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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 darwin dragonfly freebsd linux netbsd openbsd solaris
     6	
     7	// Socket control messages
     8	
     9	package syscall
    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, DragonFly BSD and
    17		// Solaris kernels still require 32-bit aligned access to
    18		// network subsystem.
    19		if darwin64Bit || dragonfly64Bit || solaris64Bit {
    20			salign = 4
    21		}
    22		return (salen + salign - 1) & ^(salign - 1)
    23	}
    24	
    25	// CmsgLen returns the value to store in the Len field of the Cmsghdr
    26	// structure, taking into account any necessary alignment.
    27	func CmsgLen(datalen int) int {
    28		return cmsgAlignOf(SizeofCmsghdr) + datalen
    29	}
    30	
    31	// CmsgSpace returns the number of bytes an ancillary element with
    32	// payload of the passed data length occupies.
    33	func CmsgSpace(datalen int) int {
    34		return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
    35	}
    36	
    37	func cmsgData(h *Cmsghdr) unsafe.Pointer {
    38		return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
    39	}
    40	
    41	// SocketControlMessage represents a socket control message.
    42	type SocketControlMessage struct {
    43		Header Cmsghdr
    44		Data   []byte
    45	}
    46	
    47	// ParseSocketControlMessage parses b as an array of socket control
    48	// messages.
    49	func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
    50		var msgs []SocketControlMessage
    51		i := 0
    52		for i+CmsgLen(0) <= len(b) {
    53			h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
    54			if err != nil {
    55				return nil, err
    56			}
    57			m := SocketControlMessage{Header: *h, Data: dbuf}
    58			msgs = append(msgs, m)
    59			i += cmsgAlignOf(int(h.Len))
    60		}
    61		return msgs, nil
    62	}
    63	
    64	func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
    65		h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    66		if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
    67			return nil, nil, EINVAL
    68		}
    69		return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
    70	}
    71	
    72	// UnixRights encodes a set of open file descriptors into a socket
    73	// control message for sending to another process.
    74	func UnixRights(fds ...int) []byte {
    75		datalen := len(fds) * 4
    76		b := make([]byte, CmsgSpace(datalen))
    77		h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
    78		h.Level = SOL_SOCKET
    79		h.Type = SCM_RIGHTS
    80		h.SetLen(CmsgLen(datalen))
    81		data := cmsgData(h)
    82		for _, fd := range fds {
    83			*(*int32)(data) = int32(fd)
    84			data = unsafe.Pointer(uintptr(data) + 4)
    85		}
    86		return b
    87	}
    88	
    89	// ParseUnixRights decodes a socket control message that contains an
    90	// integer array of open file descriptors from another process.
    91	func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
    92		if m.Header.Level != SOL_SOCKET {
    93			return nil, EINVAL
    94		}
    95		if m.Header.Type != SCM_RIGHTS {
    96			return nil, EINVAL
    97		}
    98		fds := make([]int, len(m.Data)>>2)
    99		for i, j := 0, 0; i < len(m.Data); i += 4 {
   100			fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
   101			j++
   102		}
   103		return fds, nil
   104	}
   105	

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