Integrate a governance XCM origin (#407)

* Introduce the converter into the hub

* Parachain recognises Rococo governance body as admin

* Whitespace

* Use UsingComponents for fee payment in XCM

* Fixes

* Fixes for XCM permissions

* Remove encode_call test

* Fixes

* Fixes

* Fixes

pallets/xcm/src/lib.rs

@@ -20,13 +20,17 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use cumulus_primitives_core::ParaId;
+use sp_std::convert::TryFrom;
+use cumulus_primitives_core::{ParaId, DownwardMessageHandler, InboundDownwardMessage};
 use codec::{Encode, Decode};
 use sp_runtime::traits::BadOrigin;
+use xcm::{VersionedXcm, v0::{Xcm, Junction, Outcome, ExecuteXcm}};
+use frame_support::{traits::Get, dispatch::Weight};
 pub use pallet::*;
 
 #[frame_support::pallet]
 pub mod pallet {
+	use super::*;
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 
@@ -36,16 +40,68 @@ pub mod pallet {
 
 	/// The module configuration trait.
 	#[pallet::config]
-	pub trait Config: frame_system::Config {}
+	pub trait Config: frame_system::Config {
+		/// The overarching event type.
+		type Event: From<Event<Self>> + IsType<<Self as frame_system::Config>::Event>;
+
+		type XcmExecutor: ExecuteXcm<Self::Call>;
+
+		#[pallet::constant]
+		type MaxWeight: Get<Weight>;
+	}
 
 	#[pallet::error]
-	pub enum Error<T> {}
+	pub enum Error<T> {
+	}
 
 	#[pallet::hooks]
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
 
 	#[pallet::call]
 	impl<T: Config> Pallet<T> {}
+
+	#[pallet::event]
+	#[pallet::generate_deposit(pub(super) fn deposit_event)]
+	#[pallet::metadata(T::BlockNumber = "BlockNumber")]
+	pub enum Event<T: Config> {
+		/// Downward message is invalid XCM.
+		/// \[ id \]
+		InvalidFormat([u8; 8]),
+		/// Downward message is unsupported version of XCM.
+		/// \[ id \]
+		UnsupportedVersion([u8; 8]),
+		/// Downward message executed with the given outcome.
+		/// \[ id, outcome \]
+		ExecutedDownward([u8; 8], Outcome),
+	}
+
+	/// For an incoming downward message, this just adapts an XCM executor and executes DMP messages
+	/// immediately up until some `MaxWeight` at which point it errors. Their origin is asserted to be
+	/// the Parent location.
+	impl<T: Config> DownwardMessageHandler for Pallet<T> {
+		fn handle_downward_message(msg: InboundDownwardMessage) -> Weight {
+			let id = sp_io::hashing::twox_64(&msg.msg[..]);
+			let msg = VersionedXcm::<T::Call>::decode(&mut &msg.msg[..])
+				.map(Xcm::<T::Call>::try_from);
+			match msg {
+				Ok(Ok(x)) => {
+					let weight_limit = T::MaxWeight::get();
+					let outcome = T::XcmExecutor::execute_xcm(Junction::Parent.into(), x, weight_limit);
+					let weight_used = outcome.weight_used();
+					Self::deposit_event(Event::ExecutedDownward(id, outcome));
+					weight_used
+				}
+				Ok(Err(())) => {
+					Self::deposit_event(Event::UnsupportedVersion(id));
+					0
+				},
+				Err(_) => {
+					Self::deposit_event(Event::InvalidFormat(id));
+					0
+				},
+			}
+		}
+	}
 }
 
 /// Origin for the parachains module.