fix(core): normalize signature S

ethers-contract/tests/it/contract_call.rs

@@ -16,5 +16,5 @@ fn _contract_call_into_future_is_send() {
         future
     }
 
-    is_send(contract.cache().into_future());
+    drop(is_send(contract.cache().into_future()));
 }

ethers-core/src/types/signature.rs

@@ -127,8 +127,8 @@ impl Signature {
 
     /// Retrieves the recovery signature.
     fn as_signature(&self) -> Result<(RecoverableSignature, RecoveryId), SignatureError> {
-        let recovery_id = self.recovery_id()?;
-        let signature = {
+        let mut recovery_id = self.recovery_id()?;
+        let mut signature = {
             let mut r_bytes = [0u8; 32];
             let mut s_bytes = [0u8; 32];
             self.r.to_big_endian(&mut r_bytes);
@@ -138,6 +138,14 @@ impl Signature {
             K256Signature::from_scalars(*gar, *gas)?
         };
 
+        // Normalize into "low S" form. See:
+        // - https://github.com/RustCrypto/elliptic-curves/issues/988
+        // - https://github.com/bluealloy/revm/pull/870
+        if let Some(normalized) = signature.normalize_s() {
+            signature = normalized;
+            recovery_id = RecoveryId::from_byte(recovery_id.to_byte() ^ 1).unwrap();
+        }
+
         Ok((signature, recovery_id))
     }
 
@@ -324,6 +332,16 @@ mod tests {
         assert_eq!(tx.recover_from().unwrap(), expected);
     }
 
+    #[test]
+    fn can_recover_tx_sender_not_normalized() {
+        let sig = Signature::from_str("48b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353efffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c8041b").unwrap();
+        let hash =
+            H256::from_str("5eb4f5a33c621f32a8622d5f943b6b102994dfe4e5aebbefe69bb1b2aa0fc93e")
+                .unwrap();
+        let expected = Address::from_str("0f65fe9276bc9a24ae7083ae28e2660ef72df99e").unwrap();
+        assert_eq!(sig.recover(hash).unwrap(), expected);
+    }
+
     #[test]
     fn recover_web3_signature() {
         // test vector taken from:

ethers-core/src/types/transaction/eip2718.rs

@@ -417,9 +417,9 @@ impl TypedTransaction {
 impl Decodable for TypedTransaction {
     fn decode(rlp: &rlp::Rlp) -> Result<Self, rlp::DecoderError> {
         let tx_type: Option<U64> = match rlp.is_data() {
-            true => Ok(Some(rlp.data()?.into())),
-            false => Ok(None),
-        }?;
+            true => Some(rlp.data()?.into()),
+            false => None,
+        };
         let rest = rlp::Rlp::new(
             rlp.as_raw().get(1..).ok_or(rlp::DecoderError::Custom("no transaction payload"))?,
         );