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Problem with extcap preferences in TShark (Wireshark) 3.4.2

asked 2021-01-18 07:51:33 +0000

hgiraldos gravatar image

updated 2021-01-21 15:18:06 +0000

grahamb gravatar image

I have been using these 2 extcap plugins with Wireshark (from 3.0.8 to 3.2) without problems.

I recently updated Wireshark and I have the following problems:

C:\Users\hgir>"C:\Program Files\Wireshark\tshark.exe" "-l" "-n" "-T" "pdml" "-o" "extcap.cc2531.channel:11" "-i" "TI CC2531 802.15.4 packet sniffer"

** (tshark.exe:8004): WARNING **: No such preference "extcap.cc1352r1.com_port" at line 386 of
C:\Users\hgir\AppData\Roaming\Wireshark\preferences (save preferences to remove this warning)

** (tshark.exe:8004): WARNING **: No such preference "extcap.cc1352r1.op_band" at line 390 of
C:\Users\hgir\AppData\Roaming\Wireshark\preferences (save preferences to remove this warning)

** (tshark.exe:8004): WARNING **: No such preference "extcap.cc2531.channel" at line 398 of
C:\Users\hgir\AppData\Roaming\Wireshark\preferences (save preferences to remove this warning)

The preferences related to extcap plugins do not seem to work.

I use these preferences to change the channel in tshark, so I get the following error:

tshark: -o flag "extcap.cc2531.channel:11" specifies unknown preference

I have been reviewing the doc related to extcap in the new version but I did not find any clues.

Any ideas? Any site with advanced documentation or API changes?

P.S: I have access to the source code, so I can do modifications in the plugins or in the configuration.

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We don't close answers here, instead accept the most helpful answer by clocking the checkmark icon to the left of it.

grahamb gravatar imagegrahamb ( 2021-01-24 17:44:02 +0000 )edit

Yes, I tried, but I need >50 points to accept my own answer and I do not have them, so I did not find any other way to finish this issue.

hgiraldos gravatar imagehgiraldos ( 2021-01-24 18:54:04 +0000 )edit

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answered 2021-01-21 17:08:18 +0000

hgiraldos gravatar image

updated 2021-01-24 17:31:09 +0000

To make extcap preferences work in TShark is necessary to add "currentprefs" to the command.

"C:\Program Files\Wireshark\tshark.exe" "currentprefs" "-l" "-n" "-T" "pdml" "-o" "extcap.cc2531.channel:11" "-i" "TI CC2531 802.15.4 packet sniffer"

This change was introduce in v3.0.0, commit 9c53ac0187.

Anyway, I will update the plugins at @grahamb suggested.

Edit: Fix has been merged.

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That code is only called with the -G option to dump information.
Maybe tshark should call extcap_register_preferences() on startup like the GUI does in main.cpp ?

Chuckc gravatar imageChuckc ( 2021-01-21 18:02:58 +0000 )edit

Yes, agree. I have done a merge request in wireshark's repository.

https://gitlab.com/wireshark/wireshar...

hgiraldos gravatar imagehgiraldos ( 2021-01-22 09:10:39 +0000 )edit
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answered 2021-01-18 08:46:05 +0000

grahamb gravatar image

Are the plugins actually loading, if not that might explain the lack of support for their preferences?

Does tshark -G plugins list your extcaps?

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Yes it does.

ethercat.dll            0.1.0   dissector       C:\Program Files\Wireshark\plugins\3.4\epan\ethercat.dll
...
cc1352r1.exe            0.0.1   extcap  C:\Program Files\Wireshark\extcap\cc1352r1.exe
cc2531.exe              0.0.1   extcap  C:\Program Files\Wireshark\extcap\cc2531.exe

Actually,I can use the plugins in Wireshark UI, that's what I found most strange.

hgiraldos gravatar imagehgiraldos ( 2021-01-18 09:14:12 +0000 )edit

Then try printing the preferences, this will be huge so either filter with the tools of your choice or redirect to a file and look with an editor. Using PowerShell:

tshark -G currentprefs | Select-String cc2531
grahamb gravatar imagegrahamb ( 2021-01-18 10:44:34 +0000 )edit

Yes it is present:

PS C:\Program Files\Wireshark> .\tshark.exe -G currentprefs | Select-String cc2531
extcap.cc2531.channel: 14

That means it is written in the configuration file, but I think tshark does not recognize it that is why it shows this warning:

** (tshark.exe:8004): WARNING **: No such preference "extcap.cc2531.channel" at line 398 of
C:\Users\hgir\AppData\Roaming\Wireshark\preferences (save preferences to remove this warning)
hgiraldos gravatar imagehgiraldos ( 2021-01-18 11:50:42 +0000 )edit

I'm not sure what's going on, maybe create a new profile in Wireshark to clean out old preferences, then pass that into tshark with -C.

There have been a few changes in the extcap interface that might explain the issue. Your extcaps use a manual method of constructing the output to describe the plugin options, whereas a common method is provided to do that in the current version of Wireshark, but it's not clear to me that the old manual method is wrong.

grahamb gravatar imagegrahamb ( 2021-01-18 14:23:27 +0000 )edit

I've already tried it with clean profiles and it didn't work. If you have located the commits that may have caused the problem I can test them looking for the beginning of the problem and give a proposal for fixing it.

hgiraldos gravatar imagehgiraldos ( 2021-01-18 14:31:58 +0000 )edit

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Asked: 2021-01-18 07:51:33 +0000

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Last updated: Jan 24