# Developer information for contributing to libcoap #
1. The basics
The libcoap project is a FOSS project that is dual licensed. The maintainer
for the libcoap is Olaf Bergmann <firstname.lastname@example.org>.
Any contributions have to be made dual licensed under the terms of the
* BSD 2-Clause (The BSD 2-Clause License)
* GPL v2+ (The GNU General Public License 2.0 or later)
The used VCS for libcoap is Git, the main repository is living on GitHub.
You can clone (or fork directly on GitHub) on the repository site:
Please refer also to the libcoap website for additional information
The build environment is grounded on the classical autotools, the GNU GCC and
the LLVM C-compiler (CLang) are supported. The Windows systems are not
currently supported (until someone is creating support for it).
Doxygen is used for creating a HTML based online documentation of the
The main discussion and development platform for libcoap is the mailing list
No matter if you just have a simple question, some specific problem or
want to discuss some patches, please write it to the mailing list. Please
avoid personal mailings to the maintainer (or some other contributor) if
your questions will probably be in the interest of other users too.
You can subscribe to the list here:
The archive of the list can be found on:
3. Starting contributing
As written above libcoap is maintained with the Git tools so you should be
familiar with the various git commands.
The libcoap project is using just two main branches, the 'master' branch is
holding the point releases, all the development process is going on in the
To start any contributing you first have to clone the git tree from the main
repository on GitHub:
git clone https://github.com/obgm/libcoap.git
4. Working on the source
As one golden rule you should work on improvements within *your* own local
development branch! To do so you have to first checkout the 'develop' branch
as local branch and then start on top on this branch your own branch. So
create (or better say checkout) the local 'develop' branch:
git checkout develop origin/develop
Now you can simply start your own local branch (for example 'my-develop')
with the 'origin/develop' as parent so you can later create the patches
against the the upstream development branch:
git checkout -b my-develop
At this point you can now work as known with git, modify the source, commit
the changes, amend if needed and test your work.
At some point you will have to generate patches to post them on the mailing
list (and/or push your changes into your public Git tree). It's a good idea to
post your patch series on the mailing list so other contributors will see your
work and give further suggestions or discuss your work.
To be able to send a patch series you will now create the series itself as
single patches, this will be going easy with the 'git format-patch' command
against the 'develop' branch, remind this is the upstream main development
To not mix up your series with probably unrelated patches let git place the
patches within a defined directory. Also, while create the patches, tell git to
create a cover letter patch so you can append some introducing words that will
hold probably explanations why you create the patches in the way you have done.
git format-patch --cover-letter -o ../patches4libcoap
This command will create a patch series in ../patches4libcoap where you find a
patch named '0000-cover-letter.patch'. Please modify this patch with some
useful information's for the mailing list. After finish this you now can send
your patches to email@example.com
git send-email ../patches4libcoap/* --firstname.lastname@example.org
5. Coding rules
As every FOSS project the libcoap project needs also some rules for coding.
There are loss but the main of them are important!
5.1 License and Copyright
Every new file must contain a license and the copyright holder(s). Please
take a look into existing files and adopt the needed changes to your new
5.2 Source Code Indentation
* For better reading the indentation is set to 2 characters as spaces, this
is depended on the often used nested functions like 'if-else'. Don't use
TABs any there! Avoid trailing white spaces at the end of a line.
It's appropriate to set up a modline like this one at first line within
the source file:
/* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 * -*- */
* Single lines within the source code should not be longer then 78
* If there a functions with a lot of parameters that do not fit into the above
rule split the declaration (in the *.h) and the implementation (in the *.c)
into single lines per parameter. For example like this (from src/block.c):
unsigned int len,
const unsigned char *data,
unsigned int block_num,
unsigned char block_szx);
5.3 Source Code Documentation
* A useful source code documentation is mandatory. Mostly to be done within the
source code files, but more complex description should be done in extra
* Please set up/adjust the doxygen documentation if you create new functions or
change existing functions. The doxygen documentation has to be done in the
header files as they are the public part of the libcoap and only use the
@-syntax for doxygen commands (akin to javadoc).
5.4 API Changes
* Never break the API!
Don't remove old functions and if there some changes are needed in some kind
always provide a wrapper for the old call to let the library be backward
compatible and mark the old function as @deprecated in the doxygen comment.
Please discuss needed changes on the mailing list.
5.5 Patches and Commits
* Git commits must be atomic and contain a declarative subject line (max 50
characters if possible) and a body for a statement if needed.
Use the possibility to write a good explanation why your patch/commit is
handle the changes in the way you have done. Remind that other user can
read your code but not necessary understand why the code is written this
way. Don't use something to generic like "bugfix commit".
* A patch/commit or a series of patches/commits have to ensure that the
whole project is able to build up every thing, in short: Do not break
any make target and test your work.
* Every patch/commit should handle one single logical change. If more than
one patch/commit is needed for a change explain it, respect the point
above. If your subject line become much larger than 50 characters then
typically your patch is to big for one single commit.
* Commit message should begin with a submodule or unit the commit is for. By
this your commit message helps to find thematic other changes. If you have
to search and find something with 'git log | grep [foo]' you will see why
this is useful. Examples:
rd.c: Fixed type-specifier warning
Makefile.am: Added missing src/address.c
address.[hc]: make coap_address_equals() not inline on POSIX
6. Where to start contributing?
There are various things you could starting on to contribute, the best
is you simply pick up an issue you blindly see and just improve the
situation. Please take also a look into the file TODO and choose a point
from there or point the maintainer to add other things here too.
We are always lacking on a better documentation on the source code, so
maybe you can improve the doxygen documentation.
Also a good documentation on the usage of the libcoap and the example
binaries is always improvable. So we appreciate any help on this.
* Man Pages
The source is providing some example binaries which originally just should show
how the libcoap can be used. Right now these binaries are fully usable and
quite more than simple examples on a system. There are man pages for these
binaries available, if you found there is a improvement needed please do so and
write to the mailing list explained in section 2.
Maybe you can write up some good HowTo's on the usage for these binaries. A man
page for the library itself would be also a improvement.
The libcoap library has now a lot of functions you can use.
Unfortunately there is no good user guide on how to use the libcoap in
any external project. This means there is no HowTo or CheatSheet for a
programming person available. You want to write up something?
* missed Functionality
There are some features that are still missing inside the libcoap. For
example some DTLS implementations and proxy functionality.