feat(l1): enforce per-transaction wire-size cap in mempool admission

crates/blockchain/blockchain.rs

@@ -72,6 +72,7 @@ use ethrex_common::types::{
 };
 use ethrex_common::types::{ELASTICITY_MULTIPLIER, P2PTransaction};
 use ethrex_common::types::{Fork, MempoolTransaction};
+use ethrex_common::types::{MAX_BLOB_TX_SIZE, MAX_TX_SIZE};
 use ethrex_common::utils::keccak;
 use ethrex_common::{Address, H256, TrieLogger, U256};
 pub use ethrex_common::{
@@ -2432,7 +2433,23 @@ impl Blockchain {
             .ok_or(MempoolError::NoBlockHeaderError)?;
         let config = self.storage.get_chain_config();
 
-        // NOTE: We could add a tx size limit here, but it's not in the actual spec
+        // Wire size cap: peer-policy default, not consensus. Matches geth
+        // `txMaxSize` (legacypool / blobpool), reth `DEFAULT_MAX_TX_INPUT_BYTES`,
+        // nethermind `MaxTxSize` / `MaxBlobTxSize`. For EIP-4844 the canonical
+        // encoding of `Transaction` excludes the sidecar (which lives in the
+        // adjacent `BlobsBundle`), so this caps the core tx only.
+        let encoded_len = tx.encode_canonical_to_vec().len();
+        let size_limit = if matches!(tx, Transaction::EIP4844Transaction(_)) {
+            MAX_BLOB_TX_SIZE
+        } else {
+            MAX_TX_SIZE
+        };
+        if encoded_len > size_limit {
+            return Err(MempoolError::TxSizeExceeded {
+                actual: encoded_len,
+                limit: size_limit,
+            });
+        }
 
         // Check init code size
         // [EIP-7954] - Amsterdam increases the limit

crates/blockchain/error.rs

@@ -83,6 +83,8 @@ pub enum MempoolError {
     TxMaxInitCodeSizeError,
     #[error("Transaction max data size exceeded")]
     TxMaxDataSizeError,
+    #[error("Transaction encoded size ({actual} bytes) exceeds the {limit}-byte limit")]
+    TxSizeExceeded { actual: usize, limit: usize },
     #[error("Transaction gas limit exceeded")]
     TxGasLimitExceededError,
     #[error(

crates/common/types/constants.rs

@@ -32,3 +32,13 @@ pub const FIELD_ELEMENTS_PER_EXT_BLOB: usize = 2 * FIELD_ELEMENTS_PER_BLOB;
 pub const FIELD_ELEMENTS_PER_CELL: usize = 64;
 pub const BYTES_PER_CELL: usize = FIELD_ELEMENTS_PER_CELL * BYTES_PER_FIELD_ELEMENT;
 pub const CELLS_PER_EXT_BLOB: usize = FIELD_ELEMENTS_PER_EXT_BLOB / FIELD_ELEMENTS_PER_CELL;
+
+// Mempool admission size caps — peer-policy defaults, not consensus.
+// Matches geth `txMaxSize` (legacypool) and `txMaxSize` (blobpool), reth
+// `DEFAULT_MAX_TX_INPUT_BYTES`, nethermind `MaxTxSize` / `MaxBlobTxSize`.
+/// Maximum RLP-encoded wire size for a non-blob transaction (128 KiB).
+pub const MAX_TX_SIZE: usize = 131_072;
+/// Maximum RLP-encoded core size for an EIP-4844 blob transaction (1 MiB),
+/// excluding the blob sidecar. Sidecar size is bounded separately by the
+/// per-blob byte count and the fork's max blob count.
+pub const MAX_BLOB_TX_SIZE: usize = 1_048_576;

crates/common/types/transaction.rs

@@ -3764,4 +3764,31 @@ mod tests {
             "blob-gas term missing from cost_without_base_fee() for EIP-4844"
         );
     }
+
+    #[test]
+    fn test_encoded_size_exceeds_max_tx_size() {
+        // Confirms the wire-size signal used by the mempool admission cap:
+        // an EIP-1559 tx with > 128 KiB of `data` encodes to > MAX_TX_SIZE bytes.
+        use crate::types::MAX_TX_SIZE;
+
+        let payload = vec![0u8; MAX_TX_SIZE + 1];
+        let tx = Transaction::EIP1559Transaction(EIP1559Transaction {
+            data: Bytes::from(payload),
+            ..Default::default()
+        });
+
+        assert!(
+            tx.encode_canonical_to_vec().len() > MAX_TX_SIZE,
+            "tx with > 128 KiB calldata must encode larger than MAX_TX_SIZE"
+        );
+    }
+
+    #[test]
+    fn test_encoded_size_below_max_tx_size() {
+        // A small tx encodes well below the cap.
+        use crate::types::MAX_TX_SIZE;
+
+        let tx = Transaction::EIP1559Transaction(EIP1559Transaction::default());
+        assert!(tx.encode_canonical_to_vec().len() <= MAX_TX_SIZE);
+    }
 }