feat(Page): implement page.setOfflineMode (#1032)

This patch implements page.setOfflineMode method.

Fixes #63.

docs/api.md

@@ -68,6 +68,7 @@
     + [page.setCookie(...cookies)](#pagesetcookiecookies)
     + [page.setExtraHTTPHeaders(headers)](#pagesetextrahttpheadersheaders)
     + [page.setJavaScriptEnabled(enabled)](#pagesetjavascriptenabledenabled)
+    + [page.setOfflineMode(enabled)](#pagesetofflinemodeenabled)
     + [page.setRequestInterceptionEnabled(value)](#pagesetrequestinterceptionenabledvalue)
     + [page.setUserAgent(userAgent)](#pagesetuseragentuseragent)
     + [page.setViewport(viewport)](#pagesetviewportviewport)
@@ -900,6 +901,10 @@ The extra HTTP headers will be sent with every request the page initiates.
 
 > **NOTE** changing this value won't affect scripts that have already been run. It will take full effect on the next [navigation](#pagegotourl-options).
 
+#### page.setOfflineMode(enabled)
+- `enabled` <[boolean]> When `true`, enables offline mode for the page.
+- returns: <[Promise]>
+
 #### page.setRequestInterceptionEnabled(value)
 - `value` <[boolean]> Whether to enable request interception.
 - returns: <[Promise]>

lib/NetworkManager.js

@@ -32,6 +32,8 @@ class NetworkManager extends EventEmitter {
     /** @type {!Object<string, string>} */
     this._extraHTTPHeaders = {};
 
+    this._offline = false;
+
     /** @type {?{username: string, password: string}} */
     this._credentials = null;
     /** @type {!Set<string>} */
@@ -78,6 +80,22 @@ class NetworkManager extends EventEmitter {
     return Object.assign({}, this._extraHTTPHeaders);
   }
 
+  /**
+   * @param {boolean} value
+   */
+  async setOfflineMode(value) {
+    if (this._offline === value)
+      return;
+    this._offline = value;
+    await this._client.send('Network.emulateNetworkConditions', {
+      offline: this._offline,
+      // values of 0 remove any active throttling. crbug.com/456324#c9
+      latency: 0,
+      downloadThroughput: -1,
+      uploadThroughput: -1
+    });
+  }
+
   /**
    * @param {string} userAgent
    */

lib/Page.js

@@ -149,6 +149,13 @@ class Page extends EventEmitter {
     return this._networkManager.setRequestInterceptionEnabled(value);
   }
 
+  /**
+   * @param {boolean} enabled
+   */
+  setOfflineMode(enabled) {
+    return this._networkManager.setOfflineMode(enabled);
+  }
+
   /**
    * @param {!Object} event
    */

test/test.js

@@ -328,6 +328,25 @@ describe('Page', function() {
     }));
   });
 
+  describe('Page.setOfflineMode', function() {
+    it('should work', SX(async function() {
+      await page.setOfflineMode(true);
+      let error = null;
+      await page.goto(EMPTY_PAGE).catch(e => error = e);
+      expect(error).toBeTruthy();
+      await page.setOfflineMode(false);
+      const response = await page.reload();
+      expect(response.status).toBe(200);
+    }));
+    it('should emulate navigator.onLine', SX(async function() {
+      expect(await page.evaluate(() => window.navigator.onLine)).toBe(true);
+      await page.setOfflineMode(true);
+      expect(await page.evaluate(() => window.navigator.onLine)).toBe(false);
+      await page.setOfflineMode(false);
+      expect(await page.evaluate(() => window.navigator.onLine)).toBe(true);
+    }));
+  });
+
   describe('Page.evaluateHandle', function() {
     it('should work', SX(async function() {
       const windowHandle = await page.evaluateHandle(() => window);