libyang is a YANG data modelling language parser and toolkit written (and providing API) in C. The library is used e.g. in libnetconf2, Netopeer2 or sysrepo projects.
- Parsing (and validating) schemas in YANG format.
- Parsing (and validating) schemas in YIN format.
- Parsing, validating and printing instance data in XML format.
- Parsing, validating and printing instance data in JSON format (RFC 7951).
- Manipulation with the instance data.
- Support for default values in the instance data (RFC 6243).
- Support for YANG extensions.
- Support for YANG Metadata (RFC 7952).
- yanglint - feature-rich YANG tool.
Current implementation covers YANG 1.0 (RFC 6020) as well as YANG 1.1 (RFC 7950).
We are using openSUSE Build Service to automaticaly prepare binary packages for number of GNU/Linux distros. Check
this page and follow the
instructions for your distro to install libyang package. The libyang package is built once a day from the
master branch. If you want the latest code from the devel branch, install libyang-experimental package.
- C compiler
- cmake >= 2.8.12
- libpcre2 >= 10.30 (including devel package)
- note, that PCRE is supposed to be compiled with unicode support (configure's options
--enable-utfand--enable-unicode-properties)
- doxygen (for generating documentation)
- cmocka >= 1.0.0 (for tests)
- valgrind (for enhanced testing)
- gcov (for code coverage)
- lcov (for code coverage)
- genhtml (for code coverage)
- libpcre2 >= 10.30
$ mkdir build; cd build
$ cmake ..
$ make
# make install
The library documentation can be generated directly from the source codes using Doxygen tool:
$ make doc
$ google-chrome ../doc/html/index.html
The documentation is also built hourly and available at netopeer.liberouter.org.
Set CC variable:
$ CC=/usr/bin/clang cmake ..
To change the prefix where the library, headers and any other files are installed,
set CMAKE_INSTALL_PREFIX variable:
$ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr ..
Default prefix is /usr/local.
There are two build modes:
- Release. This generates library for the production use without any debug information.
- Debug. This generates library with the debug information and disables optimization of the code.
The Debug mode is currently used as the default one. to switch to the
Release mode, enter at the command line:
$ cmake -D CMAKE_BUILD_TYPE:String="Release" ..
As for YANG extensions, libyang allows loading extension plugins. By default, the directory to store the plugins is LIBDIR/libyang. To change it, use the following cmake option with the value specifying the desired directory:
$ cmake -DPLUGINS_DIR:PATH=`pwd`"/src/extensions/" ..
The directory path can be also changed runtime via environment variable, e.g.:
$ LIBYANG_EXTENSIONS_PLUGINS_DIR=`pwd`/my/relative/path yanglint
Whenever the latest revision of a schema is supposed to be loaded (import without specific revision), it is performed in the standard way, the first time. By default, every other time when the latest revision of the same schema is needed, the one initially loaded is reused. If you know this can cause problems meaning the latest available revision of a schema can change during operation, you can force libyang to always search for the schema anew by:
$ cmake -DENABLE_LATEST_REVISIONS=OFF ..
Also, it can be efficient to store certain information about schemas that is generated during parsing so that it does not need to be generated every time the schema is used, but it will consume some additional space. You can enable this cache with:
$ cmake -DENABLE_CACHE=ON ..
Note that, with CMake, if you want to change the compiler or its options after you already ran CMake, you need to clear its cache first - the most simple way to do it is to remove all content from the 'build' directory.
All libyang functions are available via the main header:
#include <libyang/libyang.h>
To compile your program with libyang, it is necessary to link it with libyang using the following linker parameters:
-lyang
Note, that it may be necessary to call ldconfig(8) after library installation and if the
library was installed into a non-standard path, the path to libyang must be specified to the
linker. To help with setting all the compiler's options, there is libyang.pc file for
pkg-config(1) available in the source tree. The file is installed with the library.
If you are using cmake in you project, it is also possible to use the provided
FindLibYANG.cmake file to detect presence of the libyang library in the system.
libyang project includes a feature-rich tool called yanglint(1) for validation
and conversion of the schemas and YANG modeled data. The source codes are
located at /tools/lint and can be used to explore how an
application is supposed to use the libyang library. yanglint(1) binary as
well as its man page are installed together with the library itself.
There is also README describing some examples of
using yanglint.
libyang supports YANG extensions via a plugin mechanism. Some of the plugins (for
NACM or Metadata) are available out of the box and installed together with libyang.
However, when libyang is not installed and yanglint(1) is used from the build
directory, the plugins are not available. There are two options:
- Install libyang.
# make install
- Set environment variable
LIBYANG_EXTENSIONS_PLUGINS_DIRto contain path to the built extensions plugin (./src/extensionsfrom the build directory).
$ LIBYANG_EXTENSIONS_PLUGINS_DIR="`pwd`/src/extensions" ./yanglint
libyang includes several tests built with cmocka. The tests
can be found in tests subdirectory and they are designed for checking library
functionality after code changes.
The tests are by default built in the Debug build mode by running
$ make
In case of the Release mode, the tests are not built by default (it requires
additional dependency), but they can be enabled via cmake option:
$ cmake -DENABLE_BUILD_TESTS=ON ..
Note that if the necessary cmocka headers are not present in the system include paths, tests are not available despite the build mode or cmake's options.
Tests can be run by the make's test target:
$ make test
Based on the tests run, it is possible to generate code coverage report via the
make's coverage target:
$ make coverage
We provide bindings for high-level languages using SWIG generator. The bindings are optional and to enable building of the specific binding, the appropriate cmake option must be enabled, for example:
$ cmake -DJAVASCRIPT_BINDING=ON ..
More information about the specific binding can be found in their README files.
Currently supported bindings are:
- JavaScript
- cmake option:
JAVASCRIPT_BINDING - README
A YANG fuzzing target and fuzzing instructions are available in the tests/fuzz directory.
An asciinema example describing the process of fuzzing libyang2 with the yangfuzz fuzz harness is available at https://asciinema.org/a/260417.