Add basic PoW chain db store

lighthouse/db/stores/mod.rs

@@ -4,7 +4,10 @@ use super::{
 };
 
 mod block_store;
+mod pow_chain_store;
 
 pub use self::block_store::BlockStore;
+pub use self::pow_chain_store::PoWChainStore;
 
 const BLOCKS_DB_COLUMN: &str = "blocks";
+const POW_CHAIN_DB_COLUMN: &str = "powchain";

lighthouse/db/stores/pow_chain_store.rs

@@ -0,0 +1,34 @@
+use std::sync::Arc;
+use super::{
+    ClientDB,
+    DBError,
+};
+use super::POW_CHAIN_DB_COLUMN as DB_COLUMN;
+
+pub struct PoWChainStore<T>
+    where T: ClientDB
+{
+    db: Arc<T>,
+}
+
+impl<T: ClientDB> PoWChainStore<T> {
+    pub fn new(db: Arc<T>) -> Self {
+        Self {
+            db,
+        }
+    }
+
+    pub fn put_block_hash(&self, hash: &[u8])
+        -> Result<(), DBError>
+    {
+        self.db.put(DB_COLUMN, hash, &vec![0])
+    }
+
+    pub fn block_hash_exists(&self, hash: &[u8])
+        -> Result<bool, DBError>
+    {
+        self.db.exists(DB_COLUMN, hash)
+    }
+}
+
+// TODO: add tests once a memory-db is implemented