#!/usr/bin/ksh93

#
# list_active_local_tcp_ports1.ksh - list port numbers of local TCP connections
#
# Written by Roland Mainz <roland.mainz@nrubsig.org>
#

#     
# simple netstat -n parser
#    
function netstat_list_connections
{
	set -o nounset
	nameref data=$1

	compound out=( typeset stdout stderr ; integer res )

	out.stderr="${ { out.stdout="${ LC_ALL='POSIX' PATH='/usr/bin:/bin' netstat -a -n ; (( out.res=$? )) ; }" ; } 2>&1 ; }"
	if (( out.res != 0 )) ; then
		print -u2 -f $"%s: netstat returned %d exit code.\n" \
			"$0" out.res
		return 1
	fi
	if [[ "${out.stderr}" != '' ]] ; then
		#
		# Handle known Linux netstat warnings
		#
		if [[ "${out.stderr}" != $'warning, got bogus unix line.' ]] ; then
			print -u2 -f $"%s: netstat returned unknown error message %q.\n" \
				"$0" "${out.stderr}"
			return 1
		fi
	fi

	typeset -a data.connections
	typeset l
	typeset leftover
	integer dci=0 # data.connections array index

	while read l ; do 
		leftover="${l/~(Elrx)
		(?: # non-capturing group
			#
			# regex group for tcp,udp
			#
			(tcp|tcp6|udp|udp6|raw|raw6|sctp|sctp6)	# Proto
			[[:space:]]+
			([[:digit:]]+)			# Recv-Q
			[[:space:]]+
			([[:digit:]]+)			# Send-Q
			[[:space:]]+
			([^[:space:]]+)			# Local Address
			[[:space:]]+
			([^[:space:]]+)			# Foreign Address
			(?:
				|
				[[:space:]]+
				([^[:space:]]*?) 	# State (Optional)
			)
		|
			#
			# regex for unix
			#
			(unix)				# Proto
			[[:space:]]+
			([[:digit:]]+)			# RefCnt
			[[:space:]]+
			(\[.+?\])			# Flags
			[[:space:]]+
			([^[:space:]]+) 		# Type
			[[:space:]]+
			([^[:space:]]*?)		# State (optional)
			[[:space:]]+
			([[:digit:]]+)			# I-Node
			(?:
				|
				[[:space:]]+
				([^[:space:]]+)		# Path (optional)
			)
		)
			/X}"

		# If the regex above did not match then .sh.match
		# remains untouched, so we might see data from the
		# previous round.
		# So we check the "leftover" var whether it just
		# contains the dummy value of "X" to indicate a
		# successful regex match
		if [[ "$leftover" == 'X' ]] ; then
			#print -v .sh.match

			if [[ "${.sh.match[1]-}" != '' ]] ; then
				nameref dcn=data.connections[$dci]

				typeset dcn.proto="${.sh.match[1]}"
				typeset dcn.recv_q="${.sh.match[2]}"
				typeset dcn.send_q="${.sh.match[3]}"
				typeset dcn.local_address="${.sh.match[4]}"
				typeset dcn.foreign_address="${.sh.match[5]}"
				typeset dcn.state="${.sh.match[6]}"
				((dci++))
			elif [[ "${.sh.match[7]-}" != '' ]] ; then
				nameref dcn=data.connections[$dci]

				typeset dcn.proto="${.sh.match[7]}"
				typeset dcn.refcnt="${.sh.match[8]}"
				typeset dcn.flags="${.sh.match[9]}"
				typeset dcn.type="${.sh.match[10]}"
				[[ "${.sh.match[11]}" != '' ]] && typeset dcn.state="${.sh.match[11]}"
				typeset dcn.inode="${.sh.match[12]}"
				[[ "${.sh.match[13]}" != '' ]] && typeset dcn.path="${.sh.match[13]}"
				((dci++))
			fi
		else
			true
			#printf $"leftover=%q\n" "${leftover}"
		fi
	done <<<"${out.stdout}"

	return 0
}

function netstat_list_active_local_tcp_connections
{
	set -o nounset
	nameref ar=$1
	compound c
	integer port
	integer i

	netstat_list_connections c || return 1
	#print -v c
	
	[[ -v ar ]] || integer -a ar

	for i in "${!c.connections[@]}" ; do
		nameref n=c.connections[$i]
		
		# look for only for TCP connections which match
		# 127.0.*.* or IPv6 ::1 for localhost
		# 0.0.0.0 or IPv6 :: for all addresses (e.g. servers)
		if [[ "${n.proto}" == ~(El)tcp && \
			"${n.local_address}" == ~(Elr)((127\.0\..+|::1)|(::|0\.0\.0\.0|)):[[:digit:]]+ ]] ; then

			port="${n.local_address##*:}"
			#printf $"port = %d\n" port

			(( ar[port]=1 ))
		fi
	done

	return 0
}

function netstat_find_next_free_local_tcp_port
{
	set -o nounset
	compound c=( integer -a ar )
	nameref ret_free_port=$1
	integer start_port
	integer end_port
	integer i

	netstat_list_active_local_tcp_connections c.ar || return 1

	#print -v c

	(( start_port=$2 ))
	if (( $# > 2 )) ; then
		(( end_port=$3 ))
	else
		(( end_port=65535 ))
	fi

	for ((i=start_port ; i < end_port ; i++ )) ; do
		if [[ ! -v c.ar[i] ]] ; then
			(( ret_free_port=i ))
			return 0
		fi
	done
	
	return 1
}


function main
{
	if (( $# > 0 )) ; then
		integer port=-1

		print -u1 -f $"# next free TCP port:\n"
		netstat_find_next_free_local_tcp_port port "$@" || return 1
		print -f $"%d\n" port
	else
		set -o nounset
		compound c=( integer -a ar )

		print -u1 -f $"# list of open local TCP ports:\n"

		netstat_list_active_local_tcp_connections c.ar || return 1
		#print -v c

		(( ${#c.ar[@]} > 0 )) && printf $"%d\n" "${!c.ar[@]}"
	fi

	return 0
}

# main entry point
main "$@"
exit $?
# EOF.