XCM: Implement a blocking barrier

xcm/pallet-xcm/src/lib.rs

@@ -52,7 +52,8 @@ use frame_system::pallet_prelude::*;
 pub use pallet::*;
 use xcm_executor::{
 	traits::{
-		ClaimAssets, DropAssets, MatchesFungible, OnResponse, VersionChangeNotifier, WeightBounds,
+		CheckSuspension, ClaimAssets, DropAssets, MatchesFungible, OnResponse,
+		VersionChangeNotifier, WeightBounds,
 	},
 	Assets,
 };
@@ -66,6 +67,7 @@ pub trait WeightInfo {
 	fn force_default_xcm_version() -> Weight;
 	fn force_subscribe_version_notify() -> Weight;
 	fn force_unsubscribe_version_notify() -> Weight;
+	fn force_suspension() -> Weight;
 	fn migrate_supported_version() -> Weight;
 	fn migrate_version_notifiers() -> Weight;
 	fn already_notified_target() -> Weight;
@@ -110,6 +112,10 @@ impl WeightInfo for TestWeightInfo {
 		Weight::from_parts(100_000_000, 0)
 	}
 
+	fn force_suspension() -> Weight {
+		Weight::from_parts(100_000_000, 0)
+	}
+
 	fn migrate_supported_version() -> Weight {
 		Weight::from_parts(100_000_000, 0)
 	}
@@ -612,6 +618,10 @@ pub mod pallet {
 		OptionQuery,
 	>;
 
+	/// Global suspension state of the XCM executor.
+	#[pallet::storage]
+	pub(super) type XcmExecutionSuspended<T: Config> = StorageValue<_, bool, ValueQuery>;
+
 	#[pallet::genesis_config]
 	pub struct GenesisConfig {
 		/// The default version to encode outgoing XCM messages with.
@@ -908,7 +918,7 @@ pub mod pallet {
 		/// Extoll that a particular destination can be communicated with through a particular
 		/// version of XCM.
 		///
-		/// - `origin`: Must be Root.
+		/// - `origin`: Must be an origin specified by AdminOrigin.
 		/// - `location`: The destination that is being described.
 		/// - `xcm_version`: The latest version of XCM that `location` supports.
 		#[pallet::call_index(4)]
@@ -932,7 +942,7 @@ pub mod pallet {
 		/// Set a safe XCM version (the version that XCM should be encoded with if the most recent
 		/// version a destination can accept is unknown).
 		///
-		/// - `origin`: Must be Root.
+		/// - `origin`: Must be an origin specified by AdminOrigin.
 		/// - `maybe_xcm_version`: The default XCM encoding version, or `None` to disable.
 		#[pallet::call_index(5)]
 		#[pallet::weight(T::WeightInfo::force_default_xcm_version())]
@@ -947,7 +957,7 @@ pub mod pallet {
 
 		/// Ask a location to notify us regarding their XCM version and any changes to it.
 		///
-		/// - `origin`: Must be Root.
+		/// - `origin`: Must be an origin specified by AdminOrigin.
 		/// - `location`: The location to which we should subscribe for XCM version notifications.
 		#[pallet::call_index(6)]
 		#[pallet::weight(T::WeightInfo::force_subscribe_version_notify())]
@@ -970,7 +980,7 @@ pub mod pallet {
 		/// Require that a particular destination should no longer notify us regarding any XCM
 		/// version changes.
 		///
-		/// - `origin`: Must be Root.
+		/// - `origin`: Must be an origin specified by AdminOrigin.
 		/// - `location`: The location to which we are currently subscribed for XCM version
 		///   notifications which we no longer desire.
 		#[pallet::call_index(7)]
@@ -1092,6 +1102,18 @@ pub mod pallet {
 				Some(weight_limit),
 			)
 		}
+
+		/// Set or unset the global suspension state of the XCM executor.
+		///
+		/// - `origin`: Must be an origin specified by AdminOrigin.
+		/// - `suspended`: `true` to suspend, `false` to resume.
+		#[pallet::call_index(10)]
+		#[pallet::weight(T::WeightInfo::force_suspension())]
+		pub fn force_suspension(origin: OriginFor<T>, suspended: bool) -> DispatchResult {
+			T::AdminOrigin::ensure_origin(origin)?;
+			XcmExecutionSuspended::<T>::set(suspended);
+			Ok(())
+		}
 	}
 }
 
@@ -2040,6 +2062,17 @@ impl<T: Config> OnResponse for Pallet<T> {
 	}
 }
 
+impl<T: Config> CheckSuspension for Pallet<T> {
+	fn is_suspended<Call>(
+		_origin: &MultiLocation,
+		_instructions: &mut [Instruction<Call>],
+		_max_weight: Weight,
+		_weight_credit: &mut Weight,
+	) -> bool {
+		XcmExecutionSuspended::<T>::get()
+	}
+}
+
 /// Ensure that the origin `o` represents an XCM (`Transact`) origin.
 ///
 /// Returns `Ok` with the location of the XCM sender or an `Err` otherwise.

xcm/src/lib.rs

@@ -23,7 +23,6 @@
 #![no_std]
 extern crate alloc;
 
-use core::ops::ControlFlow;
 use derivative::Derivative;
 use parity_scale_codec::{Decode, Encode, Error as CodecError, Input, MaxEncodedLen};
 use scale_info::TypeInfo;
@@ -51,89 +50,6 @@ pub const MAX_XCM_DECODE_DEPTH: u32 = 8;
 /// A version of XCM.
 pub type Version = u32;
 
-/// Creates an instruction matcher from an XCM. Since XCM versions differ, we need to make a trait
-/// here to unify the interfaces among them.
-pub trait CreateMatcher {
-	/// The concrete matcher type.
-	type Matcher;
-
-	/// Method that creates and returns the matcher type from `Self`.
-	fn matcher(self) -> Self::Matcher;
-}
-
-/// API that allows to pattern-match against anything that is contained within an XCM.
-///
-/// The intended usage of the matcher API is to enable the ability to chain successive methods of
-/// this trait together, along with the ? operator for the purpose of facilitating the writing,
-/// maintenance and auditability of XCM barriers.
-///
-/// Example:
-/// ```rust
-/// use xcm::{
-/// 	v3::{Instruction, Matcher},
-/// 	CreateMatcher, MatchXcm,
-/// };
-///
-/// let mut msg = [Instruction::<()>::ClearOrigin];
-/// let res = msg
-/// 	.matcher()
-/// 	.assert_remaining_insts(1)?
-/// 	.match_next_inst(|inst| match inst {
-/// 		Instruction::<()>::ClearOrigin => Ok(()),
-/// 		_ => Err(()),
-/// 	});
-/// assert!(res.is_ok());
-///
-/// Ok::<(), ()>(())
-/// ```
-pub trait MatchXcm {
-	/// The concrete instruction type. Necessary to specify as it changes between XCM versions.
-	type Inst;
-	/// The `MultiLocation` type. Necessary to specify as it changes between XCM versions.
-	type Loc;
-	/// The error type to throw when errors happen during matching.
-	type Error;
-
-	/// Returns success if the number of instructions that still have not been iterated over
-	/// equals `n`, otherwise returns an error.
-	fn assert_remaining_insts(self, n: usize) -> Result<Self, Self::Error>
-	where
-		Self: Sized;
-
-	/// Accepts a closure `f` that contains an argument signifying the next instruction to be
-	/// iterated over. The closure can then be used to check whether the instruction matches a
-	/// given condition, and can also be used to mutate the fields of an instruction.
-	///
-	/// The closure `f` returns success when the instruction passes the condition, otherwise it
-	/// returns an error, which will ultimately be returned by this function.
-	fn match_next_inst<F>(self, f: F) -> Result<Self, Self::Error>
-	where
-		Self: Sized,
-		F: FnMut(&mut Self::Inst) -> Result<(), Self::Error>;
-
-	/// Attempts to continuously iterate through the instructions while applying `f` to each of
-	/// them, until either the last instruction or `cond` returns false.
-	///
-	/// If `f` returns an error, then iteration halts and the function returns that error.
-	/// Otherwise, `f` returns a `ControlFlow` which signifies whether the iteration breaks or
-	/// continues.
-	fn match_next_inst_while<C, F>(self, cond: C, f: F) -> Result<Self, Self::Error>
-	where
-		Self: Sized,
-		C: Fn(&Self::Inst) -> bool,
-		F: FnMut(&mut Self::Inst) -> Result<ControlFlow<()>, Self::Error>;
-
-	/// Iterate instructions forward until `cond` returns false. When there are no more instructions
-	/// to be read, an error is returned.
-	fn skip_inst_while<C>(self, cond: C) -> Result<Self, Self::Error>
-	where
-		Self: Sized,
-		C: Fn(&Self::Inst) -> bool,
-	{
-		Self::match_next_inst_while(self, cond, |_| Ok(ControlFlow::Continue(())))
-	}
-}
-
 #[derive(Clone, Eq, PartialEq, Debug)]
 pub enum Unsupported {}
 impl Encode for Unsupported {}

xcm/src/v3/mod.rs

@@ -34,14 +34,12 @@ use scale_info::TypeInfo;
 
 mod junction;
 pub(crate) mod junctions;
-mod matcher;
 mod multiasset;
 mod multilocation;
 mod traits;
 
 pub use junction::{BodyId, BodyPart, Junction, NetworkId};
 pub use junctions::Junctions;
-pub use matcher::Matcher;
 pub use multiasset::{
 	AssetId, AssetInstance, Fungibility, MultiAsset, MultiAssetFilter, MultiAssets,
 	WildFungibility, WildMultiAsset,