You are doing JSON APIs wrong.

When you use JSON to call an API – not a REST API, but something like JSON-RPC – you will usually want to encode
one of several possible messages.

Your request body looks like this:

{
    "type": "MessageWithA",
    "data": {
        "a": 5
    }
}

Or like this:

{
    "type": "MessageWithB",
    "b": 5
}

However, that’s bad. Here’s how you should do it:

{
    "messageWithA": {
        "a": 5
    }
}

Or

{
    "type": "MessageWithA",
    "data": {
        "messageWithA": {
            "a": 5
        }
    }
}

Why? Stream parsers.

Stream parsers?

There are two ways of processing a JSON telegram. The first is to read the telegram into a JSON object,
and then process the object inside-out.
This usually takes the form of

if (event["type"] == "MessageWithA") {
    handleAMessage(event["data"]);
}

However, this has the unavoidable overhead of allocating an object for every part of the JSON tree.
Especially if you are decoding into a well-typed internal data structure, you allocate this object just to throw it
away shortly after. This creates unnecessary memory overhead.

A faster way is with a stream parser. A stream parser lexes the input text into a stream of JSON tokens,
such as BeginObject, KeyString, BeginArray, String, String, Int, EndArray, EndObject for { "a": ["b", "c", 5]}.
These tokens are then consumed by a recursive parser, usually generated, that produces the internal data structure
directly. In other words, there never exists a recursive data structure for t