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.

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Look into the documentation and the section Transition Manual. That should help with basic migration and the ability to compile a project. But to actually make use of the new features, it is required to read through the whole documentation and the API.

• 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).

• C compiler
• cmake >= 2.8.12
• libpcre2 >= 10.21 (including devel package)
• note, that PCRE is supposed to be compiled with unicode support (configure's options --enable-utf and --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 >= 10.21

$ mkdir build; cd build
$ cmake ..
$ make
# make install

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 ..

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.

There are no bindings for other languages directly in this project but they are available separately.

• Rust

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 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. Additional regression tests done with a corpus of fuzzing inputs that previously caused crashes are done. Those are available in tests/fuzz and are built automatically with the cmocka unit tests.

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

Multiple YANG fuzzing targets and fuzzing instructions are available in the tests/fuzz directory.

All of the targets can be fuzzed with LLVM's LibFuzzer and AFL, and new targets can easily be added. Asciinema examples which describe the fuzzing setup for both AFL (https://asciinema.org/a/311060) and LibFuzzer (https://asciinema.org/a/311035) are available.