[JarryShaw]

• Searched for similar pull requests

• Followed the coding style (make pylint, make mypy, make isort) — not run in full; isort clean on the new test, mypy shows no errors on the changed lines

• make test passes, and a test case covers the change — only the modules listed below

• Added a changelog entry — N/A, added centrally

• fix — corrects a defect

---

Closes #1189

make(parameters=None) now writes Header Length 4 (the two HITs, RFC 7401 §5.1). read() rejects a wire length below 4, because _prml = (len - 4) * 8 would be negative but still truthy. The parameters-present path (total // 8 + 4) was already correct. test_hip_unit.py:229 pinned the old 0 and now expects 4.

Probe, HIPv1 and HIPv2: before, ProtocolError: HIPv{1,2}: invalid format. After, 40 octets, length byte 4, and it parses back to info.length == 40.

New tests/protocols/internet/test_hip_parameterless_length_unit.py: 3 passed. With the make fix reverted, 4 subtests fail. With the read guard reverted, 2 subtests fail.
Each test_hip_* module and test_option_roundtrip_unit.py pass. tests/project: 389 passed, 1 skipped. run_unittest_leg.py protocols/internet: 487 tests, 0 failures.

[JarryShaw]

Cross-review verdict on d37a27131: GOOD TO GO (ran on Sonnet; the author ran on Opus).

• The bug reproduces on main: HIP(parameters=None, ...) raises HIPv1/HIPv2: invalid format.
• Fixed on this branch: v1 and v2 each produce 40 octets with a length byte of 4, info.length == 40, and a byte-exact re-parse. I re-ran this myself.
• The new read guard is message-only: lengths 0–3 already raised ProtocolError on main. Lengths 4–7 parse identically on both sides, for v1 and v2.
• Fails without the fix: each new test fails without its half of the fix (4 and 2 subtests). run_unittest_leg.py protocols/internet: 487 tests, 0 failures.
• Nit, separate from this PR: make() with an unpadded raw-bytes parameter still rounds Header Length down. That is existing behaviour on main, and RFC 7401 requires parameters padded to 8 octets.
• UNVERIFIED: the RFC 7401 §5.1 wording was checked from memory, not re-fetched.

[github-actions]

Coverage: 88.90% (unit tier, Python 3.14, d37a27131, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18757	1034	2342	845	90.24%
pcapkit/corekit	1878	91	580	22	94.34%
pcapkit/dumpkit	142	0	42	0	100.00%
pcapkit/foundation	2442	102	852	39	94.38%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	15749	190	4008	165	98.17%
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.