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.

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: 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.

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