verify that GRANDPA pallet is not initialized before submitting initialization transaction (#1267)

* verify that GRANDPA pallet is not initialized before submitting initialization transaction

* spelling

bridges/primitives/header-chain/src/lib.rs

@@ -29,6 +29,7 @@ use sp_runtime::{generic::OpaqueDigestItemId, traits::Header as HeaderT, Runtime
 use sp_std::boxed::Box;
 
 pub mod justification;
+pub mod storage_keys;
 
 /// A type that can be used as a parameter in a dispatchable function.
 ///

bridges/primitives/header-chain/src/storage_keys.rs

@@ -0,0 +1,52 @@
+// 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/>.
+
+//! Storage keys of bridge GRANDPA pallet.
+
+/// Name of the `BestFinalized` storage map.
+pub const BEST_FINALIZED_MAP_NAME: &str = "BestFinalized";
+
+use sp_core::storage::StorageKey;
+
+/// Storage key of the best finalized header hash value in the runtime storage.
+pub fn best_finalized_hash_key(pallet_prefix: &str) -> StorageKey {
+	StorageKey(
+		bp_runtime::storage_value_final_key(
+			pallet_prefix.as_bytes(),
+			BEST_FINALIZED_MAP_NAME.as_bytes(),
+		)
+		.to_vec(),
+	)
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use hex_literal::hex;
+
+	#[test]
+	fn best_finalized_hash_key_computed_properly() {
+		// If this test fails, then something has been changed in module storage that is breaking
+		// compatibility with previous pallet.
+		let storage_key = best_finalized_hash_key("BridgeGrandpa").0;
+		assert_eq!(
+			storage_key,
+			hex!("0b06f475eddb98cf933a12262e0388dea4ebafdd473c549fdb24c5c991c5591c").to_vec(),
+			"Unexpected storage key: {}",
+			hex::encode(&storage_key),
+		);
+	}
+}