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IO::HTML(3)		       User Contributed Perl Documentation		      IO::HTML(3)

NAME
       IO::HTML - Open an HTML file with automatic charset detection

VERSION
       This document describes version 1.00 of IO::HTML, released February 23, 2013.

SYNOPSIS
	 use IO::HTML;		       # exports html_file by default
	 use HTML::TreeBuilder;

	 my $tree = HTML::TreeBuilder->new_from_file(
		      html_file('foo.html')
		    );

	 # Alternative interface:
	 open(my $in, '<:raw', 'bar.html');
	 my $encoding = IO::HTML::sniff_encoding($in, 'bar.html');

DESCRIPTION
       IO::HTML provides an easy way to open a file containing HTML while automatically
       determining its encoding.  It uses the HTML5 encoding sniffing algorithm specified in
       section 8.2.2.1 of the draft standard.

       The algorithm as implemented here is:

       1.  If the file begins with a byte order mark indicating UTF-16LE, UTF-16BE, or UTF-8,
	   then that is the encoding.

       2.  If the first 1024 bytes of the file contain a "<meta>" tag that indicates the charset,
	   and Encode recognizes the specified charset name, then that is the encoding.  (This
	   portion of the algorithm is implemented by "find_charset_in".)

	   The "<meta>" tag can be in one of two formats:

	     <meta charset="...">
	     <meta http-equiv="Content-Type" content="...charset=...">

	   The search is case-insensitive, and the order of attributes within the tag is
	   irrelevant.	Any additional attributes of the tag are ignored.  The first matching tag
	   with a recognized encoding ends the search.

       3.  If the first 1024 bytes of the file are valid UTF-8 (with at least 1 non-ASCII
	   character), then the encoding is UTF-8.

       4.  If all else fails, use the default character encoding.  The HTML5 standard suggests
	   the default encoding should be locale dependent, but currently it is always "cp1252"
	   unless you set $IO::HTML::default_encoding to a different value.  Note:
	   "sniff_encoding" does not apply this step; only "html_file" does that.

SUBROUTINES
   html_file
	 $filehandle = html_file($filename, \%options);

       This function (exported by default) is the primary entry point.	It opens the file
       specified by $filename for reading, uses "sniff_encoding" to find a suitable encoding
       layer, and applies it.  It also applies the ":crlf" layer.  If the file begins with a BOM,
       the filehandle is positioned just after the BOM.

       The optional second argument is a hashref containing options.  The possible keys are
       described under "find_charset_in".

       If "sniff_encoding" is unable to determine the encoding, it defaults to
       $IO::HTML::default_encoding, which is set to "cp1252" (a.k.a. Windows-1252) by default.
       According to the standard, the default should be locale dependent, but that is not
       currently implemented.

       It dies if the file cannot be opened.

   html_file_and_encoding
	 ($filehandle, $encoding, $bom)
	   = html_file_and_encoding($filename, \%options);

       This function (exported only by request) is just like "html_file", but returns more
       information.  In addition to the filehandle, it returns the name of the encoding used, and
       a flag indicating whether a byte order mark was found (if $bom is true, the file began
       with a BOM).  This may be useful if you want to write the file out again (especially in
       conjunction with the "html_outfile" function).

       The optional second argument is a hashref containing options.  The possible keys are
       described under "find_charset_in".

       It dies if the file cannot be opened.  The result of calling it in scalar context is
       undefined.

   html_outfile
	 $filehandle = html_outfile($filename, $encoding, $bom);

       This function (exported only by request) opens $filename for output using $encoding, and
       writes a BOM to it if $bom is true.  If $encoding is "undef", it defaults to
       $IO::HTML::default_encoding.  $encoding may be either an encoding name or an
       Encode::Encoding object.

       It dies if the file cannot be opened.

   sniff_encoding
	 ($encoding, $bom) = sniff_encoding($filehandle, $filename, \%options);

       This function (exported only by request) runs the HTML5 encoding sniffing algorithm on
       $filehandle (which must be seekable, and should have been opened in ":raw" mode).
       $filename is used only for error messages (if there's a problem using the filehandle), and
       defaults to "file" if omitted.  The optional third argument is a hashref containing
       options.  The possible keys are described under "find_charset_in".

       It returns Perl's canonical name for the encoding, which is not necessarily the same as
       the MIME or IANA charset name.  It returns "undef" if the encoding cannot be determined.
       $bom is true if the file began with a byte order mark.  In scalar context, it returns only
       $encoding.

       The filehandle's position is restored to its original position (normally the beginning of
       the file) unless $bom is true.  In that case, the position is immediately after the BOM.

       Tip: If you want to run "sniff_encoding" on a file you've already loaded into a string,
       open an in-memory file on the string, and pass that handle:

	 ($encoding, $bom) = do {
	   open(my $fh, '<', \$string);  sniff_encoding($fh)
	 };

       (This only makes sense if $string contains bytes, not characters.)

   find_charset_in
	 $encoding = find_charset_in($string_containing_HTML, \%options);

       This function (exported only by request) looks for charset information in a "<meta>" tag
       in a possibly incomplete HTML document using the "two step" algorithm specified by HTML5.
       It does not look for a BOM.  Only the first 1024 bytes of the string are checked.

       It returns Perl's canonical name for the encoding, which is not necessarily the same as
       the MIME or IANA charset name.  It returns "undef" if no charset is specified or if the
       specified charset is not recognized by the Encode module.

       The optional second argument is a hashref containing options.  The following keys are
       recognized:

       "encoding"
	   If true, return the Encode::Encoding object instead of its name.  Defaults to false.

       "need_pragma"
	   If true (the default), follow the HTML5 spec and examine the "content" attribute only
	   of "<meta http-equiv="Content-Type"".  If set to 0, relax the HTML5 spec, and look for
	   "charset=" in the "content" attribute of every meta tag.

EXPORTS
       By default, only "html_file" is exported.  Other functions may be exported on request.

       For people who prefer not to export functions, all functions beginning with "html_" have
       an alias without that prefix (e.g. you can call "IO::HTML::file(...)" instead of
       "IO::HTML::html_file(...)".  These aliases are not exportable.

       The following export tags are available:

       ":all"
	   All exportable functions.

       ":rw"
	   "html_file", "html_file_and_encoding", "html_outfile".

SEE ALSO
       The HTML5 specification, section 8.2.2.1 Determining the character encoding:
       <http://www.w3.org/TR/html5/parsing.html#determining-the-character-encoding>

DIAGNOSTICS
       "Could not read %s: %s"
	   The specified file could not be read from for the reason specified by $!.

       "Could not seek %s: %s"
	   The specified file could not be rewound for the reason specified by $!.

       "Failed to open %s: %s"
	   The specified file could not be opened for reading for the reason specified by $!.

       "No default encoding specified"
	   The "sniff_encoding" algorithm didn't find an encoding to use, and you set
	   $IO::HTML::default_encoding to "undef".

CONFIGURATION AND ENVIRONMENT
       IO::HTML requires no configuration files or environment variables.

DEPENDENCIES
       IO::HTML has no non-core dependencies for Perl 5.8.7+.  With earlier versions of Perl 5.8,
       you need to upgrade Encode to at least version 2.10, and you may need to upgrade Exporter
       to at least version 5.57.

INCOMPATIBILITIES
       None reported.

BUGS AND LIMITATIONS
       No bugs have been reported.

AUTHOR
       Christopher J. Madsen  "<perl AT cjmweb.net>"

       Please report any bugs or feature requests to "<bug-IO-HTML AT rt.cpan.org>" or through
       the web interface at <http://rt.cpan.org/Public/Bug/Report.html?Queue=IO-HTML>.

       You can follow or contribute to IO-HTML's development at
       <http://github.com/madsen/io-html>.

COPYRIGHT AND LICENSE
       This software is copyright (c) 2013 by Christopher J. Madsen.

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

DISCLAIMER OF WARRANTY
       BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE,
       TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
       COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF
       ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
       WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
       THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE
       DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

       IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT
       HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY
       THE ABOVE LICENSE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
       INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
       SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR
       LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY
       OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
       SUCH DAMAGES.

perl v5.16.3				    2013-02-23				      IO::HTML(3)
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