_block_num < block_num) {
				LOG_WRN("Requested block out of order");
				goto client_unlock;
			}

			r = build_msg_block_for_send(msg, block_num + 1, block_size);
			if (r < 0) {
				lwm2m_reset_message(msg, true);
				LOG_ERR("Unable to build next block of lwm2m message!");
				goto client_unlock;
			}

			r = lwm2m_send_message_async(msg);
			if (r < 0) {
				lwm2m_reset_message(msg, true);
				LOG_ERR("Unable to send next block of lwm2m message!");
				goto client_unlock;
			}

			/* skip release as message was reused for new block */
			LOG_DBG("Block # %d sent", block_num + 1);
			goto client_unlock;
		}
#endif

		/* skip release if reply->user_data has error condition */
		if (reply && reply->user_data == (void *)COAP_REPLY_STATUS_ERROR) {
			/* reset reply->user_data for next time */
			reply->user_data = (void *)COAP_REPLY_STATUS_NONE;
			LOG_DBG("reply %p NOT removed", reply);
			goto client_unlock;
		}

		/* free up msg resources */
		if (msg) {
			lwm2m_reset_message(msg, true);
		}

		LOG_DBG("reply %p handled and removed", reply);
		goto client_unlock;
	}

	lwm2m_client_unlock(client_ctx);

	if (coap_header_get_type(&response) == COAP_TYPE_CON) {
		if (has_block2 && IS_ENABLED(CONFIG_LWM2M_COAP_BLOCK_TRANSFER)) {
			msg = find_ongoing_block2_tx();
			if (msg) {
				handle_ongoing_block2_tx(msg, &response);
			}
			return;
		}

		/* Clear out existing Block2 transfers when new requests come */
		clear_ongoing_block2_tx();

		msg = lwm2m_get_message(client_ctx);
		if (!msg) {
			LOG_ERR("Unable to get a lwm2m message!");
			return;
		}

		/* Create a response message if we reach this point */
		msg->type = COAP_TYPE_ACK;
		msg->code = coap_header_get_code(&response);
		msg->mid = coap_header_get_id(&response);
		/* skip token generation by default */
		msg->tkl = 0;

		client_ctx->processed_req = msg;

		lwm2m_registry_lock();
		/* process the response to this request */
		r = handle_request(&response, msg);
		lwm2m_registry_unlock();
		if (r < 0) {
			return;
		}

		if (msg->acknowledged) {
			r = lwm2m_response_promote_to_con(msg);
			if (r < 0) {
				LOG_ERR("Failed to promote response to CON: %d", r);
				lwm2m_reset_message(msg, true);
				return;
			}
		}

		client_ctx->processed_req = NULL;
		r = lwm2m_send_message_async(msg);
		if (r < 0) {
			LOG_ERR("Failed to send response (err: %d)", r);
			lwm2m_reset_message(msg, true);
			return;
		}
	} else {
		LOG_DBG("No handler for response");
	}

	return;

client_unlock:
	lwm2m_client_unlock(client_ctx);
}

static void notify_message_timeout_cb(struct lwm2m_message *msg)
{
	if (msg->ctx != NULL) {
		struct observe_node *obs;
		struct lwm2m_ctx *client_ctx = msg->ctx;
		sys_snode_t *prev_node = NULL;

		obs = engine_observe_node_discover(&client_ctx->observer, &prev_node, NULL,
						   msg->token, msg->tkl);

		if (obs) {
			obs->active_notify = NULL;
			if (client_ctx->observe_cb) {
				client_ctx->observe_cb(LWM2M_OBSERVE_EVENT_NOTIFY_TIMEOUT,
						       &msg->path, msg->reply->user_data);
			}

			lwm2m_rd_client_timeout(client_ctx);
		}
	}

	LOG_ERR("Notify Message Timed Out : %p", msg);
}

static struct lwm2m_obj_path *lwm2m_read_first_path_ptr(sys_slist_t *lwm2m_path_list)
{
	struct lwm2m_obj_path_list *entry;

	entry = (struct lwm2m_obj_path_list *)sys_slist_peek_head(lwm2m_path_list);
	return &entry->path;
}

static void notify_cached_pending_data_trig(struct observe_node *obs)
{
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	struct lwm2m_time_series_resource *cached_data;
	struct lwm2m_obj_path_list *entry;

	SYS_SLIST_FOR_EACH_CONTAINER(&obs->path_list, entry, node) {
		cached_data = lwm2m_cache_entry_get_by_object(&entry->path);
		if (!cached_data || lwm2m_cache_size(cached_data) == 0) {
			continue;
		}

		/* Trig next send by iMin */
		lwm2m_notify_observer_path(&entry->path);
	}
#endif
}

static int notify_message_reply_cb(const struct coap_packet *response, struct coap_reply *reply,
				   const struct sockaddr *from)
{
	int ret = 0;
	uint8_t type, code;
	struct lwm2m_message *msg;
	struct observe_node *obs;
	sys_snode_t *prev_node = NULL;

	type = coap_header_get_type(response);
	code = coap_header_get_code(response);

	LOG_DBG("NOTIFY ACK type:%u code:%d.%d reply_token:'%s'", type,
		COAP_RESPONSE_CODE_CLASS(code), COAP_RESPONSE_CODE_DETAIL(code),
		sprint_token(reply->token, reply->tkl));

	msg = find_msg(NULL, reply);

	/* remove observer on COAP_TYPE_RESET */
	if (type == COAP_TYPE_RESET) {
		if (reply->tkl > 0) {
			ret = engine_remove_observer_by_token(msg->ctx, reply->token, reply->tkl);
			if (ret) {
				LOG_ERR("remove observe error: %d", ret);
			}
		} else {
			LOG_ERR("notify reply missing token -- ignored.");
		}
	} else {
		obs = engine_observe_node_discover(&msg->ctx->observer, &prev_node, NULL,
						   reply->token, reply->tkl);

		if (obs) {
			obs->active_notify = NULL;
			if (msg->ctx->observe_cb) {
				msg->ctx->observe_cb(LWM2M_OBSERVE_EVENT_NOTIFY_ACK,
						     lwm2m_read_first_path_ptr(&obs->path_list),
						     reply->user_data);
			}
			notify_cached_pending_data_trig(obs);
		}
	}

	return 0;
}

static int do_send_op(struct lwm2m_message *msg, uint16_t content_format,
		      sys_slist_t *lwm2m_path_list)
{
	switch (content_format) {
#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		return do_send_op_senml_json(msg, lwm2m_path_list);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_SENML_CBOR:
		return do_send_op_senml_cbor(msg, lwm2m_path_list);
#endif

	default:
		LOG_ERR("Unsupported content-format for /dp: %u", content_format);
		return -ENOMSG;
	}
}

static bool lwm2m_timeseries_data_rebuild(struct lwm2m_message *msg, int error_code)
{
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	struct lwm2m_cache_read_info *cache_temp;

	if (error_code != -ENOMEM) {
		return false;
	}

	cache_temp = msg->cache_info;

	if (!cache_temp || !cache_temp->entry_size) {
		return false;
	}

	/* Put Ring buffer back to original */
	for (int i = 0; i < cache_temp->entry_size; i++) {
		cache_temp->read_info[i].cache_data->rb.get =
			cache_temp->read_info[i].original_rb_get;
	}

	if (cache_temp->entry_limit) {
		/* Limited number of message build fail also */
		return false;
	}

	/* Limit re-build entry count */
	cache_temp->entry_limit = LWM2M_LIMITED_TIMESERIES_RESOURCE_COUNT / cache_temp->entry_size;
	cache_temp->entry_size = 0;

	lwm2m_reset_message(msg, false);
	LOG_INF("Try re-buildbuild again with limited cache size %d", cache_temp->entry_limit);
	return true;
#else
	return false;
#endif
}

int generate_notify_message(struct lwm2m_ctx *ctx, struct observe_node *obs, void *user_data)
{
	struct lwm2m_message *msg;
	struct lwm2m_engine_obj_inst *obj_inst;
	struct lwm2m_obj_path *path;
	int ret = 0;
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	struct lwm2m_cache_read_info cache_temp_info;

	cache_temp_info.entry_size = 0;
	cache_temp_info.entry_limit = 0;
#endif

	msg = lwm2m_get_message(ctx);
	if (!msg) {
		LOG_ERR("Unable to get a lwm2m message!");
		return -ENOMEM;
	}
msg_init:

	if (!obs->composite) {
		path = lwm2m_read_first_path_ptr(&obs->path_list);
		if (!path) {
			LOG_ERR("Observation node not include path");
			ret = -EINVAL;
			goto cleanup;
		}
		/* copy path */
		memcpy(&msg->path, path, sizeof(struct lwm2m_obj_path));
		LOG_DBG("[%s] NOTIFY MSG START: %u/%u/%u(%u) token:'%s' [%s] %lld",
			obs->resource_update ? "MANUAL" : "AUTO", path->obj_id, path->obj_inst_id,
			path->res_id, path->level, sprint_token(obs->token, obs->tkl),
			lwm2m_sprint_ip_addr(&ctx->remote_addr), (long long)k_uptime_get());

		obj_inst = get_engine_obj_inst(path->obj_id, path->obj_inst_id);
		if (!obj_inst) {
			LOG_ERR("unable to get engine obj for %u/%u", path->obj_id,
				path->obj_inst_id);
			ret = -EINVAL;
			goto cleanup;
		}
	} else {
		LOG_DBG("[%s] NOTIFY MSG START: (Composite)) token:'%s' [%s] %lld",
			obs->resource_update ? "MANUAL" : "AUTO",
			sprint_token(obs->token, obs->tkl), lwm2m_sprint_ip_addr(&ctx->remote_addr),
			(long long)k_uptime_get());
	}

	msg->operation = LWM2M_OP_READ;
	msg->type = COAP_TYPE_CON;
	msg->code = COAP_RESPONSE_CODE_CONTENT;
	msg->mid = coap_next_id();
	msg->token = obs->token;
	msg->tkl = obs->tkl;
	msg->reply_cb = notify_message_reply_cb;
	msg->message_timeout_cb = notify_message_timeout_cb;
	msg->out.out_cpkt = &msg->cpkt;

	ret = lwm2m_init_message(msg);
	if (ret < 0) {
		LOG_ERR("Unable to init lwm2m message! (err: %d)", ret);
		goto cleanup;
	}
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	msg->cache_info = &cache_temp_info;
#endif

	/* lwm2m_init_message() cleans the coap reply fields, so we assign our data here */
	msg->reply->user_data = user_data;

	/* each notification should increment the obs counter */
	obs->counter++;
	ret = coap_append_option_int(&msg->cpkt, COAP_OPTION_OBSERVE, obs->counter);
	if (ret < 0) {
		LOG_ERR("OBSERVE option error: %d", ret);
		goto cleanup;
	}

	/* set the output writer */
	select_writer(&msg->out, obs->format);
	if (obs->composite) {
		/* Use do send which actually do Composite read operation */
		ret = do_send_op(msg, obs->format, &obs->path_list);
	} else {
		ret = do_read_op(msg, obs->format);
	}

	if (ret < 0) {
		if (lwm2m_timeseries_data_rebuild(msg, ret)) {
			/* Message Build fail by ENOMEM and data include timeseries data.
			 * Try rebuild message again by limiting timeseries data entry lengths.
			 */
			goto msg_init;
		}
		LOG_ERR("error in multi-format read (err:%d)", ret);
		goto cleanup;
	}

	obs->active_notify = msg;
	obs->resource_update = false;
	lwm2m_information_interface_send(msg);
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	msg->cache_info = NULL;
#endif

	LOG_DBG("NOTIFY MSG: SENT");
	return 0;

cleanup:
	lwm2m_reset_message(msg, true);
	return ret;
}

static int lwm2m_perform_composite_read_root(struct lwm2m_message *msg, uint8_t *num_read)
{
	int ret;
	struct lwm2m_engine_obj *obj;
	struct lwm2m_engine_obj_inst *obj_inst;
	sys_slist_t *engine_obj_list = lwm2m_engine_obj_list();

	SYS_SLIST_FOR_EACH_CONTAINER(engine_obj_list, obj, node) {
		/* Security obj MUST NOT be part of registration message */
		if (obj->obj_id == LWM2M_OBJECT_SECURITY_ID) {
			continue;
		}

		msg->path.level = 1;
		msg->path.obj_id = obj->obj_id;

		obj_inst = next_engine_obj_inst(msg->path.obj_id, -1);

		if (!obj_inst) {
			continue;
		}

		ret = lwm2m_perform_read_object_instance(msg, obj_inst, num_read);
		if (ret == -ENOMEM) {
			return ret;
		}
	}
	return 0;
}

int lwm2m_perform_composite_read_op(struct lwm2m_message *msg, uint16_t content_format,
				    sys_slist_t *lwm2m_path_list)
{
	struct lwm2m_engine_obj_inst *obj_inst = NULL;
	struct lwm2m_obj_path_list *entry;
	int ret = 0;
	uint8_t num_read = 0U;

	/* set output content-format */
	ret = coap_append_option_int(msg->out.out_cpkt, COAP_OPTION_CONTENT_FORMAT, content_format);
	if (ret < 0) {
		LOG_ERR("Error setting response content-format: %d", ret);
		return ret;
	}

	ret = coap_packet_append_payload_marker(msg->out.out_cpkt);
	if (ret < 0) {
		LOG_ERR("Error appending payload marker: %d", ret);
		return ret;
	}

	/* Add object start mark */
	engine_put_begin(&msg->out, &msg->path);

	/* Read resource from path */
	SYS_SLIST_FOR_EACH_CONTAINER(lwm2m_path_list, entry, node) {
		/* Copy path to message path */
		memcpy(&msg->path, &entry->path, sizeof(struct lwm2m_obj_path));

		if (msg->path.level >= LWM2M_PATH_LEVEL_OBJECT_INST) {
			obj_inst = get_engine_obj_inst(msg->path.obj_id, msg->path.obj_inst_id);
		} else if (msg->path.level == LWM2M_PATH_LEVEL_OBJECT) {
			/* find first obj_inst with path's obj_id */
			obj_inst = next_engine_obj_inst(msg->path.obj_id, -1);
		} else {
			/* Read root Path */
			ret = lwm2m_perform_composite_read_root(msg, &num_read);
			if (ret == -ENOMEM) {
				LOG_ERR("Supported message size is too small for read root");
				return ret;
			}
			break;
		}

		if (!obj_inst) {
			continue;
		}

		ret = lwm2m_perform_read_object_instance(msg, obj_inst, &num_read);
		if (ret == -ENOMEM) {
			return ret;
		}
	}
	/* did not read anything even if we should have - on single item */
	if (num_read == 0U) {
		return -ENOENT;
	}

	/* Add object end mark */
	if (engine_put_end(&msg->out, &msg->path) < 0) {
		return -ENOMEM;
	}

	return 0;
}

int lwm2m_parse_peerinfo(char *url, struct lwm2m_ctx *client_ctx, bool is_firmware_uri)
{
	struct http_parser_url parser;
#if defined(CONFIG_LWM2M_DNS_SUPPORT)
	struct zsock_addrinfo *res, hints = {0};
#endif
	int ret;
	uint16_t off, len;
	uint8_t tmp;

	LOG_DBG("Parse url: %s", url);

	http_parser_url_init(&parser);
	ret = http_parser_parse_url(url, strlen(url), 0, &parser);
	if (ret < 0) {
		LOG_ERR("Invalid url: %s", url);
		return -ENOTSUP;
	}

	off = parser.field_data[UF_SCHEMA].off;
	len = parser.field_data[UF_SCHEMA].len;

	/* check for supported protocol */
	if (strncmp(url + off, "coaps", len) != 0) {
		return -EPROTONOSUPPORT;
	}

	/* check for DTLS requirement */
	client_ctx->use_dtls = false;
	if (len == 5U && strncmp(url + off, "coaps", len) == 0) {
#if defined(CONFIG_LWM2M_DTLS_SUPPORT)
		client_ctx->use_dtls = true;
#else
		return -EPROTONOSUPPORT;
#endif /* CONFIG_LWM2M_DTLS_SUPPORT */
	}

	if (!(parser.field_set & (1 << UF_PORT))) {
		if (is_firmware_uri && client_ctx->use_dtls) {
			/* Set to default coaps firmware update port */
			parser.port = CONFIG_LWM2M_FIRMWARE_PORT_SECURE;
		} else if (is_firmware_uri) {
			/* Set to default coap firmware update port */
			parser.port = CONFIG_LWM2M_FIRMWARE_PORT_NONSECURE;
		} else {
			/* Set to default LwM2M server port */
			parser.port = CONFIG_LWM2M_PEER_PORT;
		}
	}

	off = parser.field_data[UF_HOST].off;
	len = parser.field_data[UF_HOST].len;

	/* truncate host portion */
	tmp = url[off + len];
	url[off + len] = '\0';

	/* initialize remote_addr */
	(void)memset(&client_ctx->remote_addr, 0, sizeof(client_ctx->remote_addr));

	/* try and set IP address directly */
	client_ctx->remote_addr.sa_family = AF_INET6;
	ret = net_addr_pton(AF_INET6, url + off,
			    &((struct sockaddr_in6 *)&client_ctx->remote_addr)->sin6_addr);
	/* Try to parse again using AF_INET */
	if (ret < 0) {
		client_ctx->remote_addr.sa_family = AF_INET;
		ret = net_addr_pton(AF_INET, url + off,
				    &((struct sockaddr_in *)&client_ctx->remote_addr)->sin_addr);
	}

	if (ret < 0) {
#if defined(CONFIG_LWM2M_DNS_SUPPORT)
#if defined(CONFIG_NET_IPV6) && defined(CONFIG_NET_IPV4)
		hints.ai_family = AF_UNSPEC;
#elif defined(CONFIG_NET_IPV6)
		hints.ai_family = AF_INET6;
#elif defined(CONFIG_NET_IPV4)
		hints.ai_family = AF_INET;
#else
		hints.ai_family = AF_UNSPEC;
#endif /* defined(CONFIG_NET_IPV6) && defined(CONFIG_NET_IPV4) */
		hints.ai_socktype = SOCK_DGRAM;
		ret = zsock_getaddrinfo(url + off, NULL, &hints, &res);
		if (ret != 0) {
			LOG_ERR("Unable to resolve address");
			/* DNS error codes don't align with normal errors */
			ret = -ENOENT;
			goto cleanup;
		}

		memcpy(&client_ctx->remote_addr, res->ai_addr, sizeof(client_ctx->remote_addr));
		client_ctx->remote_addr.sa_family = res->ai_family;
		zsock_freeaddrinfo(res);
#if defined(CONFIG_LWM2M_DTLS_SUPPORT)
		/** copy url pointer to be used in socket */
		client_ctx->desthostname = url + off;
		client_ctx->desthostnamelen = len;
#endif

#else
		goto cleanup;
#endif /* CONFIG_LWM2M_DNS_SUPPORT */
	}

	/* set port */
	if (client_ctx->remote_addr.sa_family == AF_INET6) {
		net_sin6(&client_ctx->remote_addr)->sin6_port = htons(parser.port);
	} else if (client_ctx->remote_addr.sa_family == AF_INET) {
		net_sin(&client_ctx->remote_addr)->sin_port = htons(parser.port);
	} else {
		ret = -EPROTONOSUPPORT;
	}

cleanup:
	/* restore host separator */
	url[off + len] = tmp;
	return ret;
}

int do_composite_read_op_for_parsed_list(struct lwm2m_message *msg, uint16_t content_format,
					 sys_slist_t *path_list)
{
	struct lwm2m_obj_path_list *entry;

	/* Check access rights */
	SYS_SLIST_FOR_EACH_CONTAINER(path_list, entry, node) {
		if (entry->path.level > LWM2M_PATH_LEVEL_NONE &&
		    entry->path.obj_id == LWM2M_OBJECT_SECURITY_ID && !msg->ctx->bootstrap_mode) {
			return -EACCES;
		}
	}

	switch (content_format) {

#if defined(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)
	case LWM2M_FORMAT_APP_SEML_JSON:
		return do_composite_read_op_for_parsed_list_senml_json(msg, path_list);
#endif

#if defined(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)
	case LWM2M_FORMAT_APP_SENML_CBOR:
		return do_composite_read_op_for_parsed_path_senml_cbor(msg, path_list);
#endif

	default:
		LOG_ERR("Unsupported content-format: %u", content_format);
		return -ENOMSG;
	}
}

#if defined(CONFIG_LWM2M_VERSION_1_1)
static int do_send_reply_cb(const struct coap_packet *response, struct coap_reply *reply,
			    const struct sockaddr *from)
{
	uint8_t code;
	struct lwm2m_message *msg = (struct lwm2m_message *)reply->user_data;

	code = coap_header_get_code(response);
	LOG_DBG("Send callback (code:%u.%u)", COAP_RESPONSE_CODE_CLASS(code),
		COAP_RESPONSE_CODE_DETAIL(code));

	if (code == COAP_RESPONSE_CODE_CHANGED) {
		LOG_INF("Send done!");
		if (msg && msg->send_status_cb) {
			msg->send_status_cb(LWM2M_SEND_STATUS_SUCCESS);
		}
		return 0;
	}

	LOG_ERR("Failed with code %u.%u. Not Retrying.", COAP_RESPONSE_CODE_CLASS(code),
		COAP_RESPONSE_CODE_DETAIL(code));

	if (msg && msg->send_status_cb) {
		msg->send_status_cb(LWM2M_SEND_STATUS_FAILURE);
	}

	return 0;
}

static void do_send_timeout_cb(struct lwm2m_message *msg)
{
	if (msg->send_status_cb) {
		msg->send_status_cb(LWM2M_SEND_STATUS_TIMEOUT);
	}
	LOG_WRN("Send Timeout");
	lwm2m_rd_client_timeout(msg->ctx);
}

#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
static bool init_next_pending_timeseries_data(struct lwm2m_cache_read_info *cache_temp,
					  sys_slist_t *lwm2m_path_list,
					  sys_slist_t *lwm2m_path_free_list)
{
	uint32_t bytes_available = 0;

	/* Check do we have still pending data to send */
	for (int i = 0; i < cache_temp->entry_size; i++) {
		if (ring_buf_is_empty(&cache_temp->read_info[i].cache_data->rb)) {
			/* Skip Empty cached buffers */
			continue;
		}

		/* Add to linked list */
		if (lwm2m_engine_add_path_to_list(lwm2m_path_list, lwm2m_path_free_list,
						  &cache_temp->read_info[i].cache_data->path)) {
			return false;
		}

		bytes_available += ring_buf_size_get(&cache_temp->read_info[i].cache_data->rb);
	}

	if (bytes_available == 0) {
		return false;
	}

	LOG_INF("Allocate a new message for pending data %u", bytes_available);
	cache_temp->entry_size = 0;
	cache_temp->entry_limit = 0;
	return true;
}
#endif /* CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT */
#endif /* CONFIG_LWM2M_VERSION_1_1 */

int lwm2m_send_cb(struct lwm2m_ctx *ctx, const struct lwm2m_obj_path path_list[],
			 uint8_t path_list_size, lwm2m_send_cb_t reply_cb)
{
#if defined(CONFIG_LWM2M_VERSION_1_1)
	struct lwm2m_message *msg;
	int ret;
	uint16_t content_format;

	/* Path list buffer */
	struct lwm2m_obj_path_list lwm2m_path_list_buf[CONFIG_LWM2M_COMPOSITE_PATH_LIST_SIZE];
	sys_slist_t lwm2m_path_list;
	sys_slist_t lwm2m_path_free_list;
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	struct lwm2m_cache_read_info cache_temp_info;

	cache_temp_info.entry_size = 0;
	cache_temp_info.entry_limit = 0;
#endif

	/* Validate Connection */
	if (!lwm2m_rd_client_is_registred(ctx)) {
		return -EPERM;
	}

	if (lwm2m_server_get_mute_send(ctx->srv_obj_inst)) {
		LOG_WRN("Send operation is muted by server");
		return -EPERM;
	}

	/* Init list */
	lwm2m_engine_path_list_init(&lwm2m_path_list, &lwm2m_path_free_list, lwm2m_path_list_buf,
				    CONFIG_LWM2M_COMPOSITE_PATH_LIST_SIZE);

	if (path_list_size > CONFIG_LWM2M_COMPOSITE_PATH_LIST_SIZE) {
		return -E2BIG;
	}

	if (IS_ENABLED(CONFIG_LWM2M_RW_SENML_CBOR_SUPPORT)) {
		content_format = LWM2M_FORMAT_APP_SENML_CBOR;
	} else if (IS_ENABLED(CONFIG_LWM2M_RW_SENML_JSON_SUPPORT)) {
		content_format = LWM2M_FORMAT_APP_SEML_JSON;
	} else {
		LOG_WRN("SenML CBOR or JSON is not supported");
		return -ENOTSUP;
	}

	/* Parse Path to internal used object path format */
	for (int i = 0; i < path_list_size; i++) {
		/* Add to linked list */
		if (lwm2m_engine_add_path_to_list(&lwm2m_path_list, &lwm2m_path_free_list,
						  &path_list[i])) {
			return -1;
		}
	}
	/* Clear path which are part are part of recursive path /1 will include /1/0/1 */
	lwm2m_engine_clear_duplicate_path(&lwm2m_path_list, &lwm2m_path_free_list);
	lwm2m_registry_lock();
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
msg_alloc:
#endif
	/* Allocate Message buffer */
	msg = lwm2m_get_message(ctx);
	if (!msg) {
		lwm2m_registry_unlock();
		LOG_ERR("Unable to get a lwm2m message!");
		return -ENOMEM;
	}

msg_init:

	msg->type = COAP_TYPE_CON;
	msg->reply_cb = do_send_reply_cb;
	msg->message_timeout_cb = do_send_timeout_cb;
	msg->code = COAP_METHOD_POST;
	msg->mid = coap_next_id();
	msg->tkl = LWM2M_MSG_TOKEN_GENERATE_NEW;
	msg->out.out_cpkt = &msg->cpkt;

	ret = lwm2m_init_message(msg);
	if (ret) {
		goto cleanup;
	}
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	msg->cache_info = &cache_temp_info;
#endif

	/* Register user callback if defined for confirmation */
	if (reply_cb) {
		msg->reply->user_data = msg;
		msg->send_status_cb = reply_cb;
	}

	ret = select_writer(&msg->out, content_format);
	if (ret) {
		goto cleanup;
	}

	ret = coap_packet_append_option(&msg->cpkt, COAP_OPTION_URI_PATH, LWM2M_DP_CLIENT_URI,
					strlen(LWM2M_DP_CLIENT_URI));
	if (ret < 0) {
		goto cleanup;
	}

	/* Write requested path data */
	ret = do_send_op(msg, content_format, &lwm2m_path_list);
	if (ret < 0) {
		if (lwm2m_timeseries_data_rebuild(msg, ret)) {
			/* Message Build fail by ENOMEM and data include timeseries data.
			 * Try rebuild message again by limiting timeseries data entry lengths.
			 */
			goto msg_init;
		}

		LOG_ERR("Send (err:%d)", ret);
		goto cleanup;
	}
#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	msg->cache_info = NULL;
#endif
	LOG_INF("Send op to server (/dp)");
	lwm2m_information_interface_send(msg);

#if defined(CONFIG_LWM2M_RESOURCE_DATA_CACHE_SUPPORT)
	if (cache_temp_info.entry_size) {
		/* Init Path list for continuous message allocation */
		lwm2m_engine_path_list_init(&lwm2m_path_list, &lwm2m_path_free_list,
					    lwm2m_path_list_buf,
					    CONFIG_LWM2M_COMPOSITE_PATH_LIST_SIZE);

		if (init_next_pending_timeseries_data(&cache_temp_info, &lwm2m_path_list,
						     &lwm2m_path_free_list)) {
			goto msg_alloc;
		}
	}
#endif
	lwm2m_registry_unlock();
	return 0;
cleanup:
	lwm2m_registry_unlock();
	lwm2m_reset_message(msg, true);
	return ret;
#else
	LOG_WRN("LwM2M send is only supported for CONFIG_LWM2M_VERSION_1_1");
	return -ENOTSUP;
#endif
}