Complex RialtoParachain <> Millau relay (#1405)

* complex parachain relay

* fix spelling

bridges/relays/client-substrate/src/chain.rs

@@ -64,6 +64,20 @@ pub trait Chain: ChainBase + Clone {
 	type WeightToFee: WeightToFeePolynomial<Balance = Self::Balance>;
 }
 
+/// Substrate-based relay chain that supports parachains.
+///
+/// We assume that the parachains are supported using `runtime_parachains::paras` pallet.
+pub trait RelayChain: Chain {
+	/// Name of the `runtime_parachains::paras` pallet in the runtime of this chain.
+	const PARAS_PALLET_NAME: &'static str;
+	/// Name of the bridge parachains pallet (used in `construct_runtime` macro call) that is
+	/// deployed at the **bridged** chain.
+	///
+	/// We assume that all chains that are bridging with this `ChainWithGrandpa` are using
+	/// the same name.
+	const PARACHAINS_FINALITY_PALLET_NAME: &'static str;
+}
+
 /// Substrate-based chain that is using direct GRANDPA finality from minimal relay-client point of
 /// view.
 ///

bridges/relays/client-substrate/src/client.rs

@@ -262,6 +262,11 @@ impl<C: Chain> Client<C> {
 		Ok(*self.header_by_hash(self.best_finalized_header_hash().await?).await?.number())
 	}
 
+	/// Return header of the best finalized block.
+	pub async fn best_finalized_header(&self) -> Result<C::Header> {
+		self.header_by_hash(self.best_finalized_header_hash().await?).await
+	}
+
 	/// Returns the best Substrate header.
 	pub async fn best_header(&self) -> Result<C::Header>
 	where

bridges/relays/client-substrate/src/lib.rs

@@ -33,8 +33,8 @@ use std::time::Duration;
 pub use crate::{
 	chain::{
 		AccountKeyPairOf, BlockWithJustification, CallOf, Chain, ChainWithBalances,
-		ChainWithGrandpa, ChainWithMessages, SignParam, TransactionSignScheme, TransactionStatusOf,
-		UnsignedTransaction, WeightToFeeOf,
+		ChainWithGrandpa, ChainWithMessages, RelayChain, SignParam, TransactionSignScheme,
+		TransactionStatusOf, UnsignedTransaction, WeightToFeeOf,
 	},
 	client::{ChainRuntimeVersion, Client, OpaqueGrandpaAuthoritiesSet, Subscription},
 	error::{Error, Result},