establish new node folder for overseer, messages, and subsystems (#1200)

* establish new `node` folder for overseer, messages, and subsystems

* extract message types from overseer crate

* remove doc links

polkadot/node/messages/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "polkadot-node-messages"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+description = "Message types used by Subsystems"
+
+[dependencies]
+polkadot-primitives = { path = "../../primitives" }

polkadot/node/messages/src/lib.rs

@@ -0,0 +1,72 @@
+// Copyright 2017-2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot 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.
+
+// Polkadot 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Message types for the overseer and subsystems.
+//!
+//! These messages are intended to define the protocol by which different subsystems communicate with each
+//! other and signals that they receive from an overseer to coordinate their work.
+//! This is intended for use with the `polkadot-overseer` crate.
+//!
+//! Subsystems' APIs are defined separately from their implementation, leading to easier mocking.
+
+use polkadot_primitives::Hash;
+
+/// Signals sent by an overseer to a subsystem.
+#[derive(PartialEq, Clone, Debug)]
+pub enum OverseerSignal {
+	/// `Subsystem` should start working on block-based work, given by the relay-chain block hash.
+	StartWork(Hash),
+	/// `Subsystem` should stop working on block-based work specified by the relay-chain block hash.
+	StopWork(Hash),
+	/// Conclude the work of the `Overseer` and all `Subsystem`s.
+	Conclude,
+}
+
+/// A message type used by the Validation Subsystem.
+#[derive(Debug)]
+pub enum ValidationSubsystemMessage {
+	ValidityAttestation,
+}
+
+/// A message type used by the CandidateBacking Subsystem.
+#[derive(Debug)]
+pub enum CandidateBackingSubsystemMessage {
+	RegisterBackingWatcher,
+	Second,
+}
+
+/// A message type tying together all message types that are used across Subsystems.
+#[derive(Debug)]
+pub enum AllMessages {
+	Validation(ValidationSubsystemMessage),
+	CandidateBacking(CandidateBackingSubsystemMessage),
+}
+
+/// A message type that a subsystem receives from an overseer.
+/// It wraps signals from an overseer and messages that are circulating
+/// between subsystems.
+///
+/// It is generic over over the message type `M` that a particular `Subsystem` may use.
+#[derive(Debug)]
+pub enum FromOverseer<M: std::fmt::Debug> {
+	/// Signal from the `Overseer`.
+	Signal(OverseerSignal),
+
+	/// Some other `Subsystem`'s message.
+	Communication {
+		msg: M,
+	},
+}