Add tarball flow

[choffmeister]

Short description

In the same way that there already is a flow to generate a ZIP archive it would be nice to have the same for a simple (uncompressed) TAR ball.

Details

I already have some working code taken from one of my personal projects (see https://github.com/choffmeister/alpakka/tree/tarball-flow). The implementation is pretty straight forward. When one does not need compression (which still could be applied afterwards, like .tar -> .tar.gz), it has one big benefit over the ZIP archive stream:

It does not rely on the blocking Java Input/OutputStream API, but instead it directly uses akka.util.ByteString. So it seems to be way more efficient in terms of CPU usage (in some tests of mine I found 50% usage vs 3% CPU usage when comparing uncompressed ZIP stream vs my TAR stream).

Of course this should be integrated into the already existing Archive class. But before I invest more time to make the code fit nicely into the existing code base, I would like to know if such a feature would be merged.

[ennru]

Thank you for suggesting the work from akka/akka-stream-contrib#176 here instead.
I think this would fit nicely in Alpakka. Please go ahead.

[ennru]

Did you get to start on this? It would be great to get tar support in Alpakka.

[choffmeister]

@ennru Sorry, I did completely forgot about this. Took some time to rewrite my code to hopefully fit nicely next to Archive.zip() (see #2241)

[ennru]

Creating TAR archives is now supported with #2241.

Reading TAR archives would be great to have...