分析QNetworkAccessManager的时候，有一段设定HTTP的请求包的Header，当时没进行深入的分析。
void QHttpNetworkConnectionPrivate::prepareRequest(HttpMessagePair &messagePair)
{
    QHttpNetworkRequest &request = messagePair.first;
    QHttpNetworkReply *reply = messagePair.second;

    // add missing fields for the request
    QByteArray value;
    // check if Content-Length is provided
    QIODevice *data = request.data();
    if (data && request.contentLength() == -1) {
        if (!data->isSequential())
            request.setContentLength(data->size());
        else
            bufferData(messagePair); // ### or do chunked upload
    }
    // set the Connection/Proxy-Connection: Keep-Alive headers
#ifndef QT_NO_NETWORKPROXY
    if (networkProxy.type() == QNetworkProxy::HttpCachingProxy)  {
        value = request.headerField("proxy-connection");
        if (value.isEmpty())
            request.setHeaderField("Proxy-Connection", "Keep-Alive");
    } else {
#endif
        value = request.headerField("connection");
        if (value.isEmpty())
            request.setHeaderField("Connection", "Keep-Alive");
#ifndef QT_NO_NETWORKPROXY
    }
#endif

    // If the request had a accept-encoding set, we better not mess
    // with it. If it was not set, we announce that we understand gzip
    // and remember this fact in request.d->autoDecompress so that
    // we can later decompress the HTTP reply if it has such an
    // encoding.
    value = request.headerField("accept-encoding");
    if (value.isEmpty()) {
#ifndef QT_NO_COMPRESS
        request.setHeaderField("Accept-Encoding", "gzip");
        request.d->autoDecompress = true;
#else
        // if zlib is not available set this to false always
        request.d->autoDecompress = false;
#endif
    }
    // set the User Agent
    value = request.headerField("user-agent");
    if (value.isEmpty())
        request.setHeaderField("User-Agent", "Mozilla/5.0");
    // set the host
    value = request.headerField("host");
    if (value.isEmpty()) {
        QByteArray host = QUrl::toAce(hostName);

        int port = request.url().port();
        if (port != -1) {
            host += ':';
            host += QByteArray::number(port);
        }

        request.setHeaderField("Host", host);
    }

    reply->d_func()->requestIsPrepared = true;
}
如果想模拟IE浏览器，或者想修改成任何你希望的信息，就是在这里修改。
在设定了这些请求信息之后，发送的请求信息包是什么样子的呢？我把工具拦截的信息包具体情况贴出来：