3.9. Contribute your changes

If you have finished changing the Wireshark sources to suit your needs, you might want to contribute your changes back to the Wireshark community. You gain the following benefits by contributing your improvements:

There’s no direct way to push changes to the Git repository. Only a few people are authorised to actually make changes to the source code (check-in changed files). If you want to submit your changes, you should upload them to the code review system.

3.9.1. Some tips for a good patch

Some tips that will make the merging of your changes into Git much more likely (and you want exactly that, don’t you?):

  • Use the latest Git sources. It’s a good idea to work with the same sources that are used by the other developers. This usually makes it much easier to apply your patch. For information about the different ways to get the sources, see Section 3.3, “Obtain the Wireshark sources”.
  • Update your sources just before making a patch. For the same reasons as the previous point.
  • Inspect your patch carefully. Run git diff and make sure you aren’t adding, removing, or omitting anything you shouldn’t.
  • Find a good descriptive topic name for your patch. Short, specific names are preferred. snowcone-machine-protocol is good, your name or your company name isn’t.
  • Don’t put unrelated things into one large patch. A few smaller patches are usually easier to apply (but also don’t put every changed line into a separate patch.

In general, making it easier to understand and apply your patch by one of the maintainers will make it much more likely (and faster) that it will actually be applied.

[Note]Please remember

Wireshark is a volunteer effort. You aren’t paying to have your code reviewed and integrated.

3.9.2. Code Requirements

The core maintainers have done a lot of work fixing bugs and making code compile on the various platforms Wireshark supports.

To ensure Wireshark’s source code quality, and to reduce the workload of the core maintainers, there are some things you should think about before submitting a patch.

[Warning]Pay attention to the coding guidelines

Ignoring the code requirements will make it very likely that your patch will be rejected.

  • Follow the Wireshark source code style guide. Just because something compiles on your platform, that doesn’t mean it’ll compile on all of the other platforms for which Wireshark is built. Wireshark runs on many platforms, and can be compiled with a number of different compilers. See Section 7.2, “Coding Style”for details.
  • Submit dissectors as built-in whenever possible. Developing a new dissector as a plugin is a good idea because compiling and testing is quicker, but it’s best to convert dissectors to the built-in style before submitting for checkin. This reduces the number of files that must be installed with Wireshark and ensures your dissector will be available on all platforms.

    This is no hard-and-fast rule though. Many dissectors are straightforward so they can easily be put into "the big pile", while some are ASN.1 based which takes a different approach, and some multiple sourcefile dissectors are more suitable to be placed separate as plugin.

  • Verify that your dissector code does not use prohibited or deprecated APIs. This can be done as follows:

    $ perl <wireshark_root>/tools/checkAPIs.pl <source filename(s)>
  • Fuzz test your changes! Fuzz testing is a very effective way to automatically find a lot of dissector related bugs. You’ll take a capture file containing packets affecting your dissector and the fuzz test will randomly change bytes in this file, so that unusual code paths in your dissector are checked. There are tools available to automatically do this on any number of input files, see: http://wiki.wireshark.org/FuzzTesting for details.

3.9.3. Uploading your changes

When you’re satisfied with your changes (and obtained any necessary approval from your organization) you can upload them for review. Changes should be pushed to a magical "refs/for" branch in Gerrit. For example, to upload your new Snowcone Machine Protocol dissector you could push to refs/for/master with the topic "snowcone-machine":

$ git push ssh://[email protected]:29418/wireshark HEAD:refs/for/master/snowcone-machine

If you have git-review installed you can upload the change with a lot less typing:

# Note: The "-f" flag deletes your current branch.
$ git review -f

You can push using any Git client. Many clients have support for Gerrit, either built in or via an additional module.

You might get one of the following responses to your patch request:

  • Your patch is checked into the repository. Congratulations!
  • You are asked to provide additional information, capture files, or other material. If you haven’t fuzzed your code, you may be asked to do so.
  • Your patch is rejected. You should get a response with the reason for rejection. Common reasons include not following the style guide, buggy or insecure code, and code that won’t compile on other platforms. In each case you’ll have to fix each problem and upload another patch.
  • You don’t get any response to your patch. Possible reason: All the core developers are busy (e.g., with their day jobs or family or other commitments) and haven’t had time to look at your patch. Don’t worry, if your patch is in the review system it won’t get lost.

    If you’re concerned, feel free to add a comment to the patch or send an email to the developer’s list asking for status. But please be patient: most if not all of us do this in our spare time.

3.9.4. Backporting a change

When a bug is fixed in the master branch it might be desirable or necessary to backport the fix to a stable branch. You can do this in Git by cherry-picking the change from one branch to another. Suppose you want to backport change 1ab2c3d4 from the master branch to master-1.10. Using "pure Git" commands you would do the following:

# Create a new topic branch for the backport.
$ git checkout -b backport-g1ab2c3d4 origin/master-1.10

# Cherry-pick the change. Include a "cherry picked from..." line.
$ git cherry-pick -x 1ab2c3d4

# If there are conflicts, fix them.

# Compile and test the change.
$ make
$ ...

# OPTIONAL: Add entries to docbook/release-notes.asciidoc.
$ $EDITOR docbook/release-notes.asciidoc

# If you made any changes, update your commit:
$ git commit --amend -a

# Upload the change to Gerrit
$ git push ssh://[email protected]:29418/wireshark HEAD:refs/for/master-1.10/backport-g1ab2c3d4

If you want to cherry-pick a Gerrit change ID (e.g. I5e6f7890) you can use git review -X I5e6f7890 instead of git cherry-pick and git review instead of git push as described in the previous chapter.