route.fulfill() ignores isBase64, so binary responses arrive base64-encoded

[ker0x]

Route::fulfill() sends isBase64 through to route.fulfill(), but that option does not exist in Playwright's JS API — so every binary response served through a fulfilled route reaches the browser as the base64 string, not the decoded bytes.

Where

playwright-symfony base64-encodes binary bodies and flags them, in two places:

// src/Client/ResponseConverter.php:92
$options['body'] = base64_encode($body);
$options['isBase64'] = true;

(same in src/Client/Interception/AssetServer.php:124)

The Node server passes the options straight through:

// bin/playwright-server.js:124
fulfill: () => route.fulfill(command.options),

But route.fulfill() accepts only body (string|Buffer), contentType, headers, json, path, response, status — isBase64 appears nowhere in playwright-core@1.62.1's types.d.ts. It is a protocol-level field the Python/Java/.NET bindings set, not a public JS option. So it is dropped and the base64 text becomes the response body.

Reproduction

Fetch any font or image through an intercepted route:

const r = await fetch('/assets/…/inter-latin-wght-normal.woff2');
const b = new Uint8Array(await r.arrayBuffer());
String.fromCharCode(...b.slice(0, 8)); // "d09GMgAB"  ← base64 of "wOF2"
b.length;                              // 64344 for a 48256-byte file (4/3)

The browser then reports:

Failed to decode downloaded font: http://localhost/assets/…/inter-latin-wght-normal.woff2
OTS parsing error: invalid sfntVersion: 1680881991

1680881991 is 0x64336137, i.e. the ASCII "d3a7" — base64 text where the wOF2 magic should be.

Text types are unaffected: ResponseConverter::isBinaryContentType() excludes text/*, JSON, JS, XML and SVG, which is why HTML/CSS/JS pages work and only fonts and raster images break.

Suggested fix

Decode in the server before handing the body to Playwright:

fulfill: () => route.fulfill(
  command.options?.isBase64
    ? {...command.options, body: Buffer.from(command.options.body, 'base64'), isBase64: undefined}
    : command.options
),

Impact

In-process E2E tests render with fallback fonts and broken images, so anything asserting on rendered typography, image pixels, or layout that depends on web-font metrics is untestable. It fails silently — the request is a 200 and only the browser console shows the decode error.

Found while moving a Symfony app's E2E suite onto zenstruck/browser's PlaywrightBrowser; reproduced identically through both ResponseConverter and AssetServer, on playwright-php/playwright v1.4.0 + playwright-symfony v0.10.0.

[smnandre]

Well i jump on the occasion but if you want to play with fonts I'd enjoy a reviewer with your vision and talent to find bugs on my code :))

https://altophp.com/font/