generateinsertlayer: ensure that we close the tarwriter

[mikemccracken]

This fixes #436.

I added a test that shows the issue - the commit with the fix has the full explanation, repeated here:

generatelayer closes the tarwriter, but generateinsertlayer forgets to.

Closing the tarwriter writes the required footer of 1k of zeros.

This results in tar files that are complete but invalid, and different reading tools will behave differently:

• bsdtar doesn't complain and exits 0
• gnu tar (and security scanning tools that use it) will exit 2 with an unexpected EOF message
• python's tarfile library will raise an Unexpected EOF error
• golang's archive/tar library can raise an unexpected EOF error, but for some files created by generateinsertlayer, it just raises a plain EOF error, which means golang based tools generally ignore this and work fine, this includes umoci.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (909d140) 73.44% compared to head (7bb2940) 73.34%.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

[](https://app.codecov.io/gh/opencontainers/umoci/pull/534?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencontainers) ```diff @@ Coverage Diff @@ ## main #534 +/- ## ========================================== - Coverage 73.44% 73.34% -0.11% ========================================== Files 60 60 Lines 4891 4895 +4 ========================================== - Hits 3592 3590 -2 - Misses 940 944 +4 - Partials 359 361 +2 ``` | [Files](https://app.codecov.io/gh/opencontainers/umoci/pull/534?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencontainers) | Coverage Δ | | |---|---|---| | [oci/layer/generate.go](https://app.codecov.io/gh/opencontainers/umoci/pull/534?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencontainers#diff-b2NpL2xheWVyL2dlbmVyYXRlLmdv) | `64.48% <70.00%> (-1.54%)` | :arrow_down: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/opencontainers/umoci/pull/534/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencontainers)

[tych0]

Everything looks good to me, except you have,

(cherry picked from commit 3f53b10037f03d01412b5b0eb9e50a0053b7a156)

in your commit message, which is a mystery hash?

[tych0]

I just cleaned it up, will merge once that all passes CI

[mikemccracken]

Everything looks good to me, except you have,

(cherry picked from commit 3f53b10037f03d01412b5b0eb9e50a0053b7a156)

in your commit message, which is a mystery hash?

d'oh- thanks for taking care of this, that hash was a commit on top of the stacker fork of umoci, I should've cleaned up the message.

Thanks for the quick review guys!