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abcminiuser / python-elgato-streamdeck

Python library to control the Elgato Stream Deck.
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The LibUSB locating code is looking up the wrong library name on linux according to documentation and fails on Debian 12+ #120

Closed cpw closed 12 months ago

cpw commented 1 year ago

Describe the bug I'm getting the dreaded ('Probe failed to find any functional HID backend.', {'libusb': FileNotFoundError(2, 'No such file or directory')}) error.

To Reproduce Unclear how to reproduce, but I'm running a pretty vanilla debian 12 (sid) setup. It's reliably failing here.

StreamDeck Information StreamDeck XL (gen 1?)

System Information I'm using 0.9.4 of the library, included with the streamdeck-ui package from streamdeck-linux-gui.

I have 

libhidapi-libusb0:
  Installed: 0.14.0-1
  Candidate: 0.14.0-1

installed, and the streamdeck is 100% readable from the local user (no permission problems).

The issue is here: https://github.com/abcminiuser/python-elgato-streamdeck/blob/87f4f0fb24272f3d3ec51cdc446a4aeacafe6dce/src/StreamDeck/Transport/LibUSBHIDAPI.py#L145

The python (and linux) standard is not to include the word "lib" at the front of the library name. See: https://github.com/python/cpython/issues/86746, https://docs.python.org/dev/library/ctypes.html#ctypes.util.find_library and other sources (as you can see, there's some ridiculous gcc voodoo going on behind the scenes).

I have no idea how this has ever worked to be honest - this seems to have been the standard in linux world for at least the past 20 years or so (omitting the "lib" prefix).

Anyway, the fix I have tested locally works great - remove the "lib" prefix and everything works again.

Example from my python console tests:

python
Python 3.11.5 (main, Aug 29 2023, 15:31:31) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes.util
>>> ctypes.util.find_library("libhidapi-libusb")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.11/ctypes/util.py", line 341, in find_library
    _get_soname(_findLib_gcc(name)) or _get_soname(_findLib_ld(name))
                ^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/ctypes/util.py", line 147, in _findLib_gcc
    if not _is_elf(file):
           ^^^^^^^^^^^^^
  File "/usr/lib/python3.11/ctypes/util.py", line 99, in _is_elf
    with open(filename, 'br') as thefile:
         ^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: b'liblibhidapi-libusb.a'
>>> ctypes.util.find_library("hidapi-libusb")
'libhidapi-libusb.so.0'
>>>

As you can see, looking for the name as you specify it fails, but without the "lib" prefix, works great. As far as I can tell, this has been how it should have worked for a LONG time, so removing the lib prefix shouldn't break compatibility across a wide range of versions.

brimston3 commented 1 year ago

It "works" because the result to ctypes.util.find_library() is not used and "libhidapi-libusb.so.0" is passed through to ctypes.cdll.LoadLibrary() directly. Either way there should be exception handling around find_library() because it can except. I don't generate the exception with find_library() on debian12 so I'm not sure the difference between our configurations.

edit: after looking into it a little more, the exception consistently happens when you have the static library libhidapi-libusb.a installed.

abcminiuser commented 12 months ago

Should be resolved with 7bc21c839618991c3360e5ad499a73741ccda830.