Re: Cannot get external capture (extcap) interface to work with my new plugin.

[hdv <henri.de.veer () gmail com>]

Please also see my remarks inline too below this about the mailing list
and template/example code.

I have some additional information on the errorhandling and what goes
wrong in this case:

What I want to do is (when simulating an error in the plugin):

-open the output pipe
-issue a g_error("%s: Could not connect to AnaGate CAN \n", __func__);
-close the output pipe
-return with EXIT_FAILURE

Now the process nicely stops but not "Dumpcap", note that nothing was
sent to the pipe at all! The Wireshark gui displays no error at all,
only "<live capture in progress>", "No Packets". Stopping the capture
shows no error, it just returns to the main screen.

I could recollect vaguely that I have seen an issue with a deadlock in
that area the mailing list. So looking it up reveals this:

https://www.wireshark.org/lists/wireshark-commits/201808/msg00263.html,
and I see that I don't have it in my code tree.

Any idea if it is related to this issue?

Henri


On 4-1-2019 00:10, Dario Lombardo wrote:
> On Thu, Jan 3, 2019 at 5:36 PM hdv <henri.de.veer () gmail com
> <mailto:henri.de.veer () gmail com>> wrote:
>
>
>     On 2-1-2019 18:30, Dario Lombardo wrote:
> >     You cannot trace your code using prints because they're handled
> >     by the caller (dumpcap). Have a look at the other extcaps for
> >     --debug and --debug-file options to see how it's solved there.
>
>     I only see g_warning/g_error/g_debug messages in the other extcap
>     plugins. There is no descent example that really works from the
>     user perspective. The function g_error is not really useful
>     because it forcefully "breaks" the program. See my original post
>     where I already explained this.
>
>     Only extcap_cmdline_debug() does display something in the debug
>     log, when enabled. I see it used g_debug() that ends up in the
>     debug log file. Still a pity that you can't show any popup or
>     error message in a plugin. Or am I missing something?
>
> No you are not. This is a step missing in the original extcap code
> (wireshark side). However lately a new support for extcap toolbars has
> been added. This allows a live message passing between the gui and the
> extcap. Unfortunately it is not as straightforward as the main text
> interface and requires a reactor (or similar) to handle the messages,
> but if you take a look at extcap_example.py you'll get an idea. In C I
> haven't seen any working implementation of the toolbars: it can work
> for sure but the work required compared to python is much more.
>
>     I really would expect that the stderr channel could be used to
>     report errors in some way. Tested it, does not display anything
>     until you stop the capture. It would be better to display it
>     immediately. You should assume when anybody uses a plugin we can
>     report errors to the user in a sensible matter. The end user
>     should not need to enable debugging or build the code to get
>     errors. I my example I want to report an error to the user when
>     the plugin cannot make a connection to the external device for
>     example.
>
>     I have the impression that most extcap plugins need some
>     overhauling of code. Most are very different with respect to some
>     "boilerplate" code everybody uses. So it took me quite some time
>     to cherry pick pieces of the code which looks to be "best
>     practice". Maybe a template/skeletion could be a good idea?
>
> I'm not sure I've got your point. Which overhauling are you referring
> to and which boilerplate or best practice code are you talking about?
> Can you point to some examples?
> A template is somewhat impossible to write: the best we did was to
> have some base functions (extcap-base) and some working examples for them.
I have seen them and I also use these calls, just forget it for now to
avoid cluttering this topic. I will come back on this later.
>     So what is the status of the current extcap plugins, are they
>     still all functional? I can imagine they are harder to test
>     because some are proprietary/need special hardware.
>
> They're expected to be. If they are not, feel free to open bugs on
> bugzilla. Extcaps in the source tree except ciscodump don't require
> special hardware at all.
>
>     PS: Don't understand me wrong about the above remarks: Wireshark
>     is one of the best documented open source projects I have ever
>     seen in my 25+ years of software experience. Most projects can
>     take it as an example how to document and handle it. So I really
>     want to contribute to it, and even get it better.
>
>     Another question off topic: When not a "member" all posts to the
>     wireshark-dev mailing list are moderated so it takes some time to
>     get a post into this list. Who can become member? Is there
>     somewhere described what the procedure is? (I still have some
>     questions and remarks etc. about testing and documentation for
>     example)
>
>     Note: I have seen all documentation on the development process. I
>     did not find anything about the mailing list about any membership.
>
> It has been a loooong time since I subscribed and I don't recall how I
> did it. But googling I found this:
> https://www.wireshark.org/mailman/listinfo/wireshark-dev. Did you try it?
Yes I did that: about half a year ago, to look how the communication
between all developers passes by.  What is the criteria to moderate sent
emails to the sent wireshark-dev list?


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