From 2cfb5ab1606d1b24b5b914c7776bceb156dd8da4 Mon Sep 17 00:00:00 2001
From: Mildred Ki'Lya <mildred-pub.git@mildred.fr>
Date: Wed, 4 Mar 2020 12:51:54 +0100
Subject: [PATCH] Implement IP 4 to 6 mapping on HostIP listen addresses

In some cases, the docker container can specify a HostIP listen address
to listen to. It might be desirable to allow converting containers
listening on IPv4 only addresses to IPv6 by using a network mapping.

The IPv4 address is mapped to IPv6 by matching it to an IPv4 CIDR
provided via a command-line flag. Multiple mapping is possible.
---
 cmd/docker-ipv6nat/main.go | 30 +++++++++++++++++++++++++++++-
 state.go                   | 15 ++++++++++++++-
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/cmd/docker-ipv6nat/main.go b/cmd/docker-ipv6nat/main.go
index 54040e6..c3a73f3 100644
--- a/cmd/docker-ipv6nat/main.go
+++ b/cmd/docker-ipv6nat/main.go
@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"strings"
+	"net"
 
 	"github.com/fsouza/go-dockerclient"
 	"github.com/robbertkl/docker-ipv6nat"
@@ -18,6 +20,7 @@ var (
 	userlandProxy bool
 	version       bool
 	debug         bool
+	mapIpv4       string
 )
 
 func usage() {
@@ -43,6 +46,7 @@ func initFlags() {
 	flag.BoolVar(&retry, "retry", false, "keep retrying to reconnect after a disconnect")
 	flag.BoolVar(&version, "version", false, "show version")
 	flag.BoolVar(&debug, "debug", false, "log ruleset changes to stdout")
+	flag.StringVar(&mapIpv4, "map-ipv4", "", "IPv4 listen address mapping (IPV4/CIDR=IPV4,...)")
 
 	flag.Usage = usage
 	flag.Parse()
@@ -66,6 +70,25 @@ func main() {
 	}
 }
 
+func parseIpMapping(mapIpv4 string) (map[*net.IPNet]net.IP, error) {
+	res := map[*net.IPNet]net.IP{}
+	for _, map46 := range strings.Split(mapIpv4, ",") {
+		s := strings.Split(map46, "=")
+		if len(s)==2 && s[0] != "" && s[1] != "" {
+			_, ip4, err := net.ParseCIDR(s[0])
+			if err != nil {
+				return nil, fmt.Errorf("Cannot parse %+v IPv4, %e", map46, err)
+			}
+			ip6 := net.ParseIP(s[1])
+			if ip6 == nil {
+				return nil, fmt.Errorf("Cannot parse %+v IPv6, %e", map46)
+			}
+			res[ip4] = ip6
+		}
+	}
+	return res, nil
+}
+
 func run() error {
 	if debug {
 		log.Println("docker-ipv6nat is running in debug mode")
@@ -76,7 +99,12 @@ func run() error {
 		return err
 	}
 
-	state, err := dockeripv6nat.NewState(debug)
+	ipMap, err := parseIpMapping(mapIpv4)
+	if err != nil {
+		return err
+	}
+
+	state, err := dockeripv6nat.NewState(debug, ipMap)
 	if err != nil {
 		return err
 	}
diff --git a/state.go b/state.go
index 5ef7287..112805e 100644
--- a/state.go
+++ b/state.go
@@ -13,6 +13,8 @@ type State struct {
 	manager    *Manager
 	networks   map[string]*managedNetwork
 	containers map[string]*managedContainer
+	mapIpv4    map[*net.IPNet]net.IP
+	debug      bool
 }
 
 // fc00::/7, Unique Local IPv6 Unicast Addresses, see RFC 4193
@@ -22,7 +24,7 @@ var ulaCIDR = net.IPNet{
 }
 
 // NewState constructs a new state
-func NewState(debug bool) (*State, error) {
+func NewState(debug bool, mapIpv4 map[*net.IPNet]net.IP) (*State, error) {
 	manager, err := NewManager(debug)
 	if err != nil {
 		return nil, err
@@ -32,6 +34,7 @@ func NewState(debug bool) (*State, error) {
 		manager:    manager,
 		networks:   make(map[string]*managedNetwork),
 		containers: make(map[string]*managedContainer),
+		mapIpv4:    mapIpv4,
 	}, nil
 }
 
@@ -236,6 +239,16 @@ func (s *State) parseContainer(container *docker.Container) *managedContainer {
 
 			if binding.HostIP != "" && binding.HostIP != "0.0.0.0" {
 				ip := net.ParseIP(binding.HostIP)
+				if ip != nil && ip.To4() != nil {
+					// Try map Ipv4 to IPv6
+					for ip4net, ip6 := range s.mapIpv4 {
+						if ip4net.Contains(ip) {
+							log.Printf("Converting listen IP %v to %v (matching %v)", ip, ip6, ip4net)
+							ip = ip6
+							break
+						}
+					}
+				}
 				if ip == nil || ip.To4() != nil {
 					// Skip bindings to IPv4.
 					continue