fix: Chrome browser console warning about unsafe header access-control-expose-headers when calling Cloud Function

src/RESTController.js

@@ -111,11 +111,14 @@ const RESTController = {
           let response;
           try {
             response = JSON.parse(xhr.responseText);
+            const availableHeaders = typeof xhr.getAllResponseHeaders === 'function' ? xhr.getAllResponseHeaders() : "";
             headers = {};
-            if (typeof xhr.getResponseHeader === 'function' && xhr.getResponseHeader('access-control-expose-headers')) {
+            if (typeof xhr.getResponseHeader === 'function' && availableHeaders?.indexOf('access-control-expose-headers') >= 0) {
               const responseHeaders = xhr.getResponseHeader('access-control-expose-headers').split(', ');
               responseHeaders.forEach(header => {
-                headers[header] = xhr.getResponseHeader(header.toLowerCase());
+                if (availableHeaders.indexOf(header.toLowerCase()) >= 0) {
+                  headers[header] = xhr.getResponseHeader(header.toLowerCase());
+                }
               });
             }
           } catch (e) {

src/__tests__/RESTController-test.js

@@ -221,6 +221,9 @@
       getResponseHeader: function (header) {
         return headers[header];
       },
+      getAllResponseHeaders: function() {
+        return Object.keys(headers).map(key => `${key}: ${headers[key]}`).join('\n');
+      },
       send: function () {
         this.status = 200;
         this.responseText = '{}';
@@ -241,6 +244,9 @@
       getResponseHeader: function (header) {
         return headers[header];
       },
+      getAllResponseHeaders: function() {
+        return Object.keys(headers).map(key => `${key}: ${headers[key]}`).join('\n');
+      },
       send: function () {
         this.status = 200;
         this.responseText = '{}';
@@ -253,6 +259,63 @@
     expect(response._headers['X-Parse-Push-Status-Id']).toBe('5678');
   });
 
+  it('does not call getRequestHeader with no headers or no getAllResponseHeaders', async () => {
+    const XHR = function () {};
+    XHR.prototype = {
+      open: function () {},
+      setRequestHeader: function () {},
+      getResponseHeader: jest.fn(),
+      send: function () {
+        this.status = 200;
+        this.responseText = '{"result":"hello"}';
+        this.readyState = 4;
+        this.onreadystatechange();
+      },
+    };
+    RESTController._setXHR(XHR);
+    await RESTController.request('GET', 'classes/MyObject', {}, {});
+    expect(XHR.prototype.getResponseHeader.mock.calls.length).toBe(0);
+
+    XHR.prototype.getAllResponseHeaders = jest.fn();
+    await RESTController.request('GET', 'classes/MyObject', {}, {});
+    expect(XHR.prototype.getAllResponseHeaders.mock.calls.length).toBe(1);
+    expect(XHR.prototype.getResponseHeader.mock.calls.length).toBe(0);
+  });
+
+  it('does not invoke Chrome browser console error on getResponseHeader', async () => {
+    const headers = {
+      'access-control-expose-headers': 'a, b, c',
+      'a' : 'value',
+      'b' : 'value',
+      'c' : 'value',
+    }
+    const XHR = function () {};
+    XHR.prototype = {
+      open: function () {},
+      setRequestHeader: function () {},
+      getResponseHeader: jest.fn(key => {
+          if (Object.keys(headers).includes(key)) {
+              return headers[key];
+          }
+          throw new Error("Chrome creates a console error here.");
+      }),
+      getAllResponseHeaders: jest.fn(() => {
+          return Object.keys(headers).map(key => `${key}: ${headers[key]}`).join('\r\n');
+      }),
+      send: function () {
+        this.status = 200;
+        this.responseText = '{"result":"hello"}';
+        this.readyState = 4;
+        this.onreadystatechange();
+      },
+    };
+    RESTController._setXHR(XHR);
+    await RESTController.request('GET', 'classes/MyObject', {}, {});
+    expect(XHR.prototype.getAllResponseHeaders.mock.calls.length).toBe(1);
+    expect(XHR.prototype.getResponseHeader.mock.calls.length).toBe(4);
+  });
+
+
   it('handles invalid header', async () => {
     const XHR = function () {};
     XHR.prototype = {