text: // Copyright 2013 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 !nacl,!plan9,!windows
  
  package ipv6
  
  import (
  	"net"
  	"syscall"
  )
  
  // ReadFrom reads a payload of the received IPv6 datagram, from the
  // endpoint c, copying the payload into b. It returns the number of
  // bytes copied into b, the control message cm and the source address
  // src of the received datagram.
  func (c *payloadHandler) ReadFrom(b []byte) (n int, cm *ControlMessage, src net.Addr, err error) {
  	if !c.ok() {
  		return 0, nil, nil, syscall.EINVAL
  	}
  	oob := newControlMessage(&c.rawOpt)
  	var oobn int
  	switch c := c.PacketConn.(type) {
  	case *net.UDPConn:
  		if n, oobn, _, src, err = c.ReadMsgUDP(b, oob); err != nil {
  			return 0, nil, nil, err
  		}
  	case *net.IPConn:
  		if n, oobn, _, src, err = c.ReadMsgIP(b, oob); err != nil {
  			return 0, nil, nil, err
  		}
  	default:
  		return 0, nil, nil, errInvalidConnType
  	}
  	if cm, err = parseControlMessage(oob[:oobn]); err != nil {
  		return 0, nil, nil, err
  	}
  	if cm != nil {
  		cm.Src = netAddrToIP16(src)
  	}
  	return
  }
  
  // WriteTo writes a payload of the IPv6 datagram, to the destination
  // address dst through the endpoint c, copying the payload from b. It
  // returns the number of bytes written. The control message cm allows
  // the IPv6 header fields and the datagram path to be specified. The
  // cm may be nil if control of the outgoing datagram is not required.
  func (c *payloadHandler) WriteTo(b []byte, cm *ControlMessage, dst net.Addr) (n int, err error) {
  	if !c.ok() {
  		return 0, syscall.EINVAL
  	}
  	oob := marshalControlMessage(cm)
  	if dst == nil {
  		return 0, errMissingAddress
  	}
  	switch c := c.PacketConn.(type) {
  	case *net.UDPConn:
  		n, _, err = c.WriteMsgUDP(b, oob, dst.(*net.UDPAddr))
  	case *net.IPConn:
  		n, _, err = c.WriteMsgIP(b, oob, dst.(*net.IPAddr))
  	default:
  		return 0, errInvalidConnType
  	}
  	if err != nil {
  		return 0, err
  	}
  	return
  }
  