Implement contract_getStorage RPC API (#3944)

substrate/node/runtime/src/lib.rs

@@ -664,6 +664,21 @@ impl_runtime_apis! {
 				Err(_) => ContractExecResult::Error,
 			}
 		}
+
+		fn get_storage(
+			address: AccountId,
+			key: [u8; 32],
+		) -> contracts_rpc_runtime_api::GetStorageResult {
+			Contracts::get_storage(address, key).map_err(|rpc_err| {
+				use contracts::GetStorageError;
+				use contracts_rpc_runtime_api::{GetStorageError as RpcGetStorageError};
+				/// Map the contract error into the RPC layer error.
+				match rpc_err {
+					GetStorageError::ContractDoesntExist => RpcGetStorageError::ContractDoesntExist,
+					GetStorageError::IsTombstone => RpcGetStorageError::IsTombstone,
+				}
+			})
+		}
 	}
 
 	impl transaction_payment_rpc_runtime_api::TransactionPaymentApi<