From a3a370302a2e97a736fe5d952352bd47048c9719 Mon Sep 17 00:00:00 2001
From: Pawan Dhananjay <pawandhananjay@gmail.com>
Date: Wed, 13 Dec 2023 14:24:36 -0800
Subject: [PATCH] Use the block header to compute the canonical_root (#5003)

---
 .../beacon_chain/src/block_verification.rs    | 21 +++++++++++++++++--
 beacon_node/beacon_chain/src/metrics.rs       |  4 ++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/beacon_node/beacon_chain/src/block_verification.rs b/beacon_node/beacon_chain/src/block_verification.rs
index 145614c4b..23c9ab725 100644
--- a/beacon_node/beacon_chain/src/block_verification.rs
+++ b/beacon_node/beacon_chain/src/block_verification.rs
@@ -780,7 +780,10 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
         // it to the slasher if an error occurs, because that's the end of this block's journey,
         // and it could be a repeat proposal (a likely cause for slashing!).
         let header = block.signed_block_header();
-        Self::new_without_slasher_checks(block, chain).map_err(|e| {
+        // The `SignedBeaconBlock` and `SignedBeaconBlockHeader` have the same canonical root,
+        // but it's way quicker to calculate root of the header since the hash of the tree rooted
+        // at `BeaconBlockBody` is already computed in the header.
+        Self::new_without_slasher_checks(block, &header, chain).map_err(|e| {
             process_block_slash_info::<_, BlockError<T::EthSpec>>(
                 chain,
                 BlockSlashInfo::from_early_error_block(header, e),
@@ -791,6 +794,7 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
     /// As for new, but doesn't pass the block to the slasher.
     fn new_without_slasher_checks(
         block: Arc<SignedBeaconBlock<T::EthSpec>>,
+        block_header: &SignedBeaconBlockHeader,
         chain: &BeaconChain<T>,
     ) -> Result<Self, BlockError<T::EthSpec>> {
         // Ensure the block is the correct structure for the fork at `block.slot()`.
@@ -810,7 +814,7 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
             });
         }
 
-        let block_root = get_block_root(&block);
+        let block_root = get_block_header_root(block_header);
 
         // Disallow blocks that conflict with the anchor (weak subjectivity checkpoint), if any.
         check_block_against_anchor_slot(block.message(), chain)?;
@@ -1771,6 +1775,19 @@ pub fn get_block_root<E: EthSpec>(block: &SignedBeaconBlock<E>) -> Hash256 {
     block_root
 }
 
+/// Returns the canonical root of the given `block_header`.
+///
+/// Use this function to ensure that we report the block hashing time Prometheus metric.
+pub fn get_block_header_root(block_header: &SignedBeaconBlockHeader) -> Hash256 {
+    let block_root_timer = metrics::start_timer(&metrics::BLOCK_HEADER_PROCESSING_BLOCK_ROOT);
+
+    let block_root = block_header.message.canonical_root();
+
+    metrics::stop_timer(block_root_timer);
+
+    block_root
+}
+
 /// Verify the parent of `block` is known, returning some information about the parent block from
 /// fork choice.
 #[allow(clippy::type_complexity)]
diff --git a/beacon_node/beacon_chain/src/metrics.rs b/beacon_node/beacon_chain/src/metrics.rs
index ca04366b0..b9a748b6d 100644
--- a/beacon_node/beacon_chain/src/metrics.rs
+++ b/beacon_node/beacon_chain/src/metrics.rs
@@ -40,6 +40,10 @@ lazy_static! {
         "beacon_block_processing_block_root_seconds",
         "Time spent calculating the block root when processing a block."
     );
+    pub static ref BLOCK_HEADER_PROCESSING_BLOCK_ROOT: Result<Histogram> = try_create_histogram(
+        "beacon_block_header_processing_block_root_seconds",
+        "Time spent calculating the block root for a beacon block header."
+    );
     pub static ref BLOCK_PROCESSING_BLOB_ROOT: Result<Histogram> = try_create_histogram(
         "beacon_block_processing_blob_root_seconds",
         "Time spent calculating the blob root when processing a block."