import ./make-test-python.nix (
{ pkgs, ... }:
/*
SANE NixOS test
===============
SANE is intrisically tied to hardware, so testing it is not straightforward.
However:
- a fake webcam can be created with v4l2loopback
- sane has a backend (v4l) to use a webcam as a scanner
This test creates a webcam /dev/video0, streams a still image with some text
through this webcam, uses SANE to scan from the webcam, and uses OCR to check
that the expected text was scanned.
*/
let
text = "66263666188646651519653683416";
fontsConf = pkgs.makeFontsConf {
fontDirectories = [
pkgs.dejavu_fonts.minimal
];
};
# an image with black on white text spelling "${text}"
# for some reason, the test fails if it's jpg instead of png
# the font is quite large to make OCR easier
image =
pkgs.runCommand "image.png"
{
# only imagemagickBig can render text
nativeBuildInputs = [ pkgs.imagemagickBig ];
FONTCONFIG_FILE = fontsConf;
}
''
magick -pointsize 100 label:${text} $out
'';
in
name = "sane";
nodes.machine =
{ pkgs, config, ... }:
boot = {
# create /dev/video0 as a fake webcam whose content is filled by ffmpeg
extraModprobeConfig = ''
options v4l2loopback devices=1 max_buffers=2 exclusive_caps=1 card_label=VirtualCam
kernelModules = [ "v4l2loopback" ];
extraModulePackages = [ config.boot.kernelPackages.v4l2loopback ];
systemd.services.fake-webcam = {
wantedBy = [ "multi-user.target" ];
description = "fill /dev/video0 with ${image}";
HACK: /dev/video0 is a v4l2 only device, it misses one single v4l1
ioctl, VIDIOCSPICT. But sane only supports v4l1, so it will log that this
ioctl failed, and assume that the pixel format is Y8 (gray). So we tell
ffmpeg to produce this pixel format.
serviceConfig.ExecStart = [
"${pkgs.ffmpeg}/bin/ffmpeg -framerate 30 -re -stream_loop -1 -i ${image} -f v4l2 -pix_fmt gray /dev/video0"
hardware.sane.enable = true;
system.extraDependencies = [ image ];
environment.systemPackages = [
pkgs.fswebcam
pkgs.tesseract
pkgs.v4l-utils
environment.variables.SANE_DEBUG_V4L = "128";
testScript = ''
start_all()
machine.wait_for_unit("fake-webcam.service")
# the device only appears when ffmpeg starts producing frames
machine.wait_until_succeeds("scanimage -L | grep /dev/video0")
machine.succeed("scanimage -L >&2")
with subtest("debugging: /dev/video0 works"):
machine.succeed("v4l2-ctl --all >&2")
machine.succeed("fswebcam --no-banner /tmp/webcam.jpg")
machine.copy_from_vm("/tmp/webcam.jpg", "webcam")
# scan with the webcam
machine.succeed("scanimage -o /tmp/scan.png >&2")
machine.copy_from_vm("/tmp/scan.png", "scan")
# the image should contain "${text}"
output = machine.succeed("tesseract /tmp/scan.png -")
print(output)
assert "${text}" in output, f"expected text ${text} was not found, OCR found {output!r}"
)