Collator node workflow (#280)

* arbitrary application logic in CLI

* collation work

* split up exit and work futures in application

* collation node workflow

* typo

* indentation fix

* doc grumbles

* rename Application to Worker

* refactor Worker::exit to exit_only

substrate/polkadot/src/main.rs

@@ -19,12 +19,47 @@
 #![warn(missing_docs)]
 
 extern crate polkadot_cli as cli;
+extern crate ctrlc;
+extern crate futures;
 
 #[macro_use]
 extern crate error_chain;
 
+use cli::{ClientError, ServiceComponents, ClientBackend, PolkadotBlock, StateMachineBackend, Service};
+use futures::sync::oneshot;
+use futures::{future, Future};
+
+use std::cell::RefCell;
+
+// the regular polkadot worker simply does nothing until ctrl-c
+struct Worker;
+impl cli::Worker for Worker {
+	type Work = Self::Exit;
+	type Exit = future::MapErr<oneshot::Receiver<()>, fn(oneshot::Canceled) -> ()>;
+
+	fn exit_only(self) -> Self::Exit {
+		// can't use signal directly here because CtrlC takes only `Fn`.
+		let (exit_send, exit) = oneshot::channel();
+
+		let exit_send_cell = RefCell::new(Some(exit_send));
+		ctrlc::CtrlC::set_handler(move || {
+			if let Some(exit_send) = exit_send_cell.try_borrow_mut().expect("signal handler not reentrant; qed").take() {
+				exit_send.send(()).expect("Error sending exit notification");
+			}
+		});
+
+		exit.map_err(drop)
+	}
+
+	fn work<C: ServiceComponents>(self, _service: &Service<C>) -> Self::Exit
+		where ClientError: From<<<<C as ServiceComponents>::Backend as ClientBackend<PolkadotBlock>>::State as StateMachineBackend>::Error>,
+	{
+		self.exit_only()
+	}
+}
+
 quick_main!(run);
 
 fn run() -> cli::error::Result<()> {
-	cli::run(::std::env::args())
+	cli::run(::std::env::args(), Worker)
 }