fix($http): do not throw error if Content-Type is not application/json but response is JSON-like

Previously, when the response data was JSON-like, `$http` would try to
`JSON.parse` them and throw if they were not actually JSON. This happened even
if the `Content-Type` header was not `application/json`. As a result, it was not
possible to send `text/plain` data that looked like JSON (e.g. `{abcd}`).
The reason for not relying solely on the `Content-Type` is that many users serve
JSON data without proper headers.

This commit fixes it by returning the raw response text if `$http` fails to
parse a JSON-like response, unless the `Content-Type` header has been explicitly
set to `application/json` (in which case it will still fail with an error).

Fixes #16027

Closes #16075

Author: katsos

src/ng/http.js

@@ -137,10 +137,15 @@ function defaultHttpResponseTransform(data, headers) {
 
     if (tempData) {
       var contentType = headers('Content-Type');
-      if ((contentType && (contentType.indexOf(APPLICATION_JSON) === 0)) || isJsonLike(tempData)) {
+      var hasJsonContentType = contentType && (contentType.indexOf(APPLICATION_JSON) === 0);
+
+      if (hasJsonContentType || isJsonLike(tempData)) {
         try {
           data = fromJson(tempData);
         } catch (e) {
+          if (!hasJsonContentType) {
+            return data;
+          }
           throw $httpMinErr('baddata', 'Data must be a valid JSON object. Received: "{0}". ' +
           'Parse error: "{1}"', data, e);
         }

test/ng/httpSpec.js

@@ -1402,8 +1402,45 @@ describe('$http', function() {
             expect(errCallback.calls.mostRecent().args[0]).toEqualMinErr('$http', 'baddata');
           });
 
-        });
+          it('should not throw an error if JSON is invalid but content-type is not application/json', function() {
+            $httpBackend.expect('GET', '/url').respond('{abcd}', {'Content-Type': 'text/plain'});
+
+            $http.get('/url').then(callback);
+            $httpBackend.flush();
+
+            expect(callback).toHaveBeenCalledOnce();
+          });
+
+          it('should not throw an error if JSON is invalid but content-type is not specified', function() {
+            $httpBackend.expect('GET', '/url').respond('{abcd}');
+
+            $http.get('/url').then(callback);
+            $httpBackend.flush();
+
+            expect(callback).toHaveBeenCalledOnce();
+          });
 
+          it('should return response unprocessed if JSON is invalid but content-type is not application/json', function() {
+            var response = '{abcd}';
+            $httpBackend.expect('GET', '/url').respond(response, {'Content-Type': 'text/plain'});
+
+            $http.get('/url').then(callback);
+            $httpBackend.flush();
+
+            expect(callback.calls.mostRecent().args[0].data).toBe(response);
+          });
+
+          it('should return response unprocessed if JSON is invalid but content-type is not specified', function() {
+            var response = '{abcd}';
+            $httpBackend.expect('GET', '/url').respond(response);
+
+            $http.get('/url').then(callback);
+            $httpBackend.flush();
+
+            expect(callback.calls.mostRecent().args[0].data).toBe(response);
+          });
+
+        });
 
         it('should have access to response headers', function() {
           $httpBackend.expect('GET', '/url').respond(200, 'response', {h1: 'header1'});