Adds construct_simple_protocol macro for simplifying the creation of protocols (#897)

* Make `on_message` take the message as `&mut Option<_>`

* Make `ConsensusGossip` implement `Specialization`

* Move `new_session` into `ConsensusGossip`

* Adds `construct_simple_protocol` macro for simplifying the creation of protocols

substrate/core/network/src/consensus_gossip.rs

@@ -27,6 +27,9 @@ use runtime_primitives::generic::BlockId;
 use message::{self, generic::Message as GenericMessage};
 use protocol::Context;
 use service::Roles;
+use specialization::Specialization;
+use StatusMessage;
+use generic_message;
 
 // TODO: Add additional spam/DoS attack protection.
 const MESSAGE_LIFETIME: Duration = Duration::from_secs(600);
@@ -57,6 +60,7 @@ pub struct ConsensusGossip<B: BlockT> {
 	live_message_sinks: HashMap<B::Hash, mpsc::UnboundedSender<ConsensusMessage<B>>>,
 	messages: Vec<MessageEntry<B>>,
 	message_hashes: HashSet<B::Hash>,
+	session_start: Option<B::Hash>,
 }
 
 impl<B: BlockT> ConsensusGossip<B> where B::Header: HeaderT<Number=u64> {
@@ -67,6 +71,7 @@ impl<B: BlockT> ConsensusGossip<B> where B::Header: HeaderT<Number=u64> {
 			live_message_sinks: HashMap::new(),
 			messages: Default::default(),
 			message_hashes: Default::default(),
+			session_start: None
 		}
 	}
 
@@ -300,6 +305,55 @@ impl<B: BlockT> ConsensusGossip<B> where B::Header: HeaderT<Number=u64> {
 		self.register_message(hash, message);
 		self.propagate(protocol, generic, hash);
 	}
+
+	/// Note new consensus session.
+	pub fn new_session(&mut self, parent_hash: B::Hash) {
+		let old_session = self.session_start.take();
+		self.session_start = Some(parent_hash);
+		self.collect_garbage(|topic| old_session.as_ref().map_or(true, |h| topic != h));
+	}
+}
+
+impl<Block: BlockT> Specialization<Block> for ConsensusGossip<Block> where
+	Block::Header: HeaderT<Number=u64>
+{
+	fn status(&self) -> Vec<u8> {
+		Vec::new()
+	}
+
+	fn on_connect(&mut self, ctx: &mut Context<Block>, who: NodeIndex, status: StatusMessage<Block>) {
+		self.new_peer(ctx, who, status.roles);
+	}
+
+	fn on_disconnect(&mut self, ctx: &mut Context<Block>, who: NodeIndex) {
+		self.peer_disconnected(ctx, who);
+	}
+
+	fn on_message(&mut self, ctx: &mut Context<Block>, who: NodeIndex, message: &mut Option<message::Message<Block>>) {
+		match message.take() {
+			Some(generic_message::Message::BftMessage(msg)) => {
+				trace!(target: "gossip", "BFT message from {}: {:?}", who, msg);
+				// TODO: check signature here? what if relevant block is unknown?
+				self.on_bft_message(ctx, who, msg)
+			}
+			r => *message = r,
+		}
+	}
+
+	fn on_abort(&mut self) {
+		self.abort();
+	}
+
+	fn maintain_peers(&mut self, _ctx: &mut Context<Block>) {
+		self.collect_garbage(|_| true);
+	}
+
+	fn on_block_imported(
+		&mut self,
+		_ctx: &mut Context<Block>,
+		_hash: <Block as BlockT>::Hash,
+		_header: &<Block as BlockT>::Header)
+	{}
 }
 
 #[cfg(test)]

substrate/core/network/src/lib.rs

@@ -49,6 +49,7 @@ extern crate substrate_test_client as test_client;
 
 mod service;
 mod sync;
+#[macro_use]
 mod protocol;
 mod io;
 mod config;
@@ -74,3 +75,5 @@ pub use message::{generic as generic_message, RequestId, BftMessage, LocalizedBf
 pub use error::Error;
 pub use config::{Roles, ProtocolConfig};
 pub use on_demand::{OnDemand, OnDemandService, RemoteResponse};
+#[doc(hidden)]
+pub use runtime_primitives::traits::Block as BlockT;

substrate/core/network/src/protocol.rs

@@ -277,7 +277,7 @@ impl<B: BlockT, S: Specialization<B>, H: ExHashT> Protocol<B, S, H> {
 			GenericMessage::RemoteHeaderResponse(response) => self.on_remote_header_response(io, who, response),
 			GenericMessage::RemoteChangesRequest(request) => self.on_remote_changes_request(io, who, request),
 			GenericMessage::RemoteChangesResponse(response) => self.on_remote_changes_response(io, who, response),
-			other => self.specialization.write().on_message(&mut ProtocolContext::new(&self.context_data, io), who, other),
+			other => self.specialization.write().on_message(&mut ProtocolContext::new(&self.context_data, io), who, &mut Some(other)),
 		}
 	}
 
@@ -709,3 +709,102 @@ pub(crate) fn hash_message<B: BlockT>(message: &Message<B>) -> B::Hash {
 	let data = message.encode();
 	HashFor::<B>::hash(&data)
 }
+
+/// Construct a simple protocol that is composed of several sub protocols.
+/// Each "sub protocol" needs to implement `Specialization` and needs to provide a `new()` function.
+/// For more fine grained implementations, this macro is not usable.
+///
+/// # Example
+///
+/// ```nocompile
+/// construct_simple_protocol! {
+///     pub struct MyProtocol where Block = MyBlock {
+///         consensus_gossip: ConsensusGossip<MyBlock>,
+///         other_protocol: MyCoolStuff,
+///     }
+/// }
+/// ```
+///
+/// You can also provide an optional parameter after `where Block = MyBlock`, so it looks like
+/// `where Block = MyBlock, Status = consensus_gossip`. This will instruct the implementation to
+/// use the `status()` function from the `ConsensusGossip` protocol. By default, `status()` returns
+/// an empty vector.
+#[macro_export]
+macro_rules! construct_simple_protocol {
+	(
+		$( #[ $attr:meta ] )*
+		pub struct $protocol:ident where
+			Block = $block:ident
+			$( , Status = $status_protocol_name:ident )*
+		{
+			$( $sub_protocol_name:ident : $sub_protocol:ident $( <$protocol_block:ty> )*, )*
+		}
+	) => {
+		$( #[$attr] )*
+		pub struct $protocol {
+			$( $sub_protocol_name: $sub_protocol $( <$protocol_block> )*, )*
+		}
+
+		impl $protocol {
+			/// Instantiate a node protocol handler.
+			pub fn new() -> Self {
+				Self {
+					$( $sub_protocol_name: $sub_protocol::new(), )*
+				}
+			}
+		}
+
+		impl $crate::specialization::Specialization<$block> for $protocol {
+			fn status(&self) -> Vec<u8> {
+				$(
+					let status = self.$status_protocol_name.status();
+
+					if !status.is_empty() {
+						return status;
+					}
+				)*
+
+				Vec::new()
+			}
+
+			fn on_connect(
+				&mut self,
+				ctx: &mut $crate::Context<$block>,
+				who: $crate::NodeIndex,
+				status: $crate::StatusMessage<$block>
+			) {
+				$( self.$sub_protocol_name.on_connect(ctx, who, status); )*
+			}
+
+			fn on_disconnect(&mut self, ctx: &mut $crate::Context<$block>, who: $crate::NodeIndex) {
+				$( self.$sub_protocol_name.on_disconnect(ctx, who); )*
+			}
+
+			fn on_message(
+				&mut self,
+				ctx: &mut $crate::Context<$block>,
+				who: $crate::NodeIndex,
+				message: &mut Option<$crate::message::Message<$block>>
+			) {
+				$( self.$sub_protocol_name.on_message(ctx, who, message); )*
+			}
+
+			fn on_abort(&mut self) {
+				$( self.$sub_protocol_name.on_abort(); )*
+			}
+
+			fn maintain_peers(&mut self, ctx: &mut $crate::Context<$block>) {
+				$( self.$sub_protocol_name.maintain_peers(ctx); )*
+			}
+
+			fn on_block_imported(
+				&mut self,
+				ctx: &mut $crate::Context<$block>,
+				hash: <$block as $crate::BlockT>::Hash,
+				header: &<$block as $crate::BlockT>::Header
+			) {
+				$( self.$sub_protocol_name.on_block_imported(ctx, hash, header); )*
+			}
+		}
+	}
+}

substrate/core/network/src/specialization.rs

@@ -35,7 +35,7 @@ pub trait Specialization<B: BlockT>: Send + Sync + 'static {
 	fn on_disconnect(&mut self, ctx: &mut Context<B>, who: NodeIndex);
 
 	/// Called when a network-specific message arrives.
-	fn on_message(&mut self, ctx: &mut Context<B>, who: NodeIndex, message: ::message::Message<B>);
+	fn on_message(&mut self, ctx: &mut Context<B>, who: NodeIndex, message: &mut Option<::message::Message<B>>);
 
 	/// Called on abort.
 	fn on_abort(&mut self) { }

substrate/core/network/src/test/mod.rs

@@ -66,8 +66,8 @@ impl Specialization<Block> for DummySpecialization {
 		self.gossip.peer_disconnected(ctx, peer_id);
 	}
 
-	fn on_message(&mut self, ctx: &mut Context<Block>, peer_id: NodeIndex, message: ::message::Message<Block>) {
-		if let ::message::generic::Message::ChainSpecific(data) = message {
+	fn on_message(&mut self, ctx: &mut Context<Block>, peer_id: NodeIndex, message: &mut Option<::message::Message<Block>>) {
+		if let Some(::message::generic::Message::ChainSpecific(data)) = message.take() {
 			let gossip_message = GossipMessage::decode(&mut &data[..])
 				.expect("gossip messages all in known format; qed");
 			self.gossip.on_chain_specific(ctx, peer_id, data, gossip_message.topic)