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Formicka / exchangerate.host

Exchange rates API is a simple and lightweight free service for current and historical foreign exchange rates & crypto exchange rates.
https://exchangerate.host
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Incorrect Response from API for unsupported currencies #71

Open marination opened 3 years ago

marination commented 3 years ago

Issue: Consider the currency TMM, which is not supported by this API (which is fine): While fetching exchange rate TMM -> INR, we get 86.809808. This seems like it defaults to the value of **EUR** to INR Similarly, TMM -> USD, we get 1.168879. Again value of **EUR** to USD

Rather for any currency that does not exist, lets say ABC: ABC -> USD = 1.168879 USD -> ABC = 0

This is really not the best API design. It should maybe give back some exc/exception that says that this currency is not supported. The response is not predictable.

It does not obstruct any other currencies, except TMM (poor Turkmenistanis).

Jadarma commented 3 years ago

Yes, this seems to be a problem in the way the API handles base currencies. See also #34 and #70.

As a workaround I would suggest not querying for base currencies that are not returned in the /symbols response. Though this wouldn't really work for historical data with out-of-use currencies since the /symbols endpoint only returns the supported currencies at the time of request.

A (hacky) workaround for the time being: Unsupported currencies are just removed from the response if they are _not_ the base. If your use case allows for small rounding errors, you could always use the default base of *EUR* and calculate by proxy. Suppose you have: ```json { "base": "EUR", "rates": { "USD": 1.19397, "INR": 89.041089, } } ``` Then you could get the rate from *INR* to *USD* like so: `inrToUsd = 1 / rates.INR * rates.USD`. In my example this would be: `1 / 89.041089 * 1.19397 ~= 0.013409` which seems to match what the API returns when requesting *INR* to *USD* directly, though do note that rounding errors may occur for very inflated currencies like *IRR* or *VES*. Of course, if instead of *INR* you'd use *TMM* or other unsupported currency, you won't have the `rates.TMM` property, and you can treat that as a _Not Found_.
rtdany10 commented 3 years ago

As a workaround I would suggest not querying for base currencies that are not returned in the /symbols response.

It will be an extra API call each time since we use the /convert endpoint to get historical data. Hoping a fix is on the way!