fix: Retry when WebDriver updates are not available yet (#24)

Some WebDriver updates for Chrome and Edge lag behind the corresponding
browser releases. This will automatically retry with the previous 2
releases when a 404 is encountered.

This fixes the failure on Chrome 115 today (ChromeDriver 115 is not out
yet).

chrome.js

@@ -63,9 +63,11 @@ class ChromeWebDriverInstaller extends WebDriverInstallerBase {
    * @return {!Promise<string>}
    */
   async getBestDriverVersion(browserVersion) {
-    const majorVersion = browserVersion.split('.')[0];
-    const versionUrl = `${CDN_URL}/LATEST_RELEASE_${majorVersion}`;
-    return await InstallerUtils.fetchVersionUrl(versionUrl);
+    const idealMajorVersion = parseInt(browserVersion.split('.')[0], 10);
+    return await InstallerUtils.fetchVersionUrlWithAutomaticDowngrade(
+        idealMajorVersion,
+        /* minMajorVersion */ idealMajorVersion - 2,
+        (majorVersion) => `${CDN_URL}/LATEST_RELEASE_${majorVersion}`);
   }
 
   /**

edge.js

@@ -63,7 +63,7 @@ class EdgeWebDriverInstaller extends WebDriverInstallerBase {
    * @return {!Promise<string>}
    */
   async getBestDriverVersion(browserVersion) {
-    const majorVersion = browserVersion.split('.')[0];
+    const idealMajorVersion = parseInt(browserVersion.split('.')[0], 10);
 
     let platform;
     if (os.platform() == 'linux') {
@@ -76,8 +76,15 @@ class EdgeWebDriverInstaller extends WebDriverInstallerBase {
       throw new Error(`Unrecognized platform: ${os.platform()}`);
     }
 
-    const versionUrl = `${CDN_URL}/LATEST_RELEASE_${majorVersion}_${platform}`;
-    return await InstallerUtils.fetchVersionUrl(versionUrl, 'UTF-16LE');
+    const urlFormatter = (majorVersion) => {
+      return `${CDN_URL}/LATEST_RELEASE_${majorVersion}_${platform}`;
+    };
+
+    return await InstallerUtils.fetchVersionUrlWithAutomaticDowngrade(
+        idealMajorVersion,
+        /* minMajorVersion */ idealMajorVersion - 2,
+        urlFormatter,
+        'UTF-16LE');
   }
 
   /**

utils.js

@@ -81,7 +81,8 @@ class InstallerUtils {
     const response = await fetch(url);
     if (!response.ok) {
       throw new Error(
-          `Failed to fetch ${url}: ${response.status} ${response.statusText}`);
+          `Failed to fetch ${url}: ${response.status} ${response.statusText}`,
+          { cause: response });
     }
     return response;
   }
@@ -228,7 +229,7 @@ class InstallerUtils {
   }
 
   /**
-   * Fetch a version number from a URL.  Both Chrome and Edge use this.
+   * Fetch a version number from a URL.
    *
    * @param {string} url
    * @param {string=} encoding
@@ -241,6 +242,50 @@ class InstallerUtils {
     return data.toString(encoding).trim();
   }
 
+  /**
+   * Fetch a version number from a URL.  If not found, downgrade the major
+   * version and try again.  If a WebDriver release lags the browser release
+   * (which seems common), this will compensate.  Both Chrome and Edge use
+   * this.
+   *
+   * @param {number} idealMajorVersion
+   * @param {number} minMajorVersion
+   * @param {function(number): string} urlFormatter
+   * @param {string=} encoding
+   * @return {!Promise<string>}
+   */
+  static async fetchVersionUrlWithAutomaticDowngrade(
+      idealMajorVersion, minMajorVersion, urlFormatter, encoding) {
+    let majorVersion = idealMajorVersion;
+    let firstError = null;
+
+    while (majorVersion >= minMajorVersion) {
+      const versionUrl = urlFormatter(majorVersion);
+      try {
+        return await InstallerUtils.fetchVersionUrl(versionUrl, encoding);
+      } catch (error) {
+        if (error.cause.status != 404) {
+          // Any unexpected error (other than HTTP 404) is thrown immediately.
+          throw error;
+        }
+
+        // Save the first error in case we run out this loop.  We'll throw this
+        // one if none of the allowed versions can be found.
+        if (firstError == null) {
+          firstError = error;
+        }
+
+        // For 404 errors, decrease the major version, fall through, loop, and
+        // try again.
+        majorVersion--;
+      }
+    }
+
+    // We tried all allowed versions.  Throw the initial error, which will have
+    // details of the first URL we tried.
+    throw firstError;
+  }
+
   /**
    * Fetch the latest tag from a GitHub repo.
    *