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TLV Encoder/Decoder

Binary TLV encoding and decoding per OMA LWM2M spec §6.4.3.

This module implements the OMA LWM2M TLV (Type-Length-Value) binary content-format used for Read responses and Write requests in LWM2M 1.0.

CoAP Content-Format: application/vnd.oma.lwm2m+tlv (11542)

Enumerations​

wb_lwm2m_tlv_type_t​

TLV Identifier Types (OMA-TS-LightweightM2M_Core §6.4.3)

EnumeratorValueDescription
WB_LWM2M_TLV_TYPE_OBJECT_INSTANCE= 0x00Bits 7-6 = 00.
WB_LWM2M_TLV_TYPE_RESOURCE_INSTANCE= 0x40Bits 7-6 = 01.
WB_LWM2M_TLV_TYPE_MULTI_RESOURCE= 0x80Bits 7-6 = 10.
WB_LWM2M_TLV_TYPE_RESOURCE= 0xC0Bits 7-6 = 11.

Macros​

WB_LWM2M_CONTENT_FORMAT_TLV 11542​

application/vnd.oma.lwm2m+tlv

WB_LWM2M_CONTENT_FORMAT_JSON 11543​

application/vnd.oma.lwm2m+json

WB_LWM2M_CONTENT_FORMAT_SENML_JSON 110​

application/senml+json

Functions​

wb_lwm2m_tlv_decode_header​

Decode a single TLV record from a buffer.

int wb_lwm2m_tlv_decode_header(const uint8_t *buf, size_t buf_len, wb_lwm2m_tlv_type_t *tlv_type, uint16_t *id, size_t *value_offset, size_t *value_len)

Parameters:

  • buf (const uint8_t *): Input buffer
  • buf_len (size_t): Remaining buffer length
  • tlv_type (wb_lwm2m_tlv_type_t *): Output: TLV identifier type
  • id (uint16_t *): Output: resource/instance ID
  • value_offset (size_t *): Output: offset of the value data within buf
  • value_len (size_t *): Output: length of the value data

Returns:

Total bytes consumed (header + value), or -1 on error

On success, *tlv_type, *id, *value_offset, *value_len describe the record.

wb_lwm2m_tlv_decode_value​

Decode a TLV value into an lwm2m_value_t based on the expected type.

esp_err_t wb_lwm2m_tlv_decode_value(wb_lwm2m_res_type_t type, const uint8_t *data, size_t data_len, wb_lwm2m_value_t *value)

Parameters:

  • type (wb_lwm2m_res_type_t): Expected resource data type
  • data (const uint8_t *): Pointer to the TLV value bytes
  • data_len (size_t): Length of value bytes
  • value (wb_lwm2m_value_t *): Output: decoded value

Returns:

ESP_OK on success, ESP_ERR_INVALID_SIZE if length is unexpected

wb_lwm2m_tlv_encode_instance​

Encode an entire object instance as concatenated TLV records.

int wb_lwm2m_tlv_encode_instance(const wb_lwm2m_object_def_t *obj, uint16_t inst_id, uint8_t *buf, size_t buf_size)

Parameters:

  • obj (const wb_lwm2m_object_def_t *): Object definition
  • inst_id (uint16_t): Instance ID
  • buf (uint8_t *): Output buffer
  • buf_size (size_t): Size of output buffer

Returns:

Number of bytes written, or -1 on error

Reads each resource via its read callback and concatenates TLV records.

wb_lwm2m_tlv_encode_resource​

Encode a single resource value as a TLV record.

int wb_lwm2m_tlv_encode_resource(uint16_t res_id, const wb_lwm2m_value_t *value, uint8_t *buf, size_t buf_size)

Parameters:

  • res_id (uint16_t): Resource ID
  • value (const wb_lwm2m_value_t *): Resource value to encode
  • buf (uint8_t *): Output buffer
  • buf_size (size_t): Size of output buffer

Returns:

Number of bytes written, or -1 on error

Output format (per OMA spec §6.4.3): [type_byte] [id: 1-2 bytes] [length: 0-3 bytes] [value: N bytes]