Extract hook and add config and documentation

platform/core/src/utils/xhrRetryRequestHook.js

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+import retry from 'retry';
+
+const defaultRetryOptions = {
+  retries: process.env.DICOMWEB_CLIENT_RETRY_RETRIES || 5,
+  factor: process.env.DICOMWEB_CLIENT_RETRY_FACTOR || 3,
+  minTimeout: process.env.DICOMWEB_CLIENT_RETRY_MIN_TIMEOUT || 1 * 1000,
+  maxTimeout: process.env.DICOMWEB_CLIENT_RETRY_MAX_TIMEOUT || 60 * 1000,
+  randomize: process.env.DICOMWEB_CLIENT_RETRY_RANDOMIZE || true,
+};
+
+let retryOptions = { ...defaultRetryOptions };
+
+/**
+ * Request hook used to add retry functionality to XHR requests.
+ *
+ * @param {XMLHttpRequest} request XHR request instance
+ * @param {object} metadata Metadata about the request
+ * @param {object} metadata.url URL
+ * @param {object} metadata.method HTTP method
+ * @returns {XMLHttpRequest} request instance optionally modified
+ */
+const xhrRetryRequestHook = (request, metadata) => {
+  const { url, method } = metadata;
+
+  function faultTolerantRequestSend(...args) {
+    const operation = retry.operation(retryOptions);
+
+    operation.attempt(function operationAttempt(currentAttempt) {
+      const originalOnReadyStateChange = request.onreadystatechange;
+
+      request.onreadystatechange = function onReadyStateChange() {
+        originalOnReadyStateChange.call(request);
+        if (request.status === 429 || request.status >= 500) {
+          const errorMessage = `Attempt to request ${url} failed.`;
+          const attemptFailedError = new Error(errorMessage);
+          operation.retry(attemptFailedError);
+        }
+      };
+
+      console.warn(`Requesting ${url}... (attempt: ${currentAttempt})`);
+      request.open(method, url, true);
+      originalRequestSend.call(request, ...args);
+    });
+  }
+
+  const originalRequestSend = request.send;
+  request.send = faultTolerantRequestSend;
+
+  return request;
+};
+
+/**
+ * Returns a configured retry request hook function
+ * that can be used to add retry functionality to XHR request.
+ *
+ * Default options:
+ *   retries: 5
+ *   factor: 3
+ *   minTimeout: 1 * 1000
+ *   maxTimeout: 60 * 1000
+ *   randomize: true
+ *
+ * @param {*} options
+ * @param {*} options.retires number of retries
+ * @param {*} options.factor factor
+ * @param {*} options.minTimeout the min timeout
+ * @param {*} options.maxTimeout the max timeout
+ * @param {*} options.randomize randomize
+ * @returns {function} the configured retry request function
+ */
+export const getXHRRetryRequestHook = (options = {}) => {
+  retryOptions = { ...defaultRetryOptions };
+  if ('retries' in options) {
+    retryOptions.retries = options.retries;
+  }
+  if ('factor' in options) {
+    retryOptions.factor = options.factor;
+  }
+  if ('minTimeout' in options) {
+    retryOptions.minTimeout = options.minTimeout;
+  }
+  if ('maxTimeout' in options) {
+    retryOptions.maxTimeout = options.maxTimeout;
+  }
+  if ('randomize' in options) {
+    retryOptions.randomize = options.randomize;
+  }
+  return xhrRetryRequestHook;
+};
+
+export default getXHRRetryRequestHook;