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 linux netbsd openbsd solaris
   6
   7 // Socket control messages
   8
   9 package syscall
  10
  11 import (
  12         "runtime"
  13         "unsafe"
  14 )
  15
  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, DragonFly BSD and
  20         // Solaris kernels still require 32-bit aligned access to
  21         // network subsystem.
  22         if darwin64Bit || dragonfly64Bit || solaris64Bit {
  23                 salign = 4
  24         }
  25         // NOTE: Solaris always uses 32-bit alignment,
  26         // cf. _CMSG_DATA_ALIGNMENT in <sys/socket.h>.
  27         if runtime.GOOS == "solaris" {
  28                 salign = 4
  29         }
  30         return (salen + salign - 1) & ^(salign - 1)
  31 }
  32
  33 // CmsgLen returns the value to store in the Len field of the Cmsghdr
  34 // structure, taking into account any necessary alignment.
  35 func CmsgLen(datalen int) int {
  36         return cmsgAlignOf(SizeofCmsghdr) + datalen
  37 }
  38
  39 // CmsgSpace returns the number of bytes an ancillary element with
  40 // payload of the passed data length occupies.
  41 func CmsgSpace(datalen int) int {
  42         return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
  43 }
  44
  45 func cmsgData(h *Cmsghdr) unsafe.Pointer {
  46         return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
  47 }
  48
  49 // SocketControlMessage represents a socket control message.
  50 type SocketControlMessage struct {
  51         Header Cmsghdr
  52         Data   []byte
  53 }
  54
  55 // ParseSocketControlMessage parses b as an array of socket control
  56 // messages.
  57 func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
  58         var msgs []SocketControlMessage
  59         i := 0
  60         for i+CmsgLen(0) <= len(b) {
  61                 h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
  62                 if err != nil {
  63                         return nil, err
  64                 }
  65                 m := SocketControlMessage{Header: *h, Data: dbuf}
  66                 msgs = append(msgs, m)
  67                 i += cmsgAlignOf(int(h.Len))
  68         }
  69         return msgs, nil
  70 }
  71
  72 func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
  73         h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
  74         if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
  75                 return nil, nil, EINVAL
  76         }
  77         return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
  78 }
  79
  80 // UnixRights encodes a set of open file descriptors into a socket
  81 // control message for sending to another process.
  82 func UnixRights(fds ...int) []byte {
  83         datalen := len(fds) * 4
  84         b := make([]byte, CmsgSpace(datalen))
  85         h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
  86         h.Level = SOL_SOCKET
  87         h.Type = SCM_RIGHTS
  88         h.SetLen(CmsgLen(datalen))
  89         data := cmsgData(h)
  90         for _, fd := range fds {
  91                 *(*int32)(data) = int32(fd)
  92                 data = unsafe.Pointer(uintptr(data) + 4)
  93         }
  94         return b
  95 }
  96
  97 // ParseUnixRights decodes a socket control message that contains an
  98 // integer array of open file descriptors from another process.
  99 func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
 100         if m.Header.Level != SOL_SOCKET {
 101                 return nil, EINVAL
 102         }
 103         if m.Header.Type != SCM_RIGHTS {
 104                 return nil, EINVAL
 105         }
 106         fds := make([]int, len(m.Data)>>2)
 107         for i, j := 0, 0; i < len(m.Data); i += 4 {
 108                 fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
 109                 j++
 110         }
 111         return fds, nil
 112 }