[ws server]: should reply parse_error when deserialization fails

[niklasad1]

The server should reply with -32700 Parse error when the deserialization fails, see https://github.com/paritytech/jsonrpsee/blob/master/src/transport/ws/server.rs#L339-#L342

[tomusdrw]

The problem with this is that you need to at least extract the id of the call for the response to make any sense (in WS the user can't match request with a response in any other way). We do it like this in jsonrpc:
https://github.com/paritytech/jsonrpc/blob/master/core/src/types/request.rs#L49

[niklasad1]

Thanks, got it we do the same in jsonrpsee.

However, in the v2 we just return parse_error with id=null if the deserialization failed, see https://github.com/paritytech/jsonrpsee/blob/v2/src/ws/transport.rs#L423-#L426

After reading

If there was an error in detecting the id in the Request object (e.g. Parse error/Invalid Request), it MUST be Null.

I got a little worried that it's actually possible that we actually could detect the id when something else failed during parsing. But I think that is a bad idea because it could be parsing order dependent I guess?!

To elaborate what I mean is the following:

     # id is missing, can't be parsed
     req: {"jsonrpc":"2.0","method":"say_hello","id"}
     response:  {"jsonrpc":"2.0","error":{"code":-32700,"message":"Parse error"},"id":null}

     # invalid params but id is valid,  deserialization could fail
     req: {"jsonrpc":"2.0","method":"say_hello", "params": [1, "id": 1212}
     response:  {"jsonrpc":"2.0","error":{"code":-32700,"message":"Parse error"},"id":1212},`

[niklasad1]

Fixed by #180