Is a simple library to untar a tar.gz file from an io.Reader.
import "github.com/slimsag/untargz"
...
err := untargz.Extract(r, "destination/folder", nil)
...
This is really just a small subset of the code in https://github.com/mholt/archiver -- because it doesn't support providing an io.Reader (it requires an on-disk filename). As such, all credit for this goes to @mholt.