Document websocket-port arg, set it to random (#196)

src/index.ts

@@ -17,6 +17,13 @@ export async function start (params: GeckodriverParameters) {
   }
 
   startArgs.host = startArgs.host || DEFAULT_HOSTNAME
+
+  // By default, Geckodriver uses port 9222
+  // User might pass a port for custom runs but they should modify them for each worker
+  // For remaining use cases, to enable parallel instances we need to set the port to 0 (random)
+  // Otherwise all instances try to connect to the default port and fail
+  startArgs.websocketPort = startArgs.websocketPort ?? 0;
+
   const args = parseParams(startArgs)
   log.info(`Starting Geckodriver at ${geckoDriverPath} with params: ${args.join(' ')}`)
   return cp.spawn(geckoDriverPath, args)

src/types.ts

@@ -56,6 +56,10 @@ export interface GeckodriverParameters {
    * port to listen on
    */
   port?: number
+  /**
+   * port to use for Debugger / Webdriver BiDi
+   */
+  websocketPort?: number
   /**
    * Directory in which to create profiles. Defaults to the system temporary directory.
    */