Implement storage_at Runtime API (#30)

* Implement storage_at Runtime API

* Fix encoding 30#discussion_r441482104

frame/ethereum/src/lib.rs

@@ -30,6 +30,7 @@ use sp_runtime::{
 	traits::UniqueSaturatedInto,
 	transaction_validity::{TransactionValidity, TransactionSource, ValidTransaction}
 };
+use rlp;
 use sha3::{Digest, Keccak256};
 
 pub use frontier_rpc_primitives::TransactionStatus;

rpc/core/src/eth.rs

@@ -77,7 +77,7 @@ pub trait EthApi {
 
 	/// Returns content of the storage at given address.
 	#[rpc(name = "eth_getStorageAt")]
-	fn storage_at(&self, _: H160, _: U256, _: Option<BlockNumber>) -> BoxFuture<H256>;
+	fn storage_at(&self, _: H160, _: U256, _: Option<BlockNumber>) -> Result<H256>;
 
 	/// Returns block with given hash.
 	#[rpc(name = "eth_getBlockByHash")]

rpc/primitives/src/lib.rs

@@ -42,6 +42,7 @@ sp_api::decl_runtime_apis! {
 		fn gas_price() -> U256;
 		fn account_code_at(address: H160) -> Vec<u8>;
 		fn author() -> H160;
+		fn storage_at(address: H160, index: U256) -> H256;
 		fn block_by_number(number: u32) -> Option<EthereumBlock>;
 		fn block_transaction_count_by_number(number: u32) -> Option<U256>;
 		fn block_by_hash(hash: H256) -> Option<EthereumBlock>;

rpc/src/lib.rs

@@ -230,8 +230,23 @@ impl<B, C, SC, P, CT, BE> EthApiT for EthApi<B, C, SC, P, CT, BE> where
 		unimplemented!("proof");
 	}
 
-	fn storage_at(&self, _: H160, _: U256, _: Option<BlockNumber>) -> BoxFuture<H256> {
-		unimplemented!("storage_at");
+	fn storage_at(&self, address: H160, index: U256, number: Option<BlockNumber>) -> Result<H256> {
+		if let Some(number) = number {
+			if number != BlockNumber::Latest {
+				unimplemented!("fetch storage for past blocks is not yet supported");
+			}
+		}
+		let header = self
+			.select_chain
+			.best_chain()
+			.map_err(|_| internal_err("fetch header failed"))?;
+		Ok(
+			self.client
+				.runtime_api()
+				.storage_at(&BlockId::Hash(header.hash()), address, index)
+				.map_err(|_| internal_err("fetch runtime chain id failed"))?
+				.into(),
+		)
 	}
 
 	fn block_by_hash(&self, hash: H256, _: bool) -> Result<Option<RichBlock>> {

template/runtime/src/lib.rs

@@ -475,6 +475,12 @@ impl_runtime_apis! {
 			}
 		}
 
+		fn storage_at(address: H160, index: U256) -> H256 {
+			let mut tmp = [0u8; 32];
+			index.to_big_endian(&mut tmp);
+			evm::Module::<Runtime>::account_storages(address, H256::from_slice(&tmp[..]))
+		}
+
 		fn block_by_number(number: u32) -> Option<EthereumBlock> {
 			<ethereum::Module<Runtime>>::block_by_number(number)
 		}