#!/bin/sh

export PATH="$PATH:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

chain_exists() {
    [ $# -lt 1 -o $# -gt 2 ] && {
        echo "Usage: chain_exists <chain_name> [table]" >&2
        return 1
    }
    local chain_name="$1" ; shift
    [ $# -eq 1 ] && local table="--table $1"
    iptables $table -n --list "$chain_name" >/dev/null 2>&1
}

add_to_forward() {
        local docker_int=$1

	if [ `iptables -nvL FORWARD | grep ${docker_int} | wc -l` -eq 0 ]; then
		iptables -A FORWARD -o ${docker_int} -j DOCKER
		iptables -A FORWARD -o ${docker_int} -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
		iptables -A FORWARD -i ${docker_int} ! -o ${docker_int} -j ACCEPT
		iptables -A FORWARD -i ${docker_int} -o ${docker_int} -j ACCEPT
	fi
}

add_to_nat() {
	local docker_int=$1
	local subnet=$2

	iptables -t nat -A POSTROUTING -s ${subnet} ! -o ${docker_int} -j MASQUERADE
	iptables -t nat -A DOCKER -i ${docker_int} -j RETURN
}

add_to_docker_isolation() {
	local int_in=$1
	local int_out=$2

	iptables -A DOCKER-ISOLATION -i ${int_in} -o ${int_out} -j DROP
}

DOCKER_INT="docker0"
DOCKER_NETWORK="172.17.0.0/16"

iptables-save | grep -v -- '-j DOCKER' | iptables-restore
chain_exists DOCKER && iptables -X DOCKER
chain_exists DOCKER nat && iptables -t nat -X DOCKER

iptables -N DOCKER
iptables -N DOCKER-ISOLATION

iptables -t nat -N DOCKER

iptables -A FORWARD -j DOCKER-ISOLATION
add_to_forward ${DOCKER_INT}

iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A POSTROUTING -s ${DOCKER_NETWORK} ! -o ${DOCKER_INT} -j MASQUERADE

bridges=`docker network ls -q --filter='Driver=bridge'`

for bridge in $bridges; do
	DOCKER_NET_INT="br-$bridge"
	subnet=`docker network inspect -f '{{(index .IPAM.Config 0).Subnet}}' $bridge`

	add_to_nat ${DOCKER_NET_INT} ${subnet}
	add_to_forward ${DOCKER_NET_INT}

	for other_bridge in $bridges; do
		if [ $other_bridge != $bridge ]; then
			add_to_docker_isolation ${DOCKER_NET_INT} br-$other_bridge
                fi
        done
done

containers=`docker ps -q`

if [ `echo ${containers} | wc -c` -gt "1" ]; then
        for container in ${containers}; do
		netmode=`docker inspect -f "{{.HostConfig.NetworkMode}}" ${container}`

		if [ $netmode == "default" ]; then
			DOCKER_NET_INT=${DOCKER_INT}
			ipaddr=`docker inspect -f "{{.NetworkSettings.IPAddress}}" ${container}`
		else
			DOCKER_NET_INT=br-$(docker inspect -f "{{.NetworkSettings.Networks.${netmode}.NetworkID}}" ${container} | cut -c -12)
			ipaddr=`docker inspect -f "{{.NetworkSettings.Networks.${netmode}.IPAddress}}" ${container}`
		fi

                rules=`docker port ${container} | sed 's/ //g'`

                if [ `echo ${rules} | wc -c` -gt "1" ]; then
                        for rule in ${rules}; do
                                src=`echo ${rule} | awk -F'->' '{ print $2 }'`
                                dst=`echo ${rule} | awk -F'->' '{ print $1 }'`

                                src_ip=`echo ${src} | awk -F':' '{ print $1 }'`
                                src_port=`echo ${src} | awk -F':' '{ print $2 }'`

                                dst_port=`echo ${dst} | awk -F'/' '{ print $1 }'`
                                dst_proto=`echo ${dst} | awk -F'/' '{ print $2 }'`

                                iptables -A DOCKER -d ${ipaddr}/32 ! -i ${DOCKER_NET_INT} -o ${DOCKER_NET_INT} -p ${dst_proto} -m ${dst_proto} --dport ${dst_port} -j ACCEPT

                                iptables -t nat -A POSTROUTING -s ${ipaddr}/32 -d ${ipaddr}/32 -p ${dst_proto} -m ${dst_proto} --dport ${dst_port} -j MASQUERADE

				iptables_opt_src=""
				if [ ${src_ip} != "0.0.0.0" ]; then
					iptables_opt_src="-d ${src_ip}/32 "
				fi
				iptables -t nat -A DOCKER ${iptables_opt_src}! -i ${DOCKER_NET_INT} -p ${dst_proto} -m ${dst_proto} --dport ${src_port} -j DNAT --to-destination ${ipaddr}:${dst_port}
                        done
                fi
        done
fi

iptables -A DOCKER-ISOLATION -j RETURN
iptables -t nat -I DOCKER -i ${DOCKER_INT} -j RETURN