fix(rpc): add a buffer to call gas limit estimation (#628)

crates/sim/src/estimation/estimation.rs

@@ -11,7 +11,11 @@
 // You should have received a copy of the GNU General Public License along with Rundler.
 // If not, see https://www.gnu.org/licenses/.
 
-use std::{cmp, ops::Deref, sync::Arc};
+use std::{
+    cmp,
+    ops::{Add, Deref},
+    sync::Arc,
+};
 
 use anyhow::{anyhow, Context};
 use ethers::{
@@ -52,7 +56,11 @@ const GAS_ROUNDING: u64 = 4096;
 /// `GAS_ESTIMATION_ERROR_MARGIN` of each other.
 const GAS_ESTIMATION_ERROR_MARGIN: f64 = 0.1;
 
+/// Percentage by which to increase the verification gas limit after binary search
 const VERIFICATION_GAS_BUFFER_PERCENT: u64 = 10;
+/// Absolute value by which to increase the call gas limit after binary search
+/// TODO(danc): remove this in 0.7 entry point else users will get overcharged
+const CALL_GAS_BUFFER_VALUE: U256 = U256([3000, 0, 0, 0]);
 
 /// Offset at which the proxy target address appears in the proxy bytecode. Must
 /// be updated whenever `CallGasEstimationProxy.sol` changes.
@@ -159,10 +167,15 @@ impl<P: Provider, E: EntryPoint> GasEstimator for GasEstimatorImpl<P, E> {
         )
         .min(settings.max_verification_gas.into());
 
+        // Add a buffer to the call gas limit and clamp
+        let call_gas_limit = call_gas_limit
+            .add(CALL_GAS_BUFFER_VALUE)
+            .clamp(MIN_CALL_GAS_LIMIT, settings.max_call_gas.into());
+
         Ok(GasEstimate {
             pre_verification_gas,
             verification_gas_limit,
-            call_gas_limit: call_gas_limit.clamp(MIN_CALL_GAS_LIMIT, settings.max_call_gas.into()),
+            call_gas_limit,
         })
     }
 }
@@ -1202,7 +1215,10 @@ mod tests {
         );
 
         // input gas limit clamped with the set limit in settings and constant MIN
-        assert_eq!(estimation.call_gas_limit, U256::from(10000));
+        assert_eq!(
+            estimation.call_gas_limit,
+            U256::from(10000) + CALL_GAS_BUFFER_VALUE
+        );
     }
 
     #[tokio::test]