Parachains finality relay (#1199)

bridges/relays/parachains/src/lib.rs

@@ -0,0 +1,30 @@
+// 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(())
+	}
+}