net: name-based destination address selection

getaddrinfo() orders the addresses according to RFC 3484.

This means when IPv6 is working on a host we get results like:
    []string = {"2001:4810::110", "66.117.47.214"}

and when it's not working we get:
    []string = {"66.117.47.214", "2001:4810::110"}

thus can drop firstFavoriteAddr.

This also means /etc/gai.conf works on relevant systems.

R=rsc, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/4557058

src/pkg/net/iprawsock.go

@@ -253,7 +253,7 @@ func hostToIP(net, host string) (ip IP, err os.Error) {
 			err = err1
 			goto Error
 		}
-		addr = firstFavoriteAddr(filter, addrs)
+		addr = firstSupportedAddr(filter, addrs)
 		if addr == nil {
 			// should not happen
 			err = &AddrError{"LookupHost returned no suitable address", addrs[0]}

src/pkg/net/ipsock.go

@@ -98,23 +98,6 @@ func favoriteAddrFamily(net string, raddr, laddr sockaddr, mode string) int {
 	return syscall.AF_INET6
 }
 
-func firstFavoriteAddr(filter func(IP) IP, addrs []string) (addr IP) {
-	if filter == anyaddr {
-		// We'll take any IP address, but since the dialing code
-		// does not yet try multiple addresses, prefer to use
-		// an IPv4 address if possible.  This is especially relevant
-		// if localhost resolves to [ipv6-localhost, ipv4-localhost].
-		// Too much code assumes localhost == ipv4-localhost.
-		addr = firstSupportedAddr(ipv4only, addrs)
-		if addr == nil {
-			addr = firstSupportedAddr(anyaddr, addrs)
-		}
-	} else {
-		addr = firstSupportedAddr(filter, addrs)
-	}
-	return
-}
-
 func firstSupportedAddr(filter func(IP) IP, addrs []string) IP {
 	for _, s := range addrs {
 		if addr := filter(ParseIP(s)); addr != nil {
@@ -293,7 +276,7 @@ func hostPortToIP(net, hostport string) (ip IP, iport int, err os.Error) {
 				err = err1
 				goto Error
 			}
-			addr = firstFavoriteAddr(filter, addrs)
+			addr = firstSupportedAddr(filter, addrs)
 			if addr == nil {
 				// should not happen
 				err = &AddrError{"LookupHost returned no suitable address", addrs[0]}