qt http 下载文件 断点续传

[stweddy]

http网络编程下载文件 利用QT现有API类 QNetworkAccessManager、QNetworkRequest 、QNetworkReply，文件从头开始下载正常，断线重新继续下载时，下载速度严重下降，但是能够将文件下载完，请问如何解决下载速度变慢的问题

[stweddy]

断点续传实现部分程序如下：
QNetworkAccessManager *m_qnam = new QNetworkAccessManager();
QNetworkReply * m_reply = new QNetworkReply ();
if ((m_sProxyServerIP.isEmpty()) || (m_iProxyServerPort==0))
{
m_qnam->setProxy(QNetworkProxy::NoProxy);
}
else
{
m_qnam->setProxy(QNetworkProxy(QNetworkProxy::Socks5Proxy,m_sProxyServerIP,m_iProxyServerPort));
}

qint64 iTotalSize = fileGetSize(url);
QNetworkRequest qheader;
qheader.setUrl(url);
QString sRange = QString("bytes=%1 - %2")
.arg(QString::number(m_iDownedSize))
.arg(QString::number(iTotalSize));
qheader.setRawHeader("Range", sRange.toAscii());
qheader.setPriority(QNetworkRequest::HighPriority);

m_reply = m_qnam->get(QNetworkRequest(qheader));
connect(m_reply, SIGNAL(finished()),
this, SLOT(slotHttpFinished()));
connect(m_reply, SIGNAL(readyRead()),
this, SLOT(slotHttpReadyRead()));
connect(m_reply, SIGNAL(downloadProgress(qint64,qint64)),
this, SLOT(slotUpdateDataReadProgress(qint64,qint64)));