fix: total difficulty fallback for remote blocks (#697)

* fix: total difficulty fallback for remote blocks

* Add changeset

.changeset/mighty-turtles-wait.md

@@ -0,0 +1,5 @@
+---
+"@nomicfoundation/edr": patch
+---
+
+Fix panic due to remote nodes not returning total difficulty

crates/edr_defaults/Cargo.toml

@@ -4,6 +4,7 @@ version = "0.3.5"
 edition = "2021"
 
 [dependencies]
+ruint = "1.12.3"
 
 [lints]
 workspace = true

crates/edr_defaults/src/lib.rs

@@ -1,3 +1,5 @@
+use ruint::aliases::U256;
+
 /// The default secret keys from which the local accounts will be derived.
 pub const SECRET_KEYS: [&str; 20] = [
     // these were taken from the standard output of a run of `hardhat node`
@@ -36,3 +38,6 @@ pub const MIX_HASH_SEED: &str = "randomMixHashSeed";
 
 /// Seed value for the generator of state root hashes.
 pub const STATE_ROOT_HASH_SEED: &str = "seed";
+
+/// Terminal total difficulty for the Merge on main net
+pub const TERMINAL_TOTAL_DIFFICULTY: U256 = ruint::uint!(58750000000000000000000_U256);

crates/edr_evm/src/blockchain/remote.rs

@@ -208,9 +208,13 @@ where
             .get_block_by_hash_with_transaction_data(*hash)
             .await?
         {
+            // Geth has recently removed the total difficulty field from block RPC
+            // responses, so we fall back to the terminal total difficulty of main net to
+            // provide backwards compatibility.
+            // TODO https://github.com/NomicFoundation/edr/issues/696
             let total_difficulty = *block
                 .total_difficulty()
-                .expect("Must be present as this is not a pending transaction");
+                .unwrap_or(&edr_defaults::TERMINAL_TOTAL_DIFFICULTY);
 
             self.fetch_and_cache_block(cache, block).await?;
 
@@ -227,9 +231,13 @@ where
         cache: RwLockUpgradableReadGuard<'_, SparseBlockchainStorage<BlockT, ChainSpecT>>,
         block: ChainSpecT::RpcBlock<ChainSpecT::RpcTransaction>,
     ) -> Result<BlockT, ForkedBlockchainError> {
+        // Geth has recently removed the total difficulty field from block RPC
+        // responses, so we fall back to the terminal total difficulty of main net to
+        // provide backwards compatibility.
+        // TODO https://github.com/NomicFoundation/edr/issues/696
         let total_difficulty = *block
             .total_difficulty()
-            .expect("Must be present as this is not a pending block");
+            .unwrap_or(&edr_defaults::TERMINAL_TOTAL_DIFFICULTY);
 
         let block: RemoteBlock<ChainSpecT> =
             block.into_remote_block(self.client.clone(), self.runtime.clone())?;