libgo/go/syscall/sockcmsg_unix.go

   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 hurd linux netbsd openbsd solaris
   6
   7 // Socket control messages
   8
   9 package syscall
  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 func 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.
  64 func 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.
  79 func 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 }