add failIfNoChromeAtPort option

README.md

@@ -35,6 +35,13 @@ npm install chrome-launcher
   // Default: an available port is autoselected
   port: number;
 
+  // (optional) When a port is specified but no Chrome is found at that port:
+  // * if this option is true and there is no Chrome with that debug port, throw an error
+  // * else, launch a new Chrome with that debug port
+  // This option is useful when you wish to explicitly connect to a running Chrome, such as on a mobile device via adb
+  // Default: false
+  failIfNoChromeAtPort: boolean;
+
   // (optional) Additional flags to pass to Chrome, for example: ['--headless', '--disable-gpu']
   // See: https://github.com/GoogleChrome/chrome-launcher/blob/main/docs/chrome-flags-for-tools.md
   // Do note, many flags are set by default: https://github.com/GoogleChrome/chrome-launcher/blob/main/src/flags.ts

src/chrome-launcher.ts

@@ -33,6 +33,7 @@ export interface Options {
   chromeFlags?: Array<string>;
   prefs?: Record<string, JSONLike>;
   port?: number;
+  failIfNoChromeAtPort?: boolean;
   handleSIGINT?: boolean;
   chromePath?: string;
   userDataDir?: string|boolean;
@@ -119,6 +120,7 @@ class Launcher {
   private chromeFlags: string[];
   private prefs: Record<string, JSONLike>;
   private requestedPort?: number;
+  private failIfNoChromeAtPort?: boolean;
   private connectionPollInterval: number;
   private maxConnectionRetries: number;
   private fs: typeof fs;
@@ -142,6 +144,7 @@ class Launcher {
     this.chromeFlags = defaults(this.opts.chromeFlags, []);
     this.prefs = defaults(this.opts.prefs, {});
     this.requestedPort = defaults(this.opts.port, 0);
+    this.failIfNoChromeAtPort = opts.failIfNoChromeAtPort;
     this.chromePath = this.opts.chromePath;
     this.ignoreDefaultFlags = defaults(this.opts.ignoreDefaultFlags, false);
     this.connectionPollInterval = defaults(this.opts.connectionPollInterval, 500);
@@ -263,6 +266,10 @@ class Launcher {
             `Found existing Chrome already running using port ${this.port}, using that.`);
         return;
       } catch (err) {
+        if (this.failIfNoChromeAtPort) {
+          throw new Error(`found no Chrome at port ${this.requestedPort}`);
+        }
+
         log.log(
             'ChromeLauncher',
             `No debugging port found on port ${this.port}, launching a new Chrome.`);