Resurrect (a minimal version of) message-broker (#234)

This is mostly a copy of the predating version with exception of some
renaming and alterations (e.g. the message handler takes an inbound
downward message by value, not by reference).

cumulus/Cargo.lock

@@ -1112,6 +1112,18 @@ dependencies = [
  "tokio 0.1.22",
 ]
 
+[[package]]
+name = "cumulus-message-broker"
+version = "0.1.0"
+dependencies = [
+ "cumulus-primitives",
+ "frame-support",
+ "frame-system",
+ "parity-scale-codec",
+ "sp-inherents",
+ "sp-std",
+]
+
 [[package]]
 name = "cumulus-network"
 version = "0.1.0"
@@ -1255,6 +1267,7 @@ dependencies = [
 name = "cumulus-test-parachain-runtime"
 version = "0.1.0"
 dependencies = [
+ "cumulus-message-broker",
  "cumulus-parachain-upgrade",
  "cumulus-primitives",
  "cumulus-runtime",

cumulus/Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
 	"consensus",
+	"message-broker",
 	"network",
 	"parachain-upgrade",
 	"primitives",

cumulus/message-broker/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "cumulus-message-broker"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+# Substrate dependencies
+frame-support = { git = "https://github.com/paritytech/substrate", default-features = false , branch = "master" }
+frame-system = { git = "https://github.com/paritytech/substrate", default-features = false , branch = "master" }
+sp-inherents = { git = "https://github.com/paritytech/substrate", default-features = false , branch = "master" }
+sp-std = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
+
+# Other dependencies
+codec = { package = "parity-scale-codec", version = "1.3.0", features = [ "derive" ], default-features = false }
+
+# Cumulus dependencies
+cumulus-primitives = { path = "../primitives", default-features = false }
+
+[features]
+default = [ "std" ]
+std = [
+	"frame-support/std",
+	"frame-system/std",
+	"sp-inherents/std",
+	"cumulus-primitives/std",
+	"sp-std/std"
+]

cumulus/message-broker/src/lib.rs

@@ -0,0 +1,74 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Cumulus.
+
+// Substrate 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.
+
+// Substrate 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 Cumulus.  If not, see <http://www.gnu.org/licenses/>.
+
+//! This pallet deals with the low-level details of parachain message passing.
+//!
+//! Specifically, this pallet serves as a glue layer between cumulus collation pipeline and the
+//! runtime that hosts this pallet.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use sp_std::prelude::*;
+use frame_system::ensure_none;
+use frame_support::{decl_module, storage, weights::DispatchClass};
+use sp_inherents::{InherentData, InherentIdentifier, MakeFatalError, ProvideInherent};
+
+use cumulus_primitives::{
+	inherents::{DownwardMessagesType, DOWNWARD_MESSAGES_IDENTIFIER},
+	well_known_keys,
+	DownwardMessageHandler, InboundDownwardMessage,
+};
+
+/// Configuration trait of the message broker pallet.
+pub trait Trait: frame_system::Trait {
+	/// The downward message handlers that will be informed when a message is received.
+	type DownwardMessageHandlers: DownwardMessageHandler;
+}
+
+decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		/// An entrypoint for an inherent to deposit downward messages into the runtime. It accepts
+		/// and processes the list of downward messages.
+		#[weight = (10, DispatchClass::Mandatory)]
+		fn receive_downward_messages(origin, messages: Vec<InboundDownwardMessage>) {
+			ensure_none(origin)?;
+
+			let messages_len = messages.len() as u32;
+			for message in messages {
+				T::DownwardMessageHandlers::handle_downward_message(message);
+			}
+
+			// Store the processed_downward_messages here so that it's will be accessible from
+			// PVF's `validate_block` wrapper and collation pipeline.
+			storage::unhashed::put(
+				well_known_keys::PROCESSED_DOWNWARD_MESSAGES,
+				&messages_len,
+			);
+		}
+	}
+}
+
+impl<T: Trait> ProvideInherent for Module<T> {
+	type Call = Call<T>;
+	type Error = MakeFatalError<()>;
+	const INHERENT_IDENTIFIER: InherentIdentifier = DOWNWARD_MESSAGES_IDENTIFIER;
+
+	fn create_inherent(data: &InherentData) -> Option<Self::Call> {
+		data.get_data::<DownwardMessagesType>(&DOWNWARD_MESSAGES_IDENTIFIER)
+			.expect("Downward messages inherent data failed to decode")
+			.map(|msgs| Call::receive_downward_messages(msgs))
+	}
+}

cumulus/primitives/src/lib.rs

@@ -73,7 +73,7 @@ pub mod well_known_keys {
 #[impl_trait_for_tuples::impl_for_tuples(30)]
 pub trait DownwardMessageHandler {
 	/// Handle the given downward message.
-	fn handle_downward_message(msg: &InboundDownwardMessage);
+	fn handle_downward_message(msg: InboundDownwardMessage);
 }
 
 /// A trait which is called when the validation data is set.

cumulus/rococo-parachains/runtime/Cargo.toml

@@ -37,6 +37,7 @@ pallet-transaction-payment = { git = "https://github.com/paritytech/substrate",
 cumulus-runtime = { path = "../../runtime", default-features = false }
 cumulus-parachain-upgrade = { path = "../../parachain-upgrade", default-features = false }
 cumulus-primitives = { path = "../../primitives", default-features = false }
+cumulus-message-broker = { path = "../../message-broker", default-features = false }
 
 # Polkadot dependencies
 polkadot-parachain = { git = "https://github.com/paritytech/polkadot", default-features = false , branch = "master" }
@@ -72,5 +73,6 @@ std = [
 	"rococo-parachain-primitives/std",
 	"cumulus-runtime/std",
 	"cumulus-parachain-upgrade/std",
+	"cumulus-message-broker/std",
 	"cumulus-primitives/std",
 ]

cumulus/rococo-parachains/runtime/src/lib.rs

@@ -200,6 +200,10 @@ impl cumulus_parachain_upgrade::Trait for Runtime {
 	type OnValidationData = ();
 }
 
+impl cumulus_message_broker::Trait for Runtime {
+	type DownwardMessageHandlers = ();
+}
+
 impl parachain_info::Trait for Runtime {}
 
 construct_runtime! {
@@ -214,6 +218,7 @@ construct_runtime! {
 		Sudo: pallet_sudo::{Module, Call, Storage, Config<T>, Event<T>},
 		RandomnessCollectiveFlip: pallet_randomness_collective_flip::{Module, Call, Storage},
 		ParachainUpgrade: cumulus_parachain_upgrade::{Module, Call, Storage, Inherent, Event},
+		MessageBroker: cumulus_message_broker::{Module, Call, Inherent},
 		TransactionPayment: pallet_transaction_payment::{Module, Storage},
 		ParachainInfo: parachain_info::{Module, Storage, Config},
 	}