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fix(ipv4): from_data does not round-trip the IPv4 header of http.pcap #1150
Description
Describe the bug
from_data does not round-trip the IPv4 header of examples/captures/http.pcap. Byte 33 reads 0x3c and rebuilds as 0x40, probably the total length or IHL. By contrast, ipv4.pcap and big_endian_nanosecond.pcap round-trip fully.
Reproduction
With #1147 applied, run Frame.from_data(frame.info, num=..., header=...) over http.pcap and compare the result with the original bytes.
Expected behavior
Every IPv4 header in the tracked captures round-trips byte for byte. Check options, padding and whether the total length is recomputed.
Additional context
Found by the #1126 worker. Not yet reproduced independently.
Activity
JarryShaw commentedon Oct 6, 2026
This is not an IPv4 bug. Byte 33 is the low byte of the IPv4 total length (16 + 14 + 3), which goes from 60 to 64.
IPv4.make()computes it correctly asihl*4 + len(payload). The payloadTCP.from_datareturns is 4 bytes too long because_make_tcp_options(tcp.py:2029-2116) drops the original NOPs and re-pads each option separately. Tracked in #1151.A sweep of all 23 captures found no IPv4 field wrong once the TCP and HTTP payload faults are set aside.