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MIME::Decoder(3User Contributed Perl DocumentatioMIME::Decoder(3)

NAME
       MIME::Decoder - an object for decoding the body part of a
       MIME stream

       WARNING: This code is in an evaluation phase until 1
       August 1996.  Depending on any comments/complaints
       received before this cutoff date, the interface may change
       in a non-backwards-compatible manner.

DESCRIPTION
       This abstract class, and its private concrete subclasses
       (see below) provide an OO front end to the action of
       decoding a MIME-encoded stream.

       The constructor for MIME::Decoder takes the name of an
       encoding (base64, 7bit, etc.), and returns an instance of
       a subclass of MIME::Decoder whose decode() method will
       perform the appropriate decoding action.

       You can even create your own subclasses and "install" them
       so that MIME::Decoder will know about them, via the
       install() method

       Want to know if a given encoding is currently supported?
       Use the supported() class method.

SYNOPSIS
       Here's a simple filter program to read quoted-printable
       data from STDIN and write the decoded data to STDOUT:

	   #!/usr/bin/perl
	   use MIME::Decoder;

	   $encoding = 'quoted-printable';

	   $decoder = new MIME::Decoder $encoding or die "$encoding unsupported";
	   $decoder->decode(\*STDIN, \*STDOUT);

       The decode() method will always eat up all input to the
       end of file.

PUBLIC INTERFACE
       If all you are doing is using this class, here's all
       you'll need...

       new ENCODING
	   Class method.  Create and return a new decoder object
	   which can handle the given ENCODING.

	       my $decoder = new MIME::Decoder "7bit";

	   Returns the undefined value if no known decoders are
	   appropriate.

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       decode INSTREAM,OUTSTREAM
	   Decode the document waiting in the MIME input
	   filehandle INSTREAM, writing the decoded information
	   to the output filehandle OUTSTREAM.

       supported [ENCODING]
	   Class method.  With one arg (an ENCODING name),
	   returns truth if that encoding is currently handled,
	   and falsity otherwise.  The ENCODING will be
	   automatically coerced to lowercase:

	       if (MIME::Decoder->supported('7BIT')) {
		   # yes, we can handle it...
	       }
	       else {
		   # drop back six and punt...
	       }

	   With no args, returns all the available decoders as a
	   hash reference...  where the key is the encoding name
	   (all lowercase, like '7bit'), and the associated value
	   is true (it happens to be the name of the class that
	   handles the decoding, but you probably shouldn't rely
	   on that).  Hence:

	       my $supported = MIME::Decoder->supported;
	       if ($supported->{7bit}) {
		   # yes, we can handle it...
	       }
	       elsif ($supported->{8bit}) {
		   # yes, we can handle it...
	       }

	   You may safely modify this hash; it will not change
	   the way the module performs its lookups.  Only install
	   can do that.

	   Thanks to Achim Bohnet for suggesting this method.

SUBCLASS INTERFACE
       If you are writing/installing a new decoder, here's some
       other stuff you'll need:

       install ENCODING
	   Class method.  Install this class so that ENCODING is
	   handled by it.

PRIVATE BUILT-IN DECODERS
       You don't need to "use" any other Perl modules; the
       following are included as part of MIME::Decoder.

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       MIME::Decoder::Base64

       The built-in decoder for the "base64" encoding.

       The name was chosen to jibe with the pre-existing
       MIME::Base64 utility package, which this class actually
       uses to translate each line.

       MIME::Decoder::Binary

       The built-in decoder for a "binary" encoding (in other
       words, no encoding).

       The "binary" decoder is a special case, since it's ill-
       advised to read the input line-by-line: after all, an
       uncompressed image file might conceivably have
       loooooooooong stretches of bytes without a "\n" among
       them, and we don't want to risk blowing out our core.  So,
       we read-and-write fixed-size chunks.

       MIME::Decoder::QuotedPrint

       The built-in decoder the for "quoted-printable" encoding.

       The name was chosen to jibe with the pre-existing
       MIME::QuotedPrint utility package, which this class
       actually uses to translate each line.

       MIME::Decoder::Xbit

       The built-in decoder for both "7bit" and "8bit" encodings,
       which guarantee short lines (a maximum of 1000 characters
       per line) of US-ASCII data compatible with RFC-821.

       This decoder does a line-by-line pass-through from input
       to output, leaving the data unchanged except that an end-
       of-line sequence of CRLF is converted to a newline "\n".

WRITING A DECODER
       If you're experimenting with your own encodings, you'll
       probably want to write a decoder.  Here are the basics:

       1.  Create a module, like "MyDecoder::", for your decoder.
	   Declare it to be a subclass of MIME::Decoder.

       2.  Create the instance method MyDecoder::decode_it(), as
	   follows:

	   Your method should take as arguments the $self object
	   (natch), a filehandle opened for input, called $in,
	   and a filehandle opened for output, called $out.

	   Your method should read from the input filehandle,
	   decode this input, and print its decoded output to the

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	   $out filehandle.  You may do this however you see fit,
	   so long as the end result is the same.

	   Your method must return either undef (to indicate
	   failure), or 1 (to indicate success).

       3.  In your application program, activate your decoder for
	   one or more encodings like this:

	       require MyDecoder;

	       install MyDecoder "7bit";	# use MyDecoder to decode "7bit"
	       install MyDecoder "x-foo";	# also, use MyDecoder to decode "x-foo"

       To illustrate, here's a custom decoder class for the
       base64 encoding:

	   package MyBase64Decoder;

	   @ISA = qw(MIME::Decoder);
	   use MIME::Decoder;
	   use MIME::Base64;

	   # decode_it - the private decoding method
	   sub decode_it {
	       my ($self, $in, $out) = @_;

	       while (<$in>) {
		   my $decoded = decode_base64($_);
		   print $out $decoded;
	       }
	       1;
	   }

       That's it.

       The task was pretty simple because the "base64" encoding
       can easily and efficiently be parsed line-by-line... as
       can "quoted-printable", and even "7bit" and "8bit" (since
       all these encodings guarantee short lines, with a max of
       1000 characters).  The good news is: it is very likely
       that it will be similarly-easy to write a MIME::Decoder
       for any future standard encodings.

       The "binary" decoder, however, really required block reads
       and writes: see the section on MIME::Decoder::Binary for
       details.

SEE ALSO
       MIME::Decoder, MIME::Entity, MIME::Head, MIME::Parser.

AUTHOR
       Copyright (c) 1996 by Eryq / eryq@rhine.gsfc.nasa.gov

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       All rights reserved.  This program is free software; you
       can redistribute it and/or modify it under the same terms
       as Perl itself.

VERSION
       $Revision: 1.9 $ $Date: 1996/06/24 19:02:31 $

28/Aug/1996	       perl 5.005, patch 03			5

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