Trait ShortabilityClient

Source

pub trait ShortabilityClient: ExecutionClient {
    // Required method
    fn fetch_shortability(
        &self,
        instrument: &InstrumentNameExchange,
    ) -> impl Future<Output = Result<Shortability, UnindexedClientError>> + Send;
}

Expand description

Extension trait for clients that can say what the venue would lend for a short sale.

Answers, before an order is sent, the question a short sale otherwise learns only from its rejection: whether the instrument may be sold short, whether it is easy to borrow, how much the venue has to lend and at what fee. Each venue reports a different subset, so each field of the Shortability it returns is optional; the implementations say which fields they fill.

§Type-Level Capability

A supertrait of ExecutionClient, for the reason BracketOrderClient is one: a client whose venue has nothing to lend, or that does not report it, does not implement it. A simulated venue reads the same Shortability from a ShortabilityProvider instead.

Required Methods§

Source

fn fetch_shortability( &self, instrument: &InstrumentNameExchange, ) -> impl Future<Output = Result<Shortability, UnindexedClientError>> + Send

What the venue says about lending instrument for a short sale.

§Contract

Advisory. Ok describes the venue’s lending as it reported it, not a promise to lend: a short sale must still handle ApiError::BorrowRejected.
Not this account’s capacity. Shortability::available is what the venue has to lend, not what is left of it for this account; that is BorrowCapacityClient::fetch_borrow_capacity, where a venue reports it.
May be expensive. An implementation may make several requests, some of them heavy against the venue’s rate limit, or hold a scarce resource such as a market data line; each says what it costs. Fetch it when deciding on a short, not on every tick.
May be slow. Where the venue streams its answer rather than replying to a request, the call waits for it, up to a timeout the implementation documents: seconds, not milliseconds.
May outlive its future. An implementation that reads on a blocking thread finishes that read, and releases what it holds, even when the returned future is dropped first; each says so.

§Errors

ApiError::InstrumentInvalid for an instrument the venue does not know, or one of a kind that is not sold short by borrowing it, such as an option.
An error, rather than a Shortability with nothing known, when the venue does not answer, including when the account is not entitled to the answer, such as one without the market data subscription a venue sends it through.