# MIME::WordDecoder

This module is BETA code, which means that the interfaces are fairly stable BUT it has not been out in the community long enough to guarantee much testing. Use with caution! Please report any errors back to eryq@zeegee.com as soon as you can.

- NAME
- SYNOPSIS
- DESCRIPTION
- PUBLIC INTERFACE
- SUBCLASSES
- AUTHOR
- VERSION

## NAME

MIME::WordDecoder - decode RFC-1522 encoded words to a local representation

## SYNOPSIS

See MIME::Words for the basics of encoded words. See DESCRIPTION for how this class works.

        use MIME::WordDecoder;

        ### Get the default word-decoder (used by unmime()):
        $wd = default MIME::WordDecoder;

        ### Get a word-decoder which maps to ISO-8859-1 (Latin1):
        $wd = supported MIME::WordDecoder "ISO-8859-1";

        ### Decode a MIME string (e.g., into Latin1) via the default decoder:
        $str = $wd->decode('To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld>');

        ### Decode a string using the default decoder, non-OO style:
        $str = unmime('To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld>');

## DESCRIPTION

A MIME::WordDecoder consists, fundamentally, of a hash which maps a character set name (US-ASCII, ISO-8859-1, etc.) to a subroutine which knows how to take bytes in that character set and turn them into the target string representation. Ideally, this target representation would be Unicode, but we don't want to overspecify the translation that takes place: if you want to convert MIME strings directly to Big5, that's your own decision.

The subroutine will be invoked with two arguments: DATA (the data in the given character set), and CHARSET (the upcased character set name).

For example:

        ### Keep 7-bit characters as-is, convert 8-bit characters to '#':
        sub keep7bit {
    	local $_ = shift;
    	tr/\x00-\x7F/#/c;
    	$_;
        }

Here's a decoder which uses that:

       ### Construct a decoder:
       $wd = MIME::WordDecoder->new({'US-ASCII'   => "KEEP",   ### sub { $_[0] }
                                     'ISO-8859-1' => \&keep7bit,
                                     'ISO-8859-2' => \&keep7bit,
                                     'Big5'       => "WARN",
                                     '*'          => "DIE"});

       ### Convert some MIME text to a pure ASCII string...
       $ascii = $wd->decode('To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld>');

       ### ...which will now hold: "To: Keld J#rn Simonsen <keld>"

## PUBLIC INTERFACE

default [DECODER]
  Class method. Get/set the default DECODER object.

supported CHARSET, [DECODER]
  Class method. If just CHARSET is given, returns a decoder object which maps data into that character set (the character set is forced to all-uppercase).

          $wd = supported MIME::WordDecoder "ISO-8859-1";

  If DECODER is given, installs such an object:

          MIME::WordDecoder->supported("ISO-8859-1" =>
      				 (new MIME::WordDecoder::ISO_8859 "1"));

  You should not override this method.

new [\@HANDLERS]
  Class method, constructor. If \@HANDLERS is given, then @HANDLERS is passed to handler() to initiallize the internal map.

handler CHARSET=>\&SUBREF, ...
  Instance method. Set the handler SUBREF for a given CHARSET, for as many pairs as you care to supply.

  When performing the translation of a MIME-encoded string, a given SUBREF will be invoked when translating a block of text in character set CHARSET. The subroutine will be invoked with the following arguments:

          DATA    - the data in the given character set.
          CHARSET - the upcased character set name, which may prove useful
                    if you are using the same SUBREF for multiple CHARSETs.
          DECODER - the decoder itself, if it contains configuration information
                    that your handler function needs.

  For example:

          $wd = new MIME::WordDecoder;
          $wd->handler('US-ASCII'   => "KEEP");
          $wd->handler('ISO-8859-1' => \&handle_latin1,
      		 'ISO-8859-2' => \&handle_latin1,
      		 '*'          => "DIE");

  Notice that, much as with %SIG, the SUBREF can also be taken from a set of special keywords:

         KEEP     Pass data through unchanged.
         IGNORE   Ignore data in this character set, without warning.
         WARN     Ignore data in this character set, with warning.
         DIE      Fatal exception with "can't handle character set" message.

  The subroutine for the special CHARSET of 'raw' is used for raw (non-MIME-encoded) text, which is supposed to be US-ASCII. The handler for 'raw' defaults to whatever was specified for 'US-ASCII' at the time of construction.

  The subroutine for the special CHARSET of '*' is used for any unrecognized character set. The default action for '*' is WARN.

decode STRING
  Instance method. Decode a STRING which might contain MIME-encoded components into a local representation (e.g., UTF-8, etc.).

unmime STRING
  Function, exported. Decode the given STRING using the default() decoder. See default().

## SUBCLASSES

MIME::WordDecoder::ISO_8859
  A simple decoder which keeps US-ASCII and the 7-bit characters of ISO-8859 character sets and UTF8, and also keeps 8-bit characters from the indicated character set.

          ### Construct:
          $wd = new MIME::WordDecoder::ISO_8859 2;    ### ISO-8859-2

          ### What to translate unknown characters to (can also use empty):
          ### Default is "?".
          $wd->unknown("?");

          ### Collapse runs of unknown characters to a single unknown()?
          ### Default is false.
          $wd->collapse(1);

  According to http://czyborra.com/charsets/iso8859.html (ca. November 2000):

  ISO 8859 is a full series of 10 (and soon even more) standardized multilingual single-byte coded (8bit) graphic character sets for writing in alphabetic languages:

  1. Latin1 (West European)
  2. Latin2 (East European)
  3. Latin3 (South European)
  4. Latin4 (North European)
  5. Cyrillic
  6. Arabic
  7. Greek
  8. Hebrew
  9. Latin5 (Turkish)
  10. Latin6 (Nordic)

  The ISO 8859 charsets are not even remotely as complete as the truly great Unicode but they have been around and usable for quite a while (first registered Internet charsets for use with MIME) and have already offered a major improvement over the plain 7bit US-ASCII.

  Characters 0 to 127 are always identical with US-ASCII and the positions 128 to 159 hold some less used control characters: the so-called C1 set from ISO 6429.

MIME::WordDecoder::US_ASCII
  A subclass of the ISO-8859-1 decoder which discards 8-bit characters. You're probably better off using ISO-8859-1.

## AUTHOR

Eryq (eryq@zeegee.com), ZeeGee Software Inc (http://www.zeegee.com).

## VERSION

$Revision: 1.1 $ $Date: 2004/04/09 17:04:45 $