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