XCM Fungible Asset Implementation Guide #385

xlc · 2021-03-03T03:23:36Z

xlc
Mar 3, 2021
Maintainer

../ParachainId(source_para_id)/PalletInstance(pallet_id)/GeneralKey(key)

Breakdown:

..
- Parent. i.e. Relaychain
ParachainId(source_para_id)
- The source / reserve parachain
PalletInstance(pallet_id)
- The pallet index in the runtime
GeneralKey(key)
- Could also be GeneralIndex(index)
- Up to each parachain to decide what should be the value
- Could be scale-codec encoded of the native AssetId / CurrencyId type

Every parachain will need to define an asset transactor to handle asset related operations
AssetTransactor will use LocationConversion and AssetIdConversion to do origin mapping & asset ID mapping
AssetTransactor should gracefully handle unknown tokens
- At very minimum keep balance count, and allow user to cross-chain transfer back to source chain
- If possible, handle unknown token similar to known tokens
  - i.e. Allow transfer unknonw token and integrate with rest of the system

Convert MultiLocation to AccountId and vice versa
Parent / Relaychain
- Map to some special known address
- Avoid using all zero address to minimize confusion
ParaId
- Some special known address prefix + ParaId
AccountId32 / AccountId20
- Prepend known prefix if source format is smaller than dest format
- Identical if length are same
- Hash to dest format length if source format is larger

Convert MultiAsset to chain native AssetId / CurrencyId and vice versa
The simplest implementation is identity conversion. i.e. Use the MultiLocation from ConcreteFungible
Otherwise a hardcoded map can be used to do the conversion

All parachain that issue tokens should publish the MultiLocation of their tokens to help others to integrate with it
An unified format should be used to minimize the work required to integrate each parachains
The published format needs to be consumable by Rust code and offer a JSON representation for SDK to use
A registry could be used to collect token details from all the parachains