Wireshark-bugs: [Wireshark-bugs] [Bug 12508] Wireshark writes Enhanced Packet Blocks without Opt
Guy Harris
changed
bug 12508
| What |
Removed |
Added |
| Status |
UNCONFIRMED
|
RESOLVED
|
| Resolution |
---
|
NOTABUG
|
Comment # 1
on bug 12508
from Guy Harris
(In reply to Paul Offord from comment #0)
> Wireshark writes PCAP-NG files using Enhanced Packet Blocks (EPBs). At the
> end of the EPB, just before the trailing Block Total Length, is an Options
> block.
At the end of an EPB, or any other type of block, there *MAY BE* an options
block; to quote the pcapng specification:
3.5. Options
All the block bodies MAY embed optional fields. ...
Emphasis on "MAY".
> If there are no options, the Option Block should have a single entry
> referred to as opt_endofeopt.
Nope, the pcapng specification doesn't say that. If the lengths of the Block
Type, Block Total Length, non-option part of the Block Body, and second Block
Total Length field add up to the value of the Block Total Length field, the
block has no options.
> Wireshark does not add the opt_endofopt bytes to the EPB.
And, if there are no options, it shouldn't.
> If another program writes EPBs with the opt_endofopt Option entry, Wireshark
> misreads the blocks causing unpredictable errors.
If so, that's a *separate* bug, and you should file it as a separate bug, with
a capture file, as written by the other program, attached, demonstrating the
problem.
The file attached to *this* bug reads fine in a reasonably recent Wireshark
master branch version of Wireshark, a reasonably recent Wireshark 2.0.x branch
version of Wireshark, and a reasonably recent master branch version of tcpdump
with a reasonably recent master branch version of libpcap, so there doesn't
seem to be anything wrong with it; both EPBs have lengths that are exactly
large enough to include the Block Type, Block Total Length, fixed-length part
of the EPB, packet data (as per the captured length), 2 bytes of padding (to a
multiple of 4 bytes) in the second EPB, and the trailing Block Total Length, so
they have no options and no option parsing is done on them.
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