
=head1 NAME

Mail::Message::Body::Encode - organize general message encodings


=head1 INHERITANCE


=head1 SYNOPSIS

 my Mail::Message $msg = ...;
 my $decoded = $msg->decoded;
 my $encoded = $msg->encode(mime_type => 'image/gif',
     transfer_encoding => 'base64');

 my $body = $msg->body;
 my $decoded = $body->decoded;
 my $encoded = $body->encode(transfer_encoding => '7bit');


=head1 DESCRIPTION

Manages the message's body encodings and decodings on request of the
main program.  This package adds functionality to the L<Mail::Message::Body|Mail::Message::Body>
class when the L<decoded()|"Constructing a body"> or L<encode()|"Constructing a body"> method is called.

Four types of encodings are handled (in the right order)

=over 4

=item * eol encoding

Various operating systems have different ideas about how to encode the
line termination.  UNIX uses a LF character, MacOS uses a CR, and
Windows uses a CR/LF combination.  Messages which are transported over
Internet will always use the CRLF separator.

=item * transfer encoding

Messages transmitted over Internet have to be plain ASCII.  Complicated
characters and binary files (like images and archives) must be encoded
during transmission to an ASCII representation.

The implementation of the required encoders and decoders is found in
the L<Mail::Message::TransferEnc|Mail::Message::TransferEnc> set of packages.  The related
manual page lists the transfer encodings which are supported.

=item * mime-type translation

NOT IMPLEMENTED YET

=item * charset conversion

NOT IMPLEMENTED YET

=back



=head1 METHODS


=head2 Constructing a body


$obj-E<gt>B<check>

=over 4

Check the content of the body not to include illegal characters.  Which
characters are considered illegal depends on the encoding of this body.

A body is returned which is checked.  This may be the body where this
method is called upon, but also a new object, when serious changes had
to be made.  If the check could not be made, because the decoder is not
defined, then C<undef> is returned.

=back

$obj-E<gt>B<encode>(OPTIONS)

=over 4

Encode (translate) a L<Mail::Message::Body|Mail::Message::Body> into a different format.
See the DESCRIPTION above.  Options which are not specified will not trigger
conversions.

 Option             Defined in       Default         
 charset                             undef           
 mime_type                           undef           
 result_type                         <same as source>
 transfer_encoding                   undef           

. charset STRING

. mime_type STRING|FIELD

=over 4

Convert into the specified mime type, which can be specified as STRING
or FIELD.  The FIELD is a L<Mail::Message::Field|Mail::Message::Field>, and the STRING is
converted in such object before use.

=back

. result_type CLASS

=over 4

The type of body to be created when the body is changed to fulfill the request
on re-coding.  Also the intermediate stages in the translation process (if
needed) will use this type. CLASS must extend L<Mail::Message::Body|Mail::Message::Body>.

=back

. transfer_encoding STRING|FIELD

=back

$obj-E<gt>B<encoded>

=over 4

Encode the body to a format what is acceptable to transmit or write to
a folder file.  This returns the body where this method was called
upon when everything was already prepared, or a new encoded body
otherwise.  In either case, the body is checked.

=back

$obj-E<gt>B<unify>(BODY)

=over 4

Unify the type of the given BODY objects with the type of the called
body.  C<undef> is returned when unification is impossible.  If the
bodies have the same settings, the BODY object is returned unchanged.

Examples:

 my $bodytype = Mail::Message::Body::Lines;
 my $html  = $bodytype->new(mime_type=>'text/html', data => []);
 my $plain = $bodytype->new(mime_type=>'text/plain', ...);

 my $unified = $html->unify($plain);
 # $unified is the data of plain translated to html (if possible).

=back

=head2 About the payload


$obj-E<gt>B<isBinary>

=over 4

Returns true when the un-encoded message is binary data.  This information
is retrieved from knowledge provided by MIME::Types.

=back

$obj-E<gt>B<isText>

=over 4

Returns true when the un-encoded message contains printable
text.

=back

=head2 Internals


$obj-E<gt>B<addTransferEncHandler>(NAME, CLASS|OBJECT)

Mail::Message::Body-E<gt>B<addTransferEncHandler>(NAME, CLASS|OBJECT)

=over 4

Relate the NAMEd transfer encoding to an OBJECTs or object of the specified
CLASS.  In the latter case, an object of that CLASS will be created on the
moment that one is needed to do encoding or decoding.

The CLASS or OBJECT must extend L<Mail::Message::TransferEnc|Mail::Message::TransferEnc>.  It will
replace existing class and object for this NAME.

Why aren't you contributing this class to MailBox?

=back

$obj-E<gt>B<getTransferEncHandler>(TYPE)

=over 4

Get the transfer encoder/decoder which is able to handle TYPE, or return
undef if there is no such handler.

=back



=head1 DIAGNOSTICS

I<Warning:> No decoder defined for transfer encoding $name.

The data (message body) is encoded in a way which is not currently understood,
therefore no decoding (or recoding) can take place.

I<Warning:> No encoder defined for transfer encoding $name.

The data (message body) has been decoded, but the required encoding is
unknown.  The decoded data is returned.






=head1 REFERENCES

See the Mail::Box website at L<http://perl.overmeer.net/mailbox/> for more details.

=head1 COPYRIGHTS

Module version 2.042.
Written by Mark Overmeer (mark@overmeer.net).  See the ChangeLog for
other contributors.

Copyright (c) 2001-2003 by the author(s). All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.


