Use downloadToFile option when XHR downloads a Blob

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 4b041d4ec7e998a3f5e89b9c8366a8f3dc2c5a54..797318b8c5d62c57fb3b21b4f8de4dbdee325e64 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -276,31 +276,26 @@ Document* XMLHttpRequest::responseXML(ExceptionState& es)
 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: This causes two (or more) unnecessary copies of the data.
-        // Chromium stores blob data in the browser process, so we're pulling the data
-        // from the network only to copy it into the renderer to copy it back to the browser.
-        // Ideally we'd get the blob/file-handle from the ResourceResponse directly
-        // instead of copying the bytes. Embedders who store blob data in the
-        // same process as WebCore would at least to teach BlobData to take
-        // a SharedBuffer, even if they don't get the Blob from the network layer directly.
+        // When "blob" is specified for the responseType attribute,
+        // we redirect the downloaded data to the 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();
+        const String& filePath = m_response.downloadedFilePath();
         // If we errored out or got no data, we still return a blob, just an empty one.
-        size_t size = 0;
-        if (m_binaryResponseBuilder) {
-            RefPtr<RawData> rawData = RawData::create();
-            size = m_binaryResponseBuilder->size();
-            rawData->mutableData()->append(m_binaryResponseBuilder->data(), size);
-            blobData->appendData(rawData, 0, BlobDataItem::toEndOfFile);
+        if (!filePath.isEmpty() && m_receivedLength) {
+            blobData->appendFile(filePath);
             blobData->setContentType(responseMIMEType()); // responseMIMEType defaults to text/xml which may be incorrect.
-            m_binaryResponseBuilder.clear();
         }
-        m_responseBlob = Blob::create(blobData.release(), size);
+        m_responseBlob = Blob::create(blobData.release(), m_receivedLength);
     }
 
     return m_responseBlob.get();
@@ -752,6 +747,12 @@ void XMLHttpRequest::createRequest(ExceptionState& es)
     request.setHTTPMethod(m_method);
     request.setTargetType(ResourceRequest::TargetIsXHR);
 
+    // When "blob" is specified for the responseType attribute,
+    // we redirect the downloaded data to the file-handle directly
+    // and get the file-path as the result.
+    if (responseTypeCode() == ResponseTypeBlob)
+        request.setDownloadToFile(true);
+
     InspectorInstrumentation::willLoadXHR(scriptExecutionContext(), this, m_method, m_url, m_async, m_requestEntityBody ? m_requestEntityBody->deepCopy() : 0, m_requestHeaders, m_includeCredentials);
 
     if (m_requestEntityBody) {
@@ -776,6 +777,12 @@ void XMLHttpRequest::createRequest(ExceptionState& es)
     options.mixedContentBlockingTreatment = TreatAsActiveContent;
     options.timeoutMilliseconds = m_timeoutMilliseconds;
 
+    // Since we redirect the downloaded data to the file-handle directly
+    // when "blob" is specified for the responseType attribute,
+    // buffering is not needed.
+    if (responseTypeCode() == ResponseTypeBlob)
+        options.dataBufferingPolicy = DoNotBufferData;
+
     m_exceptionCode = 0;
     m_error = false;
 
@@ -1176,6 +1183,8 @@ void XMLHttpRequest::didReceiveResponse(unsigned long identifier, const Resource
 
 void XMLHttpRequest::didReceiveData(const char* data, int len)
 {
+    ASSERT(m_responseTypeCode != ResponseTypeBlob);
+
     if (m_error)
         return;
 
@@ -1208,7 +1217,7 @@ 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();
@@ -1237,6 +1246,38 @@ void XMLHttpRequest::didReceiveData(const char* data, int len)
     }
 }
 
+void XMLHttpRequest::didDownloadData(int len)
+{
+    ASSERT(m_responseTypeCode == ResponseTypeBlob);
+
+    if (m_error)
+        return;
+
+    if (m_state < HEADERS_RECEIVED)
+        changeState(HEADERS_RECEIVED);
+
+    if (!len)
+        return;
+
+    if (!m_error) {
+        long long expectedLength = m_response.expectedContentLength();
+        m_receivedLength += len;
+
+        if (m_async) {
+            bool lengthComputable = expectedLength > 0 && m_receivedLength <= expectedLength;
+            unsigned long long total = lengthComputable ? expectedLength : 0;
+            m_progressEventThrottle.dispatchProgressEvent(lengthComputable, m_receivedLength, total);
+        }
+
+        if (m_state != LOADING) {
+            changeState(LOADING);
+        } else {
+            // Firefox calls readyStateChanged every time it receives data, 4449442
+            callReadyStateChangeListener();
+        }
+    }
+}
+
 void XMLHttpRequest::didTimeout()
 {
     // internalAbort() calls dropProtection(), which may release the last reference.