Sync JSON web decoders (#1028)

This syncs the web JSON decoder used internally.

The new decoder uses `js_interop` instead of the Dart standard library to
improve performance when compiled to JS.

## Benchmarks

master, JS:

    protobuf_from_json_string(RunTimeRaw): 1423.134328358209 us.

PR, JS:

    protobuf_from_json_string(RunTimeRaw): 971 us. 

Wasm and VM benchmarks don't change as they keep using the old implementation.

The new implementation is slower with Wasm as it does more JS interop, so we
keep using the old one.

Author: osa1

protobuf/CHANGELOG.md

@@ -8,8 +8,12 @@
 * Some of the private `PbFieldType` members are made public, to allow using
   them in internal libraries. This type is for internal use only. ([#1027])
 
+* Improve performance of `GeneratedMessage` members: `writeToJsonMap`,
+  `writeToJson`, `mergeFromJson`, `mergeFromJsonMap`. ([#1028])
+
 [#1026]: https://github.com/google/protobuf.dart/pull/1026
 [#1027]: https://github.com/google/protobuf.dart/pull/1027
+[#1028]: https://github.com/google/protobuf.dart/pull/1028
 
 ## 4.1.1
 

protobuf/lib/src/protobuf/generated_message.dart

@@ -227,7 +227,7 @@ abstract class GeneratedMessage {
   /// Unknown field data, data for which there is no metadata for the associated
   /// field, will only be included if this message was deserialized from the
   /// same wire format.
-  Map<String, dynamic> writeToJsonMap() => _writeToJsonMap(_fieldSet);
+  Map<String, dynamic> writeToJsonMap() => json_lib.writeToJsonMap(_fieldSet);
 
   /// Returns a JSON string that encodes this message.
   ///
@@ -246,7 +246,7 @@ abstract class GeneratedMessage {
   /// Unknown field data, data for which there is no metadata for the associated
   /// field, will only be included if this message was deserialized from the
   /// same wire format.
-  String writeToJson() => jsonEncode(writeToJsonMap());
+  String writeToJson() => json_lib.writeToJsonString(_fieldSet);
 
   /// Returns an Object representing Proto3 JSON serialization of `this`.
   ///
@@ -318,27 +318,17 @@ abstract class GeneratedMessage {
     String data, [
     ExtensionRegistry extensionRegistry = ExtensionRegistry.EMPTY,
   ]) {
-    /// Disable lazy creation of Dart objects for a dart2js speedup.
-    /// This is a slight regression on the Dart VM.
-    /// TODO(skybrian) we could skip the reviver if we're running
-    /// on the Dart VM for a slight speedup.
-    final Map<String, dynamic> jsonMap = jsonDecode(
-      data,
-      reviver: _emptyReviver,
-    );
-    _mergeFromJsonMap(_fieldSet, jsonMap, extensionRegistry);
+    json_lib.mergeFromJsonString(_fieldSet, data, extensionRegistry);
   }
 
-  static Object? _emptyReviver(Object? k, Object? v) => v;
-
   /// Merges field values from a JSON object represented as a Dart map.
   ///
   /// The encoding is described in [GeneratedMessage.writeToJson].
   void mergeFromJsonMap(
     Map<String, dynamic> json, [
     ExtensionRegistry extensionRegistry = ExtensionRegistry.EMPTY,
   ]) {
-    _mergeFromJsonMap(_fieldSet, json, extensionRegistry);
+    json_lib.mergeFromJsonMap(_fieldSet, json, extensionRegistry);
   }
 
   /// Adds an extension field value to a repeated field.

protobuf/lib/src/protobuf/internal.dart

@@ -8,21 +8,15 @@
 library;
 
 import 'dart:collection' show ListBase, MapBase;
-import 'dart:convert'
-    show
-        Utf8Decoder,
-        Utf8Encoder,
-        base64Decode,
-        base64Encode,
-        jsonDecode,
-        jsonEncode;
+import 'dart:convert' show Utf8Decoder, Utf8Encoder, base64Decode, base64Encode;
 import 'dart:math' as math;
 import 'dart:typed_data' show ByteData, Endian, Uint8List;
 
 import 'package:fixnum/fixnum.dart' show Int64;
 import 'package:meta/meta.dart' show UseResult;
 
 import 'consts.dart';
+import 'json/json.dart' as json_lib;
 import 'json_parsing_context.dart';
 import 'permissive_compare.dart';
 import 'type_registry.dart';
@@ -45,7 +39,6 @@ part 'field_set.dart';
 part 'field_type.dart';
 part 'generated_message.dart';
 part 'generated_service.dart';
-part 'json.dart';
 part 'message_set.dart';
 part 'pb_list.dart';
 part 'pb_map.dart';

protobuf/lib/src/protobuf/json.dart renamed to protobuf/lib/src/protobuf/json/json.dart

@@ -2,9 +2,20 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of 'internal.dart';
+import 'dart:convert' show base64Decode, base64Encode;
 
-Map<String, dynamic> _writeToJsonMap(FieldSet fs) {
+import 'package:fixnum/fixnum.dart' show Int64;
+
+import '../consts.dart';
+import '../internal.dart';
+import '../utils.dart';
+
+// Use json_vm.dart with VM and dart2wasm, json_web.dart with dart2js.
+// json_web.dart uses JS interop for parsing, and JS interop is too slow on
+// Wasm. VM's patch performs better in Wasm.
+export 'json_vm.dart' if (dart.library.html) 'json_web.dart';
+
+Map<String, dynamic> writeToJsonMap(FieldSet fs) {
   dynamic convertToMap(dynamic fieldValue, int fieldType) {
     final baseType = PbFieldType.baseType(fieldType);
 
@@ -61,15 +72,15 @@ Map<String, dynamic> _writeToJsonMap(FieldSet fs) {
   List writeMap(PbMap fieldValue, MapFieldInfo fi) => List.from(
     fieldValue.entries.map(
       (MapEntry e) => {
-        '${PbMap._keyFieldNumber}': convertToMap(e.key, fi.keyFieldType),
-        '${PbMap._valueFieldNumber}': convertToMap(e.value, fi.valueFieldType),
+        '$mapKeyFieldNumber': convertToMap(e.key, fi.keyFieldType),
+        '$mapValueFieldNumber': convertToMap(e.value, fi.valueFieldType),
       },
     ),
   );
 
   final result = <String, dynamic>{};
-  for (final fi in fs._infosSortedByTag) {
-    final value = fs._values[fi.index!];
+  for (final fi in fs.infosSortedByTag) {
+    final value = fs.values[fi.index!];
     if (value == null || (value is List && value.isEmpty)) {
       continue; // It's missing, repeated, or an empty byte array.
     }
@@ -82,18 +93,18 @@ Map<String, dynamic> _writeToJsonMap(FieldSet fs) {
     }
     result['${fi.tagNumber}'] = convertToMap(value, fi.type);
   }
-  final extensions = fs._extensions;
+  final extensions = fs.extensions;
   if (extensions != null) {
-    for (final tagNumber in sorted(extensions._tagNumbers)) {
-      final value = extensions._values[tagNumber];
+    for (final tagNumber in sorted(extensions.tagNumbers)) {
+      final value = extensions.values[tagNumber];
       if (value is List && value.isEmpty) {
         continue; // It's repeated or an empty byte array.
       }
-      final fi = extensions._getInfoOrNull(tagNumber)!;
+      final fi = extensions.getInfoOrNull(tagNumber)!;
       result['$tagNumber'] = convertToMap(value, fi.type);
     }
   }
-  final unknownJsonData = fs._unknownJsonData;
+  final unknownJsonData = fs.unknownJsonData;
   if (unknownJsonData != null) {
     unknownJsonData.forEach((key, value) {
       result[key] = value;
@@ -104,20 +115,20 @@ Map<String, dynamic> _writeToJsonMap(FieldSet fs) {
 
 // Merge fields from a previously decoded JSON object.
 // (Called recursively on nested messages.)
-void _mergeFromJsonMap(
+void mergeFromJsonMap(
   FieldSet fs,
   Map<String, dynamic> json,
   ExtensionRegistry? registry,
 ) {
-  fs._ensureWritable();
+  fs.ensureWritable();
   final keys = json.keys;
-  final meta = fs._meta;
+  final meta = fs.meta;
   for (final key in keys) {
     var fi = meta.byTagAsString[key];
     if (fi == null) {
-      fi = registry?.getExtension(fs._messageName, int.parse(key));
+      fi = registry?.getExtension(fs.messageName, int.parse(key));
       if (fi == null) {
-        (fs._unknownJsonData ??= {})[key] = json[key];
+        (fs.unknownJsonData ??= {})[key] = json[key];
         continue;
       }
     }
@@ -144,7 +155,7 @@ void _appendJsonList(
   FieldInfo fi,
   ExtensionRegistry? registry,
 ) {
-  final repeated = fi._ensureRepeatedField(meta, fs);
+  final repeated = fi.ensureRepeatedField(meta, fs);
   // Micro optimization. Using "for in" generates the following and iterator
   // alloc:
   //   for (t1 = J.get$iterator$ax(json), t2 = fi.tagNumber, t3 = fi.type,
@@ -175,23 +186,23 @@ void _appendJsonMap(
   ExtensionRegistry? registry,
 ) {
   final entryMeta = fi.mapEntryBuilderInfo;
-  final map = fi._ensureMapField(meta, fs);
+  final map = fi.ensureMapField(meta, fs);
   for (final jsonEntryDynamic in jsonList) {
     final jsonEntry = jsonEntryDynamic as Map<String, dynamic>;
     final entryFieldSet = FieldSet(null, entryMeta);
     final convertedKey = _convertJsonValue(
       entryMeta,
       entryFieldSet,
-      jsonEntry['${PbMap._keyFieldNumber}'],
-      PbMap._keyFieldNumber,
+      jsonEntry['$mapKeyFieldNumber'],
+      mapKeyFieldNumber,
       fi.keyFieldType,
       registry,
     );
     var convertedValue = _convertJsonValue(
       entryMeta,
       entryFieldSet,
-      jsonEntry['${PbMap._valueFieldNumber}'],
-      PbMap._valueFieldNumber,
+      jsonEntry['$mapValueFieldNumber'],
+      mapValueFieldNumber,
       fi.valueFieldType,
       registry,
     );
@@ -223,10 +234,10 @@ void _setJsonField(
   // Therefore we run _validateField for debug builds only to validate
   // correctness of conversion.
   assert(() {
-    fs._validateField(fi, value);
+    fs.validateField(fi, value);
     return true;
   }());
-  fs._setFieldUnchecked(meta, fi, value);
+  fs.setFieldUnchecked(meta, fi, value);
 }
 
 /// Converts [value] from the JSON format to the Dart data type suitable for
@@ -298,7 +309,7 @@ dynamic _convertJsonValue(
         // The following call will return null if the enum value is unknown.
         // In that case, we want the caller to ignore this value, so we return
         // null from this method as well.
-        return meta._decodeEnum(tagNumber, registry, value);
+        return meta.decodeEnum(tagNumber, registry, value);
       }
       expectedType = 'int or stringified int';
       break;
@@ -333,8 +344,8 @@ dynamic _convertJsonValue(
     case PbFieldType.MESSAGE_BIT:
       if (value is Map) {
         final messageValue = value as Map<String, dynamic>;
-        final subMessage = meta._makeEmptyMessage(tagNumber, registry);
-        _mergeFromJsonMap(subMessage._fieldSet, messageValue, registry);
+        final subMessage = meta.makeEmptyMessage(tagNumber, registry);
+        mergeFromJsonMap(subMessage.fieldSet, messageValue, registry);
         return subMessage;
       }
       expectedType = 'nested message or group';

protobuf/lib/src/protobuf/json/json_vm.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert' show jsonDecode, jsonEncode;
+
+import '../internal.dart';
+import 'json.dart';
+
+String writeToJsonString(FieldSet fs) => jsonEncode(writeToJsonMap(fs));
+
+/// Merge fields from a [json] string.
+void mergeFromJsonString(
+  FieldSet fs,
+  String json,
+  ExtensionRegistry? registry,
+) {
+  final jsonMap = jsonDecode(json);
+  if (jsonMap is! Map<String, dynamic>) {
+    throw ArgumentError.value(json, 'json', 'Does not parse to a JSON object.');
+  }
+  mergeFromJsonMap(fs, jsonMap, registry);
+}