What is the recommended way of passing keyboad events to QProcess transparently? - c++

I have a GUI application, which creates a QProcess inside, catches its output and shows it on a form. I need to somehow catch key events from the form to pass them to QProcess (to make it fell as close as possible to real terminal window).
So, I suppose, I should process keyReleaseEvent() and somehow transform either event.text() (which is QString) or event.key() (which is int) to argument, suitable for process.write() (which takes char* or QByteArray). Is there some recommended way to do such a conversion (taking into account localization issues, ctrl/alt/shift modifiers and so on)? I do not really want to construct some sort of mapping from key() return values to char* strings; and text() drops modifiers.
Moreover, if I start process with command bash -c sudo something in QProcess, it exits instantly, complaining that "no tty present and no askpass program specified", so I may be doing something completely wrong...

The problem is more than just deciding what to write to the process.
You can't emulate a terminal just by reading/writing stdout/stdin of a process, it's more complicated than that. Think about the program less, or any pager, for example. How does it know how many lines to print at a time? It needs information about the terminal which isn't represented through stdin/stdout/stderr.
Emulating a terminal is beyond the scope of QProcess. If you're really sure you need to do this then use some existing Qt-based terminal emulator as a starting point (e.g. Konsole).

Related

How can I determine whether the current process has a UI open?

I am writing some library code which will rerun the current process as an administrator/root. The problem is (for linux at least) that if the calling code is a command line application the best way would be to call sudo whereas if it is a gui application, gksudo is appropriate. For completeness sake though, solutions (or pointers to solutions) for other os's are also welcome.
Also, this is useful so that for GUI apps, I can turn off printf statements.
I'd run gksu(do) if the environment variable DISPLAY is set. It doesn't really matter if the application has a GUI or not, if there's an X-server running, and we can use it, why shouldn't we?
Doesn't allow you to determine if you should disable stdout output. However, stderr output is generally captured in .xsession-errors, even if no terminal is connected, so you might not want to disable that output afterall.

Access data from terminal

I have to write a program that intercepts data from terminal and i have to parse it. After processing when the data, i have to parse it before it goes to stdout.
I can't use tee or commands like prog > file 2>&1 as the program is going to be interactive.
For example :
If the user types ls in the terminal i have to parse it then it should go operating system and then when I get the result after processing I ll have to again parse it before it's displayed in the terminal.
I did my research and I think I can achieve it through pseudo terminal interfaces ( pty ).
Please let me know if there is a better way to achieve it.
I am using cpp and bash and the platform is *nix.
Update:
I can also use libexpect from expect.
I am not sure what do you mean here - you mean interactive program as "working in another terminal communicating with user" or even displaying GUI?
How does it specify the terminal? It is probably important what is program layout here (which program starts which).
If your application uses GUI to communicate with user, then I would simply do it this way:
start bash with sdtin and stdout attached to pipes,
your program reads & writes to it's end's of those pipes, parses data, and reads/writes on it's own stdin&stdout - so it appears on it's terminal.
If you mean controlling different terminal than your application's, it gets though since system generally does not expect program operating on multiple terminals. I don't think it's possible to filter communication between terminal and already working application attached to it. Starting another process spawning another terminal might be an option - to have basically two terminals working in sync. But then you will have to synchronize both processes by some other means (named pipes, network connection or some other IPC).
If you provide more detail on your program I might provide more directed help.
PS Don't tell me that you are writing some terminal keylogger ')
EDIT:
Your program is probably GUI based then - what i would recommend would be something similar to answer linked by banuj.
Best option will probably be to create three pipes, then fork, and in child process assign corresponding ends of pipes to stdin, stdout and stderr. Then child process should exec into shell - probably bash, although I am not sure if other shells would sound better if read out loud ;) Main process will be able to read/write other ends of mentioned pipes, parsing both inputs and outputs to bash and programs it runs.
You could also exec directly to commands user specifies, but that forces you to take over tedious job of a shell - managing current directory, environment variables, job control and so on.
Using above method might however cause some trouble - some programs (usually in security related contexts - eg. su(do) asking for password) will try to bypass stdin/stdout anyway and read directly from terminal device. I am not sure what can you do in such case - programing your own terminal emulator would be an option, but I don't know if you want to go this deep into system programming for this.
If you want some code snippet's, if you don't know how to do above, just ask ;)

Is it possible to send command to console window in which my program is running?

I know the system() function but that creates it's own environment so every variable set here isn't forwarded to main console. I wonder is it possible to send command as it would be written by the user or as it would be executed by *.bat file ?
The reason I need this is that I look for a way to set env variable of parent CMD process. And yes I know that system doesn't want me to do it, but maybe there is a some workaround for that...
Idea is to create app that would set as a variable anything that is send to it via input pipe, like this:
echo Bob| setvar name
so then:
echo %name%
would produce Bob
The whole idea is to make easier setting a variable from any program output (I know how to do it with for command) with taking account of peculiarities with special batch characters like ^!% since these are allowed in file names. It would make simpler many cmd scripts.
You can certainly run programs in the same console window as your program. That's the default behavior for CreateProcess. MSDN has more details on what happens between related processes sharing a console. You'll probably want to wait for the child process to terminate before continuing to run your own program.
However, that won't help with your real goal. The window where a program runs has absolutely nothing to do with the environment variables of any of its ancestor processes. You'll have to look elsewhere for a solution to your real problem.

Is there a way to send some procesess with known pid in background?

I am new in Linux and system programming .
I Want to write a c program which finds processes whose cpu% usage are more than a specific given value and sends them to background.
anybody can help me !
I really appreciate it
I'm fairly sure that what you're asking is that you want to detect if a process is using X amount of CPU and if so, take it off the CPU for a while. There's a piece of software already that does this: It's called the kernel. I'm not aware of any way to programatically take another process off CPU unless that other program supports an external interface to reduce its load.
Most likely what you really want to do is configure the nice and other scheduler parameters of the running process so the kernel is more like to to take it off CPU when another program needs to do work.
But what underlying problem are you really trying to solve here? Maybe if you tell us that we can offer an alternate solution.
Please look at source code of process managament utilities like:
htop
top (standard unix command)
ps (standard unix command)
IMHO, You can't.
Background management ensures the shell. So, the & is interpreted for example by /bin/bash command. When pressed CTRL-Z, the kernel stopping your current fg-job, and again by your shell you can send it into background.
Youre looking for the way how to remote control the shell what running some program in fg. I don't know any 'remote-controling' way.
Ofc, here are alternative solutions, for example:
use the screen command, and you can recall the specific screen into your terminal, and can manually send process into bg.
or you can use some screen-sharing utility, to overtake a specific terminal and CTRL-Z, bg
or, you can patch bash and adding remote control functionality. ;)
or, here is something what i don't know. ;) - hm, maybe trap some user-signal handling code in the /etc/profile?
You can read a bit about here: http://en.wikipedia.org/wiki/Process_group
Honestly, after a half hour of thinking I don't get any idea why you want remotely (from the another terminal - by its PID) send some processes from the fg into the bg. Give me no sense.
Can you please tell, what you want achieve?
You probably want to reduce process priority, but I not sure it's good idea.
We send process to background generally to free shell's prompt.
The "+" means that the program "is in the foreground process group". I don't believe, however, that this state at all affects the process's scheduling.
However, you can change it with tcsetpgrp.
From the man page: "The function tcsetpgrp() makes the process group with process group ID pgrp the foreground process group on the terminal associated to fd, which must be the controlling terminal of the calling process, and still be associated with its session. Moreover, pgrp must be a (non-empty) process group belonging to the same session as the calling process."
By my reading, you just call this function and make the shell (or some other program) be the foreground process.

Async Console Output

I have a problem with my application win32 console.
The console is used to give commands to my application. However, at the same time it is used to output log messages which mostly comes from asynchronous threads. This becomes a problem when the user tries to write some input and simultaneously an async log message is printed, thus thrashing the display of the users input.
I would like to have some advice in regards to how to handle such a situtation?
Is it possible for example to dedicate the last line in the console to input, similarly to how it looks in the in-game consoles for some games?
You can use SetConsoleMode to disable input echo and line editing mode. You can then echo back input whenever your program is ready to do so. Note that this means you will need to implement things like backspace manually. And don't forget to reset the mode back when you're done with the console!
This is possible using the Console API, but it involves quite a bit of work and all the threads that use the console will have to cooperate by calling your output method rather than directly calling the Console API functions or the runtime library output functions.
The basic idea is to have your common output function write to the console screen buffer, and scroll the buffer in code rather than letting the text flow onto the last line and scroll automatically. As I recall, you'll have to parse the output for newlines and other control characters, and handle them correctly.
You might be able to get away with using "cooked" console input on the last line, although in doing so you risk problems if the user enters more text than will fit on a single line. Also, the user hitting Enter at the end of the line might cause it to scroll up. Probably best in this situation to use raw console input.
You'll want to become very familiar with Windows consoles.
Any time you have asyncronous threads trying to update the same device at once, you are going to have issues like this unless something synchronizes them.
If you have access to everyone's source code, the thing to do would probably be to create some kind of sync object that every task must use to access the console (semaphore, etc).