github.com/jgarto/itcv@v0.0.0-20180826224514-4eea09c1aa0d/_vendor/src/golang.org/x/sys/unix/sockcmsg_unix.go (about)

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