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.
5 // +build darwin freebsd linux netbsd openbsd
7 // Socket control messages
16 // Round the length of a raw sockaddr up to align it properly.
17 func cmsgAlignOf(salen int) int {
18 salign := int(sizeofPtr)
19 // NOTE: It seems like 64-bit Darwin kernel still requires 32-bit
20 // aligned access to BSD subsystem.
24 // NOTE: Solaris always uses 32-bit alignment,
25 // cf. _CMSG_DATA_ALIGNMENT in <sys/socket.h>.
26 if runtime.GOOS == "solaris" {
29 return (salen + salign - 1) & ^(salign - 1)
32 // CmsgLen returns the value to store in the Len field of the Cmsghdr
33 // structure, taking into account any necessary alignment.
34 func CmsgLen(datalen int) int {
35 return cmsgAlignOf(SizeofCmsghdr) + datalen
38 // CmsgSpace returns the number of bytes an ancillary element with
39 // payload of the passed data length occupies.
40 func CmsgSpace(datalen int) int {
41 return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
44 func cmsgData(h *Cmsghdr) unsafe.Pointer {
45 return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
48 // SocketControlMessage represents a socket control message.
49 type SocketControlMessage struct {
54 // ParseSocketControlMessage parses b as an array of socket control
56 func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
57 var msgs []SocketControlMessage
59 for i+CmsgLen(0) <= len(b) {
60 h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
64 m := SocketControlMessage{Header: *h, Data: dbuf}
65 msgs = append(msgs, m)
66 i += cmsgAlignOf(int(h.Len))
71 func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
72 h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
73 if h.Len < SizeofCmsghdr || int(h.Len) > len(b) {
74 return nil, nil, EINVAL
76 return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
79 // UnixRights encodes a set of open file descriptors into a socket
80 // control message for sending to another process.
81 func UnixRights(fds ...int) []byte {
82 datalen := len(fds) * 4
83 b := make([]byte, CmsgSpace(datalen))
84 h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
87 h.SetLen(CmsgLen(datalen))
88 data := uintptr(cmsgData(h))
89 for _, fd := range fds {
90 *(*int32)(unsafe.Pointer(data)) = int32(fd)
96 // ParseUnixRights decodes a socket control message that contains an
97 // integer array of open file descriptors from another process.
98 func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
99 if m.Header.Level != SOL_SOCKET {
102 if m.Header.Type != SCM_RIGHTS {
105 fds := make([]int, len(m.Data)>>2)
106 for i, j := 0, 0; i < len(m.Data); i += 4 {
107 fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))