`bugfix`: Check the division when inverting the rate to avoid division by zero errors.

dfinity / exchange-rate-canister

The exchange rate canister (XRC) makes use of the HTTP requests feature to provide exchange rates as a service to the IC.

Apache License 2.0

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`bugfix`: Check the division when inverting the rate to avoid division by zero errors. #186

Closed dfinity-ryancroote closed 1 year ago

dfinity-ryancroote commented 1 year ago

This PR resolves the discovered possibility of division by zero errors while inverting a rate. This is accomplished by updating the division in utils::invert_rate (renamed to utils::checked_invert_rate) to checked_div and returning the result.

When used to invert a QueriedExchangeRate, the failed results are filtered out using filter_map.
When inverting a stablecoin rate, if the rate fails to be inverted, a CallExchangeError::NoRateFound is returned.