Canonical, direction-independent flow keys - #131
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netprotocols.flow adds FlowKey (a NamedTuple, since canonicalizing the two directions is comparing two (address, port) endpoint tuples, which a plain tuple already orders natively) and flow_key(), mirroring checksum.compute()'s signature shape: the transport layer positionally, the enclosing IPv4/IPv6 header as keyword-only ip=. Both directions of one TCP/UDP conversation produce the identical key: the two endpoints are always emitted lexicographically-smaller-first. Reads whichever of IPv4.protocol / IPv6.next_header the enclosing header has (same semantic field, different attribute name). A transport layer with no ports (ICMP) returns None from both the free function and Packet.flow_key() -- no invented port-slot convention, matching this codebase's established "None rather than raising" pattern. Packet.flow_key() walks self.layers for the first IPv4/IPv6 and TCP/UDP layers and delegates to the free function, mirroring with_checksums()'s enclosing-IP scan; None if either layer is missing. Closes#89. Co-Authored-By: Claude <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01SVCFe7B1U5VeJRoUbx24vb
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This was referenced Sep 4, 2026
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Summary
Closes#89.
netprotocols.flowis a new small module (FlowKey,flow_key(), mirroringchecksum.py's footprint) that folds a TCP/UDP segment and its enclosing IPv4/IPv6 header into a key that is identical for both directions of one conversation — a request and its reply key equal, whichever one you feed in.What's included
FlowKey— aNamedTuple(not a frozen dataclass): canonicalizing the two directions is comparing two(address, port)endpoint tuples and always emitting the lexicographically smaller one first, which a plain tuple already orders natively via<=. Every other frozen dataclass in this codebase models a wire format (decode()/__bytes__/_struct); a derived key isn't one, soNamedTupleis the right tool rather than boltingorder=Trueonto a dataclass.flow_key(layer, *, ip=None)— mirrorschecksum.compute()'s signature shape (transport layer positionally, enclosing IP keyword-only). Reads whichever ofIPv4.protocol/IPv6.next_headerthe enclosing header actually has (same semantic field, different attribute name).Packet.flow_key()— the convenience method. Walksself.layersfor the first IPv4/IPv6 and TCP/UDP layers (mirroring the exact enclosing-IP scanPacket.with_checksums()already uses) and delegates to the free function.Nonefrom both forms — not an exception, and no invented port-slot convention (NetFlow's ICMP type/code-into-port trick is real prior art but unlabeled magic here) — matching this codebase's established "Nonerather than raising" pattern (the NDP accessors inicmp.py).tests/test_flow.py: both directions of a TCP conversation produce equal keys (headers constructed independently, never assembled into aPacket); IPv4 and IPv6 both work; UDP works; ICMP returnsNonefrom both the free function andPacket.flow_key();FlowKeyis hashable and works as a dict key; a missingipfor a TCP/UDP layer raisesInvalidFieldError;Packet.flow_key()matches the free function and returnsNonewhen either layer is missing.ARCHITECTURE.md's layout map lists the new module.CHANGELOG.mdentry under## [Unreleased].Verification
uv run --frozen ruff check .anduv run --frozen ruff format --check .are cleanuv run --frozen mypyis clean (strict)uv run --frozen pytestpasses locallyuv run --frozen python scripts/benchmark.py --check --threshold 15— within threshold (+37.2% vs. baseline)CHANGELOG.mdhas an entry under## [Unreleased]No new protocol/dispatch change, so that checklist block doesn't apply.
Notes
Second of the three remaining Tier 2 issues (#90 → #89 → #92, per the roadmap's #107 working agreement) — merged one at a time, not auto-merged.
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https://claude.ai/code/session_01SVCFe7B1U5VeJRoUbx24vb
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