Support RSocket as a transport

[rstoyanchev]

The RSocket protocol has all the semantics required to carry GraphQL requests. The request-response interaction maps to queries and mutations while request-stream maps to subscriptions. RSocket supports Reactive Streams signals on the wire to complete a stream from the server side or to cancel it from the client side. That means, GraphQL over RSocket does not require a spec other than agreeing on the format for serialized requests and response. For that we can follow the HTTP spec defined format "application/graphql+json".

On the implementation, this should be very straight-forward, given the transport abstractions we have in place for client and server.

[linux-china]

application/graphql+json will be added on https://github.com/rsocket/rsocket/blob/master/Extensions/WellKnownMimeTypes.md as Well-known MIME Type?

I mean RSocket payload's composite metadata contains message/x.rsocket.mime-type.v0 and its value is application/graphql+json

[viglucci]

What does the +json extension on the proposed mime type denote?

The GraphQL spec states:

A standard GraphQL POST request should use the application/json content type, and include a JSON-encoded body of the following form:

{
  "query": "...",
  "operationName": "...",
  "variables": { "myVariable": "someValue", ... }
}

...

If the "application/graphql" Content-Type header is present, treat the HTTP POST body contents as the GraphQL query string.

I suspect that a graphql RSocket implementation would translate this as either including a metadata mimetype as application/json and using the JSON representation as shown above, or as application/graphql and providing a GraphQL query string as the payload body.

Ex:

query {
  getTask(id: "0x3") {
    id
    title
    completed
    user {
      username
      name
    }
  }
}

[bclozel]

@viglucci we are referring here to the GraphQL HTTP spec: https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#content-types

"application/graphql+json" will be the required, default MIME type per that spec. The "+json" suffix is merely a standard way to describe that a MIME type's representation follows a well known format.

See also #108

[viglucci]

@bclozel Thanks for the explanation.

Right now RSocket-JS is sending GraphQL payloads as application/graphql. I'll look to migrate the payload serialization to conform with application/graphql+json to hopefully have compatibility between RSocket-JS GraphQL clients and Spring GraphQL.