QNetworkReply 返回不完整的 XML 数据

Question

我正在向远程服务器发送 HTTP GET 请求。使用各种参数我定义了我感兴趣的内容。特别是我确保 output=xml 在查询中，因为它使服务器 return 回复为 XML.

我的 class HttpRetriever 与各自的 QNetworkReply 和 QNetworkAccessManager 之间有以下联系（对于 QNetworkRequest 请参阅 slotStartRequest()):

connect(this->reply, SIGNAL(error(QNetworkReply::NetworkError)), this,
        SLOT(slotErrorRequest(QNetworkReply::NetworkError)));
connect(this->reply, &QNetworkReply::finished, this, &HttpRetriever::slotFinishRequest);
connect(this->manager, &QNetworkAccessManager::finished, this->reply, &QNetworkReply::deleteLater);
connect(this->reply, &QIODevice::readyRead, this, &HttpRetriever::slotReadyReadRequest);

此处感兴趣的插槽具有以下声明：

slotFinishRequest():

void HttpRetriever::slotFinishRequest()
{
    LOG(INFO) << "Finishing HTTP GET request from URL \"" << this->url.toString() << "\"";
    this->reply = Q_NULLPTR;

    // Reset validity of reply from a previous request
    this->validReply = false;
    // Skip validation if it's disabled
    if (!this->validateReply)
    {
        LOG(WARNING) << "Validation disabled. In order to enable it see the \"validate\" and \"validationMode\" in \"settings.ini\"";
        this->validReply = true;
    }
    else
    {
        // Validate reply
        this->validReply = validateReply();
    }

    if (!this->validReply)
    {
        return;
    }

    processReply(); // Parsing

    this->processingRequest = false;
}

slotReadyReadRequest():

void HttpRetriever::slotReadyReadRequest()
{
    LOG(INFO) << "Received data from \"" << this->url.toString() << "\"";
    this->bufferReply = this->reply->readAll();
}

在 slotFinishRequest() 里面我调用 processReply():

void HttpRetriever::processReply()
{
    LOG(INFO) << "Processing reply for request \"" << this->url.toString() << "\"";
    LOG(DEBUG) << QString(this->bufferReply);
    // Process the XML from the reply and extract necessary data

    QXmlStreamReader reader;
    reader.addData(this->bufferReply);

    // Read the XML reply and extract required data
    // TODO
    while (!reader.atEnd())
    {
        LOG(DEBUG) << "Reading XML element";
        reader.readNextStartElement();

        QXmlStreamAttributes attributes = reader.attributes();
        foreach (QXmlStreamAttribute attrib, attributes)
        {
            LOG(DEBUG) << attrib.name();
        }
    }
    if (reader.hasError())
    {
        LOG(ERROR) << "Encountered error while parsing XML data:" << reader.errorString();
    }

    LOG(INFO) << "Sending data to data fusion handler";
    // TODO
}

我通过以下插槽触发 HTTP get 请求：

void HttpRetriever::slotStartRequest(quint32 id)
{
    if (this->processingRequest)
    {
        this->reply->abort();
    }

    this->processingRequest = false;

    // The first request also instantiates the manager. If the slot is called after the instance of HafasHttpRetriever
    // is moved to a new thread this will ensure proper parenting
    if (!this->manager)
    {
        this->manager = new QNetworkAccessManager(this);
    }

    quint32 requestId = generateRequestId(stopId);
    if (!this->url.hasQuery())
    {
        LOG(WARNING) << "Attempting to start request without parameters";
    }

    // Part of the filters applied to the request to reduce the data received (for more see slotSetRequestParams())
    QUrlQuery query(this->url.query());
    query.addQueryItem("input", QString::number(requestId));
    // TODO Add more filters; see documentation

    this->url.setQuery(query);

    LOG(INFO) << "Requesting data from \"" << this->url.toString() << "\" with request ID:" << requestId;

    QNetworkRequest request(this->url);
    this->reply = this->manager->get(request);

    // Establish connections from/to the reply and the network access manager
    connect(this->reply, SIGNAL(error(QNetworkReply::NetworkError)), this,
            SLOT(slotErrorRequest(QNetworkReply::NetworkError)));
    connect(this->reply, &QNetworkReply::finished, this, &HttpRetriever::slotFinishRequest);
    connect(this->manager, &QNetworkAccessManager::finished, this->reply, &QNetworkReply::deleteLater);
    connect(this->reply, &QIODevice::readyRead, this, &HttpRetriever::slotReadyReadRequest);
}

如你所见，到目前为止我已经为我的 class 和服务器之间的网络通信奠定了基础，我还没有开始解析 XML 回复和从中提取我需要的信息。

问题是我（非常非常经常）要么

Encountered error while parsing XML data: Start tag expected.

或

Encountered error while parsing XML data: Premature end of document

在我的 processReply() 函数中。每次我收到大量回复（几百到几千行）时都会发生这种情况。当我得到一个小的（30-40 行给予或接受）时，它永远不会发生。

所以问题显然出在我接收的数据量上，它是由 QNetworkAccessManager 组合在一起的方式（或者所有这些缓冲接收到的数据块中的任何 Qt 组件）and/or 也许是我在 class 中设置网络相关组件实例的方式。我还必须在这里做一个重要的说明，即在我的浏览器（带有 HttpRequester 附加组件的最新 Firefox）中，无论它有多大，我总是收到完整的 XML是。所以这似乎是我的应用程序独有的问题，与我系统上的网络设置无关。

Answer 1

因为@Marco 没有写答案...

问题是我一直在通过分配 QNetworkReply::readAll() 的结果来重写缓冲区。按照建议使用 QByteArray::append() 解决问题。

为了防止此解决方案可能出现的问题，即您不断附加收到的每个下一个回复，需要在某些时候调用 QByteArray::clear()，例如当 finished()发出信号。当然，在将其冲入下水道之前，需要先处理其内容。

QNetworkReply 返回不完整的 XML 数据

QNetworkReply returning incomplete XML data

c++

xml

qt

http-get

qnetworkreply