Make chain && state RPCs async (#3480)

* chain+state RPCs are async now

* wrapped too long lines

* create full/light RPC impls from service

* use ordering

* post-merge fix

substrate/core/rpc/api/src/chain/error.rs

@@ -23,6 +23,9 @@ use jsonrpc_core as rpc;
 /// Chain RPC Result type.
 pub type Result<T> = std::result::Result<T, Error>;
 
+/// State RPC future Result type.
+pub type FutureResult<T> = Box<dyn rpc::futures::Future<Item = T, Error = Error> + Send>;
+
 /// Chain RPC errors.
 #[derive(Debug, derive_more::Display, derive_more::From)]
 pub enum Error {

substrate/core/rpc/api/src/chain/mod.rs

@@ -23,7 +23,7 @@ use jsonrpc_core::Result as RpcResult;
 use jsonrpc_core::futures::Future;
 use jsonrpc_derive::rpc;
 use jsonrpc_pubsub::{typed::Subscriber, SubscriptionId};
-use self::error::Result;
+use self::error::{FutureResult, Result};
 
 pub use self::gen_client::Client as ChainClient;
 
@@ -35,11 +35,11 @@ pub trait ChainApi<Number, Hash, Header, SignedBlock> {
 
 	/// Get header of a relay chain block.
 	#[rpc(name = "chain_getHeader")]
-	fn header(&self, hash: Option<Hash>) -> Result<Option<Header>>;
+	fn header(&self, hash: Option<Hash>) -> FutureResult<Option<Header>>;
 
 	/// Get header and body of a relay chain block.
 	#[rpc(name = "chain_getBlock")]
-	fn block(&self, hash: Option<Hash>) -> Result<Option<SignedBlock>>;
+	fn block(&self, hash: Option<Hash>) -> FutureResult<Option<SignedBlock>>;
 
 	/// Get hash of the n-th block in the canon chain.
 	///