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.