"ValueError: File size doesn't match" when parsing some TF2 BSPs

[piousdeer]

from srctools.bsp import BSP
BSP('pl_pier_b23.bsp')

Traceback (most recent call last):
  File "[...]", line 2, in <module>
    BSP('pl_pier_b23.bsp')
  File "[...]/.venv/lib/python3.9/site-packages/srctools/bsp.py", line 1138, in __init__
    self.read()
  File "[...]/.venv/lib/python3.9/site-packages/srctools/bsp.py", line 1274, in read
    gm_lump.data = decompress_lzma(lump_data)
  File "[...]/.venv/lib/python3.9/site-packages/srctools/binformat.py", line 192, in decompress_lzma
    raise ValueError(
ValueError: File size doesn't match. Got 31,294 bytes, expected 31,295 bytes

Map link: https://tf2maps.net/downloads/pier.854/. This seems to affect newer maps, https://tf2maps.net/downloads/backlot.2/ and some other maps I tested that haven't been updated in a long time are not affected. Some of the affected maps differ by 1 byte, some by 2 bytes.

[TeamSpen210]

Hmm, I apparently did find this when writing this code, but only saw a single null byte. So it'll accept an extra byte, but only if zero. Perhaps it's getting set to garbage data? Not sure about the 2-byte files.

[piousdeer]

The pl_pier version distributed with TF2 differs by 2 bytes:

ValueError: File size doesn't match. Got 130,062 bytes, expected 130,060 bytes

I've uploaded it here: https://send.vis.ee/download/5af1ea0f0990faab/#Lya2jHG3M-EmEK9SOppREQ

[TeamSpen210]

This is very strange, some lumps have random extra null bytes, and even a few seem to have extra data when uncompressed. Removing the checks makes it seem to parse correctly, so I may just do that. I do want to know what TF2 is actually doing so I can parse fully correctly...