api(route): allow fulfilling with a file path

docs/api.md

@@ -1011,7 +1011,7 @@ Browser-specific Coverage implementation, only available for Chromium atm. See [
     - `'load'` - consider navigation to be finished when the `load` event is fired.
     - `'domcontentloaded'` - consider navigation to be finished when the `DOMContentLoaded` event is fired.
     - `'networkidle0'` - consider navigation to be finished when there are no more than 0 network connections for at least `500` ms.
-    - `'networkidle2'` - consider navigation to be finished when there are no more than 2 network connections for at least `500` ms.  
+    - `'networkidle2'` - consider navigation to be finished when there are no more than 2 network connections for at least `500` ms.
     - `'nowait'` - do not wait.
   - `timeout` <[number]> Maximum time in milliseconds, defaults to 30 seconds, pass `0` to disable timeout. The default value can be changed by using the [browserContext.setDefaultTimeout(timeout)](#browsercontextsetdefaulttimeouttimeout) or [page.setDefaultTimeout(timeout)](#pagesetdefaulttimeouttimeout) methods.
 - returns: <[Promise]> Promise which resolves when the element matching `selector` is successfully double clicked. The Promise will be rejected if there is no element matching `selector`.
@@ -3377,8 +3377,9 @@ page.on('requestfailed', request => {
 - `response` <[Object]> Response that will fulfill this request
   - `status` <[number]> Response status code, defaults to `200`.
   - `headers` <[Object]> Optional response headers. Header values will be converted to a string.
-  - `contentType` <[string]> If set, equals to setting `Content-Type` response header
-  - `body` <[string]|[Buffer]> Optional response body
+  - `contentType` <[string]> If set, equals to setting `Content-Type` response header.
+  - `body` <[string]|[Buffer]> Optional response body.
+  - `path` <[string]> Optional file path to respond with. The content type will be inferred from file extension. If `path` is a relative path, then it is resolved relative to [current working directory](https://nodejs.org/api/process.html#process_process_cwd).
 - returns: <[Promise]>
 
 Fulfills request with given response. To use this, request interception should
@@ -3397,8 +3398,11 @@ await page.route('**/*', request => {
 });
 ```
 
-> **NOTE** Mocking responses for dataURL requests is not supported.
-> Calling `request.fulfill` for a dataURL request is a noop.
+An example of serving static file:
+
+```js
+await page.route('**/xhr_endpoint', request => request.fulfill({ path: 'mock_data.json' }));
+```
 
 #### request.headers()
 - returns: <[Object]> An object with HTTP headers associated with the request. All header names are lower-case.

src/chromium/crNetworkManager.ts

@@ -267,7 +267,7 @@ class InterceptableRequest implements network.RequestDelegate {
     });
   }
 
-  async fulfill(response: { status: number; headers: network.Headers; contentType: string; body: (string | platform.BufferType); }) {
+  async fulfill(response: network.FulfillResponse) {
     const responseBody = response.body && helper.isString(response.body) ? platform.Buffer.from(response.body) : (response.body || null);
 
     const responseHeaders: { [s: string]: string; } = {};

src/firefox/ffNetworkManager.ts

@@ -174,7 +174,7 @@ class InterceptableRequest implements network.RequestDelegate {
     });
   }
 
-  async fulfill(response: { status: number; headers: network.Headers; contentType: string; body: (string | platform.BufferType); }) {
+  async fulfill(response: network.FulfillResponse) {
     const responseBody = response.body && helper.isString(response.body) ? platform.Buffer.from(response.body) : (response.body || null);
 
     const responseHeaders: { [s: string]: string; } = {};

src/network.ts

@@ -202,10 +202,18 @@ export class Request {
     await this._delegate.abort(errorCode);
   }
 
-  async fulfill(response: { status: number; headers: Headers; contentType: string; body: (string | platform.BufferType); }) {    // Mocking responses for dataURL requests is not currently supported.
+  async fulfill(response: FulfillResponse & { path?: string }) {
     assert(this._delegate, 'Request Interception is not enabled!');
     assert(!this._interceptionHandled, 'Request is already handled!');
     this._interceptionHandled = true;
+    if (response.path) {
+      response = {
+        status: response.status,
+        headers: response.headers,
+        contentType: platform.getMimeType(response.path),
+        body: await platform.readFileBuffer(response.path)
+      };
+    }
     await this._delegate.fulfill(response);
   }
 
@@ -304,9 +312,16 @@ export class Response {
   }
 }
 
+export type FulfillResponse = {
+  status?: number,
+  headers?: Headers,
+  contentType?: string,
+  body?: string | platform.BufferType,
+};
+
 export interface RequestDelegate {
   abort(errorCode: string): Promise<void>;
-  fulfill(response: { status: number; headers: Headers; contentType: string; body: (string | platform.BufferType); }): Promise<void>;
+  fulfill(response: FulfillResponse): Promise<void>;
   continue(overrides: { method?: string; headers?: Headers; postData?: string; }): Promise<void>;
 }
 

src/platform.ts

@@ -187,6 +187,11 @@ export async function readFileAsync(file: string, encoding: string): Promise<str
   return await promisify(nodeFS.readFile)(file, encoding);
 }
 
+export async function readFileBuffer(file: string): Promise<BufferType> {
+  assertFileAccess();
+  return await promisify(nodeFS.readFile)(file);
+}
+
 export async function writeFileAsync(file: string, data: any) {
   assertFileAccess();
   return await promisify(nodeFS.writeFile)(file, data);

src/webkit/wkInterceptableRequest.ts

@@ -65,7 +65,7 @@ export class WKInterceptableRequest implements network.RequestDelegate {
     });
   }
 
-  async fulfill(response: { status: number; headers: network.Headers; contentType: string; body: (string | platform.BufferType); }) {
+  async fulfill(response: network.FulfillResponse) {
     await this._interceptedPromise;
 
     const base64Encoded = !!response.body && !helper.isString(response.body);

test/interception.spec.js

@@ -468,6 +468,17 @@ module.exports.describe = function({testRunner, expect, defaultBrowserOptions, p
       const img = await page.$('img');
       expect(await img.screenshot()).toBeGolden('mock-binary-response.png');
     });
+    it('should work with file path', async({page, server}) => {
+      await page.route('**/*', request => request.fulfill({ contentType: 'shouldBeIgnored', path: path.join(__dirname, 'assets', 'pptr.png') }));
+      await page.evaluate(PREFIX => {
+        const img = document.createElement('img');
+        img.src = PREFIX + '/does-not-exist.png';
+        document.body.appendChild(img);
+        return new Promise(fulfill => img.onload = fulfill);
+      }, server.PREFIX);
+      const img = await page.$('img');
+      expect(await img.screenshot()).toBeGolden('mock-binary-response.png');
+    });
     it('should stringify intercepted request response headers', async({page, server}) => {
       await page.route('**/*', request => {
         request.fulfill({