You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: message.go
    path of file: ./repos/sliver/vendor/github.com/godbus/dbus/v5
    
    the code of the file until where you have to start completion: package dbus

import (
	"bytes"
	"encoding/binary"
	"errors"
	"io"
	"reflect"
	"strconv"
)

const protoVersion byte = 1

// Flags represents the possible flags of a D-Bus message.
type Flags byte

const (
	// FlagNoReplyExpected signals that the message is not expected to generate
	// a reply. If this flag is set on outgoing messages, any possible reply
	// will be discarded.
	FlagNoReplyExpected Flags = 1 << iota
	// FlagNoAutoStart signals that the message bus should not automatically
	// start an application when handling this message.
	FlagNoAutoStart
	// FlagAllowInteractiveAuthorization may be set on a method call
	// message to inform the receiving side that the caller is prepared
	// to wait for interactive authorization, which might take a
	// considerable time to complete. For instance, if this flag is set,
	// it would be appropriate to query the user for passwords or
	// confirmation via Polkit or a similar framework.
	FlagAllowInteractiveAuthorization
)

// Type represents the possible types of a D-Bus message.
type Type byte

const (
	TypeMethodCall Type = 1 + iota
	TypeMethodReply
	TypeError
	TypeSignal
	typeMax
)

func (t Type) String() string {
	switch t {
	case TypeMethodCall:
		return "method call"
	case TypeMethodReply:
		return "reply"
	case TypeError:
		return "error"
	case TypeSignal:
		return "signal"
	}
	return "invalid"
}

// HeaderField represents the possible byte codes for the headers
// of a D-Bus message.
ty
    
func DecodeMessageWithFDs(rd io.Reader, fds []int) (msg *Message, err error) {
	var order binary.ByteOrder
	var hlength, length uint32
	var typ, flags, proto byte
	var headers []header

	b := make([]byte, 1)
	_, err = rd.Read(b)
	if err != nil {
		return
	}
	switch b[0] {
	case 'l':
		order = binary.LittleEndian
	case 'B':
		order = binary.BigEndian
	default:
		return nil, InvalidMessageError("invalid byte order")
	}

	dec := newDecoder(rd, order, fds)
	dec.pos = 1

	msg = new(Message)
	vs, err := dec.Decode(Signature{"yyyuu"})
	if err != nil {
		return nil, err
	}
	if err = Store(vs, &typ, &flags, &proto, &length, &msg.serial); err != nil {
		return nil, err
	}
	msg.Type = Type(typ)
	msg.Flags = Flags(flags)

	// get the header length separately because we need it later
	b = make([]byte, 4)
	_, err = io.ReadFull(rd, b)
	if err != nil {
		return nil, err
	}
	if err := binary.Read(bytes.NewBuffer(b), order, &hlength); err != nil {
		return nil, err
	}
	if hlength+length+16 > 1<<27 {
		return nil, InvalidMessageError("message is too long")
	}
	dec = newDecoder(io.MultiReader(bytes.NewBuffer(b), rd), order, fds)
	dec.pos = 12
	vs, err = dec.Decode(Signature{"a(yv)"})
	if err != nil {
		return nil, err
	}
	if err = Store(vs, &headers); err != nil {
		return nil, err
	}

	msg.Headers = make(map[HeaderField]Variant)
	for _, v := range headers {
		msg.Headers[HeaderField(v.Field)] = v.Variant
	}

	dec.align(8)
	body := make([]byte, int(length))
	if length != 0 {
		_, err := io.ReadFull(rd, body)
		if err != nil {
			return nil, err
		}
	}

	if err = msg.validateHeader(); err != nil {
		return nil, err
	}
	sig, _ := msg.Headers[FieldSignature].value.(Signature)
	if sig.str != "" {
		buf := bytes.NewBuffer(body)
		dec = newDecoder(buf, order, fds)
		vs, err := dec.Decode(sig)
		if err != nil {
			return nil, err
		}
		msg.Body = vs
	}

	return
}