Add (preflight) simulation to BanksClient (#22084)

* Add more-legitimate conversion from legacy Transaction to SanitizedTransaction

* Add Banks method with preflight checks

* Expose BanksClient method with preflight checks

* Unwrap simulation err

* Add Bank simulation method that works on unfrozen Banks

* Add simpler api

* Better name: BanksTransactionResultWithSimulation

banks-server/src/banks_server.rs

@@ -2,9 +2,14 @@ use {
     bincode::{deserialize, serialize},
     futures::{future, prelude::stream::StreamExt},
     solana_banks_interface::{
-        Banks, BanksRequest, BanksResponse, TransactionConfirmationStatus, TransactionStatus,
+        Banks, BanksRequest, BanksResponse, BanksTransactionResultWithSimulation,
+        TransactionConfirmationStatus, TransactionSimulationDetails, TransactionStatus,
+    },
+    solana_runtime::{
+        bank::{Bank, TransactionSimulationResult},
+        bank_forks::BankForks,
+        commitment::BlockCommitmentCache,
     },
-    solana_runtime::{bank::Bank, bank_forks::BankForks, commitment::BlockCommitmentCache},
     solana_sdk::{
         account::Account,
         clock::Slot,
@@ -15,7 +20,7 @@ use {
         message::{Message, SanitizedMessage},
         pubkey::Pubkey,
         signature::Signature,
-        transaction::{self, Transaction},
+        transaction::{self, SanitizedTransaction, Transaction},
     },
     solana_send_transaction_service::{
         send_transaction_service::{SendTransactionService, TransactionInfo},
@@ -242,6 +247,47 @@ impl Banks for BanksServer {
         self.bank(commitment).block_height()
     }
 
+    async fn process_transaction_with_preflight_and_commitment_and_context(
+        self,
+        ctx: Context,
+        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,
+        } = self
+            .bank(commitment)
+            .simulate_transaction_unchecked(sanitized_transaction)
+        {
+            return BanksTransactionResultWithSimulation {
+                result: Some(Err(err)),
+                simulation_details: Some(TransactionSimulationDetails {
+                    logs,
+                    units_consumed,
+                }),
+            };
+        }
+        BanksTransactionResultWithSimulation {
+            result: self
+                .process_transaction_with_commitment_and_context(ctx, transaction, commitment)
+                .await,
+            simulation_details: None,
+        }
+    }
+
     async fn process_transaction_with_commitment_and_context(
         self,
         _: Context,