all: abstract fast-path marshal and unmarshal inputs and outputs

We may want to make changes to the inputs and outputs of the fast-path
functions in the future. For example, we likely want to add the ability
for the fast-path unmarshal to report back whether the unmarshaled
message is known to be initialized.

Change the signatures of these functions to take in and return struct
types which can be extended with whatever fields we want in the future.

Change-Id: Idead360785df730283a4630ea405265b72482e62
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/215719
Reviewed-by: Joe Tsai <joetsai@google.com>

internal/impl/codec_message.go

@@ -134,9 +134,9 @@ func (mi *MessageInfo) makeCoderMethods(t reflect.Type, si structInfo) {
 	}
 
 	mi.needsInitCheck = needsInitCheck(mi.Desc)
-	if mi.methods.MarshalAppend == nil && mi.methods.Size == nil {
+	if mi.methods.Marshal == nil && mi.methods.Size == nil {
 		mi.methods.Flags |= piface.SupportMarshalDeterministic
-		mi.methods.MarshalAppend = mi.marshalAppend
+		mi.methods.Marshal = mi.marshal
 		mi.methods.Size = mi.size
 	}
 	if mi.methods.Unmarshal == nil {

internal/impl/decode.go

@@ -58,15 +58,15 @@ func (o unmarshalOptions) DiscardUnknown() bool                 { return o.flags
 func (o unmarshalOptions) Resolver() preg.ExtensionTypeResolver { return o.resolver }
 
 // unmarshal is protoreflect.Methods.Unmarshal.
-func (mi *MessageInfo) unmarshal(b []byte, m pref.Message, opts piface.UnmarshalOptions) error {
+func (mi *MessageInfo) unmarshal(m pref.Message, in piface.UnmarshalInput) (piface.UnmarshalOutput, error) {
 	var p pointer
 	if ms, ok := m.(*messageState); ok {
 		p = ms.pointer()
 	} else {
 		p = m.(*messageReflectWrapper).pointer()
 	}
-	_, err := mi.unmarshalPointer(b, p, 0, newUnmarshalOptions(opts))
-	return err
+	_, err := mi.unmarshalPointer(in.Buf, p, 0, newUnmarshalOptions(in.Options))
+	return piface.UnmarshalOutput{}, err
 }
 
 // errUnknown is returned during unmarshaling to indicate a parse error that

internal/impl/encode.go

@@ -101,15 +101,16 @@ func (mi *MessageInfo) sizePointerSlow(p pointer, opts marshalOptions) (size int
 	return size
 }
 
-// marshalAppend is protoreflect.Methods.MarshalAppend.
-func (mi *MessageInfo) marshalAppend(b []byte, m pref.Message, opts piface.MarshalOptions) ([]byte, error) {
+// marshal is protoreflect.Methods.Marshal.
+func (mi *MessageInfo) marshal(m pref.Message, in piface.MarshalInput) (piface.MarshalOutput, error) {
 	var p pointer
 	if ms, ok := m.(*messageState); ok {
 		p = ms.pointer()
 	} else {
 		p = m.(*messageReflectWrapper).pointer()
 	}
-	return mi.marshalAppendPointer(b, p, newMarshalOptions(opts))
+	b, err := mi.marshalAppendPointer(in.Buf, p, newMarshalOptions(in.Options))
+	return piface.MarshalOutput{Buf: b}, err
 }
 
 func (mi *MessageInfo) marshalAppendPointer(b []byte, p pointer, opts marshalOptions) ([]byte, error) {

internal/impl/legacy_message.go

@@ -50,7 +50,7 @@ func legacyLoadMessageInfo(t reflect.Type, name pref.FullName) *MessageInfo {
 
 	v := reflect.Zero(t).Interface()
 	if _, ok := v.(legacyMarshaler); ok {
-		mi.methods.MarshalAppend = legacyMarshalAppend
+		mi.methods.Marshal = legacyMarshal
 
 		// We have no way to tell whether the type's Marshal method
 		// supports deterministic serialization or not, but this
@@ -363,8 +363,8 @@ type legacyUnmarshaler interface {
 }
 
 var legacyProtoMethods = &piface.Methods{
-	MarshalAppend: legacyMarshalAppend,
-	Unmarshal:     legacyUnmarshal,
+	Marshal:   legacyMarshal,
+	Unmarshal: legacyUnmarshal,
 
 	// We have no way to tell whether the type's Marshal method
 	// supports deterministic serialization or not, but this
@@ -373,26 +373,28 @@ var legacyProtoMethods = &piface.Methods{
 	Flags: piface.SupportMarshalDeterministic,
 }
 
-func legacyMarshalAppend(b []byte, m protoreflect.Message, opts piface.MarshalOptions) ([]byte, error) {
+func legacyMarshal(m protoreflect.Message, in piface.MarshalInput) (piface.MarshalOutput, error) {
 	v := m.(unwrapper).protoUnwrap()
 	marshaler, ok := v.(legacyMarshaler)
 	if !ok {
-		return nil, errors.New("%T does not implement Marshal", v)
+		return piface.MarshalOutput{}, errors.New("%T does not implement Marshal", v)
 	}
 	out, err := marshaler.Marshal()
-	if b != nil {
-		out = append(b, out...)
+	if in.Buf != nil {
+		out = append(in.Buf, out...)
 	}
-	return out, err
+	return piface.MarshalOutput{
+		Buf: out,
+	}, err
 }
 
-func legacyUnmarshal(b []byte, m protoreflect.Message, opts piface.UnmarshalOptions) error {
+func legacyUnmarshal(m protoreflect.Message, in piface.UnmarshalInput) (piface.UnmarshalOutput, error) {
 	v := m.(unwrapper).protoUnwrap()
 	unmarshaler, ok := v.(legacyUnmarshaler)
 	if !ok {
-		return errors.New("%T does not implement Marshal", v)
+		return piface.UnmarshalOutput{}, errors.New("%T does not implement Marshal", v)
 	}
-	return unmarshaler.Unmarshal(b)
+	return piface.UnmarshalOutput{}, unmarshaler.Unmarshal(in.Buf)
 }
 
 // aberrantMessageType implements MessageType for all types other than pointer-to-struct.

proto/decode.go

@@ -72,7 +72,11 @@ func (o UnmarshalOptions) Unmarshal(b []byte, m Message) error {
 func (o UnmarshalOptions) unmarshalMessage(b []byte, m protoreflect.Message) error {
 	if methods := protoMethods(m); methods != nil && methods.Unmarshal != nil &&
 		!(o.DiscardUnknown && methods.Flags&protoiface.SupportUnmarshalDiscardUnknown == 0) {
-		return methods.Unmarshal(b, m, protoiface.UnmarshalOptions(o))
+		_, err := methods.Unmarshal(m, protoiface.UnmarshalInput{
+			Buf:     b,
+			Options: protoiface.UnmarshalOptions(o),
+		})
+		return err
 	}
 	return o.unmarshalMessageSlow(b, m)
 }

proto/encode.go

@@ -98,7 +98,7 @@ func (o MarshalOptions) MarshalAppend(b []byte, m Message) ([]byte, error) {
 }
 
 func (o MarshalOptions) marshalMessage(b []byte, m protoreflect.Message) ([]byte, error) {
-	if methods := protoMethods(m); methods != nil && methods.MarshalAppend != nil &&
+	if methods := protoMethods(m); methods != nil && methods.Marshal != nil &&
 		!(o.Deterministic && methods.Flags&protoiface.SupportMarshalDeterministic == 0) {
 		if methods.Size != nil {
 			sz := methods.Size(m, protoiface.MarshalOptions(o))
@@ -109,7 +109,11 @@ func (o MarshalOptions) marshalMessage(b []byte, m protoreflect.Message) ([]byte
 			}
 			o.UseCachedSize = true
 		}
-		return methods.MarshalAppend(b, m, protoiface.MarshalOptions(o))
+		out, err := methods.Marshal(m, protoiface.MarshalInput{
+			Buf:     b,
+			Options: protoiface.MarshalOptions(o),
+		})
+		return out.Buf, err
 	}
 	return o.marshalMessageSlow(b, m)
 }

proto/size.go

@@ -26,11 +26,11 @@ func sizeMessage(m protoreflect.Message) (size int) {
 	if methods != nil && methods.Size != nil {
 		return methods.Size(m, protoiface.MarshalOptions{})
 	}
-	if methods != nil && methods.MarshalAppend != nil {
+	if methods != nil && methods.Marshal != nil {
 		// This is not efficient, but we don't have any choice.
 		// This case is mainly used for legacy types with a Marshal method.
-		b, _ := methods.MarshalAppend(nil, m, protoiface.MarshalOptions{})
-		return len(b)
+		out, _ := methods.Marshal(m, protoiface.MarshalInput{})
+		return len(out.Buf)
 	}
 	return sizeMessageSlow(m)
 }

reflect/protoreflect/methods.go

@@ -19,18 +19,34 @@ type (
 		pragma.NoUnkeyedLiterals
 		Flags         supportFlags
 		Size          func(m Message, opts marshalOptions) int
-		MarshalAppend func(b []byte, m Message, opts marshalOptions) ([]byte, error)
-		Unmarshal     func(b []byte, m Message, opts unmarshalOptions) error
+		Marshal       func(m Message, in marshalInput) (marshalOutput, error)
+		Unmarshal     func(m Message, in unmarshalInput) (unmarshalOutput, error)
 		IsInitialized func(m Message) error
 	}
-	supportFlags   = uint64
+	supportFlags = uint64
+	marshalInput = struct {
+		pragma.NoUnkeyedLiterals
+		Buf     []byte
+		Options marshalOptions
+	}
+	marshalOutput = struct {
+		pragma.NoUnkeyedLiterals
+		Buf []byte
+	}
 	marshalOptions = struct {
 		pragma.NoUnkeyedLiterals
 		AllowPartial  bool
 		Deterministic bool
 		UseCachedSize bool
 	}
-
+	unmarshalInput = struct {
+		pragma.NoUnkeyedLiterals
+		Buf     []byte
+		Options unmarshalOptions
+	}
+	unmarshalOutput = struct {
+		pragma.NoUnkeyedLiterals
+	}
 	unmarshalOptions = struct {
 		pragma.NoUnkeyedLiterals
 		Merge          bool

runtime/protoiface/methods.go

@@ -25,14 +25,14 @@ type Methods = struct {
 	// MarshalAppend must be provided if a custom Size is provided.
 	Size func(m protoreflect.Message, opts MarshalOptions) int
 
-	// MarshalAppend appends the wire-format encoding of m to b, returning the result.
+	// Marshal writes the wire-format encoding of m to the provided buffer.
 	// Size should be provided if a custom MarshalAppend is provided.
 	// It must not perform required field checks.
-	MarshalAppend func(b []byte, m protoreflect.Message, opts MarshalOptions) ([]byte, error)
+	Marshal func(m protoreflect.Message, in MarshalInput) (MarshalOutput, error)
 
-	// Unmarshal parses the wire-format message in b and merges the result in m.
+	// Unmarshal parses the wire-format encoding of a message and merges the result to m.
 	// It must not reset m or perform required field checks.
-	Unmarshal func(b []byte, m protoreflect.Message, opts UnmarshalOptions) error
+	Unmarshal func(m protoreflect.Message, in UnmarshalInput) (UnmarshalOutput, error)
 
 	// IsInitialized returns an error if any required fields in m are not set.
 	IsInitialized func(m protoreflect.Message) error
@@ -48,6 +48,21 @@ const (
 	SupportUnmarshalDiscardUnknown
 )
 
+// MarshalInput is input to the marshaler.
+type MarshalInput = struct {
+	pragma.NoUnkeyedLiterals
+
+	Buf     []byte // output is appended to this buffer
+	Options MarshalOptions
+}
+
+// MarshalOutput is output from the marshaler.
+type MarshalOutput = struct {
+	pragma.NoUnkeyedLiterals
+
+	Buf []byte // contains marshaled message
+}
+
 // MarshalOptions configure the marshaler.
 //
 // This type is identical to the one in package proto.
@@ -59,6 +74,21 @@ type MarshalOptions = struct {
 	UseCachedSize bool
 }
 
+// UnmarshalInput is input to the unmarshaler.
+type UnmarshalInput = struct {
+	pragma.NoUnkeyedLiterals
+
+	Buf     []byte // input buffer
+	Options UnmarshalOptions
+}
+
+// UnmarshalOutput is output from the unmarshaler.
+type UnmarshalOutput = struct {
+	pragma.NoUnkeyedLiterals
+
+	// Contents available for future expansion.
+}
+
 // UnmarshalOptions configures the unmarshaler.
 //
 // This type is identical to the one in package proto.