How to get QByteArray from QDataStream?

Idodoqdo

Hello everyone, I want the information to be written to the variable data_ (QByteArray), here is the code

void MainWindow::slotReadyRead()
{
    QDataStream in (socket);

    in.setVersion(QDataStream::Qt_6_2);
    if (in.status() == QDataStream::Ok) {
        while(1) {
            if (next_block_size_ == 0) {
                if (socket->bytesAvailable() < 2) {
                    break;
                }
                in >> next_block_size_;
            }
            if (socket->bytesAvailable() < next_block_size_) {
                break;
            }
            QString str;
            in >> str;
            next_block_size_ = 0;
            ui->textBrowser->append(str);
        }
        data_ = socket->readAll();
        doc_ = QJsonDocument::fromJson(data_, &doc_error_);
        if (doc_error_.errorString()=="no error occurred") {
            if (doc_.object().value("type").toString() == "connect" && doc_.object().value("status").toString() == "YEs") {
                QMessageBox::information(this, "Information", "Connnect:Ok");
            } else {
                QMessageBox::information(this, "Information", "Connnect:No");
            }
        } else {
            QMessageBox::information(this, "Information", "Bad Format" + doc_error_.errorString());
        }
    } else {
        ui->textBrowser->append("Error read");
    }
}

But when I try to do the following:

//            QString str;
//            in >> str;
            in >> data_;
            next_block_size_ = 0;
//            ui->textBrowser->append(str);
        }
//        data_ = socket->readAll();
        doc_ = QJsonDocument::fromJson(data_, &doc_error_);

it doesn't work

JonB

@Idodoqdo said in How to get QByteArray from QDataStream?:

it doesn't work

What does this mean?

If you comment out putting anything in data_ what should you/we expect?

If you expect data_ = socket->readAll(); to definitely have read the whole of the data bytes for the JSON document to parse there is no guarantee it will have done so, as has been discussed many times in this forum.

Idodoqdo

@JonB
I mean how do I write from QDataStream(in) to QByteArray(data_)?

JonB

@Idodoqdo
To use QDataStream to read data that data must have been written into a QDataStream by the sender. Is that really the case here? Only you know what the sender is. If it is not a Qt program using QDataStream to write its data then you cannot use QDataStream as you are doing to read it. If it is, the reader can only read back exactly the same type as was written to it. If you are saying

QString str;
in >> str;

does work correctly, then what is in the stream is a QString. If you try to read it as a QByteArray that won't work.

So first things first: verify your other side is indeed sending a QString? Then that is what you must read from the stream, and work from there.

Reading, say, https://www.qtcentre.org/threads/71559-QDataStream-to-QByteArray-and-ViceVersa might be of some help.

Idodoqdo

@JonB
The client and server programs are written in qt
this is how the server sends:

auto Server::SendToClient(QString str) -> void
{
    data_.clear();
    QDataStream out(&data_, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_6_2);
    out << quint16(0) << str;
    out.device()->seek(0);
    out.device()->seek(data_.size() - sizeof(quint16));
    for (int i = 0; i < Sockets.size(); ++i) {
        auto socket = QPointer<QTcpSocket>(Sockets.at(i));
        if (socket) {
            socket->write(data_);
        } else {
            Sockets.removeOne(socket);
        }
    }
}

Christian Ehrlicher

@Idodoqdo said in How to get QByteArray from QDataStream?:

out << quint16(0) << str;
out.device()->seek(0);
out.device()->seek(data_.size() - sizeof(quint16));

Then do the opposite on your site. But, as @JonB already mentions make sure that you really got all bytes before trying to receive the string. For this e.g. use a custom buffer or take a look at QDataStream::startTransaction(). A forum search for this will also help: https://forum.qt.io/search?term=qdatastream starttransaction&in=posts&matchWords=all&sortBy=relevance&sortDirection=desc&showAs=posts

JonB

@Idodoqdo
As @Christian-Ehrlicher has written about the issue of making sure you collect all bytes in the stream before sending it for parsing as a JSON document.

Although it does not matter, why does your code do the

out << quint16(0) << str;
out.device()->seek(0);
out.device()->seek(data_.size() - sizeof(quint16));

seeking? What are you trying to achieve by writing a 16-bit 0 followed by a QString and then seeking to the end of the stream minus the size of a quint16? That will be two bytes before the end of the QString, what's the objective??

Idodoqdo

@JonB
I just want my client and server to communicate using Json. Maybe I don't even need QString. I want the client and server to read the data in full

JonB

@Idodoqdo said in How to get QByteArray from QDataStream?:

I want the client and server to read the data in full

You must read what I & @Christian-Ehrlicher said about buffering the incoming data, read the links he has given you in his post.

I also don't know what you are trying to achieve with the quint16(0) and the seek()ing, but it does not look right.

Idodoqdo

@JonB
At the moment, my client and server understand each other. What do you think: can it be left as it is, or is it still worth changing something? (I mean about the sending and receiving mechanism)
Server:

#include "server.h"

Server::Server() : next_block_size_(0)
{
    if (listen(QHostAddress::Any, 2323)) {
        qDebug() << "start";
    } else {
        qDebug() << "error";
    }
    db_ = QSqlDatabase::addDatabase("QPSQL");
    db_.setHostName("localhost");
    db_.setDatabaseName("postgres");
    db_.setUserName("postgres");
    db_.setPassword("12345");
    qDebug()  <<  QSqlDatabase::drivers();
    if (db_.open()) {
        qDebug() << "db open";
    } else {
        qDebug() << "db not open";
    }
}

auto Server::SendToClient(QByteArray str) -> void
{

//    data_.clear();
//    QDataStream out(&data_, QIODevice::WriteOnly);
//    out.setVersion(QDataStream::Qt_6_2);
//    out << quint16(0) << str;
//    out.device()->seek(0);
//    out.device()->seek(data_.size() - sizeof(quint16));
    for (int i = 0; i < Sockets.size(); ++i) {
        auto socket = QPointer<QTcpSocket>(Sockets.at(i));
        if (socket) {
            socket->write(str);
        } else {
            Sockets.removeOne(socket);
        }
    }
}

auto Server::MessageProcessing(QByteArray message) -> void
{
    doc_ = QJsonDocument::fromJson(message, &doc_error_);
    if (doc_error_.errorString()=="no error occurred") {
        if (doc_.object().value("type").toString() == "auth") {
            QByteArray result = "{\"type\":\"resultSelect\",\"result\":";
            QSqlQuery * query = new QSqlQuery(db_);
            query->prepare("select id from users where login = :login and pass = :pass;");
            query->bindValue(":login", "\'" + doc_.object().value("login").toString() + "\'");
            query->bindValue(":pass:", "\'" + doc_.object().value("pass").toString());
            if (query->exec()) {
                query->next();
                if (query->isNull(0)) {
                    result.append("\"no\"}");
                } else {
                    result.append("\"yes\"}");
                }
                SendToClient(result);
            } else {
                qDebug() << "invalid query";
            }
        }
    } else {
        qDebug() << "Error read message";
    }
}


auto Server::incomingConnection(qintptr socketDescriptor) -> void
{   qDebug() << "hello";
    socket = new QTcpSocket;
    socket->setSocketDescriptor(socketDescriptor);
    connect(socket, &QTcpSocket::readyRead, this, &Server::slotReadyRead);
    connect(socket, &QTcpSocket::disconnected, this, &Server::Disconnect);
    Sockets.push_back(socket);
    qDebug() << "client connected" << socketDescriptor;
    socket->write("{\"type\":\"connect\",\"status\":\"YEs\"}");
}

auto Server::slotReadyRead() -> void {
    socket = (QTcpSocket*)sender();
    QDataStream in(socket);
    in.setVersion(QDataStream::Qt_6_2);
    if (in.status() == QDataStream::Ok) {
        qDebug() << "read ...";
        while(1) {
            if (next_block_size_ == 0) {
                if (socket->bytesAvailable() < 2) {
                    break;
                }
                in >> next_block_size_;
            }
            if (socket->bytesAvailable() < next_block_size_) {
                break;
            }
            QString str;
            in >> str;
            next_block_size_ = 0;
            MessageProcessing(str.toUtf8());
//            SendToClient(str);
            break;
        }

    } else {
        qDebug() << "Error DataStream";
    }

}

auto Server::Disconnect() -> void
{
    auto socket = qobject_cast<QTcpSocket*>(sender());
    if (socket) {
        Sockets.removeOne(socket);
        socket->deleteLater();
    }
}

Client:

#include "mainwindow.h"
#include "ui_mainwindow.h"



MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    socket = nullptr;
    connect(ui->ConnectToServer, SIGNAL(released()), this, SLOT(Connect()));
    connect(ui->Auth, SIGNAL(clicked()), this, SLOT(Authorization()));
}

MainWindow::~MainWindow()
{
    delete ui;
}


void MainWindow::Connect()
{
    if (socket == nullptr) {
    socket = new QTcpSocket(this);
    connect(socket, &QTcpSocket::readyRead, this, &MainWindow::slotReadyRead);
    connect(socket, &QTcpSocket::disconnected, this, &MainWindow::Disconnect);

    qDebug() << "press connect";
    next_block_size_ = 0;
    socket->connectToHost("127.0.0.1", 2323);
    if(!socket->waitForConnected(5000))
    {

        qDebug() << "Error: " << socket->errorString();
        delete socket;
        socket = nullptr;
    }
    }

}

void MainWindow::Authorization()
{
    auth_ = new AuthorizationView;
    connect(auth_, &AuthorizationView::InfoAuth, this, &MainWindow::AuthInfo);
    auth_->setModal(true);
    auth_->exec();
}

void MainWindow::Disconnect()
{
    socket->deleteLater();
    socket = nullptr;
}

void MainWindow::SendToServer(QString str)
{
    if (socket != nullptr) {
    data_.clear();
    QDataStream out(&data_, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_6_2);
    out << quint16(0) << str;
    out.device()->seek(0);
    out.device()->seek(data_.size() - sizeof(quint16));
    socket->write(data_);
    ui->lineEdit->clear();
    }
}

void MainWindow::slotReadyRead()
{
    QDataStream in (socket);

    in.setVersion(QDataStream::Qt_6_2);
    if (in.status() == QDataStream::Ok) {
        //        while(1) {
        //            if (next_block_size_ == 0) {
        //                if (socket->bytesAvailable() < 2) {
        //                    break;
        //                }
        //                in >> next_block_size_;
        //            }
        //            if (socket->bytesAvailable() < next_block_size_) {
        //                break;
        //            }
        //            QString str;
        //            in >> str;
        //            next_block_size_ = 0;
        //            ui->textBrowser->append(str);
        //            break;
        //        }
        data_ = socket->readAll();
        doc_ = QJsonDocument::fromJson(data_, &doc_error_);
        if (doc_error_.errorString()=="no error occurred") {
            if (doc_.object().value("type").toString() == "connect" && doc_.object().value("status").toString() == "YEs") {
                QMessageBox::information(this, "Information", "Connnect:Ok");
            } else {
                QMessageBox::information(this, "Information", "Connnect:No");
            }
            if (doc_.object().value("type").toString() == "resultSelect") {
                if (doc_.object().value("result") == "yes") {
                    ui->textBrowser->append("client exist");
                } else {
                    ui->textBrowser->append("client no exist");
                }
            }
        } else {
            QMessageBox::information(this, "Information", "Bad Format" + doc_error_.errorString());
        }
    } else {
        ui->textBrowser->append("Error read");
    }
}

void MainWindow::AuthInfo(QPair<QString, QString> info)
{
    SendToServer("{\"type\":\"auth\",\"login\":\"" + info.first + "\"," + "\"pass\":\"" + info.second + "\"}");
}

Christian Ehrlicher

@Idodoqdo said in How to get QByteArray from QDataStream?:

What do you think: can it be left as it is, or is it still worth changing something?

We already told you what's wrong with a single call to readAll() but you don't seem to care so do I.