Module codec 

CoAP (RFC 7252) message codec.

Hand-rolled on purpose: the server’s encoder and the coap / coap-lite crates used as the test peer are then genuinely independent implementations, so a round trip through them is evidence rather than a tautology.

Covers the 4-byte binary header, the four message types, tokens, the option delta/length encoding with both extension forms, the payload marker, and the request/response code space, and the option values Observe (RFC 7641) and Block-wise transfer (RFC 7959) carry: BlockValue and the Observe sequence. What those options mean — registrations, reassembly, the transfer cache — is observe.rs and blockwise.rs; this file only reads and writes them. Not covered: DTLS.

Structs

BlockValue

A Block1 or Block2 option value: NUM << 4 | M << 3 | SZX (RFC 7959 §2.2).

CoapMessage

A decoded CoAP message.

MessagePrefix

The part of a message that lives at fixed offsets: the header and the token.

Enums

DecodeError

Why a datagram is not a CoAP message.

EncodeError

Why a message cannot be put on the wire.

MessageType

CoAP message type (the T field).

Constants

CODE_BAD_OPTION

CODE_BAD_REQUEST

CODE_CONTENT

CODE_CONTINUE

CODE_DELETE

CODE_EMPTY

The empty code, 0.00 — used by ACK and RST, and by a CoAP ping.

CODE_GET

CODE_INTERNAL_SERVER_ERROR

CODE_METHOD_NOT_ALLOWED

CODE_NOT_FOUND

CODE_POST

CODE_PUT

CODE_REQUEST_ENTITY_INCOMPLETE

CODE_REQUEST_ENTITY_TOO_LARGE

CODE_SERVICE_UNAVAILABLE

HEADER_LEN

Fixed CoAP header length: Ver/T/TKL, Code, Message ID.

MAX_BLOCK_NUM

Largest block number a three-byte option value can carry.

MAX_MESSAGE_LEN

Largest inbound datagram this server will process, in bytes.

MAX_OPTION_LEN

Longest value a single option may carry, in octets.

MAX_PAYLOAD_LEN

Largest payload this server will put in one message, in bytes — the largest Block2 block (SZX 6).

MAX_REPRESENTATION_LEN

Largest representation the model may return, in bytes — and the largest request body a Block1 upload may reassemble to.

MAX_SZX

The largest size exponent: SZX 6 is 1024 bytes. 7 is reserved (BERT, CoAP over TCP only).

MAX_TOKEN_LEN

Longest token a message may carry, in octets (RFC 7252 §3).

OPT_ACCEPT

OPT_BLOCK1

Block1 (RFC 7959 §2.1): which block of the request body this is.

OPT_BLOCK2

Block2 (RFC 7959 §2.1): which block of the response this is, or which one is wanted.

OPT_CONTENT_FORMAT

OPT_ETAG

OPT_IF_MATCH

OPT_IF_NONE_MATCH

OPT_LOCATION_PATH

OPT_LOCATION_QUERY

OPT_MAX_AGE

OPT_OBSERVE

Observe (RFC 7641 §2): 0 registers, 1 deregisters, and in a notification it is the sequence number.

OPT_SIZE1

Size1 (RFC 7252 §5.10.9, RFC 7959 §4): the whole request body’s length, or in a 4.13 the largest one the server will take.

OPT_SIZE2

Size2 (RFC 7959 §4): the whole representation’s length.

OPT_URI_HOST

OPT_URI_PATH

OPT_URI_PORT

OPT_URI_QUERY

PAYLOAD_MARKER

Marks the start of the payload, after any options.

VERSION

CoAP version implemented here.

Functions

code

Build a code byte from the human class.detail pair, e.g. 2.05 -> code(2, 5).

code_class

Class portion of a code byte (the digit before the dot).

code_detail

Detail portion of a code byte (the two digits after the dot).

code_to_string

Render a code byte in the conventional c.dd notation.

content_format_id

Content-Format identifier for a media type name.

content_format_name

Media type name for a Content-Format identifier.

message_prefix

Read the header and token of a datagram without touching its options or payload.

method_name

Method name for a request code, or None if this is not a request code.

parse_code_string

Parse "2.05" (or "2.05 Content") into a code byte.

reset_for

An empty Reset for the given message id (RFC 7252 §4.2).

response_to

Build the piggybacked/separate response shell for a request.

response_to_prefix

The same shell, built from a MessagePrefix — for a datagram that was refused before it was decoded, which therefore has no CoapMessage to answer from.

szx_size

Block size for a size exponent, 2^(szx + 4), clamped to SZX 6.

uint_option

A CoAP unsigned integer option value: minimum-length big-endian (RFC 7252 §3.2), so zero is the empty string rather than a zero byte.