[QT5.3:Windows7]File upload through QNetworkAccessManager, memory spiking with proxy

[mavericks]

I am using qt(5.3) on windows 7(vs2008)(below code, skipping the details) to upload a file which is on the disk. if the proxy is not enabled on the system,
upload is working fine for any size(i tried ~3gb) without spiking memory for my application(~22MB). But as i enable system proxy, memory for the application
is growing propotional to uploadProgress. It works fine with file size below 1.3GB upload. As my application is 32 bit, it crashes(bad_alloc, in qt) if i try to
upload more than 1.3GB file with proxy.

So i have following queries:
1) Are we loading complete file into memory if proxy is enabled?

2) As i guess, we are not loading complete file into memory if proxy is not enabled. Can we do same thing if proxy is enabled? If yes, how can we achieve that?

QNetworkReply* upload(const QString &title, const QString &path, const QString &payload, QNetworkRequest request, QNetworkAccessManager* nam)
 
 
 
			QHttpMultiPart *pMultipart = new QHttpMultiPart(QHttpMultiPart::FormDataType);
            QHttpPart richPart;
            richPart.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant("form-data; name=\"entity_document\""));
            richPart.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/json; charset=UTF-8"));
            richPart.setBody(payload.toUtf8());
 
            QString binaryHeader = "form-data; name=\"fileData\"; filename=\"";
            binaryHeader += title;
            binaryHeader += "\"";
 
            QHttpPart binaryHeader;
            binaryHeader.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("text/plain; charset=UTF-8"));
            binaryHeader.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant(binaryHeader));
 
            QFile *fileP = new QFile(path);
            if(!fileP->open(QIODevice::ReadOnly))
            {
               //logging the error
            }
            binaryHeader.setBodyDevice(fileP);
            fileP->setParent(pMultipart); 
 
            pMultipart->append(richPart);
            pMultipart->append(binaryHeader);
 
            m_replyP = nam->post(request, pMultipart);
            pMultipart->setParent(m_replyP);
			  //bindall(); here binding finished() and uploadProgress signal 
			  return m_replyP;
			}
 
           //Skipped normal memory cleanup

QNetworkReply* upload(const QString &title, const QString &path, const QString &payload, QNetworkRequest request, QNetworkAccessManager* nam)
		    
						
			
			QHttpMultiPart *pMultipart = new QHttpMultiPart(QHttpMultiPart::FormDataType);
            QHttpPart richPart;
            richPart.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant("form-data; name=\"entity_document\""));
            richPart.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/json; charset=UTF-8"));
            richPart.setBody(payload.toUtf8());

            QString binaryHeader = "form-data; name=\"fileData\"; filename=\"";
            binaryHeader += title;
            binaryHeader += "\"";

            QHttpPart binaryHeader;
            binaryHeader.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("text/plain; charset=UTF-8"));
            binaryHeader.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant(binaryHeader));

            QFile *fileP = new QFile(path);
            if(!fileP->open(QIODevice::ReadOnly))
            {
               //logging the error
            }
            binaryHeader.setBodyDevice(fileP);
            fileP->setParent(pMultipart); 

            pMultipart->append(richPart);
            pMultipart->append(binaryHeader);

            m_replyP = nam->post(request, pMultipart);
            pMultipart->setParent(m_replyP);
			  //bindall(); here binding finished() and uploadProgress signal 
			  return m_replyP;
			}

           //Skipped normal memory cleanup

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Applicatin initialization if Proxy is enabled on machine:

QNetworkProxy applicationProxy  = QNetworkProxy::applicationProxy();
 
               applicationProxy.setUser(user);
               applicationProxy.setPassword(password);
 
               QNetworkProxy::setApplicationProxy(applicationProxy);
               nam->setProxy(applicationProxy);

QNetworkProxy applicationProxy  = QNetworkProxy::applicationProxy();
			 
               applicationProxy.setUser(user);
               applicationProxy.setPassword(password);

               QNetworkProxy::setApplicationProxy(applicationProxy);
               nam->setProxy(applicationProxy);

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