bash-com/bind-input

#!/bin/bash


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

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

# (3) Check @PORT range #
MIN_PORT=1024;
MAX_PORT=49151;
test "$2" -gt "$MAX_PORT" -o "$2" -lt "$MIN_PORT" && echo "error: <port> must be between $MIN_PORT and $MAX_PORT" && exit 1;

# (4) Set argument explicit names #
IN_ID="$1";
IN_PT="$2";

# (5) Manage optional 'silent' argument #
DEBUG="";
test $# -ge 3 -a "$3" == "debug" && DEBUG="xx";




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

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


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

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

	exit 1;
}



# (3) Launch INPUT server
#--------------------------------------------------------#
(

	[[ $DEBUG ]] && echo " > binding port $IN_PT to $BUFFER";
	trap "kill -9 $NC_PID 2>/dev/null; on_exit;" HUP INT KILL TERM;

	infail=0;

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

		# (3) Check if port already in use
		ss -tl4 "( sport = :$IN_PT )" | grep "$IN_PT" >/dev/null;
		PORT_TAKEN=$?;

		# (4) Manage taken port #
		if [ "$PORT_TAKEN" -ne "1" ]; then
			infail="`expr $infail + 1`";

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

		# (5) Bind input
		infail="0";
		nc -lp $IN_PT >> $BUFFER 2>/dev/null&
		NC_PID=$!;
		wait $NC_PID;

	done;

)&
LOOP_PID=$!;

trap "on_exit;" HUP INT KILL TERM;

echo "$LOOP_PID";