process_xcm_message.rs

// Copyright 2020 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! Implementation of `ProcessMessage` for an `ExecuteXcm` implementation.

use frame_support::{
	ensure,
	traits::{ProcessMessage, ProcessMessageError},
};
use parity_scale_codec::{Decode, FullCodec, MaxEncodedLen};
use scale_info::TypeInfo;
use sp_io::hashing::blake2_256;
use sp_std::{fmt::Debug, marker::PhantomData};
use sp_weights::{Weight, WeightMeter};
use xcm::prelude::*;

/// A message processor that delegates execution to an [XcmExecutor].
pub struct ProcessXcmMessage<MessageOrigin, XcmExecutor, Call>(
	PhantomData<(MessageOrigin, XcmExecutor, Call)>,
);
impl<
		MessageOrigin: Into<MultiLocation> + FullCodec + MaxEncodedLen + Clone + Eq + PartialEq + TypeInfo + Debug,
		XcmExecutor: ExecuteXcm<Call>,
		Call,
	> ProcessMessage for ProcessXcmMessage<MessageOrigin, XcmExecutor, Call>
{
	type Origin = MessageOrigin;

	/// Process the given message, using no more than the remaining `weight` to do so.
	fn process_message(
		message: &[u8],
		origin: Self::Origin,
		meter: &mut WeightMeter,
	) -> Result<bool, ProcessMessageError> {
		let hash = blake2_256(message);
		let versioned_message = VersionedXcm::<Call>::decode(&mut &message[..])
			.map_err(|_| ProcessMessageError::Corrupt)?;
		let message = Xcm::<Call>::try_from(versioned_message)
			.map_err(|_| ProcessMessageError::Unsupported)?;
		let pre = XcmExecutor::prepare(message).map_err(|_| ProcessMessageError::Unsupported)?;
		let required = pre.weight_of();
		ensure!(meter.can_accrue(required), ProcessMessageError::Overweight(required));

		let (consumed, result) =
			match XcmExecutor::execute(origin.into(), pre, hash, Weight::zero()) {
				Outcome::Complete(w) => (w, Ok(true)),
				Outcome::Incomplete(w, _) => (w, Ok(false)),
				// In the error-case we assume the worst case and consume all possible weight.
				Outcome::Error(_) => (required, Err(ProcessMessageError::Unsupported)),
			};
		meter.defensive_saturating_accrue(consumed);
		result
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use frame_support::{
		assert_err, assert_ok,
		traits::{ProcessMessageError, ProcessMessageError::*},
	};
	use parity_scale_codec::Encode;
	use polkadot_test_runtime::*;
	use xcm::{v2, v3, VersionedXcm};

	const ORIGIN: Junction = Junction::OnlyChild;
	/// The processor to use for tests.
	type Processor =
		ProcessXcmMessage<Junction, xcm_executor::XcmExecutor<xcm_config::XcmConfig>, RuntimeCall>;

	#[test]
	fn process_message_trivial_works() {
		// ClearOrigin works.
		assert!(process(v2_xcm(true)).unwrap());
		assert!(process(v3_xcm(true)).unwrap());
	}

	#[test]
	fn process_message_trivial_fails() {
		// Trap makes it fail.
		assert!(!process(v3_xcm(false)).unwrap());
		assert!(!process(v3_xcm(false)).unwrap());
	}

	#[test]
	fn process_message_corrupted_fails() {
		let msgs: &[&[u8]] = &[&[], &[55, 66], &[123, 222, 233]];
		for msg in msgs {
			assert_err!(process_raw(msg), Corrupt);
		}
	}

	#[test]
	fn process_message_overweight_fails() {
		for msg in [v3_xcm(true), v3_xcm(false), v3_xcm(false), v2_xcm(false)] {
			let msg = &msg.encode()[..];

			// Errors if we stay below a weight limit of 1000.
			for i in 0..10 {
				let meter = &mut WeightMeter::from_limit((i * 10).into());
				assert_err!(
					Processor::process_message(msg, ORIGIN, meter),
					Overweight(1000.into())
				);
				assert_eq!(meter.consumed, 0.into());
			}

			// Works with a limit of 1000.
			let meter = &mut WeightMeter::from_limit(1000.into());
			assert_ok!(Processor::process_message(msg, ORIGIN, meter));
			assert_eq!(meter.consumed, 1000.into());
		}
	}

	fn v2_xcm(success: bool) -> VersionedXcm<RuntimeCall> {
		let instr = if success {
			v3::Instruction::<RuntimeCall>::ClearOrigin
		} else {
			v3::Instruction::<RuntimeCall>::Trap(1)
		};
		VersionedXcm::V3(v3::Xcm::<RuntimeCall>(vec![instr]))
	}

	fn v3_xcm(success: bool) -> VersionedXcm<RuntimeCall> {
		let instr = if success {
			v2::Instruction::<RuntimeCall>::ClearOrigin
		} else {
			v2::Instruction::<RuntimeCall>::Trap(1)
		};
		VersionedXcm::V2(v2::Xcm::<RuntimeCall>(vec![instr]))
	}

	fn process(msg: VersionedXcm<RuntimeCall>) -> Result<bool, ProcessMessageError> {
		process_raw(msg.encode().as_slice())
	}

	fn process_raw(raw: &[u8]) -> Result<bool, ProcessMessageError> {
		Processor::process_message(raw, ORIGIN, &mut WeightMeter::max_limit())
	}
}