// Copyright 2011 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

// Socket control messages

package unix

import (

	"unsafe"

)

// CmsgLen returns the value to store in the Len field of the Cmsghdr

// structure, taking into account any necessary alignment.

func CmsgLen(datalen int) int {

	return cmsgAlignOf(SizeofCmsghdr) + datalen

}

// CmsgSpace returns the number of bytes an ancillary element with

// payload of the passed data length occupies.

func CmsgSpace(datalen int) int {

	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)

}

func (h *Cmsghdr) data(offset uintptr) unsafe.Pointer {

	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)) + offset)

}

// SocketControlMessage represents a socket control message.

type SocketControlMessage struct {

	Header Cmsghdr

	Data   []byte

}

// ParseSocketControlMessage parses b as an array of socket control

// messages.

func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {

	var msgs []SocketControlMessage

	i := 0

	for i+CmsgLen(0) <= len(b) {

		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])

		if err != nil {

			return nil, err

		}

		m := SocketControlMessage{Header: *h, Data: dbuf}

		msgs = append(msgs, m)

		i += cmsgAlignOf(int(h.Len))

	}

	return msgs, nil

}

func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {

	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))

	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {

		return nil, nil, EINVAL

	}

	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil

}

// UnixRights encodes a set of open file descriptors into a socket

// control message for sending to another process.

func UnixRights(fds ...int) []byte {

	datalen := len(fds) * 4

	b := make([]byte, CmsgSpace(datalen))

	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))

	h.Level = SOL_SOCKET

	h.Type = SCM_RIGHTS

	h.SetLen(CmsgLen(datalen))

	for i, fd := range fds {

		*(*int32)(h.data(4 * uintptr(i))) = int32(fd)

	}

	return b

}

// ParseUnixRights decodes a socket control message that contains an

// integer array of open file descriptors from another process.

func ParseUnixRights(m *SocketControlMessage) ([]int, error) {

	if m.Header.Level != SOL_SOCKET {

		return nil, EINVAL

	}

	if m.Header.Type != SCM_RIGHTS {

		return nil, EINVAL

	}

	fds := make([]int, len(m.Data)>>2)

	for i, j := 0, 0; i < len(m.Data); i += 4 {

		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))

		j++

	}

	return fds, nil

}