Unexpected FieldTypeEnum while parsing specific jpegs

[rjt-gupta]

Hi! While parsing this JPEG with mitmproxy.

Traceback I got:
File "mitmproxy/contentviews/__init__.py", line 130, in get_content_view ERROR File "mitmproxy/contentviews/auto.py", line 17, in __call__ ERROR File "mitmproxy/contentviews/image/view.py", line 36, in __call__ ERROR File "mitmproxy/contentviews/image/image_parser.py", line 78, in parse_jpeg ERROR File "mitmproxy/contrib/kaitaistruct/exif_be.py", line 572, in ifd0 ERROR File "mitmproxy/contrib/kaitaistruct/exif_be.py", line 31, in __init__ ERROR File "mitmproxy/contrib/kaitaistruct/exif_be.py", line 522, in __init__ ERROR File "enum.py", line 291, in __call__ ERROR File "enum.py", line 533, in __new__ ERROR File "enum.py", line 546, in _missing_ ERROR ValueError: 9 is not a valid FieldTypeEnum ERROR

I think the main issue lies here. An unexpected FieldTypeEnum 9 is generated and throws error when field_type gets updated.

Would be glad to make changes to fix this.

[GreyCat]

The core problem lies in a fact that Python enum implementation throws an exception on encountering of value not specified in enum. Majority of other languages just treat it as null, or undefined, or just keep a numeric value. To some extent, it's being mentioned in #300, but there is no Python-specifid bug. Let us consider this one to be like that.

There are 2 ways to solve that specific problem you're mentioning:

• Implement workaround for Python (probably add it to Python KS runtime + adjusting ksc output)
• Fix exif_be to actually include value for FieldTypeEnum 9.

[rjt-gupta]

Hi! Thanks for looking into this.
I think the second way would be the best solution but not sure what would be the value for FieldTypeEnum 9 that has to be added in exif_be.
What do you think?

[KOLANICH]

Implement workaround for Python (probably add it to Python KS runtime + adjusting ksc output)

IMHO just a function returning either an IntEnum or just an integer is needed. And this behavior should be disableable. For example when debugging specs (usually I create a python script trying to parse all the files in a dir) a missing enum value means that I need something to be added.

[GreyCat]

JFYI, a similar thing already exists in Ruby runtime: https://github.com/kaitai-io/kaitai_struct_ruby_runtime/blob/master/lib/kaitai/struct/struct.rb#L478-L483

We just need similar one for Python.

[GreyCat]

Python-related problem fixed in kaitai-io/kaitai_struct_compiler@5039401

New test is called "enum_invalid": http://kaitai.io/ci/ci.html

Eventually to be implemented for all languages.

[GreyCat]

Test passes for all languages. Please reopen if any problems still remain.