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
 10package unix
 11
 12import (
 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.
 18func 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.
 24func CmsgSpace(datalen int) int {
 25	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
 26}
 27
 28func (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.
 33type SocketControlMessage struct {
 34	Header Cmsghdr
 35	Data   []byte
 36}
 37
 38// ParseSocketControlMessage parses b as an array of socket control
 39// messages.
 40func 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.
 58func 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
 69func 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.
 79func 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.
 94func 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}