net: allow "" as a hint wildcard to Resolve{IP,UDP,TCP}Addr

Also fixes comments on ResolveIPAddr.

Fixes #4476.

R=bradfitz, golang-dev
CC=golang-dev
https://golang.org/cl/6854129

src/pkg/net/ipraw_test.go

@@ -29,6 +29,9 @@ var resolveIPAddrTests = []struct {
 	{"ip6", "::1", &IPAddr{IP: ParseIP("::1")}, nil},
 	{"ip6:icmp", "::1", &IPAddr{IP: ParseIP("::1")}, nil},
 
+	{"", "127.0.0.1", &IPAddr{IP: IPv4(127, 0, 0, 1)}, nil}, // Go 1.0 behavior
+	{"", "::1", &IPAddr{IP: ParseIP("::1")}, nil},           // Go 1.0 behavior
+
 	{"l2tp", "127.0.0.1", nil, UnknownNetworkError("l2tp")},
 	{"l2tp:gre", "127.0.0.1", nil, UnknownNetworkError("l2tp:gre")},
 	{"tcp", "1.2.3.4:123", nil, UnknownNetworkError("tcp")},

src/pkg/net/iprawsock.go

@@ -24,9 +24,11 @@ func (a *IPAddr) String() string {
 
 // ResolveIPAddr parses addr as an IP address and resolves domain
 // names to numeric addresses on the network net, which must be
-// "ip", "ip4" or "ip6".  A literal IPv6 host address must be
-// enclosed in square brackets, as in "[::]".
+// "ip", "ip4" or "ip6".
 func ResolveIPAddr(net, addr string) (*IPAddr, error) {
+	if net == "" { // a hint wildcard for Go 1.0 undocumented behavior
+		net = "ip"
+	}
 	afnet, _, err := parseDialNetwork(net)
 	if err != nil {
 		return nil, err

src/pkg/net/tcp_test.go

@@ -130,6 +130,9 @@ var resolveTCPAddrTests = []struct {
 	{"tcp", "[::1]:1", &TCPAddr{IP: ParseIP("::1"), Port: 1}, nil},
 	{"tcp6", "[::1]:65534", &TCPAddr{IP: ParseIP("::1"), Port: 65534}, nil},
 
+	{"", "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
+
 	{"http", "127.0.0.1:0", nil, UnknownNetworkError("http")},
 }
 

src/pkg/net/tcpsock.go

@@ -31,6 +31,8 @@ func (a *TCPAddr) String() string {
 func ResolveTCPAddr(net, addr string) (*TCPAddr, error) {
 	switch net {
 	case "tcp", "tcp4", "tcp6":
+	case "": // a hint wildcard for Go 1.0 undocumented behavior
+		net = "tcp"
 	default:
 		return nil, UnknownNetworkError(net)
 	}

src/pkg/net/udp_test.go

@@ -22,6 +22,9 @@ var resolveUDPAddrTests = []struct {
 	{"udp", "[::1]:1", &UDPAddr{IP: ParseIP("::1"), Port: 1}, nil},
 	{"udp6", "[::1]:65534", &UDPAddr{IP: ParseIP("::1"), Port: 65534}, 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")},
 }
 

src/pkg/net/udpsock.go

@@ -35,6 +35,8 @@ func (a *UDPAddr) String() string {
 func ResolveUDPAddr(net, addr string) (*UDPAddr, error) {
 	switch net {
 	case "udp", "udp4", "udp6":
+	case "": // a hint wildcard for Go 1.0 undocumented behavior
+		net = "udp"
 	default:
 		return nil, UnknownNetworkError(net)
 	}