net: add IP.IsLocal

Fixes golang#29146

Change-Id: I69f51f943a684bdffaa9a32bea56eb2c5d881b33

Author: MaxSem

src/net/ip.go

@@ -130,6 +130,19 @@ func (ip IP) IsMulticast() bool {
 	return len(ip) == IPv6len && ip[0] == 0xff
 }
 
+// IsLocal reports whether `ip' is a local address, according to
+// RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
+func (ip IP) IsLocal() bool {
+	if ip4 := ip.To4(); ip4 != nil {
+		// Local IPv4 addresses are defined in https://tools.ietf.org/html/rfc1918
+		return ip4[0] == 10 ||
+			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
+			(ip4[0] == 192 && ip4[1] == 168)
+	}
+	// Local IPv6 addresses are defined in https://tools.ietf.org/html/rfc4193
+	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
+}
+
 // IsInterfaceLocalMulticast reports whether ip is
 // an interface-local multicast address.
 func (ip IP) IsInterfaceLocalMulticast() bool {

src/net/ip_test.go

@@ -666,6 +666,15 @@ var ipAddrScopeTests = []struct {
 	{IP.IsMulticast, IP{0xff, 0x05, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, true},
 	{IP.IsMulticast, IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
 	{IP.IsMulticast, nil, false},
+	{IP.IsLocal, nil, false},
+	{IP.IsLocal, IPv4(10, 0, 0, 0), true},
+	{IP.IsLocal, IPv4(11, 0, 0, 0), false},
+	{IP.IsLocal, IPv4(172, 16, 0, 0), true},
+	{IP.IsLocal, IPv4(172, 32, 0, 0), false},
+	{IP.IsLocal, IPv4(192, 168, 0, 0), true},
+	{IP.IsLocal, IPv4(192, 169, 0, 0), false},
+	{IP.IsLocal, IP{0xfc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, true},
+	{IP.IsLocal, IP{0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
 	{IP.IsInterfaceLocalMulticast, IPv4(224, 0, 0, 0), false},
 	{IP.IsInterfaceLocalMulticast, IPv4(0xff, 0x01, 0, 0), false},
 	{IP.IsInterfaceLocalMulticast, IPv6interfacelocalallnodes, true},