New weather provider: Yr.no (#2948)

# Added Yr.no as a weather provider

Yr.no is a free Norwegian weather service. The configuration is quite
simple:
```js
{
    weatherProvider: "yr",
    lat: 59.9171,
    lon: 10.7276,
    altitude: 30
}
```
The latitude and longitude cannot have more than 4 decimals, but that
should be plenty. To quote yr: "There is no need to ask for weather
forecasts with nanometer precision!". The altitude should be meters
above sea level and defaults to 0. If `type` is set to `current` the
symbol can display the next 1, 6 or 12 hours by setting
`currentForecastHours` (default is 1).

It states in [Getting
started-guide](https://developer.yr.no/doc/GettingStarted/) that users
of the API should cache the results and use the `Expires`-header to know
when to ask for new data. By using the `If-Modified-Since`-header we can
avoid downloading the same data over and over again. I chose not to
override the `User-Agent`-header set in
[`server.js`](https://github.com/MichMich/MagicMirror/blob/a328ce5/js/server.js#L97)
even though it does not comply with [the terms of
service](https://developer.yr.no/doc/TermsOfService/). It currently
works with the default header, and by searching the web for MagicMirror
the GitHub-repo should be easy to find without an explicit link.

I also had to make some minor changes to `server.js` and
`weatherprovider.js` to be able to send and return HTTP headers. To
handle the HTTP 304 response without body I chose to return `undefined`
so we easily can use the response as a condition: `if (response) ...`.

The documentation for the API is available here:
- [API Reference overview](https://api.met.no/weatherapi/)
-
[Locationforecast](https://api.met.no/weatherapi/locationforecast/2.0/)
- Used to get the weather forecast
- [Sunrise](https://api.met.no/weatherapi/sunrise/2.0/documentation) -
used to find sunrise and sunset times

Co-authored-by: Veeck <github@veeck.de>

CHANGELOG.md

@@ -19,6 +19,7 @@ Special thanks to: @rejas, @sdetweil, @MagMar94
 - Added css class names "today" and "tomorrow" for default calendar
 - Added Collaboration.md
 - Added new github action for dependency review (#2862)
+- Added Yr as a weather provider
 - Added config options "ignoreXOriginHeader" and "ignoreContentSecurityPolicy"
 
 ### Removed

modules/default/utils.js

@@ -0,0 +1,147 @@
+/**
+ * A function to make HTTP requests via the server to avoid CORS-errors.
+ *
+ * @param {string} url the url to fetch from
+ * @param {string} type what contenttype to expect in the response, can be "json" or "xml"
+ * @param {boolean} useCorsProxy A flag to indicate
+ * @param {Array.<{name: string, value:string}>} requestHeaders the HTTP headers to send
+ * @param {Array.<string>} expectedResponseHeaders the expected HTTP headers to recieve
+ * @returns {Promise} resolved when the fetch is done. The response headers is placed in a headers-property (provided the response does not allready contain a headers-property).
+ */
+async function performWebRequest(url, type = "json", useCorsProxy = false, requestHeaders = undefined, expectedResponseHeaders = undefined) {
+	const request = {};
+	if (useCorsProxy) {
+		url = getCorsUrl(url, requestHeaders, expectedResponseHeaders);
+	} else {
+		request.headers = getHeadersToSend(requestHeaders);
+	}
+	const response = await fetch(url, request);
+	const data = await response.text();
+
+	if (type === "xml") {
+		return new DOMParser().parseFromString(data, "text/html");
+	} else {
+		if (!data || !data.length > 0) return undefined;
+
+		const dataResponse = JSON.parse(data);
+		if (!dataResponse.headers) {
+			dataResponse.headers = getHeadersFromResponse(expectedResponseHeaders, response);
+		}
+		return dataResponse;
+	}
+}
+
+/**
+ * Gets a URL that will be used when calling the CORS-method on the server.
+ *
+ * @param {string} url the url to fetch from
+ * @param {Array.<{name: string, value:string}>} requestHeaders the HTTP headers to send
+ * @param {Array.<string>} expectedResponseHeaders the expected HTTP headers to recieve
+ * @returns {string} to be used as URL when calling CORS-method on server.
+ */
+const getCorsUrl = function (url, requestHeaders, expectedResponseHeaders) {
+	if (!url || url.length < 1) {
+		throw new Error(`Invalid URL: ${url}`);
+	} else {
+		let corsUrl = `${location.protocol}//${location.host}/cors?`;
+
+		const requestHeaderString = getRequestHeaderString(requestHeaders);
+		if (requestHeaderString) corsUrl = `${corsUrl}sendheaders=${requestHeaderString}`;
+
+		const expectedResponseHeadersString = getExpectedResponseHeadersString(expectedResponseHeaders);
+		if (requestHeaderString && expectedResponseHeadersString) {
+			corsUrl = `${corsUrl}&expectedheaders=${expectedResponseHeadersString}`;
+		} else if (expectedResponseHeadersString) {
+			corsUrl = `${corsUrl}expectedheaders=${expectedResponseHeadersString}`;
+		}
+
+		if (requestHeaderString || expectedResponseHeadersString) {
+			return `${corsUrl}&url=${url}`;
+		}
+		return `${corsUrl}url=${url}`;
+	}
+};
+
+/**
+ * Gets the part of the CORS URL that represents the HTTP headers to send.
+ *
+ * @param {Array.<{name: string, value:string}>} requestHeaders the HTTP headers to send
+ * @returns {string} to be used as request-headers component in CORS URL.
+ */
+const getRequestHeaderString = function (requestHeaders) {
+	let requestHeaderString = "";
+	if (requestHeaders) {
+		for (const header of requestHeaders) {
+			if (requestHeaderString.length === 0) {
+				requestHeaderString = `${header.name}:${encodeURIComponent(header.value)}`;
+			} else {
+				requestHeaderString = `${requestHeaderString},${header.name}:${encodeURIComponent(header.value)}`;
+			}
+		}
+		return requestHeaderString;
+	}
+	return undefined;
+};
+
+/**
+ * Gets headers and values to attatch to the web request.
+ *
+ * @param {Array.<{name: string, value:string}>} requestHeaders the HTTP headers to send
+ * @returns {object} An object specifying name and value of the headers.
+ */
+const getHeadersToSend = (requestHeaders) => {
+	const headersToSend = {};
+	if (requestHeaders) {
+		for (const header of requestHeaders) {
+			headersToSend[header.name] = header.value;
+		}
+	}
+
+	return headersToSend;
+};
+
+/**
+ * Gets the part of the CORS URL that represents the expected HTTP headers to recieve.
+ *
+ * @param {Array.<string>} expectedResponseHeaders the expected HTTP headers to recieve
+ * @returns {string} to be used as the expected HTTP-headers component in CORS URL.
+ */
+const getExpectedResponseHeadersString = function (expectedResponseHeaders) {
+	let expectedResponseHeadersString = "";
+	if (expectedResponseHeaders) {
+		for (const header of expectedResponseHeaders) {
+			if (expectedResponseHeadersString.length === 0) {
+				expectedResponseHeadersString = `${header}`;
+			} else {
+				expectedResponseHeadersString = `${expectedResponseHeadersString},${header}`;
+			}
+		}
+		return expectedResponseHeaders;
+	}
+	return undefined;
+};
+
+/**
+ * Gets the values for the expected headers from the response.
+ *
+ * @param {Array.<string>} expectedResponseHeaders the expected HTTP headers to recieve
+ * @param {Response} response the HTTP response
+ * @returns {string} to be used as the expected HTTP-headers component in CORS URL.
+ */
+const getHeadersFromResponse = (expectedResponseHeaders, response) => {
+	const responseHeaders = [];
+
+	if (expectedResponseHeaders) {
+		for (const header of expectedResponseHeaders) {
+			const headerValue = response.headers.get(header);
+			responseHeaders.push({ name: header, value: headerValue });
+		}
+	}
+
+	return responseHeaders;
+};
+
+if (typeof module !== "undefined")
+	module.exports = {
+		performWebRequest
+	};