Error and Corruption When Reopening PSD Files Saved with psd-tools

[magurotaisa]

Describe the bug
When attempting to reopen a psd file saved using psd-tools, an error occurs, preventing successful reopening.

To Reproduce

Steps to reproduce the behavior:

1. Open a PSD file using psd-tools, e.g., "error_sample.psd".
2. Save the opened PSD file as "sample.psd" using the following code in Python:

psd = PSDImage.open("error_sample.psd")
psd.save("sample.psd")

3. Try to reopen "sample.psd" using psd-tools with the following code in Python:

PSDImage.open("sample.psd")

Expected behavior
Both "error_sample.psd" and "sample.psd" should be identical, and "sample.psd" should be successfully reopened without any errors.

File and screenshots
Error file:
error_sample.psd.zip

Error log:

File ~/.pyenv/versions/3.8.10/lib/python3.8/enum.py:663, in Enum.__new__(cls, value)
    661 ve_exc = ValueError("%r is not a valid %s" % (value, cls.__name__))
    662 if result is None and exc is None:
--> 663     raise ve_exc
    664 elif exc is None:
    665     exc = TypeError(
    666             'error in %s._missing_: returned %r instead of None or a valid member'
    667             % (cls.__name__, result)
    668             )

ValueError: b'loat' is not a valid OSType

Environment

• Python [3.8.10]
• Version [v1.9.28]

Additional context
After investigating the issue, it has been discovered that the error occurs when there are layers that require clipping during the Lab to RGB conversion process.

[kyamagu]

This is likely a bug in the low-level psd structure

[oh-ok]

Found the cause of this. It affects every PSD that contains a SolidColor layer encoded with stringID instead of charID.

The redFloat, blueFloat and greenFloat keys are being written out as OSTypes rather than Pascal strings since they're in this _TERMS set:

psd-tools/src/psd_tools/psd/descriptor.py

Lines 69 to 77 in 03a14e2

	def write_length_and_key(fp, value):
	"""
	Helper to write descriptor key.
	"""
	written = write_fmt(fp, "I", 0 if value in _TERMS else len(value))
	written += write_bytes(fp, value)
	return written

Since those are the only keys with length greater than 4 (at least at the moment) you can just add a condition to only include length 4 byte strings to fix this, or move the keys to their own separate class.

psd-tools/src/psd_tools/psd/descriptor.py

Lines 52 to 56 in 03a14e2

	_TERMS = set(
	item.value for kls in (Klass, Enum, Event, Form, Key, Type, Unit) for item in kls
	)