The managed assets pattern

Intent

Creating a level of indirection between the creator of the smart contract and a potential customer.

Consequences

• There are an arbitrary amount of traders that all trade with the creator.
• The smart contract is able to run indefinitely.
• The creator does not need to play an active role in the trade: the sole purpose of the trader is to provide input to the internalSeat by offering a depositInvitation, and collect output of the internalSeat by offering a withdrawInvitation.
• The creator and the customer do not trade directly: both the customer and the creator will only trade with the internalSeat.
• Due to the fact that the withdrawing is performed by offering a withdrawInvitation, gains are given to anyone that offers a withdrawInvitation. The creator must therefore be careful not to share a withdrawInvitation with any other entity, because any entity that offers this withdrawInvitation can get the gains from the internalSeat.

Structure

Note that this seat structure diagram does not specify how the customer got hold of the customerInvitation. This is because the way that the customer obtained the customerInvitation is irrelevant for the managed assets pattern. An example of how the customer could have gotten the customerInvitation is via the independent participation pattern.

Participants

• Creator: the entity that starts an instance of the smart contract.
• Customer: the entity that wants to trade with the creator.

Implementation

const start = async zcf => {
  const { zcfSeat: internalSeat } = zcf.makeEmptySeatKit();
  const makeDepositOfferHandler = depositSeat => {
    //some reallocation to internalSeat
  }
  const makeWithdrawOfferHandler = withdrawSeat => {
    //some reallocation from internalSeat
  }
  const customerOfferHandler = customerSeat => {
    //some reallocation to internalSeat
  }
  const creatorFacet = Far('creatorFacet', {
    makeDepositInvitation: () => zcf.makeInvitation(makeDepositOfferHandler, 'deposit'),
    makeWithdrawInvitation: () => zcf.makeInvitation(makeWithdrawOfferHandler, 'withdraw')
  });
  return harden({ creatorFacet });
};
harden(start);
export { start };

The smart contract has an internal seat internalSeat which is used as a level of indirection between the creator and the customer. A customer will perform all of its trades with the internalSeat. The smart contract returns a creatorFacet. This creatorFacet provides the creator with methods to create depositInvitations and withdrawInvitations. A depositInvitation can be used in an offer to deposit inventory to the internalSeat. A withdrawInvitation can be used in an offer to withdraw gains made from the trades from the internalSeat. Note that in the code above the customerOfferHandler is not linked to any invitation. The contract designer should determine how invitations are made available to customers.

Known uses

• The oracle smart contract.
• The Over The Counter desk smart contract.

Related patterns

• The salesperson pattern: both these patterns are market places where 1 creator performs trade with an arbitrary amount of customers. The difference is that the managed assets patterns provides an extra level of indirection between the customer and the creator, while the salesperson pattern does not provide this extra level of indirection.