Go http: no such file after sending image from Qt client

I have a Go API that should save an image sent by a client. I know that the Go code works when the POST request comes from a HTML form.
When sending a multipart post request from my Qt C++ client though, the server returns an error

> http: no such file

On the client side I have a QPixmap, which I transform to a QByteArray, which I then send, but somehow I get that error from Go. I know that the length of the data sent by the client decreases when I remove

multi_part->append(image_part);

so the QPixmap should be sent.

Go code:

func apiUploadHandler(w http.ResponseWriter, req *http.Request) {
if req.Method == "POST" {
	req.ParseMultipartForm(0)
	fmt.Printf("%v %v %v", req.RemoteAddr, req.ContentLength, req.Body)
	file, fileheader, err := req.FormFile("image")
	if err != nil {
		cio.PrintMessage(1, err.Error())
		return
	}
	defer file.Close()
	var id string
	created := false
	for created != true {
		id = generateImageID()
		err = db.CheckIfImageIDInUse(id)
		if err != nil {
			if err.Error() == "Image ID '"+id+"' exists.'" {
				created = false
				continue
			} else {
				created = false
				cio.PrintMessage(1, err.Error())
				return
			}
		}
		created = true
	}
	filePath := fsys.ImgStoragePath + id + "." + strings.Split(fileheader.Filename, ".")[1]
	err = db.StoreImage(id, strings.Split(fileheader.Filename, ".")[0] /*image name*/, filePath, strings.Split(fileheader.Filename, ".")[1] /*extension*/)
	if err != nil {
		cio.PrintMessage(1, err.Error())
		return
	}
	bytesCopied, err := fsys.StoreImage(filePath, file)
	if err != nil {
		cio.PrintMessage(1, err.Error())
		return
	}
	cio.PrintMessage(0, "File "+filePath+" has been created.")
	if err != nil {
		cio.PrintMessage(1, err.Error())
		return
	}
	cio.PrintMessage(0, "Content of uploaded image ("+strconv.FormatInt(bytesCopied, 10)+" Bytes) has been copied to "+filePath+".")
	http.Redirect(w, req, "/"+id, http.StatusFound)
}

}

Qt C++ client code:

void Share::upload(const QByteArray &data) {
    QHttpMultiPart *multi_part = new          QHttpMultiPart(QHttpMultiPart::FormDataType);
    QHttpPart text_part;
    text_part.setHeader(QNetworkRequest::ContentDispositionHeader,   QVariant("form-data; name=\"text\"\""));
    text_part.setBody("Screenshot.png");
    QHttpPart image_part;
    image_part.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("image/png"));
    image_part.setHeader(QNetworkRequest::ContentDispositionHeader,  QVariant("form-data; name=\"image\""));
    image_part.setBody(data);
    multi_part->append(text_part);
    multi_part->append(image_part);
    QNetworkRequest request(QUrl("http://localhost:8000/api/upload"));
    QNetworkAccessManager *manager = new QNetworkAccessManager();
    connect(manager, SIGNAL(finished(QNetworkReply *)), this,    SLOT(reply_finished(QNetworkReply *)));
    manager->post(request, multi_part);
    qDebug() << QString(data);
}

I'm not sure but you can try to change

image_part.setHeader(QNetworkRequest::ContentDispositionHeader,  QVariant("form-data; name=\"image\""));

to something like

image_part.setHeader(QNetworkRequest::ContentDispositionHeader,  QVariant("form-data; name=\"image\"; filename=\"Screenshot.png\""));