Add health check for DNS

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

@@ -0,0 +1,117 @@
+// 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.
+
+package ipv4
+
+import (
+	"net"
+
+	"golang.org/x/net/internal/socket"
+)
+
+// BUG(mikio): On Windows, the ReadFrom and WriteTo methods of RawConn
+// are not implemented.
+
+// A packetHandler represents the IPv4 datagram handler.
+type packetHandler struct {
+	*net.IPConn
+	*socket.Conn
+	rawOpt
+}
+
+func (c *packetHandler) ok() bool { return c != nil && c.IPConn != nil && c.Conn != nil }
+
+// ReadFrom reads an IPv4 datagram from the endpoint c, copying the
+// datagram into b. It returns the received datagram as the IPv4
+// header h, the payload p and the control message cm.
+func (c *packetHandler) ReadFrom(b []byte) (h *Header, p []byte, cm *ControlMessage, err error) {
+	if !c.ok() {
+		return nil, nil, nil, errInvalidConn
+	}
+	c.rawOpt.RLock()
+	m := socket.Message{
+		Buffers: [][]byte{b},
+		OOB:     NewControlMessage(c.rawOpt.cflags),
+	}
+	c.rawOpt.RUnlock()
+	if err := c.RecvMsg(&m, 0); err != nil {
+		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
+	}
+	var hs []byte
+	if hs, p, err = slicePacket(b[:m.N]); err != nil {
+		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
+	}
+	if h, err = ParseHeader(hs); err != nil {
+		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
+	}
+	if m.NN > 0 {
+		if compatFreeBSD32 {
+			adjustFreeBSD32(&m)
+		}
+		cm = new(ControlMessage)
+		if err := cm.Parse(m.OOB[:m.NN]); err != nil {
+			return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
+		}
+	}
+	if src, ok := m.Addr.(*net.IPAddr); ok && cm != nil {
+		cm.Src = src.IP
+	}
+	return
+}
+
+func slicePacket(b []byte) (h, p []byte, err error) {
+	if len(b) < HeaderLen {
+		return nil, nil, errHeaderTooShort
+	}
+	hdrlen := int(b[0]&0x0f) << 2
+	return b[:hdrlen], b[hdrlen:], nil
+}
+
+// WriteTo writes an IPv4 datagram through the endpoint c, copying the
+// datagram from the IPv4 header h and the payload p. The control
+// message cm allows the datagram path and the outgoing interface to be
+// specified.  Currently only Darwin and Linux support this. The cm
+// may be nil if control of the outgoing datagram is not required.
+//
+// The IPv4 header h must contain appropriate fields that include:
+//
+//	Version       = <must be specified>
+//	Len           = <must be specified>
+//	TOS           = <must be specified>
+//	TotalLen      = <must be specified>
+//	ID            = platform sets an appropriate value if ID is zero
+//	FragOff       = <must be specified>
+//	TTL           = <must be specified>
+//	Protocol      = <must be specified>
+//	Checksum      = platform sets an appropriate value if Checksum is zero
+//	Src           = platform sets an appropriate value if Src is nil
+//	Dst           = <must be specified>
+//	Options       = optional
+func (c *packetHandler) WriteTo(h *Header, p []byte, cm *ControlMessage) error {
+	if !c.ok() {
+		return errInvalidConn
+	}
+	m := socket.Message{
+		OOB: cm.Marshal(),
+	}
+	wh, err := h.Marshal()
+	if err != nil {
+		return err
+	}
+	m.Buffers = [][]byte{wh, p}
+	dst := new(net.IPAddr)
+	if cm != nil {
+		if ip := cm.Dst.To4(); ip != nil {
+			dst.IP = ip
+		}
+	}
+	if dst.IP == nil {
+		dst.IP = h.Dst
+	}
+	m.Addr = dst
+	if err := c.SendMsg(&m, 0); err != nil {
+		return &net.OpError{Op: "write", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Addr: opAddr(dst), Err: err}
+	}
+	return nil
+}