Adds Snowbridge to Rococo runtime (#2522)

# Description

Adds Snowbridge to the Rococo bridge hub runtime. Includes config
changes required in Rococo asset hub.

---------

Co-authored-by: Alistair Singh <alistair.singh7@gmail.com>
Co-authored-by: ron <yrong1997@gmail.com>
Co-authored-by: Vincent Geddes <vincent.geddes@hey.com>
Co-authored-by: claravanstaden <Cats 4 life!>

bridges/snowbridge/parachain/primitives/router/src/inbound/mod.rs

@@ -0,0 +1,320 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: 2023 Snowfork <hello@snowfork.com>
+//! Converts messages from Ethereum to XCM messages
+
+#[cfg(test)]
+mod tests;
+
+use codec::{Decode, Encode};
+use core::marker::PhantomData;
+use frame_support::{traits::tokens::Balance as BalanceT, weights::Weight, PalletError};
+use scale_info::TypeInfo;
+use sp_core::{Get, RuntimeDebug, H160};
+use sp_io::hashing::blake2_256;
+use sp_runtime::MultiAddress;
+use sp_std::prelude::*;
+use xcm::prelude::{Junction::AccountKey20, *};
+use xcm_executor::traits::ConvertLocation;
+
+const MINIMUM_DEPOSIT: u128 = 1;
+
+/// Messages from Ethereum are versioned. This is because in future,
+/// we may want to evolve the protocol so that the ethereum side sends XCM messages directly.
+/// Instead having BridgeHub transcode the messages into XCM.
+#[derive(Clone, Encode, Decode, RuntimeDebug)]
+pub enum VersionedMessage {
+	V1(MessageV1),
+}
+
+/// For V1, the ethereum side sends messages which are transcoded into XCM. These messages are
+/// self-contained, in that they can be transcoded using only information in the message.
+#[derive(Clone, Encode, Decode, RuntimeDebug)]
+pub struct MessageV1 {
+	/// EIP-155 chain id of the origin Ethereum network
+	pub chain_id: u64,
+	/// The command originating from the Gateway contract
+	pub command: Command,
+}
+
+#[derive(Clone, Encode, Decode, RuntimeDebug)]
+pub enum Command {
+	/// Register a wrapped token on the AssetHub `ForeignAssets` pallet
+	RegisterToken {
+		/// The address of the ERC20 token to be bridged over to AssetHub
+		token: H160,
+		/// XCM execution fee on AssetHub
+		fee: u128,
+	},
+	/// Send a token to AssetHub or another parachain
+	SendToken {
+		/// The address of the ERC20 token to be bridged over to AssetHub
+		token: H160,
+		/// The destination for the transfer
+		destination: Destination,
+		/// Amount to transfer
+		amount: u128,
+		/// XCM execution fee on AssetHub
+		fee: u128,
+	},
+}
+
+/// Destination for bridged tokens
+#[derive(Clone, Encode, Decode, RuntimeDebug)]
+pub enum Destination {
+	/// The funds will be deposited into account `id` on AssetHub
+	AccountId32 { id: [u8; 32] },
+	/// The funds will deposited into the sovereign account of destination parachain `para_id` on
+	/// AssetHub, Account `id` on the destination parachain will receive the funds via a
+	/// reserve-backed transfer. See <https://github.com/paritytech/xcm-format#depositreserveasset>
+	ForeignAccountId32 {
+		para_id: u32,
+		id: [u8; 32],
+		/// XCM execution fee on final destination
+		fee: u128,
+	},
+	/// The funds will deposited into the sovereign account of destination parachain `para_id` on
+	/// AssetHub, Account `id` on the destination parachain will receive the funds via a
+	/// reserve-backed transfer. See <https://github.com/paritytech/xcm-format#depositreserveasset>
+	ForeignAccountId20 {
+		para_id: u32,
+		id: [u8; 20],
+		/// XCM execution fee on final destination
+		fee: u128,
+	},
+}
+
+pub struct MessageToXcm<
+	CreateAssetCall,
+	CreateAssetDeposit,
+	InboundQueuePalletInstance,
+	AccountId,
+	Balance,
+> where
+	CreateAssetCall: Get<CallIndex>,
+	CreateAssetDeposit: Get<u128>,
+	Balance: BalanceT,
+{
+	_phantom: PhantomData<(
+		CreateAssetCall,
+		CreateAssetDeposit,
+		InboundQueuePalletInstance,
+		AccountId,
+		Balance,
+	)>,
+}
+
+/// Reason why a message conversion failed.
+#[derive(Copy, Clone, TypeInfo, PalletError, Encode, Decode, RuntimeDebug)]
+pub enum ConvertMessageError {
+	/// The message version is not supported for conversion.
+	UnsupportedVersion,
+}
+
+/// convert the inbound message to xcm which will be forwarded to the destination chain
+pub trait ConvertMessage {
+	type Balance: BalanceT + From<u128>;
+	type AccountId;
+	/// Converts a versioned message into an XCM message and an optional topicID
+	fn convert(message: VersionedMessage) -> Result<(Xcm<()>, Self::Balance), ConvertMessageError>;
+}
+
+pub type CallIndex = [u8; 2];
+
+impl<CreateAssetCall, CreateAssetDeposit, InboundQueuePalletInstance, AccountId, Balance>
+	ConvertMessage
+	for MessageToXcm<
+		CreateAssetCall,
+		CreateAssetDeposit,
+		InboundQueuePalletInstance,
+		AccountId,
+		Balance,
+	> where
+	CreateAssetCall: Get<CallIndex>,
+	CreateAssetDeposit: Get<u128>,
+	InboundQueuePalletInstance: Get<u8>,
+	Balance: BalanceT + From<u128>,
+	AccountId: Into<[u8; 32]>,
+{
+	type Balance = Balance;
+	type AccountId = AccountId;
+
+	fn convert(message: VersionedMessage) -> Result<(Xcm<()>, Self::Balance), ConvertMessageError> {
+		use Command::*;
+		use VersionedMessage::*;
+		match message {
+			V1(MessageV1 { chain_id, command: RegisterToken { token, fee } }) =>
+				Ok(Self::convert_register_token(chain_id, token, fee)),
+			V1(MessageV1 { chain_id, command: SendToken { token, destination, amount, fee } }) =>
+				Ok(Self::convert_send_token(chain_id, token, destination, amount, fee)),
+		}
+	}
+}
+
+impl<CreateAssetCall, CreateAssetDeposit, InboundQueuePalletInstance, AccountId, Balance>
+	MessageToXcm<CreateAssetCall, CreateAssetDeposit, InboundQueuePalletInstance, AccountId, Balance>
+where
+	CreateAssetCall: Get<CallIndex>,
+	CreateAssetDeposit: Get<u128>,
+	InboundQueuePalletInstance: Get<u8>,
+	Balance: BalanceT + From<u128>,
+	AccountId: Into<[u8; 32]>,
+{
+	fn convert_register_token(chain_id: u64, token: H160, fee: u128) -> (Xcm<()>, Balance) {
+		let network = Ethereum { chain_id };
+		let xcm_fee: MultiAsset = (MultiLocation::parent(), fee).into();
+		let deposit: MultiAsset = (MultiLocation::parent(), CreateAssetDeposit::get()).into();
+
+		let total_amount = fee + CreateAssetDeposit::get();
+		let total: MultiAsset = (MultiLocation::parent(), total_amount).into();
+
+		let bridge_location: MultiLocation = (Parent, Parent, GlobalConsensus(network)).into();
+
+		let owner = GlobalConsensusEthereumConvertsFor::<[u8; 32]>::from_chain_id(&chain_id);
+		let asset_id = Self::convert_token_address(network, token);
+		let create_call_index: [u8; 2] = CreateAssetCall::get();
+		let inbound_queue_pallet_index = InboundQueuePalletInstance::get();
+
+		let xcm: Xcm<()> = vec![
+			// Teleport required fees.
+			ReceiveTeleportedAsset(total.into()),
+			// Pay for execution.
+			BuyExecution { fees: xcm_fee, weight_limit: Unlimited },
+			// Fund the snowbridge sovereign with the required deposit for creation.
+			DepositAsset { assets: Definite(deposit.into()), beneficiary: bridge_location },
+			// Only our inbound-queue pallet is allowed to invoke `UniversalOrigin`
+			DescendOrigin(X1(PalletInstance(inbound_queue_pallet_index))),
+			// Change origin to the bridge.
+			UniversalOrigin(GlobalConsensus(network)),
+			// Call create_asset on foreign assets pallet.
+			Transact {
+				origin_kind: OriginKind::Xcm,
+				require_weight_at_most: Weight::from_parts(400_000_000, 8_000),
+				call: (
+					create_call_index,
+					asset_id,
+					MultiAddress::<[u8; 32], ()>::Id(owner),
+					MINIMUM_DEPOSIT,
+				)
+					.encode()
+					.into(),
+			},
+			RefundSurplus,
+			// Clear the origin so that remaining assets in holding
+			// are claimable by the physical origin (BridgeHub)
+			ClearOrigin,
+		]
+		.into();
+
+		(xcm, total_amount.into())
+	}
+
+	fn convert_send_token(
+		chain_id: u64,
+		token: H160,
+		destination: Destination,
+		amount: u128,
+		asset_hub_fee: u128,
+	) -> (Xcm<()>, Balance) {
+		let network = Ethereum { chain_id };
+		let asset_hub_fee_asset: MultiAsset = (MultiLocation::parent(), asset_hub_fee).into();
+		let asset: MultiAsset = (Self::convert_token_address(network, token), amount).into();
+
+		let (dest_para_id, beneficiary, dest_para_fee) = match destination {
+			// Final destination is a 32-byte account on AssetHub
+			Destination::AccountId32 { id } => (
+				None,
+				MultiLocation { parents: 0, interior: X1(AccountId32 { network: None, id }) },
+				0,
+			),
+			// Final destination is a 32-byte account on a sibling of AssetHub
+			Destination::ForeignAccountId32 { para_id, id, fee } => (
+				Some(para_id),
+				MultiLocation { parents: 0, interior: X1(AccountId32 { network: None, id }) },
+				// Total fee needs to cover execution on AssetHub and Sibling
+				fee,
+			),
+			// Final destination is a 20-byte account on a sibling of AssetHub
+			Destination::ForeignAccountId20 { para_id, id, fee } => (
+				Some(para_id),
+				MultiLocation { parents: 0, interior: X1(AccountKey20 { network: None, key: id }) },
+				// Total fee needs to cover execution on AssetHub and Sibling
+				fee,
+			),
+		};
+
+		let total_fees = asset_hub_fee.saturating_add(dest_para_fee);
+		let total_fee_asset: MultiAsset = (MultiLocation::parent(), total_fees).into();
+		let inbound_queue_pallet_index = InboundQueuePalletInstance::get();
+
+		let mut instructions = vec![
+			ReceiveTeleportedAsset(total_fee_asset.into()),
+			BuyExecution { fees: asset_hub_fee_asset, weight_limit: Unlimited },
+			DescendOrigin(X1(PalletInstance(inbound_queue_pallet_index))),
+			UniversalOrigin(GlobalConsensus(network)),
+			ReserveAssetDeposited(asset.clone().into()),
+			ClearOrigin,
+		];
+
+		match dest_para_id {
+			Some(dest_para_id) => {
+				let dest_para_fee_asset: MultiAsset =
+					(MultiLocation::parent(), dest_para_fee).into();
+
+				instructions.extend(vec![
+					// Perform a deposit reserve to send to destination chain.
+					DepositReserveAsset {
+						assets: Definite(vec![dest_para_fee_asset.clone(), asset.clone()].into()),
+						dest: MultiLocation { parents: 1, interior: X1(Parachain(dest_para_id)) },
+						xcm: vec![
+							// Buy execution on target.
+							BuyExecution { fees: dest_para_fee_asset, weight_limit: Unlimited },
+							// Deposit asset to beneficiary.
+							DepositAsset { assets: Definite(asset.into()), beneficiary },
+						]
+						.into(),
+					},
+				]);
+			},
+			None => {
+				instructions.extend(vec![
+					// Deposit asset to beneficiary.
+					DepositAsset { assets: Definite(asset.into()), beneficiary },
+				]);
+			},
+		}
+
+		(instructions.into(), total_fees.into())
+	}
+
+	// Convert ERC20 token address to a Multilocation that can be understood by Assets Hub.
+	fn convert_token_address(network: NetworkId, token: H160) -> MultiLocation {
+		MultiLocation {
+			parents: 2,
+			interior: X2(
+				GlobalConsensus(network),
+				AccountKey20 { network: None, key: token.into() },
+			),
+		}
+	}
+}
+
+pub struct GlobalConsensusEthereumConvertsFor<AccountId>(PhantomData<AccountId>);
+impl<AccountId> ConvertLocation<AccountId> for GlobalConsensusEthereumConvertsFor<AccountId>
+where
+	AccountId: From<[u8; 32]> + Clone,
+{
+	fn convert_location(location: &MultiLocation) -> Option<AccountId> {
+		if let MultiLocation { interior: X1(GlobalConsensus(Ethereum { chain_id })), .. } = location
+		{
+			Some(Self::from_chain_id(chain_id).into())
+		} else {
+			None
+		}
+	}
+}
+
+impl<AccountId> GlobalConsensusEthereumConvertsFor<AccountId> {
+	pub fn from_chain_id(chain_id: &u64) -> [u8; 32] {
+		(b"ethereum-chain", chain_id).using_encoded(blake2_256)
+	}
+}

bridges/snowbridge/parachain/primitives/router/src/inbound/tests.rs

@@ -0,0 +1,41 @@
+use super::GlobalConsensusEthereumConvertsFor;
+use crate::inbound::CallIndex;
+use frame_support::parameter_types;
+use hex_literal::hex;
+use xcm::v3::prelude::*;
+use xcm_executor::traits::ConvertLocation;
+
+const NETWORK: NetworkId = Ethereum { chain_id: 11155111 };
+
+parameter_types! {
+	pub EthereumNetwork: NetworkId = NETWORK;
+
+	pub const CreateAssetCall: CallIndex = [1, 1];
+	pub const CreateAssetExecutionFee: u128 = 123;
+	pub const CreateAssetDeposit: u128 = 891;
+	pub const SendTokenExecutionFee: u128 = 592;
+}
+
+#[test]
+fn test_contract_location_with_network_converts_successfully() {
+	let expected_account: [u8; 32] =
+		hex!("ce796ae65569a670d0c1cc1ac12515a3ce21b5fbf729d63d7b289baad070139d");
+	let contract_location = MultiLocation { parents: 2, interior: X1(GlobalConsensus(NETWORK)) };
+
+	let account =
+		GlobalConsensusEthereumConvertsFor::<[u8; 32]>::convert_location(&contract_location)
+			.unwrap();
+
+	assert_eq!(account, expected_account);
+}
+
+#[test]
+fn test_contract_location_with_incorrect_location_fails_convert() {
+	let contract_location =
+		MultiLocation { parents: 2, interior: X2(GlobalConsensus(Polkadot), Parachain(1000)) };
+
+	assert_eq!(
+		GlobalConsensusEthereumConvertsFor::<[u8; 32]>::convert_location(&contract_location),
+		None,
+	);
+}

bridges/snowbridge/parachain/primitives/router/src/lib.rs

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: 2023 Snowfork <hello@snowfork.com>
+#![cfg_attr(not(feature = "std"), no_std)]
+
+pub mod inbound;
+pub mod outbound;

bridges/snowbridge/parachain/primitives/router/src/outbound/mod.rs

@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: 2023 Snowfork <hello@snowfork.com>
+//! Converts XCM messages into simpler commands that can be processed by the Gateway contract
+
+#[cfg(test)]
+mod tests;
+
+use core::slice::Iter;
+
+use codec::{Decode, Encode};
+
+use frame_support::{ensure, traits::Get};
+use snowbridge_core::{
+	outbound::{AgentExecuteCommand, Command, Message, SendMessage},
+	ChannelId, ParaId,
+};
+use sp_core::{H160, H256};
+use sp_std::{iter::Peekable, marker::PhantomData, prelude::*};
+use xcm::v3::prelude::*;
+use xcm_executor::traits::{ConvertLocation, ExportXcm};
+
+pub struct EthereumBlobExporter<
+	UniversalLocation,
+	EthereumNetwork,
+	OutboundQueue,
+	AgentHashedDescription,
+>(PhantomData<(UniversalLocation, EthereumNetwork, OutboundQueue, AgentHashedDescription)>);
+
+impl<UniversalLocation, EthereumNetwork, OutboundQueue, AgentHashedDescription> ExportXcm
+	for EthereumBlobExporter<UniversalLocation, EthereumNetwork, OutboundQueue, AgentHashedDescription>
+where
+	UniversalLocation: Get<InteriorMultiLocation>,
+	EthereumNetwork: Get<NetworkId>,
+	OutboundQueue: SendMessage<Balance = u128>,
+	AgentHashedDescription: ConvertLocation<H256>,
+{
+	type Ticket = (Vec<u8>, XcmHash);
+
+	fn validate(
+		network: NetworkId,
+		_channel: u32,
+		universal_source: &mut Option<InteriorMultiLocation>,
+		destination: &mut Option<InteriorMultiLocation>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket> {
+		let expected_network = EthereumNetwork::get();
+		let universal_location = UniversalLocation::get();
+
+		if network != expected_network {
+			log::trace!(target: "xcm::ethereum_blob_exporter", "skipped due to unmatched bridge network {network:?}.");
+			return Err(SendError::NotApplicable)
+		}
+
+		let dest = destination.take().ok_or(SendError::MissingArgument)?;
+		if dest != Here {
+			log::trace!(target: "xcm::ethereum_blob_exporter", "skipped due to unmatched remote destination {dest:?}.");
+			return Err(SendError::NotApplicable)
+		}
+
+		let (local_net, local_sub) = universal_source
+			.take()
+			.ok_or_else(|| {
+				log::error!(target: "xcm::ethereum_blob_exporter", "universal source not provided.");
+				SendError::MissingArgument
+			})?
+			.split_global()
+			.map_err(|()| {
+				log::error!(target: "xcm::ethereum_blob_exporter", "could not get global consensus from universal source '{universal_source:?}'.");
+				SendError::Unroutable
+			})?;
+
+		if Ok(local_net) != universal_location.global_consensus() {
+			log::trace!(target: "xcm::ethereum_blob_exporter", "skipped due to unmatched relay network {local_net:?}.");
+			return Err(SendError::NotApplicable)
+		}
+
+		let para_id = match local_sub {
+			X1(Parachain(para_id)) => para_id,
+			_ => {
+				log::error!(target: "xcm::ethereum_blob_exporter", "could not get parachain id from universal source '{local_sub:?}'.");
+				return Err(SendError::MissingArgument)
+			},
+		};
+
+		let message = message.take().ok_or_else(|| {
+			log::error!(target: "xcm::ethereum_blob_exporter", "xcm message not provided.");
+			SendError::MissingArgument
+		})?;
+
+		let mut converter = XcmConverter::new(&message, &expected_network);
+		let (agent_execute_command, message_id) = converter.convert().map_err(|err|{
+			log::error!(target: "xcm::ethereum_blob_exporter", "unroutable due to pattern matching error '{err:?}'.");
+			SendError::Unroutable
+		})?;
+
+		let source_location: MultiLocation = MultiLocation { parents: 1, interior: local_sub };
+		let agent_id = match AgentHashedDescription::convert_location(&source_location) {
+			Some(id) => id,
+			None => {
+				log::error!(target: "xcm::ethereum_blob_exporter", "unroutable due to not being able to create agent id. '{source_location:?}'");
+				return Err(SendError::Unroutable)
+			},
+		};
+
+		let channel_id: ChannelId = ParaId::from(para_id).into();
+
+		let outbound_message = Message {
+			id: Some(message_id.into()),
+			channel_id,
+			command: Command::AgentExecute { agent_id, command: agent_execute_command },
+		};
+
+		// validate the message
+		let (ticket, fee) = OutboundQueue::validate(&outbound_message).map_err(|err| {
+			log::error!(target: "xcm::ethereum_blob_exporter", "OutboundQueue validation of message failed. {err:?}");
+			SendError::Unroutable
+		})?;
+
+		// convert fee to MultiAsset
+		let fee = MultiAsset::from((MultiLocation::parent(), fee.total())).into();
+
+		Ok(((ticket.encode(), message_id), fee))
+	}
+
+	fn deliver(blob: (Vec<u8>, XcmHash)) -> Result<XcmHash, SendError> {
+		let ticket: OutboundQueue::Ticket = OutboundQueue::Ticket::decode(&mut blob.0.as_ref())
+			.map_err(|_| {
+				log::trace!(target: "xcm::ethereum_blob_exporter", "undeliverable due to decoding error");
+				SendError::NotApplicable
+			})?;
+
+		let message_id = OutboundQueue::deliver(ticket).map_err(|_| {
+			log::error!(target: "xcm::ethereum_blob_exporter", "OutboundQueue submit of message failed");
+			SendError::Transport("other transport error")
+		})?;
+
+		log::info!(target: "xcm::ethereum_blob_exporter", "message delivered {message_id:#?}.");
+		Ok(message_id.into())
+	}
+}
+
+/// Errors that can be thrown to the pattern matching step.
+#[derive(PartialEq, Debug)]
+enum XcmConverterError {
+	UnexpectedEndOfXcm,
+	EndOfXcmMessageExpected,
+	WithdrawAssetExpected,
+	DepositAssetExpected,
+	NoReserveAssets,
+	FilterDoesNotConsumeAllAssets,
+	TooManyAssets,
+	ZeroAssetTransfer,
+	BeneficiaryResolutionFailed,
+	AssetResolutionFailed,
+	InvalidFeeAsset,
+	SetTopicExpected,
+}
+
+macro_rules! match_expression {
+	($expression:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )?, $value:expr $(,)?) => {
+		match $expression {
+			$( $pattern )|+ $( if $guard )? => Some($value),
+			_ => None,
+		}
+	};
+}
+
+struct XcmConverter<'a, Call> {
+	iter: Peekable<Iter<'a, Instruction<Call>>>,
+	ethereum_network: &'a NetworkId,
+}
+impl<'a, Call> XcmConverter<'a, Call> {
+	fn new(message: &'a Xcm<Call>, ethereum_network: &'a NetworkId) -> Self {
+		Self { iter: message.inner().iter().peekable(), ethereum_network }
+	}
+
+	fn convert(&mut self) -> Result<(AgentExecuteCommand, [u8; 32]), XcmConverterError> {
+		// Get withdraw/deposit and make native tokens create message.
+		let result = self.native_tokens_unlock_message()?;
+
+		// All xcm instructions must be consumed before exit.
+		if self.next().is_ok() {
+			return Err(XcmConverterError::EndOfXcmMessageExpected)
+		}
+
+		Ok(result)
+	}
+
+	fn native_tokens_unlock_message(
+		&mut self,
+	) -> Result<(AgentExecuteCommand, [u8; 32]), XcmConverterError> {
+		use XcmConverterError::*;
+
+		// Get the reserve assets from WithdrawAsset.
+		let reserve_assets =
+			match_expression!(self.next()?, WithdrawAsset(reserve_assets), reserve_assets)
+				.ok_or(WithdrawAssetExpected)?;
+
+		// Check if clear origin exists and skip over it.
+		if match_expression!(self.peek(), Ok(ClearOrigin), ()).is_some() {
+			let _ = self.next();
+		}
+
+		// Get the fee asset item from BuyExecution or continue parsing.
+		let fee_asset = match_expression!(self.peek(), Ok(BuyExecution { fees, .. }), fees);
+		if fee_asset.is_some() {
+			let _ = self.next();
+		}
+
+		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,
+			MultiLocation { parents: 0, interior: X1(AccountKey20 { network, key }) }
+				if self.network_matches(network),
+			H160(*key)
+		)
+		.ok_or(BeneficiaryResolutionFailed)?;
+
+		// Make sure there are reserved assets.
+		if reserve_assets.len() == 0 {
+			return Err(NoReserveAssets)
+		}
+
+		// Check the the deposit asset filter matches what was reserved.
+		if reserve_assets.inner().iter().any(|asset| !deposit_assets.matches(asset)) {
+			return Err(FilterDoesNotConsumeAllAssets)
+		}
+
+		// We only support a single asset at a time.
+		ensure!(reserve_assets.len() == 1, TooManyAssets);
+		let reserve_asset = reserve_assets.get(0).ok_or(AssetResolutionFailed)?;
+
+		// If there was a fee specified verify it.
+		if let Some(fee_asset) = fee_asset {
+			// The fee asset must be the same as the reserve asset.
+			if fee_asset.id != reserve_asset.id || fee_asset.fun > reserve_asset.fun {
+				return Err(InvalidFeeAsset)
+			}
+		}
+
+		let (token, amount) = match_expression!(
+			reserve_asset,
+			MultiAsset {
+				id: Concrete(MultiLocation { parents: 0, interior: X1(AccountKey20 { network , key })}),
+				fun: Fungible(amount)
+			} if self.network_matches(network),
+			(H160(*key), *amount)
+		)
+		.ok_or(AssetResolutionFailed)?;
+
+		// transfer amount must be greater than 0.
+		ensure!(amount > 0, ZeroAssetTransfer);
+
+		// Check if there is a SetTopic and skip over it if found.
+		let topic_id = match_expression!(self.next()?, SetTopic(id), id).ok_or(SetTopicExpected)?;
+
+		Ok((AgentExecuteCommand::TransferToken { token, recipient, amount }, *topic_id))
+	}
+
+	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
+		}
+	}
+}