fix(AjaxObservable): notify with error if fails to parse json response

Catch error when parsing json response and notify observer with thrown error.
JSON could be invalid if proxy overtakes the response and in IE responseType is empty.

closes ReactiveX#3138

spec/observables/dom/ajax-spec.ts

@@ -229,6 +229,34 @@ describe('Observable.ajax', () => {
     expect(complete).to.be.true;
   });
 
+  it('should fail if fails to parse response', () => {
+    let error;
+    const obj = {
+      url: '/flibbertyJibbet',
+      responseType: 'json',
+      method: ''
+    };
+
+    Rx.Observable.ajax(obj)
+      .subscribe((x: any) => {
+        throw 'should not next';
+      }, (err: any) => {
+        error = err;
+      }, () => {
+        throw 'should not complete';
+      });
+
+    MockXMLHttpRequest.mostRecent.respondWith({
+      'status': 207,
+      'contentType': '',
+      'responseType': '',
+      'responseText': 'Wee! I am text, but should be valid JSON!'
+    });
+
+    expect(error instanceof SyntaxError).to.be.true;
+    expect(error.message).to.equal('Unexpected token W in JSON at position 0');
+  });
+
   it('should fail on 404', () => {
     let error;
     const obj = {
@@ -294,6 +322,36 @@ describe('Observable.ajax', () => {
     expect(error.status).to.equal(300);
   });
 
+  it('should fail if fails to parse error response', () => {
+    let error;
+    const obj = {
+      url: '/flibbertyJibbet',
+      normalizeError: (e: any, xhr: any, type: any) => {
+        return xhr.response || xhr.responseText;
+      },
+      responseType: 'json',
+      method: ''
+    };
+
+    Rx.Observable.ajax(obj).subscribe(x => {
+      throw 'should not next';
+    }, (err: any) => {
+      error = err;
+    }, () => {
+      throw 'should not complete';
+    });
+
+    MockXMLHttpRequest.mostRecent.respondWith({
+      'status': 404,
+      'contentType': '',
+      'responseType': '',
+      'responseText': 'Wee! I am text, but should be valid JSON!'
+    });
+
+    expect(error instanceof SyntaxError).to.be.true;
+    expect(error.message).to.equal('Unexpected token W in JSON at position 0');
+  });
+
   it('should succeed no settings', () => {
     const expected = JSON.stringify({ foo: 'bar' });
 
@@ -1037,8 +1095,6 @@ class MockXMLHttpRequest {
   protected defaultResponseValue() {
     if (this.async === false) {
       this.response = this.responseText;
-    } else {
-      throw new Error('unhandled type "' + this.responseType + '"');
     }
   }
 
@@ -1054,8 +1110,9 @@ class MockXMLHttpRequest {
     };
     this.status = response.status || 200;
     this.responseText = response.responseText;
+    const responseType = response.responseType !== undefined ? response.responseType : this.responseType;
     if (!('response' in response)) {
-      switch (this.responseType) {
+      switch (responseType) {
       case 'json':
         this.jsonResponseValue(response);
         break;

src/observable/dom/AjaxObservable.ts

@@ -217,8 +217,11 @@ export class AjaxSubscriber<T> extends Subscriber<Event> {
     this.done = true;
     const { xhr, request, destination } = this;
     const response = new AjaxResponse(e, xhr, request);
-
-    destination.next(response);
+    if (response.response === errorObject) {
+      destination.error(errorObject.e);
+    } else {
+      destination.next(response);
+    }
   }
 
   private send(): XMLHttpRequest {
@@ -316,7 +319,12 @@ export class AjaxSubscriber<T> extends Subscriber<Event> {
       if (progressSubscriber) {
         progressSubscriber.error(e);
       }
-      subscriber.error(new AjaxTimeoutError(this, request)); //TODO: Make betterer.
+      const ajaxTimeoutError = new AjaxTimeoutError(this, request); //TODO: Make betterer.
+      if (ajaxTimeoutError.response === errorObject) {
+        subscriber.error(errorObject.e);
+      } else {
+        subscriber.error(ajaxTimeoutError);
+      }
     };
     xhr.ontimeout = xhrTimeout;
     (<any>xhrTimeout).request = request;
@@ -342,7 +350,12 @@ export class AjaxSubscriber<T> extends Subscriber<Event> {
         if (progressSubscriber) {
           progressSubscriber.error(e);
         }
-        subscriber.error(new AjaxError('ajax error', this, request));
+        const ajaxError = new AjaxError('ajax error', this, request);
+        if (ajaxError.response === errorObject) {
+          subscriber.error(errorObject.e);
+        } else {
+          subscriber.error(ajaxError);
+        }
       };
       xhr.onerror = xhrError;
       (<any>xhrError).request = request;
@@ -375,7 +388,12 @@ export class AjaxSubscriber<T> extends Subscriber<Event> {
           if (progressSubscriber) {
             progressSubscriber.error(e);
           }
-          subscriber.error(new AjaxError('ajax error ' + status, this, request));
+          const ajaxError = new AjaxError('ajax error ' + status, this, request);
+          if (ajaxError.response === errorObject) {
+            subscriber.error(errorObject.e);
+          } else {
+            subscriber.error(ajaxError);
+          }
         }
       }
     };
@@ -458,15 +476,19 @@ export class AjaxError extends Error {
   }
 }
 
+function parseJson(xhr: XMLHttpRequest) {
+  if ('response' in xhr) {
+    //IE does not support json as responseType, parse it internally
+    return xhr.responseType ? xhr.response : JSON.parse(xhr.response || xhr.responseText || 'null');
+  } else {
+    return JSON.parse(xhr.responseText || 'null');
+  }
+}
+
 function parseXhrResponse(responseType: string, xhr: XMLHttpRequest) {
   switch (responseType) {
     case 'json':
-        if ('response' in xhr) {
-          //IE does not support json as responseType, parse it internally
-          return xhr.responseType ? xhr.response : JSON.parse(xhr.response || xhr.responseText || 'null');
-        } else {
-          return JSON.parse(xhr.responseText || 'null');
-        }
+        return tryCatch(parseJson)(xhr);
       case 'xml':
         return xhr.responseXML;
       case 'text':