chore: Improve the error message about download servers unavailability

lib/storage-client/storage-client.js

@@ -24,6 +24,13 @@ import {compareVersions} from 'compare-versions';
 import semver from 'semver';
 
 const MAX_PARALLEL_DOWNLOADS = 5;
+const STORAGE_INFOS = /** @type {readonly StorageInfo[]} */ ([{
+  url: GOOGLEAPIS_CDN,
+  accept: 'application/xml',
+}, {
+  url: `${CHROMELABS_URL}/chrome-for-testing/known-good-versions-with-downloads.json`,
+  accept: 'application/json',
+}]);
 
 const log = logger.getLogger('ChromedriverStorageClient');
 
@@ -60,19 +67,37 @@ export class ChromedriverStorageClient {
    * @returns {Promise<ChromedriverDetailsMapping>}
    */
   async retrieveMapping(shouldParseNotes = true) {
-    const [xmlStr, jsonStr] = await B.all([
-      [GOOGLEAPIS_CDN, 'application/xml'],
-      [`${CHROMELABS_URL}/chrome-for-testing/known-good-versions-with-downloads.json`, 'application/json'],
-    ]
-    .map(([url, contentType]) => url
-      ? retrieveData(url, {
+    /** @type {(si: StorageInfo) => Promise<string|undefined>} */
+    const retrieveResponseSafely = async (/** @type {StorageInfo} */ {url, accept}) => {
+      try {
+        return await retrieveData(url, {
           'user-agent': USER_AGENT,
-          accept: `${contentType}, */*`,
-        }, {timeout: this.timeout})
-      : B.resolve()
-    ));
+          accept: `${accept}, */*`,
+        }, {timeout: this.timeout});
+      } catch (e) {
+        log.debug(/** @type {Error} */(e).stack);
+        log.warn(
+          `Cannot retrieve Chromedrivers info from ${url}. ` +
+          `Make sure this URL is accessible from your network. ` +
+          `Original error: ${/** @type {Error} */(e).message}`
+        );
+      }
+    };
+    const [xmlStr, jsonStr] = await B.all(STORAGE_INFOS.map(retrieveResponseSafely));
+    // Apply the best effort approach and fetch the mapping from at least one server if possible.
+    // We'll fail later anyway if the target chromedriver version is not there.
+    if (!xmlStr && !jsonStr) {
+      throw new Error(
+        `Cannot retrieve the information about available Chromedrivers from ` +
+        `${STORAGE_INFOS.map(({url}) => url)}. Please make sure these URLs are avilable ` +
+        `within your local network, check Appium server logs and/or ` +
+        `consult the driver troubleshooting guide.`
+      );
+    }
     this.mapping = xmlStr ? await parseGoogleapiStorageXml(xmlStr, shouldParseNotes) : {};
-    Object.assign(this.mapping, parseKnownGoodVersionsWithDownloadsJson(jsonStr));
+    if (jsonStr) {
+      Object.assign(this.mapping, parseKnownGoodVersionsWithDownloadsJson(jsonStr));
+    }
     return this.mapping;
   }
 
@@ -392,3 +417,9 @@ export default ChromedriverStorageClient;
  * @typedef {import('../types').ChromedriverDetails} ChromedriverDetails
  * @typedef {import('../types').ChromedriverDetailsMapping} ChromedriverDetailsMapping
  */
+
+/**
+ * @typedef {Object} StorageInfo
+ * @property {string} url
+ * @property {string} accept
+ */