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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 darwin dragonfly freebsd linux netbsd openbsd solaris | |
6 | ||
7 | // Socket control messages | |
8 | ||
9 | package unix | |
10 | ||
11 | import "unsafe" | |
12 | ||
13 | // Round the length of a raw sockaddr up to align it properly. | |
14 | func cmsgAlignOf(salen int) int { | |
15 | salign := sizeofPtr | |
16 | // NOTE: It seems like 64-bit Darwin and DragonFly BSD kernels | |
17 | // still require 32-bit aligned access to network subsystem. | |
18 | if darwin64Bit || dragonfly64Bit { | |
19 | salign = 4 | |
20 | } | |
21 | return (salen + salign - 1) & ^(salign - 1) | |
22 | } | |
23 | ||
24 | // CmsgLen returns the value to store in the Len field of the Cmsghdr | |
25 | // structure, taking into account any necessary alignment. | |
26 | func CmsgLen(datalen int) int { | |
27 | return cmsgAlignOf(SizeofCmsghdr) + datalen | |
28 | } | |
29 | ||
30 | // CmsgSpace returns the number of bytes an ancillary element with | |
31 | // payload of the passed data length occupies. | |
32 | func CmsgSpace(datalen int) int { | |
33 | return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen) | |
34 | } | |
35 | ||
36 | func cmsgData(h *Cmsghdr) unsafe.Pointer { | |
37 | return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr))) | |
38 | } | |
39 | ||
40 | // SocketControlMessage represents a socket control message. | |
41 | type SocketControlMessage struct { | |
42 | Header Cmsghdr | |
43 | Data []byte | |
44 | } | |
45 | ||
46 | // ParseSocketControlMessage parses b as an array of socket control | |
47 | // messages. | |
48 | func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) { | |
49 | var msgs []SocketControlMessage | |
50 | i := 0 | |
51 | for i+CmsgLen(0) <= len(b) { | |
52 | h, dbuf, err := socketControlMessageHeaderAndData(b[i:]) | |
53 | if err != nil { | |
54 | return nil, err | |
55 | } | |
56 | m := SocketControlMessage{Header: *h, Data: dbuf} | |
57 | msgs = append(msgs, m) | |
58 | i += cmsgAlignOf(int(h.Len)) | |
59 | } | |
60 | return msgs, nil | |
61 | } | |
62 | ||
63 | func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) { | |
64 | h := (*Cmsghdr)(unsafe.Pointer(&b[0])) | |
65 | if h.Len < SizeofCmsghdr || int(h.Len) > len(b) { | |
66 | return nil, nil, EINVAL | |
67 | } | |
68 | return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil | |
69 | } | |
70 | ||
71 | // UnixRights encodes a set of open file descriptors into a socket | |
72 | // control message for sending to another process. | |
73 | func UnixRights(fds ...int) []byte { | |
74 | datalen := len(fds) * 4 | |
75 | b := make([]byte, CmsgSpace(datalen)) | |
76 | h := (*Cmsghdr)(unsafe.Pointer(&b[0])) | |
77 | h.Level = SOL_SOCKET | |
78 | h.Type = SCM_RIGHTS | |
79 | h.SetLen(CmsgLen(datalen)) | |
80 | data := cmsgData(h) | |
81 | for _, fd := range fds { | |
82 | *(*int32)(data) = int32(fd) | |
83 | data = unsafe.Pointer(uintptr(data) + 4) | |
84 | } | |
85 | return b | |
86 | } | |
87 | ||
88 | // ParseUnixRights decodes a socket control message that contains an | |
89 | // integer array of open file descriptors from another process. | |
90 | func ParseUnixRights(m *SocketControlMessage) ([]int, error) { | |
91 | if m.Header.Level != SOL_SOCKET { | |
92 | return nil, EINVAL | |
93 | } | |
94 | if m.Header.Type != SCM_RIGHTS { | |
95 | return nil, EINVAL | |
96 | } | |
97 | fds := make([]int, len(m.Data)>>2) | |
98 | for i, j := 0, 0; i < len(m.Data); i += 4 { | |
99 | fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i]))) | |
100 | j++ | |
101 | } | |
102 | return fds, nil | |
103 | } |