[logging] improve the error log for mempool #9466

When submitting same txn to mempool, we got error says "Failed to update gas price to 0"

From Zekun:

> the error message makes no sense , i thought we updated it.

it assume you submit the same txn is to update the gas price to make it higher priority. we should simply return message like txn already in mempool

Closes: #9610

api/src/tests/transactions_test.rs

@@ -614,7 +614,7 @@ async fn test_post_transaction_rejected_by_mempool() {
         resp,
         json!({
           "code": 400,
-          "message": "transaction is rejected: InvalidUpdate - Failed to update gas price to 0"
+          "message": "transaction is rejected: InvalidUpdate - Transaction already in mempool"
         }),
     );
 }

json-rpc/integration-tests/src/lib.rs

@@ -784,7 +784,7 @@ impl PublicUsageTest for MempoolValidationError {
             let resp = env.submit(&txn2);
             assert_eq!(
                 resp.error.expect("error").message,
-                "Server error: Mempool submission error: \"Failed to update gas price to 0\""
+                "Server error: Mempool submission error: \"Transaction already in mempool\""
                     .to_string(),
             );
         });

mempool/src/core_mempool/transaction_store.rs

@@ -140,9 +140,8 @@ impl TransactionStore {
                         self.index_remove(&txn);
                     }
                 } else {
-                    return MempoolStatus::new(MempoolStatusCode::InvalidUpdate).with_message(
-                        format!("Failed to update gas price to {}", txn.get_gas_price()),
-                    );
+                    return MempoolStatus::new(MempoolStatusCode::InvalidUpdate)
+                        .with_message("Transaction already in mempool".to_string());
                 }
             }
         }