Mail::Message::ConstruUserRContributed PerMail::Message::Construct::Rebuild(3)NAMEMail::Message::Construct::Rebuild - modify a Mail::Message
SYNOPSIS
my $cleanup = $msg->rebuild;
DESCRIPTION
Modifying existing messages is a pain, certainly if this has to be done
in an automated fashion. The problems are especially had when
multiparts have to be created or removed. The rebuild() method tries
to simplify this task and add some standard features.
METHODS
Constructing a message
$obj->rebuild(OPTIONS)
Reconstruct an existing message into something new. Returned is a
new message when there were modifications made, "undef" if the
message has no body left, or the original message when no
modifications had to be made.
Examples of use: you have a message which only contains html, and
you want to translate it into a multipart which contains the
original html and the textual translation of it. Or, you have a
message with parts flagged to be deleted, and you want those
changes be incorparted in the memory structure. Another
possibility: clear all the resent groups (see
Mail::Message::Head::ResentGroup) from the header, before it is
written to file.
Reconstructing is a hazardous task, where multi level multiparts
and nested messages come into play. The rebuild method tries to
simplify handing these messages for you.
-Option--Default
extra_rules []
keep_message_id <false>
rules <see text>
extra_rules => ARRAY
The standard set of rules, which is the default for the "rules"
option, is a moderest setting. In stead of copying that list
into a full set of rules of your own, you can also specify only
some additional rules which will be prependend to the default
rule set.
The order of the rules is respected, which means that you do not
always need to rewrite the whole rule is (see "rule" option).
For instance, the extra rule of "removeDeletedParts" returns an
"undef", which means that it cancels the effect of the default
rule "replaceDeletedParts".
keep_message_id => BOOLEAN
The message-id is an unique identification of the message: no two
messages with different content shall exist anywhere. However in
practice, when a message is changed during transmission, the id
is often incorrectly not changed. This may lead to complications
in application which see both messages with the same id.
rules => ARRAY
The ARRAY is a list of rules, which each describe an action which
will be called on each part which is found in the message. Most
rules probably won't match, but some will bring changes to the
content. Rules can be specified as method name, or as code
reference. See the "DETAILS" chapter in this manual page, and
recursiveRebuildPart().
By default, only the relatively safe transformations are
performed: "replaceDeletedParts", "descendMultiparts",
"descendNested", "flattenMultiparts", "flattenEmptyMultiparts".
In the future, more safe transformations may be added to this
list.
example:
# remove all deleted parts
my $cleaned = $msg->rebuild(keep_message_id => 1);
$folder->addMessage($cleaned) if defined $cleaned;
# Replace deleted parts by a place-holder
my $cleaned = $msg->rebuild
( keep_message_id => 1
, extra_rules => [ 'removeEmpty', 'flattenMultiparts' ]
);
Internals
$obj->recursiveRebuildPart(PART, OPTIONS)
-Option--Default
rules <required>
rules => ARRAY-OF-RULES
Rules are method names which can be called on messages and
message parts objects. The ARRAY can also list code references
which can be called. In any case, each rule will be called the
same way:
$code->(MESSAGE, PART)
The return can be "undef" or any complex construct based on a
Mail::Message::Part or coerceable into such a part. For each
part, all rules are called in sequence. When a rule returns a
changed object, the rules will start all over again, however
"undef" will immediately stop it.
DETAILS
Rebuilding a message
General rules
This sections describes the general configuration rules: all quite
straight forward transformations on the message structure. The rules
marked with (*) are used by default.
· descendMultiparts (*)
Apply the rules to the parts of (possibly nested) multiparts, not
only to the top-level message.
· descendNested (*)
Apply the rules to the "message/rfc822" encapsulated message as
well.
· flattenEmptyMultiparts (*)
Multipart messages which do not have any parts left are replaced by
a single part which contains the preamble, epilogue and a brief
explanation.
· flattenMultiparts (*)
When a multipart contains only one part, that part will take the
place of the multipart: the removal of a level of nesting. This
way, the preamble and epilogue of the multipart (which do not have
a meaning, officially) are lost.
· flattenNesting
Remove the "message/rfc822" encapsulation. Only the content
related lines of the encapsulated body are preserved one level
higher. Other information will be lost, which is often not too
bad.
· removeDeletedParts
All parts which are flagged for deletion are removed from the
message without leaving a trace. If a nested message is
encountered which has its encapsulated content flagged for
deletion, it will be removed as a whole.
· removeEmptyMultiparts
Multipart messages which do not have any parts left are removed.
The information in preamble and epiloge is lost.
· removeEmptyBodies
Simple message bodies which do not contain any lines of content are
removed. This will loose the information which is stored in the
headers of these bodies.
· replaceDeletedParts (*)
All parts of the message which are flagged for deletion are replace
by a message which says that the part is deleted.
You can specify a selection of these rules with rebuild(rules) and
rebuild(extra_rules).
Conversion rules
This section describes the rules which try to be smart with the
content. Please contribute with ideas and implementations.
· removeHtmlAlternativeToText
When a multipart alternative is encountered, which contains both a
plain text and an html part, then the html part is flagged for
deletion. Especially useful in combination with the
"removeDeletedParts" and "flattenMultiparts" rules.
· textAlternativeForHtml
Any "text/html" part which is not accompanied by an alternative
plain text part will have one added. You must have a working
Mail::Message::Convert::HtmlFormatText, which means that
HTML::TreeBuilder and HTML::FormatText must be installed on your
system.
Adding your own rules
If you have designed your own rule, please consider contributing this
to Mail::Box; it may be useful for other people as well.
Each rule is called
my $new = $code->($message, $part, %options)
where the %options are defined by the "rebuild()" method internals. At
least the "rules" option is passed, which is a full expansion of all
the rules which will be applied.
Your subroutine shall return $part if no changes are needed, "undef" if
the part should be removed, and any newly constructed
"Mail::Message::Part" when a change is required. It is easiest to
start looking at the source code of this package, and copy from a
comparible routine.
When you have your own routine, you simply call:
my $rebuild_message = $message->rebuild
( extra_rules => [ \&my_own_rule, 'other_rule' ] );
Modifying an existing message is a complicated job. Not only do you
need to know what you are willing to change, but you have to take care
about multiparts (possibly nested in multiple levels), rfc822
encapsulated messages, header field consistency, and so on. The
rebuild() method let you focus on the task, and takes care of the rest.
The rebuild() method uses rules to transform the one message into an
other. If one or more of the rules apply, a new message will be
returned. A simple numeric comparison tells whether the message has
changed. For example
print "No change"
if $message == $message->rebuild;
Transformation is made with a set of rules. Each rule performs only a
small step, which makes is easily configurable. The rules are ordered,
and when one makes a change to the result, the result will be passed to
all the rules again until no rule makes a change on the part anymore.
A rule may also return "undef" in which case the part will be removed
from the (resulting) message.
DIAGNOSTICS
Error: No rebuild rule $name defined.
SEE ALSO
This module is part of Mail-Box distribution version 2.097, built on
January 26, 2011. Website: http://perl.overmeer.net/mailbox/
LICENSE
Copyrights 2001-2011 by Mark Overmeer. 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://www.perl.com/perl/misc/Artistic.html
perl v5.14.12011-01-Mail::Message::Construct::Rebuild(3)
