Read consensus spec from a file instead from the CL

[barnabasbusa]

It would be great if there would be no CL dependency of the rbuilder. While the CL endpoint could be provided, it should be optional, and the chain spec config values should be able to be read from a file.

[ferranbt]

Note that even if we load chain spec config values from a file you still need a CL to listen for the beacon node events to trigger block building.

[barnabasbusa]

Thats alright. The idea is rbuilder shouldn't fail to start up just because the CL endpoint is not online yet.

[ryanschneider]

For context, the issue is a circular dependency:

• Typically its cleaner to start the EL first, since the CL will attempt to talk to the engine API on startup and thus will log errors until the EL is active (or worse case fail to start, though I'm not aware of any CLs that behave this way).
• And since we are trying to run reth and rbuilder in the same container (see WIP feat(Dockerfile): Add reth to container image so we can run both in same container for kurtosis. #200) we'd like to start the rbuilder/reth container before the CL container.
• But then rbuilder fails to start with this error (reproduced on builder-playground by changing the config to point to the wrong CL port):

2024-10-01T15:00:43.426908Z  INFO Server::run{addr=0.0.0.0:6061}: warp::server: listening on http://0.0.0.0:6061
2024-10-01T15:00:43.426916Z  INFO Server::run{addr=0.0.0.0:6060}: warp::server: listening on http://0.0.0.0:6060
Error: could not send request: error sending request for url (http://localhost:3501/eth/v1/config/spec): error trying to connect: tcp connect error: Connection refused (os error 61)

Caused by:
   0: error sending request for url (http://localhost:3501/eth/v1/config/spec): error trying to connect: tcp connect error: Connection refused (os error 61)
   1: error trying to connect: tcp connect error: Connection refused (os error 61)
   2: tcp connect error: Connection refused (os error 61)
   3: Connection refused (os error 61)

Location:
    crates/rbuilder/src/live_builder/config.rs:506:24

If rbuilder had support for getting the spec from a file, then the events stream could be best effort.

[bertmiller]

Can we "fake" the CL trigger by just sending data to the builder that emulates it? If not, I think we could we implement an API that lets us do that so we could avoid needing a CL altogether (I'm imagining running a Python script that "drives" building).

[ferranbt]

Would this work? #203

I would prefer not to load the whole CL spec since we only use one parameter.