phpman > perldoc > Mail::Message::Construct::Rebuild(3pm)

NAME
    Mail::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
    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.

   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 deleted. Especially useful in combination with the
        "flattenMultiparts" rule.

    *   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.

        When you are planning to create an automatic html to plain text filter for your email, then
        have a look at https://github.com/logological/mimestrip

        . Example: using parameter with "textAlternativeForHtml"

          my $result = $msg->rebuild
            ( extra_rules => [ 'textAlternativeForHtml' ]
            , textAlternativeForHtml => { leftmargin => 0 }
            );

    *   removeExtraAlternativeText

        [2.110] When a multipart alternative is encountered, deletes all its parts except for the
        last part (the preferred part in accordance with RFC2046). In practice, this normally
        results in the alternative plain text part being deleted of an html message. Useful in
        combination with the "flattenMultiparts" rule.

   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' ] );

DIAGNOSTICS
    Error: No rebuild rule $name defined.

SEE ALSO
    This module is part of Mail-Message distribution version 3.012, built on February 11, 2022.
    Website: http://perl.overmeer.net/CPAN/

LICENSE
    Copyrights 2001-2022 by [Mark Overmeer <markov AT 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/