packet.go (3670B)
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 }