Send image inside Json through QTcpSocket

[Tamfub]

@Christian-Ehrlicher @JonB
Ok, I guess I'll have to revise my protocol, then I'll return to the other problem later :)

[SGaist]

Hi,

@Tamfub said in Send image inside Json through QTcpSocket:

QString string = (QString)dataReceived;

dataReceived is a QByteArray, that cast is completely wrong.

[Tamfub]

@Christian-Ehrlicher @JonB
I've given a look to the fortune client and server examples and tried to toy with data.

In server.cpp, I replaced

out << fortunes[QRandomGenerator::global()->bounded(fortunes.size())];

with

QString str;
for(int i=0; i<1000000; i++)
    str.append("a");
out << str;

void Client::readFortune() became:

void Client::readFortune()
{
    in.startTransaction();

    QString data;
    in >> data;
    qDebug() << "data: " << data;

    if (!in.commitTransaction())
        return;

    qDebug() << "data (end): ";
    qDebug() << data;

//    if (nextFortune == currentFortune) {
//        QTimer::singleShot(0, this, &Client::requestNewFortune);
//        return;
//    }

//    currentFortune = nextFortune;
//    //statusLabel->setText(currentFortune);
//    qDebug() << "current: " << currentFortune;
//    getFortuneButton->setEnabled(true);
    qDebug() << "finished";
}

The output in the client is:

next:  ""
next (end): 
finished

I guess qDebug() does not print large data?

[JonB]

@Tamfub said in Send image inside Json through QTcpSocket:

I guess qDebug() does not print large data?

Do not rely on qDebug() output visibility. I think it says somewhere qDebug(qPrintable(qString)); or print QString::length().

[Tamfub]

@SGaist
Hi.
Ok, I guess I should use something like QString::fromLatin1(array), right?

[Tamfub]

@JonB
Ok, I put some printing of the sizes, and found out that receivedData.size() = 2 x sentData.size().

Server

ds << QString::fromLatin1(ba.toBase64());
qDebug() << "size: " << QString::fromLatin1(ba.toBase64()).size(); // 75684

Client

ds.startTransaction();
QByteArray data;
ds >> data;

if (!ds.commitTransaction())
        return;

qDebug() << "data(size): " << risp.size();  // 151368

How is this possible? If I try with

QByteArray str;
for(int i=0; i<1000000; i++)
       str.append("a");
ds << str;
qDebug() << "size: " << str.size();  // 1000000

instead, the two sizes match!

[JonB]

@Tamfub said in Send image inside Json through QTcpSocket:

qDebug() << "size: " << QString::fromLatin1(ba.toBase64()).size(); // 75684

qDebug() << "data(size): " << risp.size(); // 151368

What arithmetic formula do you notice connects the two numbers in your comments? :)

[Tamfub]

@JonB I already noticed the receivedData in double the sentData, I wrote it before. But I can't understand why.

[JonB]

@Tamfub
Because one is a QByteArray and one is a QString? You can't send one type, decode it as a different type, and expect them to be the same.

[mrjj]

@Tamfub
Hi
QString is 16 bit. QByteArray is 8bit

[Tamfub]

@JonB @mrjj
you're damn right, I didn't notice that. My bad :)
Thank you both! Now I will try to pack/unpack correctly.

[Tamfub]

I managed to fix the (un)packing during the sending/receiving part. Now I miss the final step: create a Pixmap from the received data and show it. To sum up:

Server

QImage imageObject;
imageObject.load(Path/to/image);
QPixmap image = QPixmap::fromImage(imageObject);

QByteArray ba;              // Construct a QByteArray object
QBuffer buffer(&ba);        // Construct a QBuffer object using the QbyteArray
image.save(&buffer, "JPG"); // Save the QImage data into the QBuffer


qjo.insert("request_type", PHOTO_REQUEST);
qjo.insert("photo", QString::fromLatin1(ba.toBase64()));

qDebug() << "Size of QString::fromLatin1(ba.toBase64())): " << QString::fromLatin1(ba.toBase64()).size();	// 470184

QJsonDocument doc(qjo);
QString strJson(doc.toJson(QJsonDocument::Compact));
info.append(strJson);
ds << info;

Client

ds.startTransaction();

QByteArray risp;
ds >> risp;
qDebug() << "risp: " << risp;

if (!ds.commitTransaction())
    return;

...

QJsonValue photo = obj.take("photo");
QByteArray ba = photo.toString().toLatin1();
qDebug() << "photo data size (latin): " << photo.toString().toLatin1().size();	// 470184
//qDebug() << "photo size (utf8): " << photo.toString().toUtf8().size();
QPixmap pm;

???  // Missing part

ui->myLabel->setPixmap(pm);

ui->myLabel has another Pixmap set at the moment. In the ??? part, I tried:

if(!pm.loadFromData(ba, "JPG")){
    qDebug() << "Error: data could not be loaded.";
    return;
}

and it always ended up printing the error message.

Then, I read this and tried

const uchar * const data = reinterpret_cast<const uchar *>(ba.constData());
qDebug() << "uchar size: " << data;

QPixmap pixmap = QPixmap::fromImage(
    QImage(
        data,
        ui->myLabel->width(),
        ui->myLabel->height(),
        QImage::Format_RGB888
    )
);

The previous Pixmap of ui->myLabel is removed, but now there is a white one. Any ideas?

[KroMignon]

@Tamfub said in Send image inside Json through QTcpSocket:

ow I miss the final step: create a Pixmap from the received data and show it. To sum up:

Have you take a look at QPixmap documentation? I think you will quickly find QPixmap::loadFromData()...

[Tamfub]

@KroMignon
Hi.
I eventually managed to show the image. I was missing:

ba = ba.fromBase64();

before pm.loadFromData(...), and now it works. Thanks!