vom/decoder.go

// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package vom

import (
	"io"
	"os"
	"reflect"

	"v.io/v23/vdl"
	"v.io/v23/verror"
)

var (
	errDecodeNil                = verror.Register(pkgPath+".errDecodeNil", verror.NoRetry, "{1:}{2:} vom: invalid decode into nil interface{}{:_}")
	errDecodeZeroTypeID         = verror.Register(pkgPath+".errDecodeZeroTypeID", verror.NoRetry, "{1:}{2:} vom: zero type id{:_}")
	errIndexOutOfRange          = verror.Register(pkgPath+".errIndexOutOfRange", verror.NoRetry, "{1:}{2:} vom: index out of range{:_}")
	errLeftOverBytes            = verror.Register(pkgPath+".errLeftOverBytes", verror.NoRetry, "{1:}{2:} vom: {3} leftover bytes{:_}")
	errUnexpectedControlByte    = verror.Register(pkgPath+".errUnexpectedControlByte", verror.NoRetry, "{1:}{2:} vom: unexpected control byte {3}{:_}")
	errDecodeValueUnhandledType = verror.Register(pkgPath+".errDecodeValueUnhandledType", verror.NoRetry, "{1:}{2:} vom: decodeValue unhandled type {3}{:_}")
	errIgnoreValueUnhandledType = verror.Register(pkgPath+".errIgnoreValueUnhandledType", verror.NoRetry, "{1:}{2:} vom: ignoreValue unhandled type {3}{:_}")
	errInvalidTypeIdIndex       = verror.Register(pkgPath+".errInvalidTypeIdIndex", verror.NoRetry, "{1:}{2:} vom: value referenced invalid index into type id table {:_}")
	errInvalidAnyIndex          = verror.Register(pkgPath+".errInvalidAnyIndex", verror.NoRetry, "{1:}{2:} vom: value referenced invalid index into anyLen table {:_}")
)

// ZDecoder manages the receipt and unmarshalling of typed values from the other
// side of a connection.
type ZDecoder struct {
	typeDec *TypeDecoder

	hasSeparateTypeDec bool // TODO(bprosnitz) This should probably be removed.

	// Stream data:
	buf *decbuf

	// Message data:
	typeIncomplete bool // Type message was flagged as having dependencies on unsent types.
	refTypes       referencedTypes
	refAnyLens     referencedAnyLens
}

// This is only used for debugging; add this as the first line of NewDecoder to
// dump formatted vom bytes to stdout:
//   r = teeDump(r)
func teeDump(r io.Reader) io.Reader {
	return io.TeeReader(r, NewDumper(NewDumpWriter(os.Stdout)))
}

// NewZDecoder returns a new ZDecoder that reads from the given reader. The
// ZDecoder understands all formats generated by the Encoder.
func NewZDecoder(r io.Reader) *ZDecoder {
	// When the TypeDecoder isn't shared, we always decode type messages in
	// Decoder.decodeValueType() and feed them to the TypeDecoder. That is,
	// the TypeDecoder will never read messages from the buffer. So we pass
	// a nil buffer to newTypeDecoder.
	buf := newDecbuf(r)
	typeDec := newTypeDecoderInternal(buf)
	return &ZDecoder{
		buf:                buf,
		typeDec:            typeDec,
		hasSeparateTypeDec: false,
	}
}

// NewZDecoderWithTypeDecoder returns a new Decoder that reads from the given
// reader. Types will be decoded separately through the given typeDec.
func NewZDecoderWithTypeDecoder(r io.Reader, typeDec *TypeDecoder) *ZDecoder {
	return &ZDecoder{
		buf:                newDecbuf(r),
		typeDec:            typeDec,
		hasSeparateTypeDec: true,
	}
}

// Decode reads the next value from the reader(s) and stores it in value v.
// The type of v need not exactly match the type of the originally encoded
// value; decoding succeeds as long as the values are compatible.
//
//   Types that are special-cased, only for v:
//     *RawBytes  - Store raw (uninterpreted) bytes in v.
//
//   Types that are special-cased, recursively throughout v:
//     *vdl.Value    - Decode into v.
//     reflect.Value - Decode into v, which must be settable.
//
// Decoding into a RawBytes captures the value in a raw form, which may be
// subsequently passed to an Encoder for transcoding.
//
// Decode(nil) always returns an error.  Use Ignore() to ignore the next value.
func (d *ZDecoder) Decode(v interface{}) error {
	if v == nil {
		return verror.New(errDecodeNil, nil)
	}
	target, err := vdl.ReflectTarget(reflect.ValueOf(v))
	if err != nil {
		return err
	}
	return d.decodeToTarget(target)
}

func (d *ZDecoder) decodeTypeDefs() error {
	if !d.hasSeparateTypeDec {
		for {
			typeNext, err := d.typeIsNext()
			if err != nil {
				return err
			}
			if !typeNext {
				break
			}
			if err := d.typeDec.readSingleType(); err != nil {
				return err
			}
		}
	}
	return nil
}

func (d *ZDecoder) decodeToTarget(target vdl.Target) error {
	if err := d.decodeTypeDefs(); err != nil {
		return err
	}
	tid, err := d.nextMessage()
	if err != nil {
		return err
	}
	valType, err := d.typeDec.lookupType(tid)
	if err != nil {
		return err
	}
	if hax, ok := target.(hasRvHack); ok {
		rv := hax.HackGetRv()
		valLen, err := d.peekValueByteLen(valType)
		if err != nil {
			return err
		}
		if isRawBytes, err := d.tryDecodeRaw(valType, valLen, rv); err != nil {
			return err
		} else if isRawBytes {
			return d.endMessage()
		}
	}
	if err := d.decodeValue(valType, target); err != nil {
		return err
	}
	return d.endMessage()
}

// Ignore ignores the next value from the reader.
func (d *ZDecoder) Ignore() error {
	if err := d.decodeTypeDefs(); err != nil {
		return err
	}
	tid, err := d.nextMessage()
	if err != nil {
		return err
	}
	valType, err := d.typeDec.lookupType(tid)
	if err != nil {
		return err
	}
	valLen, err := d.peekValueByteLen(valType)
	if err != nil {
		return err
	}

	if err := d.buf.Skip(valLen); err != nil {
		return err
	}
	return d.endMessage()
}

// decodeWireType decodes the next type definition message and returns its
// type id.
func (d *ZDecoder) decodeWireType(wt *wireType) (TypeId, error) {
	tid, err := d.nextMessage()
	if err != nil {
		return 0, err
	}
	// Decode the wire type like a regular value.
	target, err := vdl.ReflectTarget(reflect.ValueOf(wt))
	if err != nil {
		return 0, err
	}
	if err := d.decodeValue(wireTypeType, target); err != nil {
		return 0, err
	}
	return tid, d.endMessage()
}

// peekValueByteLen returns the byte length of the next value.
func (d *ZDecoder) peekValueByteLen(tt *vdl.Type) (int, error) {
	if hasChunkLen(tt) {
		// Use the explicit message length.
		return d.buf.lim, nil
	}
	// No explicit message length, but the length can be computed.
	switch {
	case tt.Kind() == vdl.Byte:
		if d.buf.version == Version80 {
			return 1, nil
		} else {
			return binaryPeekUintByteLen(d.buf)
		}
	case tt.Kind() == vdl.Array && tt.IsBytes():
		// Byte arrays are exactly their length and encoded with 1-byte header.
		return tt.Len() + 1, nil
	case tt.Kind() == vdl.String || tt.IsBytes():
		// Strings and byte lists are encoded with a length header.
		strlen, bytelen, err := binaryPeekUint(d.buf)
		switch {
		case err != nil:
			return 0, err
		case strlen > maxBinaryMsgLen:
			return 0, verror.New(errMsgLen, nil)
		}
		return int(strlen) + bytelen, nil
	default:
		// Must be a primitive, which is encoded as an underlying uint.
		return binaryPeekUintByteLen(d.buf)
	}
}

func (d *ZDecoder) decodeRaw(tt *vdl.Type, valLen int, raw *RawBytes) error {
	raw.Version = d.buf.version
	raw.Type = tt
	raw.Data = make([]byte, valLen)
	if err := d.buf.ReadIntoBuf(raw.Data); err != nil {
		return err
	}
	refTypeLen := len(d.refTypes.tids)
	if cap(raw.RefTypes) >= refTypeLen {
		raw.RefTypes = raw.RefTypes[:refTypeLen]
	} else {
		raw.RefTypes = make([]*vdl.Type, refTypeLen)
	}
	for i, tid := range d.refTypes.tids {
		var err error
		if raw.RefTypes[i], err = d.typeDec.lookupType(tid); err != nil {
			return err
		}
	}
	raw.AnyLengths = d.refAnyLens.lens
	return nil
}

type hasRvHack interface {
	HackGetRv() reflect.Value
}

func (d *ZDecoder) tryDecodeRaw(tt *vdl.Type, valLen int, rv reflect.Value) (isRawBytes bool, _ error) {
	// Dereference pointers down to at most one remaining *.
	for rv.IsValid() && rv.Kind() == reflect.Ptr && rv.Elem().IsValid() && rv.Elem().Kind() == reflect.Ptr {
		rv = rv.Elem()
	}
	if rv.IsValid() && rv.Type() == rtPtrToRawBytes {
		rb := rv.Interface().(*RawBytes)
		if rb == nil {
			rb = new(RawBytes)
			rv.Set(reflect.ValueOf(rb))
		}
		return true, d.decodeRaw(tt, valLen, rb)
	}
	if rv.IsValid() && rv.Type() == rtRawBytes {
		rb := rv.Addr().Interface().(*RawBytes)
		if err := d.decodeRaw(tt, valLen, rb); err != nil {
			return true, err
		}
		return true, nil
	}
	return false, nil
}

// decodeValue decodes the rest of the message assuming type tt.
func (d *ZDecoder) decodeValue(tt *vdl.Type, target vdl.Target) error {
	ttFrom := tt
	if tt.Kind() == vdl.Optional {
		// If the type is optional, we expect to see either WireCtrlNil or the actual
		// value, but not both.  And thus, we can just peek for the WireCtrlNil here.
		switch ctrl, err := binaryPeekControl(d.buf); {
		case err != nil:
			return err
		case ctrl == WireCtrlNil:
			d.buf.Skip(1)
			return target.FromNil(ttFrom)
		}
		tt = tt.Elem()
	}
	if tt.IsBytes() {
		len, err := binaryDecodeLenOrArrayLen(d.buf, tt)
		if err != nil {
			return err
		}
		// TODO(toddw): remove allocation
		buf := make([]byte, len)
		if err := d.buf.ReadIntoBuf(buf); err != nil {
			return err
		}
		return target.FromBytes(buf, ttFrom)
	}
	switch kind := tt.Kind(); kind {
	case vdl.Bool:
		v, err := binaryDecodeBool(d.buf)
		if err != nil {
			return err
		}
		return target.FromBool(v, ttFrom)
	case vdl.Byte, vdl.Uint16, vdl.Uint32, vdl.Uint64:
		var v uint64
		if tt.Kind() == vdl.Byte && d.buf.version == Version80 {
			b, err := d.buf.ReadByte()
			if err != nil {
				return err
			}
			v = uint64(b)
		} else {
			var err error
			v, err = binaryDecodeUint(d.buf)
			if err != nil {
				return err
			}
		}
		return target.FromUint(v, ttFrom)
	case vdl.Int8, vdl.Int16, vdl.Int32, vdl.Int64:
		if d.buf.version == Version80 && tt.Kind() == vdl.Int8 {
			return verror.New(errUnsupportedInVOMVersion, nil, "int8", d.buf.version)
		}
		v, err := binaryDecodeInt(d.buf)
		if err != nil {
			return err
		}
		return target.FromInt(v, ttFrom)
	case vdl.Float32, vdl.Float64:
		v, err := binaryDecodeFloat(d.buf)
		if err != nil {
			return err
		}
		return target.FromFloat(v, ttFrom)
	case vdl.String:
		v, err := binaryDecodeString(d.buf)
		if err != nil {
			return err
		}
		return target.FromString(v, ttFrom)
	case vdl.Enum:
		index, err := binaryDecodeUint(d.buf)
		switch {
		case err != nil:
			return err
		case index >= uint64(tt.NumEnumLabel()):
			return verror.New(errIndexOutOfRange, nil)
		}
		return target.FromEnumLabel(tt.EnumLabel(int(index)), ttFrom)
	case vdl.TypeObject:
		x, err := binaryDecodeUint(d.buf)
		if err != nil {
			return err
		}
		var tid TypeId
		if d.buf.version == Version80 {
			tid = TypeId(x)
		} else {
			tid, err = d.refTypes.ReferencedTypeId(x)
			if err != nil {
				return err
			}
		}
		typeobject, err := d.typeDec.lookupType(tid)
		if err != nil {
			return err
		}
		return target.FromTypeObject(typeobject)
	case vdl.Array, vdl.List:
		len, err := binaryDecodeLenOrArrayLen(d.buf, tt)
		if err != nil {
			return err
		}
		listTarget, err := target.StartList(ttFrom, len)
		if err != nil {
			return err
		}
		for ix := 0; ix < len; ix++ {
			elem, err := listTarget.StartElem(ix)
			if err != nil {
				return err
			}
			if err := d.decodeValue(tt.Elem(), elem); err != nil {
				return err
			}
			if err := listTarget.FinishElem(elem); err != nil {
				return err
			}
		}
		return target.FinishList(listTarget)
	case vdl.Set:
		len, err := binaryDecodeLen(d.buf)
		if err != nil {
			return err
		}
		setTarget, err := target.StartSet(ttFrom, len)
		if err != nil {
			return err
		}
		for ix := 0; ix < len; ix++ {
			key, err := setTarget.StartKey()
			if err != nil {
				return err
			}
			if err := d.decodeValue(tt.Key(), key); err != nil {
				return err
			}
			switch err := setTarget.FinishKey(key); {
			case err == vdl.ErrFieldNoExist:
				continue
			case err != nil:
				return err
			}
		}
		return target.FinishSet(setTarget)
	case vdl.Map:
		len, err := binaryDecodeLen(d.buf)
		if err != nil {
			return err
		}
		mapTarget, err := target.StartMap(ttFrom, len)
		if err != nil {
			return err
		}
		for ix := 0; ix < len; ix++ {
			key, err := mapTarget.StartKey()
			if err != nil {
				return err
			}
			if err := d.decodeValue(tt.Key(), key); err != nil {
				return err
			}
			switch field, err := mapTarget.FinishKeyStartField(key); {
			case err == vdl.ErrFieldNoExist:
				if err := d.ignoreValue(tt.Elem()); err != nil {
					return err
				}
			case err != nil:
				return err
			default:
				if err := d.decodeValue(tt.Elem(), field); err != nil {
					return err
				}
				if err := mapTarget.FinishField(key, field); err != nil {
					return err
				}
			}
		}
		return target.FinishMap(mapTarget)
	case vdl.Struct:
		fieldsTarget, err := target.StartFields(ttFrom)
		if err != nil {
			return err
		}
		// Loop through decoding the 0-based field index and corresponding field.
		decodedFields := make([]bool, tt.NumField())
		for {
			index, ctrl, err := binaryDecodeUintWithControl(d.buf)
			switch {
			case err != nil:
				return err
			case ctrl == WireCtrlEnd:
				// Fill not-yet-decoded fields with their zero values.
				for index, decoded := range decodedFields {
					if decoded {
						continue
					}
					ttfield := tt.Field(index)
					switch err := fieldsTarget.ZeroField(ttfield.Name); {
					case err == vdl.ErrFieldNoExist:
						// Ignore it.
					case err != nil:
						return err

					}
				}
				return target.FinishFields(fieldsTarget)
			case ctrl != 0:
				return verror.New(errUnexpectedControlByte, nil, ctrl)
			case index >= uint64(tt.NumField()):
				return verror.New(errIndexOutOfRange, nil)
			}
			ttfield := tt.Field(int(index))
			switch key, field, err := fieldsTarget.StartField(ttfield.Name); {
			case err == vdl.ErrFieldNoExist:
				if err := d.ignoreValue(ttfield.Type); err != nil {
					return err
				}
			case err != nil:
				return err
			default:
				if err := d.decodeValue(ttfield.Type, field); err != nil {
					return err
				}
				if err := fieldsTarget.FinishField(key, field); err != nil {
					return err
				}
			}
			decodedFields[index] = true
		}
	case vdl.Union:
		fieldsTarget, err := target.StartFields(ttFrom)
		if err != nil {
			return err
		}
		index, err := binaryDecodeUint(d.buf)
		switch {
		case err != nil:
			return err
		case index >= uint64(tt.NumField()):
			return verror.New(errIndexOutOfRange, nil)
		}
		ttfield := tt.Field(int(index))
		key, field, err := fieldsTarget.StartField(ttfield.Name)
		if err != nil {
			return err
		}
		if err := d.decodeValue(ttfield.Type, field); err != nil {
			return err
		}
		if err := fieldsTarget.FinishField(key, field); err != nil {
			return err
		}
		return target.FinishFields(fieldsTarget)
	case vdl.Any:
		elemType, valLen, err := d.readAnyHeader()
		if err != nil {
			return err
		}
		if elemType == nil {
			return target.FromNil(tt)
		}
		if hax, ok := target.(hasRvHack); ok {
			rv := hax.HackGetRv()
			if isRawBytes, err := d.tryDecodeRaw(elemType, valLen, rv); isRawBytes {
				return err
			}
		}
		return d.decodeValue(elemType, target)
	default:
		panic(verror.New(errDecodeValueUnhandledType, nil, tt))
	}
}

func (d *ZDecoder) readAnyHeader() (*vdl.Type, int, error) {
	// Read either WireCtrlNil or the index of the referenced type id.
	typeIndex, ctrl, err := binaryDecodeUintWithControl(d.buf)
	switch {
	case err != nil:
		return nil, 0, err
	case ctrl == WireCtrlNil:
		return nil, 0, nil // nil any
	case ctrl != 0:
		return nil, 0, verror.New(errUnexpectedControlByte, nil, ctrl)
	}
	var tid TypeId
	if d.buf.version == Version80 {
		tid = TypeId(typeIndex)
	} else if tid, err = d.refTypes.ReferencedTypeId(typeIndex); err != nil {
		return nil, 0, err
	}
	// Look up the referenced type id.
	ttElem, err := d.typeDec.lookupType(tid)
	if err != nil {
		return nil, 0, err
	}
	var anyLen int
	if d.buf.version != Version80 {
		// Read and lookup the index of the any byte length.  Reference the any len,
		// even if it isn't used, to report missing references.
		lenIndex, err := binaryDecodeUint(d.buf)
		if err != nil {
			return nil, 0, err
		}
		if anyLen, err = d.refAnyLens.ReferencedAnyLen(lenIndex); err != nil {
			return nil, 0, err
		}
	}
	return ttElem, anyLen, nil
}

// ignoreValue ignores the rest of the value of type t. This is used to ignore
// unknown struct fields.
func (d *ZDecoder) ignoreValue(tt *vdl.Type) error {
	// TODO(toddw): How about ignoring optional values?
	if tt.IsBytes() {
		len, err := binaryDecodeLenOrArrayLen(d.buf, tt)
		if err != nil {
			return err
		}
		return d.buf.Skip(len)
	}
	switch kind := tt.Kind(); kind {
	case vdl.Bool:
		return d.buf.Skip(1)
	case vdl.Byte:
		if d.buf.version == Version80 {
			return d.buf.Skip(1)
		} else {
			return binaryIgnoreUint(d.buf)
		}
	case vdl.Uint16, vdl.Uint32, vdl.Uint64, vdl.Int8, vdl.Int16, vdl.Int32, vdl.Int64, vdl.Float32, vdl.Float64, vdl.Enum, vdl.TypeObject:
		if d.buf.version == Version80 && tt.Kind() == vdl.Int8 {
			return verror.New(errUnsupportedInVOMVersion, nil, "int8", d.buf.version)
		}
		// The underlying encoding of all these types is based on uint.
		return binaryIgnoreUint(d.buf)
	case vdl.String:
		return binaryIgnoreString(d.buf)
	case vdl.Array, vdl.List, vdl.Set, vdl.Map:
		len, err := binaryDecodeLenOrArrayLen(d.buf, tt)
		if err != nil {
			return err
		}
		for ix := 0; ix < len; ix++ {
			if kind == vdl.Set || kind == vdl.Map {
				if err := d.ignoreValue(tt.Key()); err != nil {
					return err
				}
			}
			if kind == vdl.Array || kind == vdl.List || kind == vdl.Map {
				if err := d.ignoreValue(tt.Elem()); err != nil {
					return err
				}
			}
		}
		return nil
	case vdl.Struct:
		// Loop through decoding the 0-based field index and corresponding field.
		for {
			switch index, ctrl, err := binaryDecodeUintWithControl(d.buf); {
			case err != nil:
				return err
			case ctrl == WireCtrlEnd:
				return nil
			case ctrl != 0:
				return verror.New(errUnexpectedControlByte, nil, ctrl)
			case index >= uint64(tt.NumField()):
				return verror.New(errIndexOutOfRange, nil)
			default:
				ttfield := tt.Field(int(index))
				if err := d.ignoreValue(ttfield.Type); err != nil {
					return err
				}
			}
		}
	case vdl.Union:
		switch index, err := binaryDecodeUint(d.buf); {
		case err != nil:
			return err
		case index >= uint64(tt.NumField()):
			return verror.New(errIndexOutOfRange, nil)
		default:
			ttfield := tt.Field(int(index))
			return d.ignoreValue(ttfield.Type)
		}
	case vdl.Any:
		var elemTid TypeId
		switch x, ctrl, err := binaryDecodeUintWithControl(d.buf); {
		case err != nil:
			return err
		case ctrl == WireCtrlNil:
			return nil
		case ctrl != 0:
			return verror.New(errUnexpectedControlByte, nil, ctrl)
		case d.buf.version == Version80:
			elemTid = TypeId(x)
		default:
			if elemTid, err = d.refTypes.ReferencedTypeId(x); err != nil {
				return err
			}
		}
		elemType, err := d.typeDec.lookupType(elemTid)
		if err != nil {
			return err
		}
		return d.ignoreValue(elemType)
	default:
		panic(verror.New(errIgnoreValueUnhandledType, nil, tt))
	}
}

func (d *ZDecoder) nextMessage() (TypeId, error) {
	if leftover := d.buf.RemoveLimit(); leftover > 0 {
		return 0, verror.New(errLeftOverBytes, nil, leftover)
	}

	if d.buf.version == 0 {
		version, err := d.buf.ReadByte()
		if err != nil {
			return 0, verror.New(errEndedBeforeVersionByte, nil, err)
		}
		d.buf.version = Version(version)
		if !isAllowedVersion(d.buf.version) {
			return 0, verror.New(errBadVersionByte, nil, d.buf.version)
		}
	}

	mid, cr, err := binaryDecodeIntWithControl(d.buf)
	if err != nil {
		return 0, err
	}

	if cr == WireCtrlTypeIncomplete {
		mid, cr, err = binaryDecodeIntWithControl(d.buf)
		if err != nil {
			return 0, err
		}

		if cr != 0 || mid >= 0 {
			// only can have incomplete types on new type messages
			return 0, verror.New(errInvalid, nil)
		}

		d.typeIncomplete = true
	} else if mid < 0 {
		d.typeIncomplete = false
	}

	if cr != 0 {
		return 0, verror.New(errBadControlCode, nil)
	}

	var tid TypeId
	var hasAny, hasTypeObject bool
	var hasLength bool
	switch {
	case mid < 0:
		tid = TypeId(-mid)
		hasLength = true
		hasAny = false
		hasTypeObject = false
	case mid > 0:
		tid = TypeId(mid)
		t, err := d.typeDec.lookupType(tid)
		if err != nil {
			return 0, err
		}
		hasLength = hasChunkLen(t)
		hasAny = containsAny(t)
		hasTypeObject = containsTypeObject(t)
	default:
		return 0, verror.New(errDecodeZeroTypeID, nil)
	}

	if (hasAny || hasTypeObject) && d.buf.version != Version80 {
		l, err := binaryDecodeUint(d.buf)
		if err != nil {
			return 0, err
		}
		for i := 0; i < int(l); i++ {
			refId, err := binaryDecodeUint(d.buf)
			if err != nil {
				return 0, err
			}
			d.refTypes.AddTypeID(TypeId(refId))
		}
	}
	if hasAny && d.buf.version != Version80 {
		l, err := binaryDecodeUint(d.buf)
		if err != nil {
			return 0, err
		}
		for i := 0; i < int(l); i++ {
			refAnyLen, err := binaryDecodeLen(d.buf)
			if err != nil {
				return 0, err
			}
			d.refAnyLens.AddAnyLen(refAnyLen)
		}
	}

	if hasLength {
		chunkLen, err := binaryDecodeUint(d.buf)
		if err != nil {
			return 0, err
		}
		d.buf.SetLimit(int(chunkLen))
	}

	return tid, nil
}

func (d *ZDecoder) typeIsNext() (bool, error) {
	if d.buf.version == 0 {
		version, err := d.buf.ReadByte()
		if err != nil {
			return false, verror.New(errEndedBeforeVersionByte, nil, err)
		}
		d.buf.version = Version(version)
		if !isAllowedVersion(d.buf.version) {
			return false, verror.New(errBadVersionByte, nil, d.buf.version)
		}
	}
	mid, cr, _, err := binaryPeekIntWithControl(d.buf)
	if err != nil {
		return false, err
	}
	return mid < 0 || cr == WireCtrlTypeIncomplete, nil
}

func (d *ZDecoder) endMessage() error {
	if leftover := d.buf.RemoveLimit(); leftover > 0 {
		return verror.New(errLeftOverBytes, nil, leftover)
	}
	if err := d.refTypes.Reset(); err != nil {
		return err
	}
	if err := d.refAnyLens.Reset(); err != nil {
		return err
	}
	return nil
}

func (d *ZDecoder) reset() error {
	return nil
}

type referencedTypes struct {
	tids   []TypeId
	marker int
}

func (refTypes *referencedTypes) Reset() (err error) {
	refTypes.tids = refTypes.tids[:0]
	refTypes.marker = 0
	return
}

func (refTypes *referencedTypes) AddTypeID(tid TypeId) {
	refTypes.tids = append(refTypes.tids, tid)
}

func (refTypes *referencedTypes) ReferencedTypeId(index uint64) (TypeId, error) {
	if index >= uint64(len(refTypes.tids)) {
		return 0, verror.New(errInvalidTypeIdIndex, nil)
	}
	return refTypes.tids[index], nil
}

func (refTypes *referencedTypes) Mark() {
	refTypes.marker = len(refTypes.tids)
}

type referencedAnyLens struct {
	lens   []int
	marker int
}

func (refAnys *referencedAnyLens) Reset() (err error) {
	refAnys.lens = refAnys.lens[:0]
	return
}

func (refAnys *referencedAnyLens) AddAnyLen(len int) {
	refAnys.lens = append(refAnys.lens, len)
}

func (refAnys *referencedAnyLens) ReferencedAnyLen(index uint64) (int, error) {
	if index >= uint64(len(refAnys.lens)) {
		return 0, verror.New(errInvalidAnyIndex, nil)
	}
	return refAnys.lens[index], nil
}

func (refAnys *referencedAnyLens) Mark() {
	refAnys.marker = len(refAnys.lens)
}