Upcoming feature: allowing block builders to cancel previous submissions

[metachris]

We will allow builders to cancel previous block submissions. This will work by always using the latest submission of a builder, even if it's less valuable.

Currently it works like this:

• Once a builder submissions is validated and the highest bid for a slot+parent_hash combination, a new getHeader response is generated and saved to Redis, which will be used for the next getHeader responses:

  mev-boost-relay/services/api/service.go

  Lines 957 to 1001 in 016449f

  	// Check if there's already a bid
  	prevBid, err := api.datastore.GetGetHeaderResponse(payload.Message.Slot, payload.Message.ParentHash.String(), payload.Message.ProposerPubkey.String())
  	if err != nil {
  	log.WithError(err).Error("error getting previous bid")
  	api.RespondError(w, http.StatusInternalServerError, err.Error())
  	return
  	}
  	// Only proceed if this bid is higher than previous one
  	isMostProfitableBlock = prevBid == nil || payload.Message.Value.Cmp(&prevBid.Data.Message.Value) == 1
  	if !isMostProfitableBlock {
  	log.Debug("block submission with same or lower value")
  	w.WriteHeader(http.StatusOK)
  	return
  	}
  	// Prepare the response data
  	signedBuilderBid, err := BuilderSubmitBlockRequestToSignedBuilderBid(payload, api.blsSk, api.publicKey, api.opts.EthNetDetails.DomainBuilder)
  	if err != nil {
  	log.WithError(err).Error("could not sign builder bid")
  	api.RespondError(w, http.StatusBadRequest, err.Error())
  	return
  	}
  	getHeaderResponse := types.GetHeaderResponse{
  	Version: VersionBellatrix,
  	Data: signedBuilderBid,
  	}
  	getPayloadResponse := types.GetPayloadResponse{
  	Version: VersionBellatrix,
  	Data: payload.ExecutionPayload,
  	}
  	bidTrace := common.BidTraceV2{
  	BidTrace: *payload.Message,
  	BlockNumber: payload.ExecutionPayload.BlockNumber,
  	NumTx: uint64(len(payload.ExecutionPayload.Transactions)),
  	}
  	err = api.datastore.SaveBid(&bidTrace, &getHeaderResponse, &getPayloadResponse)
  	if err != nil {
  	log.WithError(err).Error("could not save bid and block")
  	api.RespondError(w, http.StatusBadRequest, err.Error())
  	return
  	}

Changes needed:

1. Save the latest bid of every builder
2. On every valid submission, recalculate the current best bid
3. If bid value is different from the last cached getHeader response, then update it

Notes:

• See also Should builder block submissions override previous one by same builder even if less profitable? #51
• PR: block submission cancellation #206