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 //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
6 7 // Socket control messages
8 9 package unix
10 11 import (
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.
17 func 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.
23 func CmsgSpace(datalen int) int {
24 return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
25 }
26 27 func (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.
32 type SocketControlMessage struct {
33 Header Cmsghdr
34 Data []byte
35 }
36 37 // ParseSocketControlMessage parses b as an array of socket control
38 // messages.
39 func 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 54 // ParseOneSocketControlMessage parses a single socket control message from b, returning the message header,
55 // message data (a slice of b), and the remainder of b after that single message.
56 // When there are no remaining messages, len(remainder) == 0.
57 func ParseOneSocketControlMessage(b []byte) (hdr Cmsghdr, data []byte, remainder []byte, err error) {
58 h, dbuf, err := socketControlMessageHeaderAndData(b)
59 if err != nil {
60 return Cmsghdr{}, nil, nil, err
61 }
62 if i := cmsgAlignOf(int(h.Len)); i < len(b) {
63 remainder = b[i:]
64 }
65 return *h, dbuf, remainder, nil
66 }
67 68 func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
69 h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
70 if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
71 return nil, nil, EINVAL
72 }
73 return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
74 }
75 76 // UnixRights encodes a set of open file descriptors into a socket
77 // control message for sending to another process.
78 func UnixRights(fds ...int) []byte {
79 datalen := len(fds) * 4
80 b := make([]byte, CmsgSpace(datalen))
81 h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
82 h.Level = SOL_SOCKET
83 h.Type = SCM_RIGHTS
84 h.SetLen(CmsgLen(datalen))
85 for i, fd := range fds {
86 *(*int32)(h.data(4 * uintptr(i))) = int32(fd)
87 }
88 return b
89 }
90 91 // ParseUnixRights decodes a socket control message that contains an
92 // integer array of open file descriptors from another process.
93 func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
94 if m.Header.Level != SOL_SOCKET {
95 return nil, EINVAL
96 }
97 if m.Header.Type != SCM_RIGHTS {
98 return nil, EINVAL
99 }
100 fds := make([]int, len(m.Data)>>2)
101 for i, j := 0, 0; i < len(m.Data); i += 4 {
102 fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
103 j++
104 }
105 return fds, nil
106 }
107