fix(httpBackend): should not read response data when request is aborted

When a request is aborted, it makes no sense to read the response headers or text.
Also in IE9, trying to read data (either response headers or text) from an aborted request
throws an Error c00c023f.

Fixes angular#4913

Author: Gonzalo Ruiz de Villa

src/ng/httpBackend.js

@@ -69,13 +69,19 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument,
       // always async
       xhr.onreadystatechange = function() {
         if (xhr.readyState == 4) {
-          var responseHeaders = xhr.getAllResponseHeaders();
+          var responseHeaders = null,
+              response = null;
+
+          if(!xhr.aborted) {
+            responseHeaders = xhr.getAllResponseHeaders();
+            response = xhr.responseType ? xhr.response : xhr.responseText;
+          }
 
           // responseText is the old-school way of retrieving response (supported by IE8 & 9)
           // response/responseType properties were introduced in XHR Level2 spec (supported by IE10)
           completeRequest(callback,
               status || xhr.status,
-              (xhr.responseType ? xhr.response : xhr.responseText),
+              response,
               responseHeaders);
         }
       };
@@ -101,7 +107,7 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument,
     function timeoutRequest() {
       status = -1;
       jsonpDone && jsonpDone();
-      xhr && xhr.abort();
+      xhr && (xhr.aborted = true) && xhr.abort();
     }
 
     function completeRequest(callback, status, response, headersString) {

test/ng/httpBackendSpec.js

@@ -118,6 +118,25 @@ describe('$httpBackend', function() {
     });
   });
 
+  it('should not try to read response data when request is aborted', function() {
+    callback.andCallFake(function(status, response, headers) {
+      expect(status).toBe(-1);
+      expect(response).toBe(null);
+      expect(headers).toBe(null);
+    });
+    $backend('GET', '/url', null, callback, {}, 2000);
+    xhr = MockXhr.$$lastInstance;
+    spyOn(xhr, 'abort');
+
+    fakeTimeout.flush();
+    expect(xhr.abort).toHaveBeenCalledOnce();
+
+    xhr.status = 0;
+    xhr.readyState = 4;
+    xhr.onreadystatechange();
+    expect(callback).toHaveBeenCalledOnce();
+  });
+
   it('should abort request on timeout', function() {
     callback.andCallFake(function(status, response) {
       expect(status).toBe(-1);