[JarryShaw]

• Searched for similar pull requests
• Followed the coding style (make pylint, make mypy, make isort) — ran pylint/isort/mypy on arp.py only: no new findings vs main; not the full make targets
• make test passes, and a test case covers the change — modules listed below only, not the full suite
• Added a changelog entry — N/A, added centrally after the wave

What is the purpose of your pull request?

• fix — corrects a defect

---

Closes #1139. A non-IP str protocol address now packs via bytes.fromhex, matching #1137's hardware-address fix, and non-hex input raises ProtocolError. make() derives hlen/plen from the packed sha/spa when they are omitted. It raises ProtocolError when any address disagrees with its length field. test_link_unit.py pinned 'raw' → b'raw'; it now pins hex → octets.

Probe (before → after): ARP(ptype=0x88B5, plen=2, spa='c000') reads back 6330 → c000. ARP(hlen=4) truncated silently to 24 bytes → ProtocolError. ARP(ptype=IPv6, spa='::1') wrote plen=4 with a truncated address → plen=16, 52 bytes.

Tests: in the new tests/protocols/link/test_arp_proto_addr_length_unit.py, 9 fail without the fix and all pass with it. The 3 that pass either way are the IPv4/IPv6 round-trip and explicit-length guards. All of these pass: test_link_unit 24, test_arp_pcapng_hwaddr_octets_unit 6, test_layer_placement_unit 17, test_rarp_unit 1, test_option_roundtrip_unit 6, test_generated_pcap_runtime 2, test_dispatch_reachability_unit 3, tests/project 385 (1 skipped).

[JarryShaw]

Cross-review verdict on c2acac1e0: GOOD TO GO (ran on Sonnet; author Opus)

• Default output is unchanged: ARP(), ARP().pack(oper=1) and RARP().pack(oper=3) are byte-identical to main. The only in-repo callers, examples/generators/dispatch.py:283 and :291, are unaffected. make() is keyword-only, so the default changing from 6/4 to derived cannot break a positional caller.

• Bugs reproduced on main, fixed here:

  Input	main	This PR
  non-IP spa='c000'	packs ASCII 6330	packs c000
  hlen=4	silently truncated	ProtocolError
  IPv6	28 bytes	52 bytes

• Mismatch checks: a wrong length on each of sha, tha, spa and tpa raises its own ProtocolError.

• Round trips: IPv4, IPv6, non-IP 0x88B5 and Frame Relay hardware all round-trip.

• Tests: with the fix reverted, the new module fails 9.

• mypy: the PR adds no errors; the same 4 arg-type errors are on main.

Labelled breaking: pack-path output changes. Non-IP str addresses now pack as octets, non-hex input raises, mismatched hlen/plen raises, and IPv6 output grows from 28 to 52 bytes.

[github-actions]

Coverage: 88.75% (unit tier, Python 3.14, c2acac1e0, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18757	1035	2342	846	90.23%
pcapkit/corekit	1873	91	578	22	94.33%
pcapkit/dumpkit	136	0	40	0	100.00%
pcapkit/foundation	2425	145	842	34	92.56%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	15671	188	3948	163	98.18%
pcapkit/toolkit	487	65	144	1	85.42%
pcapkit/utilities	429	4	122	4	98.55%
pcapkit/vendor	4409	2359	1006	158	42.84%

Per-file detail: the coverage-html artifact of this run.