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C++ Send Keypress/Code to a child process


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#1 firey

firey

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Posted 02 December 2012 - 03:30

Background/Description:

I have recently gotten a raspberry pi, and have decide to not use a Desktop Environment. I have QT, and other development packages installed, however without QT-Embedded, I can't use the virtual windowing tools that QT Comes with. I wanted to create a media center style PC without the fancy additions of XBMC and other media centers. As I don't have a DE/Window system I can't run anything with a gui. I wanted to make a system that would allow me to run/play movies on the pi from any of my devices (Phone, Tablet, Desktop). So I have decided to make a GUI/Server on my computer that would control the PI via TCP. I would use PHP for a web system that would create trigger files that a FileSystemWatcher would pick up for the mobile devices, and will use a direct C# gui on the desktop.

I can do this with no problem as it is done with a standard TCP Connection. I will send commands such as: ~MSFS; to Mount the Shared file system (if not done), ~PV;FileName to Play the Video using omxplayer. All of this is pretty easy and as I will drive everything from the desktop it isn't a lot of pi side stuff to do. Now the problem is.. by forking the process I lose the direct input into the program, and as I will be running it externally instead of on the device I don't get the direct CLI input. As it is all command line, I pause videos by pressing "p". I am sure there are other commands I just haven't looked into them.

The Need:

As I will be controlling it from the PC Server I want to have the ability to send commands such as ~PAUSE; or equivelant, from the desktop to the pi, and have it send the 'p' key to the omxplayer. I have read about using pipes to communicate between parent a child processes, however as I am not taking input via command line for this it would be done all internally during the TCP Packet processing, I don't know how to get that stream. In C# it would just be a memorystream or stock stream that I could just save off and call good. I am not sure if I can do that with the pipe. Now, pausing is just an example, however having the ability to pause a video is a good thing, and would really be a requirement in making it useful.

TLDR;

I am making a client/server program for my Raspberry PI, that will run a child process. I need to send a specific key to the child process when a specific packet is sent. ie) Server Sends ~PAUSE, Client Processes and sends the "p" key to the child process, which then should pause the video (as that's how it works when I run the program directly, hitting p will pause it). How do I do it?


#2 OP firey

firey

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Posted 04 December 2012 - 23:45

No one has any ideas? I found that I could write() using the FD for the stdin for the process. Will post results but if anyone had any experience though feedback would be awesome.

#3 +Karl L.

Karl L.

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Posted 06 December 2012 - 01:14

I have no experience with this specifically, but my first thought is that it sounds like a task for signals. If you don't have direct control of the other program (e.g. you didn't write it), then that might not be feasible. The GNOME Onscreen Keyboard sends virtual kepresses... somehow, so I'm sure you could download the source code and take a peak at their implementation. I would definitely be interested in your solution when you get this working though.