Add TarballFlow

[choffmeister]

In one of my personal projects I found the need to generate a simple tarball from a Source[(String, Long, Source[ByteString, _])]. I am not sure if there is enough demand for this to include it into this library here. This PR is at the moment just a simple copy paste - so no sophisticated testing.

If there is enough demand, I would be willing to improve the tests and do whatever else is needed to have it merged. So this is basically an offer with some preview code that - if wanted - would need some more work from my side.

I would love to hear feedback.

[ennru]

Hi @choffmeister,
Thank you for this suggestion to add this here! I think this would be nice to have in the Alpakka file connector which only recently got Zip support (yet unreleased).

[choffmeister]

@ennru Nice to hear. Just out of curiosity: In my project I tried ZIP archives first with the approach to use Java's ZipOutputStream in combination with akka's StreamConverters.asOutputStream. Even though I disabled compression I had massive CPU load when generating the ZIP archive. With my own Tarball implementation that does not use old Java IO streams the CPU load is minimal.

Anyway: Please let me know where I my PR needs to be improved to get to a mergeable state.

[seglo]

I second @ennru 's suggestion of contributing this to the Alpakka File connector (instead of akka-stream-contrib). I believe it would get more visibility and usage there.

[choffmeister]

Nice, didn't know that there is a File connector in alpakka. Yeah this might make more sense. Will close this and open a PR there.