Mon 11 February 2019 | -- (permalink)

So there's this vendor-supplied toolkit that I needed to get running in a Docker-ized build environment. Toolkit is a bit of a pig, but that's not the problem. The problem is that, while the core tools in the kit run as command line programs (and, indeed, pretty much have to be run that way for reproducable builds), the installation process requires X11. In Docker. Happy joy, not.

So our bag of tricks today includes:

• Xvfb -- a virtual X11 server which uses a plain file as its "frame buffer"
• xvfbwrapper -- a Python context manager wrapped around Xvfb
• ratpoison -- the Rodent-Free X11 window manager

And yes, the basic strategy is just as disgusting as you expected: run the frelling installer under Xvfb while using ratpoison to click on the buttons. Works surprisingly well, although of course very fragile. Not currently running under docker build, only under docker run, so may end up having to use docker commit to get an image out of this, but such is life.

Other tools which might be necessary or useful for this sort of thing:

• xte and visgrep from the xautomation toolkit
• display from a (recent version of) the ImageMagick package
• Xvnc if you're trying to use display from several timezones away

There's some overlap between ratpoison and xte, which one you need depends on details of what you're trying to do.

display -update 1 xwd:Xvfb_screen0 will let you watch Xvfb's frame buffer with automatic updates, making it easier for you to debug your mouse commands just by typing ratpoison or xte commands and seeing what happens. The catch is that only recent versions of display will work for this due to a bug, now fixed. The version on Debian Jessie was too old, the version on Debian Stretch is fine (it was time to upgrade that VM anyway...). In a pinch, plain old xwud will do.

Running X11 long distance ... doesn't work so well. It's almost tolerable for a lightweight program like xwud, but by the time you get to something like display it's just painful. Available evidence suggests that the X11 protocol is just too chatty for this use. But that's OK, you can solve this with one more layer of kludgery: run Xvnc on the server where you're running Docker and display, then use a VNC viewer to view the resulting X11 desktop. Even VNC is a bit slow, but it's a lot better for this than X11.

Whether you're using X11 or VNC, you'll want to tunnel it via SSH unless this is all happening in a safe environment (hint: there is no such thing as a safe environment, just threats people chose not to consider).

May post more on this once I get the wretched thing fully working.

This not a dancing elephant. It's more like a sauropod trying out for ballet.