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fix(internet): a whole IPv6 extension header rebuilt from its info gains next-layer keys and loses Shim6's protocol #2768
Description
Describe the bug
An IPv6 extension header parsed whole with extension=True rebuilds from from_data(info) with next-layer keys (__next_type__, __next_name__, nopayload) that its parse never had. HOPOPT, IPv6-Opts, IPv6-Frag, AH, MH, HIP and IPv6_Ext all do this, standalone and as the __exthdr__ infos of IPv6. IPv6_Ext (Shim6) also loses protocol. The octets are exact, and a whole IPv6 rebuild is unaffected.
Reproduction
from pcapkit.protocols.internet.ipv6_ext.protocol import IPv6_Ext
p = IPv6_Ext(bytes([59, 0, 0x80, 0, 0, 0, 0, 0]), extension=True, alias=140)
IPv6_Ext.from_data(p.info).info == p.info # False: + __next_name__, __next_type__, nopayload
IPv6_Ext.from_data(p.info, extension=True).info.protocol # None (parse: 140, Shim6)Expected behavior
from_data(info).info == info (test-coverage.rst, Round-Trip Invariants).
Additional context
from_data doesn't replay the parse's extension mode, as it already replays __short_read__. IPv6_Ext.read takes protocol only from the parse-only alias. The capture round-trip test compares .data only, which is why this went unnoticed. It is the uncut counterpart of #2761.
Activity
JarryShaw commentedon Nov 4, 2026
#2774 fixes the extension-mode keys for every header. Shim6's
protocolneeds a decision.The gap:
IPv6_Ext.readtakesprotocolfrom the parse-onlyaliaskeyword. The data model already holds the value (Data_IPv6_Ext.protocol), so_make_datacan return'alias': data.protocol. The construction-keyword check would then warn, because no signature declaresalias.__keywords__ = frozenset({'alias'})toIPv6_Ext. Measured in a scratch edit: the Shim6 rebuild is exact, with no warnings. Downside: subclasses inherit it, soHOPOPT(alias=3)is accepted and silently dropped.'alias'toOUT_OF_BAND_KEYWORDS. This adds no new member, but every protocol would then acceptaliasat construction, andtest_construction_keyword_check_unitpins that set.aliasonIPv6_Ext.__post_init__. This changes the signature and is inherited the same way as (a).Recommendation: (a). It is scoped to the extension-header family, and the new member goes where
protocol-member-order.rstplaces it. The Shim6aliasand in-IPv6 test cases are added once this is ruled.JarryShaw commentedon Nov 4, 2026
take (a)
JarryShaw commentedon Nov 4, 2026
Option (a), reconciled.
IPv6_Extdeclares__keywords__ = frozenset({'alias'}), and_make_datareturns'alias': data.protocol. A rebuilt Shim6 header then keeps itsprotocol, both standalone and inside IPv6, without a keyword warning. Subclasses inherit the keyword, soHOPOPT(alias=3)is accepted and has no effect. That was the accepted downside of (a).The change goes into #2774 as a follow-up commit. The new member goes where
protocol-member-order.rstplaces it. The Shim6alias=140and in-IPv6 cases join the #2768 test. #2774 will then close this issue.fix(internet): keep a rebuilt Shim6 header's protocol through the ali…
fix(internet): rebuild a whole extension header in the extension mode…