sockcmsg_unix.go

Documentation: golang.org/x/sys/unix

     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  //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
     6  // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris zos
     7  
     8  // Socket control messages
     9  
    10  package unix
    11  
    12  import (
    13  	"unsafe"
    14  )
    15  
    16  // CmsgLen returns the value to store in the Len field of the Cmsghdr
    17  // structure, taking into account any necessary alignment.
    18  func CmsgLen(datalen int) int {
    19  	return cmsgAlignOf(SizeofCmsghdr) + datalen
    20  }
    21  
    22  // CmsgSpace returns the number of bytes an ancillary element with
    23  // payload of the passed data length occupies.
    24  func CmsgSpace(datalen int) int {
    25  	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
    26  }
    27  
    28  func (h *Cmsghdr) data(offset uintptr) unsafe.Pointer {
    29  	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)) + offset)
    30  }
    31  
    32  // SocketControlMessage represents a socket control message.
    33  type SocketControlMessage struct {
    34  	Header Cmsghdr
    35  	Data   []byte
    36  }
    37  
    38  // ParseSocketControlMessage parses b as an array of socket control
    39  // messages.
    40  func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
    41  	var msgs []SocketControlMessage
    42  	i := 0
    43  	for i+CmsgLen(0) <= len(b) {
    44  		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
    45  		if err != nil {
    46  			return nil, err
    47  		}
    48  		m := SocketControlMessage{Header: *h, Data: dbuf}
    49  		msgs = append(msgs, m)
    50  		i += cmsgAlignOf(int(h.Len))
    51  	}
    52  	return msgs, nil
    53  }
    54  
    55  // ParseOneSocketControlMessage parses a single socket control message from b, returning the message header,
    56  // message data (a slice of b), and the remainder of b after that single message.
    57  // When there are no remaining messages, len(remainder) == 0.
    58  func ParseOneSocketControlMessage(b []byte) (hdr Cmsghdr, data []byte, remainder []byte, err error) {
    59  	h, dbuf, err := socketControlMessageHeaderAndData(b)
    60  	if err != nil {
    61  		return Cmsghdr{}, nil, nil, err
    62  	}
    63  	if i := cmsgAlignOf(int(h.Len)); i < len(b) {
    64  		remainder = b[i:]
    65  	}
    66  	return *h, dbuf, remainder, nil
    67  }
    68  
    69  func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
    70  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    71  	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
    72  		return nil, nil, EINVAL
    73  	}
    74  	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
    75  }
    76  
    77  // UnixRights encodes a set of open file descriptors into a socket
    78  // control message for sending to another process.
    79  func UnixRights(fds ...int) []byte {
    80  	datalen := len(fds) * 4
    81  	b := make([]byte, CmsgSpace(datalen))
    82  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    83  	h.Level = SOL_SOCKET
    84  	h.Type = SCM_RIGHTS
    85  	h.SetLen(CmsgLen(datalen))
    86  	for i, fd := range fds {
    87  		*(*int32)(h.data(4 * uintptr(i))) = int32(fd)
    88  	}
    89  	return b
    90  }
    91  
    92  // ParseUnixRights decodes a socket control message that contains an
    93  // integer array of open file descriptors from another process.
    94  func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
    95  	if m.Header.Level != SOL_SOCKET {
    96  		return nil, EINVAL
    97  	}
    98  	if m.Header.Type != SCM_RIGHTS {
    99  		return nil, EINVAL
   100  	}
   101  	fds := make([]int, len(m.Data)>>2)
   102  	for i, j := 0, 0; i < len(m.Data); i += 4 {
   103  		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
   104  		j++
   105  	}
   106  	return fds, nil
   107  }
   108
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