| IO::HTML - Open an HTML file with automatic charset detection |
IO::HTML - Open an HTML file with automatic charset detection
This document describes version 1.001 of IO::HTML, released June 28, 2014.
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');
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 8.2.2.2 of the draft standard.
The algorithm as implemented here is:
<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.
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. If all else fails, use the default character encoding. The HTML5 standard suggests the default encoding should be locale dependent, but currently it is alwayscp1252 unless you set
$IO::HTML::default_encoding to a different value. Note:
sniff_encoding does not apply this step; only html_file does
that.
$filehandle = html_file($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 $IO::HTML::default_encoding, which is set to cp1252
(a.k.a. Windows-1252) by default. According to the standard, the
default should be locale dependent, but that is not currently
implemented.
It dies if the file cannot be opened.
($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.
$filehandle = html_outfile($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.
$encoding may be either an encoding name or an Encode::Encoding object.
It dies if the file cannot be opened.
($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.)
$encoding = find_charset_in($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:
encodingneed_pragmacontent 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.
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:rwhtml_file, html_file_and_encoding, html_outfile.
The HTML5 specification, section 8.2.2.2 Determining the character encoding: http://www.w3.org/TR/html5/syntax.html#determining-the-character-encoding
Could not read %s: %s$!.
Could not seek %s: %s$!.
Failed to open %s: %s$!.
No default encoding specifiedsniff_encoding algorithm didn't find an encoding to use, and
you set $IO::HTML::default_encoding to undef.
IO::HTML requires no configuration files or environment variables.
IO::HTML has no non-core dependencies for Perl 5.8.7+. With earlier versions of Perl 5.8, you need to upgrade the Encode manpage to at least version 2.10, and you may need to upgrade the Exporter manpage to at least version 5.57.
None reported.
No bugs have been reported.
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.
You can follow or contribute to IO-HTML's development at https://github.com/madsen/io-html.
This software is copyright (c) 2014 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.
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.
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| IO::HTML - Open an HTML file with automatic charset detection |