[WIP] Avoid intermediate values when serializing and deserializing proto3 JSON

protobuf/benchmarks/common.dart

@@ -8,7 +8,7 @@
 /// both on the VM and when compiled to JavaScript.
 library common;
 
-import 'dart:convert' show jsonDecode, jsonEncode;
+import 'dart:convert' show jsonEncode;
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
@@ -101,35 +101,35 @@ class Factories {
         fromBuffer: (List<int> binary) => p2.GoogleMessage1.fromBuffer(binary),
         fromJson: (String json) => p2.GoogleMessage1.fromJson(json),
         fromProto3JsonString: (String json) =>
-            p2.GoogleMessage1.create()..mergeFromProto3Json(jsonDecode(json)),
+            p2.GoogleMessage1.create()..mergeFromProto3JsonString(json),
         fromProto3JsonObject: (Object json) =>
             p2.GoogleMessage1.create()..mergeFromProto3Json(json)),
     'benchmarks.proto3.GoogleMessage1': Factories._(
         fromBuffer: (List<int> binary) => p3.GoogleMessage1.fromBuffer(binary),
         fromJson: (String json) => p3.GoogleMessage1.fromJson(json),
         fromProto3JsonString: (String json) =>
-            p3.GoogleMessage1.create()..mergeFromProto3Json(jsonDecode(json)),
+            p3.GoogleMessage1.create()..mergeFromProto3JsonString(json),
         fromProto3JsonObject: (Object json) =>
             p3.GoogleMessage1.create()..mergeFromProto3Json(json)),
     'benchmarks.proto2.GoogleMessage2': Factories._(
         fromBuffer: (List<int> binary) => GoogleMessage2.fromBuffer(binary),
         fromJson: (String json) => GoogleMessage2.fromJson(json),
         fromProto3JsonString: (String json) =>
-            GoogleMessage2.create()..mergeFromProto3Json(jsonDecode(json)),
+            GoogleMessage2.create()..mergeFromProto3JsonString(json),
         fromProto3JsonObject: (Object json) =>
             GoogleMessage2.create()..mergeFromProto3Json(json)),
     'benchmarks.google_message3.GoogleMessage3': Factories._(
         fromBuffer: (List<int> binary) => GoogleMessage3.fromBuffer(binary),
         fromJson: (String json) => GoogleMessage3.fromJson(json),
         fromProto3JsonString: (String json) =>
-            GoogleMessage3.create()..mergeFromProto3Json(jsonDecode(json)),
+            GoogleMessage3.create()..mergeFromProto3JsonString(json),
         fromProto3JsonObject: (Object json) =>
             GoogleMessage3.create()..mergeFromProto3Json(json)),
     'benchmarks.google_message4.GoogleMessage4': Factories._(
         fromBuffer: (List<int> binary) => GoogleMessage4.fromBuffer(binary),
         fromJson: (String json) => GoogleMessage4.fromJson(json),
         fromProto3JsonString: (String json) =>
-            GoogleMessage4.create()..mergeFromProto3Json(jsonDecode(json)),
+            GoogleMessage4.create()..mergeFromProto3JsonString(json),
         fromProto3JsonObject: (Object json) =>
             GoogleMessage4.create()..mergeFromProto3Json(json)),
   };
@@ -231,7 +231,7 @@ class ToProto3JsonStringBenchmark extends _ProtobufBenchmark {
   void run() {
     for (final ds in datasets) {
       for (final unpacked in ds.unpacked) {
-        jsonEncode(unpacked.toProto3Json());
+        unpacked.toProto3JsonString();
       }
     }
   }

protobuf/lib/meta.dart

@@ -44,6 +44,8 @@ const GeneratedMessage_reservedNames = <String>[
   'mergeFromJsonMap',
   'mergeFromMessage',
   'mergeFromProto3Json',
+  'mergeFromProto3JsonReader',
+  'mergeFromProto3JsonString',
   'mergeUnknownFields',
   'noSuchMethod',
   'runtimeType',
@@ -52,6 +54,8 @@ const GeneratedMessage_reservedNames = <String>[
   'toBuilder',
   'toDebugString',
   'toProto3Json',
+  'toProto3JsonSink',
+  'toProto3JsonString',
   'toString',
   'unknownFields',
   'writeToBuffer',

protobuf/lib/protobuf.dart

@@ -11,18 +11,19 @@ import 'dart:math' as math;
 import 'dart:typed_data' show TypedData, Uint8List, ByteData, Endian;
 
 import 'package:fixnum/fixnum.dart' show Int64;
+import 'package:jsontool/jsontool.dart';
 import 'package:meta/meta.dart' show UseResult;
 
 import 'src/protobuf/json_parsing_context.dart';
 import 'src/protobuf/permissive_compare.dart';
 import 'src/protobuf/type_registry.dart';
 export 'src/protobuf/type_registry.dart' show TypeRegistry;
 
+part 'src/protobuf/builder_info.dart';
 part 'src/protobuf/coded_buffer.dart';
 part 'src/protobuf/coded_buffer_reader.dart';
 part 'src/protobuf/coded_buffer_writer.dart';
 part 'src/protobuf/consts.dart';
-part 'src/protobuf/builder_info.dart';
 part 'src/protobuf/event_plugin.dart';
 part 'src/protobuf/exceptions.dart';
 part 'src/protobuf/extension.dart';
@@ -37,14 +38,16 @@ part 'src/protobuf/generated_service.dart';
 part 'src/protobuf/json.dart';
 part 'src/protobuf/pb_list.dart';
 part 'src/protobuf/pb_map.dart';
+part 'src/protobuf/proto3_json_reader.dart';
+part 'src/protobuf/proto3_json_writer.dart';
 part 'src/protobuf/protobuf_enum.dart';
-part 'src/protobuf/proto3_json.dart';
 part 'src/protobuf/rpc_client.dart';
 part 'src/protobuf/unknown_field_set.dart';
-part 'src/protobuf/utils.dart';
 part 'src/protobuf/unpack.dart';
+part 'src/protobuf/utils.dart';
 part 'src/protobuf/wire_format.dart';
 
+/// Used by generated code, do not use.
 // TODO(sra): Use Int64.parse() when available - see http://dartbug.com/21915.
 Int64 parseLongInt(String text) {
   if (text.startsWith('0x')) return Int64.parseHex(text.substring(2));
@@ -54,3 +57,19 @@ Int64 parseLongInt(String text) {
 }
 
 const _utf8 = Utf8Codec(allowMalformed: true);
+
+/// Used by generated code, do not use.
+///
+/// Reads the next JSON object from the given [JsonReader].
+Object? nextJsonObject(JsonReader jsonReader) {
+  Object? json;
+  try {
+    final sink = jsonObjectWriter((result) {
+      json = result;
+    });
+    jsonReader.expectAnyValue(sink);
+  } on FormatException {
+    json = '<invalid Dart JSON object>';
+  }
+  return json;
+}

protobuf/lib/src/protobuf/builder_info.dart

@@ -41,18 +41,25 @@ class BuilderInfo {
 
   List<FieldInfo>? _sortedByTag;
 
-  // For well-known types.
-  final Object? Function(GeneratedMessage message, TypeRegistry typeRegistry)?
-      toProto3Json;
-  final Function(GeneratedMessage targetMessage, Object json,
-      TypeRegistry typeRegistry, JsonParsingContext context)? fromProto3Json;
+  /// JSON generator for well-known types.
+  final void Function(
+          GeneratedMessage msg, TypeRegistry typeRegistry, JsonSink jsonSink)?
+      writeToProto3JsonSink;
+
+  /// JSON parser for well-known types.
+  final Function(
+      GeneratedMessage msg,
+      JsonReader jsonReader,
+      TypeRegistry typeRegistry,
+      JsonParsingContext context)? mergeFromProto3JsonReader;
+
   final CreateBuilderFunc? createEmptyInstance;
 
   BuilderInfo(String? messageName,
       {PackageName package = const PackageName(''),
       this.createEmptyInstance,
-      this.toProto3Json,
-      this.fromProto3Json})
+      this.writeToProto3JsonSink,
+      this.mergeFromProto3JsonReader})
       : qualifiedMessageName = '${package.prefix}$messageName';
 
   void add<T>(

protobuf/lib/src/protobuf/generated_message.dart

@@ -208,24 +208,92 @@ abstract class GeneratedMessage {
   /// For the proto3 JSON format use: [toProto3Json].
   String writeToJson() => jsonEncode(writeToJsonMap());
 
-  /// Returns an Object representing Proto3 JSON serialization of `this`.
+  /// Returns Dart JSON object encoding this message following proto3 JSON
+  /// format.
+  ///
+  /// The returned object will have the same format as objects returned by
+  /// [jsonEncode].
+  ///
+  /// See [toProto3JsonSink] for details.
+  Object? toProto3Json(
+      {TypeRegistry typeRegistry = const TypeRegistry.empty()}) {
+    Object? object;
+    final objectSink = jsonObjectWriter((newObject) {
+      object = newObject;
+    });
+    _writeToProto3JsonSink(_fieldSet, typeRegistry, objectSink);
+    return object;
+  }
+
+  /// Returns a proto3 JSON string encoding this message.
+  ///
+  /// See [toProto3JsonSink] for details.
+  String toProto3JsonString(
+      {TypeRegistry typeRegistry = const TypeRegistry.empty()}) {
+    final buf = StringBuffer();
+    final stringSink = jsonStringWriter(buf);
+    toProto3JsonSink(typeRegistry, stringSink);
+    return buf.toString();
+  }
+
+  /// Writes proto3 JSON serialization of this message to the given [JsonSink].
   ///
   /// The key for each field is be the camel-cased name of the field.
   ///
-  /// Well-known types and their special JSON encoding are supported.
-  /// If a well-known type cannot be encoded (eg. a `google.protobuf.Timestamp`
-  /// with negative `nanoseconds`) an error is thrown.
+  /// Well-known types and their special JSON encoding are supported. If a
+  /// well-known type cannot be encoded (eg. a `google.protobuf.Timestamp` with
+  /// negative `nanoseconds`) an error is thrown.
   ///
   /// Extensions and unknown fields are not encoded.
   ///
   /// The [typeRegistry] is be used for encoding `Any` messages. If an `Any`
-  /// message encoding a type not in [typeRegistry] is encountered, an
-  /// error is thrown.
-  Object? toProto3Json(
-          {TypeRegistry typeRegistry = const TypeRegistry.empty()}) =>
-      _writeToProto3Json(_fieldSet, typeRegistry);
+  /// message encoding a type not in [typeRegistry] is encountered, an error is
+  /// thrown.
+  ///
+  /// The [newMessage] argument is for use in generated code, do not use.
+  void toProto3JsonSink(TypeRegistry typeRegistry, JsonSink jsonSink,
+      {bool newMessage = true}) {
+    _writeToProto3JsonSink(_fieldSet, typeRegistry, jsonSink,
+        newMessage: newMessage);
+  }
+
+  /// Merges field values from Dart representation of JSON following proto3
+  /// JSON format.
+  ///
+  /// [jsonObject] should be generated by [jsonDecode] or have the same format.
+  ///
+  /// See [mergeFromProto3JsonReader] documentation for details.
+  void mergeFromProto3Json(Object? jsonObject,
+          {TypeRegistry typeRegistry = const TypeRegistry.empty(),
+          bool ignoreUnknownFields = false,
+          bool supportNamesWithUnderscores = true,
+          bool permissiveEnums = false}) =>
+      mergeFromProto3JsonReader(
+        JsonReader.fromObject(jsonObject),
+        typeRegistry: typeRegistry,
+        ignoreUnknownFields: ignoreUnknownFields,
+        supportNamesWithUnderscores: supportNamesWithUnderscores,
+        permissiveEnums: permissiveEnums,
+      );
+
+  /// Marges field values from a [String] following proto3 JSON format.
+  ///
+  /// See [mergeFromProto3JsonReader] documentation for details.
+  void mergeFromProto3JsonString(String jsonString,
+          {TypeRegistry typeRegistry = const TypeRegistry.empty(),
+          bool ignoreUnknownFields = false,
+          bool supportNamesWithUnderscores = true,
+          bool permissiveEnums = false}) =>
+      mergeFromProto3JsonReader(
+        JsonReader.fromString(jsonString),
+        typeRegistry: typeRegistry,
+        ignoreUnknownFields: ignoreUnknownFields,
+        supportNamesWithUnderscores: supportNamesWithUnderscores,
+        permissiveEnums: permissiveEnums,
+      );
 
-  /// Merges field values from [json], a JSON object using proto3 encoding.
+  /// Merges field values from a [JsonReader] that reads from a JSON in proto3
+  /// JSON format.
   ///
   /// Well-known types and their special JSON encodings are supported.
   ///
@@ -252,13 +320,13 @@ abstract class GeneratedMessage {
   ///
   /// Throws [FormatException] if the JSON not formatted correctly (a String
   /// where a number was expected etc.).
-  void mergeFromProto3Json(Object? json,
+  void mergeFromProto3JsonReader(JsonReader jsonReader,
           {TypeRegistry typeRegistry = const TypeRegistry.empty(),
           bool ignoreUnknownFields = false,
           bool supportNamesWithUnderscores = true,
           bool permissiveEnums = false}) =>
-      _mergeFromProto3Json(json, _fieldSet, typeRegistry, ignoreUnknownFields,
-          supportNamesWithUnderscores, permissiveEnums);
+      _mergeFromProto3JsonReader(jsonReader, _fieldSet, typeRegistry,
+          ignoreUnknownFields, supportNamesWithUnderscores, permissiveEnums);
 
   /// Merges field values from [data], a JSON object, encoded as described by
   /// [GeneratedMessage.writeToJson].