Rpc: Return error if block does not exist (#11743) (#11748)

* Return error if block does not exist

* Update docs

(cherry picked from commit 747f8d5877)

Co-authored-by: Tyera Eulberg <teulberg@gmail.com>

core/src/rpc_error.rs

@@ -5,6 +5,7 @@ const JSON_RPC_SERVER_ERROR_0: i64 = -32000;
 const JSON_RPC_SERVER_ERROR_1: i64 = -32001;
 const JSON_RPC_SERVER_ERROR_2: i64 = -32002;
 const JSON_RPC_SERVER_ERROR_3: i64 = -32003;
+const JSON_RPC_SERVER_ERROR_4: i64 = -32004;
 
 pub enum RpcCustomError {
     NonexistentClusterRoot {
@@ -19,6 +20,9 @@ pub enum RpcCustomError {
         message: String,
     },
     SendTransactionIsNotSigned,
+    BlockNotAvailable {
+        slot: Slot,
+    },
 }
 
 impl From<RpcCustomError> for Error {
@@ -56,6 +60,11 @@ impl From<RpcCustomError> for Error {
                 message: "Transaction is not signed".to_string(),
                 data: None,
             },
+            RpcCustomError::BlockNotAvailable { slot } => Self {
+                code: ErrorCode::ServerError(JSON_RPC_SERVER_ERROR_4),
+                message: format!("Block not available for slot {}", slot,),
+                data: None,
+            },
         }
     }
 }