IPv4Option: decode Record Route, Timestamp and Router Alert values - #138
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IPv4Option had kind_name and no .value -- the three common kinds (RFC 791 section 3.1, RFC 2113) were named but their contents left raw, unlike TCPOption, which already decodes its values. Record Route: the option's own pointer byte says how many address slots are actually filled (RFC 791: pointer 4 means none yet), which is not generally the same as how much route-data capacity the option declares. .value honors that -- it returns only the recorded addresses, not the full capacity, and returns () rather than None when the pointer is legally at its minimum with nothing recorded. Timestamp: the low nibble of the second data byte is a flag that changes the entry shape -- plain millisecond timestamps for flag 0, or (address, timestamp) pairs for flag 1/3, since the address-carrying variant exists precisely so a timestamp option can identify which IP module returned each entry. The overflow counter and pointer stay undecoded (data raw covers them); mirrors TCPOption's tuple-of-pairs shape for SACK rather than inventing a NamedTuple for something a plain nested tuple already expresses. Router Alert: the 2-byte value as an int (RFC 2113 section 2; 0 is the only value currently defined). Everything else, and malformed data on one of these three (bad pointer, unrecognized flag, wrong length), degrades to None -- same contract as every other .value accessor in this tier. Part of #96. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CP7X7H4k3pBWoiAkBdxATM
This was referenced Sep 4, 2026
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Summary
Part of #96 (the IPv4Option piece — item 3).
IPv4Optionhaskind_nameand novalue. Record Route (7), Timestamp (68) and Router Alert (148) are named, and their contents left raw — unlikeTCPOption, which does decode its values.What's included
IPv4Option.value— a new property, mirroringTCPOption.value's "decode the well-known kinds, degrade toNonefor the rest or on malformed data" contract.tuple[ipaddress.IPv4Address, ...]. RFC 791 §3.1's pointer byte says how many address slots are actually filled, which is not the same as the option's total declared capacity —.valuehonors that and returns only the recorded addresses. Returns()(notNone) when the pointer is legally at its minimum (4) with nothing recorded yet;Nonefor a pointer below 4, misaligned, or pointing past the available route data (malformed, degrades rather than raises).tuple[int, ...]of plain millisecond timestamps (flag 0) ortuple[tuple[ipaddress.IPv4Address, int], ...]of (address, timestamp) pairs (flag 1 or 3 — the variant that also identifies which IP module recorded the entry). The overflow counter and pointer are not decoded here — readdataraw for those.Nonefor an unrecognized flag value or malformed entry length.int(RFC 2113 §2;0is the only value currently defined).Nonemalformed case, direct construction.Design note on Timestamp's shape: rather than inventing a new
NamedTuple, the (address, timestamp) pair mirrorsTCPOption.value's existingtuple[tuple[int, int], ...]shape for SACK — a plain nested tuple already expresses this correctly, and it's the precedent already established in this exact file's sibling module.No breaking change:
.valueis a new property;kind/data/kind_nameare unchanged.Verification
uv run --frozen ruff check .anduv run --frozen ruff format --check .are cleanuv run --frozen mypyis clean (strict,src/only)uv run --frozen pytestpasses locally (full suite)uv run --frozen python scripts/benchmark.py --check --threshold 15— 124,772 f/s, +11.0% vs. baseline, within thresholdCHANGELOG.mdhas an entry under## [Unreleased]New protocol or dispatch change — also:
Not applicable — no new protocol, no dispatch change. Deleted this block's checklist since it doesn't apply.
Notes
Part of #96 (four independent PRs by the issue's own instruction); this is the third of four — only the IPv6Routing/IPv6Option piece remains.
#96itself stays open until all four land.Part of #96.
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https://claude.ai/code/session_01CP7X7H4k3pBWoiAkBdxATM
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