Decoding on MacOS gives raw data

Hi,

Executing the following code gives me unexpected results on MacOS:

from pystrich.datamatrix import DataMatrixEncoder
import PIL
from io import BytesIO
from pylibdmtx.pylibdmtx import decode

data = 'SomeStringWithData'

print(f'Encoding: {data}')

image_bytes = DataMatrixEncoder(data).get_imagedata(cellsize=2)
image = PIL.Image.open(BytesIO(image_bytes))

results = decode(image)

print('raw results:')
print(results)

Output on MacOS 10.13.3:

Encoding: SomeStringWithData
raw results:
[Decoded(data=b'TpnfTusjohXjuiEbub\xb9AE\xbf}\xad|\xc81\xda\x9d\x9a\x95\xb2`\xf7`\x07\x01', rect=Rect(left=3, top=4, width=37, height=35))]

Whereas this works as expected on both Linux and Windows.

Basically it gives the raw data of the datamatrix instead of the parsed/decoded one.

I can’t figure out whats going on because:

• dmtxread from dmtx-utils DOES work on the same machine, suggesting the c library IS NOT at fault here
• the dmtxDecodeMatrixRegion wrapper function gives the wrong result, suggesting the c library IS at fault.

I’ve also tried having the latest version of libdmtx compiled from source on my search path instead of the one from homebrew but it gives the same result.

Is this a known issue on your end maybe?

[quicklizard99]

Included in v.0.1.8, now on PyPI.

[jbweston]

I have investigated a little more deeply and have come to the following conclusions:

1. This is not a platform-dependent bug
2. This is a problem with pylibdmtx, not the upstream library

Evidence

This is not a platform independent bug

I have managed to replicate this problem on my machine (Debian testing) with the apt installed libdmtx (v0.7.5), as has @akhmerov.

This is a problem with pylibdmtx

I used the first part of @justinvdk’s script above to generate a problematic datamatrix. I then saved this to a PNG file and read it in using the dmtxread program installed with apt, which is linked against libdmtx v0.7.5, and it produces the correct result.

What’s the problem

I believe that the API to libdmtx has changed between 2 bugfix releases, when really there should have been a minor (or even major) version release.

I used the shell script from this gist with git bisect in the libdmtx repo to find that this commit is where things stopped working. I notice that this commit actually changed the API of libdmtx by adding extra fields to some of the exported datastructures. This means that the wrappers in wrapper.py are formally incorrect, and things break in unexpected ways.’