openethereum/rpc/src/v1/helpers/subscription_manager.rs

// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

//! Generic poll manager for Pub-Sub.

use std::sync::Arc;
use std::sync::atomic::{self, AtomicBool};
use parking_lot::Mutex;

use jsonrpc_core::futures::future::{self, Either};
use jsonrpc_core::futures::sync::mpsc;
use jsonrpc_core::futures::{Sink, Future};
use jsonrpc_core::{self as core, MetaIoHandler};
use jsonrpc_pubsub::SubscriptionId;

use v1::helpers::Subscribers;
use v1::metadata::Metadata;

#[derive(Debug)]
struct Subscription {
	metadata: Metadata,
	method: String,
	params: core::Params,
	sink: mpsc::Sender<Result<core::Value, core::Error>>,
	/// a flag if subscription is still active and last returned value
	last_result: Arc<(AtomicBool, Mutex<Option<core::Output>>)>,
}

/// A struct managing all subscriptions.
/// TODO [ToDr] Depending on the method decide on poll interval.
/// For most of the methods it will be enough to poll on new block instead of time-interval.
pub struct GenericPollManager<S: core::Middleware<Metadata>> {
	subscribers: Subscribers<Subscription>,
	rpc: MetaIoHandler<Metadata, S>,
}

impl<S: core::Middleware<Metadata>> GenericPollManager<S> {
	/// Creates new poll manager
	pub fn new(rpc: MetaIoHandler<Metadata, S>) -> Self {
		GenericPollManager {
			subscribers: Default::default(),
			rpc,
		}
	}

	/// Creates new poll manager with deterministic ids.
	#[cfg(test)]
	pub fn new_test(rpc: MetaIoHandler<Metadata, S>) -> Self {
		let mut manager = Self::new(rpc);
		manager.subscribers = Subscribers::new_test();
		manager
	}

	/// Subscribes to update from polling given method.
	pub fn subscribe(&mut self, metadata: Metadata, method: String, params: core::Params)
		-> (SubscriptionId, mpsc::Receiver<Result<core::Value, core::Error>>)
	{
		let (sink, stream) = mpsc::channel(1);
		let subscription = Subscription {
			metadata,
			method,
			params,
			sink,
			last_result: Default::default(),
		};
		let id = self.subscribers.insert(subscription);
		(id, stream)
	}

	pub fn unsubscribe(&mut self, id: &SubscriptionId) -> bool {
		debug!(target: "pubsub", "Removing subscription: {:?}", id);
		self.subscribers.remove(id).map(|subscription| {
			subscription.last_result.0.store(true, atomic::Ordering::SeqCst);
		}).is_some()
	}

	pub fn tick(&self) -> Box<Future<Item=(), Error=()> + Send> {
		let mut futures = Vec::new();
		// poll all subscriptions
		for (id, subscription) in self.subscribers.iter() {
			let call = core::MethodCall {
				jsonrpc: Some(core::Version::V2),
				id: core::Id::Str(id.as_string()),
				method: subscription.method.clone(),
				params: subscription.params.clone(),
			};
			trace!(target: "pubsub", "Polling method: {:?}", call);
			let result = self.rpc.handle_call(call.into(), subscription.metadata.clone());

			let last_result = subscription.last_result.clone();
			let sender = subscription.sink.clone();

			let result = result.and_then(move |response| {
				// quick check if the subscription is still valid
				if last_result.0.load(atomic::Ordering::SeqCst) {
					return Either::B(future::ok(()))
				}

				let mut last_result = last_result.1.lock();
				if *last_result != response && response.is_some() {
					let output = response.expect("Existence proved by the condition.");
					debug!(target: "pubsub", "Got new response, sending: {:?}", output);
					*last_result = Some(output.clone());

					let send = match output {
						core::Output::Success(core::Success { result, .. }) => Ok(result),
						core::Output::Failure(core::Failure { error, .. }) => Err(error),
					};
					Either::A(sender.send(send).map(|_| ()).map_err(|_| ()))
				} else {
					trace!(target: "pubsub", "Response was not changed: {:?}", response);
					Either::B(future::ok(()))
				}
			});

			futures.push(result)
		}

		// return a future represeting all the polls
		Box::new(future::join_all(futures).map(|_| ()))
	}
}

#[cfg(test)]
mod tests {
	use std::sync::atomic::{self, AtomicBool};

	use jsonrpc_core::{MetaIoHandler, NoopMiddleware, Value, Params};
	use jsonrpc_core::futures::{Future, Stream};
	use jsonrpc_pubsub::SubscriptionId;
	use http::tokio::runtime::Runtime;

	use super::GenericPollManager;

	fn poll_manager() -> GenericPollManager<NoopMiddleware> {
		let mut io = MetaIoHandler::default();
		let called = AtomicBool::new(false);
		io.add_method("hello", move |_| {
			if !called.load(atomic::Ordering::SeqCst) {
				called.store(true, atomic::Ordering::SeqCst);
				Ok(Value::String("hello".into()))
			} else {
				Ok(Value::String("world".into()))
			}
		});
		GenericPollManager::new_test(io)
	}

	#[test]
	fn should_poll_subscribed_method() {
		// given
		let mut el = Runtime::new().unwrap();
		let mut poll_manager = poll_manager();
		let (id, rx) = poll_manager.subscribe(Default::default(), "hello".into(), Params::None);
		assert_eq!(id, SubscriptionId::String("0x416d77337e24399d".into()));

		// then
		poll_manager.tick().wait().unwrap();
		let (res, rx) = el.block_on(rx.into_future()).unwrap();
		assert_eq!(res, Some(Ok(Value::String("hello".into()))));

		// retrieve second item
		poll_manager.tick().wait().unwrap();
		let (res, rx) = el.block_on(rx.into_future()).unwrap();
		assert_eq!(res, Some(Ok(Value::String("world".into()))));

		// and no more notifications
		poll_manager.tick().wait().unwrap();
		// we need to unsubscribe otherwise the future will never finish.
		poll_manager.unsubscribe(&id);
		assert_eq!(el.block_on(rx.into_future()).unwrap().0, None);
	}
}