Ubuntu Manpage: IO::HTML - Open an HTML file with automatic charset detection

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:

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".

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) 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 v5.14.2                                       2013-02-23                                      IO::HTML(3pm)