Fix preferred ip allocation in ipam

- also provided a new utility to compute the
  host part ip address which is resilient to
  input passed in different representations.

Signed-off-by: Alessandro Boch <aboch@docker.com>

types/types.go

@@ -197,6 +197,59 @@ func CompareIPNet(a, b *net.IPNet) bool {
 	return a.IP.Equal(b.IP) && bytes.Equal(a.Mask, b.Mask)
 }
 
+// GetMinimalIP returns the address in its shortest form
+func GetMinimalIP(ip net.IP) net.IP {
+	if ip != nil && ip.To4() != nil {
+		return ip.To4()
+	}
+	return ip
+}
+
+// GetMinimalIPNet returns a copy of the passed IP Network with congruent ip and mask notation
+func GetMinimalIPNet(nw *net.IPNet) *net.IPNet {
+	if nw == nil {
+		return nil
+	}
+	if len(nw.IP) == 16 && nw.IP.To4() != nil {
+		m := nw.Mask
+		if len(m) == 16 {
+			m = m[12:16]
+		}
+		return &net.IPNet{IP: nw.IP.To4(), Mask: m}
+	}
+	return nw
+}
+
+var v4inV6MaskPrefix = []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
+
+// GetHostPartIP returns the host portion of the ip address identified by the mask.
+// IP address representation is not modified. If address and mask are not compatible
+// an error is returned.
+func GetHostPartIP(ip net.IP, mask net.IPMask) (net.IP, error) {
+	// Find the effective starting of address and mask
+	is := 0
+	ms := 0
+	if len(ip) == net.IPv6len && ip.To4() != nil {
+		is = 12
+	}
+	if len(ip[is:]) == net.IPv4len && len(mask) == net.IPv6len && bytes.Equal(mask[:12], v4inV6MaskPrefix) {
+		ms = 12
+	}
+
+	// Check if address and mask are semantically compatible
+	if len(ip[is:]) != len(mask[ms:]) {
+		return nil, fmt.Errorf("cannot compute host portion ip address as ip and mask are not compatible: (%#v, %#v)", ip, mask)
+	}
+
+	// Compute host portion
+	out := GetIPCopy(ip)
+	for i := 0; i < len(mask[ms:]); i++ {
+		out[is+i] &= ^mask[ms+i]
+	}
+
+	return out, nil
+}
+
 const (
 	// NEXTHOP indicates a StaticRoute with an IP next hop.
 	NEXTHOP = iota

types/types_test.go

@@ -2,6 +2,7 @@ package types
 
 import (
 	"flag"
+	"net"
 	"testing"
 )
 
@@ -109,3 +110,61 @@ func TestErrorConstructors(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestUtilGetHostPortionIP(t *testing.T) {
+	input := []struct {
+		ip   net.IP
+		mask net.IPMask
+		host net.IP
+		err  error
+	}{
+		{ // ip in v4Inv6 representation, mask in v4 representation
+			ip:   net.IPv4(172, 28, 30, 1),
+			mask: []byte{0xff, 0xff, 0xff, 0},
+			host: net.IPv4(0, 0, 0, 1),
+		},
+		{ // ip and mask in v4Inv6 representation
+			ip:   net.IPv4(172, 28, 30, 2),
+			mask: []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0},
+			host: net.IPv4(0, 0, 0, 2),
+		},
+		{ // ip in v4 representation, mask in v4Inv6 representation
+			ip:   net.IPv4(172, 28, 30, 3)[12:],
+			mask: []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0},
+			host: net.IPv4(0, 0, 0, 3)[12:],
+		},
+		{ // ip and mask in v4 representation
+			ip:   net.IPv4(172, 28, 30, 4)[12:],
+			mask: []byte{0xff, 0xff, 0xff, 0},
+			host: net.IPv4(0, 0, 0, 4)[12:],
+		},
+		{ // ip and mask as v6
+			ip:   net.ParseIP("2005:2004:2002:2001:FFFF:ABCD:EEAB:00CD"),
+			mask: []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0, 0, 0},
+			host: net.ParseIP("0::AB:00CD"),
+		},
+	}
+
+	for _, i := range input {
+		h, err := GetHostPartIP(i.ip, i.mask)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !i.host.Equal(h) {
+			t.Fatalf("Failed to return expected host ip. Expected: %s. Got: %s", i.host, h)
+		}
+	}
+
+	// ip as v6 and mask as v4 are not compatible
+	if _, err := GetHostPartIP(net.ParseIP("2005:2004:2002:2001:FFFF:ABCD:EEAB:00CD"), []byte{0xff, 0xff, 0xff, 0}); err == nil {
+		t.Fatalf("Unexpected success")
+	}
+	// ip as v4 and non conventional mask
+	if _, err := GetHostPartIP(net.ParseIP("173.32.4.5"), []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, 0xff, 0}); err == nil {
+		t.Fatalf("Unexpected success")
+	}
+	// ip as v4 and non conventional mask
+	if _, err := GetHostPartIP(net.ParseIP("173.32.4.5"), []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, 0xff, 0xff, 0xff, 0}); err == nil {
+		t.Fatalf("Unexpected success")
+	}
+}