Libidn2 README -- Introduction information

Libidn2 is a free software implementation of IDNA2008, Punycode and Unicode TR46. Its purpose is to encode and decode internationalized domain names.

For technical reference, see:

• IDNA2008 Framework
• IDNA2008 Protocol
• IDNA2008 Unicode tables
• IDNA2008 Bidi rule
• Punycode
• Unicode IDNA Compatibility Processing

The library contains functionality to convert internationalized domain names to and from ASCII Compatible Encoding (ACE).

The API consists of two main functions, idn2_to_ascii_8z for converting data from UTF-8 to ASCII Compatible Encoding (ACE), and idn2_to_unicode_8z8z to convert ACE names into UTF-8 format. There are several variations of these main functions, which accept UTF-32, or input in the local system encoding. All functions assume zero-terminated strings.

This library is backwards (API) compatible with the libidn library. Replacing the idna.h header with idn2.h into a program is sufficient to switch the application from IDNA2003 to IDNA2008 as supported by this library.

Libidn2 is believed to be a complete IDNA2008 and TR46 implementation, it contains an extensive test-suite, and is included in the continuous fuzzing project OSS-Fuzz.

You can check the current test code coverage here and the current fuzzing code coverage here.

License

The installed C library libidn2 is dual-licensed under LGPLv3+|GPLv2+, while the rest of the package is GPLv3+. See the file COPYING for detailed information.

Online docs

API reference

Manual

Obtaining the source

Software releases of libidn2 can be downloaded from https://ftp.gnu.org/gnu/libidn/ and ftp://ftp.gnu.org/gnu/libidn/

Development of libidn2 is organized through GitLab website, and there is an issue tracker for reporting bugs.

Dependencies

To build Libidn2 you will need a POSIX shell to run ./configure and the Unix make tool.

• Bash
• Make

The shared libidn2 library uses GNU libunistring for Unicode processing and GNU libiconv for character set conversion. You should install them before building and installing libidn2. See the following links for more information on these packages:

• Unistring
• iconv

Note that the iconv dependency is optional -- it is required for the functions involving locale to UTF conversions -- but is recommended.

If you wish to build the project from version controlled sources, rebuild all generated files (e.g., run autoreconf), or modify some source code files, you will need to have additional tools installed. None of the following tools are necessary if you build Libidn2 in the usual way (i.e., ./configure && make).

• Automake
• Autoconf
• Libtool
• Gettext
• Texinfo
• Gperf
• Gengetopt
• help2man
• Tar
• Gzip
• Texlive & epsf (for PDF manual)
• GTK-DOC (for API manual)
• Git
• Perl
• Valgrind (optional)
• abi-compliance-checker

The software is typically distributed with your operating system, and the instructions for installing them differ. Here are some hints:

Debian 10.x, Ubuntu 20.04:

apt-get install git autoconf automake libtool gettext autopoint gperf
apt-get install libunistring-dev valgrind gengetopt help2man
apt-get install texinfo git2cl gtk-doc-tools
apt-get install abi-compliance-checker abigail-tools

Contributing

See the contributing document.

Estimating code coverage

Dependencies:

• lcov (for code coverage)

To test the code coverage of the test suite use the following:

$ ./configure --enable-code-coverage
$ make && make check && make code-coverage-capture

The current coverage report can be found here.

Fuzzing

Libidn2 is being continuously fuzzed by OSS-Fuzz.

Of course you can do local fuzzing on your own, see fuzz/README.md for instructions.

The code coverage of our fuzzers can be found here.