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