Make relay CLI generic (#849)

* Start generalizing rialto-millau commands. * cargo fmt --all * Introduce generic balance. * Unify message payloads. * cargo fmt --all * init - generic * Attempt to unify send message. * Start moving things around. * cargo fmt --all * Move init-bridge. * cargo fmt --all * Improve UX of bridge argument. * Fix clippy. * Fix docs and scripts. * Add docs. * Apply suggestions from code review Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com> * Fix copyright. * Add issue numbers. * More todos. * Update comments. Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>
2026-05-31 02:51:01 +00:00 · 2021-04-01 12:49:49 +02:00
parent b6d034afaf
commit 904b9f4da5
22 changed files with 896 additions and 879 deletions
@@ -0,0 +1,137 @@
+// 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/>.
+
+use crate::cli::{CliChain, SourceConnectionParams, TargetConnectionParams, TargetSigningParams};
+use bp_runtime::Chain as ChainBase;
+use codec::Encode;
+use pallet_bridge_grandpa::InitializationData;
+use relay_substrate_client::{Chain, TransactionSignScheme};
+use sp_core::{Bytes, Pair};
+use structopt::{clap::arg_enum, StructOpt};
+
+/// Initialize bridge pallet.
+#[derive(StructOpt)]
+pub struct InitBridge {
+	/// A bridge instance to initalize.
+	#[structopt(possible_values = &InitBridgeName::variants(), case_insensitive = true)]
+	bridge: InitBridgeName,
+	#[structopt(flatten)]
+	source: SourceConnectionParams,
+	#[structopt(flatten)]
+	target: TargetConnectionParams,
+	#[structopt(flatten)]
+	target_sign: TargetSigningParams,
+}
+
+// TODO [#851] Use kebab-case.
+arg_enum! {
+	#[derive(Debug)]
+	/// Bridge to initialize.
+	pub enum InitBridgeName {
+		MillauToRialto,
+		RialtoToMillau,
+		WestendToMillau,
+	}
+}
+
+macro_rules! select_bridge {
+	($bridge: expr, $generic: tt) => {
+		match $bridge {
+			InitBridgeName::MillauToRialto => {
+				type Source = relay_millau_client::Millau;
+				type Target = relay_rialto_client::Rialto;
+
+				fn encode_init_bridge(
+					init_data: InitializationData<<Source as ChainBase>::Header>,
+				) -> <Target as Chain>::Call {
+					rialto_runtime::SudoCall::sudo(Box::new(
+						rialto_runtime::BridgeGrandpaMillauCall::initialize(init_data).into(),
+					))
+					.into()
+				}
+
+				$generic
+			}
+			InitBridgeName::RialtoToMillau => {
+				type Source = relay_rialto_client::Rialto;
+				type Target = relay_millau_client::Millau;
+
+				fn encode_init_bridge(
+					init_data: InitializationData<<Source as ChainBase>::Header>,
+				) -> <Target as Chain>::Call {
+					let initialize_call = millau_runtime::BridgeGrandpaRialtoCall::<
+						millau_runtime::Runtime,
+						millau_runtime::RialtoGrandpaInstance,
+					>::initialize(init_data);
+					millau_runtime::SudoCall::sudo(Box::new(initialize_call.into())).into()
+				}
+
+				$generic
+			}
+			InitBridgeName::WestendToMillau => {
+				type Source = relay_westend_client::Westend;
+				type Target = relay_millau_client::Millau;
+
+				fn encode_init_bridge(
+					init_data: InitializationData<<Source as ChainBase>::Header>,
+				) -> <Target as Chain>::Call {
+					// at Westend -> Millau initialization we're not using sudo, because otherwise our deployments
+					// may fail, because we need to initialize both Rialto -> Millau and Westend -> Millau bridge.
+					// => since there's single possible sudo account, one of transaction may fail with duplicate nonce error
+					millau_runtime::BridgeGrandpaWestendCall::<
+						millau_runtime::Runtime,
+						millau_runtime::WestendGrandpaInstance,
+					>::initialize(init_data)
+					.into()
+				}
+
+				$generic
+			}
+		}
+	};
+}
+
+impl InitBridge {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		select_bridge!(self.bridge, {
+			let source_client = crate::rialto_millau::source_chain_client::<Source>(self.source).await?;
+			let target_client = crate::rialto_millau::target_chain_client::<Target>(self.target).await?;
+			let target_sign =
+				Target::target_signing_params(self.target_sign).map_err(|e| anyhow::format_err!("{}", e))?;
+
+			crate::headers_initialize::initialize(
+				source_client,
+				target_client.clone(),
+				target_sign.public().into(),
+				move |transaction_nonce, initialization_data| {
+					Bytes(
+						Target::sign_transaction(
+							*target_client.genesis_hash(),
+							&target_sign,
+							transaction_nonce,
+							encode_init_bridge(initialization_data),
+						)
+						.encode(),
+					)
+				},
+			)
+			.await;
+
+			Ok(())
+		})
+	}
+}
@@ -0,0 +1,500 @@
+// 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/>.
+
+//! Deal with CLI args of substrate-to-substrate relay.
+
+use std::convert::TryInto;
+
+use crate::rialto_millau::cli as rialto_millau;
+use bp_messages::LaneId;
+use codec::{Decode, Encode};
+use frame_support::weights::Weight;
+use sp_runtime::app_crypto::Ss58Codec;
+use structopt::{clap::arg_enum, StructOpt};
+
+mod init_bridge;
+mod relay_headers;
+
+/// Parse relay CLI args.
+pub fn parse_args() -> Command {
+	Command::from_args()
+}
+
+/// Substrate-to-Substrate bridge utilities.
+#[derive(StructOpt)]
+#[structopt(about = "Substrate-to-Substrate relay")]
+pub enum Command {
+	/// Start headers relay between two chains.
+	///
+	/// The on-chain bridge component should have been already initialized with
+	/// `init-bridge` sub-command.
+	RelayHeaders(relay_headers::RelayHeaders),
+	/// Start messages relay between two chains.
+	///
+	/// Ties up to `Messages` pallets on both chains and starts relaying messages.
+	/// Requires the header relay to be already running.
+	RelayMessages(RelayMessages),
+	/// Initialize on-chain bridge pallet with current header data.
+	///
+	/// Sends initialization transaction to bootstrap the bridge with current finalized block data.
+	InitBridge(init_bridge::InitBridge),
+	/// Send custom message over the bridge.
+	///
+	/// Allows interacting with the bridge by sending messages over `Messages` component.
+	/// The message is being sent to the source chain, delivered to the target chain and dispatched
+	/// there.
+	SendMessage(SendMessage),
+	/// Generate SCALE-encoded `Call` for choosen network.
+	///
+	/// The call can be used either as message payload or can be wrapped into a transaction
+	/// and executed on the chain directly.
+	EncodeCall(EncodeCall),
+	/// Generate SCALE-encoded `MessagePayload` object that can be sent over selected bridge.
+	///
+	/// The `MessagePayload` can be then fed to `Messages::send_message` function and sent over
+	/// the bridge.
+	EncodeMessagePayload(EncodeMessagePayload),
+	/// Estimate Delivery and Dispatch Fee required for message submission to messages pallet.
+	EstimateFee(EstimateFee),
+	/// Given a source chain `AccountId`, derive the corresponding `AccountId` for the target chain.
+	DeriveAccount(DeriveAccount),
+}
+
+impl Command {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RelayHeaders(arg) => arg.run().await?,
+			Self::RelayMessages(arg) => arg.run().await?,
+			Self::InitBridge(arg) => arg.run().await?,
+			Self::SendMessage(arg) => arg.run().await?,
+			Self::EncodeCall(arg) => arg.run().await?,
+			Self::EncodeMessagePayload(arg) => arg.run().await?,
+			Self::EstimateFee(arg) => arg.run().await?,
+			Self::DeriveAccount(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// Start message relayer process.
+#[derive(StructOpt)]
+pub enum RelayMessages {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::RelayMessages),
+}
+
+impl RelayMessages {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// Send bridge message.
+#[derive(StructOpt)]
+pub enum SendMessage {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::SendMessage),
+}
+
+impl SendMessage {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// A call to encode.
+#[derive(StructOpt)]
+pub enum EncodeCall {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::EncodeCall),
+}
+
+impl EncodeCall {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// A `MessagePayload` to encode.
+#[derive(StructOpt)]
+pub enum EncodeMessagePayload {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::EncodeMessagePayload),
+}
+
+impl EncodeMessagePayload {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// Estimate Delivery & Dispatch Fee command.
+#[derive(StructOpt)]
+pub enum EstimateFee {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::EstimateFee),
+}
+
+impl EstimateFee {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+/// Given a source chain `AccountId`, derive the corresponding `AccountId` for the target chain.
+///
+/// The (derived) target chain `AccountId` is going to be used as dispatch origin of the call
+/// that has been sent over the bridge.
+/// This account can also be used to receive target-chain funds (or other form of ownership),
+/// since messages sent over the bridge will be able to spend these.
+#[derive(StructOpt)]
+pub enum DeriveAccount {
+	#[structopt(flatten)]
+	RialtoMillau(rialto_millau::DeriveAccount),
+}
+
+impl DeriveAccount {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		match self {
+			Self::RialtoMillau(arg) => arg.run().await?,
+		}
+		Ok(())
+	}
+}
+
+arg_enum! {
+	#[derive(Debug)]
+	/// The origin to use when dispatching the message on the target chain.
+	///
+	/// - `Target` uses account existing on the target chain (requires target private key).
+	/// - `Origin` uses account derived from the source-chain account.
+	pub enum Origins {
+		Target,
+		Source,
+	}
+}
+
+/// Generic balance type.
+#[derive(Debug)]
+pub struct Balance(pub u128);
+
+impl std::str::FromStr for Balance {
+	type Err = <u128 as std::str::FromStr>::Err;
+
+	fn from_str(s: &str) -> Result<Self, Self::Err> {
+		Ok(Self(s.parse()?))
+	}
+}
+
+impl Balance {
+	/// Cast balance to `u64` type, panicking if it's too large.
+	pub fn cast(&self) -> u64 {
+		self.0.try_into().expect("Balance is too high for this chain.")
+	}
+}
+
+/// Generic account id with custom parser.
+#[derive(Debug, Clone)]
+pub struct AccountId {
+	account: sp_runtime::AccountId32,
+	ss58_format: sp_core::crypto::Ss58AddressFormat,
+}
+
+impl std::fmt::Display for AccountId {
+	fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+		write!(fmt, "{}", self.account.to_ss58check_with_version(self.ss58_format))
+	}
+}
+
+impl std::str::FromStr for AccountId {
+	type Err = String;
+
+	fn from_str(s: &str) -> Result<Self, Self::Err> {
+		let (account, ss58_format) = sp_runtime::AccountId32::from_ss58check_with_version(s)
+			.map_err(|err| format!("Unable to decode SS58 address: {:?}", err))?;
+		Ok(Self { account, ss58_format })
+	}
+}
+
+const SS58_FORMAT_PROOF: &str = "u16 -> Ss58Format is infallible; qed";
+
+impl AccountId {
+	/// Create new SS58-formatted address from raw account id.
+	pub fn from_raw<T: CliChain>(account: sp_runtime::AccountId32) -> Self {
+		Self {
+			account,
+			ss58_format: T::ss58_format().try_into().expect(SS58_FORMAT_PROOF),
+		}
+	}
+
+	/// Enforces formatting account to be for given [`CliChain`] type.
+	///
+	/// This will change the `ss58format` of the account to match the requested one.
+	/// Note that a warning will be produced in case the current format does not match
+	/// the requested one, but the conversion always succeeds.
+	pub fn enforce_chain<T: CliChain>(&mut self) {
+		let original = self.clone();
+		self.ss58_format = T::ss58_format().try_into().expect(SS58_FORMAT_PROOF);
+		log::debug!("{} SS58 format: {} (RAW: {})", self, self.ss58_format, self.account);
+		if original.ss58_format != self.ss58_format {
+			log::warn!(
+				target: "bridge",
+				"Address {} does not seem to match {}'s SS58 format (got: {}, expected: {}).\nConverted to: {}",
+				original,
+				T::NAME,
+				original.ss58_format,
+				self.ss58_format,
+				self,
+			)
+		}
+	}
+
+	/// Returns the raw (no SS58-prefixed) account id.
+	pub fn raw_id(&self) -> sp_runtime::AccountId32 {
+		self.account.clone()
+	}
+}
+
+/// Bridge-supported network definition.
+///
+/// Used to abstract away CLI commands.
+pub trait CliChain: relay_substrate_client::Chain {
+	/// Chain's current version of the runtime.
+	const RUNTIME_VERSION: sp_version::RuntimeVersion;
+
+	/// Crypto keypair type used to send messages.
+	///
+	/// In case of chains supporting multiple cryptos, pick one used by the CLI.
+	type KeyPair: sp_core::crypto::Pair;
+
+	/// Bridge Message Payload type.
+	///
+	/// TODO [#854] This should be removed in favour of target-specifc types.
+	type MessagePayload;
+
+	/// Numeric value of SS58 format.
+	fn ss58_format() -> u16;
+
+	/// Parse CLI call and encode it to be dispatched on this specific chain.
+	fn encode_call(call: crate::rialto_millau::cli::Call) -> Result<Self::Call, String>;
+
+	/// Construct message payload to be sent over the bridge.
+	fn encode_message(message: crate::rialto_millau::cli::MessagePayload) -> Result<Self::MessagePayload, String>;
+
+	/// Maximal extrinsic weight (from the runtime).
+	fn max_extrinsic_weight() -> Weight;
+
+	/// Convert CLI signing parameters of `Source` chain into a `KeyPair` instance.
+	fn source_signing_params(params: SourceSigningParams) -> Result<Self::KeyPair, String> {
+		use sp_core::crypto::Pair;
+		Self::KeyPair::from_string(&params.source_signer, params.source_signer_password.as_deref())
+			.map_err(|e| format!("Failed to parse source-signer: {:?}", e))
+	}
+
+	/// Convert CLI signing parameters of `Target` chain into a `KeyPair` instance.
+	fn target_signing_params(params: TargetSigningParams) -> Result<Self::KeyPair, String> {
+		use sp_core::crypto::Pair;
+		Self::KeyPair::from_string(&params.target_signer, params.target_signer_password.as_deref())
+			.map_err(|e| format!("Failed to parse target-signer: {:?}", e))
+	}
+}
+
+/// Lane id.
+#[derive(Debug)]
+pub struct HexLaneId(pub LaneId);
+
+impl From<HexLaneId> for LaneId {
+	fn from(lane_id: HexLaneId) -> LaneId {
+		lane_id.0
+	}
+}
+
+impl std::str::FromStr for HexLaneId {
+	type Err = hex::FromHexError;
+
+	fn from_str(s: &str) -> Result<Self, Self::Err> {
+		let mut lane_id = LaneId::default();
+		hex::decode_to_slice(s, &mut lane_id)?;
+		Ok(HexLaneId(lane_id))
+	}
+}
+
+/// Nicer formatting for raw bytes vectors.
+#[derive(Encode, Decode)]
+pub struct HexBytes(pub Vec<u8>);
+
+impl std::str::FromStr for HexBytes {
+	type Err = hex::FromHexError;
+
+	fn from_str(s: &str) -> Result<Self, Self::Err> {
+		Ok(Self(hex::decode(s)?))
+	}
+}
+
+impl std::fmt::Debug for HexBytes {
+	fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+		write!(fmt, "0x{}", hex::encode(&self.0))
+	}
+}
+
+impl HexBytes {
+	/// Encode given object and wrap into nicely formatted bytes.
+	pub fn encode<T: Encode>(t: &T) -> Self {
+		Self(t.encode())
+	}
+}
+
+/// Prometheus metrics params.
+#[derive(StructOpt)]
+pub struct PrometheusParams {
+	/// Do not expose a Prometheus metric endpoint.
+	#[structopt(long)]
+	pub no_prometheus: bool,
+	/// Expose Prometheus endpoint at given interface.
+	#[structopt(long, default_value = "127.0.0.1")]
+	pub prometheus_host: String,
+	/// Expose Prometheus endpoint at given port.
+	#[structopt(long, default_value = "9616")]
+	pub prometheus_port: u16,
+}
+
+impl From<PrometheusParams> for Option<relay_utils::metrics::MetricsParams> {
+	fn from(cli_params: PrometheusParams) -> Option<relay_utils::metrics::MetricsParams> {
+		if !cli_params.no_prometheus {
+			Some(relay_utils::metrics::MetricsParams {
+				host: cli_params.prometheus_host,
+				port: cli_params.prometheus_port,
+			})
+		} else {
+			None
+		}
+	}
+}
+
+/// Either explicit or maximal allowed value.
+#[derive(Debug)]
+pub enum ExplicitOrMaximal<V> {
+	/// User has explicitly specified argument value.
+	Explicit(V),
+	/// Maximal allowed value for this argument.
+	Maximal,
+}
+
+impl<V: std::str::FromStr> std::str::FromStr for ExplicitOrMaximal<V>
+where
+	V::Err: std::fmt::Debug,
+{
+	type Err = String;
+
+	fn from_str(s: &str) -> Result<Self, Self::Err> {
+		if s.to_lowercase() == "max" {
+			return Ok(ExplicitOrMaximal::Maximal);
+		}
+
+		V::from_str(s)
+			.map(ExplicitOrMaximal::Explicit)
+			.map_err(|e| format!("Failed to parse '{:?}'. Expected 'max' or explicit value", e))
+	}
+}
+
+/// Create chain-specific set of configuration objects: connection parameters,
+/// signing parameters and bridge initialisation parameters.
+#[macro_export]
+macro_rules! declare_chain_options {
+	($chain:ident, $chain_prefix:ident) => {
+		paste::item! {
+			#[doc = $chain " connection params."]
+			#[derive(StructOpt)]
+			pub struct [<$chain ConnectionParams>] {
+				#[doc = "Connect to " $chain " node at given host."]
+				#[structopt(long, default_value = "127.0.0.1")]
+				pub [<$chain_prefix _host>]: String,
+				#[doc = "Connect to " $chain " node websocket server at given port."]
+				#[structopt(long)]
+				pub [<$chain_prefix _port>]: u16,
+				#[doc = "Use secure websocket connection."]
+				#[structopt(long)]
+				pub [<$chain_prefix _secure>]: bool,
+			}
+
+			#[doc = $chain " signing params."]
+			#[derive(StructOpt)]
+			pub struct [<$chain SigningParams>] {
+				#[doc = "The SURI of secret key to use when transactions are submitted to the " $chain " node."]
+				#[structopt(long)]
+				pub [<$chain_prefix _signer>]: String,
+				#[doc = "The password for the SURI of secret key to use when transactions are submitted to the " $chain " node."]
+				#[structopt(long)]
+				pub [<$chain_prefix _signer_password>]: Option<String>,
+			}
+		}
+	};
+}
+
+// TODO [#852] Use structop renames instead of different fields.
+// TODO [#852] Add Into<ConnectionParams>?
+declare_chain_options!(Source, source);
+declare_chain_options!(Target, target);
+
+#[cfg(test)]
+mod tests {
+	use std::str::FromStr;
+
+	use super::*;
+
+	#[test]
+	fn should_format_addresses_with_ss58_format() {
+		// given
+		let rialto1 = "5sauUXUfPjmwxSgmb3tZ5d6yx24eZX4wWJ2JtVUBaQqFbvEU";
+		let rialto2 = "5rERgaT1Z8nM3et2epA5i1VtEBfp5wkhwHtVE8HK7BRbjAH2";
+		let millau1 = "752paRyW1EGfq9YLTSSqcSJ5hqnBDidBmaftGhBo8fy6ypW9";
+		let millau2 = "74GNQjmkcfstRftSQPJgMREchqHM56EvAUXRc266cZ1NYVW5";
+
+		let expected = vec![rialto1, rialto2, millau1, millau2];
+
+		// when
+		let parsed = expected
+			.iter()
+			.map(|s| AccountId::from_str(s).unwrap())
+			.collect::<Vec<_>>();
+
+		let actual = parsed.iter().map(|a| format!("{}", a)).collect::<Vec<_>>();
+
+		assert_eq!(actual, expected)
+	}
+}
@@ -0,0 +1,91 @@
+// 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/>.
+
+use crate::cli::{CliChain, PrometheusParams, SourceConnectionParams, TargetConnectionParams, TargetSigningParams};
+use structopt::{clap::arg_enum, StructOpt};
+
+/// Start headers relayer process.
+#[derive(StructOpt)]
+pub struct RelayHeaders {
+	/// A bridge instance to relay headers for.
+	#[structopt(possible_values = &RelayHeadersBridge::variants(), case_insensitive = true)]
+	bridge: RelayHeadersBridge,
+	#[structopt(flatten)]
+	source: SourceConnectionParams,
+	#[structopt(flatten)]
+	target: TargetConnectionParams,
+	#[structopt(flatten)]
+	target_sign: TargetSigningParams,
+	#[structopt(flatten)]
+	prometheus_params: PrometheusParams,
+}
+
+// TODO [#851] Use kebab-case.
+arg_enum! {
+	#[derive(Debug)]
+	/// Headers relay bridge.
+	pub enum RelayHeadersBridge {
+		MillauToRialto,
+		RialtoToMillau,
+		WestendToMillau,
+	}
+}
+
+macro_rules! select_bridge {
+	($bridge: expr, $generic: tt) => {
+		match $bridge {
+			RelayHeadersBridge::MillauToRialto => {
+				type Source = relay_millau_client::Millau;
+				type Target = relay_rialto_client::Rialto;
+				type Finality = crate::rialto_millau::millau_headers_to_rialto::MillauFinalityToRialto;
+
+				$generic
+			}
+			RelayHeadersBridge::RialtoToMillau => {
+				type Source = relay_rialto_client::Rialto;
+				type Target = relay_millau_client::Millau;
+				type Finality = crate::rialto_millau::rialto_headers_to_millau::RialtoFinalityToMillau;
+				$generic
+			}
+			RelayHeadersBridge::WestendToMillau => {
+				type Source = relay_westend_client::Westend;
+				type Target = relay_millau_client::Millau;
+				type Finality = crate::rialto_millau::westend_headers_to_millau::WestendFinalityToMillau;
+				$generic
+			}
+		}
+	};
+}
+
+impl RelayHeaders {
+	/// Run the command.
+	pub async fn run(self) -> anyhow::Result<()> {
+		select_bridge!(self.bridge, {
+			let source_client = crate::rialto_millau::source_chain_client::<Source>(self.source).await?;
+			let target_client = crate::rialto_millau::target_chain_client::<Target>(self.target).await?;
+			let target_sign =
+				Target::target_signing_params(self.target_sign).map_err(|e| anyhow::format_err!("{}", e))?;
+
+			crate::finality_pipeline::run(
+				Finality::new(target_client.clone(), target_sign),
+				source_client,
+				target_client,
+				self.prometheus_params.into(),
+			)
+			.await
+		})
+	}
+}