sockcmsg_unix.go

Documentation: syscall

     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
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