machine: testing of getLocalIP

machine/coreos.go

@@ -119,27 +119,38 @@ func readLocalMachineID(root string) (string, error) {
 	return mID, nil
 }
 
-func getLocalIP() string {
+func getLocalIP() (got string) {
 	iface := getDefaultGatewayIface()
 	if iface == nil {
-		return ""
+		return
 	}
 
 	addrs, err := iface.Addrs()
 	if err != nil || len(addrs) == 0 {
-		return ""
+		return
 	}
 
 	for _, addr := range addrs {
 		// Attempt to parse the address in CIDR notation
 		// and assert that it is IPv4 and global unicast
 		ip, _, err := net.ParseCIDR(addr.String())
-		if err == nil && ip.To4() != nil && ip.IsGlobalUnicast() {
-			return ip.String()
+		if err != nil {
+			continue
 		}
+
+		if !usableAddress(ip) {
+			continue
+		}
+
+		got = ip.String()
+		break
 	}
 
-	return ""
+	return
+}
+
+func usableAddress(ip net.IP) bool {
+	return ip.To4() != nil && ip.IsGlobalUnicast()
 }
 
 func getDefaultGatewayIface() *net.Interface {

machine/coreos_test.go

@@ -2,6 +2,7 @@ package machine
 
 import (
 	"io/ioutil"
+	"net"
 	"os"
 	"path/filepath"
 	"testing"
@@ -49,3 +50,35 @@ func TestReadLocalMachineIDFound(t *testing.T) {
 		t.Fatalf("Received incorrect machID %q, expected 'pingpong'", machID)
 	}
 }
+
+func TestUsableAddress(t *testing.T) {
+	tests := []struct {
+		ip net.IP
+		ok bool
+	}{
+		// unicast IPv4 usable
+		{net.ParseIP("192.168.1.12"), true},
+
+		// unicast IPv6 unusable
+		{net.ParseIP("2001:DB8::3"), false},
+
+		// link-local IPv4/6 unusable
+		{net.ParseIP("127.0.0.12"), false},
+		{net.ParseIP("::1"), false},
+
+		// unspecified (all zeros) IPv46 unusable
+		{net.ParseIP("0.0.0.0"), false},
+		{net.ParseIP("::"), false},
+
+		// multicast IPv4/6 unusable
+		{net.ParseIP("239.255.255.250"), false},
+		{net.ParseIP("ffx2::4"), false},
+	}
+
+	for i, tt := range tests {
+		ok := usableAddress(tt.ip)
+		if tt.ok != ok {
+			t.Errorf("case %d: expected %v usable %t, got %t", i, tt.ip, tt.ok, ok)
+		}
+	}
+}