portal-bridge: Serve light client bootstrap data

[ogenev]

What was wrong?

Closes #849

How was it fixed?

For every slot, we request the latest finalized block root, if a new finalized block root is available, request and serve new LightClientBootstrap data.

To-Do

• Add entry to the release notes (may forgo for trivial changes)
• Clean up commit history

[njgheorghita]

Looks good! How hard would it be to add a peertest scenario for serve_light_client_bootstrap()? If it's not too complex to mock out the http req/res to the pandaops node, there shouldn't be too much more to add to the full data lifecycle here

[carver]

Sweet, getting closer!

Feel free to ping me if I wasn't clear on any of the comments.

[carver]

It looks like portal_clients is only ever used as a reference below, so we can skip the clone before passing it in by converting the argument into a references, right?

Suggested change

	async fn serve_light_client_bootstrap(
	api: ConsensusApi,
	portal_clients: Vec<HttpClient>,
	async fn serve_light_client_bootstrap(
	api: ConsensusApi,
	portal_clients: &Vec<HttpClient>,

[ogenev]

I had to wrap this inside an Arc because we want to share it between threads.

[carver]

I have a hunch we can get rid of the mutex, but I'm not sure how to explain it. The easiest way I could think of was to show an example with the Atomic, which is the same principle I think. See #873

[ogenev]

Added some thoughts on the PR.

[carver]

Something feels backwards about building the serialized value here just to throw it away for the decoded version. It seems more direct to add a new() so we can do something like:

Suggested change

	let mut content_bytes = ForkName::Capella.as_fork_digest().to_vec();
	content_bytes.append(&mut bootstrap.as_ssz_bytes());
	let content_value = BeaconContentValue::decode(&content_bytes)?;
	let content_value = BeaconContentValue::LightClientBootstrap(ForkVersionedLightClientBootstrap::new(bootstrap));

Since the bootstrap is typed with the fork, it seems like we can match on it inside new to determine the fork.

As a side-benefit, this code block becomes agnostic to the ssz encoding, which seems like what we want.

[ogenev]

Adding From<LightClientBootstrapCapella> for ForkVersionedLightClientBootstrap did the trick, we can then use .into() instead of new().