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Add engine_newPayloadSyncContextV1 #318

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Add engine_newPayloadSyncContextV1 #318

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81825fd
Add `engine_newPayloadHeaderV1`
etan-status Oct 31, 2022
029af74
Merge branch 'main' into lc-eph
etan-status Nov 4, 2022
1d42525
Satisfy spellcheck
etan-status Nov 4, 2022
d794b90
Change from SSZ to RLP hash
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08c0030
Cleanup
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Improve wording
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Synchronize layout
etan-status Nov 4, 2022
c86db03
Consistent format to refer to newPayload response
etan-status Nov 4, 2022
53beebe
Add new fields to nullability check
etan-status Nov 4, 2022
baa849c
Extend requirement for withdrawals
etan-status Nov 4, 2022
c206bc8
Only pass minimal sync context information
etan-status Nov 28, 2022
d7be255
Typo
etan-status Nov 28, 2022
17b4222
Always return `SYNCING` for `newPayloadSyncContext`
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53 changes: 53 additions & 0 deletions src/engine/specification.md
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ This document specifies the Engine API methods that the Consensus Layer uses to
- [Timeouts](#timeouts)
- [Structures](#structures)
- [ExecutionPayloadV1](#executionpayloadv1)
- [ExecutionPayloadHeaderV1](#executionpayloadheaderv1)
- [ForkchoiceStateV1](#forkchoicestatev1)
- [PayloadAttributesV1](#payloadattributesv1)
- [PayloadStatusV1](#payloadstatusv1)
Expand All @@ -41,6 +42,11 @@ This document specifies the Engine API methods that the Consensus Layer uses to
- [Request](#request-3)
- [Response](#response-3)
- [Specification](#specification-3)
- [Optional endpoints](#optional-endpoints)
- [engine_newPayloadHeaderV1](#engine_newpayloadheaderv1)
- [Request](#request-4)
- [Response](#response-4)
- [Specification](#specification-4)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->

Expand Down Expand Up @@ -174,6 +180,25 @@ This structure maps on the [`ExecutionPayload`](https://github.com/ethereum/cons
- `blockHash`: `DATA`, 32 Bytes
- `transactions`: `Array of DATA` - Array of transaction objects, each object is a byte list (`DATA`) representing `TransactionType || TransactionPayload` or `LegacyTransaction` as defined in [EIP-2718](https://eips.ethereum.org/EIPS/eip-2718)

### ExecutionPayloadHeaderV1

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I don't think a full ExecutionPayloadHeader is required to trigger the beacon sync, only blockNumber and blockHash are sufficient and rest EL clients can fetch off the wire, since they would anyway need to fetch full block body for transactions to eventually execute the block (and if we are being liberal we can include parentHash as well)
So may be we can call it ExecutionPayloadHeaderSlim or something

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For LES use case, having access to logs_bloom is also useful to determine whether a block contains useful information.

The one truly questionable field is the transactionsRoot though – it being an SSZ root may make it difficult to get a VALID / INVALID classification from the EL without it also knowing how to create and verify those. For that one, I see three options:

  1. transactionsRoot is not useful for any use case, in this case just drop it from the engine API structure, diverging from the beacon chain structure.
  2. transactionsRoot would be useful as an RLP hash for some use cases, in this case extend the beacon chain structure with RLP transactionsHash that lives next to the transactions in both ExecutionPayload and ExecutionPayloadHeader.
  3. transactionsRoot is still useful in SSZ format, in this case just keep as is. Maybe for MEV blinded blocks to prove inclusion of particular tx against censoring, but those proofs could also be rooted in stateRoot I guess?

On CL light client front, the extra size for full header is not substantially different from including just a couple of the fields, as proof size goes up for individual fields. So, full ExecutionPayloadHeader can be expected to be available. Any subset is alright for the engine API.

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Makes sense, so...

for execution nodes running full protocol, it won't matter what kind of transactionsRoot we provide since they would still need to download the block off the wire (as you observed) using their own peers as they do in normal beacon sync when they don't have parents.

Now for les we could make it easy by having the RLP transactions hash that the blockhash lines up and they don't have to download anything off wire (unless there is a missing header update in which case they will again have to)

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ethereum/consensus-specs#3078
Opened a proposal here to add those RLP hashes to the ExecutionPayload / ExecutionPayloadHeader as well, from Capella onward. This would make this much easier, removing the need for RLP computations in CL, or for SSZ computations in EL.

This structure maps on the [`ExecutionPayloadHeader`](https://github.com/ethereum/consensus-specs/blob/dev/specs/bellatrix/beacon-chain.md#executionpayloadheader) structure of the beacon chain spec. The fields are encoded as follows:

- `parentHash`: `DATA`, 32 Bytes
- `feeRecipient`: `DATA`, 20 Bytes
- `stateRoot`: `DATA`, 32 Bytes
- `receiptsRoot`: `DATA`, 32 Bytes
- `logsBloom`: `DATA`, 256 Bytes
- `prevRandao`: `DATA`, 32 Bytes
- `blockNumber`: `QUANTITY`, 64 Bits
- `gasLimit`: `QUANTITY`, 64 Bits
- `gasUsed`: `QUANTITY`, 64 Bits
- `timestamp`: `QUANTITY`, 64 Bits
- `extraData`: `DATA`, 0 to 32 Bytes
- `baseFeePerGas`: `QUANTITY`, 256 Bits
- `blockHash`: `DATA`, 32 Bytes
- `transactionsRoot`: `DATA`, 32 Bytes - `hash_tree_root(transactions)`, not the keccak256 hash but instead the Consensus Layer [SSZ merkle root](https://github.com/ethereum/consensus-specs/blob/dev/ssz/simple-serialize.md)

### ForkchoiceStateV1

This structure encapsulates the fork choice state. The fields are encoded as follows:
Expand Down Expand Up @@ -396,3 +421,31 @@ The payload build process is specified as follows:
7. Considering the absence of the `TERMINAL_TOTAL_DIFFICULTY` value (i.e. when a value has not been decided), Consensus Layer and Execution Layer client software **MUST** use `115792089237316195423570985008687907853269984665640564039457584007913129638912` value (equal to`2**256-2**10`) for the `terminalTotalDifficulty` input parameter of this call.

[json-rpc-spec]: https://playground.open-rpc.org/?schemaUrl=https://raw.githubusercontent.com/ethereum/execution-apis/assembled-spec/openrpc.json&uiSchema[appBar][ui:splitView]=false&uiSchema[appBar][ui:input]=false&uiSchema[appBar][ui:examplesDropdown]=false

## Optional endpoints

### engine_newPayloadHeaderV1

#### Request

* method: `engine_newPayloadHeaderV1`
* params:
1. [`ExecutionPayloadHeaderV1`](#ExecutionPayloadHeaderV1)
* timeout: 8s

#### Response

* result: [`PayloadStatusV1`](#PayloadStatusV1)
* error: code and message set in case an exception happens while processing the payload.

#### Specification

1. Execution Layer client software **MUST** handle calls to this endpoint the same as [`engine_newPayloadV1`](#engine_getpayloadv1) and provide compatible responses. When needed, Execution Layer client software **MUST** obtain the block's transactions autonomously.

2. Consensus Layer client software **SHOULD NOT** use this endpoint for validator duties. Instead, the [`engine_newPayloadV1`](#engine_getpayloadv1) endpoint **SHOULD** be used to reduce sync latency and maximize validator rewards.

3. Consensus Layer client software **MAY** use this endpoint during [optimistic sync](https://github.com/ethereum/consensus-specs/blob/dev/sync/optimistic.md) to inform Execution Layer client software about blocks far in the future. Execution Layer client software **MUST** support switching to this future block if requested to do so with [`engine_forkchoiceUpdatedV1`](#engine_forkchoiceupdatedv1). This allows the Execution Layer client software to sync close to current wall time without having to wait for optimistic sync to catch up.

4. Consensus Layer [light clients](https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/light-client/sync-protocol.md) **MAY** use this endpoint together with [`engine_forkchoiceUpdatedV1`](#engine_forkchoiceupdatedv1) to sync Execution Layer client software. Execution Layer client software **MUST** support syncing with only those two endpoints. Notably, syncing **MUST NOT** require [`engine_newPayloadV1`](#engine_getpayloadv1) calls. Furthermore, Execution Layer client software **MAY** also support syncing with solely `engine_forkchoiceUpdatedV1` calls.

5. Client software **MAY** offer configuration options to limit the sync scope to use case dependent data (e.g., only sync transactions relating to a certain wallet). This enables combined Consensus Layer / Execution Layer light client experiences.