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When Contributing Source Code
This document is intended to offer guidelines that can be useful to keep in
mind when you decide to contribute to the project. This concerns new features
as well as corrections to existing flaws or bugs.
1. Learning cURL
1.1 Join the Community
1.2 License
1.3 What To Read
2. cURL Coding Standards
2.1 Naming
2.2 Indenting
2.3 Commenting
2.4 Line Lengths
2.5 General Style
2.6 Non-clobbering All Over
2.7 Platform Dependent Code
2.8 Write Separate Patches
2.9 Patch Against Recent Sources
2.10 Document
2.11 Test Cases
3. Pushing Out Your Changes
3.1 Write Access to git Repository
3.2 How To Make a Patch with git
3.3 How To Make a Patch without git
3.4 How to get your changes into the main sources
3.5 Write good commit messages
3.6 Please don't send pull requests
1. Learning cURL
1.1 Join the Community
Skip over to and join the appropriate mailing
list(s). Read up on details before you post questions. Read this file before
you start sending patches! We prefer patches and discussions being held on
the mailing list(s), not sent to individuals.
Before posting to one of the curl mailing lists, please read up on the mailing
list etiquette:
We also hang out on IRC in #curl on
1.2. License
When contributing with code, you agree to put your changes and new code under
the same license curl and libcurl is already using unless stated and agreed
If you add a larger piece of code, you can opt to make that file or set of
files to use a different license as long as they don't enforce any changes to
the rest of the package and they make sense. Such "separate parts" can not be
GPL licensed (as we don't want copyleft to affect users of libcurl) but they
must use "GPL compatible" licenses (as we want to allow users to use libcurl
properly in GPL licensed environments).
When changing existing source code, you do not alter the copyright of the
original file(s). The copyright will still be owned by the original
creator(s) or those who have been assigned copyright by the original
By submitting a patch to the curl project, you are assumed to have the right
to the code and to be allowed by your employer or whatever to hand over that
patch/code to us. We will credit you for your changes as far as possible, to
give credit but also to keep a trace back to who made what changes. Please
always provide us with your full real name when contributing!
1.3 What To Read
Source code, the man pages, the INTERNALS document, TODO, KNOWN_BUGS, the
most recent CHANGES. Just lurking on the libcurl mailing list is gonna give
you a lot of insights on what's going on right now. Asking there is a good
idea too.
2. cURL Coding Standards
2.1 Naming
Try using a non-confusing naming scheme for your new functions and variable
names. It doesn't necessarily have to mean that you should use the same as in
other places of the code, just that the names should be logical,
understandable and be named according to what they're used for. File-local
functions should be made static. We like lower case names.
See the INTERNALS document on how we name non-exported library-global
2.2 Indenting
Please try using the same indenting levels and bracing method as all the
other code already does. It makes the source code a lot easier to follow if
all of it is written using the same style. We don't ask you to like it, we
just ask you to follow the tradition! ;-) This mainly means: 2-level indents,
using spaces only (no tabs) and having the opening brace ({) on the same line
as the if() or while().
Also note that we use if() and while() with no space before the parenthesis.
2.3 Commenting
Comment your source code extensively using C comments (/* comment */), DO NOT
use C++ comments (// this style). Commented code is quality code and enables
future modifications much more. Uncommented code risk having to be completely
replaced when someone wants to extend things, since other persons' source
code can get quite hard to read.
2.4 Line Lengths
We write source lines shorter than 80 columns.
2.5 General Style
Keep your functions small. If they're small you avoid a lot of mistakes and
you don't accidentally mix up variables etc.
2.6 Non-clobbering All Over
When you write new functionality or fix bugs, it is important that you don't
fiddle all over the source files and functions. Remember that it is likely
that other people have done changes in the same source files as you have and
possibly even in the same functions. If you bring completely new
functionality, try writing it in a new source file. If you fix bugs, try to
fix one bug at a time and send them as separate patches.
2.7 Platform Dependent Code
Use #ifdef HAVE_FEATURE to do conditional code. We avoid checking for
particular operating systems or hardware in the #ifdef lines. The
HAVE_FEATURE shall be generated by the configure script for unix-like systems
and they are hard-coded in the config-[system].h files for the others.
2.8 Write Separate Patches
It is annoying when you get a huge patch from someone that is said to fix 511
odd problems, but discussions and opinions don't agree with 510 of them - or
509 of them were already fixed in a different way. Then the patcher needs to
extract the single interesting patch from somewhere within the huge pile of
source, and that gives a lot of extra work. Preferably, all fixes that
correct different problems should be in their own patch with an attached
description exactly what they correct so that all patches can be selectively
applied by the maintainer or other interested parties.
2.9 Patch Against Recent Sources
Please try to get the latest available sources to make your patches
against. It makes the life of the developers so much easier. The very best is
if you get the most up-to-date sources from the git repository, but the
latest release archive is quite OK as well!
2.10 Document
Writing docs is dead boring and one of the big problems with many open source
projects. Someone's gotta do it. It makes it a lot easier if you submit a
small description of your fix or your new features with every contribution so
that it can be swiftly added to the package documentation.
The documentation is always made in man pages (nroff formatted) or plain
ASCII files. All HTML files on the web site and in the release archives are
generated from the nroff/ASCII versions.
2.11 Test Cases
Since the introduction of the test suite, we can quickly verify that the main
features are working as they're supposed to. To maintain this situation and
improve it, all new features and functions that are added need to be tested
in the test suite. Every feature that is added should get at least one valid
test case that verifies that it works as documented. If every submitter also
posts a few test cases, it won't end up as a heavy burden on a single person!
3. Pushing Out Your Changes
3.1 Write Access to git Repository
If you are a frequent contributor, or have another good reason, you can of
course get write access to the git repository and then you'll be able to push
your changes straight into the git repo instead of sending changes by mail as
patches. Just ask if this is what you'd want. You will be required to have
posted a few quality patches first, before you can be granted push access.
3.2 How To Make a Patch with git
You need to first checkout the repository:
git clone git://
You then proceed and edit all the files you like and you commit them to your
local repository:
git commit [file]
As usual, group your commits so that you commit all changes that at once that
constitutes a logical change. See also section "3.5 Write good commit
Once you have done all your commits and you're happy with what you see, you
can make patches out of your changes that are suitable for mailing:
git format-patch remotes/origin/master
This creates files in your local directory named NNNN-[name].patch for each
Now send those patches off to the curl-library list. You can of course opt to
do that with the 'get send-email' command.
3.3 How To Make a Patch without git
Keep a copy of the unmodified curl sources. Make your changes in a separate
source tree. When you think you have something that you want to offer the
curl community, use GNU diff to generate patches.
If you have modified a single file, try something like:
diff -u unmodified-file.c my-changed-one.c > my-fixes.diff
If you have modified several files, possibly in different directories, you
can use diff recursively:
diff -ur curl-original-dir curl-modified-sources-dir > my-fixes.diff
The GNU diff and GNU patch tools exist for virtually all platforms, including
all kinds of Unixes and Windows:
For unix-like operating systems:
For Windows:
3.4 How to get your changes into the main sources
Submit your patch to the curl-library mailing list.
Make the patch against as recent sources as possible.
Make sure your patch adheres to the source indent and coding style of already
existing source code. Failing to do so just adds more work for me.
Respond to replies on the list about the patch and answer questions and/or
fix nits/flaws. This is very important. I will take lack of replies as a sign
that you're not very anxious to get your patch accepted and I tend to simply
drop such patches from my TODO list.
If you've followed the above paragraphs and your patch still hasn't been
incorporated after some weeks, consider resubmitting it to the list.
3.5 Write good commit messages
A short guide to how to do fine commit messages in the curl project.
---- start ----
[area]: [short line describing the main effect]
[separate the above single line from the rest with an empty line]
[full description, no wider than 72 columns that describe as much as
possible as to why this change is made, and possibly what things
it fixes and everything else that is related]
---- stop ----
Don't forget to use commit --author="" if you commit someone else's work,
and make sure that you have your own user and email setup correctly in git
before you commit
3.6 Please don't send pull requests
With git (and expecially github) it is easy and tempting to send a pull
request to one or more people in the curl project to have changes merged this
way instead of mailing patches to the curl-library mailing list.
We don't like that. We want them mailed for these reasons:
- Peer review. Anyone and everyone on the list can review, comment and
improve on the patch. Pull requests limit this ability.
- Anyone can merge the patch into their own trees for testing and those who
have push rights can push it to the main repo. It doesn't have to be anyone
the patch author knows beforehand.
- Commit messages can be tweaked and changed if merged locally instead of
using github. Merges directly on github requires the changes to be perfect
already, which they seldomly are.
- Merges on github prevents rebases and even enforces --no-ff which is a git
style we don't otherwise use in the project
However: once patches have been reviewed and deemed fine on list they are
perfectly OK to be pulled from a published git tree.