more refactoring

polkadot/xcm/src/lib.rs

@@ -29,17 +29,22 @@ use derivative::Derivative;
 use frame_support::dispatch::GetDispatchInfo;
 use scale_info::TypeInfo;
 
+mod xcm;
+pub (crate) use xcm::XcmBase;
+
 pub mod v3;
 pub mod v4;
 pub mod v5;
 pub mod v6;
+pub mod traits;
 
 pub mod lts {
 	pub use super::v4::*;
 }
 
 pub mod latest {
-	pub use super::v5::*;
+	pub use super::v6::*;
+	pub use crate::traits::*;
 }
 
 mod double_encoded;
@@ -518,7 +523,7 @@ pub type AlwaysLts = AlwaysV4;
 
 pub mod prelude {
 	pub use super::{
-		latest::prelude::*, AlwaysLatest, AlwaysLts, AlwaysV3, AlwaysV4, AlwaysV5, GetVersion,
+		latest::{prelude::*, SendXcm}, AlwaysLatest, AlwaysLts, AlwaysV3, AlwaysV4, AlwaysV5, GetVersion,
 		IdentifyVersion, IntoVersion, Unsupported, Version as XcmVersion, VersionedAsset,
 		VersionedAssetId, VersionedAssets, VersionedInteriorLocation, VersionedLocation,
 		VersionedResponse, VersionedXcm, WrapVersion,

polkadot/xcm/src/traits.rs

@@ -0,0 +1,336 @@
+// Copyright (C) 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/>.
+
+use alloc::fmt::Debug;
+use core::result;
+use crate::latest::prelude::*;
+use crate::latest::{Result, Error};
+
+pub trait IntoInstruction<Instruction> {
+	fn into_instruction(self) -> Instruction;
+}
+
+pub trait WeightProvider<Instruction> {
+	fn get_weight(inst: &Instruction) -> sp_weights::Weight;
+}
+
+pub trait PreparedMessage {
+	fn weight_of(&self) -> Weight;
+}
+
+pub enum Weightless {}
+impl PreparedMessage for Weightless {
+	fn weight_of(&self) -> Weight {
+		unreachable!()
+	}
+}
+
+/// Type of XCM message executor.
+pub trait ExecuteXcm<Call> {
+	type Prepared: PreparedMessage;
+	fn prepare(message: Xcm<Call>) -> result::Result<Self::Prepared, Xcm<Call>>;
+	fn execute(
+		origin: impl Into<Location>,
+		pre: Self::Prepared,
+		id: &mut XcmHash,
+		weight_credit: Weight,
+	) -> Outcome;
+	fn prepare_and_execute(
+		origin: impl Into<Location>,
+		message: Xcm<Call>,
+		id: &mut XcmHash,
+		weight_limit: Weight,
+		weight_credit: Weight,
+	) -> Outcome {
+		let pre = match Self::prepare(message) {
+			Ok(x) => x,
+			Err(_) => return Outcome::Error { error: Error::WeightNotComputable },
+		};
+		let xcm_weight = pre.weight_of();
+		if xcm_weight.any_gt(weight_limit) {
+			return Outcome::Error { error: Error::WeightLimitReached(xcm_weight) }
+		}
+		Self::execute(origin, pre, id, weight_credit)
+	}
+
+	/// Deduct some `fees` to the sovereign account of the given `location` and place them as per
+	/// the convention for fees.
+	fn charge_fees(location: impl Into<Location>, fees: Assets) -> Result;
+}
+
+impl<C> ExecuteXcm<C> for () {
+	type Prepared = Weightless;
+	fn prepare(message: Xcm<C>) -> result::Result<Self::Prepared, Xcm<C>> {
+		Err(message)
+	}
+	fn execute(_: impl Into<Location>, _: Self::Prepared, _: &mut XcmHash, _: Weight) -> Outcome {
+		unreachable!()
+	}
+	fn charge_fees(_location: impl Into<Location>, _fees: Assets) -> Result {
+		Err(Error::Unimplemented)
+	}
+}
+
+pub trait Reanchorable: Sized {
+	/// Type to return in case of an error.
+	type Error: Debug;
+
+	/// Mutate `self` so that it represents the same location from the point of view of `target`.
+	/// The context of `self` is provided as `context`.
+	///
+	/// Does not modify `self` in case of overflow.
+	fn reanchor(
+		&mut self,
+		target: &Location,
+		context: &InteriorLocation,
+	) -> core::result::Result<(), ()>;
+
+	/// Consume `self` and return a new value representing the same location from the point of view
+	/// of `target`. The context of `self` is provided as `context`.
+	///
+	/// Returns the original `self` in case of overflow.
+	fn reanchored(
+		self,
+		target: &Location,
+		context: &InteriorLocation,
+	) -> core::result::Result<Self, Self::Error>;
+}
+
+impl Reanchorable for AssetId {
+	type Error = ();
+
+	/// Mutate the asset to represent the same value from the perspective of a new `target`
+	/// location. The local chain's location is provided in `context`.
+	fn reanchor(&mut self, target: &Location, context: &InteriorLocation) -> result::Result<(), ()> {
+		self.0.reanchor(target, context)?;
+		Ok(())
+	}
+
+	fn reanchored(mut self, target: &Location, context: &InteriorLocation) -> result::Result<Self, ()> {
+		match self.reanchor(target, context) {
+			Ok(()) => Ok(self),
+			Err(()) => Err(()),
+		}
+	}
+}
+
+impl Reanchorable for Location {
+	type Error = Self;
+
+	/// Mutate `self` so that it represents the same location from the point of view of `target`.
+	/// The context of `self` is provided as `context`.
+	///
+	/// Does not modify `self` in case of overflow.
+	fn reanchor(&mut self, target: &Location, context: &InteriorLocation) -> result::Result<(), ()> {
+		// TODO: https://github.com/paritytech/polkadot/issues/4489 Optimize this.
+
+		// 1. Use our `context` to figure out how the `target` would address us.
+		let inverted_target = context.invert_target(target)?;
+
+		// 2. Prepend `inverted_target` to `self` to get self's location from the perspective of
+		// `target`.
+		self.prepend_with(inverted_target).map_err(|_| ())?;
+
+		// 3. Given that we know some of `target` context, ensure that any parents in `self` are
+		// strictly needed.
+		self.simplify(target.interior());
+
+		Ok(())
+	}
+
+	/// Consume `self` and return a new value representing the same location from the point of view
+	/// of `target`. The context of `self` is provided as `context`.
+	///
+	/// Returns the original `self` in case of overflow.
+	fn reanchored(mut self, target: &Location, context: &InteriorLocation) -> result::Result<Self, Self> {
+		match self.reanchor(target, context) {
+			Ok(()) => Ok(self),
+			Err(()) => Err(self),
+		}
+	}
+}
+
+/// Result value when attempting to send an XCM message.
+pub type SendResult<T> = result::Result<(T, Assets), SendError>;
+
+/// Utility for sending an XCM message to a given location.
+///
+/// These can be amalgamated in tuples to form sophisticated routing systems. In tuple format, each
+/// router might return `NotApplicable` to pass the execution to the next sender item. Note that
+/// each `NotApplicable` might alter the destination and the XCM message for to the next router.
+///
+/// # Example
+/// ```rust
+/// # use codec::Encode;
+/// # use staging_xcm::latest::{prelude::*, Weight};
+/// # use staging_xcm::VersionedXcm;
+/// # use std::convert::Infallible;
+///
+/// /// A sender that only passes the message through and does nothing.
+/// struct Sender1;
+/// impl SendXcm for Sender1 {
+///     type Ticket = Infallible;
+///     fn validate(_: &mut Option<Location>, _: &mut Option<Xcm<()>>) -> SendResult<Infallible> {
+///         Err(SendError::NotApplicable)
+///     }
+///     fn deliver(_: Infallible) -> Result<XcmHash, SendError> {
+///         unreachable!()
+///     }
+/// }
+///
+/// /// A sender that accepts a message that has two junctions, otherwise stops the routing.
+/// struct Sender2;
+/// impl SendXcm for Sender2 {
+///     type Ticket = ();
+///     fn validate(destination: &mut Option<Location>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
+///         match destination.as_ref().ok_or(SendError::MissingArgument)?.unpack() {
+///             (0, [j1, j2]) => Ok(((), Assets::new())),
+///             _ => Err(SendError::Unroutable),
+///         }
+///     }
+///     fn deliver(_: ()) -> Result<XcmHash, SendError> {
+///         Ok([0; 32])
+///     }
+/// }
+///
+/// /// A sender that accepts a message from a parent, passing through otherwise.
+/// struct Sender3;
+/// impl SendXcm for Sender3 {
+///     type Ticket = ();
+///     fn validate(destination: &mut Option<Location>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
+///         match destination.as_ref().ok_or(SendError::MissingArgument)?.unpack() {
+///             (1, []) => Ok(((), Assets::new())),
+///             _ => Err(SendError::NotApplicable),
+///         }
+///     }
+///     fn deliver(_: ()) -> Result<XcmHash, SendError> {
+///         Ok([0; 32])
+///     }
+/// }
+///
+/// // A call to send via XCM. We don't really care about this.
+/// # fn main() {
+/// let call: Vec<u8> = ().encode();
+/// let message = Xcm(vec![Instruction::Transact {
+///     origin_kind: OriginKind::Superuser,
+///     call: call.into(),
+///     fallback_max_weight: None,
+/// }]);
+/// let message_hash = message.using_encoded(sp_io::hashing::blake2_256);
+///
+/// // Sender2 will block this.
+/// assert!(send_xcm::<(Sender1, Sender2, Sender3)>(Parent.into(), message.clone()).is_err());
+///
+/// // Sender3 will catch this.
+/// assert!(send_xcm::<(Sender1, Sender3)>(Parent.into(), message.clone()).is_ok());
+/// # }
+/// ```
+pub trait SendXcm {
+	/// Intermediate value which connects the two phases of the send operation.
+	type Ticket;
+
+	/// Check whether the given `_message` is deliverable to the given `_destination` and if so
+	/// determine the cost which will be paid by this chain to do so, returning a `Validated` token
+	/// which can be used to enact delivery.
+	///
+	/// The `destination` and `message` must be `Some` (or else an error will be returned) and they
+	/// may only be consumed if the `Err` is not `NotApplicable`.
+	///
+	/// If it is not a destination which can be reached with this type but possibly could by others,
+	/// then this *MUST* return `NotApplicable`. Any other error will cause the tuple
+	/// implementation to exit early without trying other type fields.
+	fn validate(
+		destination: &mut Option<Location>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket>;
+
+	/// Actually carry out the delivery operation for a previously validated message sending.
+	fn deliver(ticket: Self::Ticket) -> result::Result<XcmHash, SendError>;
+
+	/// Ensure `[Self::delivery]` is successful for the given `location` when called in benchmarks.
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful_delivery(_location: Option<Location>) {}
+}
+
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+impl SendXcm for Tuple {
+	for_tuples! { type Ticket = (#( Option<Tuple::Ticket> ),* ); }
+
+	fn validate(
+		destination: &mut Option<Location>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket> {
+		let mut maybe_cost: Option<Assets> = None;
+		let one_ticket: Self::Ticket = (for_tuples! { #(
+			if maybe_cost.is_some() {
+				None
+			} else {
+				match Tuple::validate(destination, message) {
+					Err(SendError::NotApplicable) => None,
+					Err(e) => { return Err(e) },
+					Ok((v, c)) => {
+						maybe_cost = Some(c);
+						Some(v)
+					},
+				}
+			}
+		),* });
+		if let Some(cost) = maybe_cost {
+			Ok((one_ticket, cost))
+		} else {
+			Err(SendError::NotApplicable)
+		}
+	}
+
+	fn deliver(one_ticket: Self::Ticket) -> result::Result<XcmHash, SendError> {
+		for_tuples!( #(
+			if let Some(validated) = one_ticket.Tuple {
+				return Tuple::deliver(validated);
+			}
+		)* );
+		Err(SendError::Unroutable)
+	}
+
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful_delivery(location: Option<Location>) {
+		for_tuples!( #(
+			return Tuple::ensure_successful_delivery(location.clone());
+		)* );
+	}
+}
+
+/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
+/// both in `Some` before passing them as mutable references into `T::send_xcm`.
+pub fn validate_send<T: SendXcm>(dest: Location, msg: Xcm<()>) -> SendResult<T::Ticket> {
+	T::validate(&mut Some(dest), &mut Some(msg))
+}
+
+/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
+/// both in `Some` before passing them as mutable references into `T::send_xcm`.
+///
+/// Returns either `Ok` with the price of the delivery, or `Err` with the reason why the message
+/// could not be sent.
+///
+/// Generally you'll want to validate and get the price first to ensure that the sender can pay it
+/// before actually doing the delivery.
+pub fn send_xcm<T: SendXcm>(
+	dest: Location,
+	msg: Xcm<()>,
+) -> result::Result<(XcmHash, Assets), SendError> {
+	let (ticket, price) = T::validate(&mut Some(dest), &mut Some(msg))?;
+	let hash = T::deliver(ticket)?;
+	Ok((hash, price))
+}