Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 12368] New: Returning 0 for "this isn't my packet" doesn't work for zero-lengt

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Bug ID	12368
Summary	Returning 0 for "this isn't my packet" doesn't work for zero-length packets
Product	Wireshark
Version	Git
Hardware	All
OS	All
Status	UNCONFIRMED
Severity	Normal
Priority	Low
Component	Dissection engine (libwireshark)
Assignee	bugzilla-admin@wireshark.org
Reporter	guy@alum.mit.edu

Build Information:
N/A
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As indicated in bug 12366, there can be zero-length packets for some protocols.

Dissectors currently return the number of bytes they've dissected, with a
return value of 0 meaning "this isn't a packet for my protocol".

That doesn't distinguish between "this is my packet, but it'z zero-length" and
"this isn't my packet".

We need a better way to indicate "this isn't my packet", distinct from
indicating how many packet bytes were dissected.

There are callers that need to know how many packet bytes were dissected, so
simply changing dissectors to return an "accepted vs. rejected" Boolean and not
providing an indication of how many packet bytes were dissected won't work.

We could return a structure with both bits of information, but that's a bit
more of a pain to write (C90 doesn't support returning anonymous structure
values), and the return operation is more generated code (most if not all C
calling sequences don't support returning a short structure in two registers).

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