estargz: support lossless compression #453
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AkihiroSuda
reviewed
Sep 9, 2021
estargz/testutil.go
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| sw := NewWriterWithCompressor(wantBuf, cl) | ||
| sw.ChunkSize = tt.chunkSize | ||
| if err := sw.AppendTar(tarBlob); err != nil { | ||
| t.Fatalf("faield to append tar to want stargz: %v", err) |
AkihiroSuda
approved these changes
Sep 9, 2021
Signed-off-by: Kohei Tokunaga <[email protected]>
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moby/buildkit#2352
Currently, eStargz writer (
estargz.Writer) rewrites tar headers of the original tar so it's not possible to recover the original tar blob from the result eStargz. This lossy behaviour can be problematic when the client needs to convert tar to eStargz and then recover the original tar from the result eStargz.For solving this issue, this commit adds
AppendTarLossLessAPI toestargz.Writer. This allows creating eStargz without changing the original tar blob.estargz.UnpackAPI enables to decompress the eStargz and get the original tar blob.Note that this losslessness implies a limitation that the writer cannot support compressing a tar that contains a file named
stargz.index.jsonbecause estargz cannot be created without overwriting that file. When the caller appends an eStargz blob to the writer, it should be decompressed to a tar usingestargz.UnpackAPI.cc @tonistiigi
Thank you for the discussion.