Parachains finality relay (#1199)

bridges/primitives/parachains/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "bp-parachains"
+description = "Primitives of parachains module."
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "3.0.0", default-features = false, features = ["derive"] }
+scale-info = { version = "2.1.1", default-features = false, features = ["derive"] }
+serde = { version = "1.0", optional = true, features = ["derive"] }
+
+# Bridge dependencies
+
+bp-polkadot-core = { path = "../polkadot-core", default-features = false }
+bp-runtime = { path = "../runtime", default-features = false }
+
+# Substrate dependencies
+
+frame-support = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-core = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"bp-polkadot-core/std",
+	"bp-runtime/std",
+	"codec/std",
+	"frame-support/std",
+	"scale-info/std",
+	"serde",
+	"sp-core/std",
+]

bridges/primitives/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/>.
+
+//! Primitives of parachains module.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use bp_polkadot_core::{
+	parachains::{ParaHash, ParaId},
+	BlockNumber as RelayBlockNumber,
+};
+use codec::{Decode, Encode};
+use frame_support::{Blake2_128Concat, RuntimeDebug, Twox64Concat};
+use scale_info::TypeInfo;
+use sp_core::storage::StorageKey;
+
+/// Best known parachain head hash.
+#[derive(Clone, Decode, Encode, PartialEq, RuntimeDebug, TypeInfo)]
+pub struct BestParaHeadHash {
+	/// Number of relay block where this head has been read.
+	///
+	/// Parachain head is opaque to relay chain. So we can't simply decode it as a header of
+	/// parachains and call `block_number()` on it. Instead, we're using the fact that parachain
+	/// head is always built on top of previous head (because it is blockchain) and relay chain
+	/// always imports parachain heads in order. What it means for us is that at any given
+	/// **finalized** relay block `B`, head of parachain will be ancestor (or the same) of all
+	/// parachain heads available at descendants of `B`.
+	pub at_relay_block_number: RelayBlockNumber,
+	/// Hash of parachain head.
+	pub head_hash: ParaHash,
+}
+
+/// Returns runtime storage key of given parachain head at the source chain.
+///
+/// The head is stored by the `paras` pallet in the `Heads` map.
+pub fn parachain_head_storage_key_at_source(
+	paras_pallet_name: &str,
+	para_id: ParaId,
+) -> StorageKey {
+	bp_runtime::storage_map_final_key::<Twox64Concat>(paras_pallet_name, "Heads", &para_id.encode())
+}
+
+/// Returns runtime storage key of best known parachain head at the target chain.
+///
+/// The head is stored by the `pallet-bridge-parachains` pallet in the `BestParaHeads` map.
+pub fn parachain_head_storage_key_at_target(
+	bridge_parachains_pallet_name: &str,
+	para_id: ParaId,
+) -> StorageKey {
+	bp_runtime::storage_map_final_key::<Blake2_128Concat>(
+		bridge_parachains_pallet_name,
+		"BestParaHeads",
+		&para_id.encode(),
+	)
+}