1IO::HTML(3) User Contributed Perl Documentation IO::HTML(3)
2
6 IO::HTML - Open an HTML file with automatic charset detection
7
9 This document describes version 1.004 of IO::HTML, released September
10 26, 2020.
11
13 use IO::HTML; # exports html_file by default
14 use HTML::TreeBuilder;
15 my $tree = HTML::TreeBuilder->new_from_file(
17 html_file('foo.html')
18 );
19 # Alternative interface:
21 open(my $in, '<:raw', 'bar.html');
22 my $encoding = IO::HTML::sniff_encoding($in, 'bar.html');
23
25 IO::HTML provides an easy way to open a file containing HTML while
26 automatically determining its encoding. It uses the HTML5 encoding
27 sniffing algorithm specified in section 8.2.2.2 of the draft standard.
28 The algorithm as implemented here is:
30 1. If the file begins with a byte order mark indicating UTF-16LE,
32 UTF-16BE, or UTF-8, then that is the encoding.
33 2. If the first $bytes_to_check bytes of the file contain a "<meta>"
35 tag that indicates the charset, and Encode recognizes the specified
36 charset name, then that is the encoding. (This portion of the
37 algorithm is implemented by "find_charset_in".)
38 The "<meta>" tag can be in one of two formats:
40 <meta charset="...">
42 <meta http-equiv="Content-Type" content="...charset=...">
43 The search is case-insensitive, and the order of attributes within
45 the tag is irrelevant. Any additional attributes of the tag are
46 ignored. The first matching tag with a recognized encoding ends
47 the search.
48 3. If the first $bytes_to_check bytes of the file are valid UTF-8
50 (with at least 1 non-ASCII character), then the encoding is UTF-8.
51 4. If all else fails, use the default character encoding. The HTML5
53 standard suggests the default encoding should be locale dependent,
54 but currently it is always "cp1252" unless you set
55 $IO::HTML::default_encoding to a different value. Note:
56 "sniff_encoding" does not apply this step; only "html_file" does
57 that.
58
60 html_file
61 $filehandle = html_file($filename, \%options);
62 This function (exported by default) is the primary entry point. It
64 opens the file specified by $filename for reading, uses
65 "sniff_encoding" to find a suitable encoding layer, and applies it. It
66 also applies the ":crlf" layer. If the file begins with a BOM, the
67 filehandle is positioned just after the BOM.
68 The optional second argument is a hashref containing options. The
70 possible keys are described under "find_charset_in".
71 If "sniff_encoding" is unable to determine the encoding, it defaults to
73 $IO::HTML::default_encoding, which is set to "cp1252" (a.k.a.
74 Windows-1252) by default. According to the standard, the default
75 should be locale dependent, but that is not currently implemented.
76 It dies if the file cannot be opened, or if "sniff_encoding" cannot
78 determine the encoding and $IO::HTML::default_encoding has been set to
79 "undef".
80 html_file_and_encoding
82 ($filehandle, $encoding, $bom)
83 = html_file_and_encoding($filename, \%options);
84 This function (exported only by request) is just like "html_file", but
86 returns more information. In addition to the filehandle, it returns
87 the name of the encoding used, and a flag indicating whether a byte
88 order mark was found (if $bom is true, the file began with a BOM).
89 This may be useful if you want to write the file out again (especially
90 in conjunction with the "html_outfile" function).
91 The optional second argument is a hashref containing options. The
93 possible keys are described under "find_charset_in".
94 It dies if the file cannot be opened, or if "sniff_encoding" cannot
96 determine the encoding and $IO::HTML::default_encoding has been set to
97 "undef".
98 The result of calling "html_file_and_encoding" in scalar context is
100 undefined (in the C sense of there is no guarantee what you'll get).
101 html_outfile
103 $filehandle = html_outfile($filename, $encoding, $bom);
104 This function (exported only by request) opens $filename for output
106 using $encoding, and writes a BOM to it if $bom is true. If $encoding
107 is "undef", it defaults to $IO::HTML::default_encoding. $encoding may
108 be either an encoding name or an Encode::Encoding object.
109 It dies if the file cannot be opened, or if both $encoding and
111 $IO::HTML::default_encoding are "undef".
112 sniff_encoding
114 ($encoding, $bom) = sniff_encoding($filehandle, $filename, \%options);
115 This function (exported only by request) runs the HTML5 encoding
117 sniffing algorithm on $filehandle (which must be seekable, and should
118 have been opened in ":raw" mode). $filename is used only for error
119 messages (if there's a problem using the filehandle), and defaults to
120 "file" if omitted. The optional third argument is a hashref containing
121 options. The possible keys are described under "find_charset_in".
122 It returns Perl's canonical name for the encoding, which is not
124 necessarily the same as the MIME or IANA charset name. It returns
125 "undef" if the encoding cannot be determined. $bom is true if the file
126 began with a byte order mark. In scalar context, it returns only
127 $encoding.
128 The filehandle's position is restored to its original position
130 (normally the beginning of the file) unless $bom is true. In that
131 case, the position is immediately after the BOM.
132 Tip: If you want to run "sniff_encoding" on a file you've already
134 loaded into a string, open an in-memory file on the string, and pass
135 that handle:
136 ($encoding, $bom) = do {
138 open(my $fh, '<', \$string); sniff_encoding($fh)
139 };
140 (This only makes sense if $string contains bytes, not characters.)
142 find_charset_in
144 $encoding = find_charset_in($string_containing_HTML, \%options);
145 This function (exported only by request) looks for charset information
147 in a "<meta>" tag in a possibly-incomplete HTML document using the "two
148 step" algorithm specified by HTML5. It does not look for a BOM. The
149 "<meta>" tag must begin within the first $IO::HTML::bytes_to_check
150 bytes of the string.
151 It returns Perl's canonical name for the encoding, which is not
153 necessarily the same as the MIME or IANA charset name. It returns
154 "undef" if no charset is specified or if the specified charset is not
155 recognized by the Encode module.
156 The optional second argument is a hashref containing options. The
158 following keys are recognized:
159 "encoding"
161 If true, return the Encode::Encoding object instead of its name.
162 Defaults to false.
163 "need_pragma"
165 If true (the default), follow the HTML5 spec and examine the
166 "content" attribute only of "<meta http-equiv="Content-Type"". If
167 set to 0, relax the HTML5 spec, and look for "charset=" in the
168 "content" attribute of every meta tag.
169
171 By default, only "html_file" is exported. Other functions may be
172 exported on request.
173 For people who prefer not to export functions, all functions beginning
175 with "html_" have an alias without that prefix (e.g. you can call
176 IO::HTML::file(...) instead of IO::HTML::html_file(...). These aliases
177 are not exportable.
178 The following export tags are available:
180 ":all"
182 All exportable functions.
183 ":rw"
185 "html_file", "html_file_and_encoding", "html_outfile".
186
188 The HTML5 specification, section 8.2.2.2 Determining the character
189 encoding:
190 <http://www.w3.org/TR/html5/syntax.html#determining-the-character-encoding>
191
193 "Could not read %s: %s"
194 The specified file could not be read from for the reason specified
195 by $!.
196 "Could not seek %s: %s"
198 The specified file could not be rewound for the reason specified by
199 $!.
200 "Failed to open %s: %s"
202 The specified file could not be opened for reading for the reason
203 specified by $!.
204 "No default encoding specified"
206 The "sniff_encoding" algorithm didn't find an encoding to use, and
207 you set $IO::HTML::default_encoding to "undef".
208
210 There are two global variables that affect IO::HTML. If you need to
211 change them, you should do so using "local" if possible:
212 my $file = do {
214 # This file may define the charset later in the header
215 local $IO::HTML::bytes_to_check = 4096;
216 html_file(...);
217 };
218 $bytes_to_check
220 This is the number of bytes that "sniff_encoding" will read from
221 the stream. It is also the number of bytes that "find_charset_in"
222 will search for a "<meta>" tag containing charset information. It
223 must be a positive integer.
224 The HTML 5 specification recommends using the default value of
226 1024, but some pages do not follow the specification.
227 $default_encoding
229 This is the encoding that "html_file" and "html_file_and_encoding"
230 will use if no encoding can be detected by "sniff_encoding". The
231 default value is "cp1252" (a.k.a. Windows-1252).
232 Setting it to "undef" will cause the file subroutines to croak if
234 "sniff_encoding" fails to determine the encoding.
235 ("sniff_encoding" itself does not use $default_encoding).
236
238 IO::HTML has no non-core dependencies for Perl 5.8.7+. With earlier
239 versions of Perl 5.8, you need to upgrade Encode to at least version
240 2.10, and you may need to upgrade Exporter to at least version 5.57.
241
243 None reported.
244
246 No bugs have been reported.
247
249 Christopher J. Madsen "<perl AT cjmweb.net>"
250 Please report any bugs or feature requests to
252 "<bug-IO-HTML AT rt.cpan.org>" or through the web interface at
253 <http://rt.cpan.org/Public/Bug/Report.html?Queue=IO-HTML>.
254 You can follow or contribute to IO-HTML's development at
256 <https://github.com/madsen/io-html>.
257
259 This software is copyright (c) 2020 by Christopher J. Madsen.
260 This is free software; you can redistribute it and/or modify it under
262 the same terms as the Perl 5 programming language system itself.
263
265 BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
266 FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT
267 WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER
268 PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND,
269 EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
270 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
271 ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH
272 YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
273 NECESSARY SERVICING, REPAIR, OR CORRECTION.
274 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
276 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
277 REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENSE, BE LIABLE
278 TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR
279 CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
280 SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
281 RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A
282 FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
283 SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
284 DAMAGES.
285perl v5.36.0 2023-01-20 IO::HTML(3)