XCM Executor

Branch/Release: release-polkadot-v1.10.0

Source Code

Purpose

XcmExecutor is responsible for executing XCM messages locally.

XcmExecutor is usually the assignment for pallet_xcm::Config::XcmExecutor and is thereby used to execute XCM in that pallet.

Note XcmExecutor is not a pallet, but rather it is a struct type parameterized by a Config trait. The inner config is the trait Config which parameterizes the outer config struct XcmExecutor<Config>. Both the inner and outer configs are configured in the runtime.

Inner Config

The inner trait Config used to parameterize XcmExecutor has the following associated types.

• Handlers:
  • XcmSender -- How to send an onward XCM message. Type must implement the trait SendXcm.
  • AssetTransactor -- How to withdraw and deposit an asset. Type must implement the trait TransactAsset.
  • Trader -- The means of purchasing weight credit for XCM execution. Type must implement the trait WeightTrader.
  • ResponseHandler -- What to do when a response of a query is found. Type must implement the trait OnResponse.
  • AssetTrap -- The general asset trap handler for when assets are left in the Holding Register at the end of execution. Type must implement the trait DropAssets.
  • AssetLocker -- Handler for asset locking. Type must implement the trait AssetLock.
  • AssetExchanger -- Handler for exchanging assets. Type must implement the trait AssetExchange.
  • AssetClaims -- The handler for when there is an instruction to claim assets. Type must implement the trait ClaimAssets.
  • SubscriptionService -- The handler for version subscription requests. Type must implement the trait VersionChangeNotifier.
  • FeeManager -- Configure the fees. Type must implement the trait FeeManager.
  • MessageExporter -- The method of exporting a message. Type must implement the trait ExportXcm.
  • CallDispatcher -- The call dispatcher used by XCM. Type must implement the trait CallDispatcher<Self::RuntimeCall>.
  • HrmpNewChannelOpenRequestHandler -- Allows optional logic execution for the HrmpNewChannelOpenRequest XCM notification.
  • HrmpChannelAcceptedHandler -- Allows optional logic execution for the HrmpChannelAccepted XCM notification.
  • HrmpChannelClosingHandler -- Allows optional logic execution for the HrmpChannelClosing XCM notification.
• Filters:
  • IsReserve -- Combinations of (Asset, Location) pairs which we trust as reserves. Type must implement the trait ContainsPair<MultiAsset, MultiLocation>.
  • IsTeleporter -- Combinations of (Asset, Location) pairs which we trust as teleporters. Type must implement the trait ContainsPair<MultiAsset, MultiLocation>.
  • Aliasers -- A list of (Origin, Target) pairs allowing a given Origin to be substituted with its corresponding Target pair. Type must implement the trait ContainsPair<MultiLocation, MultiLocation>.
  • Barrier -- Whether or not to execute the XCM at all. Type must implement ShouldExecute.
  • UniversalAliases -- The origin locations and specific universal junctions to which they are allowed to elevate themselves. Type must implement the trait Contains<(MultiLocation, Junction)>.
  • SafeCallFilter -- The safe call filter for Transact. Use this type to explicitly whitelist calls that cannot undergo recursion. Type must implement the trait Contains<Self::RuntimeCall>.
• Converters:
  • OriginConverter -- How to get a call origin from a OriginKind value. Type must implement the trait ConvertOrigin<<Self::RuntimeCall as Dispatchable>::RuntimeOrigin>.
• Accessors:
  • Weigher -- The means of determining an XCM message's weight. Type must implement the trait WeightBounds<Self::RuntimeCall>.
  • PalletInstancesInfo -- Information on all pallets. Type must implement the trait PalletsInfoAccess.
• Constants:
  • UniversalLocation -- This chain's Universal Location. Type must implement the trait Get<InteriorMultiLocation>.
  • MaxAssetsIntoHolding -- The maximum number of assets we target to have in the Holding Register at any one time. Type must implement the trait Get<u32>.
• Common configs:
  • RuntimeCall

Outer Config

The outer struct XcmExecutor<Config> configures the following fields:

• holding -- Assets allowed in the holding register. Type must be Assets.
• holding_limit -- The maximum number of assets in the holding register. Type must be usize.
• context -- Type must be XcmContext.
• trader -- Type must be Config::Trader which must implement the trait WeightTrader.
• error -- The most recent error result and instruction index into the fragment in which it occurred, if any. Type must be Option<(u32, XcmError)>.
• total_surplus -- Type must be Weight.
• total_refunded -- Type must be Weight.
• error_handler -- Type must be Xcm<Config::RuntimeCall>.
• error_handler_weight -- Type must be Weight.
• appendix -- Type must be Xcm<Config::RuntimeCall>.
• appendix_weight -- Type must be Weight.
• transact_status -- Type must be MaybeErrorCode.
• fees_mode -- Type must be FeesMode.