docker import - no longer understands tgz format

[stevenschlansker]

Part of our "from scratch" build flow includes building an Ubuntu image from scratch (via debootstrap) and then importing it:
tar -cz -C $DEBOOTSTRAP_DIR . | docker import -

This worked fine in Docker 1.8.3, but seems to now fail on both 1.10.0 and 1.10.1:

[steven@Anesthetize:~/ot-code]% tar -cz -C test-dir . | docker import -
Error response from daemon: ApplyLayer exit status 1 stdout:  stderr: archive/tar: invalid tar header
[steven@Anesthetize:~/ot-code]% tar -c -C test-dir . | docker import - 
sha256:246a98fa9b25b3e21b08c436afd137ad5c8731dee0e535424bafc834ae9a7362
[steven@Anesthetize:~/ot-code]% tar -c -C test-dir -f test.tgz . && docker import test.tgz
sha256:567c4b5809f777f20464ead76864734a5ad45738e3d281f695b9f30cdf5a6f2f

So you can stream a tar just fine, or import a tgz file, but not stream a tgz.
I believe this is a regression, although I don't know exactly which intermediate version broke it.

[thaJeztah]

Looks like a duplicate of #20296, which is fixed by #20367

[stevenschlansker]

Cool, sorry for the dupe -- it's really hard to sort through all the bugs, after spending 20 minutes looking at the open ones I couldn't go through all the closed ones too :)

Reading through the diff, it looks like it now unconditionally decompresses things -- but i don't know the code well and assume you guys know what you are doing :)

Thanks!