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// 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 protocmp provides protobuf specific options for the
// "" package.
// The primary feature is the Transform option, which transform proto.Message
// types into a Message map that is suitable for cmp to introspect upon.
// All other options in this package must be used in conjunction with Transform.
package protocmp
import (
var (
enumV2Type = reflect.TypeOf((*protoreflect.Enum)(nil)).Elem()
messageV1Type = reflect.TypeOf((*protoiface.MessageV1)(nil)).Elem()
messageV2Type = reflect.TypeOf((*proto.Message)(nil)).Elem()
// Enum is a dynamic representation of a protocol buffer enum that is
// suitable for cmp.Equal and cmp.Diff to compare upon.
type Enum struct {
num protoreflect.EnumNumber
ed protoreflect.EnumDescriptor
// Descriptor returns the enum descriptor.
// It returns nil for a zero Enum value.
func (e Enum) Descriptor() protoreflect.EnumDescriptor {
return e.ed
// Number returns the enum value as an integer.
func (e Enum) Number() protoreflect.EnumNumber {
return e.num
// Equal reports whether e1 and e2 represent the same enum value.
func (e1 Enum) Equal(e2 Enum) bool {
if e1.ed.FullName() != e2.ed.FullName() {
return false
return e1.num == e2.num
// String returns the name of the enum value if known (e.g., "ENUM_VALUE"),
// otherwise it returns the formatted decimal enum number (e.g., "14").
func (e Enum) String() string {
if ev := e.ed.Values().ByNumber(e.num); ev != nil {
return string(ev.Name())
return strconv.Itoa(int(e.num))
const (
messageTypeKey = "@type"
messageInvalidKey = "@invalid"
type messageType struct {
md protoreflect.MessageDescriptor
xds map[protoreflect.FullName]protoreflect.ExtensionDescriptor
func (t messageType) String() string {
return string(
func (t1 messageType) Equal(t2 messageType) bool {
return ==
// Message is a dynamic representation of a protocol buffer message that is
// suitable for cmp.Equal and cmp.Diff to directly operate upon.
// Every populated known field (excluding extension fields) is stored in the map
// with the key being the short name of the field (e.g., "field_name") and
// the value determined by the kind and cardinality of the field.
// Singular scalars are represented by the same Go type as protoreflect.Value,
// singular messages are represented by the Message type,
// singular enums are represented by the Enum type,
// list fields are represented as a Go slice, and
// map fields are represented as a Go map.
// Every populated extension field is stored in the map with the key being the
// full name of the field surrounded by brackets (e.g., "[]")
// and the value determined according to the same rules as known fields.
// Every unknown field is stored in the map with the key being the field number
// encoded as a decimal string (e.g., "132") and the value being the raw bytes
// of the encoded field (as the protoreflect.RawFields type).
// Message values must not be created by or mutated by users.
type Message map[string]interface{}
// Descriptor return the message descriptor.
// It returns nil for a zero Message value.
func (m Message) Descriptor() protoreflect.MessageDescriptor {
mt, _ := m[messageTypeKey].(messageType)
// ProtoReflect returns a reflective view of m.
// It only implements the read-only operations of protoreflect.Message.
// Calling any mutating operations on m panics.
func (m Message) ProtoReflect() protoreflect.Message {
return (reflectMessage)(m)
// ProtoMessage is a marker method from the legacy message interface.
func (m Message) ProtoMessage() {}
// Reset is the required Reset method from the legacy message interface.
func (m Message) Reset() {
panic("invalid mutation of a read-only message")
// String returns a formatted string for the message.
// It is intended for human debugging and has no guarantees about its
// exact format or the stability of its output.
func (m Message) String() string {
switch {
case m == nil:
return "<nil>"
case !m.ProtoReflect().IsValid():
return "<invalid>"
return string(appendMessage(nil, m))
type option struct{}
// Transform returns a cmp.Option that converts each proto.Message to a Message.
// The transformation does not mutate nor alias any converted messages.
// The google.protobuf.Any message is automatically unmarshaled such that the
// "value" field is a Message representing the underlying message value
// assuming it could be resolved and properly unmarshaled.
// This does not directly transform higher-order composite Go types.
// For example, []*foopb.Message is not transformed into []Message,
// but rather the individual message elements of the slice are transformed.
func Transform(...option) cmp.Option {
// NOTE: There are currently no custom options for Transform,
// but the use of an unexported type keeps the future open.
// addrType returns a pointer to t if t isn't a pointer or interface.
addrType := func(t reflect.Type) reflect.Type {
if k := t.Kind(); k == reflect.Interface || k == reflect.Ptr {
return t
return reflect.PtrTo(t)
// TODO: Should this transform protoreflect.Enum types to Enum as well?
return cmp.FilterPath(func(p cmp.Path) bool {
ps := p.Last()
if isMessageType(addrType(ps.Type())) {
return true
// Check whether the concrete values of an interface both satisfy
// the Message interface.
if ps.Type().Kind() == reflect.Interface {
vx, vy := ps.Values()
if !vx.IsValid() || vx.IsNil() || !vy.IsValid() || vy.IsNil() {
return false
return isMessageType(addrType(vx.Elem().Type())) && isMessageType(addrType(vy.Elem().Type()))
return false
}, cmp.Transformer("protocmp.Transform", func(v interface{}) Message {
// For user convenience, shallow copy the message value if necessary
// in order for it to implement the message interface.
if rv := reflect.ValueOf(v); rv.IsValid() && rv.Kind() != reflect.Ptr && !isMessageType(rv.Type()) {
pv := reflect.New(rv.Type())
v = pv.Interface()
m := protoimpl.X.MessageOf(v)
switch {
case m == nil:
return nil
case !m.IsValid():
return Message{messageTypeKey: messageType{md: m.Descriptor()}, messageInvalidKey: true}
return transformMessage(m)
func isMessageType(t reflect.Type) bool {
// Avoid tranforming the Message itself.
if t == reflect.TypeOf(Message(nil)) || t == reflect.TypeOf((*Message)(nil)) {
return false
return t.Implements(messageV1Type) || t.Implements(messageV2Type)
func transformMessage(m protoreflect.Message) Message {
mx := Message{}
mt := messageType{md: m.Descriptor(), xds: make(map[protoreflect.FullName]protoreflect.FieldDescriptor)}
// Handle known and extension fields.
m.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
s := string(fd.Name())
if fd.IsExtension() {
s = "[" + string(fd.FullName()) + "]"
mt.xds[fd.FullName()] = fd
switch {
case fd.IsList():
mx[s] = transformList(fd, v.List())
case fd.IsMap():
mx[s] = transformMap(fd, v.Map())
mx[s] = transformSingular(fd, v)
return true
// Handle unknown fields.
for b := m.GetUnknown(); len(b) > 0; {
num, _, n := wire.ConsumeField(b)
s := strconv.Itoa(int(num))
b2, _ := mx[s].(protoreflect.RawFields)
mx[s] = append(b2, b[:n]...)
b = b[n:]
// Expand Any messages.
if == "google.protobuf.Any" {
// TODO: Expose Transform option to specify a custom resolver?
s, _ := mx["type_url"].(string)
b, _ := mx["value"].([]byte)
mt, err := protoregistry.GlobalTypes.FindMessageByURL(s)
if mt != nil && err == nil {
m2 := mt.New()
err := proto.UnmarshalOptions{AllowPartial: true}.Unmarshal(b, m2.Interface())
if err == nil {
mx["value"] = transformMessage(m2)
mx[messageTypeKey] = mt
return mx
func transformList(fd protoreflect.FieldDescriptor, lv protoreflect.List) interface{} {
t := protoKindToGoType(fd.Kind())
rv := reflect.MakeSlice(reflect.SliceOf(t), lv.Len(), lv.Len())
for i := 0; i < lv.Len(); i++ {
v := reflect.ValueOf(transformSingular(fd, lv.Get(i)))
return rv.Interface()
func transformMap(fd protoreflect.FieldDescriptor, mv protoreflect.Map) interface{} {
kfd := fd.MapKey()
vfd := fd.MapValue()
kt := protoKindToGoType(kfd.Kind())
vt := protoKindToGoType(vfd.Kind())
rv := reflect.MakeMapWithSize(reflect.MapOf(kt, vt), mv.Len())
mv.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
kv := reflect.ValueOf(transformSingular(kfd, k.Value()))
vv := reflect.ValueOf(transformSingular(vfd, v))
rv.SetMapIndex(kv, vv)
return true
return rv.Interface()
func transformSingular(fd protoreflect.FieldDescriptor, v protoreflect.Value) interface{} {
switch fd.Kind() {
case protoreflect.EnumKind:
return Enum{num: v.Enum(), ed: fd.Enum()}
case protoreflect.MessageKind, protoreflect.GroupKind:
return transformMessage(v.Message())
return v.Interface()
func protoKindToGoType(k protoreflect.Kind) reflect.Type {
switch k {
case protoreflect.BoolKind:
return reflect.TypeOf(bool(false))
case protoreflect.Int32Kind, protoreflect.Sint32Kind, protoreflect.Sfixed32Kind:
return reflect.TypeOf(int32(0))
case protoreflect.Int64Kind, protoreflect.Sint64Kind, protoreflect.Sfixed64Kind:
return reflect.TypeOf(int64(0))
case protoreflect.Uint32Kind, protoreflect.Fixed32Kind:
return reflect.TypeOf(uint32(0))
case protoreflect.Uint64Kind, protoreflect.Fixed64Kind:
return reflect.TypeOf(uint64(0))
case protoreflect.FloatKind:
return reflect.TypeOf(float32(0))
case protoreflect.DoubleKind:
return reflect.TypeOf(float64(0))
case protoreflect.StringKind:
return reflect.TypeOf(string(""))
case protoreflect.BytesKind:
return reflect.TypeOf([]byte(nil))
case protoreflect.EnumKind:
return reflect.TypeOf(Enum{})
case protoreflect.MessageKind, protoreflect.GroupKind:
return reflect.TypeOf(Message{})
panic("invalid kind")