Add get_clock to BanksClient (#18591)

(cherry picked from commit d30a36641e)

Co-authored-by: Kirill Fomichev <fanatid@ya.ru>

banks-client/src/lib.rs

@@ -10,8 +10,14 @@ use futures::{future::join_all, Future, FutureExt};
 pub use solana_banks_interface::{BanksClient as TarpcClient, TransactionStatus};
 use solana_banks_interface::{BanksRequest, BanksResponse};
 use solana_program::{
-    clock::Slot, fee_calculator::FeeCalculator, hash::Hash, program_pack::Pack, pubkey::Pubkey,
-    rent::Rent, sysvar::Sysvar,
+    clock::Clock,
+    clock::Slot,
+    fee_calculator::FeeCalculator,
+    hash::Hash,
+    program_pack::Pack,
+    pubkey::Pubkey,
+    rent::Rent,
+    sysvar::{self, Sysvar},
 };
 use solana_sdk::{
     account::{from_account, Account},
@@ -115,6 +121,17 @@ impl BanksClient {
         self.send_transaction_with_context(context::current(), transaction)
     }
 
+    /// Return the cluster clock
+    pub fn get_clock(&mut self) -> impl Future<Output = io::Result<Clock>> + '_ {
+        self.get_account(sysvar::clock::id()).map(|result| {
+            let clock_sysvar = result?
+                .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "Clock sysvar not present"))?;
+            from_account::<Clock, _>(&clock_sysvar).ok_or_else(|| {
+                io::Error::new(io::ErrorKind::Other, "Failed to deserialize Clock sysvar")
+            })
+        })
+    }
+
     /// Return the fee parameters associated with a recent, rooted blockhash. The cluster
     /// will use the transaction's blockhash to look up these same fee parameters and
     /// use them to calculate the transaction fee.