Add health check for DNS

vendor/golang.org/x/net/ipv4/control_unix.go

@@ -0,0 +1,73 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package ipv4
+
+import (
+	"unsafe"
+
+	"golang.org/x/net/internal/iana"
+	"golang.org/x/net/internal/socket"
+)
+
+func setControlMessage(c *socket.Conn, opt *rawOpt, cf ControlFlags, on bool) error {
+	opt.Lock()
+	defer opt.Unlock()
+	if so, ok := sockOpts[ssoReceiveTTL]; ok && cf&FlagTTL != 0 {
+		if err := so.SetInt(c, boolint(on)); err != nil {
+			return err
+		}
+		if on {
+			opt.set(FlagTTL)
+		} else {
+			opt.clear(FlagTTL)
+		}
+	}
+	if so, ok := sockOpts[ssoPacketInfo]; ok {
+		if cf&(FlagSrc|FlagDst|FlagInterface) != 0 {
+			if err := so.SetInt(c, boolint(on)); err != nil {
+				return err
+			}
+			if on {
+				opt.set(cf & (FlagSrc | FlagDst | FlagInterface))
+			} else {
+				opt.clear(cf & (FlagSrc | FlagDst | FlagInterface))
+			}
+		}
+	} else {
+		if so, ok := sockOpts[ssoReceiveDst]; ok && cf&FlagDst != 0 {
+			if err := so.SetInt(c, boolint(on)); err != nil {
+				return err
+			}
+			if on {
+				opt.set(FlagDst)
+			} else {
+				opt.clear(FlagDst)
+			}
+		}
+		if so, ok := sockOpts[ssoReceiveInterface]; ok && cf&FlagInterface != 0 {
+			if err := so.SetInt(c, boolint(on)); err != nil {
+				return err
+			}
+			if on {
+				opt.set(FlagInterface)
+			} else {
+				opt.clear(FlagInterface)
+			}
+		}
+	}
+	return nil
+}
+
+func marshalTTL(b []byte, cm *ControlMessage) []byte {
+	m := socket.ControlMessage(b)
+	m.MarshalHeader(iana.ProtocolIP, sysIP_RECVTTL, 1)
+	return m.Next(1)
+}
+
+func parseTTL(cm *ControlMessage, b []byte) {
+	cm.TTL = int(*(*byte)(unsafe.Pointer(&b[:1][0])))
+}