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  • Adrian Catangiu's avatar
    pallet-xcm: add new extrinsic for asset transfers using explicit XCM transfer types (#3695) · 1e971b8d
    Adrian Catangiu authored
    
    
    # Description
    
    Add `transfer_assets_using()` for transferring assets from local chain
    to destination chain using explicit XCM transfer types such as:
    - `TransferType::LocalReserve`: transfer assets to sovereign account of
    destination chain and forward a notification XCM to `dest` to mint and
    deposit reserve-based assets to `beneficiary`.
    - `TransferType::DestinationReserve`: burn local assets and forward a
    notification to `dest` chain to withdraw the reserve assets from this
    chain's sovereign account and deposit them to `beneficiary`.
    - `TransferType::RemoteReserve(reserve)`: burn local assets, forward XCM
    to `reserve` chain to move reserves from this chain's SA to `dest`
    chain's SA, and forward another XCM to `dest` to mint and deposit
    reserve-based assets to `beneficiary`. Typically the remote `reserve` is
    Asset Hub.
    - `TransferType::Teleport`: burn local assets and forward XCM to `dest`
    chain to mint/teleport assets and deposit them to `beneficiary`.
    
    By default, an asset's reserve is its origin chain. But sometimes we may
    want to explicitly use another chain as reserve (as long as allowed by
    runtime `IsReserve` filter).
    
    This is very helpful for transferring assets with multiple configured
    reserves (such as Asset Hub ForeignAssets), when the transfer strictly
    depends on the used reserve.
    
    E.g. For transferring Foreign Assets over a bridge, Asset Hub must be
    used as the reserve location.
    
    # Example usage scenarios
    
    ## Transfer bridged ethereum ERC20-tokenX between ecosystem parachains.
    
    ERC20-tokenX is registered on AssetHub as a ForeignAsset by the
    Polkadot<>Ethereum bridge (Snowbridge). Its asset_id is something like
    `(parents:2, (GlobalConsensus(Ethereum), Address(tokenX_contract)))`.
    Its _original_ reserve is Ethereum (only we can't use Ethereum as a
    reserve in local transfers); but, since tokenX is also registered on
    AssetHub as a ForeignAsset, we can use AssetHub as a reserve.
    
    With this PR we can transfer tokenX from ParaA to ParaB while using
    AssetHub as a reserve.
    
    ## Transfer AssetHub ForeignAssets between parachains
    
    AssetA created on ParaA but also registered as foreign asset on Asset
    Hub. Can use AssetHub as a reserve.
    
    And all of the above can be done while still controlling transfer type
    for `fees` so mixing assets in same transfer is supported.
    
    # Tests
    
    Added integration tests for showcasing:
    - transferring local (not bridged) assets from parachain over bridge
    using local Asset Hub reserve,
    - transferring foreign assets from parachain to Asset Hub,
    - transferring foreign assets from Asset Hub to parachain,
    - transferring foreign assets from parachain to parachain using local
    Asset Hub reserve.
    
    ---------
    
    Co-authored-by: default avatarBranislav Kontur <[email protected]>
    Co-authored-by: command-bot <>
    1e971b8d