From 106e1b98ba348b1c74b1b9b6e779f0fe14206a3e Mon Sep 17 00:00:00 2001
From: Mikhail Kalinin <noblesse.knight@gmail.com>
Date: Wed, 31 Mar 2021 15:35:55 +0600
Subject: [PATCH] Add parent_hash, number to ApplicationPayload

---
 specs/merge/beacon-chain.md | 28 +++++++++++++++++-----------
 specs/merge/fork-choice.md  |  2 +-
 specs/merge/validator.md    |  6 +++---
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/specs/merge/beacon-chain.md b/specs/merge/beacon-chain.md
index 55994188a..ab08f46aa 100644
--- a/specs/merge/beacon-chain.md
+++ b/specs/merge/beacon-chain.md
@@ -81,13 +81,14 @@ class BeaconBlockBody(phase0.BeaconBlockBody):
 
 #### `BeaconState`
 
-*Note*: `BeaconState` fields remain unchanged other than addition of `application_state_root` and `application_block_hash`.
+*Note*: `BeaconState` fields remain unchanged other than addition of application payload fields.
 
 ```python
 class BeaconState(phase0.BeaconState):
     # Application-layer
     application_state_root: Bytes32  # [New in Merge]
     application_block_hash: Bytes32  # [New in Merge]
+    application_block_number: uint64 # [New in Merge]
 ```
 
 ### New containers
@@ -99,8 +100,10 @@ The application payload included in a `BeaconBlockBody`.
 ```python
 class ApplicationPayload(Container):
     block_hash: Bytes32  # Hash of application block
+    parent_hash: Bytes32
     coinbase: Bytes20
     state_root: Bytes32
+    number: uint64
     gas_limit: uint64
     gas_used: uint64
     receipt_root: Bytes32
@@ -161,15 +164,18 @@ def process_application_payload(state: BeaconState, body: BeaconBlockBody) -> No
     Note: This function is designed to be able to be run in parallel with the other `process_block` sub-functions
     """
 
-    if is_transition_completed(state):
-        application_state = get_application_state(state.application_state_root)
-        application_state_transition(application_state, body.application_payload)
-
-        state.application_state_root = body.application_payload.state_root
-        state.application_block_hash = body.application_payload.block_hash
-    elif is_transition_block(state, body):
-        assert body.application_payload == ApplicationPayload(block_hash=body.application_payload.block_hash)
-        state.application_block_hash = body.application_payload.block_hash
-    else:
+    if not is_transition_completed(state):
         assert body.application_payload == ApplicationPayload()
+        return
+
+    if not is_transition_block(state, body):
+        assert body.application_payload.parent_hash == state.application_block_hash
+        assert body.application_payload.number == state.application_block_number + 1
+
+    application_state = get_application_state(state.application_state_root)
+    application_state_transition(application_state, body.application_payload)
+
+    state.application_state_root = body.application_payload.state_root
+    state.application_block_hash = body.application_payload.block_hash
+    state.application_block_number = body.application_payload.number
 ```
diff --git a/specs/merge/fork-choice.md b/specs/merge/fork-choice.md
index 430128c12..8425358bf 100644
--- a/specs/merge/fork-choice.md
+++ b/specs/merge/fork-choice.md
@@ -77,7 +77,7 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
     # [New in Merge]
     if is_transition_block(pre_state, block.body):
         # Delay consideration of block until PoW block is processed by the PoW node
-        pow_block = get_pow_block(block.body.application_payload.block_hash)
+        pow_block = get_pow_block(block.body.application_payload.parent_hash)
         assert pow_block.is_processed
         assert is_valid_transition_block(pow_block)
 
diff --git a/specs/merge/validator.md b/specs/merge/validator.md
index 0a8c3d5b2..46deec5b4 100644
--- a/specs/merge/validator.md
+++ b/specs/merge/validator.md
@@ -57,12 +57,12 @@ The body of this function is implementation dependent.
 def get_application_payload(state: BeaconState) -> ApplicationPayload:
     if not is_transition_completed(state):
         pow_block = get_pow_chain_head()
-        if pow_block.total_difficulty < TRANSITION_TOTAL_DIFFICULTY:
+        if not is_valid_transition_block(pow_block):
             # Pre-merge, empty payload
             return ApplicationPayload()
         else:
-            # Signify merge via last PoW block_hash and an otherwise empty payload
-            return ApplicationPayload(block_hash=pow_block.block_hash)
+            # Signify merge via producing on top of the last PoW block
+            return produce_application_payload(pow_block.block_hash)
 
     # Post-merge, normal payload
     application_parent_hash = state.application_block_hash