phpMan > perldoc > IO::HTML

NAME
    IO::HTML - Open an HTML file with automatic charset detection

VERSION
    This document describes version 1.004 of IO::HTML, released September 26, 2020.

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 $bytes_to_check 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 $bytes_to_check 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, or if "sniff_encoding" cannot determine the encoding and
    $IO::HTML::default_encoding has been set to "undef".

  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, or if "sniff_encoding" cannot determine the encoding and
    $IO::HTML::default_encoding has been set to "undef".

    The result of calling "html_file_and_encoding" in scalar context is undefined (in the C sense of
    there is no guarantee what you'll get).

  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, or if both $encoding and $IO::HTML::default_encoding are
    "undef".

  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. The "<meta>" tag must begin within the first $IO::HTML::bytes_to_check bytes of
    the string.

    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
    There are two global variables that affect IO::HTML. If you need to change them, you should do
    so using "local" if possible:

      my $file = do {
        # This file may define the charset later in the header
        local $IO::HTML::bytes_to_check = 4096;
        html_file(...);
      };

    $bytes_to_check
        This is the number of bytes that "sniff_encoding" will read from the stream. It is also the
        number of bytes that "find_charset_in" will search for a "<meta>" tag containing charset
        information. It must be a positive integer.

        The HTML 5 specification recommends using the default value of 1024, but some pages do not
        follow the specification.

    $default_encoding
        This is the encoding that "html_file" and "html_file_and_encoding" will use if no encoding
        can be detected by "sniff_encoding". The default value is "cp1252" (a.k.a. Windows-1252).

        Setting it to "undef" will cause the file subroutines to croak if "sniff_encoding" fails to
        determine the encoding. ("sniff_encoding" itself does not use $default_encoding).

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) 2020 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
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    EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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    OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE
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