QTcpSocket 连接传入空数据问题答案

【问题标题】：QTcpSocket connection incoming empty data IssueQTcpSocket 连接传入空数据问题
【发布时间】：2014-10-06 08:15:58
【问题描述】：

我正在尝试使用 qtcpsocket 连接在服务器和客户端之间发送数据。当我发送小尺寸数据时，一切都很好。但是当大小增加时，从 tcpsocket 读取的数据变为空:(。

//启用连接

bool ClientService::enableConnection()
{
    qDebug() << Q_FUNC_INFO << "Invoked";
    const int iTimeout = 5 * 1000;
    m_socket.connectToHost(settings.getServerIP(), PORT);
    if (!m_socket.waitForConnected(iTimeout))
    {
        emit error();
        qDebug() << Q_FUNC_INFO << m_socket.errorString();
        return false;
    }

    qDebug() << Q_FUNC_INFO << "Exits";
    return true;
}

// 一旦所有数据都写入QDataStream，就向服务器发送数据

bool ClientService::sendToServer(QByteArray block)
{
    qDebug() << Q_FUNC_INFO << "Invoked";
    bool sendStatus = false;
    if (QTcpSocket::ConnectedState == m_socket.state())
    {
        if (-1 != m_socket.write(block))
        {
            m_socket.waitForBytesWritten();
            sendStatus = true;
        }
        else
        {
            qDebug() << Q_FUNC_INFO << "error in write";
        }
    }
    else
    {
        qDebug() << Q_FUNC_INFO << "socket is not connected";
    }

    if (!sendStatus)
    {
        qDebug() << Q_FUNC_INFO << "emits error signal";
        emit error();
    }

    qDebug() << Q_FUNC_INFO << "Exits" << sendStatus;
    return sendStatus;
}

// 等到收到来自服务器的响应

bool ClientService::waitForServerResponse()
{
    qDebug() << Q_FUNC_INFO << "Invoked";
    const int iTimeout = 5 * 1000;
    while (m_socket.bytesAvailable() < (int)sizeof(quint16))
    {
        if (!m_socket.waitForReadyRead(iTimeout))
        {
            emit error();
            qDebug() << Q_FUNC_INFO << m_socket.errorString();
            return false;
        }
    }

    quint16 blockSize;
    QDataStream inputStream(&m_socket);
    inputStream.setVersion(QDataStream::Qt_4_0);
    inputStream >> blockSize;

    while (m_socket.bytesAvailable() < blockSize)
    {
        if (!m_socket.waitForReadyRead(iTimeout))
        {
            emit error();
            qDebug() << Q_FUNC_INFO << m_socket.errorString();
            return false;
        }
    }

    qDebug() << Q_FUNC_INFO << "Exits";
    return true;
}

// 收到响应后关闭连接

void ClientService::disableConnection()
{
    qDebug() << Q_FUNC_INFO << "Invoked";
    m_socket.disconnectFromHost();
    qDebug() << Q_FUNC_INFO << "Exits";
    return;
}

//要发送的数据

int  ClientService::syncMasters(SyncMaster syncMasterData)
{
    qDebug() << Q_FUNC_INFO << "Invoked";

    int syncStatus = -1;

    if(enableConnection())
    {
        qDebug() << Q_FUNC_INFO << "connection enabled";
        //  typecast to ensure cross platform compatibility
        const qint32 mode_int = static_cast<qint32>(SYNC_MASTERS_QUERY);
        QByteArray block;
        QDataStream outputStream(&block, QIODevice::WriteOnly);
        outputStream.setVersion(QDataStream::Qt_4_0);
        outputStream << (quint16)0;
        outputStream << mode_int;       // saying query mode to server

        // group master data
        outputStream << syncMasterData.groupMasterList.count();
        qDebug() << Q_FUNC_INFO << "groupmaster count" <<
                                    syncMasterData.groupMasterList.count();

        foreach (GroupMaster groupMasterItem, syncMasterData.groupMasterList)
        {
            outputStream << groupMasterItem.groupCode;
            outputStream << groupMasterItem.groupDescription;
            outputStream << groupMasterItem.kotPrinterNo;
            outputStream << groupMasterItem.image;
            outputStream << groupMasterItem.sortId;

            qDebug() << Q_FUNC_INFO <<
                        "code"      << groupMasterItem.groupCode         <<
                        "desc"      << groupMasterItem.groupDescription  <<
                        "kot "      << groupMasterItem.kotPrinterNo      <<
                        "image"     << groupMasterItem.image             <<
                        "sort id"   << groupMasterItem.sortId;
        }

        // subgroup master data
        outputStream << syncMasterData.subGroupMasterList.count();
        qDebug() << Q_FUNC_INFO << "subgroupmaster count" <<
                                    syncMasterData.subGroupMasterList.count();

        foreach (SubGroupMaster subGroupMasterItem,
                                syncMasterData.subGroupMasterList)
        {
            outputStream << subGroupMasterItem.groupCode;
            outputStream << subGroupMasterItem.subGroupCode;
            outputStream << subGroupMasterItem.subGroupDescription;

            qDebug() << Q_FUNC_INFO <<
                    "gpcode"    << subGroupMasterItem.groupCode     <<
                    "subgpcode" << subGroupMasterItem.subGroupCode  <<
                    "desc"      << subGroupMasterItem.subGroupDescription;
        }

        // item master data
        outputStream << syncMasterData.itemMasterList.count();
        qDebug() << Q_FUNC_INFO << "item master count" <<
                                    syncMasterData.itemMasterList.count();

        foreach (ItemMaster ItemMasterItem, syncMasterData.itemMasterList)
        {
            outputStream << ItemMasterItem.itemCode;
            outputStream << ItemMasterItem.itemName;
            outputStream << ItemMasterItem.groupCode;
            outputStream << ItemMasterItem.subGroupCode;
            outputStream << ItemMasterItem.imagePath;
            outputStream << ItemMasterItem.productId;
            outputStream << ItemMasterItem.itemPriceType;
            outputStream << ItemMasterItem.itemPrice;
            outputStream << ItemMasterItem.kotPrinterNumber;
            outputStream << ItemMasterItem.sortId;

            qDebug() << Q_FUNC_INFO <<
                        "item code"     << ItemMasterItem.itemCode      <<
                        "item name"     << ItemMasterItem.itemName      <<
                        "group code"    << ItemMasterItem.groupCode     <<
                        "subgp code"    << ItemMasterItem.subGroupCode  <<
                        "image path"    << ItemMasterItem.imagePath     <<
                        "product id"    << ItemMasterItem.productId     <<
                        "item pricetype"<< ItemMasterItem.itemPriceType <<
                        "item price"    << ItemMasterItem.itemPrice     <<
                        "kot"           << ItemMasterItem.kotPrinterNumber<<
                        "sortId"        << ItemMasterItem.sortId;
        }

        // side item master data
        outputStream << syncMasterData.sideItemMasterList.count();
        qDebug() << Q_FUNC_INFO << "side item master count" <<
                                    syncMasterData.sideItemMasterList.count();

        foreach (SideItemMaster sideItemMasterItem,
                                        syncMasterData.sideItemMasterList)
        {
            outputStream << sideItemMasterItem.itemCode;
            outputStream << sideItemMasterItem.sideItemCode;
            outputStream << sideItemMasterItem.lineNumber;
            outputStream << sideItemMasterItem.sideItemPrice;
            outputStream << sideItemMasterItem.sideItemPriceType;

            qDebug() << Q_FUNC_INFO <<
                    "item code"     << sideItemMasterItem.itemCode      <<
                    "sideitem code" << sideItemMasterItem.sideItemCode  <<
                    "line no"       << sideItemMasterItem.lineNumber    <<
                    "sideitem pric" << sideItemMasterItem.sideItemPrice <<
                    "siditm prc typ"<< sideItemMasterItem.sideItemPriceType;
        }

        // price master data
        outputStream << syncMasterData.priceMasterList.count();
        qDebug() << Q_FUNC_INFO << "price master count" <<
                                    syncMasterData.priceMasterList.count();

        foreach (PriceMaster priceMasterItem, syncMasterData.priceMasterList)
        {
            outputStream << priceMasterItem.itemCode;
            outputStream << priceMasterItem.itemPriceType;
            outputStream << priceMasterItem.promoCode;
            outputStream << priceMasterItem.validFromDate;
            outputStream << priceMasterItem.validToDate;
            outputStream << priceMasterItem.validFromTime;
            outputStream << priceMasterItem.validToTime;
            outputStream << priceMasterItem.unitCode;
            outputStream << priceMasterItem.itemPrice;
            outputStream << priceMasterItem.specialPrice;
            outputStream << priceMasterItem.unitDescription;

            qDebug() << Q_FUNC_INFO <<
                        "item code"     << priceMasterItem.itemCode         <<
                        "itm prc typ"   << priceMasterItem.itemPriceType    <<
                        "promo code"    << priceMasterItem.promoCode        <<
                        "validfrmdt"    << priceMasterItem.validFromDate    <<
                        "vld to dt"     << priceMasterItem.validToDate      <<
                        "vld frm tm"    << priceMasterItem.validFromTime    <<
                        "vld to tm"     << priceMasterItem.validToTime      <<
                        "unit code"     << priceMasterItem.unitCode         <<
                        "item price"    << priceMasterItem.itemPrice        <<
                        "spcl price"    << priceMasterItem.specialPrice     <<
                        "unit desc"     << priceMasterItem.unitDescription;
        }

        outputStream.device()->seek(0);
        outputStream << (quint16)(block.size() - sizeof(quint16));

        if(sendToServer(block))
        {
            qDebug() << Q_FUNC_INFO << "query sent to server successfully";

            if (waitForServerResponse())
            {
                qDebug() << Q_FUNC_INFO << "read set status from server";

                QDataStream inputStream(&m_socket);
                inputStream.setVersion(QDataStream::Qt_4_0);
                inputStream >> syncStatus;
            }
        }

        disableConnection();
    }

    qDebug() << Q_FUNC_INFO << "Exits" << syncStatus;
    return syncStatus;
}

//读取也类似

void ServerFunctionThread::syncMasters()
{
    qDebug() << Q_FUNC_INFO << "Invoked";

    SyncMaster syncMasterData;

    int groupCount      = 0,
        subGroupCount   = 0,
        itemCount       = 0,
        sideItemCount   = 0,
        priceCount      = 0;

    QDataStream inputStream(&tcpSocket);
    inputStream.setVersion(QDataStream::Qt_4_0);

    // group master data reception
    inputStream >> groupCount;
    qDebug() << Q_FUNC_INFO << "group master Count" << groupCount;

    while (groupCount--)
    {
        GroupMaster groupMasterItem;
        inputStream >> groupMasterItem.groupCode;
        inputStream >> groupMasterItem.groupDescription;
        inputStream >> groupMasterItem.kotPrinterNo;
        inputStream >> groupMasterItem.image;
        inputStream >> groupMasterItem.sortId;

        syncMasterData.groupMasterList.append(groupMasterItem);

        qDebug() << Q_FUNC_INFO <<
                    "code"      << groupMasterItem.groupCode         <<
                    "desc"      << groupMasterItem.groupDescription  <<
                    "kot "      << groupMasterItem.kotPrinterNo      <<
                    "image"     << groupMasterItem.image             <<
                    "sort id"   << groupMasterItem.sortId;

    }
.
.
...

有人可以帮我知道写入 QDataStream 的数据是否有大小限制... 因为从我的日志连接仍然存在并且我得到响应。但是读取的数据很少，接收到的数据是空的。

【问题讨论】：

与其在套接字上等待字节可用，我建议使用 QTcpSocket 的 readyRead 信号让您知道何时有数据可用：qt-project.org/doc/qt-4.8/qiodevice.html#readyRead
也可以在将数据写入socket后调用flush()
@Merlin069：据我所知，每次有新数据可用时都会发出 readyRead。所以我应该在整个数据以正确的顺序读取数据后获取数据
这是个问题吗？是的，每次有新数据可用时都会发出 readyRead，但它可能只是数据的一部分，您需要将其连接到缓冲区中。最好先将数据大小作为第一个字节发送，然后您就知道连续调用 readyRead 的期望值是多少。
不，我的意思是我无法使用 readyRead，因为我可能无法弄清楚哪些数据已经到来。因为我要发送不同类型的数据，例如组 {}、子组{}、项目{}...使用 readyRead 对我来说很麻烦

标签： qt

【解决方案1】：

问题已解决。 :)

从客户端传递到服务器的数据大小导致了该问题。由于我在数据大小变大时使用了 quint16，因此服务器无法知道确切的传入数据大小。所以我把类型改为quint32。问题就解决了。

outputStream << (quint32)0;

// 结束

outputStream.device()->seek(0);
outputStream << (quint32)(block.size() - sizeof(quint32));

服务器端也等待quint32

中接收到的数据大小

【讨论】：