diff --git a/vendor/google.golang.org/protobuf/internal/impl/codec_field.go b/vendor/google.golang.org/protobuf/internal/impl/codec_field.go
new file mode 100644
index 0000000..cb4b482
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/codec_field.go
@@ -0,0 +1,830 @@
+// Copyright 2019 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.
+
+package impl
+
+import (
+	"fmt"
+	"reflect"
+	"sync"
+
+	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/internal/errors"
+	"google.golang.org/protobuf/proto"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+	preg "google.golang.org/protobuf/reflect/protoregistry"
+	piface "google.golang.org/protobuf/runtime/protoiface"
+)
+
+type errInvalidUTF8 struct{}
+
+func (errInvalidUTF8) Error() string     { return "string field contains invalid UTF-8" }
+func (errInvalidUTF8) InvalidUTF8() bool { return true }
+func (errInvalidUTF8) Unwrap() error     { return errors.Error }
+
+// initOneofFieldCoders initializes the fast-path functions for the fields in a oneof.
+//
+// For size, marshal, and isInit operations, functions are set only on the first field
+// in the oneof. The functions are called when the oneof is non-nil, and will dispatch
+// to the appropriate field-specific function as necessary.
+//
+// The unmarshal function is set on each field individually as usual.
+func (mi *MessageInfo) initOneofFieldCoders(od pref.OneofDescriptor, si structInfo) {
+	fs := si.oneofsByName[od.Name()]
+	ft := fs.Type
+	oneofFields := make(map[reflect.Type]*coderFieldInfo)
+	needIsInit := false
+	fields := od.Fields()
+	for i, lim := 0, fields.Len(); i < lim; i++ {
+		fd := od.Fields().Get(i)
+		num := fd.Number()
+		// Make a copy of the original coderFieldInfo for use in unmarshaling.
+		//
+		// oneofFields[oneofType].funcs.marshal is the field-specific marshal function.
+		//
+		// mi.coderFields[num].marshal is set on only the first field in the oneof,
+		// and dispatches to the field-specific marshaler in oneofFields.
+		cf := *mi.coderFields[num]
+		ot := si.oneofWrappersByNumber[num]
+		cf.ft = ot.Field(0).Type
+		cf.mi, cf.funcs = fieldCoder(fd, cf.ft)
+		oneofFields[ot] = &cf
+		if cf.funcs.isInit != nil {
+			needIsInit = true
+		}
+		mi.coderFields[num].funcs.unmarshal = func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+			var vw reflect.Value         // pointer to wrapper type
+			vi := p.AsValueOf(ft).Elem() // oneof field value of interface kind
+			if !vi.IsNil() && !vi.Elem().IsNil() && vi.Elem().Elem().Type() == ot {
+				vw = vi.Elem()
+			} else {
+				vw = reflect.New(ot)
+			}
+			out, err := cf.funcs.unmarshal(b, pointerOfValue(vw).Apply(zeroOffset), wtyp, &cf, opts)
+			if err != nil {
+				return out, err
+			}
+			vi.Set(vw)
+			return out, nil
+		}
+	}
+	getInfo := func(p pointer) (pointer, *coderFieldInfo) {
+		v := p.AsValueOf(ft).Elem()
+		if v.IsNil() {
+			return pointer{}, nil
+		}
+		v = v.Elem() // interface -> *struct
+		if v.IsNil() {
+			return pointer{}, nil
+		}
+		return pointerOfValue(v).Apply(zeroOffset), oneofFields[v.Elem().Type()]
+	}
+	first := mi.coderFields[od.Fields().Get(0).Number()]
+	first.funcs.size = func(p pointer, _ *coderFieldInfo, opts marshalOptions) int {
+		p, info := getInfo(p)
+		if info == nil || info.funcs.size == nil {
+			return 0
+		}
+		return info.funcs.size(p, info, opts)
+	}
+	first.funcs.marshal = func(b []byte, p pointer, _ *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+		p, info := getInfo(p)
+		if info == nil || info.funcs.marshal == nil {
+			return b, nil
+		}
+		return info.funcs.marshal(b, p, info, opts)
+	}
+	first.funcs.merge = func(dst, src pointer, _ *coderFieldInfo, opts mergeOptions) {
+		srcp, srcinfo := getInfo(src)
+		if srcinfo == nil || srcinfo.funcs.merge == nil {
+			return
+		}
+		dstp, dstinfo := getInfo(dst)
+		if dstinfo != srcinfo {
+			dst.AsValueOf(ft).Elem().Set(reflect.New(src.AsValueOf(ft).Elem().Elem().Elem().Type()))
+			dstp = pointerOfValue(dst.AsValueOf(ft).Elem().Elem()).Apply(zeroOffset)
+		}
+		srcinfo.funcs.merge(dstp, srcp, srcinfo, opts)
+	}
+	if needIsInit {
+		first.funcs.isInit = func(p pointer, _ *coderFieldInfo) error {
+			p, info := getInfo(p)
+			if info == nil || info.funcs.isInit == nil {
+				return nil
+			}
+			return info.funcs.isInit(p, info)
+		}
+	}
+}
+
+func makeWeakMessageFieldCoder(fd pref.FieldDescriptor) pointerCoderFuncs {
+	var once sync.Once
+	var messageType pref.MessageType
+	lazyInit := func() {
+		once.Do(func() {
+			messageName := fd.Message().FullName()
+			messageType, _ = preg.GlobalTypes.FindMessageByName(messageName)
+		})
+	}
+
+	return pointerCoderFuncs{
+		size: func(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+			m, ok := p.WeakFields().get(f.num)
+			if !ok {
+				return 0
+			}
+			lazyInit()
+			if messageType == nil {
+				panic(fmt.Sprintf("weak message %v is not linked in", fd.Message().FullName()))
+			}
+			return sizeMessage(m, f.tagsize, opts)
+		},
+		marshal: func(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+			m, ok := p.WeakFields().get(f.num)
+			if !ok {
+				return b, nil
+			}
+			lazyInit()
+			if messageType == nil {
+				panic(fmt.Sprintf("weak message %v is not linked in", fd.Message().FullName()))
+			}
+			return appendMessage(b, m, f.wiretag, opts)
+		},
+		unmarshal: func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+			fs := p.WeakFields()
+			m, ok := fs.get(f.num)
+			if !ok {
+				lazyInit()
+				if messageType == nil {
+					return unmarshalOutput{}, errUnknown
+				}
+				m = messageType.New().Interface()
+				fs.set(f.num, m)
+			}
+			return consumeMessage(b, m, wtyp, opts)
+		},
+		isInit: func(p pointer, f *coderFieldInfo) error {
+			m, ok := p.WeakFields().get(f.num)
+			if !ok {
+				return nil
+			}
+			return proto.CheckInitialized(m)
+		},
+		merge: func(dst, src pointer, f *coderFieldInfo, opts mergeOptions) {
+			sm, ok := src.WeakFields().get(f.num)
+			if !ok {
+				return
+			}
+			dm, ok := dst.WeakFields().get(f.num)
+			if !ok {
+				lazyInit()
+				if messageType == nil {
+					panic(fmt.Sprintf("weak message %v is not linked in", fd.Message().FullName()))
+				}
+				dm = messageType.New().Interface()
+				dst.WeakFields().set(f.num, dm)
+			}
+			opts.Merge(dm, sm)
+		},
+	}
+}
+
+func makeMessageFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
+	if mi := getMessageInfo(ft); mi != nil {
+		funcs := pointerCoderFuncs{
+			size:      sizeMessageInfo,
+			marshal:   appendMessageInfo,
+			unmarshal: consumeMessageInfo,
+			merge:     mergeMessage,
+		}
+		if needsInitCheck(mi.Desc) {
+			funcs.isInit = isInitMessageInfo
+		}
+		return funcs
+	} else {
+		return pointerCoderFuncs{
+			size: func(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return sizeMessage(m, f.tagsize, opts)
+			},
+			marshal: func(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return appendMessage(b, m, f.wiretag, opts)
+			},
+			unmarshal: func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+				mp := p.AsValueOf(ft).Elem()
+				if mp.IsNil() {
+					mp.Set(reflect.New(ft.Elem()))
+				}
+				return consumeMessage(b, asMessage(mp), wtyp, opts)
+			},
+			isInit: func(p pointer, f *coderFieldInfo) error {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return proto.CheckInitialized(m)
+			},
+			merge: mergeMessage,
+		}
+	}
+}
+
+func sizeMessageInfo(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+	return protowire.SizeBytes(f.mi.sizePointer(p.Elem(), opts)) + f.tagsize
+}
+
+func appendMessageInfo(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+	b = protowire.AppendVarint(b, f.wiretag)
+	b = protowire.AppendVarint(b, uint64(f.mi.sizePointer(p.Elem(), opts)))
+	return f.mi.marshalAppendPointer(b, p.Elem(), opts)
+}
+
+func consumeMessageInfo(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.BytesType {
+		return out, errUnknown
+	}
+	v, n := protowire.ConsumeBytes(b)
+	if n < 0 {
+		return out, errDecode
+	}
+	if p.Elem().IsNil() {
+		p.SetPointer(pointerOfValue(reflect.New(f.mi.GoReflectType.Elem())))
+	}
+	o, err := f.mi.unmarshalPointer(v, p.Elem(), 0, opts)
+	if err != nil {
+		return out, err
+	}
+	out.n = n
+	out.initialized = o.initialized
+	return out, nil
+}
+
+func isInitMessageInfo(p pointer, f *coderFieldInfo) error {
+	return f.mi.checkInitializedPointer(p.Elem())
+}
+
+func sizeMessage(m proto.Message, tagsize int, _ marshalOptions) int {
+	return protowire.SizeBytes(proto.Size(m)) + tagsize
+}
+
+func appendMessage(b []byte, m proto.Message, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	b = protowire.AppendVarint(b, wiretag)
+	b = protowire.AppendVarint(b, uint64(proto.Size(m)))
+	return opts.Options().MarshalAppend(b, m)
+}
+
+func consumeMessage(b []byte, m proto.Message, wtyp protowire.Type, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.BytesType {
+		return out, errUnknown
+	}
+	v, n := protowire.ConsumeBytes(b)
+	if n < 0 {
+		return out, errDecode
+	}
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     v,
+		Message: m.ProtoReflect(),
+	})
+	if err != nil {
+		return out, err
+	}
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return out, nil
+}
+
+func sizeMessageValue(v pref.Value, tagsize int, opts marshalOptions) int {
+	m := v.Message().Interface()
+	return sizeMessage(m, tagsize, opts)
+}
+
+func appendMessageValue(b []byte, v pref.Value, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	m := v.Message().Interface()
+	return appendMessage(b, m, wiretag, opts)
+}
+
+func consumeMessageValue(b []byte, v pref.Value, _ protowire.Number, wtyp protowire.Type, opts unmarshalOptions) (pref.Value, unmarshalOutput, error) {
+	m := v.Message().Interface()
+	out, err := consumeMessage(b, m, wtyp, opts)
+	return v, out, err
+}
+
+func isInitMessageValue(v pref.Value) error {
+	m := v.Message().Interface()
+	return proto.CheckInitialized(m)
+}
+
+var coderMessageValue = valueCoderFuncs{
+	size:      sizeMessageValue,
+	marshal:   appendMessageValue,
+	unmarshal: consumeMessageValue,
+	isInit:    isInitMessageValue,
+	merge:     mergeMessageValue,
+}
+
+func sizeGroupValue(v pref.Value, tagsize int, opts marshalOptions) int {
+	m := v.Message().Interface()
+	return sizeGroup(m, tagsize, opts)
+}
+
+func appendGroupValue(b []byte, v pref.Value, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	m := v.Message().Interface()
+	return appendGroup(b, m, wiretag, opts)
+}
+
+func consumeGroupValue(b []byte, v pref.Value, num protowire.Number, wtyp protowire.Type, opts unmarshalOptions) (pref.Value, unmarshalOutput, error) {
+	m := v.Message().Interface()
+	out, err := consumeGroup(b, m, num, wtyp, opts)
+	return v, out, err
+}
+
+var coderGroupValue = valueCoderFuncs{
+	size:      sizeGroupValue,
+	marshal:   appendGroupValue,
+	unmarshal: consumeGroupValue,
+	isInit:    isInitMessageValue,
+	merge:     mergeMessageValue,
+}
+
+func makeGroupFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
+	num := fd.Number()
+	if mi := getMessageInfo(ft); mi != nil {
+		funcs := pointerCoderFuncs{
+			size:      sizeGroupType,
+			marshal:   appendGroupType,
+			unmarshal: consumeGroupType,
+			merge:     mergeMessage,
+		}
+		if needsInitCheck(mi.Desc) {
+			funcs.isInit = isInitMessageInfo
+		}
+		return funcs
+	} else {
+		return pointerCoderFuncs{
+			size: func(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return sizeGroup(m, f.tagsize, opts)
+			},
+			marshal: func(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return appendGroup(b, m, f.wiretag, opts)
+			},
+			unmarshal: func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+				mp := p.AsValueOf(ft).Elem()
+				if mp.IsNil() {
+					mp.Set(reflect.New(ft.Elem()))
+				}
+				return consumeGroup(b, asMessage(mp), num, wtyp, opts)
+			},
+			isInit: func(p pointer, f *coderFieldInfo) error {
+				m := asMessage(p.AsValueOf(ft).Elem())
+				return proto.CheckInitialized(m)
+			},
+			merge: mergeMessage,
+		}
+	}
+}
+
+func sizeGroupType(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+	return 2*f.tagsize + f.mi.sizePointer(p.Elem(), opts)
+}
+
+func appendGroupType(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+	b = protowire.AppendVarint(b, f.wiretag) // start group
+	b, err := f.mi.marshalAppendPointer(b, p.Elem(), opts)
+	b = protowire.AppendVarint(b, f.wiretag+1) // end group
+	return b, err
+}
+
+func consumeGroupType(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.StartGroupType {
+		return out, errUnknown
+	}
+	if p.Elem().IsNil() {
+		p.SetPointer(pointerOfValue(reflect.New(f.mi.GoReflectType.Elem())))
+	}
+	return f.mi.unmarshalPointer(b, p.Elem(), f.num, opts)
+}
+
+func sizeGroup(m proto.Message, tagsize int, _ marshalOptions) int {
+	return 2*tagsize + proto.Size(m)
+}
+
+func appendGroup(b []byte, m proto.Message, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	b = protowire.AppendVarint(b, wiretag) // start group
+	b, err := opts.Options().MarshalAppend(b, m)
+	b = protowire.AppendVarint(b, wiretag+1) // end group
+	return b, err
+}
+
+func consumeGroup(b []byte, m proto.Message, num protowire.Number, wtyp protowire.Type, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.StartGroupType {
+		return out, errUnknown
+	}
+	b, n := protowire.ConsumeGroup(num, b)
+	if n < 0 {
+		return out, errDecode
+	}
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     b,
+		Message: m.ProtoReflect(),
+	})
+	if err != nil {
+		return out, err
+	}
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return out, nil
+}
+
+func makeMessageSliceFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
+	if mi := getMessageInfo(ft); mi != nil {
+		funcs := pointerCoderFuncs{
+			size:      sizeMessageSliceInfo,
+			marshal:   appendMessageSliceInfo,
+			unmarshal: consumeMessageSliceInfo,
+			merge:     mergeMessageSlice,
+		}
+		if needsInitCheck(mi.Desc) {
+			funcs.isInit = isInitMessageSliceInfo
+		}
+		return funcs
+	}
+	return pointerCoderFuncs{
+		size: func(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+			return sizeMessageSlice(p, ft, f.tagsize, opts)
+		},
+		marshal: func(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+			return appendMessageSlice(b, p, f.wiretag, ft, opts)
+		},
+		unmarshal: func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+			return consumeMessageSlice(b, p, ft, wtyp, opts)
+		},
+		isInit: func(p pointer, f *coderFieldInfo) error {
+			return isInitMessageSlice(p, ft)
+		},
+		merge: mergeMessageSlice,
+	}
+}
+
+func sizeMessageSliceInfo(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+	s := p.PointerSlice()
+	n := 0
+	for _, v := range s {
+		n += protowire.SizeBytes(f.mi.sizePointer(v, opts)) + f.tagsize
+	}
+	return n
+}
+
+func appendMessageSliceInfo(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+	s := p.PointerSlice()
+	var err error
+	for _, v := range s {
+		b = protowire.AppendVarint(b, f.wiretag)
+		siz := f.mi.sizePointer(v, opts)
+		b = protowire.AppendVarint(b, uint64(siz))
+		b, err = f.mi.marshalAppendPointer(b, v, opts)
+		if err != nil {
+			return b, err
+		}
+	}
+	return b, nil
+}
+
+func consumeMessageSliceInfo(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.BytesType {
+		return out, errUnknown
+	}
+	v, n := protowire.ConsumeBytes(b)
+	if n < 0 {
+		return out, errDecode
+	}
+	m := reflect.New(f.mi.GoReflectType.Elem()).Interface()
+	mp := pointerOfIface(m)
+	o, err := f.mi.unmarshalPointer(v, mp, 0, opts)
+	if err != nil {
+		return out, err
+	}
+	p.AppendPointerSlice(mp)
+	out.n = n
+	out.initialized = o.initialized
+	return out, nil
+}
+
+func isInitMessageSliceInfo(p pointer, f *coderFieldInfo) error {
+	s := p.PointerSlice()
+	for _, v := range s {
+		if err := f.mi.checkInitializedPointer(v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func sizeMessageSlice(p pointer, goType reflect.Type, tagsize int, _ marshalOptions) int {
+	s := p.PointerSlice()
+	n := 0
+	for _, v := range s {
+		m := asMessage(v.AsValueOf(goType.Elem()))
+		n += protowire.SizeBytes(proto.Size(m)) + tagsize
+	}
+	return n
+}
+
+func appendMessageSlice(b []byte, p pointer, wiretag uint64, goType reflect.Type, opts marshalOptions) ([]byte, error) {
+	s := p.PointerSlice()
+	var err error
+	for _, v := range s {
+		m := asMessage(v.AsValueOf(goType.Elem()))
+		b = protowire.AppendVarint(b, wiretag)
+		siz := proto.Size(m)
+		b = protowire.AppendVarint(b, uint64(siz))
+		b, err = opts.Options().MarshalAppend(b, m)
+		if err != nil {
+			return b, err
+		}
+	}
+	return b, nil
+}
+
+func consumeMessageSlice(b []byte, p pointer, goType reflect.Type, wtyp protowire.Type, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.BytesType {
+		return out, errUnknown
+	}
+	v, n := protowire.ConsumeBytes(b)
+	if n < 0 {
+		return out, errDecode
+	}
+	mp := reflect.New(goType.Elem())
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     v,
+		Message: asMessage(mp).ProtoReflect(),
+	})
+	if err != nil {
+		return out, err
+	}
+	p.AppendPointerSlice(pointerOfValue(mp))
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return out, nil
+}
+
+func isInitMessageSlice(p pointer, goType reflect.Type) error {
+	s := p.PointerSlice()
+	for _, v := range s {
+		m := asMessage(v.AsValueOf(goType.Elem()))
+		if err := proto.CheckInitialized(m); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Slices of messages
+
+func sizeMessageSliceValue(listv pref.Value, tagsize int, opts marshalOptions) int {
+	list := listv.List()
+	n := 0
+	for i, llen := 0, list.Len(); i < llen; i++ {
+		m := list.Get(i).Message().Interface()
+		n += protowire.SizeBytes(proto.Size(m)) + tagsize
+	}
+	return n
+}
+
+func appendMessageSliceValue(b []byte, listv pref.Value, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	list := listv.List()
+	mopts := opts.Options()
+	for i, llen := 0, list.Len(); i < llen; i++ {
+		m := list.Get(i).Message().Interface()
+		b = protowire.AppendVarint(b, wiretag)
+		siz := proto.Size(m)
+		b = protowire.AppendVarint(b, uint64(siz))
+		var err error
+		b, err = mopts.MarshalAppend(b, m)
+		if err != nil {
+			return b, err
+		}
+	}
+	return b, nil
+}
+
+func consumeMessageSliceValue(b []byte, listv pref.Value, _ protowire.Number, wtyp protowire.Type, opts unmarshalOptions) (_ pref.Value, out unmarshalOutput, err error) {
+	list := listv.List()
+	if wtyp != protowire.BytesType {
+		return pref.Value{}, out, errUnknown
+	}
+	v, n := protowire.ConsumeBytes(b)
+	if n < 0 {
+		return pref.Value{}, out, errDecode
+	}
+	m := list.NewElement()
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     v,
+		Message: m.Message(),
+	})
+	if err != nil {
+		return pref.Value{}, out, err
+	}
+	list.Append(m)
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return listv, out, nil
+}
+
+func isInitMessageSliceValue(listv pref.Value) error {
+	list := listv.List()
+	for i, llen := 0, list.Len(); i < llen; i++ {
+		m := list.Get(i).Message().Interface()
+		if err := proto.CheckInitialized(m); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+var coderMessageSliceValue = valueCoderFuncs{
+	size:      sizeMessageSliceValue,
+	marshal:   appendMessageSliceValue,
+	unmarshal: consumeMessageSliceValue,
+	isInit:    isInitMessageSliceValue,
+	merge:     mergeMessageListValue,
+}
+
+func sizeGroupSliceValue(listv pref.Value, tagsize int, opts marshalOptions) int {
+	list := listv.List()
+	n := 0
+	for i, llen := 0, list.Len(); i < llen; i++ {
+		m := list.Get(i).Message().Interface()
+		n += 2*tagsize + proto.Size(m)
+	}
+	return n
+}
+
+func appendGroupSliceValue(b []byte, listv pref.Value, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	list := listv.List()
+	mopts := opts.Options()
+	for i, llen := 0, list.Len(); i < llen; i++ {
+		m := list.Get(i).Message().Interface()
+		b = protowire.AppendVarint(b, wiretag) // start group
+		var err error
+		b, err = mopts.MarshalAppend(b, m)
+		if err != nil {
+			return b, err
+		}
+		b = protowire.AppendVarint(b, wiretag+1) // end group
+	}
+	return b, nil
+}
+
+func consumeGroupSliceValue(b []byte, listv pref.Value, num protowire.Number, wtyp protowire.Type, opts unmarshalOptions) (_ pref.Value, out unmarshalOutput, err error) {
+	list := listv.List()
+	if wtyp != protowire.StartGroupType {
+		return pref.Value{}, out, errUnknown
+	}
+	b, n := protowire.ConsumeGroup(num, b)
+	if n < 0 {
+		return pref.Value{}, out, errDecode
+	}
+	m := list.NewElement()
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     b,
+		Message: m.Message(),
+	})
+	if err != nil {
+		return pref.Value{}, out, err
+	}
+	list.Append(m)
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return listv, out, nil
+}
+
+var coderGroupSliceValue = valueCoderFuncs{
+	size:      sizeGroupSliceValue,
+	marshal:   appendGroupSliceValue,
+	unmarshal: consumeGroupSliceValue,
+	isInit:    isInitMessageSliceValue,
+	merge:     mergeMessageListValue,
+}
+
+func makeGroupSliceFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
+	num := fd.Number()
+	if mi := getMessageInfo(ft); mi != nil {
+		funcs := pointerCoderFuncs{
+			size:      sizeGroupSliceInfo,
+			marshal:   appendGroupSliceInfo,
+			unmarshal: consumeGroupSliceInfo,
+			merge:     mergeMessageSlice,
+		}
+		if needsInitCheck(mi.Desc) {
+			funcs.isInit = isInitMessageSliceInfo
+		}
+		return funcs
+	}
+	return pointerCoderFuncs{
+		size: func(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+			return sizeGroupSlice(p, ft, f.tagsize, opts)
+		},
+		marshal: func(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+			return appendGroupSlice(b, p, f.wiretag, ft, opts)
+		},
+		unmarshal: func(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+			return consumeGroupSlice(b, p, num, wtyp, ft, opts)
+		},
+		isInit: func(p pointer, f *coderFieldInfo) error {
+			return isInitMessageSlice(p, ft)
+		},
+		merge: mergeMessageSlice,
+	}
+}
+
+func sizeGroupSlice(p pointer, messageType reflect.Type, tagsize int, _ marshalOptions) int {
+	s := p.PointerSlice()
+	n := 0
+	for _, v := range s {
+		m := asMessage(v.AsValueOf(messageType.Elem()))
+		n += 2*tagsize + proto.Size(m)
+	}
+	return n
+}
+
+func appendGroupSlice(b []byte, p pointer, wiretag uint64, messageType reflect.Type, opts marshalOptions) ([]byte, error) {
+	s := p.PointerSlice()
+	var err error
+	for _, v := range s {
+		m := asMessage(v.AsValueOf(messageType.Elem()))
+		b = protowire.AppendVarint(b, wiretag) // start group
+		b, err = opts.Options().MarshalAppend(b, m)
+		if err != nil {
+			return b, err
+		}
+		b = protowire.AppendVarint(b, wiretag+1) // end group
+	}
+	return b, nil
+}
+
+func consumeGroupSlice(b []byte, p pointer, num protowire.Number, wtyp protowire.Type, goType reflect.Type, opts unmarshalOptions) (out unmarshalOutput, err error) {
+	if wtyp != protowire.StartGroupType {
+		return out, errUnknown
+	}
+	b, n := protowire.ConsumeGroup(num, b)
+	if n < 0 {
+		return out, errDecode
+	}
+	mp := reflect.New(goType.Elem())
+	o, err := opts.Options().UnmarshalState(piface.UnmarshalInput{
+		Buf:     b,
+		Message: asMessage(mp).ProtoReflect(),
+	})
+	if err != nil {
+		return out, err
+	}
+	p.AppendPointerSlice(pointerOfValue(mp))
+	out.n = n
+	out.initialized = o.Flags&piface.UnmarshalInitialized != 0
+	return out, nil
+}
+
+func sizeGroupSliceInfo(p pointer, f *coderFieldInfo, opts marshalOptions) int {
+	s := p.PointerSlice()
+	n := 0
+	for _, v := range s {
+		n += 2*f.tagsize + f.mi.sizePointer(v, opts)
+	}
+	return n
+}
+
+func appendGroupSliceInfo(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+	s := p.PointerSlice()
+	var err error
+	for _, v := range s {
+		b = protowire.AppendVarint(b, f.wiretag) // start group
+		b, err = f.mi.marshalAppendPointer(b, v, opts)
+		if err != nil {
+			return b, err
+		}
+		b = protowire.AppendVarint(b, f.wiretag+1) // end group
+	}
+	return b, nil
+}
+
+func consumeGroupSliceInfo(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (unmarshalOutput, error) {
+	if wtyp != protowire.StartGroupType {
+		return unmarshalOutput{}, errUnknown
+	}
+	m := reflect.New(f.mi.GoReflectType.Elem()).Interface()
+	mp := pointerOfIface(m)
+	out, err := f.mi.unmarshalPointer(b, mp, f.num, opts)
+	if err != nil {
+		return out, err
+	}
+	p.AppendPointerSlice(mp)
+	return out, nil
+}
+
+func asMessage(v reflect.Value) pref.ProtoMessage {
+	if m, ok := v.Interface().(pref.ProtoMessage); ok {
+		return m
+	}
+	return legacyWrapMessage(v).Interface()
+}