Documentation
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Overview ¶
Package coap decodes Constrained Application Protocol (RFC 7252) packets — the application-layer protocol used by constrained IoT devices (6LoWPAN, Thread, OpenThread, Zigbee IP). Pure offline parser; no transport, no hardware.
Wrap-vs-native judgement: CoAP is a fully public IETF specification (RFC 7252). The walker is bit-level decoding over a 4-byte fixed header + variable-length token + option list + optional payload. Wrapping a FAP for this would require an SD-card install + a firmware-fork dependency for a pure parser. Native delivers offline analysis — operators paste a captured CoAP packet from Wireshark / any UDP sniffer and inspect every field without re-running the capture.
Pairs with the existing IoT decoders:
- mqtt_packet_decode for MQTT (the IP-side broker protocol)
- zigbee_zcl_decode for the Zigbee application layer
- ieee802154_decode + zigbee_nwk_decode + zigbee_aps_decode for the underlying mesh stack
Together they cover the IoT application-layer + mesh-network surface.
What this package covers:
- Fixed header decode: 2-bit version + 2-bit type (Confirmable / Non-Confirmable / Acknowledgement / Reset)
- 4-bit token length + 8-bit code + 16-bit message ID
- Code decode: request methods (GET / POST / PUT / DELETE / FETCH / PATCH / iPATCH) + response codes (2.01 Created / 2.04 Changed / 2.05 Content / 4.04 Not Found / 5.00 Internal Server Error / etc.) with documented names
- Token extraction (0-8 bytes)
- Option list walking with delta + length nibble encoding (delta extension byte 13 = +1 byte extension, 14 = +2 byte extension; same encoding for length)
- Per-option-number name lookup for the documented options (Uri-Host, Uri-Port, Uri-Path, Uri-Query, Content-Format, Accept, Max-Age, ETag, If-Match, If-None-Match, Location- Path, Location-Query, Observe, Block1/2, Size1/2, Proxy- Uri, Proxy-Scheme)
- Payload extraction (after the 0xFF marker)
What this package does NOT cover (deliberately out of scope):
- CoAP over DTLS unwrap (operators bring the decrypted CoAP payload post-DTLS)
- Option-value type interpretation past the raw bytes (e.g. Block1/2 size+M+NUM extraction would be a follow-on)
- Observe / OSCORE security extensions
- CoAP over TCP (RFC 8323)
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Header ¶
type Header struct {
Raw int `json:"raw"`
// Version (bits 7..6 of byte 0) — should be 1.
Version int `json:"version"`
// Type (bits 5..4 of byte 0).
Type int `json:"type"`
TypeName string `json:"type_name"`
// TokenLength (bits 3..0 of byte 0) — 0..8 bytes.
TokenLength int `json:"token_length"`
// Code (byte 1) — request method or response code packed as
// (class << 5) | (detail). 0.01..0.04 = requests; 2.xx /
// 4.xx / 5.xx = responses.
Code int `json:"code"`
CodeText string `json:"code_text"`
CodeName string `json:"code_name"`
// MessageID (bytes 2..3, big-endian).
MessageID int `json:"message_id"`
}
Header is the decoded 4-byte CoAP fixed header.
type Option ¶
type Option struct {
// Number is the absolute option number (computed by summing
// the delta nibbles across the option list).
Number int `json:"number"`
// Name is the canonical option name when in our catalog,
// "" otherwise.
Name string `json:"name,omitempty"`
// Length is the option value length in bytes.
Length int `json:"length"`
// ValueHex is the operator-facing hex rendering of the
// value bytes. Always populated.
ValueHex string `json:"value_hex,omitempty"`
// ValueString is the UTF-8 string interpretation when the
// option is a documented string type (Uri-Host, Uri-Path,
// Uri-Query, Location-Path, etc.).
ValueString string `json:"value_string,omitempty"`
// ValueUint is the unsigned-integer interpretation when the
// option is a documented uint type (Uri-Port, Content-Format,
// Accept, Max-Age, etc.). nil for non-uint options.
ValueUint *uint64 `json:"value_uint,omitempty"`
}
Option is one decoded CoAP option entry.
type Packet ¶
type Packet struct {
Header Header `json:"header"`
// TokenHex is the 0-8 byte token, hex-rendered.
TokenHex string `json:"token_hex,omitempty"`
// Options is the ordered list of decoded options.
Options []Option `json:"options,omitempty"`
// PayloadHex is the payload after the 0xFF marker.
PayloadHex string `json:"payload_hex,omitempty"`
// PayloadString is the UTF-8 string interpretation when
// printable.
PayloadString string `json:"payload_string,omitempty"`
}
Packet is the top-level decoded CoAP packet.
func Decode ¶
Decode parses a hex-encoded CoAP packet. Tolerates ':' / '-' / '_' / whitespace separators.
func DecodeBytes ¶
DecodeBytes is the byte-slice variant of Decode.
type Type ¶
type Type int
Type is the 2-bit message type field at bits 5..4 of byte 0.
const ( // TypeConfirmable — server must ACK; client retransmits. TypeConfirmable Type = 0 // TypeNonConfirmable — fire-and-forget; no ACK. TypeNonConfirmable Type = 1 // TypeAcknowledgement — response to a Confirmable request. TypeAcknowledgement Type = 2 // TypeReset — message could not be processed; reset peer. TypeReset Type = 3 )
Source Files