daemon: automatically set network EnableIPv6 if needed

PR 4f47013feb added a validation step to `NetworkCreate` to ensure
no IPv6 subnet could be set on a network if its `EnableIPv6` parameter
is false.

Before that, the daemon was accepting such request but was doing nothing
with the IPv6 subnet.

This validation step is now deleted, and we automatically set
`EnableIPv6` if an IPv6 subnet was specified.

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

api/types/network/ipam.go

@@ -30,7 +30,28 @@ const (
 	ip6 ipFamily = "IPv6"
 )
 
-func ValidateIPAM(ipam *IPAM, enableIPv6 bool) error {
+// HasIPv6Subnets checks whether there's any IPv6 subnets in the ipam parameter. It ignores any invalid Subnet and nil
+// ipam.
+func HasIPv6Subnets(ipam *IPAM) bool {
+	if ipam == nil {
+		return false
+	}
+
+	for _, cfg := range ipam.Config {
+		subnet, err := netip.ParsePrefix(cfg.Subnet)
+		if err != nil {
+			continue
+		}
+
+		if subnet.Addr().Is6() {
+			return true
+		}
+	}
+
+	return false
+}
+
+func ValidateIPAM(ipam *IPAM) error {
 	if ipam == nil {
 		return nil
 	}
@@ -51,10 +72,6 @@ func ValidateIPAM(ipam *IPAM, enableIPv6 bool) error {
 			errs = append(errs, fmt.Errorf("invalid subnet %s: it should be %s", subnet, subnet.Masked()))
 		}
 
-		if !enableIPv6 && subnetFamily == ip6 {
-			errs = append(errs, fmt.Errorf("invalid subnet %s: IPv6 has not been enabled for this network", subnet))
-		}
-
 		if ipRangeErrs := validateIPRange(cfg.IPRange, subnet, subnetFamily); len(ipRangeErrs) > 0 {
 			errs = append(errs, ipRangeErrs...)
 		}

api/types/network/ipam_test.go

@@ -30,12 +30,6 @@ func TestNetworkWithInvalidIPAM(t *testing.T) {
 				"invalid auxiliary address DefaultGatewayIPv4: parent subnet is an IPv4 block",
 			},
 		},
-		{
-			name:           "IPv6 subnet is discarded when IPv6 is disabled",
-			ipam:           IPAM{Config: []IPAMConfig{{Subnet: "2001:db8::/32"}}},
-			ipv6:           false,
-			expectedErrors: []string{"invalid subnet 2001:db8::/32: IPv6 has not been enabled for this network"},
-		},
 		{
 			name: "Invalid data - Subnet",
 			ipam: IPAM{Config: []IPAMConfig{{Subnet: "foobar"}}},
@@ -128,7 +122,7 @@ func TestNetworkWithInvalidIPAM(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			errs := ValidateIPAM(&tc.ipam, tc.ipv6)
+			errs := ValidateIPAM(&tc.ipam)
 			if tc.expectedErrors == nil {
 				assert.NilError(t, errs)
 				return

daemon/network.go

@@ -303,6 +303,10 @@ func (daemon *Daemon) createNetwork(cfg *config.Config, create types.NetworkCrea
 		return nil, errdefs.Forbidden(errors.New(`This node is not a swarm manager. Use "docker swarm init" or "docker swarm join" to connect this node to swarm and try again.`))
 	}
 
+	if network.HasIPv6Subnets(create.IPAM) {
+		create.EnableIPv6 = true
+	}
+
 	var warning string
 	nw, err := daemon.GetNetworkByName(create.Name)
 	if err != nil {
@@ -347,9 +351,10 @@ func (daemon *Daemon) createNetwork(cfg *config.Config, create types.NetworkCrea
 		nwOptions = append(nwOptions, libnetwork.NetworkOptionConfigOnly())
 	}
 
-	if err := network.ValidateIPAM(create.IPAM, create.EnableIPv6); err != nil {
+	if err := network.ValidateIPAM(create.IPAM); err != nil {
 		return nil, errdefs.InvalidParameter(err)
 	}
+
 	if create.IPAM != nil {
 		ipam := create.IPAM
 		v4Conf, v6Conf, err := getIpamConfig(ipam.Config)