Binarydata over QJsonObject becomes to big.

themts

Hey guys,

I have a websocket communication where I'm using QJsonDocument for serialization.
I also have to transmit binary-data so I encapsulate it as a base64 String.
I would expect a 33% data-increase over a direct binary transmission but my data becomes nearly 3 times as big:

Bin-Data around 236 kByte while Json-Data is around 631 kByte.
Am I doing something wrong?

QByteArray ba = qryAtt.value("attachment").toByteArray(); //get data from sql-query
qDebug() << "SIZE:" << ba.size(); //236432

QJsonObject obj {
  {"fileName", qryAtt.value("fileName").toString()},
  ...
  {"attachment", QString(ba.toBase64())}
};

THX
mts

JonB

@themts
I don't know what you expect, but this seems to have nothing to do with JSON or websockets. Just look at the size of what ba.toBase64() returns.

themts

no, that is not the point.
The base64 itself has the size that I expected.
Binary: 236432
Base64: 315244
33% bigger

but why does my QJson object have a size of around 631000 byte ?

jsulm

@themts Store your JSON in a file and take a look at it to see what exactly is in there.

themts

that is a little bit strange.
The file itself has an expected size and also the content looks normal.
I created a file before I send the data and when I received the data. Both are identical.

BUT:

void ...onBinaryMessageReceived(const QByteArray &message)
{
    qDebug() << "onBinaryMessageReceived" << message.size(); // HERE it tells me 631476

    //Json
    QJsonDocument doc = QJsonDocument::fromBinaryData(message);

Christian Ehrlicher

Why do you use QJsonDocument::from/toBinaryData at all? QStrings are utf-16 encoded in binary representation so 2 * 315244 = 630488 bytes + rest.

themts

@Christian-Ehrlicher Yes! You are absolutely right... toJson converts to UTF-8 and so it is working as expected.
Thank you!