EPF Dev Update #10

Just to add a bit of context to my updates, I'll be sticking my project links here in furture updates.

Update for week 11 (2023/1/9 - 2023/1/16)

Proposed a new PR to add a getBlobsSideCar to Beacon API spec (ethereum/beacon-APIs#286)
Progressed further with the builder updates for EIP-4844 in Lighthouse (lighthouse/3808). More details in below section.
There have been active discussions on the oustanding Beacon API & Builder spec update PRs, hopefully these will be finalised soon:
- Add and update types for Capella (builder-specs#60)
- Add and update types for EIP-4844 (builder-specs#61)
Next week I plan to continue to work on tests for the builder updates and Beacon API changes I did last week (Add Beacon API endpoint (/lighthouse) to download blobs by block ID #3830)

Lighthouse: Builder updates for EIP-4844

PR: Builder updates for Blobs (EIP-4844)

So I wanted to drop down some notes on this PR because the work turns out to be much bigger than I thought, and it's not even finished yet. I think I've implemented most of the draft spec changes and will start working on tests. As of now, the spec changes haven't been implemented in the builder client (mev-boost), so all testing will be done against mocks, which will need some updates as well.

Details of changes I've made so far:

Make BuilderBid into a superstruct, so that a new blob_kzg_commitments field can be introduced to just the Eip4844 variant / version of BuilderBid. SuperStruct is a Rust library for working with versioned data.
Make serialization / deserialization work for the BuilderBid superstruct. This ended up being a relatively small change but took me a while to figure out how to get this working, as I wasn't familiar with serde, a framework for serializing and deserializing Rust data structures.
In order to verify the serialization/deserializtion works for all BuilderBid variants (Merge, Capella, Eip4844), I implemented a few tests here. The tests deserialize a predefined JSON input into a BuilderBid object, and serialize the object into a JSON string, and then it verifies the output against the original JSON. And it worked \o/
Implement handling of new field blob_kzg_commitments from the Builder getHeader endpoint. The blob_kzg_commitments is now added to the beacon blocks before validators sign them.
Implement handling of BlobsSidecar received from the Builder submitBlindedBlock endpoint. The blobs that are recieved, together with the full beacon block is then broadcasted to other beacon nodes.