Provided by: libmail-message-perl_3.012-1_all bug

NAME

       Mail::Message::Head - the header of one message

INHERITANCE

        Mail::Message::Head
          is a Mail::Reporter

        Mail::Message::Head is extended by
          Mail::Message::Head::Complete
          Mail::Message::Head::Delayed
          Mail::Message::Head::Subset

SYNOPSIS

        my $head = Mail::Message::Head->new;
        $head->add('From: me@localhost');
        $head->add(From => 'me@localhost');
        $head->add(Mail::Message::Field->new(From => 'me'));
        my $subject = $head->get('subject');
        my @rec = $head->get('received');
        $head->delete('From');

DESCRIPTION

       "Mail::Message::Head" MIME headers are part of Mail::Message messages, which are grouped
       in Mail::Box folders.

       ATTENTION!!! most functionality about e-mail headers is described in
       Mail::Message::Head::Complete, which is a matured header object.  Other kinds of headers
       will be translated to that type when time comes.

       On this page, the general methods which are available on any header are described.  Read
       about differences in the sub-class specific pages.

       Extends "DESCRIPTION" in Mail::Reporter.

OVERLOADED

       overload: ""
           (stringifaction) The header, when used as string, will format as if
           Mail::Message::Head::Complete::string() was called, so return a nicely folder full
           header.  An exception is made for Carp, which will get a simplified string to avoid
           unreadible messages from "croak" and "confess".

           example: using a header object as string

            print $head;     # implicit stringification by print
            $head->print;    # the same

            print "$head";   # explicit stringication

       overload: bool
           When the header does not contain any lines (which is illegal, according to the RFCs),
           false is returned.  In all other cases, a true value is produced.

METHODS

       Extends "METHODS" in Mail::Reporter.

   Constructors
       Extends "Constructors" in Mail::Reporter.

       Mail::Message::Head->build( [PAIR|$field]-LIST )
           A fast way to construct a header with many lines.  The PAIRs are "(name, content)"
           pairs of the header, but it is also possible to pass Mail::Message::Field objects.   A
           Mail::Message::Head::Complete header is created by simply calling
           Mail::Message::Head::Complete::build(), and then each field is added.  Double field
           names are permitted.

           example:

            my $subject = Mail::Message::Field->new(Subject => 'xyz');

            my $head = Mail::Message::Head->build
             ( From     => 'me@example.com'
             , To       => 'you@anywhere.aq'
             , $subject
             , Received => 'one'
             , Received => 'two'
             );

            print ref $head;
             # -->  Mail::Message::Head::Complete

       Mail::Message::Head->new(%options)
           Create a new message header object.  The object will store all the fields of a header.
           When you get information from the header, it will be returned to you as
           Mail::Message::Field objects, although the fields may be stored differently
           internally.

           If you try to instantiate a Mail::Message::Head, you will automatically be upgraded to
           a Mail::Message::Head::Complete --a full head.

            -Option    --Defined in     --Default
             field_type                   Mail::Message::Field::Fast
             log         Mail::Reporter   'WARNINGS'
             message                      undef
             modified                     <false>
             trace       Mail::Reporter   'WARNINGS'

           field_type => CLASS
             The type of objects that all the fields will have.  This must be an extension of
             Mail::Message::Field.

           log => LEVEL
           message => MESSAGE
             The MESSAGE where this header belongs to.  Usually, this is not known at creation of
             the header, but sometimes it is.  If not, call the message() method later to set it.

           modified => BOOLEAN
           trace => LEVEL

   The header
       $obj->isDelayed()
           Headers may only be partially read, in which case they are called delayed.  This
           method returns true if some header information still needs to be read. Returns false
           if all header data has been read.  Will never trigger completion.

       $obj->isEmpty()
           Are there any fields defined in the current header?  Be warned that the header will
           not be loaded for this: delayed headers will return true in any case.

       $obj->isModified()
           Returns whether the header has been modified after being read.

           example:

            if($head->isModified) { ... }

       $obj->knownNames()
           Like Mail::Message::Head::Complete::names(), but only returns the known header fields,
           which may be less than "names" for header types which are partial.  "names()" will
           trigger completion, where "knownNames()" does not.

       $obj->message( [$message] )
           Get (after setting) the message where this header belongs to.  This does not trigger
           completion.

       $obj->modified( [BOOLEAN] )
           Sets the modified flag to BOOLEAN.  Without value, the current setting is returned,
           but in that case you can better use isModified().  Changing this flag will not trigger
           header completion.

           example:

            $head->modified(1);
            if($head->modified) { ... }
            if($head->isModified) { ... }

       $obj->orderedFields()
           Returns the fields ordered the way they were read or added.

   Access to the header
       $obj->get( $name, [$index] )
           Get the data which is related to the field with the $name.  The case of the characters
           in $name does not matter.

           If there is only one data element defined for the $name, or if there is an $index
           specified as the second argument, only the specified element will be returned. If the
           field $name matches more than one header the return value depends on the context. In
           LIST context, all values will be returned in the order they are read. In SCALAR
           context, only the last value will be returned.

           example:

            my $head = Mail::Message::Head->new;
            $head->add('Received: abc');
            $head->add('Received: xyz');
            $head->add('Subject: greetings');

            my @rec_list   = $head->get('Received');
            my $rec_scalar = $head->get('Received');
            print ",@rec_list,$rec_scalar,"     # ,abc xyz, xyz,
            print $head->get('Received', 0);    # abc
            my @sub_list   = $head->get('Subject');
            my $sub_scalar = $head->get('Subject');
            print ",@sub_list,$sub_scalar,"     # ,greetings, greetings,

       $obj->study( $name, [$index] )
           Like get(), but puts more effort in understanding the contents of the field.
           Mail::Message::Field::study() will be called for the field with the specified
           FIELDNAME, which returns Mail::Message::Field::Full objects. In scalar context only
           the last field with that name is returned.  When an $index is specified, that element
           is returned.

   About the body
       $obj->guessBodySize()
           Try to estimate the size of the body of this message, but without parsing the header
           or body.  The result might be "undef" or a few percent of the real size.  It may even
           be very far of the real value, that's why this is a guess.

       $obj->isMultipart()
           Returns whether the body of the related message is a multipart body.  May trigger
           completion, when the "Content-Type" field is not defined.

   Internals
       $obj->addNoRealize($field)
           Add a field, like Mail::Message::Head::Complete::add() does, but avoid the loading of
           a possibly partial header.  This method does not test the validity of the argument,
           nor flag the header as changed.  This does not trigger completion.

       $obj->addOrderedFields($fields)
       $obj->fileLocation()
           Returns the location of the header in the file, as a pair begin and end.  The begin is
           the first byte of the header.  The end is the first byte after the header.

       $obj->load()
           Be sure that the header is loaded.  This returns the loaded header object.

       $obj->moveLocation($distance)
           Move the registration of the header in the file.

       $obj->read($parser)
           Read the header information of one message into this header structure.  This method is
           called by the folder object (some Mail::Box sub-class), which passes the $parser as an
           argument.

       $obj->setNoRealize($field)
           Set a field, but avoid the loading of a possibly partial header as set() does.  This
           method does not test the validity of the argument, nor flag the header as changed.
           This does not trigger completion.

   Error handling
       Extends "Error handling" in Mail::Reporter.

       $obj->AUTOLOAD()
           Inherited, see "Error handling" in Mail::Reporter

       $obj->addReport($object)
           Inherited, see "Error handling" in Mail::Reporter

       $obj->defaultTrace( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )
       Mail::Message::Head->defaultTrace( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )
           Inherited, see "Error handling" in Mail::Reporter

       $obj->errors()
           Inherited, see "Error handling" in Mail::Reporter

       $obj->log( [$level, [$strings]] )
       Mail::Message::Head->log( [$level, [$strings]] )
           Inherited, see "Error handling" in Mail::Reporter

       $obj->logPriority($level)
       Mail::Message::Head->logPriority($level)
           Inherited, see "Error handling" in Mail::Reporter

       $obj->logSettings()
           Inherited, see "Error handling" in Mail::Reporter

       $obj->notImplemented()
           Inherited, see "Error handling" in Mail::Reporter

       $obj->report( [$level] )
           Inherited, see "Error handling" in Mail::Reporter

       $obj->reportAll( [$level] )
           Inherited, see "Error handling" in Mail::Reporter

       $obj->trace( [$level] )
           Inherited, see "Error handling" in Mail::Reporter

       $obj->warnings()
           Inherited, see "Error handling" in Mail::Reporter

   Cleanup
       Extends "Cleanup" in Mail::Reporter.

       $obj->DESTROY()
           Inherited, see "Cleanup" in Mail::Reporter

DETAILS

   Ordered header fields
       Many Perl implementations make a big mistake by disturbing the order of header fields.
       For some fields (especially the resent groups, see Mail::Message::Head::ResentGroup) the
       order shall be maintained.

       MailBox will keep the order of the fields as they were found in the source.  When your add
       a new field, it will be added at the end.  If your replace a field with a new value, it
       will stay in the original order.

   Head class implementation
       The header of a MIME message object contains a set of lines, which are called fields (by
       default represented by Mail::Message::Field objects).  Dependent on the situation, the
       knowledge about the fields can be in one of three situations, each represented by a sub-
       class of this module:

       •   Mail::Message::Head::Complete

           In this case, it is sure that all knowledge about the header is available.  When you
           get() information from the header and it is not there, it will never be there.

       •   Mail::Message::Head::Subset

           There is no certainty whether all header lines are known (probably not).  This may be
           caused as result of reading a fast index file, as described in Mail::Box::MH::Index.
           The object is automatically transformed into a Mail::Message::Head::Complete when all
           header lines must be known.

       •   Mail::Message::Head::Partial

           A partial header is like a subset header: probably the header is incomplete.  The
           means that you are not sure whether a get() for a field fails because the field is not
           a part of the message or that it fails because it is not yet known to the program.
           Where the subset header knows where to get the other fields, the partial header does
           not know it.  It cannot hide its imperfection.

       •   Mail::Message::Head::Delayed

           In this case, there is no single field known.  Access to this header will always
           trigger the loading of the full header.

   Subsets of header fields
       Message headers can be quite large, and therefore MailBox provides simplified access to
       some subsets of information.  You can grab these sets of fields together, create and
       delete them as group.

       On the moment, the following sets are defined:

       •   Mail::Message::Head::ResentGroup

           A resent group is a set of fields which is used to log one step in the transmission of
           the message from the original sender to the destination.

           Each step adds a set of headers to indicate when the message was received and how it
           was forwarded (without modification).  These fields are best created using
           Mail::Message::bounce().

       •   Mail::Message::Head::ListGroup

           Fields which are used to administer and log mailing list activity.  Mailing list
           software has to play trics with the original message to be able to get the reply on
           that message back to the mailing list.  Usually a large number of lines are added.

       •   Mail::Message::Head::SpamGroup

           A set of fields which contains header fields which are produced by spam detection
           software.  You may want to remove these fields when you store a message for a longer
           period of time.

DIAGNOSTICS

       Error: Package $package does not implement $method.
           Fatal error: the specific package (or one of its superclasses) does not implement this
           method where it should. This message means that some other related classes do
           implement this method however the class at hand does not.  Probably you should
           investigate this and probably inform the author of the package.

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@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/