NAME¶
IO::HTML - Open an HTML file with automatic charset detection
VERSION¶
This document describes version 1.001 of IO::HTML, released June 28, 2014.
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 8.2.2.2 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 8.2.2.2 Determining the character encoding:
<
http://www.w3.org/TR/html5/syntax.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
<
https://github.com/madsen/io-html>.
COPYRIGHT AND LICENSE¶
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.
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
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LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR
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