banks-client: Add `simulate_transaction` implementation (#25830)

banks-client/src/lib.rs

@@ -138,6 +138,18 @@ impl BanksClient {
             .map_err(Into::into)
     }
 
+    pub fn simulate_transaction_with_commitment_and_context(
+        &mut self,
+        ctx: Context,
+        transaction: Transaction,
+        commitment: CommitmentLevel,
+    ) -> impl Future<Output = Result<BanksTransactionResultWithSimulation, BanksClientError>> + '_
+    {
+        self.inner
+            .simulate_transaction_with_commitment_and_context(ctx, transaction, commitment)
+            .map_err(Into::into)
+    }
+
     pub fn get_account_with_commitment_and_context(
         &mut self,
         ctx: Context,
@@ -300,6 +312,29 @@ impl BanksClient {
         self.process_transactions_with_commitment(transactions, CommitmentLevel::default())
     }
 
+    /// Simulate a transaction at the given commitment level
+    pub fn simulate_transaction_with_commitment(
+        &mut self,
+        transaction: Transaction,
+        commitment: CommitmentLevel,
+    ) -> impl Future<Output = Result<BanksTransactionResultWithSimulation, BanksClientError>> + '_
+    {
+        self.simulate_transaction_with_commitment_and_context(
+            context::current(),
+            transaction,
+            commitment,
+        )
+    }
+
+    /// Simulate a transaction at the default commitment level
+    pub fn simulate_transaction(
+        &mut self,
+        transaction: Transaction,
+    ) -> impl Future<Output = Result<BanksTransactionResultWithSimulation, BanksClientError>> + '_
+    {
+        self.simulate_transaction_with_commitment(transaction, CommitmentLevel::default())
+    }
+
     /// Return the most recent rooted slot. All transactions at or below this slot
     /// are said to be finalized. The cluster will not fork to a higher slot.
     pub fn get_root_slot(&mut self) -> impl Future<Output = Result<Slot, BanksClientError>> + '_ {
@@ -516,6 +551,11 @@ mod tests {
 
             let recent_blockhash = banks_client.get_latest_blockhash().await?;
             let transaction = Transaction::new(&[&genesis.mint_keypair], message, recent_blockhash);
+            let simulation_result = banks_client
+                .simulate_transaction(transaction.clone())
+                .await
+                .unwrap();
+            assert!(simulation_result.result.unwrap().is_ok());
             banks_client.process_transaction(transaction).await.unwrap();
             assert_eq!(banks_client.get_balance(bob_pubkey).await?, 1);
             Ok(())

banks-interface/src/lib.rs

@@ -67,6 +67,10 @@ pub trait Banks {
         transaction: Transaction,
         commitment: CommitmentLevel,
     ) -> Option<transaction::Result<()>>;
+    async fn simulate_transaction_with_commitment_and_context(
+        transaction: Transaction,
+        commitment: CommitmentLevel,
+    ) -> BanksTransactionResultWithSimulation;
     async fn get_account_with_commitment_and_context(
         address: Pubkey,
         commitment: CommitmentLevel,

banks-server/src/banks_server.rs

@@ -161,6 +161,38 @@ fn verify_transaction(
     }
 }
 
+fn simulate_transaction(
+    bank: &Bank,
+    transaction: Transaction,
+) -> BanksTransactionResultWithSimulation {
+    let sanitized_transaction = match SanitizedTransaction::try_from_legacy_transaction(transaction)
+    {
+        Err(err) => {
+            return BanksTransactionResultWithSimulation {
+                result: Some(Err(err)),
+                simulation_details: None,
+            };
+        }
+        Ok(tx) => tx,
+    };
+    let TransactionSimulationResult {
+        result,
+        logs,
+        post_simulation_accounts: _,
+        units_consumed,
+        return_data,
+    } = bank.simulate_transaction_unchecked(sanitized_transaction);
+    let simulation_details = TransactionSimulationDetails {
+        logs,
+        units_consumed,
+        return_data,
+    };
+    BanksTransactionResultWithSimulation {
+        result: Some(result),
+        simulation_details: Some(simulation_details),
+    }
+}
+
 #[tarpc::server]
 impl Banks for BanksServer {
     async fn send_transaction_with_context(self, _: Context, transaction: Transaction) {
@@ -252,41 +284,25 @@ impl Banks for BanksServer {
         transaction: Transaction,
         commitment: CommitmentLevel,
     ) -> BanksTransactionResultWithSimulation {
-        let sanitized_transaction =
-            match SanitizedTransaction::try_from_legacy_transaction(transaction.clone()) {
-                Err(err) => {
-                    return BanksTransactionResultWithSimulation {
-                        result: Some(Err(err)),
-                        simulation_details: None,
-                    };
-                }
-                Ok(tx) => tx,
-            };
-        if let TransactionSimulationResult {
-            result: Err(err),
-            logs,
-            post_simulation_accounts: _,
-            units_consumed,
-            return_data,
-        } = self
-            .bank(commitment)
-            .simulate_transaction_unchecked(sanitized_transaction)
-        {
-            return BanksTransactionResultWithSimulation {
-                result: Some(Err(err)),
-                simulation_details: Some(TransactionSimulationDetails {
-                    logs,
-                    units_consumed,
-                    return_data,
-                }),
-            };
-        }
-        BanksTransactionResultWithSimulation {
-            result: self
+        let mut simulation_result =
+            simulate_transaction(&self.bank(commitment), transaction.clone());
+        // Simulation was ok, so process the real transaction and replace the
+        // simulation's result with the real transaction result
+        if let Some(Ok(_)) = simulation_result.result {
+            simulation_result.result = self
                 .process_transaction_with_commitment_and_context(ctx, transaction, commitment)
-                .await,
-            simulation_details: None,
+                .await;
         }
+        simulation_result
+    }
+
+    async fn simulate_transaction_with_commitment_and_context(
+        self,
+        _: Context,
+        transaction: Transaction,
+        commitment: CommitmentLevel,
+    ) -> BanksTransactionResultWithSimulation {
+        simulate_transaction(&self.bank(commitment), transaction)
     }
 
     async fn process_transaction_with_commitment_and_context(