snowbridge_outbound_queue_primitives/v2/converter/

convert.rs

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: 2023 Snowfork <hello@snowfork.com>
//! Converts XCM messages into InboundMessage that can be processed by the Gateway contract

use codec::DecodeAll;
use core::slice::Iter;
use frame_support::{ensure, BoundedVec};
use snowbridge_core::{AgentIdOf, TokenId, TokenIdOf};

use crate::v2::{
	message::{Command, Message},
	ContractCall,
};

use crate::v2::convert::XcmConverterError::{AssetResolutionFailed, FilterDoesNotConsumeAllAssets};
use sp_core::H160;
use sp_runtime::traits::MaybeConvert;
use sp_std::{iter::Peekable, marker::PhantomData, prelude::*};
use xcm::prelude::*;
use xcm_executor::traits::ConvertLocation;
use XcmConverterError::*;

/// Errors that can be thrown to the pattern matching step.
#[derive(PartialEq, Debug)]
pub enum XcmConverterError {
	UnexpectedEndOfXcm,
	EndOfXcmMessageExpected,
	WithdrawAssetExpected,
	DepositAssetExpected,
	NoReserveAssets,
	FilterDoesNotConsumeAllAssets,
	TooManyAssets,
	ZeroAssetTransfer,
	BeneficiaryResolutionFailed,
	AssetResolutionFailed,
	InvalidFeeAsset,
	SetTopicExpected,
	ReserveAssetDepositedExpected,
	InvalidAsset,
	UnexpectedInstruction,
	TooManyCommands,
	AliasOriginExpected,
	InvalidOrigin,
	TransactDecodeFailed,
	TransactParamsDecodeFailed,
	FeeAssetResolutionFailed,
	CallContractValueInsufficient,
	NoCommands,
}

macro_rules! match_expression {
	($expression:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )?, $value:expr $(,)?) => {
		match $expression {
			$( $pattern )|+ $( if $guard )? => Some($value),
			_ => None,
		}
	};
}

pub struct XcmConverter<'a, ConvertAssetId, Call> {
	iter: Peekable<Iter<'a, Instruction<Call>>>,
	ethereum_network: NetworkId,
	_marker: PhantomData<ConvertAssetId>,
}
impl<'a, ConvertAssetId, Call> XcmConverter<'a, ConvertAssetId, Call>
where
	ConvertAssetId: MaybeConvert<TokenId, Location>,
{
	pub fn new(message: &'a Xcm<Call>, ethereum_network: NetworkId) -> Self {
		Self {
			iter: message.inner().iter().peekable(),
			ethereum_network,
			_marker: Default::default(),
		}
	}

	fn next(&mut self) -> Result<&'a Instruction<Call>, XcmConverterError> {
		self.iter.next().ok_or(XcmConverterError::UnexpectedEndOfXcm)
	}

	fn peek(&mut self) -> Result<&&'a Instruction<Call>, XcmConverterError> {
		self.iter.peek().ok_or(XcmConverterError::UnexpectedEndOfXcm)
	}

	fn network_matches(&self, network: &Option<NetworkId>) -> bool {
		if let Some(network) = network {
			*network == self.ethereum_network
		} else {
			true
		}
	}

	/// Extract the fee asset item from PayFees(V5)
	fn extract_remote_fee(&mut self) -> Result<u128, XcmConverterError> {
		use XcmConverterError::*;
		let reserved_fee_assets = match_expression!(self.next()?, WithdrawAsset(fee), fee)
			.ok_or(WithdrawAssetExpected)?;
		ensure!(reserved_fee_assets.len() == 1, AssetResolutionFailed);
		let reserved_fee_asset =
			reserved_fee_assets.inner().first().cloned().ok_or(AssetResolutionFailed)?;
		let (reserved_fee_asset_id, reserved_fee_amount) = match reserved_fee_asset {
			Asset { id: asset_id, fun: Fungible(amount) } => Ok((asset_id, amount)),
			_ => Err(AssetResolutionFailed),
		}?;
		let fee_asset =
			match_expression!(self.next()?, PayFees { asset: fee }, fee).ok_or(InvalidFeeAsset)?;
		let (fee_asset_id, fee_amount) = match fee_asset {
			Asset { id: asset_id, fun: Fungible(amount) } => Ok((asset_id, *amount)),
			_ => Err(AssetResolutionFailed),
		}?;
		// Check the fee asset is Ether (XCM is evaluated in Ethereum context).
		ensure!(fee_asset_id.0 == Here.into(), InvalidFeeAsset);
		ensure!(reserved_fee_asset_id.0 == Here.into(), InvalidFeeAsset);
		ensure!(reserved_fee_amount >= fee_amount, InvalidFeeAsset);
		Ok(fee_amount)
	}

	/// Extract ethereum native assets
	fn extract_ethereum_native_assets(
		&mut self,
		enas: &Assets,
		deposit_assets: &AssetFilter,
		recipient: H160,
	) -> Result<Vec<Command>, XcmConverterError> {
		let mut commands: Vec<Command> = Vec::new();
		for ena in enas.clone().into_inner().into_iter() {
			// Check the the deposit asset filter matches what was reserved.
			if !deposit_assets.matches(&ena) {
				return Err(FilterDoesNotConsumeAllAssets);
			}

			// only fungible asset is allowed
			let (token, amount) = match ena {
				Asset { id: AssetId(inner_location), fun: Fungible(amount) } =>
					match inner_location.unpack() {
						(0, [AccountKey20 { network, key }]) if self.network_matches(network) =>
							Ok((H160(*key), amount)),
						// To allow ether
						(0, []) => Ok((H160([0; 20]), amount)),
						_ => Err(AssetResolutionFailed),
					},
				_ => Err(AssetResolutionFailed),
			}?;

			// transfer amount must be greater than 0.
			ensure!(amount > 0, ZeroAssetTransfer);

			commands.push(Command::UnlockNativeToken { token, recipient, amount });
		}
		Ok(commands)
	}

	/// Extract polkadot native assets
	fn extract_polkadot_native_assets(
		&mut self,
		pnas: &Assets,
		deposit_assets: &AssetFilter,
		recipient: H160,
	) -> Result<Vec<Command>, XcmConverterError> {
		let mut commands: Vec<Command> = Vec::new();
		ensure!(pnas.len() > 0, NoReserveAssets);
		for pna in pnas.clone().into_inner().into_iter() {
			if !deposit_assets.matches(&pna) {
				return Err(FilterDoesNotConsumeAllAssets);
			}

			// Only fungible is allowed
			let Asset { id: AssetId(asset_id), fun: Fungible(amount) } = pna else {
				return Err(AssetResolutionFailed);
			};

			// transfer amount must be greater than 0.
			ensure!(amount > 0, ZeroAssetTransfer);

			// Ensure PNA already registered
			let token_id = TokenIdOf::convert_location(&asset_id).ok_or(InvalidAsset)?;
			ConvertAssetId::maybe_convert(token_id).ok_or(InvalidAsset)?;

			commands.push(Command::MintForeignToken { token_id, recipient, amount });
		}
		Ok(commands)
	}

	/// Convert the XCM into an outbound message which can be dispatched to
	/// the Gateway contract on Ethereum
	///
	/// Assets being transferred can either be Polkadot-native assets (PNA)
	/// or Ethereum-native assets (ENA).
	///
	/// The XCM is evaluated in Ethereum context.
	///
	/// Expected Input Syntax:
	/// ```ignore
	/// WithdrawAsset(ETH)
	/// PayFees(ETH)
	/// ReserveAssetDeposited(PNA) | WithdrawAsset(ENA)
	/// AliasOrigin(Origin)
	/// DepositAsset(Asset)
	/// Transact() [OPTIONAL]
	/// SetTopic(Topic)
	/// ```
	/// Notes:
	/// a. Fee asset will be checked and currently only Ether is allowed
	/// b. For a specific transfer, either `ReserveAssetDeposited` or `WithdrawAsset` should be
	/// 	present
	/// c. `ReserveAssetDeposited` and `WithdrawAsset` can also be present in any order within the
	/// 	same message
	/// d. Currently, teleport asset is not allowed, transfer types other than
	/// 	above will cause the conversion to fail
	/// e. Currently, `AliasOrigin` is always required, can distinguish the V2 process from V1.
	/// 	it's required also for dispatching transact from that specific origin.
	/// f. SetTopic is required for tracing the message all the way along.
	pub fn convert(&mut self) -> Result<Message, XcmConverterError> {
		// Get fee amount
		let fee_amount = self.extract_remote_fee()?;

		// Get ENA reserve asset from WithdrawAsset.
		let mut enas =
			match_expression!(self.peek(), Ok(WithdrawAsset(reserve_assets)), reserve_assets);
		if enas.is_some() {
			let _ = self.next();
		}

		// Get PNA reserve asset from ReserveAssetDeposited
		let pnas = match_expression!(
			self.peek(),
			Ok(ReserveAssetDeposited(reserve_assets)),
			reserve_assets
		);
		if pnas.is_some() {
			let _ = self.next();
		}

		// Try to get ENA again if it is after PNA
		if enas.is_none() {
			enas =
				match_expression!(self.peek(), Ok(WithdrawAsset(reserve_assets)), reserve_assets);
			if enas.is_some() {
				let _ = self.next();
			}
		}
		// Check AliasOrigin.
		let origin_location = match_expression!(self.next()?, AliasOrigin(origin), origin)
			.ok_or(AliasOriginExpected)?;
		let origin = AgentIdOf::convert_location(origin_location).ok_or(InvalidOrigin)?;

		let (deposit_assets, beneficiary) = match_expression!(
			self.next()?,
			DepositAsset { assets, beneficiary },
			(assets, beneficiary)
		)
		.ok_or(DepositAssetExpected)?;

		// assert that the beneficiary is AccountKey20.
		let recipient = match_expression!(
			beneficiary.unpack(),
			(0, [AccountKey20 { network, key }])
				if self.network_matches(network),
			H160(*key)
		)
		.ok_or(BeneficiaryResolutionFailed)?;

		let mut commands: Vec<Command> = Vec::new();

		// ENA transfer commands
		if let Some(enas) = enas {
			commands.append(&mut self.extract_ethereum_native_assets(
				enas,
				deposit_assets,
				recipient,
			)?);
		}

		// PNA transfer commands
		if let Some(pnas) = pnas {
			commands.append(&mut self.extract_polkadot_native_assets(
				pnas,
				deposit_assets,
				recipient,
			)?);
		}

		// Transact commands
		let transact_call = match_expression!(self.peek(), Ok(Transact { call, .. }), call);
		if let Some(transact_call) = transact_call {
			let _ = self.next();
			let transact =
				ContractCall::decode_all(&mut transact_call.clone().into_encoded().as_slice())
					.map_err(|_| TransactDecodeFailed)?;
			match transact {
				ContractCall::V1 { target, calldata, gas, value } => commands
					.push(Command::CallContract { target: target.into(), calldata, gas, value }),
			}
		}

		ensure!(commands.len() > 0, NoCommands);

		// ensure SetTopic exists
		let topic_id = match_expression!(self.next()?, SetTopic(id), id).ok_or(SetTopicExpected)?;

		let message = Message {
			id: (*topic_id).into(),
			origin,
			fee: fee_amount,
			commands: BoundedVec::try_from(commands).map_err(|_| TooManyCommands)?,
		};

		// All xcm instructions must be consumed before exit.
		if self.next().is_ok() {
			return Err(EndOfXcmMessageExpected);
		}

		Ok(message)
	}
}