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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.
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.
The License Issue
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!
What To Read
Source code, the man pages, the INTERNALS document, the TODO, 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.
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
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().
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.
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.
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.
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.
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.
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 CVS repository, but the
latest release archive is quite OK as well!
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.
Write Access to CVS Repository
If you are a frequent contributor, or have another good reason, you can of
course get write access to the CVS repository and then you'll be able to
check-in all your changes straight into the CVS tree instead of sending all
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 write access.
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!
How To Make a Patch
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: