1// Copyright 2011 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// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
6
7// Socket control messages
8
9package syscall
10
11import (
12	"unsafe"
13)
14
15// CmsgLen returns the value to store in the Len field of the Cmsghdr
16// structure, taking into account any necessary alignment.
17func CmsgLen(datalen int) int {
18	return cmsgAlignOf(SizeofCmsghdr) + datalen
19}
20
21// CmsgSpace returns the number of bytes an ancillary element with
22// payload of the passed data length occupies.
23func CmsgSpace(datalen int) int {
24	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
25}
26
27func (h *Cmsghdr) data(offset uintptr) unsafe.Pointer {
28	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)) + offset)
29}
30
31// SocketControlMessage represents a socket control message.
32type SocketControlMessage struct {
33	Header Cmsghdr
34	Data   []byte
35}
36
37// ParseSocketControlMessage parses b as an array of socket control
38// messages.
39func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
40	var msgs []SocketControlMessage
41	i := 0
42	for i+CmsgLen(0) <= len(b) {
43		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
44		if err != nil {
45			return nil, err
46		}
47		m := SocketControlMessage{Header: *h, Data: dbuf}
48		msgs = append(msgs, m)
49		i += cmsgAlignOf(int(h.Len))
50	}
51	return msgs, nil
52}
53
54func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
55	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
56	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
57		return nil, nil, EINVAL
58	}
59	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
60}
61
62// UnixRights encodes a set of open file descriptors into a socket
63// control message for sending to another process.
64func UnixRights(fds ...int) []byte {
65	datalen := len(fds) * 4
66	b := make([]byte, CmsgSpace(datalen))
67	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
68	h.Level = SOL_SOCKET
69	h.Type = SCM_RIGHTS
70	h.SetLen(CmsgLen(datalen))
71	for i, fd := range fds {
72		*(*int32)(h.data(4 * uintptr(i))) = int32(fd)
73	}
74	return b
75}
76
77// ParseUnixRights decodes a socket control message that contains an
78// integer array of open file descriptors from another process.
79func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
80	if m.Header.Level != SOL_SOCKET {
81		return nil, EINVAL
82	}
83	if m.Header.Type != SCM_RIGHTS {
84		return nil, EINVAL
85	}
86	fds := make([]int, len(m.Data)>>2)
87	for i, j := 0, 0; i < len(m.Data); i += 4 {
88		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
89		j++
90	}
91	return fds, nil
92}
93