I investigated this problem.

Here is the toggle conditions:

- The format is FORMAT_ALONE, this is the legacy .lzma container format.
- The file's header recorded "Uncompressed Size".
- The file doesn't have "End of Payload Marker" or "End of Stream Marker".

Otherwise, liblzma's internal state doesn't hold any bytes that can be output. 

Good news is:

- lzma module's default compressing format is FORMAT_XZ, not FORMAT_ALONE.
- Even FORMAT_ALONE files generated by lzma module (underlying xz library), always have "End of Payload Marker".
- Maybe FORMAT_ALONE format is being outdated in the world.

Attached file test_bad_files.py, test `DecompressReader.read(size=-1)` function [1] with different max_length values (from -1 to 1000, exclude 0), can ensure that the needs_input mechanism works properly.
Usage: modify `DIR` variable to bad files' folder.

[1] https://github.com/python/cpython/blob/v3.8.0b1/Lib/_compression.py#L72-L111