ttar cannot remove existing directory

[knweiss]

I've created a small ttar testcase for a problem I ran into while working on this PR: prometheus/node_exporter#871:

#!/bin/sh
echo "*** Create 1st archive"
mkdir -p ttar_testcase/sys/bus/cpu/devices/cpu0
ttar -C ttar_testcase/ -c -f ttar_testcase/sys1.ttar sys
echo

echo "*** Create 2nd archive"
rmdir ttar_testcase/sys/bus/cpu/devices/cpu0
mkdir -p ttar_testcase/sys/devices/system/cpu/cpu0
pushd ttar_testcase/sys/bus/cpu/devices/
ln -s ../../../devices/system/cpu/cpu0 .
popd
ttar -C ttar_testcase/ -c -f ttar_testcase/sys2.ttar sys
echo

echo "*** Remove directory"
rm -rf ttar_testcase/sys/*

echo "*** Extract 1st archive"
ttar -C ttar_testcase/ -x -f ttar_testcase/sys1.ttar
echo

echo "*** Extract 2nd archive over first archive"
ttar -C ttar_testcase/ -x -f ttar_testcase/sys2.ttar
echo

echo "*** Extract 2nd archive over first archive - now with sh -x"
sh -x ttar -C ttar_testcase/ -x -f ttar_testcase/sys2.ttar 2>&1 | tail -n 5

Let's run it:

$ sh ttar_testcase.sh
*** Create 1st archive
/home/knweiss/ttar_testcase

*** Create 2nd archive
/home/knweiss/ttar_testcase/sys/bus/cpu/devices
~/ttar_testcase/sys/bus/cpu/devices ~
~
/home/knweiss/ttar_testcase

*** Remove directory
*** Extract 1st archive
/home/knweiss/ttar_testcase

*** Extract 2nd archive over first archive
/home/knweiss/ttar_testcase
rm: cannot remove 'sys/bus/cpu/devices/cpu0': Is a directory

*** Extract 2nd archive over first archive - now with sh -x
+ [[ Path: sys/bus/cpu/devices/cpu0 =~ ^Path: (.*)$ ]]
+ path=sys/bus/cpu/devices/cpu0
+ '[' -e sys/bus/cpu/devices/cpu0 ']'
+ rm sys/bus/cpu/devices/cpu0
rm: cannot remove 'sys/bus/cpu/devices/cpu0': Is a directory

I.e. ttar is unable to remove an existing directory. The rm fails here:

   246          if [[ $line =~ ^Path:\ (.*)$ ]]; then
   247              path=${BASH_REMATCH[1]}
   248              if [ -e "$path" ] || [ -L "$path" ]; then
>  249                  rm "$path"
   250              fi

[ideaship]

@knweiss I refactored the code. It still passes the testcase you helpfully supplied. But it may no longer suit your needs, because it will fail if the directory is not empty. We may have to change the "rmdir" back to "rm -r" after all. I need to think about this.

[knweiss]

@ideaship I had the same worries regarding security implications yesterday after sending the pull request.

Unfortunately, it now really no longer suits my needs in node-exporter as the directory is not empty in this case.

[ideaship]

@knweiss GNU tar does the same thing as ttar. It removes empty directories, but aborts with "Cannot open: File exists" if a directory is not empty. I do not want ttar to deviate from user expectations in a potentially dangerous way.

While not the default, GNU tar does have an option "--recursive-unlink" which does what you are looking for. Would such an option work for you?

[knweiss]

@ideaship I think we can leave it as-is (rmdir) because clearing the directory tree before extraction is the better solution anyway.

[ideaship]

Okay. I am closing the issue then.