KarpelesLab / slirp / 23943906717

71%

push

github

Add vtcp sub-package: foundation for shared RFC-compliant TCP stack

Phase 1 of the vtcp implementation — core building blocks with 88% test
coverage. These components will be composed into the full TCP connection
engine (Phase 2) which will then replace the three ad-hoc TCP
implementations currently in slirp, vclient, and the virtual listener.

Components:

  seqspace.go — TCP sequence number arithmetic with 32-bit wraparound.
    SeqBefore, SeqAfter, SeqInRange, etc.

  segment.go — TCP segment parsing and serialization (raw bytes, no IP).
    ParseSegment, Marshal, SegLen (accounts for SYN/FIN consuming seq).

  options.go — TCP option parse/build for all modern options:
    MSS (RFC 793), Window Scale (RFC 7323), Timestamps (RFC 7323),
    SACK-Permitted and SACK blocks (RFC 2018).

  sendbuf.go — Send buffer tracking app data through the pipeline:
    queued → sent/unacked → acknowledged. Sequence-indexed with
    retransmit support.

  recvbuf.go — Receive buffer with out-of-order segment reassembly
    and SACK scoreboard generation. Handles overlapping segments,
    duplicates, and gap-filling.

  rto.go — RFC 6298 RTO calculator: SRTT/RTTVAR smoothing, Karn's
    algorithm (don't sample retransmits), exponential backoff.

  congestion.go — CongestionController interface + NewReno (RFC 5681):
    slow start, congestion avoidance, fast retransmit (3 dup ACKs),
    fast recovery with cwnd inflation. Initial window per RFC 6928.

  doc.go — Package doc, State enum (RFC 793 states), flag constants,
    SegmentWriter callback type, default parameters.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

437 of 501 new or added lines in 8 files covered. (87.23%)

3174 of 3927 relevant lines covered (80.83%)

10.92 hits per line