=head1 NAME

Unicode::UTF8 - Encoding and decoding of UTF-8 encoding form

=head1 SYNOPSIS

    use Unicode::UTF8 qw[decode_utf8 encode_utf8 read_utf8];
    
    use warnings FATAL => 'utf8'; # fatalize encoding glitches
    $string = decode_utf8($octets);
    $octets = encode_utf8($string);
    
    $count = read_utf8($fh, $buf, $length);

=head1 DESCRIPTION

This module provides functions to encode and decode UTF-8 encoding form as 
specified by Unicode and ISO/IEC 10646:2011.

=head1 FUNCTIONS

=head2 decode_utf8

    $string = decode_utf8($octets);
    $string = decode_utf8($octets, $fallback);

Returns a decoded representation of C<$octets> in UTF-8 encoding as a character
string.

C<$fallback> is an optional C<CODE> reference which provides a error-handling 
mechanism, allowing customization of error handling. The default error-handling 
mechanism is to replace any ill-formed UTF-8 sequences with REPLACEMENT
CHARACTER (U+FFFD).

    $string = $fallback->($octets, $is_usv, $position);

C<$fallback> is invoked with three arguments: C<$octets>, C<$is_usv> and 
C<$position>. C<$octets> is a sequence of one or more octets containing the 
maximal subpart of the ill-formed subsequence or encoded code point which 
can't be interchanged. C<$is_usv> is a boolean indicating whether or not 
C<$octets> represent a encoded Unicode scalar value. C<$position> is a 
unsigned integer containing the zero based octet position at which the error 
occurred within the octets provided to C<decode_utf8()>. C<$fallback> must 
return a character string consisting of zero or more Unicode scalar values. 
Unicode scalar values consist of code points in the range U+0000..U+D7FF and 
U+E000..U+10FFFF.

=head2 encode_utf8

    $octets = encode_utf8($string);
    $octets = encode_utf8($string, $fallback);

Returns an encoded representation of C<$string> in UTF-8 encoding as an octet
string.

C<$fallback> is an optional C<CODE> reference which provides a error-handling 
mechanism, allowing customization of error handling. The default error-handling 
mechanism is to replace any code points which can't be interchanged or represented 
in UTF-8 encoding form with REPLACEMENT CHARACTER (U+FFFD).

    $string = $fallback->($codepoint, $is_usv, $position);

C<$fallback> is invoked with three arguments: C<$codepoint>, C<$is_usv> and 
C<$position>. C<$codepoint> is a unsigned integer containing the code point 
which can't be interchanged or represented in UTF-8 encoding form. C<$is_usv> 
is a boolean indicating whether or not C<$codepoint> is a Unicode scalar value. 
C<$position> is a unsigned integer containing the zero based character position 
at which the error occurred within the string provided to C<encode_utf8()>. 
C<$fallback> must return a character string consisting of zero or more Unicode 
scalar values.Unicode scalar values consist of code points in the range 
U+0000..U+D7FF and U+E000..U+10FFFF.

=head2 read_utf8  

    $count = read_utf8($fh, $buf, $length);
    $count = read_utf8($fh, $buf, $length, $offset);

Reads up to C<$length> UTF-8 encoded characters (code points) from the file handle
C<$fh>, decoding and validating them in place, and stores the result in C<$buf>.
Returns the number of characters actually read, C<0> at end of file, or C<undef>
on a read error (with C<$!> set).

Because C<read_utf8> reads and validates the octets directly, there is no need to
apply a PerlIO encoding layer (such as C<:encoding(UTF-8)> or C<:utf8>) to C<$fh>.
The handle should be a plain byte handle; the bytes are validated and decoded by
C<read_utf8> itself.

If C<$offset> is specified, the read data is written into C<$buf> starting at that
character offset, preserving the existing content before it. A negative C<$offset>
counts back from the end of C<$buf>. If the offset is past the end of the string,
C<$buf> is zero-filled up to the offset first.

Ill-formed and truncated input is not fatal: each maximal ill-formed subpart is
replaced with the Unicode replacement character U+FFFD and a warning is emitted in
the C<utf8> warnings category. The returned count includes the substituted code
points.

Tied file handles are not supported.

Since version 0.71.

=head2 valid_utf8

    $boolean = valid_utf8($octets);

Returns a boolean indicating whether or not the given C<$octets> consist of 
well-formed UTF-8 sequences.

Since version 0.60.

=head1 EXPORTS

None by default. All functions can be exported using the C<:all> tag or individually.

=head1 DIAGNOSTICS

=over 4

=item Can't decode a wide character string

(F) Wide character in octets.

=item Can't validate a wide character string

(F) Wide character in octets.

=item Can't decode ill-formed UTF-8 octet sequence <%s> in position %u

(W utf8) Encountered an ill-formed UTF-8 octet sequence. <%s> contains a 
hexadecimal representation of the maximal subpart of the ill-formed subsequence.

=item Can't represent surrogate code point U+%X in position %u

(W utf8, surrogate) Surrogate code points are designated only for surrogate code 
units in the UTF-16 character encoding form. Surrogates consist of code points 
in the range U+D800 to U+DFFF.

=item Can't represent super code point \x{%X} in position %u

(W utf8, non_unicode) Code points greater than U+10FFFF. Perl's extended codespace.

=item Can't decode ill-formed UTF-X octet sequence <%s> in position %u

(F) Encountered an ill-formed octet sequence in Perl's internal representation 
of wide characters.

=back

The sub-categories: C<surrogate> and C<non_unicode> is only available on Perl 5.14
or greater. See L<perllexwarn> for available categories and hierarchies.

=head1 COMPARISON

Here is a summary of features for comparison with L<Encode>'s UTF-8 implementation:

=over 4

=item *

Simple API which makes use of Perl's standard warning categories.

=item *

Implements Unicode's recommended practice for using U+FFFD.

=item *

Better diagnostics in warning messages

=item *

Detects and reports inconsistency in Perl's internal representation of 
wide characters (UTF-X)

=item *

Preserves taintedness of decoded C<$octets> or encoded C<$string>

=item *

Better performance ~ 600% - 1200% (JA: 600%, AR: 700%, SV: 900%, EN: 1200%, 
see benchmarks directory in git repository)

=back

=head1 CONFORMANCE

It's the author's belief that this UTF-8 implementation is conformant with 
the Unicode Standard Version 6.0. Any deviations from the Unicode Standard 
is to be considered a bug.

=head1 SEE ALSO

=over 4

=item L<Encode>

=item L<Encode::Simple>

=item L<http://www.unicode.org/>

=back

=head1 SUPPORT

=head2 BUGS

Please report any bugs through the web interface at 
L<https://github.com/chansen/p5-unicode-utf8/issues>.
You will be automatically notified of any progress on the request by the system.

=head2 SOURCE CODE

This is open source software. The code repository is available for public 
review and contribution under the terms of the license.

L<http://github.com/chansen/p5-unicode-utf8>

    git clone http://github.com/chansen/p5-unicode-utf8

=head1 AUTHOR

Christian Hansen C<chansen@cpan.org>

=head1 COPYRIGHT

Copyright 2011-2026 by Christian Hansen.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

