orml-xtokens

[shaunxw]

Cross-chain token transfer support.

orml-xtokens assumes other parachains also use xtoken protocol, and their impl is trustworthy (or exactly orml-xtokens).

Chains using orml-xtokens might need to whitelist para_id's to ensure this.

Basic data structure

/// To identify different chain
enum ChainId {
    RelayChain,
    ParaChain(ParaId)
}

/// To identify currency type and it's 'owner' chain
struct XCurrencyId {
    /// The owner chain
    chain_id: ChainId, 
    currency_id: Vec<u8>, // more flexible compared to int
}

enum XCMPMessage {
    Transfer {
        currency_id: XCurrencyId,
        dest: AccountId,
        amount: Balance,
    }
}

Dispatchable calls

transfer

• Prerequisite: must be aware of self para_id
• do transfer
  • To relaychain
  • To parachain
    • Relaychain tokens.
    • Owned parachain tokens.
    • Non-owned known parachain tokens.
    • Non-owned unknown parachain tokens.

Message handling

Bookkeeping

• Impl DownwardMessageHandler
• Impl XCMPMessageHandler

[xlc]

Also should refactor the current native relay balance conversion code to a more generic version that allow support precision conversion between other parachains.

Something like

trait BalanceConversion {
  fn convert(from: XCurrencyId, to: XCurrencyId, value: Balance) -> (Balance, Balance)   // (converted_value, pre_convert_dust_value)
}

[shaunxw]

Finished.