qpress / qz1 extension

This is a quick note to my future self. As we're using qpress less in favor of lz4 that has been available on Ubuntu Focal and above, we're inclined to forget what the .qz1 extension means.

Wondering what files with the .qz1 extension do?

This concerns single stream qpress compressed files.

Historically qpress uses the .qp extension, but that concerns multifile archives. The qpress binary can write compressed streams to stdout, but it will not decompress them to stdout. When using streams of data, we often prefer not touching the disk in between. For that reason there are also qlzip1 and qlzcat1.

What does the 1 in .qz1 mean?

The qpress source also has other levels (2 and 3). They need to be set at compile time, so switching at will is not possible. More importantly, qlzip1 does not write a header that specifies which level we're dealing with. Trying to decompress a level 3 stream with a level 1 binary would fail.

Where are qpress, qlzip1 and qlzcat1?

Originally, the source code and a summary could be found at https://www.quicklz.com/. Today however, this page is suspended.

The applications one might use can be found at GitHub/ossobv/qpress-deb. See the Releases page for sources and precompiled binaries.