ECB exchange rates

Use case

A Swedish shop keeps its books in kronor, and a visitor from Oslo or Berlin still wants to know what a bag of coffee costs in their money. Osysharp.Shop shows it as an estimate ("≈ €14.58", and "charged as 165 kr" wherever money changes hands) from rates a provider supplies. This kit is that provider: the ECB's euro foreign exchange reference rates, published once a working day at about 16:00 CET — public, free, no key.

Source: https://www.ecb.europa.eu/stats/policy_and_exchange_rates/euro_reference_exchange_rates/html/index.en.html, read from https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml. The ECB publishes these rates for information purposes only, which is how the shop uses them: nothing is charged at them.

Install and use

app MyShop {
  use Osysharp.Shop@1 { egress "api.resend.com"; secret "ResendApiKey"; }
  use Osysharp.Shop.Ecb@0 { egress "www.ecb.europa.eu"; }
  …
}

using Osysharp.Shop.Ecb;

app.Shop = new ShopSetup { …, ExchangeRates = new EcbRates(), DisplayCurrencies = ["EUR", "NOK", "DKK", "USD"] };

The shop's rate job asks the ECB as it starts and every six hours; cross rates against the shop's own currency are worked out from the euro sheet (1 SEK in USD = USD per euro ÷ SEK per euro). A sheet with no date or no rates — a maintenance page served as 200 — is refused rather than stored.

Source and tests

model/Ecb.osy (EcbRates : IExchangeRates, EcbSheet(xml)), and tests in tests/ecb.test.osy with every call to the ECB stubbed.

Get it

Add the kit to your app’s manifest:

app MyApp {
  use Osysharp.Shop.Ecb@0 {
    egress "www.ecb.europa.eu";
  }
}

Then run osy lock: it downloads the release, verifies it by its content address and pins that version in osyrin.lock. osy kits Osysharp.Shop.Ecb shows what the kit is for, from inside your app.