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 "darwin", "dragonfly", "solaris":
    22  		// NOTE: It seems like 64-bit Darwin, DragonFly BSD and
    23  		// Solaris kernels still require 32-bit aligned access to
    24  		// network subsystem.
    25  		if sizeofPtr == 8 {
    26  			salign = 4
    27  		}
    28  	case "openbsd":
    29  		// OpenBSD armv7 requires 64-bit alignment.
    30  		if runtime.GOARCH == "arm" {
    31  			salign = 8
    32  		}
    33  	}
    34  
    35  	return (salen + salign - 1) & ^(salign - 1)
    36  }
    37  
    38  // CmsgLen returns the value to store in the Len field of the Cmsghdr
    39  // structure, taking into account any necessary alignment.
    40  func CmsgLen(datalen int) int {
    41  	return cmsgAlignOf(SizeofCmsghdr) + datalen
    42  }
    43  
    44  // CmsgSpace returns the number of bytes an ancillary element with
    45  // payload of the passed data length occupies.
    46  func CmsgSpace(datalen int) int {
    47  	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
    48  }
    49  
    50  func cmsgData(h *Cmsghdr) unsafe.Pointer {
    51  	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
    52  }
    53  
    54  // SocketControlMessage represents a socket control message.
    55  type SocketControlMessage struct {
    56  	Header Cmsghdr
    57  	Data   []byte
    58  }
    59  
    60  // ParseSocketControlMessage parses b as an array of socket control
    61  // messages.
    62  func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
    63  	var msgs []SocketControlMessage
    64  	i := 0
    65  	for i+CmsgLen(0) <= len(b) {
    66  		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
    67  		if err != nil {
    68  			return nil, err
    69  		}
    70  		m := SocketControlMessage{Header: *h, Data: dbuf}
    71  		msgs = append(msgs, m)
    72  		i += cmsgAlignOf(int(h.Len))
    73  	}
    74  	return msgs, nil
    75  }
    76  
    77  func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
    78  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    79  	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
    80  		return nil, nil, EINVAL
    81  	}
    82  	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
    83  }
    84  
    85  // UnixRights encodes a set of open file descriptors into a socket
    86  // control message for sending to another process.
    87  func UnixRights(fds ...int) []byte {
    88  	datalen := len(fds) * 4
    89  	b := make([]byte, CmsgSpace(datalen))
    90  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    91  	h.Level = SOL_SOCKET
    92  	h.Type = SCM_RIGHTS
    93  	h.SetLen(CmsgLen(datalen))
    94  	data := cmsgData(h)
    95  	for _, fd := range fds {
    96  		*(*int32)(data) = int32(fd)
    97  		data = unsafe.Pointer(uintptr(data) + 4)
    98  	}
    99  	return b
   100  }
   101  
   102  // ParseUnixRights decodes a socket control message that contains an
   103  // integer array of open file descriptors from another process.
   104  func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
   105  	if m.Header.Level != SOL_SOCKET {
   106  		return nil, EINVAL
   107  	}
   108  	if m.Header.Type != SCM_RIGHTS {
   109  		return nil, EINVAL
   110  	}
   111  	fds := make([]int, len(m.Data)>>2)
   112  	for i, j := 0, 0; i < len(m.Data); i += 4 {
   113  		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
   114  		j++
   115  	}
   116  	return fds, nil
   117  }
   118  

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