Source file src/syscall/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 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 := sizeofPtr
    19  
    20  	switch runtime.GOOS {
    21  	case "aix":
    22  		// There is no alignment on AIX.
    23  		salign = 1
    24  	case "darwin", "dragonfly", "illumos", "solaris":
    25  		// NOTE: It seems like 64-bit Darwin, DragonFly BSD and
    26  		// Solaris kernels still require 32-bit aligned access to
    27  		// network subsystem.
    28  		if sizeofPtr == 8 {
    29  			salign = 4
    30  		}
    31  	case "netbsd", "openbsd":
    32  		// NetBSD and OpenBSD armv7 require 64-bit alignment.
    33  		if runtime.GOARCH == "arm" {
    34  			salign = 8
    35  		}
    36  	}
    37  
    38  	return (salen + salign - 1) & ^(salign - 1)
    39  }
    40  
    41  // CmsgLen returns the value to store in the Len field of the Cmsghdr
    42  // structure, taking into account any necessary alignment.
    43  func CmsgLen(datalen int) int {
    44  	return cmsgAlignOf(SizeofCmsghdr) + datalen
    45  }
    46  
    47  // CmsgSpace returns the number of bytes an ancillary element with
    48  // payload of the passed data length occupies.
    49  func CmsgSpace(datalen int) int {
    50  	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
    51  }
    52  
    53  func cmsgData(h *Cmsghdr) unsafe.Pointer {
    54  	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
    55  }
    56  
    57  // SocketControlMessage represents a socket control message.
    58  type SocketControlMessage struct {
    59  	Header Cmsghdr
    60  	Data   []byte
    61  }
    62  
    63  // ParseSocketControlMessage parses b as an array of socket control
    64  // messages.
    65  func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
    66  	var msgs []SocketControlMessage
    67  	i := 0
    68  	for i+CmsgLen(0) <= len(b) {
    69  		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
    70  		if err != nil {
    71  			return nil, err
    72  		}
    73  		m := SocketControlMessage{Header: *h, Data: dbuf}
    74  		msgs = append(msgs, m)
    75  		i += cmsgAlignOf(int(h.Len))
    76  	}
    77  	return msgs, nil
    78  }
    79  
    80  func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
    81  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    82  	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
    83  		return nil, nil, EINVAL
    84  	}
    85  	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
    86  }
    87  
    88  // UnixRights encodes a set of open file descriptors into a socket
    89  // control message for sending to another process.
    90  func UnixRights(fds ...int) []byte {
    91  	datalen := len(fds) * 4
    92  	b := make([]byte, CmsgSpace(datalen))
    93  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    94  	h.Level = SOL_SOCKET
    95  	h.Type = SCM_RIGHTS
    96  	h.SetLen(CmsgLen(datalen))
    97  	data := cmsgData(h)
    98  	for _, fd := range fds {
    99  		*(*int32)(data) = int32(fd)
   100  		data = unsafe.Pointer(uintptr(data) + 4)
   101  	}
   102  	return b
   103  }
   104  
   105  // ParseUnixRights decodes a socket control message that contains an
   106  // integer array of open file descriptors from another process.
   107  func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
   108  	if m.Header.Level != SOL_SOCKET {
   109  		return nil, EINVAL
   110  	}
   111  	if m.Header.Type != SCM_RIGHTS {
   112  		return nil, EINVAL
   113  	}
   114  	fds := make([]int, len(m.Data)>>2)
   115  	for i, j := 0, 0; i < len(m.Data); i += 4 {
   116  		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
   117  		j++
   118  	}
   119  	return fds, nil
   120  }
   121  

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