Bug 658683: Make xhr.response not create a new ArrayBuffer every time it is accessed. r=sicking. Additional fixes by sicking, r=peterv

content/base/src/nsXMLHttpRequest.cpp

@@ -426,7 +426,8 @@ nsXMLHttpRequest::nsXMLHttpRequest()
     mErrorLoad(PR_FALSE), mTimerIsActive(PR_FALSE),
     mProgressEventWasDelayed(PR_FALSE),
     mLoadLengthComputable(PR_FALSE), mLoadTotal(0),
-    mFirstStartRequestSeen(PR_FALSE)
+    mFirstStartRequestSeen(PR_FALSE),
+    mResultArrayBuffer(nsnull) 
 {
   mResponseBodyUnicode.SetIsVoid(PR_TRUE);
   nsLayoutStatics::AddRef();
@@ -450,6 +451,12 @@ nsXMLHttpRequest::~nsXMLHttpRequest()
   nsLayoutStatics::Release();
 }
 
+void
+nsXMLHttpRequest::RootResultArrayBuffer()
+{
+  nsContentUtils::PreserveWrapper(static_cast<nsPIDOMEventTarget*>(this), this);
+}
+
 /**
  * This Init method is called from the factory constructor.
  */
@@ -572,9 +579,9 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsXMLHttpRequest,
                                                        nsIXMLHttpRequestUpload)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
-
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsXMLHttpRequest,
                                                 nsXHREventTarget)
+  tmp->mResultArrayBuffer = nsnull;
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mContext)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mChannel)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mReadRequest)
@@ -592,6 +599,14 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsXMLHttpRequest,
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mUpload)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(nsXMLHttpRequest,
+                                               nsXHREventTarget)
+  if(tmp->mResultArrayBuffer) {
+    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_CALLBACK(tmp->mResultArrayBuffer,
+                                               "mResultArrayBuffer")
+  }
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
 DOMCI_DATA(XMLHttpRequest, nsXMLHttpRequest)
 
 // QueryInterface implementation for nsXMLHttpRequest
@@ -839,27 +854,20 @@ NS_IMETHODIMP nsXMLHttpRequest::GetResponseText(nsAString& aResponseText)
   return rv;
 }
 
-nsresult nsXMLHttpRequest::GetResponseArrayBuffer(jsval *aResult)
+nsresult nsXMLHttpRequest::CreateResponseArrayBuffer(JSContext *aCx)
 {
-  JSContext *cx = nsContentUtils::GetCurrentJSContext();
+  if (!aCx)
-  if (!cx)
     return NS_ERROR_FAILURE;
 
-  if (!(mState & (XML_HTTP_REQUEST_DONE |
-                  XML_HTTP_REQUEST_LOADING))) {
-    *aResult = JSVAL_NULL;
-    return NS_OK;
-  }
-
   PRInt32 dataLen = mResponseBody.Length();
-  JSObject *obj = js_CreateArrayBuffer(cx, dataLen);
+  RootResultArrayBuffer();
-  if (!obj)
+  mResultArrayBuffer = js_CreateArrayBuffer(aCx, dataLen);
+  if (!mResultArrayBuffer) {
     return NS_ERROR_FAILURE;
-
+  }
-  *aResult = OBJECT_TO_JSVAL(obj);
 
   if (dataLen > 0) {
-    js::ArrayBuffer *abuf = js::ArrayBuffer::fromJSObject(obj);
+    js::ArrayBuffer *abuf = js::ArrayBuffer::fromJSObject(mResultArrayBuffer);
     NS_ASSERTION(abuf, "What happened?");
     memcpy(abuf->data, mResponseBody.BeginReading(), dataLen);
   }
@@ -954,7 +962,11 @@ NS_IMETHODIMP nsXMLHttpRequest::GetResponse(JSContext *aCx, jsval *aResult)
 
   case XML_HTTP_RESPONSE_TYPE_ARRAYBUFFER:
     if (mState & XML_HTTP_REQUEST_DONE) {
-      rv = GetResponseArrayBuffer(aResult);
+      if (!mResultArrayBuffer) {  
+         rv = CreateResponseArrayBuffer(aCx);
+         NS_ENSURE_SUCCESS(rv, rv);
+      }
+      *aResult = OBJECT_TO_JSVAL(mResultArrayBuffer);
     } else {
       *aResult = JSVAL_NULL;
     }
@@ -1073,6 +1085,7 @@ nsXMLHttpRequest::Abort()
   mResponseBodyUnicode.SetIsVoid(PR_TRUE);
   mResponseBlob = nsnull;
   mState |= XML_HTTP_REQUEST_ABORTED;
+  mResultArrayBuffer = nsnull;
   
   if (!(mState & (XML_HTTP_REQUEST_UNSENT |
                   XML_HTTP_REQUEST_OPENED |

content/base/src/nsXMLHttpRequest.h

@@ -208,10 +208,10 @@ public:
 
   void SetRequestObserver(nsIRequestObserver* aObserver);
 
-  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(nsXMLHttpRequest,
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(nsXMLHttpRequest,
                                            nsXHREventTarget)
-
   PRBool AllowUploadProgress();
+  void RootResultArrayBuffer();
   
 protected:
   friend class nsMultipartProxyListener;
@@ -224,7 +224,7 @@ protected:
                 PRUint32 toOffset,
                 PRUint32 count,
                 PRUint32 *writeCount);
-  nsresult GetResponseArrayBuffer(jsval *aResult);
+  nsresult CreateResponseArrayBuffer(JSContext* aCx);
   void CreateResponseBlob(nsIRequest *request);
   // Change the state of the object with this. The broadcast argument
   // determines if the onreadystatechange listener should be called.
@@ -345,6 +345,8 @@ protected:
   
   nsCOMPtr<nsIAsyncVerifyRedirectCallback> mRedirectCallback;
   nsCOMPtr<nsIChannel> mNewRedirectChannel;
+  
+  JSObject* mResultArrayBuffer;
 };
 
 // helper class to expose a progress DOM Event

content/base/test/test_XHR.html

@@ -134,6 +134,16 @@ ab = xhr.response;
 ok(ab != null, "should have a non-null arraybuffer");
 arraybuffer_equals_to(ab, "\xaa\xee\0\x03\xff\xff\xff\xff\xbb\xbb\xbb\xbb");
 
+// test array buffer GetResult returns the same object
+xhr = new XMLHttpRequest();
+xhr.open("GET", 'file_XHR_binary1.bin', false); 
+xhr.responseType = 'arraybuffer';
+xhr.send(null)
+is(xhr.status, 200, "wrong status");
+checkResponseTextAccessThrows(xhr);
+checkResponseXMLAccessThrows(xhr);
+is(xhr.response, xhr.response, "returns the same ArrayBuffer");
+
 // test response (responseType='blob')
 var onloadCount = 0;
 function checkOnloadCount() {

xpcom/glue/nsCycleCollectionParticipant.h

@@ -436,6 +436,20 @@ public:
                  "not the nsISupports pointer we expect");                     \
     _class *tmp = Downcast(s);
 
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(_class, _base_class)    \
+  void                                                                         \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(void *p,                        \
+                                               TraceCallback aCallback,        \
+                                               void *aClosure)                 \
+  {                                                                            \
+    nsISupports *s = static_cast<nsISupports*>(p);                             \
+    NS_ASSERTION(CheckForRightISupports(s),                                    \
+                 "not the nsISupports pointer we expect");                     \
+    _class *tmp = static_cast<_class*>(Downcast(s));                           \
+    NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Trace(s,                       \
+                                                      aCallback,               \
+                                                      aClosure);
+
 #define NS_IMPL_CYCLE_COLLECTION_TRACE_NATIVE_BEGIN(_class)                    \
   void                                                                         \
   NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(void *p,                        \