#!/bin/sh

# Start an ephemeral X server.

#

# This is useful for when you want to lauch an X server for a specific

# process. When that process exits, the X server will be killed.

# 

XSERVER=Xvfb

WINMGR=

prog=$0

usage() {

  echo "Usage: $prog [-x XSERVER] [-w WINDOWMANAGER] [-q] [-h] <command>"

  echo "-h   this help"

  echo "-q   quiet"

  echo "-w   window manager process to start once Xserver is up"

  echo "     (default: '$WINMGR')"

  echo "-x   Xserver (and args) to run"

  echo "     (default: '$XSERVER')"

  echo

  echo "This tool will pick an unused DISPLAY value (:0, :1, etc) and"

  echo "start an Xserver on that display, then run your command."

  echo

  echo "Examples:"

  echo "  $prog -x 'Xephyr -screen 1280x720' xterm"

  echo "  $prog -x 'Xvnc -httpd /usr/share/vnc/classes -geometry 1024x768 -depth 24' -w "gnome-session" firefox"

}

quiet() {

  [ "0$QUIET" -eq 1 ]

}

test_x_available() {

  xsocket=$1

  ! test -S $xsocket

}

test_x_healthy() {

  xpid=$1

  xsocket=$2

  displaynum=$3

  # Try xterm to see if X is up.

  if which xterm > /dev/null 2>&1 ; then

    DISPLAY=:$displaynum xterm -e 'true'

    return $?

  fi

  # Try xdotool if available, if xterm is not.

  if which xdotool > /dev/null 2>&1 ; then

    DISPLAY=:$displaynum xdotool getmouselocation > /dev/null 2>&1

    return $?

  fi

  # Try lsof if no X clients (above) are available

  if which lsof > /dev/null 2>&1 ; then

    lsof -p $xpid | grep -qF $xsocket

    return $?

  fi

  echo "Unable to determine if X is healthy (no tools available)"

  return false

}

cleanup() {

  if [ ! -z "$winmgrpid" ] ; then

    kill -TERM "$winmgrpid" || true

  fi

  kill -TERM "$xpid" || true

  pkill -KILL -P $$ || true

}

eval "set -- $( (POSIXLY_CORRECT=1 getopt -s sh +x:w:qh "$@" || echo " "FAIL) | tr -d '\n' )"

while [ "0$#" -gt 0 ] ; do

  case $1 in

    -x) XSERVER="$2"; shift ;;

    -w) WINMGR="$2"; shift ;;

    -q) QUIET=1 ;;

    -h) usage; exit ;;

    --) shift; break ;;

  esac

  shift

done

if [ "$1" = "FAIL" ] ; then

  usage

  exit 1

fi

num=-1

XSERVERNAME=${XSERVER%% *}

if ! which "$XSERVERNAME" > /dev/null 2>&1 ; then

  echo "Unable to find $XSERVERNAME. Aborting."

  cleanup

  exit 1

fi

while true; do 

  num=$(expr $num + 1)

  xsocket=/tmp/.X11-unix/X$num

  quiet || echo "Trying :$num"

  test_x_available $xsocket || continue

  (

    if quiet ; then

      exec > /dev/null

      exec 2> /dev/null

    fi

    echo set -- $XSERVER

    set -- $XSERVER

    cmd=$1

    shift

    exec $cmd :$num "$@"

  ) &

  xpid=$!

  healthy=0

  for i in 1 2 3 4 5 6 7 8 9 ; do

    # Break early if the xserver died

    #ps -p $xpid > /dev/null 2>&1 || break

    kill -0 $xpid > /dev/null 2>&1 || break

    # See if the xserver got a hold of the display socket.

    # If so, the server is up and healthy.

    sleep 1

    if test_x_healthy $xpid $xsocket $num ; then

      quiet || echo "$XSERVERNAME looks healthy. Moving on."

      healthy=1

      break

    fi

    sleep 0.2 || sleep 1 # In case your sleep doesn't take subsecond values

  done

  if [ "0$healthy" -eq 1 ] ; then

    break

  fi

done

export DISPLAY=:$num

quiet || echo "Using display: $DISPLAY"

if [ ! -z "$WINMGR" -a "$WINMGR" != "none" ] ; then

  if ! which $WINMGR > /dev/null 2>&1 ; then

    echo "Cannot find $WINMGR. Aborting."

    cleanup

    exit 1

  fi

  WINMGRNAME=${WINMGR%% *}

  quiet || echo "Starting window manager: $WINMGRNAME"

  (

    if quiet ; then

      exec > /dev/null

      exec 2> /dev/null

    fi

    $WINMGR

  ) &

  winmgrpid=$!

  # Wait for the window manager to startup

  quiet || echo "Waiting for window manager '$WINMGRNAME' to be healthy."

  # Wait for the window manager to start.

  for i in 1 2 3 4 5 6 7 8 9 10 ABORT ; do 

    # A good signal that the WM has started is that the WM_STATE property is

    # set or that any NETWM/ICCCM property is set.

    if xprop -root | egrep -q 'WM_STATE|^_NET' ; then

      quiet || echo "$WINMGRNAME looks healthy. Moving on."

      break;

    fi

    sleep .5

    if [ "$i" = "ABORT" ] ; then

      quiet || echo "Window manager ($WINMGRNAME) seems to have failed starting up."

      cleanup

      exit 1

    fi

  done

fi

quiet || echo "Running: $@"

(

  "$@"

)

exitcode=$?

cleanup

exit $exitcode