.Net Protocol Buffers to JSON, JsonFormatReader class does not handle outmost curly braces?

Question

I am working on using Google Protocol Buffers, using the protobuf-csharp-port library (https://code.google.com/p/protobuf-csharp-port/). The Google.ProtocolBuffers.Serialization class has a JsonFormatReader / JsonFormatWriter class, when I use them they do not place beginning and ending curly braces to the JSON document, nor they can read the same document they write if I add beginning and ending braces.

So for example Calling

        PB.ProtoBufMessage message = CreateMyMessage();

        string json;
        using (StringWriter sw = new StringWriter())
        {
            ICodedOutputStream output = JsonFormatWriter.CreateInstance(sw);

            message.WriteTo(output);
            output.Flush();
            json = sw.ToString();
        }

Creates:

"\"field1\":\"prop1\",\"field2\":1,\"subitem\":{\"x\":0,\"y\":0,\"z\":0}"

If I try to parse

String jsonmessage = "{\"field1\":\"prop1\",\"field2\":1,\"subitem\":{\"x\":0,\"y\":0,\"z\":0}}"

using

    PB.ProtoBufMessage copy;
    ICodedInputStream input = JsonFormatReader.CreateInstance(jsonmessage);
    copy = PB.ProtoBufMessage.CreateBuilder().MergeFrom(input).Build();

I get the following:

(1:1) error: Unexpected token '{', expected: '"'.

   at Google.ProtocolBuffers.Serialization.JsonCursor.Assert(Boolean cond, Char expected)
   at Google.ProtocolBuffers.Serialization.JsonCursor.Consume(Char ch)
   at Google.ProtocolBuffers.Serialization.JsonCursor.ReadString()
   at Google.ProtocolBuffers.Serialization.JsonFormatReader.PeekNext(String& field)
   at Google.ProtocolBuffers.Serialization.AbstractReader.Google.ProtocolBuffers.ICodedInputStream.ReadTag(UInt32& fieldTag, String& fieldName)
   at ...

Why is the { } missing, and is this valid JSON?

Answer 1

You need to write/read message start/end. Like:

output.WriteMessageStart();
message.WriteTo(output);
output.WriteMessageEnd();

Similary wilhe reading:

input.ReadMessageStart();
builder.MergeFrom(input);
input.ReadMessageEnd();

The above code works with json and binary reader/writers.