packet.go

Documentation: golang.org/x/net/ipv4

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ipv4
     6  
     7  import (
     8  	"net"
     9  
    10  	"golang.org/x/net/internal/socket"
    11  )
    12  
    13  // BUG(mikio): On Windows, the ReadFrom and WriteTo methods of RawConn
    14  // are not implemented.
    15  
    16  // A packetHandler represents the IPv4 datagram handler.
    17  type packetHandler struct {
    18  	*net.IPConn
    19  	*socket.Conn
    20  	rawOpt
    21  }
    22  
    23  func (c *packetHandler) ok() bool { return c != nil && c.IPConn != nil && c.Conn != nil }
    24  
    25  // ReadFrom reads an IPv4 datagram from the endpoint c, copying the
    26  // datagram into b. It returns the received datagram as the IPv4
    27  // header h, the payload p and the control message cm.
    28  func (c *packetHandler) ReadFrom(b []byte) (h *Header, p []byte, cm *ControlMessage, err error) {
    29  	if !c.ok() {
    30  		return nil, nil, nil, errInvalidConn
    31  	}
    32  	c.rawOpt.RLock()
    33  	m := socket.Message{
    34  		Buffers: [][]byte{b},
    35  		OOB:     NewControlMessage(c.rawOpt.cflags),
    36  	}
    37  	c.rawOpt.RUnlock()
    38  	if err := c.RecvMsg(&m, 0); err != nil {
    39  		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
    40  	}
    41  	var hs []byte
    42  	if hs, p, err = slicePacket(b[:m.N]); err != nil {
    43  		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
    44  	}
    45  	if h, err = ParseHeader(hs); err != nil {
    46  		return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
    47  	}
    48  	if m.NN > 0 {
    49  		if compatFreeBSD32 {
    50  			adjustFreeBSD32(&m)
    51  		}
    52  		cm = new(ControlMessage)
    53  		if err := cm.Parse(m.OOB[:m.NN]); err != nil {
    54  			return nil, nil, nil, &net.OpError{Op: "read", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Err: err}
    55  		}
    56  	}
    57  	if src, ok := m.Addr.(*net.IPAddr); ok && cm != nil {
    58  		cm.Src = src.IP
    59  	}
    60  	return
    61  }
    62  
    63  func slicePacket(b []byte) (h, p []byte, err error) {
    64  	if len(b) < HeaderLen {
    65  		return nil, nil, errHeaderTooShort
    66  	}
    67  	hdrlen := int(b[0]&0x0f) << 2
    68  	return b[:hdrlen], b[hdrlen:], nil
    69  }
    70  
    71  // WriteTo writes an IPv4 datagram through the endpoint c, copying the
    72  // datagram from the IPv4 header h and the payload p. The control
    73  // message cm allows the datagram path and the outgoing interface to be
    74  // specified.  Currently only Darwin and Linux support this. The cm
    75  // may be nil if control of the outgoing datagram is not required.
    76  //
    77  // The IPv4 header h must contain appropriate fields that include:
    78  //
    79  //	Version       = <must be specified>
    80  //	Len           = <must be specified>
    81  //	TOS           = <must be specified>
    82  //	TotalLen      = <must be specified>
    83  //	ID            = platform sets an appropriate value if ID is zero
    84  //	FragOff       = <must be specified>
    85  //	TTL           = <must be specified>
    86  //	Protocol      = <must be specified>
    87  //	Checksum      = platform sets an appropriate value if Checksum is zero
    88  //	Src           = platform sets an appropriate value if Src is nil
    89  //	Dst           = <must be specified>
    90  //	Options       = optional
    91  func (c *packetHandler) WriteTo(h *Header, p []byte, cm *ControlMessage) error {
    92  	if !c.ok() {
    93  		return errInvalidConn
    94  	}
    95  	m := socket.Message{
    96  		OOB: cm.Marshal(),
    97  	}
    98  	wh, err := h.Marshal()
    99  	if err != nil {
   100  		return err
   101  	}
   102  	m.Buffers = [][]byte{wh, p}
   103  	dst := new(net.IPAddr)
   104  	if cm != nil {
   105  		if ip := cm.Dst.To4(); ip != nil {
   106  			dst.IP = ip
   107  		}
   108  	}
   109  	if dst.IP == nil {
   110  		dst.IP = h.Dst
   111  	}
   112  	m.Addr = dst
   113  	if err := c.SendMsg(&m, 0); err != nil {
   114  		return &net.OpError{Op: "write", Net: c.IPConn.LocalAddr().Network(), Source: c.IPConn.LocalAddr(), Addr: opAddr(dst), Err: err}
   115  	}
   116  	return nil
   117  }
   118
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