Always serialize 64-bit integers as strings in JSON.

lib/src/protobuf/json.dart

 // Copyright (c) 2015, 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.
 
 part of protobuf;
 
-// Range of integers in JSON (53-bit integers).
-Int64 _MAX_JSON_INT = new Int64.fromInts(0x200000, 0);
-Int64 _MIN_JSON_INT = -_MAX_JSON_INT;
-
 Map<String, dynamic> _writeToJsonMap(_FieldSet fs) {
   convertToMap(fieldValue, fieldType) {
     int baseType = PbFieldType._baseType(fieldType);
 
     if (_isRepeated(fieldType)) {
       return new List.from(fieldValue.map((e) => convertToMap(e, baseType)));
     }
 
     switch (baseType) {
       case PbFieldType._BOOL_BIT:
       case PbFieldType._STRING_BIT:
       case PbFieldType._FLOAT_BIT:
       case PbFieldType._DOUBLE_BIT:
       case PbFieldType._INT32_BIT:
       case PbFieldType._SINT32_BIT:
       case PbFieldType._UINT32_BIT:
       case PbFieldType._FIXED32_BIT:
       case PbFieldType._SFIXED32_BIT:
         return fieldValue;
       case PbFieldType._BYTES_BIT:
         // Encode 'bytes' as a base64-encoded string.
         return BASE64.encode(fieldValue as List<int>);
       case PbFieldType._ENUM_BIT:
         return fieldValue.value; // assume |value| < 2^52
       case PbFieldType._INT64_BIT:
       case PbFieldType._SINT64_BIT:
       case PbFieldType._UINT64_BIT:
       case PbFieldType._FIXED64_BIT:
       case PbFieldType._SFIXED64_BIT:
-        // Use strings for 64-bit integers which cannot fit in doubles.
-        if (_MIN_JSON_INT <= fieldValue && fieldValue <= _MAX_JSON_INT) {
-          return fieldValue.toInt();
-        }
         return fieldValue.toString();
       case PbFieldType._GROUP_BIT:
       case PbFieldType._MESSAGE_BIT:
         return fieldValue.writeToJsonMap();
       default:
         throw 'Unknown type $fieldType';
     }
   }
 
   var result = <String, dynamic>{};
@@ skipping 134 matching lines @@
             subMessage._fieldSet, value as Map<String, dynamic>, registry);
         return subMessage;
       }
       expectedType = 'nested message or group';
       break;
     default:
       throw new ArgumentError('Unknown type $fieldType');
   }
   throw new ArgumentError('Expected type $expectedType, got $value');
 }