zipfile.ZipFile fails to read zstd-compressed file consisting of multiple frames

Bug report

Bug description:

I have a ZIP file archive.zip that contains a file data.npy. This file is compressed with zstd, consisting of two zstd frames. When I try to read this in with zipfile, I get a BadZipFile: Bad CRC-32 for file 'data.npy' error.

import zipfile
with zipfile.ZipFile("archive.zip", "r") as z:
  with z.open("data.npy", "r") as f:
    data = f.read() # -> BadZipFile: Bad CRC-32 ...

The error is a red herring, though: When I disable CRC checking, there is no exception thrown, but the data read is in fact only the data from the first zstd frame. The second frame gets ignored completely (and thus the checksum is wrong).

import zipfile
with zipfile.ZipFile("archive.zip", "r") as z:
  with z.open("data.npy", "r") as f:
    f._update_crc = lambda newdata: None
    data = f.read() # -> result only contains data from first frame

As independent cross-check, I tested decompressing the file with both 7z and WinRAR without issues. So I don't think the file is somehow invalid. This is the file: archive.zip

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-154537

再現コードは添付されたアーカイブに対して zipfile.ZipFile.open と z.open を使用します。まず、CPython の zipfile 実装で 2 フレームの zstd ケースを再現してください。data.npy を読み取ると両方のフレームが返され、通常の CRC チェックが成功し、この動作をカバーする回帰テストがあることを完了条件とします。