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
5package ipv4
6
7import (
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.
17type packetHandler struct {
18	*net.IPConn
19	*socket.Conn
20	rawOpt
21}
22
23func (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.
28func (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
63func 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
91func (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