fix(security): support XSSI prefixes with and without commas.

Some implementations use an XSSI prefix with a trailing comma, some without.
This changes Angular to support both.

Author: mprobst

modules/@angular/http/src/backends/xhr_backend.ts

@@ -13,7 +13,7 @@ import {Observable} from 'rxjs/Observable';
 import {Observer} from 'rxjs/Observer';
 import {isSuccess, getResponseURL} from '../http_utils';
 
-const XSSI_PREFIX = ')]}\',\n';
+const XSSI_PREFIX = /^\)\]\}',?\n/;
 
 /**
  * Creates connections using `XMLHttpRequest`. Given a fully-qualified
@@ -46,9 +46,7 @@ export class XHRConnection implements Connection {
         // IE10)
         let body = isPresent(_xhr.response) ? _xhr.response : _xhr.responseText;
         // Implicitly strip a potential XSSI prefix.
-        if (isString(body) && body.startsWith(XSSI_PREFIX)) {
-          body = body.substring(XSSI_PREFIX.length);
-        }
+        if (isString(body)) body = body.replace(XSSI_PREFIX, '');
         let headers = Headers.fromResponseHeaderString(_xhr.getAllResponseHeaders());
 
         let url = getResponseURL(_xhr);

modules/@angular/http/test/backends/xhr_backend_spec.ts

@@ -472,6 +472,17 @@ export function main() {
            existingXHRs[0].dispatchEvent('load');
          }));
 
+      it('should strip XSSI prefixes', inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
+           var conn = new XHRConnection(sampleRequest, new MockBrowserXHR(), new ResponseOptions());
+           conn.response.subscribe((res: Response) => {
+             expect(res.text()).toBe('{json: "object"}');
+             async.done();
+           });
+           existingXHRs[0].setStatusCode(200);
+           existingXHRs[0].setResponseText(')]}\'\n{json: "object"}');
+           existingXHRs[0].dispatchEvent('load');
+         }));
+
       it('should strip XSSI prefixes', inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
            var conn = new XHRConnection(sampleRequest, new MockBrowserXHR(), new ResponseOptions());
            conn.response.subscribe((res: Response) => {
@@ -491,7 +502,7 @@ export function main() {
              async.done();
            });
            existingXHRs[0].setStatusCode(404);
-           existingXHRs[0].setResponseText(')]}\',\n{json: "object"}');
+           existingXHRs[0].setResponseText(')]}\'\n{json: "object"}');
            existingXHRs[0].dispatchEvent('load');
          }));