RPC to query transaction fee + weight + info (#3876)

* initial version for testing

* New version that compiles

* optional at block parameter

* Fix some more view grumbles.

* Update srml/transaction-payment/src/lib.rs

substrate/node/rpc/src/lib.rs

@@ -32,6 +32,7 @@
 use std::sync::Arc;
 
 use node_primitives::{Block, AccountId, Index, Balance};
+use node_runtime::UncheckedExtrinsic;
 use sr_primitives::traits::ProvideRuntimeApi;
 use transaction_pool::txpool::{ChainApi, Pool};
 
@@ -42,18 +43,23 @@ pub fn create<C, P, M>(client: Arc<C>, pool: Arc<Pool<P>>) -> jsonrpc_core::IoHa
 	C: Send + Sync + 'static,
 	C::Api: srml_system_rpc::AccountNonceApi<Block, AccountId, Index>,
 	C::Api: srml_contracts_rpc::ContractsRuntimeApi<Block, AccountId, Balance>,
+	C::Api: srml_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance, UncheckedExtrinsic>,
 	P: ChainApi + Sync + Send + 'static,
 	M: jsonrpc_core::Metadata + Default,
 {
 	use srml_system_rpc::{System, SystemApi};
 	use srml_contracts_rpc::{Contracts, ContractsApi};
+	use srml_transaction_payment_rpc::{TransactionPayment, TransactionPaymentApi};
 
 	let mut io = jsonrpc_core::IoHandler::default();
 	io.extend_with(
 		SystemApi::to_delegate(System::new(client.clone(), pool))
 	);
 	io.extend_with(
-		ContractsApi::to_delegate(Contracts::new(client))
+		ContractsApi::to_delegate(Contracts::new(client.clone()))
+	);
+	io.extend_with(
+		TransactionPaymentApi::to_delegate(TransactionPayment::new(client))
 	);
 	io
 }