Relay subcommand that performs token RLT <> MLAU token swap (#1141)

* token swap relay

* token swap subcommand fixes

* fmt

* removed debug traces

* removed commented code

bridges/relays/bin-substrate/Cargo.toml

@@ -15,6 +15,7 @@ log = "0.4.14"
 num-format = "0.4"
 num-traits = "0.2"
 paste = "1.0"
+rand = "0.8"
 structopt = "0.3"
 strum = { version = "0.21.0", features = ["derive"] }
 
@@ -28,6 +29,7 @@ bp-millau = { path = "../../primitives/chain-millau" }
 bp-polkadot = { path = "../../primitives/chain-polkadot" }
 bp-rialto = { path = "../../primitives/chain-rialto" }
 bp-rococo = { path = "../../primitives/chain-rococo" }
+bp-token-swap = { path = "../../primitives/token-swap" }
 bp-wococo = { path = "../../primitives/chain-wococo" }
 bp-runtime = { path = "../../primitives/runtime" }
 bp-westend = { path = "../../primitives/chain-westend" }
@@ -35,7 +37,9 @@ bridge-runtime-common = { path = "../../bin/runtime-common" }
 finality-relay = { path = "../finality" }
 messages-relay = { path = "../messages" }
 millau-runtime = { path = "../../bin/millau/runtime" }
+pallet-bridge-dispatch = { path = "../../modules/dispatch" }
 pallet-bridge-messages = { path = "../../modules/messages" }
+pallet-bridge-token-swap = { path = "../../modules/token-swap" }
 relay-kusama-client = { path = "../client-kusama" }
 relay-millau-client = { path = "../client-millau" }
 relay-polkadot-client = { path = "../client-polkadot" }
@@ -51,6 +55,7 @@ substrate-relay-helper = { path = "../lib-substrate-relay" }
 # Substrate Dependencies
 
 frame-support = { git = "https://github.com/paritytech/substrate", branch = "master" }
+pallet-balances = { git = "https://github.com/paritytech/substrate", branch = "master" }
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master" }
 sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master" }

bridges/relays/bin-substrate/src/cli/mod.rs

@@ -36,6 +36,7 @@ mod relay_headers;
 mod relay_headers_and_messages;
 mod relay_messages;
 mod resubmit_transactions;
+mod swap_tokens;
 
 /// Parse relay CLI args.
 pub fn parse_args() -> Command {
@@ -89,6 +90,8 @@ pub enum Command {
 	DeriveAccount(derive_account::DeriveAccount),
 	/// Resubmit transactions with increased tip if they are stalled.
 	ResubmitTransactions(resubmit_transactions::ResubmitTransactions),
+	/// Swap tokens using token-swap bridge.
+	SwapTokens(swap_tokens::SwapTokens),
 }
 
 impl Command {
@@ -120,6 +123,7 @@ impl Command {
 			Self::EstimateFee(arg) => arg.run().await?,
 			Self::DeriveAccount(arg) => arg.run().await?,
 			Self::ResubmitTransactions(arg) => arg.run().await?,
+			Self::SwapTokens(arg) => arg.run().await?,
 		}
 		Ok(())
 	}

bridges/relays/bin-substrate/src/cli/swap_tokens.rs

@@ -0,0 +1,640 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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.
+
+// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Tokens swap using token-swap bridge pallet.
+
+use codec::Encode;
+use num_traits::One;
+use rand::random;
+use structopt::StructOpt;
+use strum::{EnumString, EnumVariantNames, VariantNames};
+
+use frame_support::dispatch::GetDispatchInfo;
+use relay_substrate_client::{
+	AccountIdOf, AccountPublicOf, BalanceOf, BlockNumberOf, CallOf, Chain, ChainWithBalances, Client,
+	Error as SubstrateError, HashOf, SignatureOf, Subscription, TransactionSignScheme, TransactionStatusOf,
+	UnsignedTransaction,
+};
+use sp_core::{blake2_256, storage::StorageKey, Bytes, Pair, H256, U256};
+use sp_runtime::traits::{Convert, Header as HeaderT};
+
+use crate::cli::{
+	Balance, CliChain, SourceConnectionParams, SourceSigningParams, TargetConnectionParams, TargetSigningParams,
+};
+
+/// Swap tokens.
+#[derive(StructOpt)]
+pub struct SwapTokens {
+	/// A bridge instance to use in token swap.
+	#[structopt(possible_values = SwapTokensBridge::VARIANTS, case_insensitive = true)]
+	bridge: SwapTokensBridge,
+
+	#[structopt(flatten)]
+	source: SourceConnectionParams,
+	#[structopt(flatten)]
+	source_sign: SourceSigningParams,
+
+	#[structopt(flatten)]
+	target: TargetConnectionParams,
+	#[structopt(flatten)]
+	target_sign: TargetSigningParams,
+
+	#[structopt(subcommand)]
+	swap_type: TokenSwapType,
+	/// Source chain balance that source signer wants to swap.
+	#[structopt(long)]
+	source_balance: Balance,
+	/// Target chain balance that target signer wants to swap.
+	#[structopt(long)]
+	target_balance: Balance,
+}
+
+/// Token swap type.
+#[derive(StructOpt, Debug, PartialEq, Eq, Clone)]
+pub enum TokenSwapType {
+	/// The `target_sign` is temporary and only have funds for single swap.
+	NoLock,
+	/// This swap type prevents `source_signer` from restarting the swap after it has been completed.
+	LockUntilBlock {
+		/// Number of blocks before the swap expires.
+		#[structopt(long)]
+		blocks_before_expire: u32,
+		/// Unique swap nonce.
+		#[structopt(long)]
+		swap_nonce: Option<U256>,
+	},
+}
+
+/// Swap tokens bridge.
+#[derive(Debug, EnumString, EnumVariantNames)]
+#[strum(serialize_all = "kebab_case")]
+pub enum SwapTokensBridge {
+	/// Use token-swap pallet deployed at Millau to swap tokens with Rialto.
+	MillauToRialto,
+}
+
+macro_rules! select_bridge {
+	($bridge: expr, $generic: tt) => {
+		match $bridge {
+			SwapTokensBridge::MillauToRialto => {
+				type Source = relay_millau_client::Millau;
+				type Target = relay_rialto_client::Rialto;
+
+				type FromSwapToThisAccountIdConverter = bp_rialto::AccountIdConverter;
+
+				use bp_millau::{
+					derive_account_from_rialto_id as derive_source_account_from_target_account,
+					TO_MILLAU_ESTIMATE_MESSAGE_FEE_METHOD as ESTIMATE_TARGET_TO_SOURCE_MESSAGE_FEE_METHOD,
+					WITH_RIALTO_TOKEN_SWAP_PALLET_NAME as TOKEN_SWAP_PALLET_NAME,
+				};
+				use bp_rialto::{
+					derive_account_from_millau_id as derive_target_account_from_source_account,
+					TO_RIALTO_ESTIMATE_MESSAGE_FEE_METHOD as ESTIMATE_SOURCE_TO_TARGET_MESSAGE_FEE_METHOD,
+				};
+
+				const SOURCE_CHAIN_ID: bp_runtime::ChainId = bp_runtime::MILLAU_CHAIN_ID;
+				const TARGET_CHAIN_ID: bp_runtime::ChainId = bp_runtime::RIALTO_CHAIN_ID;
+
+				const SOURCE_SPEC_VERSION: u32 = millau_runtime::VERSION.spec_version;
+				const TARGET_SPEC_VERSION: u32 = rialto_runtime::VERSION.spec_version;
+
+				const SOURCE_TO_TARGET_LANE_ID: bp_messages::LaneId = *b"swap";
+				const TARGET_TO_SOURCE_LANE_ID: bp_messages::LaneId = [0, 0, 0, 0];
+
+				$generic
+			}
+		}
+	};
+}
+
+impl SwapTokens {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		select_bridge!(self.bridge, {
+			let source_client = self.source.to_client::<Source>().await?;
+			let source_sign = self.source_sign.to_keypair::<Target>()?;
+			let target_client = self.target.to_client::<Target>().await?;
+			let target_sign = self.target_sign.to_keypair::<Target>()?;
+
+			// names of variables in this function are matching names used by the `pallet-bridge-token-swap`
+
+			// prepare token swap intention
+			let token_swap = self
+				.prepare_token_swap::<Source, Target>(&source_client, &source_sign, &target_sign)
+				.await?;
+
+			// group all accounts that will be used later
+			let accounts = TokenSwapAccounts {
+				source_account_at_bridged_chain: derive_target_account_from_source_account(
+					bp_runtime::SourceAccount::Account(token_swap.source_account_at_this_chain.clone()),
+				),
+				target_account_at_this_chain: derive_source_account_from_target_account(
+					bp_runtime::SourceAccount::Account(token_swap.target_account_at_bridged_chain.clone()),
+				),
+				source_account_at_this_chain: token_swap.source_account_at_this_chain.clone(),
+				target_account_at_bridged_chain: token_swap.target_account_at_bridged_chain.clone(),
+				swap_account: FromSwapToThisAccountIdConverter::convert(token_swap.using_encoded(blake2_256).into()),
+			};
+
+			// account balances are used to demonstrate what's happening :)
+			let initial_balances = read_account_balances(&accounts, &source_client, &target_client).await?;
+
+			// before calling something that may fail, log what we're trying to do
+			log::info!(target: "bridge", "Starting swap: {:?}", token_swap);
+			log::info!(target: "bridge", "Swap accounts: {:?}", accounts);
+			log::info!(target: "bridge", "Initial account balances: {:?}", initial_balances);
+
+			//
+			// Step 1: swap is created
+			//
+
+			// prepare `Currency::transfer` call that will happen at the target chain
+			let bridged_currency_transfer: CallOf<Target> = pallet_balances::Call::transfer(
+				accounts.source_account_at_bridged_chain.clone().into(),
+				token_swap.target_balance_at_bridged_chain,
+			)
+			.into();
+			let bridged_currency_transfer_weight = bridged_currency_transfer.get_dispatch_info().weight;
+
+			// sign message
+			let bridged_chain_spec_version = TARGET_SPEC_VERSION;
+			let signature_payload = pallet_bridge_dispatch::account_ownership_digest(
+				&bridged_currency_transfer,
+				&accounts.swap_account,
+				&bridged_chain_spec_version,
+				SOURCE_CHAIN_ID,
+				TARGET_CHAIN_ID,
+			);
+			let bridged_currency_transfer_signature: SignatureOf<Target> = target_sign.sign(&signature_payload).into();
+
+			// prepare `create_swap` call
+			let target_public_at_bridged_chain: AccountPublicOf<Target> = target_sign.public().into();
+			let swap_delivery_and_dispatch_fee: BalanceOf<Source> =
+				crate::cli::estimate_fee::estimate_message_delivery_and_dispatch_fee(
+					&source_client,
+					ESTIMATE_SOURCE_TO_TARGET_MESSAGE_FEE_METHOD,
+					SOURCE_TO_TARGET_LANE_ID,
+					bp_message_dispatch::MessagePayload {
+						spec_version: TARGET_SPEC_VERSION,
+						weight: bridged_currency_transfer_weight,
+						origin: bp_message_dispatch::CallOrigin::TargetAccount(
+							accounts.swap_account.clone(),
+							target_public_at_bridged_chain.clone(),
+							bridged_currency_transfer_signature.clone(),
+						),
+						dispatch_fee_payment: bp_runtime::messages::DispatchFeePayment::AtTargetChain,
+						call: bridged_currency_transfer.encode(),
+					},
+				)
+				.await?;
+			let create_swap_call: CallOf<Source> = pallet_bridge_token_swap::Call::create_swap(
+				token_swap.clone(),
+				target_public_at_bridged_chain,
+				swap_delivery_and_dispatch_fee,
+				bridged_chain_spec_version,
+				bridged_currency_transfer.encode(),
+				bridged_currency_transfer_weight,
+				bridged_currency_transfer_signature,
+			)
+			.into();
+
+			// start tokens swap
+			let source_genesis_hash = *source_client.genesis_hash();
+			let create_swap_signer = source_sign.clone();
+			let swap_created_at = wait_until_transaction_is_finalized::<Source>(
+				source_client
+					.submit_and_watch_signed_extrinsic(
+						accounts.source_account_at_this_chain.clone(),
+						move |_, transaction_nonce| {
+							Bytes(
+								Source::sign_transaction(
+									source_genesis_hash,
+									&create_swap_signer,
+									relay_substrate_client::TransactionEra::immortal(),
+									UnsignedTransaction::new(create_swap_call, transaction_nonce),
+								)
+								.encode(),
+							)
+						},
+					)
+					.await?,
+			)
+			.await?;
+
+			// read state of swap after it has been created
+			let token_swap_hash: H256 = token_swap.using_encoded(blake2_256).into();
+			let token_swap_storage_key = bp_runtime::storage_map_final_key_identity(
+				TOKEN_SWAP_PALLET_NAME,
+				pallet_bridge_token_swap::PENDING_SWAPS_MAP_NAME,
+				token_swap_hash.as_ref(),
+			);
+			match read_token_swap_state(&source_client, swap_created_at, &token_swap_storage_key).await? {
+				Some(bp_token_swap::TokenSwapState::Started) => {
+					log::info!(target: "bridge", "Swap has been successfully started");
+					let intermediate_balances =
+						read_account_balances(&accounts, &source_client, &target_client).await?;
+					log::info!(target: "bridge", "Intermediate balances: {:?}", intermediate_balances);
+				}
+				Some(token_swap_state) => {
+					return Err(anyhow::format_err!(
+						"Fresh token swap has unexpected state: {:?}",
+						token_swap_state,
+					))
+				}
+				None => return Err(anyhow::format_err!("Failed to start token swap")),
+			};
+
+			//
+			// Step 2: message is being relayed to the target chain and dispathed there
+			//
+
+			// wait until message is dispatched at the target chain and dispatch result delivered back to source chain
+			let token_swap_state = wait_until_token_swap_state_is_changed(
+				&source_client,
+				&token_swap_storage_key,
+				bp_token_swap::TokenSwapState::Started,
+			)
+			.await?;
+			let is_transfer_succeeded = match token_swap_state {
+				Some(bp_token_swap::TokenSwapState::Started) => {
+					unreachable!("wait_until_token_swap_state_is_changed only returns if state is not Started; qed",)
+				}
+				None => return Err(anyhow::format_err!("Fresh token swap has disappeared unexpectedly")),
+				Some(bp_token_swap::TokenSwapState::Confirmed) => {
+					log::info!(
+						target: "bridge",
+						"Transfer has been successfully dispatched at the target chain. Swap can be claimed",
+					);
+					true
+				}
+				Some(bp_token_swap::TokenSwapState::Failed) => {
+					log::info!(
+						target: "bridge",
+						"Transfer has been dispatched with an error at the target chain. Swap can be cancelled",
+					);
+					false
+				}
+			};
+
+			// by this time: (1) token swap account has been created and (2) if transfer has been successfully
+			// dispatched, both target chain balances have changed
+			let intermediate_balances = read_account_balances(&accounts, &source_client, &target_client).await?;
+			log::info!(target: "bridge", "Intermediate balances: {:?}", intermediate_balances);
+
+			// transfer has been dispatched, but we may need to wait until block where swap can be claimed/cancelled
+			if let bp_token_swap::TokenSwapType::LockClaimUntilBlock(ref last_available_block_number, _) =
+				token_swap.swap_type
+			{
+				wait_until_swap_unlocked(
+					&source_client,
+					last_available_block_number + BlockNumberOf::<Source>::one(),
+				)
+				.await?;
+			}
+
+			//
+			// Step 3: we may now claim or cancel the swap
+			//
+
+			if is_transfer_succeeded {
+				log::info!(target: "bridge", "Claiming the swap swap");
+
+				// prepare `claim_swap` message that will be sent over the bridge
+				let claim_swap_call: CallOf<Source> = pallet_bridge_token_swap::Call::claim_swap(token_swap).into();
+				let claim_swap_message = bp_message_dispatch::MessagePayload {
+					spec_version: SOURCE_SPEC_VERSION,
+					weight: claim_swap_call.get_dispatch_info().weight,
+					origin: bp_message_dispatch::CallOrigin::SourceAccount(
+						accounts.target_account_at_bridged_chain.clone(),
+					),
+					dispatch_fee_payment: bp_runtime::messages::DispatchFeePayment::AtSourceChain,
+					call: claim_swap_call.encode(),
+				};
+				let claim_swap_delivery_and_dispatch_fee: BalanceOf<Target> =
+					crate::cli::estimate_fee::estimate_message_delivery_and_dispatch_fee(
+						&target_client,
+						ESTIMATE_TARGET_TO_SOURCE_MESSAGE_FEE_METHOD,
+						TARGET_TO_SOURCE_LANE_ID,
+						claim_swap_message.clone(),
+					)
+					.await?;
+				let send_message_call: CallOf<Target> = pallet_bridge_messages::Call::send_message(
+					TARGET_TO_SOURCE_LANE_ID,
+					claim_swap_message,
+					claim_swap_delivery_and_dispatch_fee,
+				)
+				.into();
+
+				// send `claim_swap` message
+				let target_genesis_hash = *target_client.genesis_hash();
+				let _ = wait_until_transaction_is_finalized::<Target>(
+					target_client
+						.submit_and_watch_signed_extrinsic(
+							accounts.target_account_at_bridged_chain.clone(),
+							move |_, transaction_nonce| {
+								Bytes(
+									Target::sign_transaction(
+										target_genesis_hash,
+										&target_sign,
+										relay_substrate_client::TransactionEra::immortal(),
+										UnsignedTransaction::new(send_message_call, transaction_nonce),
+									)
+									.encode(),
+								)
+							},
+						)
+						.await?,
+				)
+				.await?;
+
+				// wait until swap state is updated
+				let token_swap_state = wait_until_token_swap_state_is_changed(
+					&source_client,
+					&token_swap_storage_key,
+					bp_token_swap::TokenSwapState::Confirmed,
+				)
+				.await?;
+				if token_swap_state != None {
+					return Err(anyhow::format_err!(
+						"Confirmed token swap state has been changed to {:?} unexpectedly"
+					));
+				}
+			} else {
+				log::info!(target: "bridge", "Cancelling the swap");
+				let cancel_swap_call: CallOf<Source> =
+					pallet_bridge_token_swap::Call::cancel_swap(token_swap.clone()).into();
+				let _ = wait_until_transaction_is_finalized::<Source>(
+					source_client
+						.submit_and_watch_signed_extrinsic(
+							accounts.source_account_at_this_chain.clone(),
+							move |_, transaction_nonce| {
+								Bytes(
+									Source::sign_transaction(
+										source_genesis_hash,
+										&source_sign,
+										relay_substrate_client::TransactionEra::immortal(),
+										UnsignedTransaction::new(cancel_swap_call, transaction_nonce),
+									)
+									.encode(),
+								)
+							},
+						)
+						.await?,
+				)
+				.await?;
+			}
+
+			// print final balances
+			let final_balances = read_account_balances(&accounts, &source_client, &target_client).await?;
+			log::info!(target: "bridge", "Final account balances: {:?}", final_balances);
+
+			Ok(())
+		})
+	}
+
+	/// Prepare token swap intention.
+	async fn prepare_token_swap<Source: CliChain, Target: CliChain>(
+		&self,
+		source_client: &Client<Source>,
+		source_sign: &Source::KeyPair,
+		target_sign: &Target::KeyPair,
+	) -> anyhow::Result<
+		bp_token_swap::TokenSwap<
+			BlockNumberOf<Source>,
+			BalanceOf<Source>,
+			AccountIdOf<Source>,
+			BalanceOf<Target>,
+			AccountIdOf<Target>,
+		>,
+	>
+	where
+		AccountIdOf<Source>: From<<Source::KeyPair as Pair>::Public>,
+		AccountIdOf<Target>: From<<Target::KeyPair as Pair>::Public>,
+		BalanceOf<Source>: From<u64>,
+		BalanceOf<Target>: From<u64>,
+	{
+		// accounts that are directly controlled by participants
+		let source_account_at_this_chain: AccountIdOf<Source> = source_sign.public().into();
+		let target_account_at_bridged_chain: AccountIdOf<Target> = target_sign.public().into();
+
+		// balances that we're going to swap
+		let source_balance_at_this_chain: BalanceOf<Source> = self.source_balance.cast().into();
+		let target_balance_at_bridged_chain: BalanceOf<Target> = self.target_balance.cast().into();
+
+		// prepare token swap intention
+		Ok(bp_token_swap::TokenSwap {
+			swap_type: self.prepare_token_swap_type(&source_client).await?,
+			source_balance_at_this_chain,
+			source_account_at_this_chain: source_account_at_this_chain.clone(),
+			target_balance_at_bridged_chain,
+			target_account_at_bridged_chain: target_account_at_bridged_chain.clone(),
+		})
+	}
+
+	/// Prepare token swap type.
+	async fn prepare_token_swap_type<Source: Chain>(
+		&self,
+		source_client: &Client<Source>,
+	) -> anyhow::Result<bp_token_swap::TokenSwapType<BlockNumberOf<Source>>> {
+		match self.swap_type {
+			TokenSwapType::NoLock => Ok(bp_token_swap::TokenSwapType::TemporaryTargetAccountAtBridgedChain),
+			TokenSwapType::LockUntilBlock {
+				blocks_before_expire,
+				ref swap_nonce,
+			} => {
+				let blocks_before_expire: BlockNumberOf<Source> = blocks_before_expire.into();
+				let current_source_block_number = *source_client.best_header().await?.number();
+				Ok(bp_token_swap::TokenSwapType::LockClaimUntilBlock(
+					current_source_block_number + blocks_before_expire,
+					swap_nonce.unwrap_or_else(|| {
+						U256::from(random::<u128>())
+							.overflowing_mul(U256::from(random::<u128>()))
+							.0
+					}),
+				))
+			}
+		}
+	}
+}
+
+/// Accounts that are participating in the swap.
+#[derive(Debug)]
+struct TokenSwapAccounts<ThisAccountId, BridgedAccountId> {
+	source_account_at_this_chain: ThisAccountId,
+	source_account_at_bridged_chain: BridgedAccountId,
+	target_account_at_bridged_chain: BridgedAccountId,
+	target_account_at_this_chain: ThisAccountId,
+	swap_account: ThisAccountId,
+}
+
+/// Swap accounts balances.
+#[derive(Debug)]
+struct TokenSwapBalances<ThisBalance, BridgedBalance> {
+	source_account_at_this_chain_balance: Option<ThisBalance>,
+	source_account_at_bridged_chain_balance: Option<BridgedBalance>,
+	target_account_at_bridged_chain_balance: Option<BridgedBalance>,
+	target_account_at_this_chain_balance: Option<ThisBalance>,
+	swap_account_balance: Option<ThisBalance>,
+}
+
+/// Read swap accounts balances.
+async fn read_account_balances<Source: ChainWithBalances, Target: ChainWithBalances>(
+	accounts: &TokenSwapAccounts<AccountIdOf<Source>, AccountIdOf<Target>>,
+	source_client: &Client<Source>,
+	target_client: &Client<Target>,
+) -> anyhow::Result<TokenSwapBalances<BalanceOf<Source>, BalanceOf<Target>>> {
+	Ok(TokenSwapBalances {
+		source_account_at_this_chain_balance: read_account_balance(
+			&source_client,
+			&accounts.source_account_at_this_chain,
+		)
+		.await?,
+		source_account_at_bridged_chain_balance: read_account_balance(
+			&target_client,
+			&accounts.source_account_at_bridged_chain,
+		)
+		.await?,
+		target_account_at_bridged_chain_balance: read_account_balance(
+			&target_client,
+			&accounts.target_account_at_bridged_chain,
+		)
+		.await?,
+		target_account_at_this_chain_balance: read_account_balance(
+			&source_client,
+			&accounts.target_account_at_this_chain,
+		)
+		.await?,
+		swap_account_balance: read_account_balance(&source_client, &accounts.swap_account).await?,
+	})
+}
+
+/// Read account balance.
+async fn read_account_balance<C: ChainWithBalances>(
+	client: &Client<C>,
+	account: &AccountIdOf<C>,
+) -> anyhow::Result<Option<BalanceOf<C>>> {
+	match client.free_native_balance(account.clone()).await {
+		Ok(balance) => Ok(Some(balance)),
+		Err(SubstrateError::AccountDoesNotExist) => Ok(None),
+		Err(error) => Err(anyhow::format_err!(
+			"Failed to read balance of {} account {:?}: {:?}",
+			C::NAME,
+			account,
+			error,
+		)),
+	}
+}
+
+/// Wait until transaction is included into finalized block.
+///
+/// Returns the hash of the finalized block with transaction.
+async fn wait_until_transaction_is_finalized<C: Chain>(
+	subscription: Subscription<TransactionStatusOf<C>>,
+) -> anyhow::Result<HashOf<C>> {
+	loop {
+		let transaction_status = subscription.next().await?;
+		match transaction_status {
+			Some(TransactionStatusOf::<C>::FinalityTimeout(_))
+			| Some(TransactionStatusOf::<C>::Usurped(_))
+			| Some(TransactionStatusOf::<C>::Dropped)
+			| Some(TransactionStatusOf::<C>::Invalid)
+			| None => {
+				return Err(anyhow::format_err!(
+					"We've been waiting for finalization of {} transaction, but it now has the {:?} status",
+					C::NAME,
+					transaction_status,
+				))
+			}
+			Some(TransactionStatusOf::<C>::Finalized(block_hash)) => {
+				log::trace!(
+					target: "bridge",
+					"{} transaction has been finalized at block {}",
+					C::NAME,
+					block_hash,
+				);
+				return Ok(block_hash);
+			}
+			_ => {
+				log::trace!(
+					target: "bridge",
+					"Received intermediate status of {} transaction: {:?}",
+					C::NAME,
+					transaction_status,
+				);
+			}
+		}
+	}
+}
+
+/// Waits until token swap state is changed from `Started` to something else.
+async fn wait_until_token_swap_state_is_changed<C: Chain>(
+	client: &Client<C>,
+	swap_state_storage_key: &StorageKey,
+	previous_token_swap_state: bp_token_swap::TokenSwapState,
+) -> anyhow::Result<Option<bp_token_swap::TokenSwapState>> {
+	log::trace!(target: "bridge", "Waiting for token swap state change");
+	loop {
+		async_std::task::sleep(C::AVERAGE_BLOCK_INTERVAL).await;
+
+		let best_block = client.best_finalized_header_number().await?;
+		let best_block_hash = client.block_hash_by_number(best_block).await?;
+		log::trace!(target: "bridge", "Inspecting {} block {}/{}", C::NAME, best_block, best_block_hash);
+
+		let token_swap_state = read_token_swap_state(client, best_block_hash, swap_state_storage_key).await?;
+		match token_swap_state {
+			Some(new_token_swap_state) if new_token_swap_state == previous_token_swap_state => {}
+			_ => {
+				log::trace!(
+					target: "bridge",
+					"Token swap state has been changed from {:?} to {:?}",
+					previous_token_swap_state,
+					token_swap_state,
+				);
+				return Ok(token_swap_state);
+			}
+		}
+	}
+}
+
+/// Waits until swap can be claimed or cancelled.
+async fn wait_until_swap_unlocked<C: Chain>(
+	client: &Client<C>,
+	required_block_number: BlockNumberOf<C>,
+) -> anyhow::Result<()> {
+	log::trace!(target: "bridge", "Waiting for token swap unlock");
+	loop {
+		async_std::task::sleep(C::AVERAGE_BLOCK_INTERVAL).await;
+
+		let best_block = client.best_finalized_header_number().await?;
+		let best_block_hash = client.block_hash_by_number(best_block).await?;
+		if best_block >= required_block_number {
+			return Ok(());
+		}
+
+		log::trace!(target: "bridge", "Skipping {} block {}/{}", C::NAME, best_block, best_block_hash);
+	}
+}
+
+/// Read state of the active token swap.
+async fn read_token_swap_state<C: Chain>(
+	client: &Client<C>,
+	at_block: C::Hash,
+	swap_state_storage_key: &StorageKey,
+) -> anyhow::Result<Option<bp_token_swap::TokenSwapState>> {
+	Ok(client
+		.storage_value(swap_state_storage_key.clone(), Some(at_block))
+		.await?)
+}