Reenable optimization on XMLHttpRequest's receive-as-blob functionality

Source/core/xml/XMLHttpRequest.cpp

Index: Source/core/xml/XMLHttpRequest.cpp
diff --git a/Source/core/xml/XMLHttpRequest.cpp b/Source/core/xml/XMLHttpRequest.cpp
index 155d442a87685d72eb63d6880596e1f05334d727..2a585245b23d0b254675ac78d083214150baeb33 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -171,6 +171,7 @@ XMLHttpRequest::XMLHttpRequest(ExecutionContext* context, PassRefPtr<SecurityOri
     , m_timeoutMilliseconds(0)
     , m_state(UNSENT)
     , m_createdDocument(false)
+    , m_downloadedBlobLength(0)
     , m_error(false)
     , m_uploadEventsAllowed(true)
     , m_uploadComplete(false)
@@ -276,26 +277,26 @@ Document* XMLHttpRequest::responseXML(ExceptionState& exceptionState)
 Blob* XMLHttpRequest::responseBlob()
 {
     ASSERT(m_responseTypeCode == ResponseTypeBlob);
+    ASSERT(!m_binaryResponseBuilder.get());
 
     // We always return null before DONE.
     if (m_error || m_state != DONE)
         return 0;
 
     if (!m_responseBlob) {
-        // FIXME: Once RedirectToFileResourceHandler is fixed in Chromium,
-        // re-enable download-to-file optimization introduced by Blink revision
-        // 163141.
+        // When responseType is set to "blob", we redirect the downloaded data
+        // to a file-handle directly in the browser process. We get the
+        // file-path from the ResourceResponse directly instead of copying the
+        // bytes between the browser and the renderer.
         OwnPtr<BlobData> blobData = BlobData::create();
-        size_t size = 0;
-        if (m_binaryResponseBuilder.get() && m_binaryResponseBuilder->size() > 0) {
-            RefPtr<RawData> rawData = RawData::create();
-            size = m_binaryResponseBuilder->size();
-            rawData->mutableData()->append(m_binaryResponseBuilder->data(), size);
-            blobData->appendData(rawData, 0, BlobDataItem::toEndOfFile);
+        String filePath = m_response.downloadedFilePath();
+        // If we errored out or got no data, we still return a blob, just an
+        // empty one.
+        if (!filePath.isEmpty() && m_downloadedBlobLength) {
+            blobData->appendFile(filePath);
             blobData->setContentType(responseMIMEType()); // responseMIMEType defaults to text/xml which may be incorrect.
-            m_binaryResponseBuilder.clear();
         }
-        m_responseBlob = Blob::create(BlobDataHandle::create(blobData.release(), size));
+        m_responseBlob = Blob::create(BlobDataHandle::create(blobData.release(), m_downloadedBlobLength));
     }
 
     return m_responseBlob.get();
@@ -854,6 +855,13 @@ void XMLHttpRequest::createRequest(ExceptionState& exceptionState)
     // TODO(tsepez): Specify TreatAsActiveContent per http://crbug.com/305303.
     resourceLoaderOptions.mixedContentBlockingTreatment = TreatAsPassiveContent;
 
+    // When responseType is set to "blob", we redirect the downloaded data to a
+    // file-handle directly.
+    if (responseTypeCode() == ResponseTypeBlob) {
+        request.setDownloadToFile(true);
+        resourceLoaderOptions.dataBufferingPolicy = DoNotBufferData;
+    }
+
     m_exceptionCode = 0;
     m_error = false;
 
@@ -977,6 +985,7 @@ void XMLHttpRequest::clearResponse()
     m_responseDocument = nullptr;
 
     m_responseBlob = nullptr;
+    m_downloadedBlobLength = 0;
 
     m_responseStream = nullptr;
 
@@ -1314,6 +1323,8 @@ void XMLHttpRequest::didReceiveResponse(unsigned long identifier, const Resource
 
 void XMLHttpRequest::didReceiveData(const char* data, int len)
 {
+    ASSERT(m_responseTypeCode != ResponseTypeBlob);
+
     if (m_error)
         return;
 
@@ -1346,7 +1357,7 @@ void XMLHttpRequest::didReceiveData(const char* data, int len)
 
     if (useDecoder) {
         m_responseText = m_responseText.concatenateWith(m_decoder->decode(data, len));
-    } else if (m_responseTypeCode == ResponseTypeArrayBuffer || m_responseTypeCode == ResponseTypeBlob) {
+    } else if (m_responseTypeCode == ResponseTypeArrayBuffer) {
         // Buffer binary data.
         if (!m_binaryResponseBuilder)
             m_binaryResponseBuilder = SharedBuffer::create();
@@ -1363,6 +1374,29 @@ void XMLHttpRequest::didReceiveData(const char* data, int len)
     trackProgress(len);
 }
 
+void XMLHttpRequest::didDownloadData(int dataLength)
+{
+    ASSERT(m_responseTypeCode == ResponseTypeBlob);
+
+    if (m_error)
+        return;
+
+    if (m_state < HEADERS_RECEIVED)
+        changeState(HEADERS_RECEIVED);
+
+    if (!dataLength)
+        return;
+
+    // readystatechange event handler may do something to put this XHR in error
+    // state. We need to check m_error again here.
+    if (m_error)
+        return;
+
+    m_downloadedBlobLength += dataLength;
+
+    trackProgress(dataLength);
+}
+
 void XMLHttpRequest::handleDidTimeout()
 {
     WTF_LOG(Network, "XMLHttpRequest %p handleDidTimeout()", this);