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fix(schema): a SchemaField reads its declared span but packs only the bytes its nested schema consumed #1292
Description
Describe the bug
Unpack hands the nested schema the whole declared span (schema.py:955-958, data.read(length)), but the nested schema reads less, and pack emits only what it consumed. The enclosing length field still says the old size, so the output is internally inconsistent and the unread octets are gone.
To Reproduce
class In(Schema): x = UInt8Field()
class Out2(Schema):
n = UInt8Field(); inner = SchemaField(length=lambda pkt: pkt["n"], schema=In); tail = UInt8Field()
Out2.unpack(bytes.fromhex("0302eeee04"), 5, None).pack().hex() # "030204"n is still 3 but eeee is lost.
Repro: /tmp/rtissues/corekit-repro.py (check D6) on origin/main 11ae68e.
Expected behavior
The unread octets are kept (as padding or a remainder) and re-emitted, or the span shrinks to match.
Found by the corekit round-trip audit (#1202). The repro was re-checked by an independent verifier, and I re-ran it on main at 11ae68ebf.
Activity
JarryShaw commentedon Oct 7, 2026
Blocked until the core schema PR for #1274/#1275/#1265/#1285 merges, because both edit
protocols/schema/schema.py.JarryShaw commentedon Oct 7, 2026
Unblocked: #1331 merged at 20:41Z. Back to
pending.JarryShaw commentedon Oct 7, 2026
Partly fixed by #1374 (parse → pack byte-exact). The parse →
from_datahalf is filed as #1380; close this once both have merged.fix(schema): Schema.pack keeps option padding, SchemaField spans and …
fix(schema): Schema.pack keeps option padding, SchemaField spans and …
JarryShaw commentedon Oct 8, 2026
Both halves have merged: parse → pack in #1374, parse →
from_datain #1397 (which closed #1380). Closing.