Qt Websocket sending json

Christian Ehrlicher

And what's the acutal error? sendTextMessage() takes a QString but QJsonDocument::toJson() returns a (utf-8) encoded QByteArray so you should convert it to a QString first.

Kris Revi

@Christian-Ehrlicher well not any error

i know to send like this

connect(ui->pushButton, &QPushButton::clicked, [=]() { socket.sendBinary("doStuff", 0); });

with

void Socket::sendBinary(const QString &bName, const QJsonValue bValue)
{
    webSocket.sendTextMessage(QJsonDocument(QJsonObject{{bName, bValue}}).toJson(QJsonDocument::Compact));
}

but how can i send {"seg":{"fx":0}}

SGaist

Hi,

Exactly as @Christian-Ehrlicher wrote: make a QString out of the QByteArray generated by toJson.

Kris Revi

like this?

void Socket::sendBinary(const QString &bName, const QJsonValue bValue)
{    
    QJsonObject obj;
    obj.insert("seq", "{'fx':0}");
    QJsonDocument doc(obj);
    QString strJson(doc.toJson(QJsonDocument::Compact));

    webSocket.sendTextMessage(strJson);
}

SGaist

QString::fromUtf8 since you know that QJsonDocument::toJson returns an UTF-8 encoded document.

Kris Revi

@SGaist am i doing something wrong?

void Socket::sendBinary(const QString &bName, const QJsonValue bValue)
{
    QJsonObject obj;
    obj.insert("seq", "{'fx':10}");
    QJsonDocument doc(obj);
    QString strJson(doc.toJson(QJsonDocument::Compact));
    QString s2 = QString::fromUtf8(strJson.toUtf8().constData());

    webSocket.sendTextMessage(s2);

    qDebug() << s2;

}

JonB

@Kris-Revi Why, what are you finding that is wrong?

Kris Revi

@JonB this is the ouput

"{\"seq\":\"{'fx':10}\"}"

but on the ESP32 that controlls the Led Strip the pattern does not change

im using the WLED software installed on the ESP32 and im trying to make a simple App in Qt to controll it via Websocket! i can connect and i can easily change brightness by sending "bri", 0-255

but to change pattern i was told to send {"seg":{"fx":0}}

Kris Revi

@JonB as you can see here

https://kno.wled.ge/interfaces/json-api/

    "seg": [{
      "start": 0,
      "stop": 20,
      "len": 20,
      "col": [
        [255, 160, 0, 0],
        [0, 0, 0, 0],
        [0, 0, 0, 0]
      ],
      "fx": 0,
      "sx": 127,
      "ix": 127,
      "pal": 0,
      "sel": true,
      "rev": false,
      "cln": -1
    }]

JonB

@Kris-Revi said in Qt Websocket sending json:

"{\"seq\":\"{'fx':10}\"}"

{"seg":{"fx":0}}

First, these are similar. The debugger (if that's what you're using to view output, you do not say) with show literal "s as \".

Where I think you are showing a difference:

obj.insert("seq", "{'fx':10}");

You are inserting a single object with the literal string "{'fx':10}" as its value. But {"seg":{"fx":0}} looks more like an outer object with object {"fx":0} as its value, so you are not constructing your JSON correctly. But that has nothing to do with websocket or how you send the JSON.

Kris Revi

@JonB said in Qt Websocket sending json:

First, these are similar. The debugger (if that's what you're using to view output, you do not say)

yea the debugger (Application Output)...

how do i construct the json right with the outer object? i have only done the "easy" ("bri", 0-255)....

JonB

@Kris-Revi
I haven't looked up what the available functions are, but I imagine you need something more like:

    QJsonObject obj. obj2;
    obj2.insert("fx", 10);
    obj.insert("seq", obj2);

SGaist

@Kris-Revi said in Qt Websocket sending json:

@SGaist am i doing something wrong?

void Socket::sendBinary(const QString &bName, const QJsonValue bValue)
{
    QJsonObject obj;
    obj.insert("seq", "{'fx':10}");
    QJsonDocument doc(obj);
    QString strJson(doc.toJson(QJsonDocument::Compact));
    QString s2 = QString::fromUtf8(strJson.toUtf8().constData());

    webSocket.sendTextMessage(s2);

    qDebug() << s2;

}

Two things in fact:
First, the single quotes around fx, it's invalid.
Second, the triple conversion. There's no need for s2.

QByteArray jsonMessage(doc.toJson(QJsonDocument::Compact));
QString stringMessage = QString::fromUtf8(jsonMessage);