Re: Wireshark-dev Digest, Vol 173, Issue 14

Re: Wireshark-dev Digest, Vol 173, Issue 14

[Amanda Shafack]

Hi Jonathan,

I have completed the MyFirstContribution tutorial
(https://git-scm.com/docs/MyFirstContribution). You can find my work
in this repo (https://github.com/lkmandy/git/tree/psuh).

Also, regarding my initial starter contribution, I chose the
"micro-project" titled "Avoid pipes in git related commands in test
scripts" (source https://bit.ly/3iZQcT2).
Emily has approved the micro-project.

I plan to complete the micro-project and then move on to more research
on Git's HTTP protocol and other resources you've pointed out.

Let me know your thoughts on this, thanks.


On Tue, Oct 13, 2020 at 1:00 PM <wireshark-dev-request@wireshark.org> wrote:
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> Today's Topics:
>
>    1. lua decoder accessing info from layers above (Fulko Hew)
>    2. Re: lua decoder accessing info from layers above (John Thacker)
>    3. Re: lua decoder accessing info from layers above (Guy Harris)
>    4. Re: Introduction - An Outreachy 2020 Applicant (Jonathan Nieder)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 12 Oct 2020 19:59:46 -0400
> From: Fulko Hew <fulko.hew@gmail.com>
> To: Developer support list for Wireshark <wireshark-dev@wireshark.org>
> Subject: [Wireshark-dev] lua decoder accessing info from layers above
> Message-ID:
>         <CAGuV3hNXvRDUL02bmLxbkOLEgbOWQSPwj7sSne8CYCcgrNhPQg@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I'm trying to update/improve someone else's decoder written in Lua.
> It's for a simple UDP (and TCP) based protocol.
> But I need to be able to get access to the upper layer
> to be able to decode it easily.
>
> Can someone provide an example of how to determine if the higher layer was
> UDP or TCP?
>
> Thanks
> Fulko
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>
> ------------------------------
>
> Message: 2
> Date: Mon, 12 Oct 2020 20:33:37 -0400
> From: John Thacker <johnthacker@gmail.com>
> To: Developer support list for Wireshark <wireshark-dev@wireshark.org>
> Subject: Re: [Wireshark-dev] lua decoder accessing info from layers
>         above
> Message-ID:
>         <CAP_QLgo5PYz79BXQvoQyiQGjZ-FqBVq__ybRg10xQ3DYd3KUQQ@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> On Mon, Oct 12, 2020, 8:00 PM Fulko Hew <fulko.hew@gmail.com> wrote:
>
> >
> > I'm trying to update/improve someone else's decoder written in Lua.
> > It's for a simple UDP (and TCP) based protocol.
> > But I need to be able to get access to the upper layer
> > to be able to decode it easily.
> >
> > Can someone provide an example of how to determine if the higher layer was
> > UDP or TCP?
> >
>
> If all you need to know is whether it was called from TCP or UDP, then a
> typical approach is to create slightly different dissector functions, one
> for TCP and one for UDP (they can then call a common function, setting a
> parameter) and register the TCP dissector with TCP and the UDP dissector
> with UDP. That approach for C dissectors is demonstrated, for example, here:
>
> https://gitlab.com/wireshark/wireshark/-/blob/master/doc/README.heuristic
>
> And it's pretty similar for Lua dissectors using some of the examples
> linked from here:
>
> https://gitlab.com/wireshark/wireshark/-/wikis/Lua
>
> John Thacker
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> ------------------------------
>
> Message: 3
> Date: Mon, 12 Oct 2020 17:55:06 -0700
> From: Guy Harris <gharris@sonic.net>
> To: Developer support list for Wireshark <wireshark-dev@wireshark.org>
> Subject: Re: [Wireshark-dev] lua decoder accessing info from layers
>         above
> Message-ID: <93FB74E3-88D0-408F-883D-F0385A916EA0@sonic.net>
> Content-Type: text/plain;       charset=us-ascii
>
> On Oct 12, 2020, at 5:33 PM, John Thacker <johnthacker@gmail.com> wrote:
>
> > If all you need to know is whether it was called from TCP or UDP, then a typical approach is to create slightly different dissector functions,
>
> ...or, in that particular case, slightly *less* different functions, given that UDP provides a packet-based service (so that packet boundaries are provided for you, unless you have to send packets that don't fit in a UDP datagram and add your own reassembly - but, even there, *fragment* boundaries would probably be provided by UDP), while TCP provides a byte-stream service (with *no* packet boundary information).
>
>
>
> ------------------------------
>
> Message: 4
> Date: Mon, 12 Oct 2020 20:10:56 -0700
> From: Jonathan Nieder <jrnieder@gmail.com>
> To: Developer support list for Wireshark <wireshark-dev@wireshark.org>
> Cc: Emily Shaffer <emilyshaffer@google.com>, git@vger.kernel.com
> Subject: Re: [Wireshark-dev] Introduction - An Outreachy 2020
>         Applicant
> Message-ID: <20201013031056.GC3814681@google.com>
> Content-Type: text/plain; charset=us-ascii
>
> Richard Sharpe wrote:
> > Amanda Shafack wrote:
>
> >> Good day.
> >>
> >> I'm Amanda Shafack, an Outreachy 2020 applicant who wishes to
> >> contribute to the "Add Git protocol support to Wireshark" project.
> >>
> >> I have some experience coding in C and I hope to enhance
> >> my skill set by contributing to this project.
> >>
> >> In addition, I'm fascinated by network protocols and it's really
> >> exciting to get my hands around these concepts in a real-world
> >> project.
> >>
> >> I'm currently going through the project description and contribution
> >> guidelines.
> >
> > Welcome. There are many helpful people on the list.
> >
> > It would be useful if you can point us to a protocol description
> > document but that can wait until help is needed. It may be that all
> > the online resources are sufficient, but if not, do not hesitate to
> > use this list to ask questions.
>
> There's an overview of Git's HTTP protocol in the Pro Git book:
>
>   https://git-scm.com/book/en/v2/Git-Internals-Transfer-Protocols
>
> The official protocol spec in git.git (https://git.kernel.org/pub/scm/git/git.git)
> is split between a few files:
>
>   Documentation/technical/protocol-common.txt:
>     conventions for protocol docs
>
>   Documentation/technical/pack-protocol.txt:
>     overview of Git protocol
>
>   Documentation/technical/protocol-capabilities.txt:
>     optional capabilities
>
>   Documentation/technical/protocol-v2:
>     protocol v2, the new default (more about this is at
>     https://opensource.googleblog.com/2018/05/introducing-git-protocol-version-2.html)
>
>   Documentation/technical/http-protocol.txt:
>     how this works with http
>
>   Documentation/technical/pack-format.txt:
>     packed representation of Git objects (used both on disk and over
>     the wire)
>
> Amanda, if you have any questions, please don't hesitate to ask
> (#git-devel on IRC is the best place for that, and email works as
> well).  I am there around 15:00-24:00 UTC most days.  In addition to
> working on your initial starter contributions, we can start to put
> together a plan for the project.
>
> Richard, to set expectations: the internship period for accepted
> interns starts in December: https://www.outreachy.org/apply/project-selection/.
> Until then, potential interns are often not free full time, so we
> focus on smaller contributions that help get their feet wet in the
> codebase.
>
> Excited,
> Jonathan
>
>
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>
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> End of Wireshark-dev Digest, Vol 173, Issue 14
> **********************************************



-- 

Cheers!

Amanda  Shafack

Re: Introduction - An Outreachy 2020 Applicant

[Jonathan Nieder]

Hi Amanda,

Amanda Shafack wrote:

> Also, regarding my initial starter contribution, I chose the
> "micro-project" titled "Avoid pipes in git related commands in test
> scripts" (source https://bit.ly/3iZQcT2).

Thanks, sounds good.

> I plan to complete the micro-project and then move on to more research
> on Git's HTTP protocol and other resources you've pointed out.
>
> Let me know your thoughts on this, thanks.

I think that a good next step after the Git micro-project is to get to
know wireshark --- this would involve building wireshark, finding
something to change, and then changing it.

https://gitlab.com/wireshark/wireshark/-/wikis/Development/ describes
how to download and build wireshark.  Then for something to change, I
have a few different ideas:

a. tighten the error handling in epan/dissectors/packet-git.c
   (for example, what happens when there are not exactly 4 hexdigits
   at the beginning of a pkt-line?).  Git's
   Documentation/technical/protocol-common.txt describes the pkt-line
   format and Documentation/technical/pack-protocol.txt describes the
   Git transport dissected by packet-git.

b. add tests for the Git dissector.  test/README.test and the page it
   links to describe how wireshark's tests work

c. try to parse out the service name and protocol version in
   epan/dissectors/packet-git.c.  Git's
   Documentation/technical/protocol-v2.txt describes where we can find
   that information

That would get us more comfortable with the wireshark codebase and
would help prepare for fleshing out a plan for the internship.

Thoughts?

Sincerely,
Jonathan