traits.rs 8.97 KB
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// 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/>.

//! Cross-Consensus Message format data structures.

use core::result;
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use parity_scale_codec::{Encode, Decode};
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use super::{MultiLocation, Xcm};

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#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug)]
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pub enum Error {
	Undefined,
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	Overflow,
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	/// The operation is intentionally unsupported.
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	Unimplemented,
	UnhandledXcmVersion,
	UnhandledXcmMessage,
	UnhandledEffect,
	EscalationOfPrivilege,
	UntrustedReserveLocation,
	UntrustedTeleportLocation,
	DestinationBufferOverflow,
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	/// The message and destination was recognized as being reachable but the operation could not be completed.
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	/// A human-readable explanation of the specific issue is provided.
	SendFailed(#[codec(skip)] &'static str),
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	/// The message and destination combination was not recognized as being reachable.
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	CannotReachDestination(MultiLocation, Xcm<()>),
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	MultiLocationFull,
	FailedToDecode,
	BadOrigin,
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	ExceedsMaxMessageSize,
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	FailedToTransactAsset(#[codec(skip)] &'static str),
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	/// Execution of the XCM would potentially result in a greater weight used than the pre-specified
	/// weight limit. The amount that is potentially required is the parameter.
	WeightLimitReached(Weight),
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	Wildcard,
	/// The case where an XCM message has specified a optional weight limit and the weight required for
	/// processing is too great.
	///
	/// Used by:
	/// - `Transact`
	TooMuchWeightRequired,
	/// The fees specified by the XCM message were not found in the holding account.
	///
	/// Used by:
	/// - `BuyExecution`
	NotHoldingFees,
	/// The weight of an XCM message is not computable ahead of execution. This generally means at least part
	/// of the message is invalid, which could be due to it containing overly nested structures or an invalid
	/// nested data segment (e.g. for the call in `Transact`).
	WeightNotComputable,
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	/// The XCM did not pass the barrier condition for execution. The barrier condition differs on different
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	/// chains and in different circumstances, but generally it means that the conditions surrounding the message
	/// were not such that the chain considers the message worth spending time executing. Since most chains
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	/// lift the barrier to execution on appropriate payment, presentation of an NFT voucher, or based on the
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	/// message origin, it means that none of those were the case.
	Barrier,
	/// Indicates that it is not possible for a location to have an asset be withdrawn or transferred from its
	/// ownership. This probably means it doesn't own (enough of) it, but may also indicate that it is under a
	/// lock, hold, freeze or is otherwise unavailable.
	NotWithdrawable,
	/// Indicates that the consensus system cannot deposit an asset under the ownership of a particular location.
	LocationCannotHold,
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	/// The assets given to purchase weight is are insufficient for the weight desired.
	TooExpensive,
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	/// The given asset is not handled.
	AssetNotFound,
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}

impl From<()> for Error {
	fn from(_: ()) -> Self {
		Self::Undefined
	}
}

pub type Result = result::Result<(), Error>;

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/// Local weight type; execution time in picoseconds.
pub type Weight = u64;

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/// Outcome of an XCM execution.
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#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug)]
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pub enum Outcome {
	/// Execution completed successfully; given weight was used.
	Complete(Weight),
	/// Execution started, but did not complete successfully due to the given error; given weight was used.
	Incomplete(Weight, Error),
	/// Execution did not start due to the given error.
	Error(Error),
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}

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impl Outcome {
	pub fn ensure_complete(self) -> Result {
		match self {
			Outcome::Complete(_) => Ok(()),
			Outcome::Incomplete(_, e) => Err(e),
			Outcome::Error(e) => Err(e),
		}
	}
	pub fn ensure_execution(self) -> result::Result<Weight, Error> {
		match self {
			Outcome::Complete(w) => Ok(w),
			Outcome::Incomplete(w, _) => Ok(w),
			Outcome::Error(e) => Err(e),
		}
	}
	/// How much weight was used by the XCM execution attempt.
	pub fn weight_used(&self) -> Weight {
		match self {
			Outcome::Complete(w) => *w,
			Outcome::Incomplete(w, _) => *w,
			Outcome::Error(_) => 0,
		}
	}
}

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/// Type of XCM message executor.
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pub trait ExecuteXcm<Call> {
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	/// Execute some XCM `message` from `origin` using no more than `weight_limit` weight. The weight limit is
	/// a basic hard-limit and the implementation may place further restrictions or requirements on weight and
	/// other aspects.
	fn execute_xcm(origin: MultiLocation, message: Xcm<Call>, weight_limit: Weight) -> Outcome {
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		log::debug!(
			target: "xcm::execute_xcm",
			"origin: {:?}, message: {:?}, weight_limit: {:?}",
			origin,
			message,
			weight_limit,
		);
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		Self::execute_xcm_in_credit(origin, message, weight_limit, 0)
	}

	/// Execute some XCM `message` from `origin` using no more than `weight_limit` weight.
	///
	/// Some amount of `weight_credit` may be provided which, depending on the implementation, may allow
	/// execution without associated payment.
	fn execute_xcm_in_credit(
		origin: MultiLocation,
		message: Xcm<Call>,
		weight_limit: Weight,
		weight_credit: Weight,
	) -> Outcome;
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}

impl<C> ExecuteXcm<C> for () {
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	fn execute_xcm_in_credit(
		_origin: MultiLocation,
		_message: Xcm<C>,
		_weight_limit: Weight,
		_weight_credit: Weight,
	) -> Outcome {
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		Outcome::Error(Error::Unimplemented)
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	}
}

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/// Utility for sending an XCM message.
///
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/// These can be amalgamated in tuples to form sophisticated routing systems. In tuple format, each router might return
/// `CannotReachDestination` to pass the execution to the next sender item. Note that each `CannotReachDestination`
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/// might alter the destination and the XCM message for to the next router.
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///
///
/// # Example
/// ```rust
/// # use xcm::v0::{MultiLocation, Xcm, Junction, Error, OriginKind, SendXcm, Result};
/// # use parity_scale_codec::Encode;
///
/// /// A sender that only passes the message through and does nothing.
/// struct Sender1;
/// impl SendXcm for Sender1 {
///     fn send_xcm(destination: MultiLocation, message: Xcm<()>) -> Result {
///         return Err(Error::CannotReachDestination(destination, message))
///     }
/// }
///
/// /// A sender that accepts a message that has an X2 junction, otherwise stops the routing.
/// struct Sender2;
/// impl SendXcm for Sender2 {
///     fn send_xcm(destination: MultiLocation, message: Xcm<()>) -> Result {
///         if let MultiLocation::X2(j1, j2) = destination {
///             Ok(())
///         } else {
///             Err(Error::Undefined)
///         }
///     }
/// }
///
/// /// A sender that accepts a message from an X1 parent junction, passing through otherwise.
/// struct Sender3;
/// impl SendXcm for Sender3 {
///     fn send_xcm(destination: MultiLocation, message: Xcm<()>) -> Result {
///         match destination {
///             MultiLocation::X1(j) if j == Junction::Parent => Ok(()),
///             _ => Err(Error::CannotReachDestination(destination, message)),
///         }
///     }
/// }
///
/// // A call to send via XCM. We don't really care about this.
/// # fn main() {
/// let call: Vec<u8> = ().encode();
/// let message = Xcm::Transact { origin_type: OriginKind::Superuser, require_weight_at_most: 0, call: call.into() };
/// let destination = MultiLocation::X1(Junction::Parent);
///
/// assert!(
///     // Sender2 will block this.
///     <(Sender1, Sender2, Sender3) as SendXcm>::send_xcm(destination.clone(), message.clone())
///         .is_err()
/// );
///
/// assert!(
///     // Sender3 will catch this.
///     <(Sender1, Sender3) as SendXcm>::send_xcm(destination.clone(), message.clone())
///         .is_ok()
/// );
/// # }
/// ```
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pub trait SendXcm {
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	/// Send an XCM `message` to a given `destination`.
	///
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	/// If it is not a destination which can be reached with this type but possibly could by others, then it *MUST*
	/// return `CannotReachDestination`. Any other error will cause the tuple implementation to exit early without
	/// trying other type fields.
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	fn send_xcm(destination: MultiLocation, message: Xcm<()>) -> Result;
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}

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#[impl_trait_for_tuples::impl_for_tuples(30)]
impl SendXcm for Tuple {
	fn send_xcm(destination: MultiLocation, message: Xcm<()>) -> Result {
		for_tuples!( #(
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			// we shadow `destination` and `message` in each expansion for the next one.
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			let (destination, message) = match Tuple::send_xcm(destination, message) {
				Err(Error::CannotReachDestination(d, m)) => (d, m),
				o @ _ => return o,
			};
		)* );
		Err(Error::CannotReachDestination(destination, message))
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	}
}