Simplify hasUserDefinedIPAddress, and centralize validation

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/container_operations.go

@@ -592,9 +592,9 @@ func (daemon *Daemon) getNetworkSandbox(container *container.Container) libnetwo
 	return sb
 }
 
-// hasUserDefinedIPAddress returns whether the passed endpoint configuration contains IP address configuration
-func hasUserDefinedIPAddress(epConfig *networktypes.EndpointSettings) bool {
-	return epConfig != nil && epConfig.IPAMConfig != nil && (len(epConfig.IPAMConfig.IPv4Address) > 0 || len(epConfig.IPAMConfig.IPv6Address) > 0)
+// hasUserDefinedIPAddress returns whether the passed IPAM configuration contains IP address configuration
+func hasUserDefinedIPAddress(ipamConfig *networktypes.EndpointIPAMConfig) bool {
+	return ipamConfig != nil && (len(ipamConfig.IPv4Address) > 0 || len(ipamConfig.IPv6Address) > 0)
 }
 
 // User specified ip address is acceptable only for networks with user specified subnets.
@@ -602,9 +602,18 @@ func validateNetworkingConfig(n libnetwork.Network, epConfig *networktypes.Endpo
 	if n == nil || epConfig == nil {
 		return nil
 	}
-	if !hasUserDefinedIPAddress(epConfig) {
+	if !containertypes.NetworkMode(n.Name()).IsUserDefined() {
+		if hasUserDefinedIPAddress(epConfig.IPAMConfig) && !enableIPOnPredefinedNetwork() {
+			return runconfig.ErrUnsupportedNetworkAndIP
+		}
+		if len(epConfig.Aliases) > 0 && !serviceDiscoveryOnDefaultNetwork() {
+			return runconfig.ErrUnsupportedNetworkAndAlias
+		}
+	}
+	if !hasUserDefinedIPAddress(epConfig.IPAMConfig) {
 		return nil
 	}
+
 	_, _, nwIPv4Configs, nwIPv6Configs := n.Info().IpamConfig()
 	for _, s := range []struct {
 		ipConfigured  bool
@@ -653,14 +662,7 @@ func cleanOperationalData(es *network.EndpointSettings) {
 
 func (daemon *Daemon) updateNetworkConfig(container *container.Container, n libnetwork.Network, endpointConfig *networktypes.EndpointSettings, updateSettings bool) error {
 
-	if !containertypes.NetworkMode(n.Name()).IsUserDefined() {
-		if hasUserDefinedIPAddress(endpointConfig) && !enableIPOnPredefinedNetwork() {
-			return runconfig.ErrUnsupportedNetworkAndIP
-		}
-		if endpointConfig != nil && len(endpointConfig.Aliases) > 0 && !serviceDiscoveryOnDefaultNetwork() {
-			return runconfig.ErrUnsupportedNetworkAndAlias
-		}
-	} else {
+	if containertypes.NetworkMode(n.Name()).IsUserDefined() {
 		addShortID := true
 		shortID := stringid.TruncateID(container.ID)
 		for _, alias := range endpointConfig.Aliases {