RFC: WebSockets support in Massa API

[aoudiamoncef]

Problem

Actually, in order to explore Massa blockchain, ours consumers are using short pooling HTTP requests
which imply some drawbacks:

• Less efficient resources consumption used to handle incoming HTTP requests.
• Retrieved data could be stale or outdated between two calls.
• The temporary data is lost if it's not requested at time.

Proposition

Massa node tends to produce a consequent amount of data in real time which could be efficiently served over WebSockets.

The first proposed subscriptions tend to share the state of the Blockchain which was the most common usage from consumers feedbacks.

We'll implement a new JSON-RPC API which supports HTTP + WS. It'll unify the actual private and public API's. It'll be available as an experimental feature in the next release, new ports will be dedicated to it.

Websocket subscriptions

To be implemented:

• subscribe_blocks/unsubscribe_blocks
• subscribe_blocks_headers/unsubscribe_blocks_headers

Candidats:

• subscribe_endorsements/unsubscribe_endorsements
• subscribe_operations/unsubscribe_operations
• subscribe_execution_events/unsubscribe_execution_events

Technical stack:
We'll use jsonrpsee crate as a server which supports both HTTP/WebSockets. It offers a bunch of features and tweaks as it’s based on tokio-tower and hyper crates. It’s already used in production ready project as substrate.

[AurelienFT]

I think you can add some explanations on how you will fetch the datas from the differents modules. I think using channels could be great.

Also I checked a bit how jsonrpsee implemented it and they follow the eth implementation so I think we will have 1 method for the websocket and as first parameter we will specify to which value we ant to subscribe, is that ok ?

[AurelienFT]

It's still unclear to me. foo_sub is kind of a namespace but with the name after the _ reused in the name of the method ? Why there is a need for such a namespace and not only a method name ?

[aoudiamoncef]

You could remove foo and make it as a namespace in the parent macro.
It's a small difference in the result(notification) of subscription :

{
  "jsonrpc":"2.0",
   "method":"foo_subNotif" instead of "foo_sub", you are controlling the name of this field.
   "params":["subscription":"someID", "result":"some string"]
}

Complete examples in crate documentation

[AurelienFT]

I might be dumb but I don't see why we can't just call the method subscribe and having the data we want to subscribe as first parameter ? It's more easy than this namespace thing

[aoudiamoncef]

For the Massa implementation, we don't use any namespace.

So we be KISS as possible.

This is a concret example of usage from Polkadot dashboard

It's a kind of convention to separate subscribe/unsubscribe requests from notifications(responses).

[AurelienFT]

Yes ok. Let's see a first example with blocks and blocks headers.