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Contributing to the Exiv2 Project

Contents

1. Introduction

We welcome any help, for example contributing lens data (images), code contributions and bug reports.

2. Contributing code via GitHub

Code contributions can be performed via pull requests (PR) on GitHub (if you cannot or do not want to use GitHub, see 3. Contributing code via email). For this to work you first need to create a user account on GitHub if you don't already have one. A pull request should preferable contain only one new feature, bug fix, etc. Since it is not uncommon to work on several PRs at the same time it is recommended to create a new branch for each PR. In this way PRs can easily be separated and the review and merge process becomes cleaner. As a rule-of-thumb:

  • PRs should be kept at a manageable size. Try to focus on just one goal per PR. If you find yourself doing several things in a PR that were not expected, then try to split the different tasks into different PRs.
  • Commits should always change a single logical unit so that cherry-picking & reverting is simple.
  • Commit messages should be as informative and concise as possible. The first line of the commit message should be < 80 characters and describe the commit briefly. If the 80 characters are too short for a summary, then consider splitting the commit. Optionally, add one blank line below the short summary and write a more detailed explanation if necessary.

See the GIT_GUIDELINES.md file for a more detailed description of the git workflow.

Below we outline the recommended steps in the code contribution workflow. We use your-username to refer to your username on GitHub, exiv2_upstream is used when we set the upstream remote repository for Exiv2 (we could have picked any name but try to avoid already used names like, in particular, origin and main), and we use the name my-new-feature for the branch that we create (e.g., the branch name should reflect the code change being made).

Important: If your PR lives for a long time, then don't press the button Update branch in the Pull Request view, instead follow the steps below, as that avoids additional merge commits.

Once you have a GitHub login:

  1. Fork the Exiv2 git repository to your GitHub account by pressing the Fork button at: https://github.com/Exiv2/exiv2 (more details here).

  2. Then start a terminal (or use your favorite git GUI app) and clone your fork of the Exiv2 repo:

     $ git clone https://github.com:your-username/exiv2.git
 $ cd exiv2

  3. Add a new remote pointing to upstream exiv2 repository:

    $ git remote add exiv2_upstream https://github.com/Exiv2/exiv2.git

    and verify that you have the two remotes configured correctly:

    $ git remote -v
exiv2_upstream  https://github.com/Exiv2/exiv2.git (fetch)
exiv2_upstream  https://github.com/Exiv2/exiv2.git (push)
origin  https://github.com/your-username/exiv2.git (fetch)
origin  https://github.com/your-username/exiv2.git (push)

  4. Next, create a branch for your PR from exiv2_upstream/main (which we also need to fetch first):

     $ git fetch exiv2_upstream main
 $ git checkout -b my-new-feature exiv2_upstream/main --no-track

    NB: This is an important step to avoid dragging in old commits!

  5. Configure the project and check that it builds (if not, please report a bug):

     $ rm -rf build
 $ cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
 $ cmake --build build --parallel

  6. Now, make your change(s), add tests for your changes, and commit each change:

     ...

 $ git commit -m "Commit message 1"

 ...

 $ git commit -m "Commit message 2"

    Please keep in mind that the project has a Continuous Integration job to check that your new code is satisfying the format defined in the file .clang-format. Use your preferred text editor, IDE or method to make sure your code is properly formatted before creating the PR.

    Note: You can use the script contrib/scripts/clangFormatWholeProject.sh to format the whole project.

  7. Make sure the tests pass:

     $ ctest

    Exiv2's (new) test system is described in more detail in the doc.md and writing_tests.md files, and a description of the old test system can be found in the Redmine wiki: How do I run the test suite for Exiv2

  8. Push the changes to your fork on GitHub:

     $ git push origin my-new-feature

  9. Create the PR by pressing the New pull request button on: https://github.com/your-username/exiv2. Please select the option "Allow edits from maintainers" as outlined here.

  10. Now wait for an Exiv2 project member(s) to respond to your PR. Follow the discussion on your PR at GitHub. You may have to do some updates to your PR until it gets accepted.

  11. After the PR has been reviewed you must rebase your repo copy since there may have been several changes to the upstream repository.

    Switch to your branch again

    $ git checkout my-new-feature

    And rebase it on top of main:

    $ git pull --rebase exiv2_upstream main

    When you perform a rebase the commit history is rewritten and, therefore, the next time you try to push your branch to your fork repository you will need to use the --force-with-lease option:

    $ git push --force-with-lease

Also, follow the coding guidelines outlined in CODING_GUIDELINES.md.

3. Contributing Code via email

If you cannot or do not want to use GitHub, you can still submit patches via email by using our sourcehut mirror.

Prepare your changes in your local clone of the GitHub or sourcehut repository following our CODING_GUIDELINES.md and GIT_GUIDELINES.md. Send your patches to the ~d4n/exiv2-patches@lists.sr.ht mailing list. Please use git send-email as outlined in https://git-send-email.io/ to simplify the integration of your patches.

4. Contributing Lens Data

In order for the Exiv2 project to support a new lens we need an example image containing the Exif metadata of that lens. This is a good way for non-programmers to contribute to the project and example images can be submitted using the following procedure:

  1. Create a new Issue by pressing the New issue button here: https://github.com/Exiv2/exiv2/issues,
  2. In the new Issue, enter/add the lens mount and full lens name for each lens,
  3. Take a (small) .jpg image (with the lens cap on) with each lens and transfer the .jpg file(s) to disk without processing it in a desktop or server software (this is important to preserve the exif metadata in the file),
  4. Attach the .jpg image(s) to the Issue (one can just drag-and-drop the image(s) or paste it/them from the clipboard).

Note that we are not only interested in non-supported lenses since we also look for example images to expand and improve the Exiv2 code tests.

5. Reporting Bugs

Bugs should be reported by creating Issues on GitHub. However, before reporting a bug first check the Issue list if the bug is already known, and only if you cannot find any previous bug report then create a new Issue. When reporting a bug try to describe the problem in as much detail as possible and if the bug is triggered by an input file then attach that file to the GitHub Issue, too.