python-zstandard produces incomplete data after decompress

I originally filed this against urllib3 in https://github.com/urllib3/urllib3/issues/3008 but the investigation so far is showing that urllib3 is providing the correct data to python-zstandard.

Environment info

OS Windows-10-10.0.22621-SP0
Python 3.10.11
urllib3 2.0.1

pip freeze results:

appdirs==1.4.4
certifi==2022.9.24
charset-normalizer==2.1.1
colorama==0.4.6
flake8==5.0.4
idna==3.4
mccabe==0.7.0
numpy==1.23.4
pycodestyle==2.9.1
pydiffx==1.1
pyflakes==2.5.0
python-gitlab==3.12.0
RBTools==4.0
requests==2.28.1
requests-toolbelt==0.10.1
six==1.16.0
texttable==1.6.7
tqdm==4.64.1
typing_extensions==4.4.0
urllib3==2.0.1
zstandard==0.21.0

Sample code

Example source data to decompress

I have attached a zip of text.txt.zstd because GitHub doesn't support attaching .zstd files. This file text.txt.zstd contains the raw data passed to ZstdDecoder.decompress(). Extract that text.txt.zstd file out of the zip then run:

import zstandard as zstd

print('Using zstandard backend: %s' % zstd.backend)

with open(r'C:\utils\temp\text.txt.zstd', 'rb') as f:
    data = f.read()

print('decompressed %d into %d bytes' %
      (len(data), len(zstd.decompress(data))))

My output is:

Using zstandard backend: cext
decompressed 2554 into 1048576 bytes

Whereas downloading zstd 1.5.5 and running zstd.exe text.txt.zstd -d -o hi.txt produces 8724469 bytes and a valid text file.

Inizia estraendo il file allegato text.txt.zstd ed eseguendo l’esempio Python zstandard fornito, quindi confrontalo con l’output da riga di comando di zstd 1.5.5. Traccia il motivo per cui zstd.decompress(data) si arresta a 1,048,576 byte nonostante il risultato valido di 8,724,469 byte restituito da zstd.exe; il lavoro è completato quando il binding Python restituisce i dati decompressi completi.