The POST method also supports the "multipart/form-data" content used
for *Form-based File Upload* as specified in RFC 1867. You trigger
this content format by specifying a content type of 'form-data' as
one of the request headers. If one of the values in the $form_ref is
an array reference, then it is treated as a file part specification
with the following interpretation:

  [ $file, $filename, Header => Value... ]
  [ undef, $filename, Header => Value,..., Content => $content ]

The first value in the array ($file) is the name of a file to open.
This file will be read and its content placed in the request. The
routine will croak if the file can't be opened. Use an "undef" as
$file value if you want to specify the content directly with a
"Content" header. The $filename is the filename to report in the
request. If this value is undefined, then the basename of the $file
will be used. You can specify an empty string as $filename if you
want to suppress sending the filename when you provide a $file
value.

If a $file is provided by no "Content-Type" header, then
"Content-Type" and "Content-Encoding" will be filled in
automatically with the values returned by
LWP::MediaTypes::guess_media_type()

Sending my ~/.profile to the survey used as example above can be
achieved by this:

  POST 'http://www.perl.org/survey.cgi',
       Content_Type => 'form-data',
       Content      => [ name  => 'Gisle Aas',
                         email => 'gisle@aas.no',
                         gender => 'M',
                         born   => '1964',
                         init   => ["$ENV{HOME}/.profile"],
                       ]

This will create a HTTP::Request object that almost looks this (the
boundary and the content of your ~/.profile is likely to be
different):

  POST http://www.perl.org/survey.cgi
  Content-Length: 388
  Content-Type: multipart/form-data; boundary="6G+f"

  --6G+f
  Content-Disposition: form-data; name="name"

  Gisle Aas
  --6G+f
  Content-Disposition: form-data; name="email"

  gisle@aas.no
  --6G+f
  Content-Disposition: form-data; name="gender"

  M
  --6G+f
  Content-Disposition: form-data; name="born"

  1964
  --6G+f
  Content-Disposition: form-data; name="init"; filename=".profile"
  Content-Type: text/plain

  PATH=/local/perl/bin:$PATH
  export PATH

  --6G+f--

If you set the $DYNAMIC_FILE_UPLOAD variable (exportable) to some
TRUE value, then you get back a request object with a subroutine
closure as the content attribute. This subroutine will read the
content of any files on demand and return it in suitable chunks.
This allow you to upload arbitrary big files without using lots of
memory. You can even upload infinite files like /dev/audio if you
wish; however, if the file is not a plain file, there will be no
Content-Length header defined for the request. Not all servers (or
server applications) like this. Also, if the file(s) change in size
between the time the Content-Length is calculated and the time that
the last chunk is delivered, the subroutine will "Croak".
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