lib.rs

// Copyright 2020-2021 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/>.

//! Helper datatypes for cumulus. This includes the [`ParentAsUmp`] routing type which will route
//! messages into an [`UpwardMessageSender`] if the destination is `Parent`.

#![cfg_attr(not(feature = "std"), no_std)]

use sp_std::marker::PhantomData;
use codec::Encode;
use cumulus_primitives_core::UpwardMessageSender;
use xcm::{WrapVersion, latest::prelude::*};

/// Xcm router which recognises the `Parent` destination and handles it by sending the message into
/// the given UMP `UpwardMessageSender` implementation. Thus this essentially adapts an
/// `UpwardMessageSender` trait impl into a `SendXcm` trait impl.
///
/// NOTE: This is a pretty dumb "just send it" router; we will probably want to introduce queuing
/// to UMP eventually and when we do, the pallet which implements the queuing will be responsible
/// for the `SendXcm` implementation.
pub struct ParentAsUmp<T, W>(PhantomData<(T, W)>);
impl<T: UpwardMessageSender, W: WrapVersion> SendXcm for ParentAsUmp<T, W> {
	fn send_xcm(dest: MultiLocation, msg: Xcm<()>) -> Result<(), XcmError> {
		if dest.contains_parents_only(1) {
			// An upward message for the relay chain.
			let versioned_xcm = W::wrap_version(&dest, msg)
				.map_err(|()| XcmError::DestinationUnsupported)?;
			let data = versioned_xcm.encode();

			T::send_upward_message(data)
				.map_err(|e| XcmError::SendFailed(e.into()))?;

			Ok(())
		} else {
			// Anything else is unhandled. This includes a message this is meant for us.
			Err(XcmError::CannotReachDestination(dest, msg))
		}
	}
}