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// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// A payloadHandler represents the IPv4 datagram payload handler.
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type payloadHandler struct {
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func (c *payloadHandler) ok() bool { return c != nil && c.c != nil }
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// ReadFrom reads a payload of the received IPv4 datagram, from the
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// endpoint c, copying the payload into b. It returns the number of
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// bytes copied into b, the control message cm and the source address
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// src of the received datagram.
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func (c *payloadHandler) ReadFrom(b []byte) (n int, cm *ControlMessage, src net.Addr, err error) {
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return 0, nil, nil, syscall.EINVAL
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oob := newControlMessage(&c.rawOpt)
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switch rd := c.c.(type) {
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if n, oobn, _, src, err = rd.ReadMsgUDP(b, oob); err != nil {
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return 0, nil, nil, err
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nb := make([]byte, len(b)+maxHeaderLen)
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if n, oobn, _, src, err = rd.ReadMsgIP(nb, oob); err != nil {
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return 0, nil, nil, err
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hdrlen := (int(b[0]) & 0x0f) << 2
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return 0, nil, nil, errInvalidConnType
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if cm, err = parseControlMessage(oob[:oobn]); err != nil {
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return 0, nil, nil, err
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cm.Src = netAddrToIP4(src)
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// WriteTo writes a payload of the IPv4 datagram, to the destination
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// address dst through the endpoint c, copying the payload from b. It
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// returns the number of bytes written. The control message cm allows
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// the datagram path and the outgoing interface to be specified.
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// Currently only Linux supports this. The cm may be nil if control
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// of the outgoing datagram is not required.
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func (c *payloadHandler) WriteTo(b []byte, cm *ControlMessage, dst net.Addr) (n int, err error) {
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return 0, syscall.EINVAL
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oob := marshalControlMessage(cm)
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return 0, errMissingAddress
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switch wr := c.c.(type) {
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n, _, err = wr.WriteMsgUDP(b, oob, dst.(*net.UDPAddr))
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n, _, err = wr.WriteMsgIP(b, oob, dst.(*net.IPAddr))
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return 0, errInvalidConnType