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Re: [Wireshark-dev] Using a tap to make a dissector work?
From: Jeff Morriss <jeff.morriss.ws_at_nospam>Date: Tue Mar 08 2011 - 14:55:09 GMT
To: Developer support list for Wireshark <wireshark-dev@wireshark.org>
Sake Blok wrote:
> Hi,
>
> The buildbots are failing on the test.sh script because:
>
> sake@macsake-wifi:~/Wireshark/trunk/test$ ../tshark -r dhcp.pcap -w - > tmp.cap
> tshark: Taps aren't supported when saving to a pipe.
> sake@macsake-wifi:~/Wireshark/trunk/test$
>
> I tracked this down to http://anonsvn.wireshark.org/viewvc?view=revision&revision=35323 in which the tap functionality is used to track mappings that determine how packets should be dissected.
>
> This basically makes writing to a pipe in tshark impossible unless the protocol would be dissabled. What would be the proper way to go?
>
> 1) From a quick view of the code, the tap has been used as the conversation tracking wireshark provides does not provide the proper hooks for this kind of traffic. Should we change the conversation tracking to a more general framework? Or maybe map the indices that are available to the variables that are available (if this is at all possible). But then we need to make sure there will be no overlapping (which kinda calls for a general framework again).
>
> 2) Allow taps to be used in dissectors and remove the check in tshark? Tshark does not know whether the tap is producing output or not, so maybe we need to have a flag with each tap to state whether it will produce output or not.
>
> 3) Just leave things as they are and disable this protocol by default (as has been done to PRP)?
>
> Any ideas?
Just for cross-referencing purposes:
This issue is tracked in
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=5445 . There, Guy
suggested:
> The trick might be to have multiple types of taps, such as ones that produce no
> output, and are allowed to be unconditionally run, and ones that produce
> output, which are not allowed to be unconditionally run. Dissection will be
> forced on in TShark if one of the latter type of taps is listening, but will
> not be forced on if only the former type of taps is listening.
That sounds similar to (2) above.
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