toProto3JSON doesn't correctly handle map of bytes

[mjameswh]

We have some protobuf messages that contain fields of type map<string, bytes>. Both protobufjs and proto3-json-serializer's fromProto3JSON appears to work properly with those fields.

However, passing such messages through toProto3JSON results in incorrect behaviors while handling the bytes value.

• In proto3-json-serializer v2.0.0, there is no error, but the Buffer object is passed unmodified to the output object;
• In proto3-json-serializer v2.0.2, I get the following error message:

Error: toProto3JSON: don't know how to convert value my_buffer_content
 at convertSingleValue (/.../node_modules/proto3-json-serializer/typescript/src/toproto3json.ts:50:11)
 at toProto3JSON (/.../node_modules/proto3-json-serializer/typescript/src/toproto3json.ts:149:13)
 at /.../node_modules/proto3-json-serializer/typescript/src/toproto3json.ts:137:22
 at Array.map (<anonymous>)
 at toProto3JSON (/.../node_modules/proto3-json-serializer/typescript/src/toproto3json.ts:134:27)
 ... truncated ...

The bytes values are Buffer objects. I would expect toProto3JSON to convert them to base64-encoded strings, just like it does for a simple bytes field.

I haven't tested, but from looking at the code, I believe that repeated bytes likely suffer from the same incorrect behavior.

Environment details

• Node.js version: 20.17.0
• npm version: 10.8.2
• proto3-json-serializer version: 2.0.0 - 2.0.2

Steps to reproduce

1. Start with the official proto3-json-serializer repo's main branch;

2. In test-fixture/proto/test.proto, modify the message MessageWithMap to:

     message MessageWithMap {
         map<string, MapValue> map_field = 3;
         map<string, string> string_map_field = 4;
         map<string, int64> long_map_field = 5;
   +     map<string, bytes> bytes_map_field = 6;
     }

3. In typescript/test/unit/map.ts, add this to both message and json:

         'minus one': '-1',
         zero: '0',
       },
   +   bytesMapField: {
   +     key1: 'dmFsdWUgMQo=',
   +     key2: 'dmFsdWUgMgo=',
   +   },
     };
   

4. Run tests: npm test

5. Observe test failure