Table of Contents
xlab - X Window System Script Recording and Playback
options ] ...
xlab is a program which sits between an X client
and an X server, monitors the events flowing from the server to the client,
and records events in a script file. The script file name for recording
is specified using the -r option. xlab is useful as part of a regression
test system, as it can automate the playing of fixed sequences of operations
into an application program based on X. xlab can play back events from
a script file (specified using the -p option) to a client.
detect application-program failures during playback. To do so, it detects
the failure of windows to appear as necessary for playback, and reports
errors when windows do not appear within one second of when they are expected.
A failure of a window to appear is symptomatic of several classes of application
failures, including failure of a popup to appear and an application crash.
xlab functions as a protocol interposition process. It attaches to the
X server as if it were a client, and a client attaches to xlab as if it
were an X server. This allows xlab to be used for testing standard unmodified
client application programs.
By adjusting the host and/or display number,
clients can be made to attach to xlab instead of the X server.
server <-----> xlab
All bytes from the server are sent to xlab which sends them on to the
client. All bytes from the client are sent to xlab which passes them on
to the server. xlab is transparent to both the server and the client.
- Requests the recording of a session and defines the script file to be
written during recording.
- Requests the playback of a session
and defines the script file to be played back. The beginning of playback
is deferred until the client program attaches.
the percent time contraction to be used during playback. -d50 plays back
a session at 50% speed, and -d200 plays it back at double speed. Changing
playback speeds may foul up the client's detection of double clicks. The
default time contraction is 100 percent (1:1 playback:record).
- Specifies the double-click-time in milliseconds. During playback when time
is contracted or expanded, ButtonPress events with short delays from the
previous event are handled specially so that they do not get misrecognized
by the client.
- Specifies the number of seconds to wait
between the time the client attaches and the first event is played back.
This allows complex clients to complete drawing before playback begins.
The default is five seconds.
- Defines the display number. The display
number is added to the input and output port to give the actual ports which
are used by xlab.
- Specifies the hostname on which xlab should look
for its X server.
- Prints a help message.
- Determines the port
that xlab will use to connect to the server (default is 0). For example,
if xlab were run with the options "-hlaser -o0" it would connect to the DISPLAY
named "laser:0". In the normal case it is not necessary to specify -h or
-o options: xlab connects, via TCP, to the local host's zeroth display.
- Specify the port that xlab will use to take requests from clients (default
is 1). For example, if xlab were running on the host named "hobie," and
the option -i3 were specified, clients for recording or playback would
attach to the DISPLAY named "hobie:3". Normally, it is not necessary to
specify the -i option, and clients should be made to connect via TCP to
- Quiet output mode. Gives only the names of requests, replies,
errors, and events, but does not indicate contents.
the level of verbosity which xlab will provide. The print-level can be 0
(same as quiet mode), 1, 2, 3, 4. The larger numbers give more and more
output. For example, a successful setup returns a string which is the name
of the vendor of the X server. At level 1, the explicit field giving the
length of the string is suppressed since it can be inferred from the string.
At level 2 and above the length is explicitly printed.
has a command interpreter, which allows to read commands at any time from
the keyboard, a pipe (for GUI interaction) or a file (for complete automation).
the grab timeout. If any active grab (server, pointer, or keyboard) originating
from the program under test lasts longer than this time (default 30 seconds)
the xlab program terminates, releasing the grab. This feature is handy
for use in debugging situations in which grabs deadlock the server.
- Terminates the program. If some clients are still connected on xlab,
they will be terminated as well.
- record filename
- Starts recording user input
xevents (keyboard and mouse) in the specified filename (same as -r option).
- replay filename
- Starts replaying events from the specified filename (same
as -p option).
When running with xlab, three processes are involved,
potentially all on different machines:
- stop record
- Stop the current recording.
- stop replay
- Stop the
- X server
- The X server will run on
machine (or host) "A", display "B". ("A" is a machine name; "B" is a display
- xlab must be told where the X server is (what machine
and what display), and, in addition, the port-number on which to listen
for X clients. The options for xlab are "-h<Xserver-host>" and "-d<display-number>".
In this example, -hA and -dB. Typically the display-number is not given. xlab
will not try to connect to the server until the client connects to xlab.
- X client
- The client should connect to xlab rather than to the server. To
avoid changing the code for the client, xlab listens on the same port as
the server for connecting clients. If the server and xlab are on different
machines, this works well. However, if the server and xlab are on the same
machine, this creates a port conflict. To resolve this conflict, xlab can
be given a different input or output port number, as necessary, to avoid
the port that the server is listening to. The client must connect to this
offset port number. The input port for xlab is set by -i<port-number>; the output
port is set by -o<port-number>. The default input port is 1; the default output
port is 0. These ports are offset by the X11 base (6000) and the display
number. The client attaches to xlab by changing its display number by the
xlab -hbagel -r/tmp/record
The X server would be expected
to be found on "bagel", display 0 (the default). xlab and the client would
both be running on "cleo". The client program would think it was connecting
to an X server on "cleo:1". This X server is actually xlab, which would
record events and pass through requests and events to the real X server
running on "bagel:0".
server (bagel:0) <---> xlab -hbagel <---> client -d cleo:1
As it runs, xlab records input events for the client to the file /tmp/record.
The X server would be expected to be found on the local
host, display 0 (the default). xlab and the client would be running on the
same local host. The client would connect to "localhost:1", the xlab program,
which in turn would connect to the real X server on "localhost:0".
(localhost:0) <---> xlab <---> client -display localhost:1
As it runs, xlab plays back pre-recorded events for the client from the
file /tmp/record. If all is well, the recorded session should be reproduced.
The X Version 11 is the only protocol recognized.
scheme on playback is extremely limited. At this time xlab can be confused
if the client behaves differently at the replay (window id matching scheme),
but may be fixed soon.
The assumptions made about the similarity between
the recorded and played back client sessions are easy to break. Two modes
have to be supported: strict respect of recorded delays, and synchronization
according to the protocol instead of timers.
The number of available commands
from is still limited (only record, replay, stop). Command interpreter will
not work well if commands are read from a file. It's ok if commands are
read from keyboard or a pipe.
A second replay in the same session doesn't
work well. It is necessary to exit from xlab and restart.
Image capture function
(for comparison between recording and replay) not yet implemented.
Recorded file not yet compressed.
, X11 and PEX
Table of Contents