Here at work we have an old mainframe running an xmodem assembler routine. The mainframe is connected to a modem pool by means of a router. We can access the xmodem mainframe routine by means of the router's ip address.
The following snippets can be used to receive and send a file from or to the mainframe.
# start quick and EXTREMELY dirty xmodem transfert
sub xmodemrecv
{
print $sock "\x15"; #NAK
A000: while(1) {
SOH: while(1) {
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; } #SOH
last SOH if ( $buf eq "\x01" ) || ( $buf eq "\x04" )
}
# leave if last byte received is an EOT
last A000 if ($buf eq "\x04");
# last byte received was SOH
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
$seq = unpack("c",$buf);
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
$cseq = unpack("c",$buf);
$mseq = - ($seq & 255) -1; # just for fun we calculate the cmpl se
+q as well
if (sysread($sock,$buf,128) <= 0) { die "*** died$! ***\n"; }
$sum = 0;
for ($i = 0; $i < 128; $i++) {
$sum += unpack("c",substr($buf,$i,1));
}
$sum = pack("c",($sum & 255));
print "$buf";
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
$crc = $buf;
if ($crc eq $sum) {
# packet ok
print $sock "\x06"; #ACK
} else {
# packet nok - crc differs
print $sock "\x15"; #NAK
}
}
print $sock "\x06"; #ACK
}
# start quick and EXTREMELY dirty xmodem transfert
sub xmodemsend
{
# reading the file to be send
open (BET ,"filename") || die "*** coudn't open filename ***\n";
$tosend = <BET>;
close BET || die "*** couldn't close filename ***\n";
# wait for #NAK
WNAK: while(1) {
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
if ($buf eq "\x18") { die "*** CAN received from bs2000 ***\n"; }
last WNAK if ( $buf eq "\x15" );
print "$buf"; # print characters bcs after A020 comes TRASEC OK te
+xt
}
# start of transfert
$tel = 1;
$ptr = 0;
A000: while(1) {
$ctel = pack("c",($tel & 255));
$mtel = pack("c",- ($tel & 255));
$sum = 0;
$buf = "";
for ($i = 0; $i < 128; $i++) {
$byte = substr($tosend,$i+$ptr,1);
$buf = "$buf$byte";
$sum += unpack("c",$byte);
}
$sum = pack("c",($sum & 255)); # calculate checksum
syswrite($sock,"\x01$ctel$mtel$buf$sum",132); # send complete bloc
+k
print "$buf";
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
if ($buf ne "\x06" && $buf ne "\x15" && $buf ne "\x18") {
die "*** no ACK, NAK nor CAN recevied after blocktransfert ***\n
+";
}
if ($buf eq "\x18") { #CAN
return;
}
if ($buf eq "\x06") { #ACK
# packet ok
$tel++;
$ptr += 128;
}
last A000 if $ptr eq length($tosend);
if ($ptr > length($tosend)) { die "*** cannot happen :) ***\n"; }
if ($buf eq "\x15") { #NAK
# packet nok - crc differs
}
}
print $sock "\x04"; # EOT
if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
if ($buf ne "\x06") { die "*** no ACK received after xmodem send ***
+\n"; }
}
