pallet_xcm_precompiles/

lib.rs

// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.
// 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.

// Ensure we're `no_std` when compiling for Wasm.
#![cfg_attr(not(feature = "std"), no_std)]

extern crate alloc;

use alloc::vec::Vec;
use codec::DecodeAll;
use core::{fmt, marker::PhantomData, num::NonZero};
use frame_support::dispatch::RawOrigin;
use pallet_revive::{
	precompiles::{
		alloy::{self, sol_types::SolValue},
		AddressMatcher, Error, Ext, Precompile,
	},
	DispatchInfo, ExecOrigin as Origin, Weight,
};
use pallet_xcm::{Config, WeightInfo};
use tracing::error;
use xcm::{v5, IdentifyVersion, VersionedLocation, VersionedXcm};
use xcm_executor::traits::WeightBounds;

alloy::sol!("src/interface/IXcm.sol");
use IXcm::IXcmCalls;

#[cfg(test)]
mod mock;
#[cfg(test)]
mod tests;

const LOG_TARGET: &str = "xcm::precompiles";

fn revert(error: &impl fmt::Debug, message: &str) -> Error {
	error!(target: LOG_TARGET, ?error, "{}", message);
	Error::Revert(message.into())
}

// We don't allow XCM versions older than 5.
fn ensure_xcm_version<V: IdentifyVersion>(input: &V) -> Result<(), Error> {
	let version = input.identify_version();
	if version < v5::VERSION {
		return Err(Error::Revert("Only XCM version 5 and onwards are supported.".into()));
	}
	Ok(())
}

pub struct XcmPrecompile<T>(PhantomData<T>);

impl<Runtime> Precompile for XcmPrecompile<Runtime>
where
	Runtime: crate::Config + pallet_revive::Config,
{
	type T = Runtime;
	const MATCHER: AddressMatcher = AddressMatcher::Fixed(NonZero::new(10).unwrap());
	const HAS_CONTRACT_INFO: bool = false;
	type Interface = IXcm::IXcmCalls;

	fn call(
		_address: &[u8; 20],
		input: &Self::Interface,
		env: &mut impl Ext<T = Self::T>,
	) -> Result<Vec<u8>, Error> {
		frame_support::ensure!(
			!env.is_delegate_call(),
			pallet_revive::Error::<Self::T>::PrecompileDelegateDenied,
		);

		let origin = env.caller();
		let frame_origin = match origin {
			Origin::Root => RawOrigin::Root.into(),
			Origin::Signed(account_id) => RawOrigin::Signed(account_id.clone()).into(),
		};

		match input {
			IXcmCalls::send(_) | IXcmCalls::execute(_) if env.is_read_only() => {
				Err(Error::Error(pallet_revive::Error::<Self::T>::StateChangeDenied.into()))
			},
			IXcmCalls::send(IXcm::sendCall { destination, message }) => {
				// Charged before decoding; see `WeightInfo::decode_xcm`.
				env.charge(
					<Runtime as Config>::WeightInfo::decode_xcm(
						message.len().saturating_add(destination.len()) as u32,
					)
					.saturating_add(<Runtime as Config>::WeightInfo::send()),
				)?;

				let final_destination = VersionedLocation::decode_all(&mut &destination[..])
					.map_err(|error| {
						revert(&error, "XCM send failed: Invalid destination format")
					})?;

				ensure_xcm_version(&final_destination)?;

				let final_message =
					VersionedXcm::<()>::decode_all_with_mem_and_depth_limit(&mut &message[..])
						.map_err(|error| {
							revert(&error, "XCM send failed: Invalid message format")
						})?;

				ensure_xcm_version(&final_message)?;

				pallet_xcm::Pallet::<Runtime>::send(
					frame_origin,
					final_destination.into(),
					final_message.into(),
				)
				.map(|_| Vec::new())
				.map_err(|error| {
					revert(
						&error,
						"XCM send failed: destination or message format may be incompatible",
					)
				})
			},
			IXcmCalls::execute(IXcm::executeCall { message, weight }) => {
				// Executing weighs the blob too, via `prepare`. Kept separate from the execution
				// charge below, which gets refunded and would otherwise give this back.
				env.charge(<Runtime as Config>::WeightInfo::weigh_message(message.len() as u32))?;

				let max_weight = Weight::from_parts(weight.refTime, weight.proofSize);
				let weight_to_charge =
					max_weight.saturating_add(<Runtime as Config>::WeightInfo::execute());
				let charged_amount = env.charge(weight_to_charge)?;

				let final_message = VersionedXcm::decode_all_with_mem_and_depth_limit(
					&mut &message[..],
				)
				.map_err(|error| revert(&error, "XCM execute failed: Invalid message format"))?;

				ensure_xcm_version(&final_message)?;

				let result = pallet_xcm::Pallet::<Runtime>::execute(
					frame_origin,
					final_message.into(),
					max_weight,
				);

				let pre = DispatchInfo {
					call_weight: weight_to_charge,
					extension_weight: Weight::zero(),
					..Default::default()
				};

				// Adjust gas using actual weight or fallback to initially charged weight
				let actual_weight = frame_support::dispatch::extract_actual_weight(&result, &pre);
				env.adjust_gas(charged_amount, actual_weight);

				result.map(|_| Vec::new()).map_err(|error| {
					revert(
							&error,
							"XCM execute failed: message may be invalid or execution constraints not satisfied"
						)
				})
			},
			IXcmCalls::weighMessage(IXcm::weighMessageCall { message }) => {
				// Charged before decoding; see `WeightInfo::weigh_message`.
				env.charge(<Runtime as Config>::WeightInfo::weigh_message(message.len() as u32))?;

				let converted_message = VersionedXcm::decode_all_with_mem_and_depth_limit(
					&mut &message[..],
				)
				.map_err(|error| revert(&error, "XCM weightMessage: Invalid message format"))?;

				ensure_xcm_version(&converted_message)?;

				let mut final_message = converted_message.try_into().map_err(|error| {
					revert(&error, "XCM weightMessage: Conversion to Xcm failed")
				})?;

				let weight = <<Runtime>::Weigher>::weight(&mut final_message, Weight::MAX)
					.map_err(|error| {
						revert(&error, "XCM weightMessage: Failed to calculate weight")
					})?;

				let final_weight =
					IXcm::Weight { proofSize: weight.proof_size(), refTime: weight.ref_time() };

				Ok(final_weight.abi_encode())
			},
		}
	}
}