ADD should behave consistently with relative paths and URIs for extracting tarballs

[xenoterracide]

Docker version 1.8.1, build d12ea79
Containers: 27
Images: 153
Storage Driver: devicemapper
 Pool Name: docker-254:0-6957350-pool
 Pool Blocksize: 65.54 kB
 Backing Filesystem: extfs
 Data file: /dev/loop0
 Metadata file: /dev/loop1
 Data Space Used: 5.43 GB
 Data Space Total: 107.4 GB
 Data Space Available: 63.38 GB
 Metadata Space Used: 8.86 MB
 Metadata Space Total: 2.147 GB
 Metadata Space Available: 2.139 GB
 Udev Sync Supported: true
 Deferred Removal Enabled: false
 Data loop file: /var/lib/docker/devicemapper/devicemapper/data
 Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
 Library Version: 1.02.102 (2015-07-07)
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 4.1.6-1-ARCH
Operating System: Arch Linux
CPUs: 4
Total Memory: 7.509 GiB
Name: slave-vi
ID: QOZQ:A2YV:Z5RG:PWMW:3OYD:TF4V:FSLU:QXLC:YZN6:PPK6:AR43:6OY4
Linux slave-vi 4.1.6-1-ARCH #1 SMP PREEMPT Mon Aug 17 08:52:28 CEST 2015 x86_64 GNU/Linux

fetch file before running dockerfile
wget https://cpan.metacpan.org/authors/id/X/XE/XENO/Pod-Spell-1.17.tar.gz

FROM busybox:latest
MAINTAINER Caleb Cushing <xenoterracide@gmail.com>
WORKDIR /tmp

ENV MIRROR https://cpan.metacpan.org/authors/id/X/XE/XENO/
ENV FILENAME Pod-Spell-1.17.tar.gz

ADD $FILENAME local/
RUN ls -1 local

ADD $MIRROR/$FILENAME remote/
RUN ls -1 remote

IMHO, the 2 ls's should print the same thing, however the second does not extract a tarball.

ADD foo.tar.gz, ADD http://...bz2, ADD ftp://...tar.xz , etc, should act consistently, meaning adding from a remote should extract the tarball.

[duglin]

ahh its like pouring salt on a wound :-)

[phemmer]

see #14934 & #11174

[LK4D4]

This indeed would be breaking change. We have couple of unfortunate design decisions in dockerfile handling and it's sad that we can't fix them now because some people use them as features.