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fix(tcp): reserved bits in the TCP header and in POCSP/Quick-Start options are written back as zero #1211

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#1348
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fix(tcp): reserved bits in the TCP header and in POCSP/Quick-Start options are written back as zero#1211
#1348
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fixPull requests that fix a defect (fix: subject prefix)

Description

@JarryShaw
JarryShaw
opened on Oct 7, 2026

Describe the bug
The header's reserved nibble and the reserved bits of the POCSP and Quick-Start options are neither mapped by the schema nor carried by the data model, so a rebuild writes them as zero. See schema/transport/tcp.py:1118-1121 (header), :598-601 (POCSP) and :678-685 (QS), and the reader at transport/tcp.py:472.

To Reproduce
A header with byte 12 = 5e rebuilds with 50. A POCSP option 0a033f00 rebuilds as 0a030000. QS 1b08834012345679 rebuilds as 1b08034012345678.

Expected behavior
The reserved bits round-trip unchanged.

Found by the transport round-trip audit (#1202). I re-ran the repro on main at 630f0a581.

Activity

  1. JarryShaw
    added
    fixPull requests that fix a defect (fix: subject prefix)
    pendingAccepted and unstarted - nobody is on it and nothing blocks it
    on Oct 7, 2026
  2. JarryShaw
    added this to PyPCAPKiton Oct 7, 2026
  3. JarryShaw
    moved this to Pending in PyPCAPKiton Oct 7, 2026

  4. JarryShaw commented on Oct 7, 2026

    @JarryShaw
    JarryShaw
    on Oct 7, 2026
    OwnerAuthor

    Blocked until the MPTCP PR for #1212–#1217/#1220 merges, because both edit transport/tcp.py and its schema and data modules.

  5. JarryShaw
    added
    blockedDeferred pending another issue or decision; see the last comment for what unblocks it
    and removed
    pendingAccepted and unstarted - nobody is on it and nothing blocks it
    on Oct 7, 2026

  6. JarryShaw commented on Oct 7, 2026

    @JarryShaw
    JarryShaw
    on Oct 7, 2026
    OwnerAuthor

    Unblocked: #1254 merged at 19:08Z, so the file conflict is gone. Back to pending until a worker picks it up.

  7. JarryShaw
    added
    pendingAccepted and unstarted - nobody is on it and nothing blocks it
    wipWork in flight - a covering PR is open or an agent is actively on it
    and removed
    blockedDeferred pending another issue or decision; see the last comment for what unblocks it
    pendingAccepted and unstarted - nobody is on it and nothing blocks it
    on Oct 7, 2026
  8. JarryShaw
    added 2 commits that reference this issue on Oct 7, 2026

    fix(tcp)!: reserved bits, post-EOOL octets and the UTO granularity ro…

    72615ea

    fix(tcp)!: reserved bits, post-EOOL octets and the UTO granularity ro…

    51eb712
  9. JarryShaw
    closed this as completedin #1348on Oct 7, 2026
  10. JarryShaw
    removed
    wipWork in flight - a covering PR is open or an agent is actively on it
    on Oct 7, 2026
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