Source file src/syscall/sockcmsg_unix.go

     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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