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