tar is closed before gzip writer

[michalmiddleton]

Describe the bug
Hi, while poking around and testing zstd compression instead of gzip, I think I discovered a logical error in the code.
It's quite possible this issue never surfaced when using gzip.

Issue:
When closing file, tar and gzip writers, tar writer gets closed before gzip writer:

docker-volume-backup/cmd/backup/archive.go

Line 75 in 1e36bd3

err = gzipWriter.Close()

Imo, the order of closing should be gzip -> tar -> file.

I noticed it when troubleshooting one zst archive that had a corrupted block at the end.

[m90]

I'm not entirely sure about your reasoning. For how I understand it, the tarWriter would need to be closed first, else the code would risk that the tarWriter tries to write to the already closed gzipWriter.

Or, to spell it out: tarWriter writes to gzipWriter writes to file, which means they will be closed in that exact order.

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I also tried applying your suggestion here: 82456e3 but this makes all tests fail with the following error at runtime:

error creating archive: compress: error closing tar writer: flate: closed writer

Maybe the issue you ran into when trying to use zstd was caused by something else?