
=head1 NAME

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


=head1 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


=head1 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 Mail::Message::Field $subject = $head->get('subject');
 my Mail::Message::Field @rec = $head->get('received');
 $head->delete('From');


=head1 DESCRIPTION

C<Mail::Message::Head> MIME headers are part of L<Mail::Message|Mail::Message> messages,
which are grouped in L<Mail::Box|Mail::Box> folders.

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

The header of a MIME message object contains a set of lines, which are
called I<fields> (by default represented by L<Mail::Message::Field|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:

=over 4

=item * L<Mail::Message::Head::Complete|Mail::Message::Head::Complete>

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

=item * L<Mail::Message::Head::Subset|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
L<Mail::Box::MH::Index|Mail::Box::MH::Index>.  The object is automatically transformed
into a L<Mail::Message::Head::Complete|Mail::Message::Head::Complete> when all header lines must be known.

=item * L<Mail::Message::Head::Partial|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 L<get()|"Access to the header"> 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.

=item * L<Mail::Message::Head::Delayed|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.

=back

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


=head1 OVERLOADED


overload: B<"">

=over 4

(stringifaction) The header, when used as string, will format as if
L<Mail::Message::Head::Complete::string()|"Access to the header"> 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 C<croak>
and C<confess>.

I<Example:> using a header object as string


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

 print "$head";   # explicit stringication

=back

overload: B<bool>

=over 4

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.

=back


=head1 METHODS


=head2 Constructors


$obj-E<gt>B<build>(FIELDS)

=over 4

A fast way to construct a header with many lines.
The FIELDS are (name, content) pairs of the header.   A
L<Mail::Message::Head::Complete|Mail::Message::Head::Complete> header is created by simply calling
L<Mail::Message::Head::Complete::build()|"Constructors">, and then each field
is added.  Double field names are permitted.

I<Example:> 

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

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

=back

Mail::Message::Head-E<gt>B<new>(OPTIONS)

=over 4

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 L<Mail::Message::Field|Mail::Message::Field> objects, although
the fields may be stored differently internally.

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

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

. field_type CLASS

=over 4

The type of objects that all the fields will have.  This must be
an extension of L<Mail::Message::Field|Mail::Message::Field>.

=back

. log LEVEL

. message MESSAGE

=over 4

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.

=back

. modified BOOLEAN

. trace LEVEL

=back

=head2 The header


$obj-E<gt>B<isDelayed>

=over 4

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.

=back

$obj-E<gt>B<isEmpty>

=over 4

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.

=back

$obj-E<gt>B<isModified>

=over 4

Returns whether the header has been modified after being read.

I<Example:> 

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

=back

$obj-E<gt>B<knownNames>

=over 4

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

=back

$obj-E<gt>B<message>([MESSAGE])

=over 4

Get (after setting) the message where this header belongs to.
This does not trigger completion.

=back

$obj-E<gt>B<modified>([BOOLEAN])

=over 4

Sets the modified flag to BOOLEAN.  Without value, the current setting is
returned, but in that case you can better use L<isModified()|"The header">.
Changing this flag will not trigger header completion.

I<Example:> 

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

=back

$obj-E<gt>B<orderedFields>

=over 4

Retuns the fields ordered the way they were read or added.

=back

=head2 Access to the header


$obj-E<gt>B<get>(NAME [,INDEX])

=over 4

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.

I<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,

=back

=head2 About the body


$obj-E<gt>B<guessBodySize>

=over 4

Try to estimate the size of the body of this message, but without parsing
the header or body.  The result might be C<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.

=back

$obj-E<gt>B<isMultipart>

=over 4

Returns whether the body of the related message is a multipart body.
May trigger completion, when the C<Content-Type> field is not defined.

=back

=head2 Internals


$obj-E<gt>B<addNoRealize>(FIELD)

=over 4

Add a field, like L<Mail::Message::Head::Complete::add()|"Access to the header"> 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.

=back

$obj-E<gt>B<addOrderedFields>(FIELDS)

=over 4

=back

$obj-E<gt>B<fileLocation>

=over 4

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.

=back

$obj-E<gt>B<load>

=over 4

Be sure that the header is loaded.  This returns the loaded header
object.

=back

$obj-E<gt>B<moveLocation>(DISTANCE)

=over 4

Move the registration of the header in the file.

=back

$obj-E<gt>B<read>(PARSER)

=over 4

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

=back

$obj-E<gt>B<setNoRealize>(FIELD)

=over 4

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.

=back

=head2 Error handling


$obj-E<gt>B<AUTOLOAD>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<defaultTrace>([LEVEL, [LEVEL])

Mail::Message::Head-E<gt>B<defaultTrace>([LEVEL, [LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<errors>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<log>([LEVEL [,STRINGS]])

Mail::Message::Head-E<gt>B<log>([LEVEL [,STRINGS]])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<logPriority>(LEVEL)

Mail::Message::Head-E<gt>B<logPriority>(LEVEL)

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<logSettings>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<notImplemented>

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<report>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<reportAll>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<trace>([LEVEL])

=over 4

See L<Mail::Reporter/"Error handling">

=back

$obj-E<gt>B<warnings>

=over 4

See L<Mail::Reporter/"Error handling">

=back

=head2 Cleanup


$obj-E<gt>B<DESTROY>

=over 4

See L<Mail::Reporter/"Cleanup">

=back

$obj-E<gt>B<inGlobalDestruction>

=over 4

See L<Mail::Reporter/"Cleanup">

=back



=head1 DIAGNOSTICS

I<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.






=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.


