mime::decoder(3)

NAME

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

SYNOPSIS

Before reading further, you should see MIME::Tools to make
sure that you understand where this module fits into the
grand scheme of things.  Go on, do it now.  I'll wait.
Ready?  Ok...
Decoding a data stream
Here's a simple filter program to read quoted-printable
data from STDIN (until EOF) and write the decoded data to
STDOUT:
    use MIME::Decoder;
    $decoder = new MIME::Decoder 'quoted-printable' or die
"unsupported";
    $decoder->decode(TDIN, TDOUT);
Encoding a data stream
Here's a simple filter program to read binary data from
STDIN (until EOF) and write base64-encoded data to STDOUT:
    use MIME::Decoder;
    $decoder  =  new MIME::Decoder 'base64' or die "unsupported";
    $decoder->encode(TDIN, TDOUT);
Non-standard encodings
You can write and install your own decoders so that
MIME::Decoder will know about them:
    use MyBase64Decoder;
    install MyBase64Decoder 'base64';
You can also test if a given encoding is supported:
    if (supported MIME::Decoder 'x-uuencode') {
        ### we can uuencode!
    }

DESCRIPTION

This abstract class, and its private concrete subclasses
(see below) provide an OO front end to the actions of...

� Decoding a MIME-encoded stream

� Encoding a raw data stream into 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, and whose
"encode()" method will perform the appropriate encoding
action.

PUBLIC INTERFACE

Standard interface

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

new ENCODING: Class method, constructor. 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.
best ENCODING: Class method, constructor. Exactly like new(), except that this defaults any unsupported encoding to
"binary", after raising a suitable warning (it's a
fatal error if there's no binary decoder).

my $decoder = best MIME::Decoder "x-gzip64";; Will either return a decoder, or a raise a fatal
exception.
decode INSTREAM,OUTSTREAM: Instance method. Decode the document waiting in the input handle INSTREAM, writing the decoded information
to the output handle OUTSTREAM.; Read the section in this document on I/O handles for
more information about the arguments. Note that you
can still supply old-style unblessed filehandles for
INSTREAM and OUTSTREAM.; Returns true on success, throws exception on failure.
encode INSTREAM,OUTSTREAM: Instance method. Encode the document waiting in the input filehandle INSTREAM, writing the encoded infor
mation to the output stream OUTSTREAM.; Read the section in this document on I/O handles for
more information about the arguments. Note that you
can still supply old-style unblessed filehandles for
INSTREAM and OUTSTREAM.; Returns true on success, throws exception on failure.
encoding: Instance method. Return the encoding that this object was created to handle, coerced to all lowercase (e.g.,
"base64").
head [HEAD]: Instance method. Completely optional: some decoders need to know a little about the file they are encod
ing/decoding; e.g., x-uu likes to have the filename.
The HEAD is any object which responds to messages
like:

$head->mime_attr('content-disposition.filename');
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 automati
cally coerced to lowercase:

if (supported MIME::Decoder '7BIT') {
### yes, we can handle it...

}
else {

### drop back six and punt...

}; With no args, returns a reference to a hash of all
available decoders, where the key is the encoding name
(all lowercase, like '7bit'), and the value is true
(it happens to be the name of the class that handles
the decoding, but you probably shouldn't rely on
that). 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 (or installing) a new decoder subclass, there are some other methods you'll need to know about:
decode_it INSTREAM,OUTSTREAM: Abstract instance method. The back-end of the decode method. It takes an input handle opened for reading
(INSTREAM), and an output handle opened for writing
(OUTSTREAM).; If you are writing your own decoder subclass, you must
override this method in your class. Your method
should read from the input handle via "getline()" or
"read()", decode this input, and print the decoded
data to the output handle via "print()". You may do
this however you see fit, so long as the end result is
the same.; Note that unblessed references and globrefs are auto
matically turned into I/O handles for you by
"decode()", so you don't need to worry about it.; Your method must return either "undef" (to indicate
failure), or 1 (to indicate success). It may also
throw an exception to indicate failure.
encode_it INSTREAM,OUTSTREAM: Abstract instance method. The back-end of the encode method. It takes an input handle opened for reading
(INSTREAM), and an output handle opened for writing
(OUTSTREAM).; If you are writing your own decoder subclass, you must
override this method in your class. Your method
should read from the input handle via "getline()" or
"read()", encode this input, and print the encoded
data to the output handle via "print()". You may do
this however you see fit, so long as the end result is
the same.; Note that unblessed references and globrefs are auto
matically turned into I/O handles for you by
"encode()", so you don't need to worry about it.; Your method must return either "undef" (to indicate
failure), or 1 (to indicate success). It may also
throw an exception to indicate failure.
filter IN, OUT, COMMAND...: Class method, utility. If your decoder involves an external program, you can invoke them easily through
this method. The command must be a "filter": a com
mand that reads input from its STDIN (which will come
from the IN argument) and writes output to its STDOUT
(which will go to the OUT argument).; For example, here's a decoder that un-gzips its data:

sub decode_it {
my ($self, $in, $out) = @_;
$self->filter($in, $out, "gzip -d -");

}; The usage is similar to IPC::Open2::open2 (which it
uses internally), so you can specify COMMAND as a sin
gle argument or as an array.
init ARGS...: Instance method. Do any necessary initialization of the new instance, taking whatever arguments were given
to "new()". Should return the self object on success,
undef on failure.
install ENCODINGS...: Class method. Install this class so that each encod ing in ENCODINGS is handled by it:

install MyBase64Decoder 'base64', 'x-base64super';; You should not override this method.
uninstall ENCODINGS...: Class method. Uninstall support for encodings. This is a way to turn off the decoding of "experimental"
encodings. For safety, always use MIME::Decoder
directly:

uninstall MIME::Decoder 'x-uu', 'x-uuencode';; You should not override this method.

DECODER SUBCLASSES

You don't need to "use" any other Perl modules; the fol lowing "standard" subclasses are included as part of MIME::Decoder:: Class: Handles encodings:
-----------------------------------------------------------MIME::Decoder::Binary binary
MIME::Decoder::NBit 7bit, 8bit
MIME::Decoder::Base64 base64
MIME::Decoder::QuotedPrint quoted-printable
The following "non-standard" subclasses are also included:: Class: Handles encodings:
-----------------------------------------------------------MIME::Decoder::UU x-uu, x-uuencode
MIME::Decoder::Gzip64 x-gzip64 **; requires gzip!

NOTES

Input/Output handles

As of MIME-tools 2.0, this class has to play nice with the
new MIME::Body class... which means that input and output
routines cannot just assume that they are dealing with
filehandles.

Therefore, all that MIME::Decoder and its subclasses require (and, thus, all that they can assume) is that INSTREAMs and OUTSTREAMs are objects which respond to a subset of the messages defined in the IO::Handle inter face; minimally:: print
getline
read(BUF,NBYTES)
For backwards compatibilty, if you supply a scalar file handle name (like "STDOUT") or an unblessed glob reference (like "TDOUT") where an INSTREAM or OUTSTREAM is expected, this package will automatically wrap it in an object that fits these criteria, via IO::Wrap.
Thanks to Achim Bohnet for suggesting this more-generic I/O model.
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 following instance methods in your class, as described above:: decode_it
encode_it
init
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 "quoted-printable" encoding:: package MyQPDecoder;; @ISA = qw(MIME::Decoder);
use MIME::Decoder;
use MIME::QuotedPrint;; ### decode_it - the private decoding method
sub decode_it {
my ($self, $in, $out) = @_;; while (defined($_ = $in->getline)) {
my $decoded = decode_qp($_);
$out->print($decoded);
} 1;
}
### encode_it - the private encoding method sub encode_it { my ($self, $in, $out) = @_;
my ($buf, $nread) = ('', 0); while ($in->read($buf, 60)) { my $encoded = encode_qp($buf); $out->print($encoded);
} 1;
}
That's it. The task was pretty simple because the "quoted-printable" encoding can easily be converted line-by-line... as can 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 "MIME::Decoder::Binary" for details.

AUTHOR

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

VERSION

$Revision: 5.403 $ $Date: 2000/11/04 19:54:46 $

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