net: more accurate IPv4-in-IPv6 API test

R=rsc
CC=golang-dev
https://golang.org/cl/4172045

diff --git a/src/pkg/net/iprawsock.go b/src/pkg/net/iprawsock.go
index 262b69d0682ad7c8e3d74fede0b35b6c7224b3fb..81a918ce5cb710909e10aa5623e59430258e3302 100644 (file)
--- a/src/pkg/net/iprawsock.go
+++ b/src/pkg/net/iprawsock.go
@@ -245,7 +245,7 @@ func hostToIP(host string) (ip IP, err os.Error) {
                        err = err1
                        goto Error
                }
-               addr = ParseIP(addrs[0])
+               addr = firstSupportedAddr(addrs)
                if addr == nil {
                        // should not happen
                        err = &AddrError{"LookupHost returned invalid address", addrs[0]}

diff --git a/src/pkg/net/ipsock.go b/src/pkg/net/ipsock.go
index 4ba6a55b96f70cae0d09065620deaac9f027eeab..ae4204b48aa48b1bf092cb81621afff554e476d5 100644 (file)
--- a/src/pkg/net/ipsock.go
+++ b/src/pkg/net/ipsock.go
@@ -18,19 +18,34 @@ import (
 // Unfortunately, we need to run on kernels built without IPv6 support too.
 // So probe the kernel to figure it out.
 func kernelSupportsIPv6() bool {
-       // FreeBSD does not support this sort of interface.
-       if syscall.OS == "freebsd" {
+       s, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
+       if err != 0 {
                return false
        }
-       fd, e := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
-       if fd >= 0 {
-               closesocket(fd)
+       defer closesocket(s)
+
+       la := &TCPAddr{IP: IPv4(127, 0, 0, 1)}
+       sa, oserr := la.toAddr().sockaddr(syscall.AF_INET6)
+       if oserr != nil {
+               return false
        }
-       return e == 0
+
+       return syscall.Bind(s, sa) == 0
 }
 
 var preferIPv4 = !kernelSupportsIPv6()
 
+func firstSupportedAddr(addrs []string) (addr IP) {
+       for _, s := range addrs {
+               addr = ParseIP(s)
+               if !preferIPv4 || addr.To4() != nil {
+                       break
+               }
+               addr = nil
+       }
+       return addr
+}
+
 // TODO(rsc): if syscall.OS == "linux", we're supposd to read
 // /proc/sys/net/core/somaxconn,
 // to take advantage of kernels that have raised the limit.
@@ -208,7 +223,7 @@ func hostPortToIP(net, hostport string) (ip IP, iport int, err os.Error) {
                                err = err1
                                goto Error
                        }
-                       addr = ParseIP(addrs[0])
+                       addr = firstSupportedAddr(addrs)
                        if addr == nil {
                                // should not happen
                                err = &AddrError{"LookupHost returned invalid address", addrs[0]}