chr(1) + message type + data

##</code><code>##

<set up bits including point to database and other stuff>
my $poll = 0;
my $messages = 0;

# make the socket
my $socket = IO::Socket::INET->new(
        LocalHost => '<hostname>',
        LocalPort => 1066,
        Proto => 'tcp',
        Listen => 5,
        Reuse => 1,
) or die "Socket could not be created : $!";

# accept connections
while (my $new_sock = $socket->accept()) {
        while (1) {
                say "Waiting!";
                my $buf="";
                # loop until start of message control (chr(1))
                while (read($new_sock,$buf,1)) { last if $buf eq chr(1);}
                read($new_sock,$buf,1);
                if ($buf eq "0") {
                        # handle the POLL message
                        # byte 1 = ASCII start of header (1)
                        # byte 2 = '0' - poll message ID
                        # byte 3 = number of messages since last poll - 4 bytes
                        # following don't seem to be sent.
                        # byte 7 = ASCII CR (13)
                        # byte 8 = ASCII LF (10)
                        # already have initial bytes now get payload
                        read($new_sock,$poll,4);
                        say "POLL : $poll";
                        SendPollReply($new_sock);
                        SendSNMP("0","0","--",undef,undef);
                } else {
                        # Other messages look like they are Cr/LF terminated
                        $buf .= <$new_sock>;
                        $messages++;
                        say "Buffer : $buf  Poll : $poll   Messages : $messages";
                        # only send traps for message group "A" or "C"
                        if ($buf =~ /([AC])(.{8})((\+\+|--))(\d{8})(.{10})/msx) {
                                my $message_group = $1;
                                my $station_code = $2;
                                my $change_type = $3;
                                my $date_time = $5;
                                my $point_name = $6;
                                SendSNMP($message_group,$station_code,$change_type,$date_time,$point_name);
                        }
                }
        }

}

close($socket);

sub SendPollReply {
        my $new_sock = shift;
        # send the poll reply
        # byte 1 = ASCII start of header chr(1)
        # byte 2 = '0' - response message ID
        # byte 3 = number of messages since last poll - 4 bytes
        # byte 7 = Error status '0' if OK
        # byte 8 = ASCII CR (13)
        # byte 9 = ASCII LF (10)
        SendMessage( $new_sock,"0".sprintf("%04d",$messages)."0");
        $messages=0;
}

# wrap message back to poller in required start/end characters
sub SendMessage {
        my ($new_sock,$message) = @_;
        $message = chr(1).$message.chr(13).chr(10); 
        say "REPLY : $message";
        print $new_sock $message;
}