Storage map iter (#148)

* Add example file

* Fmt

* Add KeyIter.

* Add iter method to store proc-macro.

* Fetch all values at once.

* Update docs.

* Run rustfmt.

Co-authored-by: Andrew Jones <ascjones@gmail.com>

src/rpc.rs

@@ -122,7 +122,7 @@ impl<T: Runtime> Rpc<T> {
     /// Fetch a storage key
     pub async fn storage(
         &self,
-        key: StorageKey,
+        key: &StorageKey,
         hash: Option<T::Hash>,
     ) -> Result<Option<StorageData>, Error> {
         let params = Params::Array(vec![to_json_value(key)?, to_json_value(hash)?]);
@@ -132,8 +132,8 @@ impl<T: Runtime> Rpc<T> {
     }
 
     /// Returns the keys with prefix with pagination support.
-	/// Up to `count` keys will be returned.
-	/// If `start_key` is passed, return next keys in storage in lexicographic order.
+    /// Up to `count` keys will be returned.
+    /// If `start_key` is passed, return next keys in storage in lexicographic order.
     pub async fn storage_keys_paged(
         &self,
         prefix: Option<StorageKey>,
@@ -170,6 +170,19 @@ impl<T: Runtime> Rpc<T> {
             .map_err(Into::into)
     }
 
+    /// Query historical storage entries
+    pub async fn query_storage_at(
+        &self,
+        keys: &[StorageKey],
+        at: Option<T::Hash>,
+    ) -> Result<Vec<StorageChangeSet<<T as System>::Hash>>, Error> {
+        let params = Params::Array(vec![to_json_value(keys)?, to_json_value(at)?]);
+        self.client
+            .request("state_queryStorage", params)
+            .await
+            .map_err(Into::into)
+    }
+
     /// Fetch the genesis hash
     pub async fn genesis_hash(&self) -> Result<T::Hash, Error> {
         let block_zero = Some(ListOrValue::Value(NumberOrHex::Number(0)));