bash-com/bind-output

#!/bin/bash


# (1) Init.
#--------------------------------------------------------#
# (1) Get current absolute dir
ROOT=$(dirname `realpath $0`);

# (2) Check argc
test $# -lt 3 && echo -e "error: too fewarguments\n\n\e[1mUSAGE\e[0m\n\tbind-output <id> <ip> <port>\n\n\e[1mARGUMENTS\e[0m\n\t<id>\tThe identifier of the output (buffer name)\n\t<ip>\tThe ip or host of the target\n\t<port>\tThe port to connect to\n" && exit 1;

# (3) Check @PORT range #
MIN_PORT=1024;
MAX_PORT=49151;
test "$3" -gt "$MAX_PORT" -o "$3" -lt "$MIN_PORT" && echo "error: <port> must be between $MIN_PORT and $MAX_PORT" && exit 1;

# (4) Set argument explicit names #
OUT_ID="$1";
OUT_IP="$2";
OUT_PT="$3";

# (5) Manage optional 'silent' argument #
DEBUG="";
test $# -ge 4 -a "$4" == "debug" && DEBUG="xx";



# (2) Prepare buffer
#--------------------------------------------------------#
# (1) Create buffer path
BUFFER="/tmp/outbuf_$OUT_ID";

# (2) Create/Flush buffer
# test -f $BUFFER && rm $BUFFER;
echo -n "" > $BUFFER;

# (3) Remove buffer + kill loop #
on_exit(){
	[[ $DEBUG ]] && echo " < closing binding from $BUFFER to $OUT_IP:$OUT_PT";
	rm $BUFFER 2>/dev/null && ( [[ $DEBUG ]] && echo " < $BUFFER deleted" );

	kill -INT $LOOP_PID 2>/dev/null;

	exit 1;
}



# (3) Launch OUTPUT server
#--------------------------------------------------------#
(
	[[ $DEBUG ]] && echo " > binding $BUFFER to $OUT_IP:$OUT_PT";
	trap "kill -9 $NC_PID 2>/dev/null; on_exit;" HUP INT KILL TERM;

	outfail=0;

	# (1) kill script after 10 failures
	while [ $outfail -lt 10 ]; do

		# (3) Check if port open
		nc -z $OUT_IP $OUT_PT >/dev/null 2>&1;
		PORT_CLOSED=$?;

		# (4) Manage taken port #
		if [ "$PORT_CLOSED" -eq "1" ]; then
			outfail="`expr $outfail + 1`";

			test "$outfail" -gt "1" && sleep .5;
			continue;
		fi;

		# (5) Bind output
		outfail="0";
		tail -f $BUFFER | nc $OUT_IP $OUT_PT 2> /dev/null &
		NC_PID=$!;
		wait $NC_PID;

	done;

)&
LOOP_PID=$!;



trap "on_exit;" HUP INT KILL TERM;

echo -n "$LOOP_PID";