remove prepare_payload

setup.py

@@ -497,7 +497,7 @@ def imports(cls, preset_name: str):
         return super().imports(preset_name) + f'''
 from typing import Protocol
 from eth2spec.altair import {preset_name} as altair
-from eth2spec.utils.ssz.ssz_typing import Bytes20, ByteList, ByteVector, uint256, Union
+from eth2spec.utils.ssz.ssz_typing import Bytes8, Bytes20, ByteList, ByteVector, uint256, Union
 '''
 
     @classmethod
@@ -527,16 +527,12 @@ class NoopExecutionEngine(ExecutionEngine):
     def execute_payload(self: ExecutionEngine, execution_payload: ExecutionPayload) -> bool:
         return True
 
-    def notify_forkchoice_updated(self: ExecutionEngine, head_block_hash: Hash32, finalized_block_hash: Hash32) -> None:
+    def notify_forkchoice_updated(self: ExecutionEngine,
+                                  head_block_hash: Hash32,
+                                  finalized_block_hash: Hash32,
+                                  payload_attributes: Optional[PayloadAttributes]) -> None:
         pass
 
-    def prepare_payload(self: ExecutionEngine,
-                        parent_hash: Hash32,
-                        timestamp: uint64,
-                        random: Bytes32,
-                        feeRecipient: ExecutionAddress) -> PayloadId:
-        raise NotImplementedError("no default block production")
-
     def get_payload(self: ExecutionEngine, payload_id: PayloadId) -> ExecutionPayload:
         raise NotImplementedError("no default block production")
 
@@ -683,7 +679,7 @@ def combine_dicts(old_dict: Dict[str, T], new_dict: Dict[str, T]) -> Dict[str, T
 
 ignored_dependencies = [
     'bit', 'boolean', 'Vector', 'List', 'Container', 'BLSPubkey', 'BLSSignature',
-    'Bytes1', 'Bytes4', 'Bytes20', 'Bytes32', 'Bytes48', 'Bytes96', 'Bitlist', 'Bitvector',
+    'Bytes1', 'Bytes4', 'Bytes8', 'Bytes20', 'Bytes32', 'Bytes48', 'Bytes96', 'Bitlist', 'Bitvector',
     'uint8', 'uint16', 'uint32', 'uint64', 'uint128', 'uint256',
     'bytes', 'byte', 'ByteList', 'ByteVector',
     'Dict', 'dict', 'field', 'ceillog2', 'floorlog2', 'Set',

specs/merge/fork-choice.md

@@ -12,6 +12,7 @@
   - [`ExecutionEngine`](#executionengine)
     - [`notify_forkchoice_updated`](#notify_forkchoice_updated)
 - [Helpers](#helpers)
+  - [`PayloadAttributes`](#payloadattributes)
   - [`PowBlock`](#powblock)
   - [`get_pow_block`](#get_pow_block)
   - [`is_valid_terminal_pow_block`](#is_valid_terminal_pow_block)
@@ -43,15 +44,33 @@ This function performs two actions *atomically*:
 * Applies finality to the execution state: it irreversibly persists the chain of all execution payloads
 and corresponding state, up to and including `finalized_block_hash`.
 
+Additionally, if `payload_attributes` is provided, this function sets in motion a payload build process on top of
+`head_block_hash` with the result to be gathered by a followup call to  `get_payload`.
+
 ```python
-def notify_forkchoice_updated(self: ExecutionEngine, head_block_hash: Hash32, finalized_block_hash: Hash32) -> None:
+def notify_forkchoice_updated(self: ExecutionEngine,
+                              head_block_hash: Hash32,
+                              finalized_block_hash: Hash32,
+                              payload_attributes: Optional[PayloadAttributes]) -> None:
     ...
 ```
 
 *Note*: The call of the `notify_forkchoice_updated` function maps on the `POS_FORKCHOICE_UPDATED` event defined in the [EIP-3675](https://eips.ethereum.org/EIPS/eip-3675#definitions).
 
 ## Helpers
 
+### `PayloadAttributes`
+
+Used to signal to initiate the payload build process via `notify_forkchoice_updated`.
+
+```python
+@dataclass
+class PayloadAttributes(object):
+    timestamp: uint64
+    random: Bytes32
+    fee_recipient: ExecutionAddress
+```
+
 ### `PowBlock`
 
 ```python

specs/merge/validator.md

@@ -11,9 +11,12 @@
 - [Introduction](#introduction)
 - [Prerequisites](#prerequisites)
 - [Custom types](#custom-types)
+- [Helpers](#helpers)
+  - [`get_pow_block_at_terminal_total_difficulty`](#get_pow_block_at_terminal_total_difficulty)
+  - [`get_terminal_pow_block`](#get_terminal_pow_block)
+  - [`get_payload_id`](#get_payload_id)
 - [Protocols](#protocols)
   - [`ExecutionEngine`](#executionengine)
-    - [`prepare_payload`](#prepare_payload)
     - [`get_payload`](#get_payload)
 - [Beacon chain responsibilities](#beacon-chain-responsibilities)
   - [Block proposal](#block-proposal)
@@ -39,38 +42,73 @@ Please see related Beacon Chain doc before continuing and use them as a referenc
 
 | Name | SSZ equivalent | Description |
 | - | - | - |
-| `PayloadId` | `uint64` | Identifier of a payload building process |
+| `PayloadId` | `Bytes8` | Identifier of a payload building process |
 
-## Protocols
+## Helpers
 
-### `ExecutionEngine`
+### `get_pow_block_at_terminal_total_difficulty`
+
+```python
+def get_pow_block_at_terminal_total_difficulty(pow_chain: Sequence[PowBlock]) -> Optional[PowBlock]:
+    # `pow_chain` abstractly represents all blocks in the PoW chain
+    for block in pow_chain:
+        parent = get_pow_block(block.parent_hash)
+        block_reached_ttd = block.total_difficulty >= TERMINAL_TOTAL_DIFFICULTY
+        parent_reached_ttd = parent.total_difficulty >= TERMINAL_TOTAL_DIFFICULTY
+        if block_reached_ttd and not parent_reached_ttd:
+            return block
+
+    return None
+```
 
-*Note*: `prepare_payload` and `get_payload` functions are added to the `ExecutionEngine` protocol for use as a validator.
+### `get_terminal_pow_block`
 
-The body of each of these functions is implementation dependent.
-The Engine API may be used to implement them with an external execution engine.
+```python
+def get_terminal_pow_block(pow_chain: Sequence[PowBlock]) -> Optional[PowBlock]:
+    if TERMINAL_BLOCK_HASH != Hash32():
+        # Terminal block hash override takes precedence over terminal total difficulty
+        pow_block_overrides = [block for block in pow_chain if block.block_hash == TERMINAL_BLOCK_HASH]
+        if not any(pow_block_overrides):
+            return None
+        return pow_block_overrides[0]
 
-#### `prepare_payload`
+    return get_pow_block_at_terminal_total_difficulty(pow_chain)
+```
 
-Given the set of execution payload attributes, `prepare_payload` initiates a process of building an execution payload
-on top of the execution chain tip identified by `parent_hash`.
+### `get_payload_id`
+
+Given the `head_block_hash` and the `payload_attributes` that were used to
+initiate the build process via `notify_forkchoice_updated`, `get_payload_id()`
+returns the `payload_id` used to retrieve the payload via `get_payload`.
 
 ```python
-def prepare_payload(self: ExecutionEngine,
-                    parent_hash: Hash32,
-                    timestamp: uint64,
-                    random: Bytes32,
-                    fee_recipient: ExecutionAddress) -> PayloadId:
-    """
-    Return ``payload_id`` that is used to obtain the execution payload in a subsequent ``get_payload`` call.
-    """
-    ...
+def get_payload_id(parent_hash: Hash32, payload_attributes: PayloadAttributes) -> PayloadId:
+    return PayloadId(
+        hash(
+            parent_hash
+            + uint_to_bytes(payload_attributes.timestamp)
+            + payload_attributes.random
+            + payload_attributes.fee_recipient
+        )[0:8]
+    )
 ```
 
+*Note*: This function does *not* use simple serialize `hash_tree_root` as to
+avoid requiring simple serialize hashing capabilities in the Execution Layer.
+
+## Protocols
+
+### `ExecutionEngine`
+
+*Note*: `get_payload` function is added to the `ExecutionEngine` protocol for use as a validator.
+
+The body of this function is implementation dependent.
+The Engine API may be used to implement it with an external execution engine.
+
 #### `get_payload`
 
 Given the `payload_id`, `get_payload` returns the most recent version of the execution payload that
-has been built since the corresponding call to `prepare_payload` method.
+has been built since the corresponding call to `notify_forkchoice_updated` method.
 
 ```python
 def get_payload(self: ExecutionEngine, payload_id: PayloadId) -> ExecutionPayload:
@@ -92,38 +130,17 @@ All validator responsibilities remain unchanged other than those noted below. Na
 
 To obtain an execution payload, a block proposer building a block on top of a `state` must take the following actions:
 
-1. Set `payload_id = prepare_execution_payload(state, pow_chain, fee_recipient, execution_engine)`, where:
+1. Set `payload_id = prepare_execution_payload(state, pow_chain, finalized_block_hash, fee_recipient, execution_engine)`, where:
     * `state` is the state object after applying `process_slots(state, slot)` transition to the resulting state of the parent block processing
     * `pow_chain` is a list that abstractly represents all blocks in the PoW chain
+    * `finalized_block_hash` is the hash of the latest finalized execution payload (`Hash32()` if none yet finalized)
     * `fee_recipient` is the value suggested to be used for the `coinbase` field of the execution payload
 
 
 ```python
-def get_pow_block_at_terminal_total_difficulty(pow_chain: Sequence[PowBlock]) -> Optional[PowBlock]:
-    # `pow_chain` abstractly represents all blocks in the PoW chain
-    for block in pow_chain:
-        parent = get_pow_block(block.parent_hash)
-        block_reached_ttd = block.total_difficulty >= TERMINAL_TOTAL_DIFFICULTY
-        parent_reached_ttd = parent.total_difficulty >= TERMINAL_TOTAL_DIFFICULTY
-        if block_reached_ttd and not parent_reached_ttd:
-            return block
-
-    return None
-
-
-def get_terminal_pow_block(pow_chain: Sequence[PowBlock]) -> Optional[PowBlock]:
-    if TERMINAL_BLOCK_HASH != Hash32():
-        # Terminal block hash override takes precedence over terminal total difficulty
-        pow_block_overrides = [block for block in pow_chain if block.block_hash == TERMINAL_BLOCK_HASH]
-        if not any(pow_block_overrides):
-            return None
-        return pow_block_overrides[0]
-
-    return get_pow_block_at_terminal_total_difficulty(pow_chain)
-
-
 def prepare_execution_payload(state: BeaconState,
                               pow_chain: Sequence[PowBlock],
+                              finalized_block_hash: Hash32,
                               fee_recipient: ExecutionAddress,
                               execution_engine: ExecutionEngine) -> Optional[PayloadId]:
     if not is_merge_complete(state):
@@ -137,9 +154,14 @@ def prepare_execution_payload(state: BeaconState,
         # Post-merge, normal payload
         parent_hash = state.latest_execution_payload_header.block_hash
 
-    timestamp = compute_timestamp_at_slot(state, state.slot)
-    random = get_randao_mix(state, get_current_epoch(state))
-    return execution_engine.prepare_payload(parent_hash, timestamp, random, fee_recipient)
+    # Set the forkchoice head and initiate the payload build process
+    payload_attributes = PayloadAttributes(
+        timestamp=compute_timestamp_at_slot(state, state.slot),
+        random=get_randao_mix(state, get_current_epoch(state)),
+        fee_recipient=fee_recipient,
+    )
+    execution_engine.notify_forkchoice_updated(parent_hash, finalized_block_hash, payload_attributes)
+    return get_payload_id(parent_hash, payload_attributes)
 ```
 
 2. Set `block.body.execution_payload = get_execution_payload(payload_id, execution_engine)`, where: