#!/bin/ksh
#This shellscript is tcp_receiver.
#Split the standard input into separate files for each port number.
#The names of the files are /tmp/$$.$port
#Then feed each file to the correct program in the directory given as a
#command line argument.
#Sample use: tcp_receiver 0_receiverhost

if [[ $# -ne 1 ]]
then
	echo $0: needs one directory name as a command line argument 1>&2
	exit 1
fi

cat > /tmp/$$

while [[ -s /tmp/$$ ]]
do
	#Read the three-byte TCP header.
	length=`chopoff 1 /tmp/$$`
	port=`chopoff 1 /tmp/$$`
	sequence_number=`chopoff 1 /tmp/$$`

	#Demultiplex: write the TCP segment to the file for that port number.
	echo $length'\c' >> /tmp/$$.$port
	echo $port'\c' >> /tmp/$$.$port
	echo $sequence_number'\c' >> /tmp/$$.$port
	chopoff $((length - 3)) /tmp/$$ | tr '\012' X >> /tmp/$$.$port
	echo >> /tmp/$$.$port
done

rm /tmp/$$

for prog in $1/*
do
	port=`echo ${prog##*/} | sed 's/\(.\).*/\1/'`

	if [[ -s /tmp/$$.$port ]]
	then
		sort +0.1n -0.2 /tmp/$$.$port |
		tr -d '\012' < /tmp/$$.$port |
		tr X '\012' > /tmp/$$.$port.sorted
		rm /tmp/$$.$port

		while [[ -s /tmp/$$.$port.sorted ]]
		do
			length=`chopoff 1 /tmp/$$.$port.sorted`
			chopoff 1 /tmp/$$.$port.sorted > /dev/null  #Discard prort number.
			chopoff 1 /tmp/$$.$port.sorted > /dev/null  #Discard sequence number.
			chopoff $((length - 3)) /tmp/$$.$port.sorted | $prog
		done

		rm /tmp/$$.$port.sorted
	fi
done

exit 0