fix: don't error on navigating to a download link (microsoft#328)

Author: Skn0tt

src/tab.ts

@@ -66,7 +66,26 @@ export class Tab {
   }
 
   async navigate(url: string) {
-    await this.page.goto(url, { waitUntil: 'domcontentloaded' });
+    const downloadEvent = this.page.waitForEvent('download').catch(() => {});
+    try {
+      await this.page.goto(url, { waitUntil: 'domcontentloaded' });
+    } catch (_e: unknown) {
+      const e = _e as Error;
+      const mightBeDownload =
+        e.message.includes('net::ERR_ABORTED') // chromium
+        || e.message.includes('Download is starting'); // firefox + webkit
+      if (!mightBeDownload)
+        throw e;
+
+      // on chromium, the download event is fired *after* page.goto rejects, so we wait a lil bit
+      const download = await Promise.race([
+        downloadEvent,
+        new Promise(resolve => setTimeout(resolve, 500)),
+      ]);
+      if (!download)
+        throw e;
+    }
+
     // Cap load event to 5 seconds, the page is operational at this point.
     await this.page.waitForLoadState('load', { timeout: 5000 }).catch(() => {});
   }

tests/files.spec.ts

@@ -119,3 +119,21 @@ test('clicking on download link emits download', async ({ startClient }, testInf
 ### Downloads
 - Downloaded file test.txt to ${path.join(outputDir, 'test.txt')}`);
 });
+
+test('navigating to download link emits download', async ({ client, server, mcpBrowser }) => {
+  test.skip(mcpBrowser === 'webkit' && process.platform === 'linux', 'https://github.com/microsoft/playwright/blob/8e08fdb52c27bb75de9bf87627bf740fadab2122/tests/library/download.spec.ts#L436');
+  server.route('/download', (req, res) => {
+    res.writeHead(200, {
+      'Content-Type': 'text/plain',
+      'Content-Disposition': 'attachment; filename=test.txt',
+    });
+    res.end('Hello world!');
+  });
+
+  expect(await client.callTool({
+    name: 'browser_navigate',
+    arguments: {
+      url: server.PREFIX + '/download',
+    },
+  })).toContainTextContent('### Downloads');
+});