>> Thanks for the debugging.  The stream comes from within a matlab 'mat'
>> file.  I maintain the scipy matlab file readers; the variables within
>> these files are zlib compressed streams.
>
> So this would be a Matlab issue, right?

Yes, except scipy and numpy aim in part to be an open-source
replacement for matlab, so we very much want to be able to read their
files.

>>  Is there (should there be) a safe and maintained way to allow me to
>> read a stream that does not return Z_STREAM_END?
>
> Decompressor objects allow you to do that, but I cannot tell you how
> "maintained" it is. If it has to be maintained, we could add an unit
> test for it so that regressions get detected. It would be nice if you
> could provide a very short zlib stream reproducing the issue

This is the only .mat file stream I have yet come across that causes
the error.  It is possible to knock a portion off the end of a valid
stream to reproduce the problem?