use strict;
use LWP::UserAgent;

my $url = 'http://www.example.com/';
my $filename = 'test.file';

open CONTENT, "<", $filename
  or die "Couldn't open $filename : $!";
binmode CONTENT;

my $callback = sub {
  my $content;
  my $size = read( CONTENT, $content, 51200 );
  $content = ""
    unless $size;
  $content;
};

my $ua = LWP::UserAgent->new();
$ua->post($url,$callback);