Price Authority

A priceAuthority can be used in contracts (usually specified in the terms of a contract) to provide a price feed, on-demand quotes, and wakeups for various time and price conditions.

Examples

To see a priceAuthority in use, see the Loan contract and the Call Spread contracts.

Receiving a Quote

A priceAuthority has a number of different methods that will return official priceQuotes. A priceQuote is a record with an amount and a payment, where the amount is also the current balance of the payment:

const { quoteAmount, quotePayment } = priceQuote;

Because these are ERTP amounts and payments, they have issuers. And the payments are minted by an ERTP mint. A quote issuer and mint may be shared by several priceAuthorities, and a priceAuthority may use several quoteIssuers.

Importantly, you can confirm the brand of a quote and that it was minted by the mint associated with the quoteIssuer by using the quoteIssuer to obtain the quoteAmount of the quotePayment:

const verifiedQuoteAmount = await E(quoteIssuer).getAmountOf(quotePayment);

Once you have a quoteAmount (or a verifiedQuoteAmount), you can extract the quoted amounts:

const [{ value: { amountIn, amountOut, timestamp, timer }] = quoteAmount;

This means that the priceAuthority asserts that when timestamp according to timer happened, you could sell amountIn and receive amountOut for it. amountIn and amountOut are ERTP amounts for the brandIn and brandOut you requested.

Mutable Price Quotes

MutableQuote's method getPromise() returns a Promise for a PriceQuote, which is the same as what is returned by the quoteWhenLTE() API method and variants. Effectively, the non-mutable price quote methods return a single PriceQuote, while the mutable price quote methods return a reusable object which can be manipulated by changing its trigger levels or by cancelling it.

API Reference

The Price Authority API reference is a section of the Zoe API reference