Add x-platform update indicator

Summary: Use the new multi-platform update endpoint to indicate when new updates are available for Linux or Windows.

Reviewed By: danielbuechele

Differential Revision: D16939899

fbshipit-source-id: 11c1dc0d4fd19362a1163c613a7b7116c5edf996

src/utils/publicVersionChecker.tsx

@@ -0,0 +1,80 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import os from 'os';
+import config from '../fb-stubs/config';
+
+const getPlatformSpecifier = (): string => {
+  switch (os.platform()) {
+    case 'win32':
+      return 'windows';
+    case 'linux':
+      return 'linux';
+    case 'darwin':
+      return 'mac';
+    default:
+      throw new Error('Unsupported platform.');
+  }
+};
+
+/**
+ * @param resp A parsed JSON object retrieved from the update server.
+ */
+const parseResponse = (resp: any): VersionCheckResult => {
+  const version = resp.version;
+  const platforms = resp.platforms;
+
+  if (!version || !platforms) {
+    return {kind: 'error', msg: 'Incomplete response.'};
+  }
+
+  const platformSpecifier = getPlatformSpecifier();
+  const platform = platforms[platformSpecifier];
+  if (!platform) {
+    return {kind: 'error', msg: `Unsupported platform: ${platformSpecifier}.`};
+  }
+
+  return {
+    kind: 'update-available',
+    url: platform,
+    version,
+  };
+};
+
+export type VersionCheckResult =
+  | {
+      kind: 'update-available';
+      url: string;
+      version: string;
+    }
+  | {
+      kind: 'up-to-date';
+    }
+  | {
+      kind: 'error';
+      msg: string;
+    };
+
+export async function checkForUpdate(
+  currentVersion: string,
+): Promise<VersionCheckResult> {
+  return fetch(`${config.updateServer}?version=${currentVersion}`).then(
+    (res: Response) => {
+      switch (res.status) {
+        case 204:
+          return {kind: 'up-to-date'};
+        case 200:
+          return res.json().then(parseResponse);
+        default:
+          return {
+            kind: 'error',
+            msg: `Server responded with ${res.statusText}.`,
+          };
+      }
+    },
+  );
+}