Allow multiple bids compatible with the head view (#5497)

This is an alternative to #5491 requested by @nflaig. In this PR we are
not as strict as to only allow exactly what the proposer would do, but
rather check that it is one of the two paths.

Author: potuz

specs/gloas/fork-choice.md

@@ -421,9 +421,9 @@ follows the node's payload status. For a *full* node from the previous slot, it
 considers the PTC view on both payload timeliness and data availability.
 
 ```python
-def should_build_on_full(store: Store, head: ForkChoiceNode) -> bool:
+def should_build_on_full(store: Store, head: ForkChoiceNode, slot: Slot) -> bool:
     assert head.payload_status != PAYLOAD_STATUS_PENDING
-    if store.blocks[head.root].slot + 1 != get_current_slot(store):
+    if store.blocks[head.root].slot + 1 != slot:
         return head.payload_status == PAYLOAD_STATUS_FULL
     if head.payload_status == PAYLOAD_STATUS_EMPTY:
         return False

specs/gloas/p2p-interface.md

@@ -428,7 +428,8 @@ where `store` is the fork choice store, and the alias
   limitation defined in the consensus layer -- i.e. validate that
   `len(bid.blob_kzg_commitments) <= get_blob_parameters(compute_epoch_at_slot(bid.slot)).max_blobs_per_block`.
 - _[IGNORE]_ this is the first signed bid seen with a valid signature from the
-  given builder for this slot.
+  given builder for the tuple
+  `(bid.slot, bid.parent_block_hash, bid.parent_block_root)`.
 - _[IGNORE]_ this bid is the highest value bid seen for the tuple
   `(bid.slot, bid.parent_block_hash, bid.parent_block_root)`.
 - _[IGNORE]_ `bid.value` is less or equal than the builder's excess balance --
@@ -438,8 +439,8 @@ where `store` is the fork choice store, and the alias
   `is_gas_limit_target_compatible(parent_gas_limit, bid.gas_limit, proposer_preferences.target_gas_limit)`
   is `True` where `parent_gas_limit` is the `gas_limit` of that execution
   payload.
-- _[IGNORE]_ `bid.parent_block_root` is the hash tree root of a known beacon
-  block in fork choice.
+- _[IGNORE]_ The bid is compatible with the current head branch, i.e.
+  `is_bid_compatible_with_head(store, bid)` returns `True`.
 - _[REJECT]_ The bid is for a higher slot than its parent block -- i.e. validate
   that `bid.slot` is greater than the slot of the block with root
   `bid.parent_block_root`.
@@ -467,6 +468,32 @@ def is_gas_limit_target_compatible(
     return gas_limit == min_gas_limit
 ```
 
+```python
+def is_bid_compatible_with_head(store: Store, bid: ExecutionPayloadBid) -> bool:
+    """
+    Check if ``bid`` is compatible with the head branch.
+    """
+    head_node = get_head(store)
+    head_block = store.blocks[head_node.root]
+    head_bid = head_block.body.signed_execution_payload_bid.message
+
+    builds_on_parent_block = bid.parent_block_root == head_block.parent_root
+    builds_on_parent_payload = bid.parent_block_hash == head_bid.parent_block_hash
+
+    if builds_on_parent_block and builds_on_parent_payload:
+        return True
+
+    if bid.parent_block_root != head_node.root:
+        return False
+
+    builds_on_head_payload = bid.parent_block_hash == head_bid.block_hash
+
+    if should_build_on_full(store, head_node, bid.slot):
+        return builds_on_head_payload
+
+    return builds_on_parent_payload
+```
+
 *Note*: Implementations SHOULD include DoS prevention measures to mitigate spam
 from malicious builders submitting numerous bids with minimal value increments.
 Possible strategies include: (1) only forwarding bids that exceed the current

specs/gloas/validator.md

@@ -212,8 +212,8 @@ top of a `state` MUST take the following actions in order to construct the
   - The `bid.slot` is for the proposal block slot.
   - The `bid.parent_block_hash` equals
     `state.latest_execution_payload_bid.block_hash` if
-    `should_build_on_full(store, head)` is true, otherwise
-    `state.latest_execution_payload_bid.parent_block_hash`.
+    `should_build_on_full(store, head, get_current_slot(store))` is true,
+    otherwise `state.latest_execution_payload_bid.parent_block_hash`.
   - The `bid.parent_block_root` equals the current block's `parent_root`.
   - The `bid.prev_randao` equals
     `get_randao_mix(state, get_current_epoch(state))`.
@@ -248,9 +248,9 @@ parent's execution payload. The proposer constructs this field as follows:
 
 - If the parent block is pre-Gloas (first Gloas block), set
   `parent_execution_requests` to an empty `ExecutionRequests()`.
-- If `should_build_on_full(store, head)` returns `True` (the proposer is
-  building on the parent's full payload), set `parent_execution_requests` to
-  `store.payloads[head.root].execution_requests`.
+- If `should_build_on_full(store, head, get_current_slot(store))` returns `True`
+  (the proposer is building on the parent's full payload), set
+  `parent_execution_requests` to `store.payloads[head.root].execution_requests`.
 - Otherwise (the proposer is building on the parent's empty variant), set
   `parent_execution_requests` to an empty `ExecutionRequests()`.
 
@@ -319,10 +319,11 @@ def get_execution_requests(execution_requests_list: Sequence[bytes]) -> Executio
 ##### ExecutionPayload
 
 *Note*: `prepare_execution_payload` is modified to build on the parent's full
-payload or its empty variant, as decided by `should_build_on_full(store, head)`,
-which determines the withdrawals source and the execution head for the new
-payload. When building on a full parent, `apply_parent_execution_payload` is
-called so that withdrawals are computed against the post-processing state.
+payload or its empty variant, as decided by
+`should_build_on_full(store, head, get_current_slot(store))`, which determines
+the withdrawals source and the execution head for the new payload. When building
+on a full parent, `apply_parent_execution_payload` is called so that withdrawals
+are computed against the post-processing state.
 
 ```python
 def prepare_execution_payload(
@@ -340,7 +341,7 @@ def prepare_execution_payload(
 ) -> Optional[PayloadId]:
     # [New in Gloas:EIP7732]
     parent_bid = state.latest_execution_payload_bid
-    if should_build_on_full(store, head):
+    if should_build_on_full(store, head, get_current_slot(store)):
         envelope = store.payloads[head.root]
         # Make a copy of the state to avoid mutability issues
         state = copy(state)

specs/heze/validator.md

@@ -145,7 +145,7 @@ def prepare_execution_payload(
     execution_engine: ExecutionEngine,
 ) -> Optional[PayloadId]:
     parent_bid = state.latest_execution_payload_bid
-    if should_build_on_full(store, head):
+    if should_build_on_full(store, head, get_current_slot(store)):
         envelope = store.payloads[head.root]
         # Make a copy of the state to avoid mutability issues
         state = copy(state)