Terminate on any unsupported version instead of sending code 2 - #40
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A challenger's next read after sending CHALLENGE is exactly the 32-byte CHALLENGE-RESPONSE hash, so a response code written into that stream is indistinguishable from the start of a hash. Close without responding (SPEC SS10.5); code 2 remains for unsupported MESSAGE versions, where the peer's first read is always a response code. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This was referenced Aug 10, 2026
Follows the revised ruling in markmnl/fmsg#29: an unsupported version is one we do not know how to respond in, so both branches of readVersionOrChallenge now TERMINATE without writing anything — the message-version branch (first byte <= 128) as well as the challenge branch. Code 2 is therefore never sent on the wire. RejectCodeUnsupportedVersion and its responseCodeName case are removed, with 2 left unassigned so the numbering is unchanged; responseCodeName falls through to unknown(2) if one is ever read from a peer. Its host_test row goes with it.
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Design correction from spec review (markmnl/fmsg#29): an unsupported version is one we don't know how to respond in, so the listener MUST TERMINATE without writing anything — on both first-byte branches.
Changes
readVersionOrChallengecloses without writing on both unsupported branches.RejectCodeUnsupportedVersionand itsresponseCodeNamecase are removed; 2 is left unassigned so existing numbering is unchanged, matching the spec's code table (which already has an unassigned 104).responseCodeNamefalls through tounknown(2)should one ever be read from a peer.host_test.gotable row is dropped.go build,go vet,go test ./...all pass.History
An earlier v0.5.0 spec draft split the two branches — REJECT 2 for the message-version branch, TERMINATE for the challenge branch — and an earlier revision of this PR implemented that split. Review settled on the simpler rule: terminate in both cases. This PR now implements that, and depends on markmnl/fmsg#29 landing with it.
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