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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 0.04 of IO::HTML, released February 4, 2012.

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.

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

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

       (This only makes sense if "utf8::is_utf8($string)" is false.)

   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
       <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
       <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
       <http://github.com/madsen/io-html>.

COPYRIGHT AND LICENSE
       This software is copyright (c) 2012 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 v5.16.2                                     2012-02-04                                      IO::HTML(3)