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# 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

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

You can check the current test code coverage
[here]( and the
current fuzzing code coverage

# License

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

# Online docs

[API reference](


# Obtaining the source

Software releases of libidn2 can be downloaded from and

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

# Building & Dependencies

To build Libidn2 you will need a POSIX shell, the Unix "make" tool,
and a C compiler.

 * [Bash](
 * [Make](
 * [C compiler](

When building from a released *.tar.* archive, after unpacking you
build the package like this:

make check

The Libidn2 library may use GNU libunistring for Unicode processing
and GNU libiconv for character set conversion.  It is recommended to
install them before building and installing libidn2.  See the
following links for more information on these packages:

 * [Unistring](
 * [iconv](

The iconv dependency is optional -- it is required for the functions
involving locale to UTF8 conversions -- but is recommended.

When the recommended libunistring is not available, libidn2 uses
internal replacement functionality which increases the size of the
library.  To use the internal libunistring-replacement rather than the
system libunistring (even when deemed to be sufficient) you may use:

./configure --with-included-libunistring

# Contributing

See [the contributing document](

# Estimating code coverage

 * [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/` for instructions.

The code coverage of our fuzzers can be found [here](