I already did simulate the POST-request into a file for debugging and forgot to tell you (yesterday I was very exhausted after 20 hours of coding ;-).

Instead of noticing this error with the missing "\r\n" I just noticed the different lengths:
Between the stated "Content-Length" and the real length of the content there were always some bytes discrepancy - the bigger the file, the bigger the difference in length.

So after I added the "\r\n" between header and body I used a static header with a manually calculated (correct) length. And it worked.

Then I got the idea, that the linebreaks in the script itself and/or the linebreaks in the file could be the problem.

So I converted all "\r\n" in the script into "\n" and printed everything to a file and the byte-discrepancies didn't change a bit.

Next I noticed that I missed to use "binmode" for my output file that I used for debugging.
Then I added "binmode" and SHAZZAM: The difference between the lengths still were some bytes, but for files with difference in size it always stayed a constant 4 bytes.


I'd still like to know if someone can figure out why there is this 4-byte-discrepancy.
But if noone knows/cares to share I can live with this dirty fix ;-)


At last, my working code:

#!/usr/bin/perl
use warnings;
use strict;
use Socket;

my $buffersize = 2 * 1024 * 1024;

my $host = "127.0.0.1";
my $path = "/debug.php";
my $url  = "http://".$host.$path;
my $local_file = "testfile.rar";
my $local_path = "F:\\skript\\";

my $user = "cardman";
my $pass = "yvan eht nioj";
my $serverid = 666;

my $upfile = shift || $local_path.$local_file;

system("cls");
print STDOUT "Starting upload to ".$url."\r\n\r\n";

$| = 1;

my ($iaddr, $paddr, $proto);
$iaddr = inet_aton($host);
$paddr = sockaddr_in(80, $iaddr);
$proto = getprotobyname('tcp');
unless(socket(SOCK, PF_INET, SOCK_STREAM, $proto)) { die "Couldn't ini
+t socket: $!"; }
unless(connect(SOCK, $paddr)) { die "Couldn't connect: $!\r\n"; }

my $boundary = "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz";

my @data = (
    "--".$boundary."",
    "Content-Disposition: form-data; name=\"username\"",
    "",
    "".$user."",
    "--".$boundary."",
    "Content-Disposition: form-data; name=\"password\"",
    "",
    "".$pass."",
    "--".$boundary."",
    "Content-Disposition: form-data; name=\"serverid\"",
    "",
    "".$serverid."",
    "--".$boundary."",
    "Content-Disposition: form-data; name=\"file\"; filename=\"".$loca
+l_file."\"",
    "Content-Type: application/octet-stream",
    "",
    "",
);

open (FILE,"< $upfile") or die "$!\n";
binmode FILE;

my $data = join("\r\n", @data);
my $length = 0;
$length += length($data);        # length of the data to be POST'ed
$length += -s FILE;                # filesize
$length += length($boundary);    # boundary is added once more at the 
+end of all the file-chunks
$length += 4;                    # adding 4 bytes (no idea as to why, 
+but it works -- tested with 4 rng-files: 5 byte, 2mb, 15mb and 100mb)

my @head = (
    "POST ".$path." HTTP/1.1",
    "Host: ".$host."",
    "Content-Length: $length",
    "Connection: close",
    "Content-Type: multipart/form-data; boundary=".$boundary."",
    "",
    "",
);
my $header = join("\r\n", @head).$data;

# FOR DEBUGGING
# open (FILE2,"< $upfile") or die "$!\n";    binmode FILE;
# open(LOG, ">".$local_path."headers.txt"); binmode LOG;
# print LOG $header;
# while(sysread(FILE2, my $buf, 8)) { print LOG $buf; }
# print LOG "\r\n--".$boundary."--";
# close LOG; close FILE2;

select SOCK;
$| = 1;
binmode SOCK;

print SOCK $header;

while(sysread(FILE, my $buf, $buffersize))
{
    if(length($buf) < $buffersize) {
        $buf = $buf."\r\n--".$boundary."--";
        syswrite SOCK, $buf, length($buf);
     } else {
        syswrite SOCK, $buf, $buffersize;
    }
 }
close FILE;

my @response = (<SOCK>);
shutdown SOCK, 1;

print STDOUT "Result:\n-------\n @response";
close SOCK;
[download]

Thanks to you both for helping me so quickly :-)
Kay