# Roll up, Roll up. Test your backend

Nick Lamb (njl98r@ecs.soton.ac.uk)
Thu, 31 Dec 1998 15:32:43 +0000 (GMT)

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--1318610500-70641457-915118363=:29443
Content-Type: TEXT/PLAIN; charset=US-ASCII

A while back I reported that SANE 1.0 has a broken PNM device driver.
While I was waiting for it to be fixed (someone?) I offered to write
a test frontend that would spot this sort of stupidity. Here it is.

I have added functionality to SANE's scanimage so that it can hopefully
detect broken SANE backends. A patch attached to this mail. I can also
make it available for HTTP if anyone asks.

The file scanimage-test-patch is a patch to be applied directly to the
file frontend/scanimage.c.

I would like to see this patch, or something similar, applied before
SANE 1.0.1 is made available, but it should perhaps be enclosed in
#ifdefs so that by default the test features aren't compiled in. This
is especially the case if some hardware+backend combos are still
broken when shipped with 1.0.1 -- I hope that doesn't happen.

What does it do?
----------------

This frontend detects problems with SANE backends which do not fully
meet the SANE specification. In this first version I have concentrated
on a problem which several backends "In the wild" are known to have.
In particular this version checks that the backend correctly handles
sane_read(...) even for unusual and varying buffer length values. It
detects backends which overflow the buffer or incorrectly report the
amount of data read and it also detects backends which sometimes don't
write any data even after a blocking read.

Why should I use it?
--------------------

If you're a SANE end-user you probably don't want to try this. If you
do try it, and it detects a problem with a backend you use, please
report it to the SANE developers mailing list, where hopefully someone
will notice and take appropriate action.

If you're a SANE frontend developer, you probably don't want to try
this. The exception is if your frontend has problems in sane_read(...)
on some backends, but not others. In that case this patch may help
you to show that the problem is in the backend, and you can breathe
a sigh of relief.

If you're a SANE backend developer, and you have working code, you
really should try this frontend. Any properly working backend should
pass with no trouble, but those which don't are a problem. In the
future hopefully a program somewhat like this one will form part of
a self-certification test for new SANE backends...

If you're a SANE backend developer, but you don't yet have working code
you should be reminded that sane_read(...) is used very politely by
the two commonest frontends, scanimage and xscanimage. Your code should
be written to work with /any/ frontend, and that means this one too.

If you're a core developer, please take a look at this and see if you
think the tests done here should be _required_ before a backend is
made part of the core SANE distribution in future. Also please try it
with any backends for which you have appropriate hardware, as a double
check in case the maintainer doesn't see this.

How do I compile it?
--------------------

After applying the patch, simply recompile and (optionally) re-install
the scanimage frontend. The new code should work on all the platforms
for which scanimage itself was tested. It works for me (TM)

How do I use it?
----------------

Simply add the parameter --test or -T to an ordinary scanimage run, and
the test code is invoked in place of the ordinary scanimage sane_read
code. Unlike a normal scan, there is no data written to stdout for the
test scan.

e.g. scanimage -d pnm:0 -T --filename /path/to/some.ppm

After some initial diagnostic messages, there are a series of lines
each containing a description of the test being performed, then either
PASS or FAIL and a brief explanation of the problem.

It is NOT acceptable for a backend to FAIL any of the tests. If it is
not possible to handle the extreme values tried by --test in your
backend (e.g. due to hardware limitations) then you should return a
suitable SANE error status and note the limitation under BUGS in the
manual page for your backend.

Feedback
--------

I have only tested this on an Intel PC with no physical scanners. For
testing I used only the PNM:0 and PNM:1 devices. Therefore I cannot
say for sure that this works with _any_ known scanners in the real world
I hope some of you will help rectify that by sending me bug reports.

I would also appreciate info about other ways in which some backends are
known not to meet the SANE standard. This code should evolve to test
for compliance as thoroughly as possible.

Nick
njl195@zepler.org.uk

--1318610500-70641457-915118363=:29443
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--1318610500-70641457-915118363=:29443--

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