[pallet-revive] implement the ref_time_left API (#6908)

This PR implements the ref_time_left API method. Solidity knows only a
single "gas" dimension; Solidity contracts will use this to query the
gas left.

---------

Signed-off-by: xermicus <cyrill@parity.io>
Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Co-authored-by: command-bot <>

prdoc/pr_6908.prdoc

+title: '[pallet-revive] implement the ref_time_left API'
+doc:
+- audience: Runtime Dev
+  description: This PR implements the ref_time_left API method. Solidity knows only
+    a single "gas" dimension; Solidity contracts will use this to query the gas left.
+crates:
+- name: pallet-revive-fixtures
+  bump: minor
+- name: pallet-revive
+  bump: minor
+- name: pallet-revive-uapi
+  bump: minor

substrate/frame/revive/fixtures/contracts/ref_time_left.rs

+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![no_std]
+#![no_main]
+
+extern crate common;
+use uapi::{HostFn, HostFnImpl as api, ReturnFlags};
+
+#[no_mangle]
+#[polkavm_derive::polkavm_export]
+pub extern "C" fn deploy() {
+	assert!(api::ref_time_left() > api::ref_time_left());
+}
+
+#[no_mangle]
+#[polkavm_derive::polkavm_export]
+pub extern "C" fn call() {
+	api::return_value(ReturnFlags::empty(), &api::ref_time_left().to_le_bytes());
+}

substrate/frame/revive/src/benchmarking/mod.rs

@@ -671,6 +671,18 @@ mod benchmarks {
 		);
 	}
 
+	#[benchmark(pov_mode = Measured)]
+	fn seal_ref_time_left() {
+		build_runtime!(runtime, memory: [vec![], ]);
+
+		let result;
+		#[block]
+		{
+			result = runtime.bench_ref_time_left(memory.as_mut_slice());
+		}
+		assert_eq!(result.unwrap(), runtime.ext().gas_meter().gas_left().ref_time());
+	}
+
 	#[benchmark(pov_mode = Measured)]
 	fn seal_balance() {
 		build_runtime!(runtime, memory: [[0u8;32], ]);

substrate/frame/revive/src/tests.rs

@@ -1874,6 +1874,27 @@ fn lazy_batch_removal_works() {
 	});
 }
 
+#[test]
+fn ref_time_left_api_works() {
+	let (code, _) = compile_module("ref_time_left").unwrap();
+
+	ExtBuilder::default().existential_deposit(100).build().execute_with(|| {
+		let _ = <Test as Config>::Currency::set_balance(&ALICE, 1_000_000);
+
+		// Create fixture: Constructor calls ref_time_left twice and asserts it to decrease
+		let Contract { addr, .. } =
+			builder::bare_instantiate(Code::Upload(code)).build_and_unwrap_contract();
+
+		// Call the contract: It echoes back the ref_time returned by the ref_time_left API.
+		let received = builder::bare_call(addr).build_and_unwrap_result();
+		assert_eq!(received.flags, ReturnFlags::empty());
+
+		let returned_value = u64::from_le_bytes(received.data[..8].try_into().unwrap());
+		assert!(returned_value > 0);
+		assert!(returned_value < GAS_LIMIT.ref_time());
+	});
+}
+
 #[test]
 fn lazy_removal_partial_remove_works() {
 	let (code, _hash) = compile_module("self_destruct").unwrap();

substrate/frame/revive/src/wasm/runtime.rs

@@ -306,6 +306,8 @@ pub enum RuntimeCosts {
 	CallerIsRoot,
 	/// Weight of calling `seal_address`.
 	Address,
+	/// Weight of calling `seal_ref_time_left`.
+	RefTimeLeft,
 	/// Weight of calling `seal_weight_left`.
 	WeightLeft,
 	/// Weight of calling `seal_balance`.
@@ -462,6 +464,7 @@ impl<T: Config> Token<T> for RuntimeCosts {
 			CallerIsOrigin => T::WeightInfo::seal_caller_is_origin(),
 			CallerIsRoot => T::WeightInfo::seal_caller_is_root(),
 			Address => T::WeightInfo::seal_address(),
+			RefTimeLeft => T::WeightInfo::seal_ref_time_left(),
 			WeightLeft => T::WeightInfo::seal_weight_left(),
 			Balance => T::WeightInfo::seal_balance(),
 			BalanceOf => T::WeightInfo::seal_balance_of(),
@@ -1701,6 +1704,14 @@ pub mod env {
 		Ok(result?)
 	}
 
+	/// Returns the amount of ref_time left.
+	/// See [`pallet_revive_uapi::HostFn::ref_time_left`].
+	#[stable]
+	fn ref_time_left(&mut self, memory: &mut M) -> Result<u64, TrapReason> {
+		self.charge_gas(RuntimeCosts::RefTimeLeft)?;
+		Ok(self.ext.gas_meter().gas_left().ref_time())
+	}
+
 	/// Call into the chain extension provided by the chain if any.
 	/// See [`pallet_revive_uapi::HostFn::call_chain_extension`].
 	fn call_chain_extension(

substrate/frame/revive/uapi/src/host.rs

@@ -398,6 +398,9 @@ pub trait HostFn: private::Sealed {
 	/// - `offset`: Byte offset into the returned data
 	fn return_data_copy(output: &mut &mut [u8], offset: u32);
 
+	/// Returns the amount of ref_time left.
+	fn ref_time_left() -> u64;
+
 	/// Stores the current block number of the current contract into the supplied buffer.
 	///
 	/// # Parameters

substrate/frame/revive/uapi/src/host/riscv64.rs

@@ -76,6 +76,7 @@ mod sys {
 		pub fn address(out_ptr: *mut u8);
 		pub fn weight_to_fee(ref_time: u64, proof_size: u64, out_ptr: *mut u8);
 		pub fn weight_left(out_ptr: *mut u8, out_len_ptr: *mut u32);
+		pub fn ref_time_left() -> u64;
 		pub fn get_immutable_data(out_ptr: *mut u8, out_len_ptr: *mut u32);
 		pub fn set_immutable_data(ptr: *const u8, len: u32);
 		pub fn balance(out_ptr: *mut u8);
@@ -440,6 +441,10 @@ impl HostFn for HostFnImpl {
 		extract_from_slice(output, output_len as usize);
 	}
 
+	fn ref_time_left() -> u64 {
+		unsafe { sys::ref_time_left() }
+	}
+
 	#[cfg(feature = "unstable-api")]
 	fn block_hash(block_number_ptr: &[u8; 32], output: &mut [u8; 32]) {
 		unsafe { sys::block_hash(block_number_ptr.as_ptr(), output.as_mut_ptr()) };