Add offline gather / audit

Fixes #21. Deeply enjoyable.

aggregators/can-load-offline/index.js

@@ -27,12 +27,19 @@ class WorksOffline extends Aggregate {
 
   static get criteria() {
     const serviceWorker = require('../../audits/offline/service-worker').name;
+    const worksOffline = require('../../audits/offline/works-offline').name;
+
     const criteria = {};
     criteria[serviceWorker] = {
       value: true,
       weight: 1
     };
 
+    criteria[worksOffline] = {
+      value: true,
+      weight: 1
+    };
+
     return criteria;
   }
 }

audits/offline/works-offline.js

@@ -0,0 +1,52 @@
+/**
+ * @license
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+const Audit = require('../audit');
+
+class WorksOffline extends Audit {
+  /**
+   * @override
+   */
+  static get tags() {
+    return ['Offline'];
+  }
+
+  /**
+   * @override
+   */
+  static get name() {
+    return 'works offline';
+  }
+
+  /**
+   * @override
+   */
+  static get description() {
+    return 'URL responds with a 200 when offline';
+  }
+
+  /**
+   * @param {!Artifacts} artifacts
+   * @return {!AuditResult}
+   */
+  static audit(artifacts) {
+    return WorksOffline.generateAuditResult(artifacts.responseCode === 200);
+  }
+}
+
+module.exports = WorksOffline;

gatherers/offline.js

@@ -0,0 +1,74 @@
+/**
+ * @license
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+const Gather = require('./gather');
+
+// Request the current page by issuing a sync request to ''.
+const requestPage = `
+  (function() {
+    var request = new XMLHttpRequest();
+    request.open('GET', '', false);
+    request.send(null);
+    return request.status;
+  })();
+`;
+
+class Offline extends Gather {
+
+  static goOffline(driver) {
+    return driver.sendCommand('Network.emulateNetworkConditions', {
+      offline: true,
+      latency: 0,
+      downloadThroughput: 0,
+      uploadThroughput: 0
+    });
+  }
+
+  static goOnline(driver) {
+    return driver.sendCommand('Network.emulateNetworkConditions', {
+      offline: false,
+      latency: 0,
+      downloadThroughput: 0,
+      uploadThroughput: 0
+    });
+  }
+
+  static getOfflinePageStatus(driver) {
+    return driver.sendCommand('Runtime.evaluate', {
+      expression: requestPage
+    });
+  }
+
+  static gather(options) {
+    const driver = options.driver;
+
+    // TODO eventually we will want to walk all network
+    // requests that the page initially made and retry them.
+    return Offline.goOffline(driver).then(_ => {
+      let responseCode;
+
+      return Offline.getOfflinePageStatus(driver).then(ret => {
+        responseCode = ret.result.value;
+      }).then(_ => Offline.goOnline(driver)).then(_ => {
+        return {responseCode};
+      });
+    });
+  }
+}
+
+module.exports = Offline;

index.js

@@ -31,11 +31,14 @@ const gatherers = [
   require('./gatherers/viewport'),
   require('./gatherers/theme-color'),
   require('./gatherers/html'),
-  require('./gatherers/manifest')
+  require('./gatherers/manifest'),
+  require('./gatherers/offline')
 ];
+
 const audits = [
   require('./audits/security/is-on-https'),
   require('./audits/offline/service-worker'),
+  require('./audits/offline/works-offline'),
   require('./audits/mobile-friendly/viewport'),
   require('./audits/performance/first-meaningful-paint'),
   require('./audits/manifest/exists'),
@@ -48,6 +51,7 @@ const audits = [
   require('./audits/manifest/start-url'),
   require('./audits/html/meta-theme-color')
 ];
+
 const aggregators = [
   require('./aggregators/will-get-add-to-homescreen-prompt'),
   require('./aggregators/launches-with-splash-screen'),