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Fix estargz compression loses the original tar metadata #2352

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merged 1 commit into from
Sep 24, 2021
Merged

Fix estargz compression loses the original tar metadata #2352

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8 changes: 4 additions & 4 deletions cache/blobs.go
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@ func computeBlobChain(ctx context.Context, sr *immutableRef, createIfNeeded bool
case compression.Gzip:
mediaType = ocispecs.MediaTypeImageLayerGzip
case compression.EStargz:
compressorFunc, finalize = writeEStargz()
compressorFunc, finalize = compressEStargz()
mediaType = ocispecs.MediaTypeImageLayerGzip
case compression.Zstd:
compressorFunc = zstdWriter
Expand Down Expand Up @@ -314,7 +314,7 @@ func ensureCompression(ctx context.Context, ref *immutableRef, compressionType c
}

// Resolve converters
layerConvertFunc, err := getConverter(desc, compressionType)
layerConvertFunc, err := getConverter(ctx, ref.cm.ContentStore, desc, compressionType)
if err != nil {
return nil, err
} else if layerConvertFunc == nil {
Expand Down Expand Up @@ -343,12 +343,12 @@ func ensureCompression(ctx context.Context, ref *immutableRef, compressionType c
}
newDesc, err := layerConvertFunc(ctx, ref.cm.ContentStore, desc)
if err != nil {
return nil, err
return nil, errors.Wrapf(err, "failed to convert")
}

// Start to track converted layer
if err := ref.addCompressionBlob(ctx, *newDesc, compressionType); err != nil {
return nil, err
return nil, errors.Wrapf(err, "failed to add compression blob")
}
return nil, nil
})
Expand Down
96 changes: 68 additions & 28 deletions cache/converter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,30 +13,40 @@ import (
"github.com/containerd/containerd/images/converter"
"github.com/containerd/containerd/labels"
"github.com/klauspost/compress/zstd"
"github.com/moby/buildkit/identity"
"github.com/moby/buildkit/util/compression"
digest "github.com/opencontainers/go-digest"
ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)

// needsConversion indicates whether a conversion is needed for the specified mediatype to
// needsConversion indicates whether a conversion is needed for the specified descriptor to
// be the compressionType.
func needsConversion(mediaType string, compressionType compression.Type) (bool, error) {
func needsConversion(ctx context.Context, cs content.Store, desc ocispecs.Descriptor, compressionType compression.Type) (bool, error) {
mediaType := desc.MediaType
switch compressionType {
case compression.Uncompressed:
if !images.IsLayerType(mediaType) || compression.FromMediaType(mediaType) == compression.Uncompressed {
return false, nil
}
case compression.Gzip:
if !images.IsLayerType(mediaType) || compression.FromMediaType(mediaType) == compression.Gzip {
esgz, err := isEStargz(ctx, cs, desc.Digest)
if err != nil {
return false, err
}
if (!images.IsLayerType(mediaType) || compression.FromMediaType(mediaType) == compression.Gzip) && !esgz {
return false, nil
}
case compression.Zstd:
if !images.IsLayerType(mediaType) || compression.FromMediaType(mediaType) == compression.Zstd {
return false, nil
}
case compression.EStargz:
if !images.IsLayerType(mediaType) {
esgz, err := isEStargz(ctx, cs, desc.Digest)
if err != nil {
return false, err
}
if !images.IsLayerType(mediaType) || esgz {
return false, nil
}
default:
Expand All @@ -47,9 +57,9 @@ func needsConversion(mediaType string, compressionType compression.Type) (bool,

// getConverter returns converter function according to the specified compression type.
// If no conversion is needed, this returns nil without error.
func getConverter(desc ocispecs.Descriptor, compressionType compression.Type) (converter.ConvertFunc, error) {
if needs, err := needsConversion(desc.MediaType, compressionType); err != nil {
return nil, err
func getConverter(ctx context.Context, cs content.Store, desc ocispecs.Descriptor, compressionType compression.Type) (converter.ConvertFunc, error) {
if needs, err := needsConversion(ctx, cs, desc, compressionType); err != nil {
return nil, errors.Wrapf(err, "failed to determine conversion needs")
} else if !needs {
// No conversion. No need to return an error here.
return nil, nil
Expand All @@ -61,7 +71,27 @@ func getConverter(desc ocispecs.Descriptor, compressionType compression.Type) (c
switch from {
case compression.Uncompressed:
case compression.Gzip, compression.Zstd:
c.decompress = cdcompression.DecompressStream
c.decompress = func(ctx context.Context, desc ocispecs.Descriptor) (r io.ReadCloser, err error) {
ra, err := cs.ReaderAt(ctx, desc)
if err != nil {
return nil, err
}
esgz, err := isEStargz(ctx, cs, desc.Digest)
if err != nil {
return nil, err
} else if esgz {
r, err = decompressEStargz(io.NewSectionReader(ra, 0, ra.Size()))
if err != nil {
return nil, err
}
} else {
r, err = cdcompression.DecompressStream(io.NewSectionReader(ra, 0, ra.Size()))
if err != nil {
return nil, err
}
}
return &readCloser{r, ra.Close}, nil
}
default:
return nil, errors.Errorf("unsupported source compression type %q from mediatype %q", from, desc.MediaType)
}
Expand All @@ -77,7 +107,7 @@ func getConverter(desc ocispecs.Descriptor, compressionType compression.Type) (c
return zstd.NewWriter(w)
}
case compression.EStargz:
compressorFunc, finalize := writeEStargz()
compressorFunc, finalize := compressEStargz()
c.compress = func(w io.Writer) (io.WriteCloser, error) {
return compressorFunc(w, ocispecs.MediaTypeImageLayerGzip)
}
Expand All @@ -91,27 +121,15 @@ func getConverter(desc ocispecs.Descriptor, compressionType compression.Type) (c

type conversion struct {
target compression.Type
decompress func(io.Reader) (cdcompression.DecompressReadCloser, error)
decompress func(context.Context, ocispecs.Descriptor) (io.ReadCloser, error)
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change it to ReaderAt or ReadSeeker instead. We should be able to define conversions for all supported compressions as a single array and then unit test them with random (tarball) data making sure that compression is lossless.

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was there an issue with this?

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change it to ReaderAt or ReadSeeker instead.

IIUC cdcompression.DecompressReadCloser is not seekable. So if we want to make it seekable we need to change the current decompress implementation to store the decompressed blob to somewhere seekable (e.g. content store) then return the readseeker. Does this change SGTY?

compress func(w io.Writer) (io.WriteCloser, error)
finalize func(context.Context, content.Store) (map[string]string, error)
}

func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispecs.Descriptor) (*ocispecs.Descriptor, error) {
// prepare the source and destination
info, err := cs.Info(ctx, desc.Digest)
if err != nil {
return nil, err
}
labelz := info.Labels
if labelz == nil {
labelz = make(map[string]string)
}
ra, err := cs.ReaderAt(ctx, desc)
if err != nil {
return nil, err
}
defer ra.Close()
ref := fmt.Sprintf("convert-from-%s-to-%s", desc.Digest, c.target.String())
labelz := make(map[string]string)
ref := fmt.Sprintf("convert-from-%s-to-%s-%s", desc.Digest, c.target.String(), identity.NewID())
w, err := cs.Writer(ctx, content.WithRef(ref))
if err != nil {
return nil, err
Expand All @@ -133,9 +151,16 @@ func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispec

// convert this layer
diffID := digest.Canonical.Digester()
var rdr io.Reader = io.NewSectionReader(ra, 0, ra.Size())
if c.decompress != nil {
rc, err := c.decompress(rdr)
var rdr io.Reader
if c.decompress == nil {
ra, err := cs.ReaderAt(ctx, desc)
if err != nil {
return nil, err
}
defer ra.Close()
rdr = io.NewSectionReader(ra, 0, ra.Size())
} else {
rc, err := c.decompress(ctx, desc)
if err != nil {
return nil, err
}
Expand All @@ -157,7 +182,7 @@ func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispec
if err := w.Close(); err != nil {
return nil, err
}
info, err = cs.Info(ctx, w.Digest())
info, err := cs.Info(ctx, w.Digest())
if err != nil {
return nil, err
}
Expand All @@ -166,6 +191,7 @@ func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispec
newDesc.MediaType = c.target.DefaultMediaType()
newDesc.Digest = info.Digest
newDesc.Size = info.Size
newDesc.Annotations = nil
if c.finalize != nil {
a, err := c.finalize(ctx, cs)
if err != nil {
Expand All @@ -180,3 +206,17 @@ func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispec
}
return &newDesc, nil
}

type readCloser struct {
io.ReadCloser
closeFunc func() error
}

func (rc *readCloser) Close() error {
err1 := rc.ReadCloser.Close()
err2 := rc.closeFunc()
if err1 != nil {
return errors.Wrapf(err1, "failed to close: %v", err2)
}
return err2
}