net: apply tcp4/tcp6 restrictions to literals in ResolveTCPAddr

The restrictions were already being applied to the IP addresses
received from the host resolver. Apply the same restrictions to
literal IP addresses not passed to the host resolver.

For example, ResolveTCPAddr("tcp4", "[2001:db8::1]:http") used
to succeed and now does not (that's not an IPv4 address).

Perhaps a bit surprisingly,
ResolveTCPAddr("tcp4", "[::ffff:127.0.0.1]:http") succeeds,
behaving identically to ResolveTCPAddr("tcp4", "127.0.0.1:http"), and
ResolveTCPAddr("tcp6", "[::ffff:127.0.0.1]:http") fails,
behaving identically to ResolveTCPAddr("tcp6", "127.0.0.1:http").
Even so, it seems right to match (by reusing) the existing filtering
as applied to addresses resolved by the host C library.
If anyone can make a strong argument for changing the filtering
of IPv4-inside-IPv6 addresses, the fix can be applied to all
the code paths in a separate CL.

Fixes #14037.

Change-Id: I690dfdcbe93d730e11e00ea387fa7484cd524341
Reviewed-on: https://go-review.googlesource.com/32100
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/dial.go

@@ -230,7 +230,7 @@ func (r *Resolver) resolveAddrList(ctx context.Context, op, network, addr string
 		}
 	}
 	if len(naddrs) == 0 {
-		return nil, errNoSuitableAddress
+		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: hint.String()}
 	}
 	return naddrs, nil
 }

src/net/error_test.go

@@ -230,23 +230,27 @@ func TestDialAddrError(t *testing.T) {
 	} {
 		var err error
 		var c Conn
+		var op string
 		if tt.lit != "" {
 			c, err = Dial(tt.network, JoinHostPort(tt.lit, "0"))
+			op = fmt.Sprintf("Dial(%q, %q)", tt.network, JoinHostPort(tt.lit, "0"))
 		} else {
 			c, err = DialTCP(tt.network, nil, tt.addr)
+			op = fmt.Sprintf("DialTCP(%q, %q)", tt.network, tt.addr)
 		}
 		if err == nil {
 			c.Close()
-			t.Errorf("%s %q/%v: should fail", tt.network, tt.lit, tt.addr)
+			t.Errorf("%s succeeded, want error", op)
 			continue
 		}
 		if perr := parseDialError(err); perr != nil {
-			t.Error(perr)
+			t.Errorf("%s: %v", op, perr)
 			continue
 		}
-		aerr, ok := err.(*OpError).Err.(*AddrError)
+		operr := err.(*OpError).Err
+		aerr, ok := operr.(*AddrError)
 		if !ok {
-			t.Errorf("%s %q/%v: should be AddrError: %v", tt.network, tt.lit, tt.addr, err)
+			t.Errorf("%s: %v is %#T, want *AddrError", op, err, operr)
 			continue
 		}
 		want := tt.lit
@@ -254,7 +258,7 @@ func TestDialAddrError(t *testing.T) {
 			want = tt.addr.IP.String()
 		}
 		if aerr.Addr != want {
-			t.Fatalf("%s: got %q; want %q", tt.network, aerr.Addr, want)
+			t.Errorf("%s: %v, error Addr=%q, want %q", op, err, aerr.Addr, want)
 		}
 	}
 }

src/net/ipsock.go

@@ -76,7 +76,7 @@ func (addrs addrList) partition(strategy func(Addr) bool) (primaries, fallbacks
 // yielding a list of Addr objects. Known filters are nil, ipv4only,
 // and ipv6only. It returns every address when the filter is nil.
 // The result contains at least one address when error is nil.
-func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr) Addr) (addrList, error) {
+func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr) Addr, originalAddr string) (addrList, error) {
 	var addrs addrList
 	for _, ip := range ips {
 		if filter == nil || filter(ip) {
@@ -84,21 +84,19 @@ func filterAddrList(filter func(IPAddr) bool, ips []IPAddr, inetaddr func(IPAddr
 		}
 	}
 	if len(addrs) == 0 {
-		return nil, errNoSuitableAddress
+		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: originalAddr}
 	}
 	return addrs, nil
 }
 
-// ipv4only reports whether the kernel supports IPv4 addressing mode
-// and addr is an IPv4 address.
+// ipv4only reports whether addr is an IPv4 address.
 func ipv4only(addr IPAddr) bool {
-	return supportsIPv4 && addr.IP.To4() != nil
+	return addr.IP.To4() != nil
 }
 
-// ipv6only reports whether the kernel supports IPv6 addressing mode
-// and addr is an IPv6 address except IPv4-mapped IPv6 address.
+// ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
 func ipv6only(addr IPAddr) bool {
-	return supportsIPv6 && len(addr.IP) == IPv6len && addr.IP.To4() == nil
+	return len(addr.IP) == IPv6len && addr.IP.To4() == nil
 }
 
 // SplitHostPort splits a network address of the form "host:port",
@@ -228,20 +226,21 @@ func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addr
 	if host == "" {
 		return addrList{inetaddr(IPAddr{})}, nil
 	}
-	// Try as a literal IP address.
-	var ip IP
-	if ip = parseIPv4(host); ip != nil {
-		return addrList{inetaddr(IPAddr{IP: ip})}, nil
-	}
-	var zone string
-	if ip, zone = parseIPv6(host, true); ip != nil {
-		return addrList{inetaddr(IPAddr{IP: ip, Zone: zone})}, nil
-	}
-	// Try as a DNS name.
-	ips, err := r.LookupIPAddr(ctx, host)
-	if err != nil {
-		return nil, err
+
+	// Try as a literal IP address, then as a DNS name.
+	var ips []IPAddr
+	if ip := parseIPv4(host); ip != nil {
+		ips = []IPAddr{{IP: ip}}
+	} else if ip, zone := parseIPv6(host, true); ip != nil {
+		ips = []IPAddr{{IP: ip, Zone: zone}}
+	} else {
+		// Try as a DNS name.
+		ips, err = r.LookupIPAddr(ctx, host)
+		if err != nil {
+			return nil, err
+		}
 	}
+
 	var filter func(IPAddr) bool
 	if net != "" && net[len(net)-1] == '4' {
 		filter = ipv4only
@@ -249,7 +248,7 @@ func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addr
 	if net != "" && net[len(net)-1] == '6' {
 		filter = ipv6only
 	}
-	return filterAddrList(filter, ips, inetaddr)
+	return filterAddrList(filter, ips, inetaddr, host)
 }
 
 func loopbackIP(net string) IP {

src/net/ipsock_test.go

@@ -205,13 +205,13 @@ var addrListTests = []struct {
 		nil,
 	},
 
-	{nil, nil, testInetaddr, nil, nil, nil, errNoSuitableAddress},
+	{nil, nil, testInetaddr, nil, nil, nil, &AddrError{errNoSuitableAddress.Error(), "ADDR"}},
 
-	{ipv4only, nil, testInetaddr, nil, nil, nil, errNoSuitableAddress},
-	{ipv4only, []IPAddr{{IP: IPv6loopback}}, testInetaddr, nil, nil, nil, errNoSuitableAddress},
+	{ipv4only, nil, testInetaddr, nil, nil, nil, &AddrError{errNoSuitableAddress.Error(), "ADDR"}},
+	{ipv4only, []IPAddr{{IP: IPv6loopback}}, testInetaddr, nil, nil, nil, &AddrError{errNoSuitableAddress.Error(), "ADDR"}},
 
-	{ipv6only, nil, testInetaddr, nil, nil, nil, errNoSuitableAddress},
-	{ipv6only, []IPAddr{{IP: IPv4(127, 0, 0, 1)}}, testInetaddr, nil, nil, nil, errNoSuitableAddress},
+	{ipv6only, nil, testInetaddr, nil, nil, nil, &AddrError{errNoSuitableAddress.Error(), "ADDR"}},
+	{ipv6only, []IPAddr{{IP: IPv4(127, 0, 0, 1)}}, testInetaddr, nil, nil, nil, &AddrError{errNoSuitableAddress.Error(), "ADDR"}},
 }
 
 func TestAddrList(t *testing.T) {
@@ -220,8 +220,8 @@ func TestAddrList(t *testing.T) {
 	}
 
 	for i, tt := range addrListTests {
-		addrs, err := filterAddrList(tt.filter, tt.ips, tt.inetaddr)
-		if err != tt.err {
+		addrs, err := filterAddrList(tt.filter, tt.ips, tt.inetaddr, "ADDR")
+		if !reflect.DeepEqual(err, tt.err) {
 			t.Errorf("#%v: got %v; want %v", i, err, tt.err)
 		}
 		if tt.err != nil {

src/net/net.go

@@ -519,7 +519,7 @@ func (e *AddrError) Error() string {
 	}
 	s := e.Err
 	if e.Addr != "" {
-		s += " " + e.Addr
+		s = "address " + e.Addr + ": " + s
 	}
 	return s
 }

src/net/tcpsock_test.go

@@ -311,6 +311,16 @@ var resolveTCPAddrTests = []resolveTCPAddrTest{
 	{"tcp", ":12345", &TCPAddr{Port: 12345}, nil},
 
 	{"http", "127.0.0.1:0", nil, UnknownNetworkError("http")},
+
+	{"tcp", "127.0.0.1:http", &TCPAddr{IP: ParseIP("127.0.0.1"), Port: 80}, nil},
+	{"tcp", "[::ffff:127.0.0.1]:http", &TCPAddr{IP: ParseIP("::ffff:127.0.0.1"), Port: 80}, nil},
+	{"tcp", "[2001:db8::1]:http", &TCPAddr{IP: ParseIP("2001:db8::1"), Port: 80}, nil},
+	{"tcp4", "127.0.0.1:http", &TCPAddr{IP: ParseIP("127.0.0.1"), Port: 80}, nil},
+	{"tcp4", "[::ffff:127.0.0.1]:http", &TCPAddr{IP: ParseIP("127.0.0.1"), Port: 80}, nil},
+	{"tcp4", "[2001:db8::1]:http", nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: "2001:db8::1"}},
+	{"tcp6", "127.0.0.1:http", nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: "127.0.0.1"}},
+	{"tcp6", "[::ffff:127.0.0.1]:http", nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: "::ffff:127.0.0.1"}},
+	{"tcp6", "[2001:db8::1]:http", &TCPAddr{IP: ParseIP("2001:db8::1"), Port: 80}, nil},
 }
 
 func TestResolveTCPAddr(t *testing.T) {
@@ -318,21 +328,17 @@ func TestResolveTCPAddr(t *testing.T) {
 	defer func() { testHookLookupIP = origTestHookLookupIP }()
 	testHookLookupIP = lookupLocalhost
 
-	for i, tt := range resolveTCPAddrTests {
+	for _, tt := range resolveTCPAddrTests {
 		addr, err := ResolveTCPAddr(tt.network, tt.litAddrOrName)
-		if err != tt.err {
-			t.Errorf("#%d: %v", i, err)
-		} else if !reflect.DeepEqual(addr, tt.addr) {
-			t.Errorf("#%d: got %#v; want %#v", i, addr, tt.addr)
-		}
-		if err != nil {
+		if !reflect.DeepEqual(addr, tt.addr) || !reflect.DeepEqual(err, tt.err) {
+			t.Errorf("ResolveTCPAddr(%q, %q) = %v, %v, want %v, %v", tt.network, tt.litAddrOrName, addr, err, tt.addr, tt.err)
 			continue
 		}
-		rtaddr, err := ResolveTCPAddr(addr.Network(), addr.String())
-		if err != nil {
-			t.Errorf("#%d: %v", i, err)
-		} else if !reflect.DeepEqual(rtaddr, addr) {
-			t.Errorf("#%d: got %#v; want %#v", i, rtaddr, addr)
+		if err == nil {
+			addr2, err := ResolveTCPAddr(addr.Network(), addr.String())
+			if !reflect.DeepEqual(addr2, tt.addr) || err != tt.err {
+				t.Errorf("(%q, %q): ResolveTCPAddr(%q, %q) = %v, %v, want %v, %v", tt.network, tt.litAddrOrName, addr.Network(), addr.String(), addr2, err, tt.addr, tt.err)
+			}
 		}
 	}
 }