=encoding utf8

=head1 NAME

Mail::Message::Construct::Build - building a Mail::Message from components

=head1 SYNOPSIS

 my $msg1 = Mail::Message->build
   ( From => 'me', data => "only two\nlines\n");

 my $msg2 = Mail::Message->buildFromBody($body);

 Mail::Message->build
   ( From     => 'me@myhost.com'
   , To       => 'you@yourhost.com'
   , Subject  => "Read our folder!"

   , data     => \@lines
   , file     => 'folder.pdf'
   )->send(via => 'postfix');

=head1 DESCRIPTION

Complex functionality on L<Mail::Message|Mail::Message> objects is implemented in
different files which are autoloaded.  This file implements the
building of messages from various simpler components.

=head1 METHODS

=head2 Constructing a message

=over 4

=item Mail::Message-E<gt>B<build>( [$message|$part|$body], $content )

Simplified message object builder.  In case a $message or message $part is
specified, a new message is created with the same body to start with, but
new headers.  A $body may be specified as well.  However, there are more
ways to add data simply.

The $content is a list of key-value pairs and header field objects.
The keys which start with a capital are used as header-lines.  Lower-cased
fields are used for other purposes as listed below.  Each field may be used
more than once.  Pairs where the value is C<undef> are ignored.

If more than one C<data>, C<file>, and C<attach> is specified,
a multi-parted message is created.  Some C<Content-*> fields are
treated separately: to enforce the content lines of the produced
message body B<after> it has been created.  For instance, to explicitly
state that you wish a C<multipart/alternative> in stead of the default
C<multipart/mixed>.  If you wish to specify the type per datum, you need
to start playing with L<Mail::Message::Body|Mail::Message::Body> objects yourself.

This C<build> method will use L<buildFromBody()|Mail::Message::Construct::Build/"Constructing a message"> when the body object has
been constructed.  Together, they produce your message.

 -Option--Default
  attach  undef
  data    undef
  file    undef
  files   [ ]
  head    undef

=over 2

=item attach => BODY|PART|MESSAGE|ARRAY

One attachment to the message.  Each attachment can be full $message, a
$part, or a $body.
Any $message will get encapsulated into a C<message/rfc822> body.
You can specify many items (may be of different types) at once.

 attach => $folder->message(3)->decoded  # body
 attach => $folder->message(3)           # message
 attach => [ $msg1, $msg2->part(6), $msg3->body ];

=item data => STRING|ARRAY-OF-LINES

The text for one part, specified as one STRING, or an ARRAY of lines.  Each
line, including the last, must be terminated by a newline.  This argument
is passed to L<Mail::Message::Body::new(data)|Mail::Message::Body/"Constructors"> to
construct one.

  data => [ "line 1\n", "line 2\n" ]     # array of lines
  data => <<'TEXT'                       # string
 line 1
 line 2
 TEXT

=item file => FILENAME|FILEHANDLE|IOHANDLE|ARRAY

Create a body where the data is read from the specified FILENAME,
FILEHANDLE, or object of type IO::Handle.  Also this body is used
to create a L<Mail::Message::Body|Mail::Message::Body>. [2.119] You may even pass more
than one file at once: 'file' and 'files' option are equivalent.

 my $in = IO::File->new('/etc/passwd', 'r');

 file  => 'picture.jpg'                   # filename
 file  => \*MYINPUTFILE                   # file handle
 file  => $in                             # any IO::Handle
 files => [ 'picture.jpg', \*MYINPUTFILE, $in ]

 open my $in, '<:raw', '/etc/passwd';    # alternative for IO::File

=item files => ARRAY-OF-FILE

Alias for option C<file>.

=item head => HEAD

Start with a prepared header, otherwise one is created.

=back

example: 

 my $msg = Mail::Message->build
  ( From    => 'me@home.nl'
  , To      => Mail::Address->new('your name', 'you@yourplace.aq')
  , Cc      => 'everyone@example.com'
  , Subject => "Let's talk",
  , $other_message->get('Bcc')

  , data   => [ "This is\n", "the first part of\n", "the message\n" ]
  , file   => 'myself.gif'
  , file   => 'you.jpg'
  , attach => $signature
  );

 my $msg = Mail::Message->build
  ( To     => 'you'
  , 'Content-Type' => 'text/html'
  , data   => "<html></html>"
  );

=item Mail::Message-E<gt>B<buildFromBody>($body, [$head], $headers)

Shape a message around a $body.  Bodies have information about their
content in them, which is used to construct a header for the message.
You may specify a $head object which is pre-initialized, or one is
created for you (also when $head is C<undef>).
Next to that, more $headers can be specified which are stored in that
header.

Header fields are added in order, and before the header lines as
defined by the body are taken.  They may be supplied as key-value
pairs or L<Mail::Message::Field|Mail::Message::Field> objects.  In case of a key-value
pair, the field's name is to be used as key and the value is a
string, address (L<Mail::Address|Mail::Address> object), or array of addresses.

A C<Date>, C<Message-Id>, and C<MIME-Version> field are added unless
supplied.

example: 

 my $type = Mail::Message::Field->new('Content-Type', 'text/html'
   , 'charset="us-ascii"');

 my @to   = ( Mail::Address->new('Your name', 'you@example.com')
            , 'world@example.info'
            );

 my $msg  = Mail::Message->buildFromBody
   ( $body
   , From => 'me@example.nl'
   , To   => \@to
   , $type
   );

=back

=head1 DETAILS

=head2 Building a message

=head3 Rapid building

Most messages you need to construct are relatively simple.  Therefore,
this module provides a method to prepare a message with only one method
call: L<build()|Mail::Message::Construct::Build/"Constructing a message">.

=head3 Compared to MIME::Entity::build()

The C<build> method in MailBox is modelled after the C<build> method
as provided by MIMETools, but with a few simplifications:

=over 4

=item When a keys starts with a capital, than it is always a header field

=item When a keys is lower-cased, it is always something else

=item You use the real field-names, not abbreviations

=item All field names are accepted

=item You may specify field objects between key-value pairs

=item A lot of facts are auto-detected, like content-type and encoding

=item You can create a multipart at once

=back

Hum, reading the list above... what is equivalent?  L<MIME::Entity> is
not that simple after all!  Let's look at an example from MIME::Entity's
manual page:

 ### Create the top-level, and set up the mail headers:
 $top = MIME::Entity->build(Type     => "multipart/mixed",
                            From     => 'me@myhost.com',
                            To       => 'you@yourhost.com',
                            Subject  => "Hello, nurse!");
                                                                                
 ### Attachment #1: a simple text document:
 $top->attach(Path=>"./testin/short.txt");
                                                                                
 ### Attachment #2: a GIF file:
 $top->attach(Path        => "./docs/mime-sm.gif",
              Type        => "image/gif",
              Encoding    => "base64");
                                                                                
 ### Attachment #3: text we'll create with text we have on-hand:
 $top->attach(Data => $contents);
                                                                                
The MailBox equivalent could be

 my $msg = Mail::Message->build
   ( From     => 'me@myhost.com'
   , To       => 'you@yourhost.com'
   , Subject  => "Hello, nurse!"

   , file     => "./testin/short.txt"
   , file     => "./docs/mime-sm.gif"
   , data     => $contents
   );

One of the simplifications is that L<MIME::Types|MIME::Types> is used to lookup
the right content type and optimal transfer encoding.  Good values
for content-disposition and such are added as well.

=head3 build, starting with nothing

See L<build()|Mail::Message::Construct::Build/"Constructing a message">.

=head3 buildFromBody, body becomes message

See L<buildFromBody()|Mail::Message::Construct::Build/"Constructing a message">.

=head3 The Content-* fields

The various C<Content-*> fields are not as harmless as they look.  For
instance, the "Content-Type" field will have an effect on the default
transfer encoding.

When a message is built this way:

 my $msg = Mail::Message->build
  ( 'Content-Type' => 'video/mpeg3'
  , 'Content-Transfer-Encoding' => 'base64'
  , 'Content-Disposition' => 'attachment'
  , file => '/etc/passwd'
  );

then first a C<text/plain> body is constructed (MIME::Types does not
find an extension on the filename so defaults to C<text/plain>), with
no encoding.  Only when that body is ready, the new type and requested
encodings are set.  The content of the body will get base64 encoded,
because it is requested that way.

What basically happens is this:

 my $head = ...other header lines...;
 my $body = Mail::Message::Body::Lines->new(file => '/etc/passwd');
 $body->type('video/mpeg3');
 $body->transferEncoding('base64');
 $body->diposition('attachment');
 my $msg  = Mail::Message->buildFromBody($body, $head);
 
A safer way to construct the message is:

 my $body = Mail::Message::Body::Lines->new
  ( file              => '/etc/passwd'
  , mime_type         => 'video/mpeg3'
  , transfer_encoding => 'base64'
  , disposition       => 'attachment'
  );

 my $msg  = Mail::Message->buildFromBody
  ( $body
  , ...other header lines...
  );

In the latter program, you will immediately start with a body of
the right type.

=head1 DIAGNOSTICS

=over 4

=item Error: Only build() Mail::Message's; they are not in a folder yet

You may wish to construct a message to be stored in a some kind
of folder, but you need to do that in two steps.  First, create a
normal L<Mail::Message|Mail::Message>, and then add it to the folder.  During this
L<Mail::Box::addMessage()|Mail::Box/"The folder"> process, the message will get L<coerce()|Mail::Message/"Internals">-d
into the right message type, adding storage information and the like.

=back

=head1 SEE ALSO

This module is part of Mail-Message distribution version 3.004,
built on December 21, 2017.

Do not forget to read
L<Mail::Box-Overview>,
L<Mail::Box-Cookbook>, and
L<Mail::Box-Index>.
Examples are included in the Mail-Box distribution, directories 'examples'
and 'scripts'.

Browseable manuals, papers, and other released material van be found
at  Website: F<http://perl.overmeer.net/mailbox/>

The central modules (in separate distributions) in the MailBox suite are:
L<Mail::Message>,
L<Mail::Box>,
L<Mail::Box::IMAP4>,
L<Mail::Box::POP3>,
L<Mail::Box::Parser::C>,
L<Mail::Box::Dbx> (unpublished),
L<Mail::Transport>,
L<Object::Realize::Later>, and
L<User::Identity>.

Please post questions or ideas to the author F<markov@cpan.org>.

=head1 LICENSE

Copyrights 2001-2017 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 F<http://dev.perl.org/licenses/>

