feat: Automatically fetch and install drivers

Drivers are automatically fetched and installed to a cache in your
home directory.  They will always match the local browser version,
without the need for any manual intervention.  This is done using the
webdriver-installer module (also by me).

README.md

@@ -19,12 +19,15 @@ npm install --save-dev karma-local-wd-launcher
 
 ## Drivers
 
-This launcher assumes that drivers such as `chromedriver`, `geckodriver`, and
-`safaridriver` (Mac only) are already installed, executable, and in your `PATH`.
+This launcher will use the
+[`webdriver-installer`](https://www.npmjs.com/package/webdriver-installer)
+module to automatically download and install driver binaries for your local
+browsers.  These will be cached in a folder called `.webdriver-installer-cache`
+in your home directory.
 
 Alternately, you may use the environment variables `CHROMEDRIVER_PATH`,
 `GECKODRIVER_PATH`, or `SAFARIDRIVER_PATH` to indicate where these drivers are
-installed.
+already installed.
 
 
 ## Configuration

index.js

@@ -15,10 +15,19 @@
  * Supports Chrome, Firefox, and Safari.
  */
 
+const fs = require('fs');
 const os = require('os');
+const path = require('path');
 const url = require('url');
 const wd = require('wd');
 
+const {installWebDrivers} = require('webdriver-installer');
+
+const DRIVER_CACHE = path.join(os.homedir(), '.webdriver-installer-cache');
+fs.mkdirSync(DRIVER_CACHE, {recursive: true});
+
+let driversInstalledPromise = null;
+
 // Map nodejs OS names to Selenium platform names.
 const PLATFORM_MAP = {
   'darwin': 'Mac',
@@ -32,6 +41,14 @@ const LocalWebDriverBase = function(
 
   this.browserName = browserName;
 
+  if (driverCommand[0] == '/') {
+    // Absolute path.  Keep it.
+  } else {
+    // File name.  Assume it's in our driver cache.
+    driverCommand = path.join(DRIVER_CACHE, driverCommand);
+  }
+
+  // Checked by the base class to determine what command to run.
   this.DEFAULT_CMD = {
     linux: driverCommand,
     darwin: driverCommand,
@@ -43,7 +60,8 @@ const LocalWebDriverBase = function(
   // Called by the base class to get arguments to pass to the driver command.
   this._getOptions = () => argsFromPort(port.toString());
 
-  this.ENV_CMD = driverCommand.toUpperCase() + '_PATH';
+  // An environment variable that can be used to override the command path.
+  this.ENV_CMD = driverCommand.toUpperCase().replace('-', '_') + '_PATH';
 
   const config = {
     protocol: 'http:',
@@ -110,7 +128,18 @@ const LocalWebDriverBase = function(
   const originalStart = this.start;
   let previousUrl = null;
 
-  this.start = (url) => {
+  this.start = async (url) => {
+    // If we haven't installed drivers yet in this session, start the
+    // installation process now.
+    if (!driversInstalledPromise) {
+      // TODO: Tie logging for this to karma log settings.
+      driversInstalledPromise =
+          installWebDrivers(DRIVER_CACHE, /* logging= */ false);
+    }
+
+    // Wait for drivers to be installed for all local browsers.
+    await driversInstalledPromise;
+
     previousUrl = url;
     originalStart.call(this, url);
   };

package.json

@@ -17,7 +17,8 @@
   ],
   "author": "Joey Parrish <[email protected]>",
   "dependencies": {
-    "wd": "^1.14.0"
+    "wd": "^1.14.0",
+    "webdriver-installer": "^1.0.0"
   },
   "peerDependencies": {
     "karma": "^6.2.0"