1 files changed, 25 insertions, 20 deletions
diff --git a/vendor/golang.org/x/net/internal/nettest/helper_bsd.go b/vendor/golang.org/x/net/internal/nettest/helper_bsd.go
index b2308a0e8..a6e433b58 100644
--- a/vendor/golang.org/x/net/internal/nettest/helper_bsd.go
+++ b/vendor/golang.org/x/net/internal/nettest/helper_bsd.go
@@ -13,6 +13,23 @@ import (
 	"syscall"
 )
 
+var darwinVersion int
+
+func init() {
+	if runtime.GOOS == "darwin" {
+		// See http://support.apple.com/kb/HT1633.
+		s, err := syscall.Sysctl("kern.osrelease")
+		if err != nil {
+			return
+		}
+		ss := strings.Split(s, ".")
+		if len(ss) == 0 {
+			return
+		}
+		darwinVersion, _ = strconv.Atoi(ss[0])
+	}
+}
+
 func supportsIPv6MulticastDeliveryOnLoopback() bool {
 	switch runtime.GOOS {
 	case "freebsd":
@@ -22,27 +39,15 @@ func supportsIPv6MulticastDeliveryOnLoopback() bool {
 		// packets correctly.
 		return false
 	case "darwin":
-		// See http://support.apple.com/kb/HT1633.
-		s, err := syscall.Sysctl("kern.osrelease")
-		if err != nil {
-			return false
-		}
-		ss := strings.Split(s, ".")
-		if len(ss) == 0 {
-			return false
-		}
-		// OS X 10.9 (Darwin 13) or above seems to do the
-		// right thing; preserving the packet header as it's
-		// needed for the checksum calcuration with pseudo
-		// header on loopback multicast delivery process.
-		// If not, you'll probably see what is the slow-acting
-		// kernel crash caused by lazy mbuf corruption.
-		// See ip6_mloopback in netinet6/ip6_output.c.
-		if mjver, err := strconv.Atoi(ss[0]); err != nil || mjver < 13 {
-			return false
-		}
-		return true
+		return !causesIPv6Crash()
 	default:
 		return true
 	}
 }
+
+func causesIPv6Crash() bool {
+	// We see some kernel crash when running IPv6 with IP-level
+	// options on Darwin kernel version 12 or below.
+	// See golang.org/issues/17015.
+	return darwinVersion < 13
+}