rjw-metoffice

rjw-metoffice

A Rust crate to help use the Met Office Global Spot site-specific weather forecast API.

Global Spot provides hourly, three-hourly, and daily forecasts for 20,000 locations worldwide. You will need an API key from the Weather DataHub website, which will allow you to make 360 API requests per day for free.

This crate is HTTP client agnostic: it helps you construct URLs to request a forecast type at a given location, and parses the returned JSON. It does not do any IO itself, so you will need to pair it with your preferred HTTP client.

Quickstart

Here's a simple example using the ureq blocking HTTP client to look up hourly forecasts for Sana’a, Yemen.

let [lat, lon] = [15.348333, 44.206389];
let url = Forecast::<Hourly>::url_for_location(lat.try_into()?, lon.try_into()?);
let response = ureq::get(url.to_string())
    .header("apikey", API_KEY)
    .call()?;
let json_bytes = response.into_body().read_to_vec()?;
let forecast: Forecast<Hourly> = json_bytes.as_slice().try_into()?;
for hour in forecast.predictions {
    println!("{}    {}", hour.time.in_tz("Asia/Riyadh")?, hour.temperature)
}

API key HTTP header

You must add a apikey header to the HTTP request containing your Met Office Weather DataHub API key. This library cannot do this for you, so please consult the documentation for the HTTP client you are using.

Missing data

Note that hourly forecasts are missing certain data in for the last three time points, and the daily forecasts are missing data for the first day (which is in the past). This is just what is returned from the API, please see the module documentation for details.

no_std and memory usage

This crate does not require the Rust standard library (std), so it is possible to use it on embedded devices. However, it does still require a memory allocator and the JSON text returned from the API is quite large: 24 KiB for hourly forecasts, 28 KiB for three-hourly, and 12 KiB for daily.

The main Forecast struct takes just under 10 KiB for hourly and three-hourly forecasts, and 2 KiB for daily forecasts. You will need to budget JSON + Forecast as the JSON parsing does allocate.