[cln-rpc] Support REST server

[jblachly]

Motivated by cashubtc/cdk#1249

Summary

the cln-rpc rust crate is a great way to interact with a CLN node, but works only over a Unix domain socket.

Request

Given that the JSON-RPC is the same over local socket and HTTP REST server, it seems like the crate could support CLN's REST server with just some minor surgery.

Potential Solution

pub struct ClnRpc {
    transport: Transport,
    // Remove UnixStream
}

pub enum Transport {
    Unix(PathBuf),
    Http(Url),  // e.g., Url::parse("http://localhost:8080/")?
}

and then match on Transport in ClnRpc::call.

Before I did any work on this, I wanted to get a concept thumbs up or down from the maintainers

[ShahanaFarooqui]

Have you had a chance to review our existing clnrest plugin?

• Documentation
• Source Code

We also have an open PR, Clnrest: dynamic paths, which will be able to better support Cashu requirements.

Could you please let us know if you still propose this solution and why?