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dmicmp API Reference

See dmicmp.md for the design rationale behind this API.

Types

Type	Description
`dmicmp_header_t`	Parsed common ICMP header fields: `type`, `code`, `checksum` (parse output only), `identifier`/`sequence` (Echo Request/Reply only)
`dmicmp_v4_dest_unreachable_code_t`	Enum of ICMPv4 Destination Unreachable codes: `dmicmp_v4_dest_unreachable_net`/`_host`/`_protocol`/`_port`
`dmicmp_echo_reply_handler_t`	Callback registered via `dmicmp_register_echo_listener()`

Constants

Constant	Value	Description
`DMICMP_HEADER_LEN`	8	Length of the common ICMP header (identical layout for v4 and v6)
`DMICMP_V4_TYPE_ECHO_REPLY`	0	ICMPv4 Echo Reply
`DMICMP_V4_TYPE_DEST_UNREACHABLE`	3	ICMPv4 Destination Unreachable
`DMICMP_V4_TYPE_ECHO_REQUEST`	8	ICMPv4 Echo Request
`DMICMP_V6_TYPE_DEST_UNREACHABLE`	1	ICMPv6 Destination Unreachable (receive-only)
`DMICMP_V6_TYPE_ECHO_REQUEST`	128	ICMPv6 Echo Request (receive-only)
`DMICMP_V6_TYPE_ECHO_REPLY`	129	ICMPv6 Echo Reply (receive-only)

Functions

Header build/parse

Function	Description
`dmicmp_build_header()`	Build the 8-byte common ICMP header into a buffer (checksum field left 0)
`dmicmp_parse_header()`	Parse the 8-byte common ICMP header from a buffer

Checksum

Function	Description
`dmicmp_v4_checksum_valid()`	Verify an ICMPv4 message's checksum (no pseudo-header)
`dmicmp_v6_checksum_valid()`	Verify an ICMPv6 message's checksum (IPv6 pseudo-header required, RFC 4443 2.3)

Sending

Function	Description
`dmicmp_v4_send_error()`	General-purpose: send an arbitrary ICMPv4 error message (any type/code) quoting a given original packet - destination, RFC 792 quote, and checksum all filled in automatically
`dmicmp_v4_send_dest_unreachable()`	Thin wrapper over `dmicmp_v4_send_error()` fixed to Destination Unreachable, with a type-safe code enum - usable by other protocol modules (e.g. a future dmudp Port Unreachable), not just internally
`dmicmp_v4_send_echo_request()`	Send an ICMPv4 Echo Request (a "ping") - register a listener first if you want to know about the reply

Echo reply listener registry

Function	Description
`dmicmp_register_echo_listener()`	Register a callback for the next Echo Reply carrying a given identifier (either family)
`dmicmp_unregister_echo_listener()`	Undo `dmicmp_register_echo_listener()` - safe no-op if unregistered

What's not here yet

No dmicmp_v6_send_*() - blocked on dmip_v6_send() not existing yet (no NDP module). Incoming ICMPv6 is still parsed and checksum-validated correctly; an Echo Request or unclaimed protocol that would need a v6 reply is logged and dropped instead.
No dedicated wrapper for Time Exceeded, Redirect, or other RFC 792 message types - reachable today via the general-purpose dmicmp_v4_send_error() primitive, without a dedicated function.