Thanks for the answer. The problem with Zippy is that it doesn't support gzips with multiple members ie. multiple concatenated gzips (which is according to the standard RFC 1952 still valid gzip and all unix tools normally support that).
The culprit in Zippy is <https://github.com/guzba/zippy/blob/master/src/zippy/gzip.nim#L64> where it's reading size and CRC from the end of the whole file. But this doesn't work if we concatenate a.gz with b.gz because then at the end of the file is size and CRC from b.gz but zippy tries to use it to verify a.gz. So the result is Error: unhandled exception: Checksum verification failed [ZippyError] Run
