/ 
Mail-Message-3.015
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/ Mail::Message::Body::Encode

NAME

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

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');

DESCRIPTION

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

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

  • 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.

  • 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 Mail::Message::TransferEnc set of packages. The related manual page lists the transfer encodings which are supported.

  • mime-type translation

    NOT IMPLEMENTED YET

  • charset conversion

METHODS

Constructing a body

$obj->charsetDetect(%options)

[3.013] This is tricky. It is hard to detect whether the body originates from the program, or from an external source. And what about a database database? are those octets or strings? Please read "Autodetection of character-set" in Mail::Message::Body.

-Option  --Default
 external  <false>
external => BOOLEAN

Do only consider externally valid character-sets, implicitly: PERL is not an acceptable answer.

Mail::Message::Body->charsetDetectAlgorithm( [CODE|undef|METHOD] )

[3.013] When a body object does not specify its character-set, but that detail is required, then it gets autodetected. The default algorithm is implemented in charsetDetect(). You may change this default algorithm, or pass option charset_detect for each call to encode().

When you call this method with an explicit undef, you reset the default. (Without parameter) the current algorithm (CODE or method name) is returned.

$obj->check()

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 undef is returned.

$obj->encode(%options)

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

-Option           --Default
 charset            PERL
 charset_detect     <built-in>
 mime_type          undef
 result_type        <same as source>
 transfer_encoding  undef
charset => CHARSET|'PERL'

Only applies when the mime_type is textual.

If the CHARSET is explicitly specified (for instance iso-8859-10, then the data is being interpreted as raw bytes (blob), not as text. However, in case of PERL, it is considered to be an internal representation of characters (either latin1 or Perl's utf8 --not the same as utf-8--, you should not want to know).

This setting overrules the charset attribute in the mime_type FIELD.

charset_detect => CODE

[3.013] When the body does not contain an explicit charset specification, then the RFC says it is us-ascii. In reality, this is not true: it is just an unknown character set. This often happens when text files are included as attachment, for instance a footer attachment.

When you want to be smarter than the default charset detector, you can provide your own function for this parameter. The function will get the transfer-decoded version of this body. You can change the default globally via charsetDetectAlgorithm().

mime_type => STRING|FIELD

Convert into the specified mime type, which can be specified as STRING or FIELD. The FIELD is a Mail::Message::Field-object, representing a Content-Type mime header. The STRING must be valid content for such header, and will be converted into a FIELD object.

The FIELD may contain attributes. Usually, it has a charset attribute, which explains the CHARSET of the content after content transfer decoding. The charset option will update/add this attribute. Otherwise (hopefully in rare cases) the CHARSET will be auto-detected when the body gets decoded.

result_type => CLASS

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 Mail::Message::Body.

transfer_encoding => STRING|FIELD
$obj->encoded(%options)

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.

-Option        --Default
 charset_detect  <the default>
charset_detect => CODE

See charsetDetectAlgorithm().

$obj->unify($body)

Unify the type of the given $body objects with the type of the called body. 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).

About the payload

$obj->dispositionFilename( [$directory] )

Various fields are searched for filename and name attributes. Without $directory, the name found will be returned unmodified.

When a $directory is given, a filename is composed. For security reasons, only the basename of the found name gets used and many potentially dangerous characters removed. If no name was found, or when the found name is already in use, then an unique name is generated.

Don't forget to read RFC6266 section 4.3 for the security aspects in your email application.

$obj->isBinary()

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

$obj->isText()

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

Internals

$obj->addTransferEncHandler( $name, <$class|$object> )
Mail::Message::Body->addTransferEncHandler( $name, <$class|$object> )

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 Mail::Message::TransferEnc. It will replace existing class and object for this $name.

Why aren't you contributing this class to MailBox?

$obj->getTransferEncHandler($type)

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

DIAGNOSTICS

Warning: Charset $name is not known

The encoding or decoding of a message body encounters a character set which is not understood by Perl's Encode module.

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.

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.

SEE ALSO

This module is part of Mail-Message distribution version 3.015, built on December 11, 2023. Website: http://perl.overmeer.net/CPAN/

LICENSE

Copyrights 2001-2023 by [Mark Overmeer <markov@cpan.org>]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://dev.perl.org/licenses/