Implement basic upward & downward messages (#118)

* Start by replacing branch names and set `DownwardMessage`

* Add the upward-message crate

* Add Kusama & Polkadot

* More work on getting the upward messages working

* Fix build

* Begin to integrate it into the test Parachain

* Update

* Make everything compile again

* Switch to westend and print parachain account on startup

* Use MultiSignature etc

* Fix validate block

* Some downward messages work

* Update git reference

* More downward messages integration

* Update test runtime for downward messages

* Enable downward message handler and withdraw send tokens

* Add some docs

* Begin to implement simple XCMP

* More work

* Fixes and make parachain id configurable

* Make parachain ID be part of the genesis

* Finishing the XCMP message demo

* Update and fixes tests

* Update branch

primitives/src/xcmp.rs

@@ -0,0 +1,42 @@
+// 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/>.
+
+//! XMCP related primitives
+
+use polkadot_primitives::parachain::Id as ParaId;
+use sp_std::vec::Vec;
+
+/// A raw XCMP message that is being send between two Parachain's.
+#[derive(codec::Encode, codec::Decode)]
+pub struct RawXCMPMessage {
+	/// Parachain sending the message.
+	pub from: ParaId,
+	/// SCALE encoded message.
+	pub data: Vec<u8>,
+}
+
+/// Something that can handle XCMP messages.
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+pub trait XCMPMessageHandler<Message: codec::Decode> {
+	/// Handle a XCMP message.
+	fn handle_xcmp_message(src: ParaId, msg: &Message);
+}
+
+/// Something that can send XCMP messages.
+pub trait XCMPMessageSender<Message: codec::Encode> {
+	/// Send a XCMP message to the given parachain.
+	fn send_xcmp_message(dest: ParaId, msg: &Message) -> Result<(), ()>;
+}