client: fix justifications migration (paritytech#8489)

* client: rename variables

* client: fix justifications migration

* client: fix compilation

client/db/src/lib.rs

@@ -561,10 +561,10 @@ impl<Block: BlockT> sc_client_api::blockchain::Backend<Block> for BlockchainDb<B
 
 	fn justifications(&self, id: BlockId<Block>) -> ClientResult<Option<Justifications>> {
 		match read_db(&*self.db, columns::KEY_LOOKUP, columns::JUSTIFICATIONS, id)? {
-			Some(justification) => match Decode::decode(&mut &justification[..]) {
-				Ok(justification) => Ok(Some(justification)),
+			Some(justifications) => match Decode::decode(&mut &justifications[..]) {
+				Ok(justifications) => Ok(Some(justifications)),
 				Err(err) => return Err(sp_blockchain::Error::Backend(
-					format!("Error decoding justification: {}", err)
+					format!("Error decoding justifications: {}", err)
 				)),
 			}
 			None => Ok(None),

client/db/src/upgrade.rs

@@ -25,7 +25,7 @@ use std::path::{Path, PathBuf};
 use sp_runtime::traits::Block as BlockT;
 use crate::{columns, utils::DatabaseType};
 use kvdb_rocksdb::{Database, DatabaseConfig};
-use codec::Encode;
+use codec::{Decode, Encode};
 
 /// Version file name.
 const VERSION_FILE_NAME: &'static str = "db_version";
@@ -83,7 +83,12 @@ fn migrate_2_to_3<Block: BlockT>(db_path: &Path, _db_type: DatabaseType) -> sp_b
 	let mut transaction = db.transaction();
 	for key in keys {
 		if let Some(justification) = db.get(columns::JUSTIFICATIONS, &key).map_err(db_err)? {
-			// Tag each Justification with the hardcoded ID for GRANDPA. Avoid the dependency on the GRANDPA crate
+			// Tag each justification with the hardcoded ID for GRANDPA to avoid the dependency on
+			// the GRANDPA crate.
+			// NOTE: when storing justifications the previous API would get a `Vec<u8>` and still
+			// call encode on it.
+			let justification = Vec::<u8>::decode(&mut &justification[..])
+				.map_err(|_| sp_blockchain::Error::Backend("Invalid justification blob".into()))?;
 			let justifications = sp_runtime::Justifications::from((*b"FRNK", justification));
 			transaction.put_vec(columns::JUSTIFICATIONS, &key, justifications.encode());
 		}