QProcess start for mstsc (Remote Desktop) generates finished() signal immediately

m4kas

Hi QT forum.
I'm working on QT application (Windows) that can initiate RDP session with other machine and I'm facing problems with keeping track of started "mstsc" process, as "process->start" call for RDP application immediately generates the "finished()" signal despite the fact, that RDP session is in progress. After RDP session is closed, no additional "finished()" signal occur.

I'm using next code:

QProcess *process = new QProcess();
rdp_processes_list.append(process);
connect(process, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(rdp_process_finished(int, QProcess::ExitStatus)));
connect(process, SIGNAL(error(QProcess::ProcessError)), this, SLOT(rdp_process_error(QProcess::ProcessError)));
// start cmd and start mstsc app with /wait key to wait till RDP session is closed.
process->start("cmd", QStringList() << "/c" << "start" << "/wait" << "mstsc" << "/v" << machine_address);
// returns true if process started successfully
process->waitForStarted(-1);

Tried also to do same without cmd involved:

process->start("mstsc", QStringList() << "/v" << machine_address);

And observe the same result - finished() signal is being generated immediately.

Passing "cmd /c start /w mstsc /v 172.16.30.113" command into Windows Run menu (Win + R) opens cmd, which opens my RDP session. CMD is closed right after RDP session is closed and this is the expected behavior, which I want to be used by QT.

Tried also to execute notepad app in same way:

QProcess *process = new QProcess();
rdp_processes_list.append(process);
connect(process, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(rdp_process_finished(int, QProcess::ExitStatus)));
connect(process, SIGNAL(error(QProcess::ProcessError)), this, SLOT(rdp_process_error(QProcess::ProcessError)));
// start cmd and start mstsc app with /wait key to wait till RDP session is closed.
process->start("notepad");
// returns true if process started successfully
process->waitForStarted(-1);

And in this case I observe another (correct) behavior - finished() signal is being generated right after notepad app is closed, so this may rather be related to mstsc app behavior. Can someone please suggest me what else I can try to fix / workaround it?

QT version used: 5.13.2

m4kas

As mentioned on microsoft forum post, most likely when building 32-bit app (which I was doing), it makes mstsc call of 32-bit version mstsc, which calls the correct 64-bit version and closes original process that was called from QT app.
Switched my QT project to build 64 bit application and it fixed my problem - now finished() signal is being emitted exactly after RDP session finished.
@Christian-Ehrlicher @JonB @mrjj thanks for your inputs.
Issue is solved.

Christian Ehrlicher

According to mstsc help /v needs the ip directly -->

process->start("mstsc", {"/v:"+ machine_address});

m4kas

@Christian-Ehrlicher
Thanks for your message.
Call as you suggested still immediately generates finished() signal.

JonB

@m4kas
I'm afraid I know nothing about mstsc. But as your code stands, for all I know it might not be on the path of the cmd and we would not know.

I would start by hooking slots for anything on stdout and particularly on stderr. Windows/DOS has a way of sending you messages on stderr when (failing to) start processes. Note that this is not the same as hooking to error signal. I would also look at what the finished exit status is, just in case there is a clue there. Finally I would also hook onto started & stateChanged signals. That's what I do when debugging odd behaviour!

m4kas

@JonB
Thanks for your reply and suggestions.
finished() signal is being emitted with QProcess::NormalExit exitStatus
Agree, stderr can contain something useful even though the RDP session with the target machine is being started correctly (at least, from user perspective), so I'll start with trying to read info from stderr and processing started & stateChanged signals.

JonB

@m4kas
Do those. Also while I think of it cmd /k ... is the same as cmd /c ... but should keep the Command Prompt window open. Try that to see what it has to show?

m4kas

@JonB
With /k finished() signal is not being emitted at all, even after RDP session is closed.

m4kas

Updated my code in next way:

void MainWindow::on_tbl_machines_doubleClicked(const QModelIndex &index)
{
    QString machine_address = ui->tbl_machines->model()->index(index.row(), 1).data().toString();
    QString machine_user = ui->tbl_machines->model()->index(index.row(), 4).data().toString();
    QString machine_password = ui->tbl_machines->model()->index(index.row(), 5).data().toString();

    // cmdkey /generic:<servername> /user:<username> /pass:<password>
    QStringList arg_list= QStringList() << QString("/generic:%1").arg(machine_address) << QString("/user:%1").arg(machine_user) << QString("/pass:%1").arg(machine_password);
    QProcess::execute("cmdkey", arg_list);

    QProcess *process = new QProcess();
    rdp_processes_list.append(process);
    connect(process, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(rdp_process_finished(int, QProcess::ExitStatus)));
    connect(process, SIGNAL(error(QProcess::ProcessError)), this, SLOT(rdp_process_error(QProcess::ProcessError)));
    connect(process, SIGNAL(started()), this, SLOT(rdp_process_started()));
    connect(process, SIGNAL(stateChanged(QProcess::ProcessState)), this, SLOT(rdp_process_state_changed(QProcess::ProcessState)));
    // start cmd and start mstsc app with /wait key to wait till RDP session is closed.
    process->start("cmd", QStringList() << "/c" << "start" << "/wait" << "mstsc" << "/v" << machine_address);
    // returns true if process started successfully
    process->waitForStarted(-1);
    process->waitForReadyRead(-1);
    qDebug() << "readAllStandardError:" << process->readAllStandardError();
    qDebug() << "readAllStandardOutput:" << process->readAllStandardOutput();
}

/* SLOTS */

void MainWindow::rdp_process_started()
{
    qDebug() << "started slot: Process started";
}

void MainWindow::rdp_process_state_changed(QProcess::ProcessState newState)
{
    qDebug() << "stateChanged slot: Process state changed. New state: " << newState;
}

void MainWindow::rdp_process_finished(int exitCode, QProcess::ExitStatus exitStatus)
{
    qDebug() << "finished slot: Exit code: " << exitCode << " Exit status: " << exitStatus;
}

void MainWindow::rdp_process_error(QProcess::ProcessError error)
{
    qDebug() << "error slot: Process error:  " << error;
}

And got next messages from qDebug():

CMDKEY: Credential added successfully.
stateChanged slot: Process state changed. New state:  QProcess::Starting
stateChanged slot: Process state changed. New state:  QProcess::Running
started slot: Process started
stateChanged slot: Process state changed. New state:  QProcess::NotRunning
finished slot: Exit code:  0  Exit status:  QProcess::NormalExit
readAllStandardError: ""
readAllStandardOutput: ""

So, it does not look mstsc want to say something to me...

Christian Ehrlicher

int main(int argc, char* argv[])
{
    QApplication a(argc, argv);

    QProcess* proc = new QProcess;
    QObject::connect(proc, &QProcess::started,
        []() { qDebug() << "started";  });
    QObject::connect(proc, &QProcess::stateChanged,
        [](QProcess::ProcessState s) { qDebug() << "stateChanged:" << s;  });
    QObject::connect(proc, qOverload<int,QProcess::ExitStatus>(&QProcess::finished),
        [](int c, QProcess::ExitStatus s) { 
        qDebug() << "finished:" << c << s;
        QCoreApplication::quit(); 
    });
    proc->start("mstsc", { "/v:127.0.0.1" });
    return a.exec();
}

-->
stateChanged: QProcess::Running
started
// connect dialog is shown, I kill it
stateChanged: QProcess::NotRunning
finished: 0 QProcess::NormalExit

Works perfectly fine for me. Still don't understand why everyone wants to use cmd /c to run a simple windows executable...

m4kas

@Christian-Ehrlicher
My log when using your code:

stateChanged: QProcess::Starting
stateChanged: QProcess::Running
started
stateChanged: QProcess::NotRunning
finished: 0 QProcess::NormalExit
// RDP session is still in progress

Update: when using your code, but not with loopback, but with real remote machine IP . Using with loopback gives error about "could not connect to another console session".

Christian Ehrlicher

I don't know what exactly mstsc is doing but maybe it's detaching the rdp connection internally so the mstsc process is not running when the rdp session is open. Take a look into your running taskmanager/processes when you have an open rdp connection if the mstsc process which you're using for connecting is still there. I would say it's not the case.

m4kas

@Christian-Ehrlicher
Yes, I can see mstsc.exe in active processes list after QT reported finished() for that process.

Christian Ehrlicher

@m4kas said in QProcess start for mstsc (Remote Desktop) generates finished() signal immediately:

I can see mstsc.exe in active processes list after

And is it exactly this process which was started from Qt? Check the process id.

m4kas

@Christian-Ehrlicher
Good catch!
PIDs really differs. Now I will try to understand how track the process, that is being started by mstsc I am starting...

mrjj

@m4kas
Hi
I think you are going to need to use the APIs
https://docs.microsoft.com/en-us/windows/win32/termserv/terminal-services-administration

m4kas

As mentioned on microsoft forum post, most likely when building 32-bit app (which I was doing), it makes mstsc call of 32-bit version mstsc, which calls the correct 64-bit version and closes original process that was called from QT app.
Switched my QT project to build 64 bit application and it fixed my problem - now finished() signal is being emitted exactly after RDP session finished.
@Christian-Ehrlicher @JonB @mrjj thanks for your inputs.
Issue is solved.

mrjj

@m4kas
Good digging!