Builder API for blobs

[realbigsean]

Description

This hasn't been spec'd out as far as I can tell, but it is something we should keep in mind. flashbots/mev-boost#392

We would at least have to make sure we are following to whatever versioning scheme is implemented in the API, and I wonder if there is apetite for blinded blobs, in which case we'd end up having to make blobs generic over Payload: AbstractExecPayload

[realbigsean]

Thinking about this further - we will need blob_kzg_commitments in the builder bid so we can include them in a block, and we'll probably need to change the response for submitting a signed block to a builder to be changed from an ExecutionPayload to a SignedBeaconBlockAndBlobsSidecar or at least something that includes blobs and the kzg proof

[jimmygchen]

@0xGabi and I have started making changes on the builder spec and hopefully have a draft PR on the builder spec changes soon. I've summarised the discussions so far on this page: https://hackmd.io/@jimmygchen/B1dLR74Io

sequenceDiagram
    participant validator
    participant consensus
    participant mev_boost
    Title: Block Proposal with Builder API (EIP-4844)
    validator->>consensus: GET v2/validator/blinded_blocks/{slot}
    consensus->>mev_boost: GET v1/builder/header/{slot}/{parent_hash}/{pubkey}
    mev_boost-->>consensus: GET v1/builder/header/{slot}/{parent_hash}/{pubkey} response
    Note left of mev_boost: add `blob_kzg_commitments` to response (`SignedBuilderBid`)
    consensus-->>validator: GET v2/validator/blinded_blocks/{slot} response
    Note left of consensus: add `blob_kzg_commitments` to response
    Note over validator: include `blob_kzg_commitments` in block and sign the header
    validator->>consensus: POST beacon/blinded_blocks
    consensus->>mev_boost: POST /eth/v1/builder/blinded_blocks
    mev_boost-->>consensus: POST /eth/v1/builder/blinded_blocks response
    Note left of mev_boost: revealed payload will have to include `blobs_sidecar` and kzg proof
    Note over consensus: construct block and broadcast block

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[jimmygchen]

@0xGabi and I are working on this change, will hopefully have a draft PR soon!

[jimmygchen]

Task Tracking

Beacon Node

• produceBlindedBlock endpoint updates (Builder flow for Deneb & Blobs #4428)
  • Handle new Deneb BuilderBid response from builder endpoint (new BlindedBlobsBundle type)
  • Build BlockContents response (containing kzg_commitments, proof and blinded_blob_sidecars)
• submitBlindedBlock endpoint updates
  • Handle SignedBlockContents request and forward to builder
  • Handle unblinded ExecutionPayloadAndBlobsBundle response from builder endpoint, and publish block

Validator Client

• Handle produceBlindedBlock response from Beacon API (Builder flow for Deneb & Blobs #4428)
• Individual signing of blinded_blob_sidecars
• Build SignedBlockContents and submit to Beacon API (submitBlindedBlock)

[realbigsean]

Completed in:
#4607
#4428