fix: re-add validate_against_parent_4844 to optimism header validation (#8835)

crates/consensus/common/src/validation.rs

@@ -6,6 +6,7 @@ use reth_primitives::{
         eip4844::{DATA_GAS_PER_BLOB, MAX_DATA_GAS_PER_BLOCK},
         MAXIMUM_EXTRA_DATA_SIZE,
     },
+    eip4844::calculate_excess_blob_gas,
     ChainSpec, GotExpected, Hardfork, Header, SealedBlock, SealedHeader,
 };
 
@@ -229,6 +230,41 @@ pub fn validate_against_parent_timestamp(
     Ok(())
 }
 
+/// Validates that the EIP-4844 header fields are correct with respect to the parent block. This
+/// ensures that the `blob_gas_used` and `excess_blob_gas` fields exist in the child header, and
+/// that the `excess_blob_gas` field matches the expected `excess_blob_gas` calculated from the
+/// parent header fields.
+pub fn validate_against_parent_4844(
+    header: &SealedHeader,
+    parent: &SealedHeader,
+) -> Result<(), ConsensusError> {
+    // From [EIP-4844](https://eips.ethereum.org/EIPS/eip-4844#header-extension):
+    //
+    // > For the first post-fork block, both parent.blob_gas_used and parent.excess_blob_gas
+    // > are evaluated as 0.
+    //
+    // This means in the first post-fork block, calculate_excess_blob_gas will return 0.
+    let parent_blob_gas_used = parent.blob_gas_used.unwrap_or(0);
+    let parent_excess_blob_gas = parent.excess_blob_gas.unwrap_or(0);
+
+    if header.blob_gas_used.is_none() {
+        return Err(ConsensusError::BlobGasUsedMissing)
+    }
+    let excess_blob_gas = header.excess_blob_gas.ok_or(ConsensusError::ExcessBlobGasMissing)?;
+
+    let expected_excess_blob_gas =
+        calculate_excess_blob_gas(parent_excess_blob_gas, parent_blob_gas_used);
+    if expected_excess_blob_gas != excess_blob_gas {
+        return Err(ConsensusError::ExcessBlobGasDiff {
+            diff: GotExpected { got: excess_blob_gas, expected: expected_excess_blob_gas },
+            parent_excess_blob_gas,
+            parent_blob_gas_used,
+        })
+    }
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;