phpman > perldoc > MIME::Decoder(3pm)

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(\*STDIN, \*STDOUT);

  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(\*STDIN, \*STDOUT);

  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 information 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 encoding/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 automatically 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 automatically 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 automatically 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 command 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 single 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 encoding 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 following "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 interface; minimally:

          print
          getline
          read(BUF,NBYTES)

    *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) = @_;
            local $_;
            while (defined($_ = $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.

SEE ALSO
    MIME::Tools, other MIME::Decoder subclasses.

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

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

    1;