TxEip7702: add payload length methods (#1152)

* TxEip7702: add payload length methods

* clean up

crates/consensus/src/transaction/eip7702.rs

@@ -1,7 +1,7 @@
 use crate::{EncodableSignature, SignableTransaction, Signed, Transaction, TxType};
 use alloy_eips::eip2930::AccessList;
 use alloy_primitives::{keccak256, Bytes, ChainId, Signature, TxKind, U256};
-use alloy_rlp::{BufMut, Decodable, Encodable, Header};
+use alloy_rlp::{length_of_length, BufMut, Decodable, Encodable, Header};
 use core::mem;
 
 #[cfg(not(feature = "std"))]
@@ -269,6 +269,19 @@ impl TxEip7702 {
         self.input.len() + // input
         self.authorization_list.capacity() * mem::size_of::<SignedAuthorization>() // authorization_list
     }
+
+    /// Output the length of the RLP signed transaction encoding, _without_ a RLP string header.
+    pub fn payload_len_with_signature_without_header(&self, signature: &Signature) -> usize {
+        let payload_length = self.fields_len() + signature.rlp_vrs_len();
+        // 'transaction type byte length' + 'header length' + 'payload length'
+        1 + length_of_length(payload_length) + payload_length
+    }
+
+    /// Output the length of the RLP signed transaction encoding. This encodes with a RLP header.
+    pub fn payload_len_with_signature(&self, signature: &Signature) -> usize {
+        let len = self.payload_len_with_signature_without_header(signature);
+        length_of_length(len) + len
+    }
 }
 
 impl Transaction for TxEip7702 {
@@ -356,10 +369,66 @@ impl Decodable for TxEip7702 {
 
 #[cfg(all(test, feature = "k256"))]
 mod tests {
+    use core::str::FromStr;
+
     use super::TxEip7702;
     use crate::SignableTransaction;
     use alloy_eips::eip2930::AccessList;
-    use alloy_primitives::{address, b256, hex, Address, Signature, TxKind, U256};
+    use alloy_primitives::{address, b256, hex, Address, Bytes, Signature, TxKind, U256};
+
+    #[test]
+    fn test_payload_len_with_signature_without_header() {
+        let tx = TxEip7702 {
+            chain_id: 1u64,
+            nonce: 0,
+            max_fee_per_gas: 0x4a817c800,
+            max_priority_fee_per_gas: 0x3b9aca00,
+            gas_limit: 2,
+            to: TxKind::Create,
+            value: U256::ZERO,
+            input: Bytes::from(vec![1, 2]),
+            access_list: Default::default(),
+            authorization_list: Default::default(),
+        };
+
+        let signature = Signature::from_rs_and_parity(
+            U256::from_str("0xc569c92f176a3be1a6352dd5005bfc751dcb32f57623dd2a23693e64bf4447b0")
+                .unwrap(),
+            U256::from_str("0x1a891b566d369e79b7a66eecab1e008831e22daa15f91a0a0cf4f9f28f47ee05")
+                .unwrap(),
+            1,
+        )
+        .unwrap();
+
+        assert_eq!(tx.payload_len_with_signature_without_header(&signature), 91);
+    }
+
+    #[test]
+    fn test_payload_len_with_signature() {
+        let tx = TxEip7702 {
+            chain_id: 1u64,
+            nonce: 0,
+            max_fee_per_gas: 0x4a817c800,
+            max_priority_fee_per_gas: 0x3b9aca00,
+            gas_limit: 2,
+            to: TxKind::Create,
+            value: U256::ZERO,
+            input: Bytes::from(vec![1, 2]),
+            access_list: Default::default(),
+            authorization_list: Default::default(),
+        };
+
+        let signature = Signature::from_rs_and_parity(
+            U256::from_str("0xc569c92f176a3be1a6352dd5005bfc751dcb32f57623dd2a23693e64bf4447b0")
+                .unwrap(),
+            U256::from_str("0x1a891b566d369e79b7a66eecab1e008831e22daa15f91a0a0cf4f9f28f47ee05")
+                .unwrap(),
+            1,
+        )
+        .unwrap();
+
+        assert_eq!(tx.payload_len_with_signature(&signature), 93);
+    }
 
     #[test]
     fn encode_decode_eip7702() {