Return errors from eth_call RPC (#2498)

* propagate call errors

* add error code for execution error

rpc/src/v1/helpers/errors.rs

@@ -21,7 +21,7 @@ macro_rules! rpc_unimplemented {
 }
 
 use std::fmt;
-use ethcore::error::Error as EthcoreError;
+use ethcore::error::{Error as EthcoreError, CallError};
 use ethcore::account_provider::{Error as AccountError};
 use fetch::FetchError;
 use jsonrpc_core::{Error, ErrorCode, Value};
@@ -34,6 +34,7 @@ mod codes {
 	pub const NO_NEW_WORK: i64 = -32003;
 	pub const UNKNOWN_ERROR: i64 = -32009;
 	pub const TRANSACTION_ERROR: i64 = -32010;
+	pub const EXECUTION_ERROR: i64 = -32015;
 	pub const ACCOUNT_LOCKED: i64 = -32020;
 	pub const PASSWORD_INVALID: i64 = -32021;
 	pub const ACCOUNT_ERROR: i64 = -32023;
@@ -109,6 +110,14 @@ pub fn invalid_params<T: fmt::Debug>(param: &str, details: T) -> Error {
 	}
 }
 
+pub fn execution<T: fmt::Debug>(data: T) -> Error {
+	Error {
+		code: ErrorCode::ServerError(codes::EXECUTION_ERROR),
+		message: "Transaction execution error.".into(),
+		data: Some(Value::String(format!("{:?}", data))),
+	}
+}
+
 pub fn state_pruned() -> Error {
 	Error {
 		code: ErrorCode::ServerError(codes::UNSUPPORTED_REQUEST),
@@ -219,4 +228,10 @@ pub fn from_transaction_error(error: EthcoreError) -> Error {
 	}
 }
 
-
+pub fn from_call_error(error: CallError) -> Error {
+	match error {
+		CallError::StatePruned => state_pruned(),
+		CallError::Execution(e) => execution(e),
+		CallError::TransactionNotFound => internal("{}, this should not be the case with eth_call, most likely a bug.", CallError::TransactionNotFound),
+	}
+}

rpc/src/v1/impls/eth.rs

@@ -593,7 +593,10 @@ impl<C, S: ?Sized, M, EM> Eth for EthClient<C, S, M, EM> where
 			num => take_weak!(self.client).call(&signed, num.into(), Default::default()),
 		};
 
-		Ok(r.map(|e| Bytes(e.output)).unwrap_or(Bytes::new(vec![])))
+		match r {
+			Ok(b) => Ok(Bytes(b.output)),
+			Err(e) => Err(errors::from_call_error(e)),
+		}
 	}
 
 	fn estimate_gas(&self, request: CallRequest, num: Trailing<BlockNumber>) -> Result<RpcU256, Error> {