Parachains finality relay (#1199)

bridges/relays/parachains/Cargo.toml

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+[package]
+name = "parachains-relay"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
+
+[dependencies]
+async-std = "1.6.5"
+async-trait = "0.1.40"
+backoff = "0.2"
+futures = "0.3.5"
+linked-hash-map = "0.5.3"
+log = "0.4.11"
+num-traits = "0.2"
+parking_lot = "0.11.0"
+relay-utils = { path = "../utils" }
+
+# Bridge dependencies
+
+bp-parachains = { path = "../../primitives/parachains" }
+bp-polkadot-core = { path = "../../primitives/polkadot-core" }
+relay-substrate-client = { path = "../client-substrate" }
+
+[dev-dependencies]
+codec = { package = "parity-scale-codec", version = "3.0.0" }
+relay-substrate-client = { path = "../client-substrate", features = ["test-helpers"] }
+sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }

bridges/relays/parachains/src/lib.rs

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+// 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 std::fmt::Debug;
+
+use relay_substrate_client::Chain;
+
+pub mod parachains_loop;
+pub mod parachains_loop_metrics;
+
+/// Finality proofs synchronization pipeline.
+pub trait ParachainsPipeline: 'static + Clone + Debug + Send + Sync {
+	/// Relay chain which is storing parachain heads in its `paras` module.
+	type SourceChain: Chain;
+	/// Target chain (either relay or para) which wants to know about new parachain heads.
+	type TargetChain: Chain;
+}

bridges/relays/parachains/src/parachains_loop_metrics.rs

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+// 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 relay_utils::metrics::{Metric, PrometheusError, Registry};
+
+/// Parachains sync metrics.
+#[derive(Clone)]
+pub struct ParachainsLoopMetrics;
+
+impl ParachainsLoopMetrics {
+	/// Create and register parachains loop metrics.
+	pub fn new(_prefix: Option<&str>) -> Result<Self, PrometheusError> {
+		Ok(ParachainsLoopMetrics)
+	}
+}
+
+impl Metric for ParachainsLoopMetrics {
+	fn register(&self, _registry: &Registry) -> Result<(), PrometheusError> {
+		Ok(())
+	}
+}