(core) Export to Excel and Send to drive

Summary:
Implementing export to excel and send to Google Drive feature.

As part of this feature few things were implemented:
- Server side google authentication exposed on url: (docs, docs-s, or localhost:8080)/auth/google
- Exporting grist documents as an excel file (xlsx)
- Storing exported grist document (in excel format) in Google Drive as a spreadsheet document.

Server side google authentication requires one new environmental variables
- GOOGLE_CLIENT_SECRET (required) used by authentication handler

Test Plan: Browser tests for exporting to excel.

Reviewers: paulfitz, dsagal

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2924

app/common/UserAPI.ts

@@ -344,6 +344,13 @@ export interface DocAPI {
   // is HEAD, the result will contain a copy of any rows added or updated.
   compareVersion(leftHash: string, rightHash: string): Promise<DocStateComparison>;
   getDownloadUrl(template?: boolean): string;
+  /**
+   * Exports current document to the Google Drive as a spreadsheet file. To invoke this method, first
+   * acquire "code" via Google Auth Endpoint (see ShareMenu.ts for an example).
+   * @param code Authorization code returned from Google (requested via Grist's Google Auth Endpoint)
+   * @param title Name of the spreadsheet that will be created (should use a Grist document's title)
+   */
+  sendToDrive(code: string, title: string): Promise<{url: string}>;
 }
 
 // Operations that are supported by a doc worker.
@@ -775,4 +782,11 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
   public getDownloadUrl(template: boolean = false) {
     return this._url + `/download?template=${Number(template)}`;
   }
+
+  public async sendToDrive(code: string, title: string): Promise<{url: string}> {
+    const url = new URL(`${this._url}/send-to-drive`);
+    url.searchParams.append('title', title);
+    url.searchParams.append('code', code);
+    return this.requestJson(url.href);
+  }
 }

app/common/gutil.ts

@@ -133,7 +133,7 @@ export function undef<T extends Array<any>>(...list: T): Undef<T> {
  */
 export function safeJsonParse(json: string, defaultVal: any): any {
   try {
-    return JSON.parse(json);
+    return json !== '' && json !== undefined ? JSON.parse(json) : defaultVal;
   } catch (e) {
     return defaultVal;
   }