net: ensure that ResolveTCPAddr(addr.String()) reproduces addr

And same for UDP.

Fixes #6465.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/13740048

src/pkg/net/cgo_unix.go

@@ -155,6 +155,9 @@ func cgoLookupCNAME(name string) (cname string, err error, completed bool) {
 }
 
 func copyIP(x IP) IP {
+	if len(x) < 16 {
+		return x.To16()
+	}
 	y := make(IP, len(x))
 	copy(y, x)
 	return y

src/pkg/net/ip.go

@@ -312,6 +312,15 @@ func (ip IP) String() string {
 	return s
 }
 
+// ipEmptyString is like ip.String except that it returns
+// an empty string when ip is unset.
+func ipEmptyString(ip IP) string {
+	if len(ip) == 0 {
+		return ""
+	}
+	return ip.String()
+}
+
 // MarshalText implements the encoding.TextMarshaler interface.
 // The encoding is the same as returned by String.
 func (ip IP) MarshalText() ([]byte, error) {

src/pkg/net/ipraw_test.go

@@ -52,8 +52,8 @@ func init() {
 	}
 	if ips, err := LookupIP("localhost"); err == nil && len(ips) > 1 && supportsIPv4 && supportsIPv6 {
 		resolveIPAddrTests = append(resolveIPAddrTests, []resolveIPAddrTest{
-			{"ip", "localhost", &IPAddr{IP: IPv4(127, 0, 0, 1).To4()}, nil},
-			{"ip4", "localhost", &IPAddr{IP: IPv4(127, 0, 0, 1).To4()}, nil},
+			{"ip", "localhost", &IPAddr{IP: IPv4(127, 0, 0, 1)}, nil},
+			{"ip4", "localhost", &IPAddr{IP: IPv4(127, 0, 0, 1)}, nil},
 			{"ip6", "localhost", &IPAddr{IP: IPv6loopback}, nil},
 		}...)
 	}

src/pkg/net/ipsock.go

@@ -116,11 +116,11 @@ func firstSupportedAddr(filter func(IP) IP, ips []IP, inetaddr func(IP) netaddr)
 }
 
 // ipv4only returns IPv4 addresses that we can use with the kernel's
-// IPv4 addressing modes.  It returns IPv4-mapped IPv6 addresses as
-// IPv4 addresses and returns other IPv6 address types as nils.
+// IPv4 addressing modes. If ip is an IPv4 address, ipv4only returns ip.
+// Otherwise it returns nil.
 func ipv4only(ip IP) IP {
-	if supportsIPv4 {
-		return ip.To4()
+	if supportsIPv4 && ip.To4() != nil {
+		return ip
 	}
 	return nil
 }

src/pkg/net/ipsock_test.go

@@ -26,7 +26,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -39,7 +39,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -51,7 +51,7 @@ var firstFavoriteAddrTests = []struct {
 			IPv4(192, 168, 0, 1),
 		},
 		testInetaddr,
-		&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+		&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 		nil,
 	},
 	{
@@ -74,7 +74,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -89,7 +89,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -104,7 +104,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -119,7 +119,7 @@ var firstFavoriteAddrTests = []struct {
 		},
 		testInetaddr,
 		addrList{
-			&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+			&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 			&TCPAddr{IP: IPv6loopback, Port: 5682},
 		},
 		nil,
@@ -132,7 +132,7 @@ var firstFavoriteAddrTests = []struct {
 			IPv6loopback,
 		},
 		testInetaddr,
-		&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+		&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 		nil,
 	},
 	{
@@ -142,7 +142,7 @@ var firstFavoriteAddrTests = []struct {
 			IPv4(127, 0, 0, 1),
 		},
 		testInetaddr,
-		&TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5682},
+		&TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5682},
 		nil,
 	},
 

src/pkg/net/tcp_test.go

@@ -292,6 +292,8 @@ var resolveTCPAddrTests = []resolveTCPAddrTest{
 	{"", "127.0.0.1:0", &TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 0}, nil}, // Go 1.0 behavior
 	{"", "[::1]:0", &TCPAddr{IP: ParseIP("::1"), Port: 0}, nil},         // Go 1.0 behavior
 
+	{"tcp", ":12345", &TCPAddr{Port: 12345}, nil},
+
 	{"http", "127.0.0.1:0", nil, UnknownNetworkError("http")},
 }
 
@@ -305,8 +307,8 @@ func init() {
 	}
 	if ips, err := LookupIP("localhost"); err == nil && len(ips) > 1 && supportsIPv4 && supportsIPv6 {
 		resolveTCPAddrTests = append(resolveTCPAddrTests, []resolveTCPAddrTest{
-			{"tcp", "localhost:5", &TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5}, nil},
-			{"tcp4", "localhost:6", &TCPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 6}, nil},
+			{"tcp", "localhost:5", &TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 5}, nil},
+			{"tcp4", "localhost:6", &TCPAddr{IP: IPv4(127, 0, 0, 1), Port: 6}, nil},
 			{"tcp6", "localhost:7", &TCPAddr{IP: IPv6loopback, Port: 7}, nil},
 		}...)
 	}
@@ -319,7 +321,17 @@ func TestResolveTCPAddr(t *testing.T) {
 			t.Fatalf("ResolveTCPAddr(%q, %q) failed: %v", tt.net, tt.litAddrOrName, err)
 		}
 		if !reflect.DeepEqual(addr, tt.addr) {
-			t.Fatalf("got %#v; expected %#v", addr, tt.addr)
+			t.Fatalf("ResolveTCPAddr(%q, %q) = %#v, want %#v", tt.net, tt.litAddrOrName, addr, tt.addr)
+		}
+		if err == nil {
+			str := addr.String()
+			addr1, err := ResolveTCPAddr(tt.net, str)
+			if err != nil {
+				t.Fatalf("ResolveTCPAddr(%q, %q) [from %q]: %v", tt.net, str, tt.litAddrOrName, err)
+			}
+			if !reflect.DeepEqual(addr1, addr) {
+				t.Fatalf("ResolveTCPAddr(%q, %q) [from %q] = %#v, want %#v", tt.net, str, tt.litAddrOrName, addr1, addr)
+			}
 		}
 	}
 }

src/pkg/net/tcpsock.go

@@ -18,10 +18,11 @@ func (a *TCPAddr) String() string {
 	if a == nil {
 		return "<nil>"
 	}
+	ip := ipEmptyString(a.IP)
 	if a.Zone != "" {
-		return JoinHostPort(a.IP.String()+"%"+a.Zone, itoa(a.Port))
+		return JoinHostPort(ip+"%"+a.Zone, itoa(a.Port))
 	}
-	return JoinHostPort(a.IP.String(), itoa(a.Port))
+	return JoinHostPort(ip, itoa(a.Port))
 }
 
 func (a *TCPAddr) toAddr() Addr {

src/pkg/net/udp_test.go

@@ -5,60 +5,31 @@
 package net
 
 import (
-	"fmt"
 	"reflect"
 	"runtime"
+	"strings"
 	"testing"
 )
 
-type resolveUDPAddrTest struct {
-	net           string
-	litAddrOrName string
-	addr          *UDPAddr
-	err           error
-}
-
-var resolveUDPAddrTests = []resolveUDPAddrTest{
-	{"udp", "127.0.0.1:0", &UDPAddr{IP: IPv4(127, 0, 0, 1), Port: 0}, nil},
-	{"udp4", "127.0.0.1:65535", &UDPAddr{IP: IPv4(127, 0, 0, 1), Port: 65535}, nil},
-
-	{"udp", "[::1]:1", &UDPAddr{IP: ParseIP("::1"), Port: 1}, nil},
-	{"udp6", "[::1]:65534", &UDPAddr{IP: ParseIP("::1"), Port: 65534}, nil},
-
-	{"udp", "[::1%en0]:1", &UDPAddr{IP: ParseIP("::1"), Port: 1, Zone: "en0"}, nil},
-	{"udp6", "[::1%911]:2", &UDPAddr{IP: ParseIP("::1"), Port: 2, Zone: "911"}, nil},
-
-	{"", "127.0.0.1:0", &UDPAddr{IP: IPv4(127, 0, 0, 1), Port: 0}, nil}, // Go 1.0 behavior
-	{"", "[::1]:0", &UDPAddr{IP: ParseIP("::1"), Port: 0}, nil},         // Go 1.0 behavior
-
-	{"sip", "127.0.0.1:0", nil, UnknownNetworkError("sip")},
-}
-
-func init() {
-	if ifi := loopbackInterface(); ifi != nil {
-		index := fmt.Sprintf("%v", ifi.Index)
-		resolveUDPAddrTests = append(resolveUDPAddrTests, []resolveUDPAddrTest{
-			{"udp6", "[fe80::1%" + ifi.Name + "]:3", &UDPAddr{IP: ParseIP("fe80::1"), Port: 3, Zone: zoneToString(ifi.Index)}, nil},
-			{"udp6", "[fe80::1%" + index + "]:4", &UDPAddr{IP: ParseIP("fe80::1"), Port: 4, Zone: index}, nil},
-		}...)
-	}
-	if ips, err := LookupIP("localhost"); err == nil && len(ips) > 1 && supportsIPv4 && supportsIPv6 {
-		resolveUDPAddrTests = append(resolveUDPAddrTests, []resolveUDPAddrTest{
-			{"udp", "localhost:5", &UDPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 5}, nil},
-			{"udp4", "localhost:6", &UDPAddr{IP: IPv4(127, 0, 0, 1).To4(), Port: 6}, nil},
-			{"udp6", "localhost:7", &UDPAddr{IP: IPv6loopback, Port: 7}, nil},
-		}...)
-	}
-}
-
 func TestResolveUDPAddr(t *testing.T) {
-	for _, tt := range resolveUDPAddrTests {
-		addr, err := ResolveUDPAddr(tt.net, tt.litAddrOrName)
+	for _, tt := range resolveTCPAddrTests {
+		net := strings.Replace(tt.net, "tcp", "udp", -1)
+		addr, err := ResolveUDPAddr(net, tt.litAddrOrName)
 		if err != tt.err {
-			t.Fatalf("ResolveUDPAddr(%q, %q) failed: %v", tt.net, tt.litAddrOrName, err)
+			t.Fatalf("ResolveUDPAddr(%q, %q) failed: %v", net, tt.litAddrOrName, err)
+		}
+		if !reflect.DeepEqual(addr, (*UDPAddr)(tt.addr)) {
+			t.Fatalf("ResolveUDPAddr(%q, %q) = %#v, want %#v", net, tt.litAddrOrName, addr, tt.addr)
 		}
-		if !reflect.DeepEqual(addr, tt.addr) {
-			t.Fatalf("got %#v; expected %#v", addr, tt.addr)
+		if err == nil {
+			str := addr.String()
+			addr1, err := ResolveUDPAddr(net, str)
+			if err != nil {
+				t.Fatalf("ResolveUDPAddr(%q, %q) [from %q]: %v", net, str, tt.litAddrOrName, err)
+			}
+			if !reflect.DeepEqual(addr1, addr) {
+				t.Fatalf("ResolveUDPAddr(%q, %q) [from %q] = %#v, want %#v", net, str, tt.litAddrOrName, addr1, addr)
+			}
 		}
 	}
 }

src/pkg/net/udpsock.go

@@ -22,10 +22,11 @@ func (a *UDPAddr) String() string {
 	if a == nil {
 		return "<nil>"
 	}
+	ip := ipEmptyString(a.IP)
 	if a.Zone != "" {
-		return JoinHostPort(a.IP.String()+"%"+a.Zone, itoa(a.Port))
+		return JoinHostPort(ip+"%"+a.Zone, itoa(a.Port))
 	}
-	return JoinHostPort(a.IP.String(), itoa(a.Port))
+	return JoinHostPort(ip, itoa(a.Port))
 }
 
 func (a *UDPAddr) toAddr() Addr {