Forwards block root iterators (#672)

* Implement forwards block root iterators

* Clean up errors and docs

beacon_node/store/src/memory_store.rs

@@ -1,29 +1,35 @@
 use super::{Error, Store};
+use crate::forwards_iter::SimpleForwardsBlockRootsIterator;
 use crate::impls::beacon_state::{get_full_state, store_full_state};
 use parking_lot::RwLock;
 use std::collections::HashMap;
+use std::marker::PhantomData;
+use std::sync::Arc;
 use types::*;
 
 type DBHashMap = HashMap<Vec<u8>, Vec<u8>>;
 
 /// A thread-safe `HashMap` wrapper.
-pub struct MemoryStore {
+pub struct MemoryStore<E: EthSpec> {
     db: RwLock<DBHashMap>,
+    _phantom: PhantomData<E>,
 }
 
-impl Clone for MemoryStore {
+impl<E: EthSpec> Clone for MemoryStore<E> {
     fn clone(&self) -> Self {
         Self {
             db: RwLock::new(self.db.read().clone()),
+            _phantom: PhantomData,
         }
     }
 }
 
-impl MemoryStore {
+impl<E: EthSpec> MemoryStore<E> {
     /// Create a new, empty database.
     pub fn open() -> Self {
         Self {
             db: RwLock::new(HashMap::new()),
+            _phantom: PhantomData,
         }
     }
 
@@ -34,10 +40,12 @@ impl MemoryStore {
     }
 }
 
-impl Store for MemoryStore {
+impl<E: EthSpec> Store<E> for MemoryStore<E> {
+    type ForwardsBlockRootsIterator = SimpleForwardsBlockRootsIterator;
+
     /// Get the value of some key from the database. Returns `None` if the key does not exist.
     fn get_bytes(&self, col: &str, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
-        let column_key = MemoryStore::get_key_for_col(col, key);
+        let column_key = Self::get_key_for_col(col, key);
 
         Ok(self
             .db
@@ -48,7 +56,7 @@ impl Store for MemoryStore {
 
     /// Puts a key in the database.
     fn put_bytes(&self, col: &str, key: &[u8], val: &[u8]) -> Result<(), Error> {
-        let column_key = MemoryStore::get_key_for_col(col, key);
+        let column_key = Self::get_key_for_col(col, key);
 
         self.db.write().insert(column_key, val.to_vec());
 
@@ -57,14 +65,14 @@ impl Store for MemoryStore {
 
     /// Return true if some key exists in some column.
     fn key_exists(&self, col: &str, key: &[u8]) -> Result<bool, Error> {
-        let column_key = MemoryStore::get_key_for_col(col, key);
+        let column_key = Self::get_key_for_col(col, key);
 
         Ok(self.db.read().contains_key(&column_key))
     }
 
     /// Delete some key from the database.
     fn key_delete(&self, col: &str, key: &[u8]) -> Result<(), Error> {
-        let column_key = MemoryStore::get_key_for_col(col, key);
+        let column_key = Self::get_key_for_col(col, key);
 
         self.db.write().remove(&column_key);
 
@@ -72,20 +80,26 @@ impl Store for MemoryStore {
     }
 
     /// Store a state in the store.
-    fn put_state<E: EthSpec>(
-        &self,
-        state_root: &Hash256,
-        state: &BeaconState<E>,
-    ) -> Result<(), Error> {
+    fn put_state(&self, state_root: &Hash256, state: &BeaconState<E>) -> Result<(), Error> {
         store_full_state(self, state_root, state)
     }
 
     /// Fetch a state from the store.
-    fn get_state<E: EthSpec>(
+    fn get_state(
         &self,
         state_root: &Hash256,
         _: Option<Slot>,
     ) -> Result<Option<BeaconState<E>>, Error> {
         get_full_state(self, state_root)
     }
+
+    fn forwards_block_roots_iterator(
+        store: Arc<Self>,
+        start_slot: Slot,
+        end_state: BeaconState<E>,
+        end_block_root: Hash256,
+        _: &ChainSpec,
+    ) -> Self::ForwardsBlockRootsIterator {
+        SimpleForwardsBlockRootsIterator::new(store, start_slot, end_state, end_block_root)
+    }
 }