137 lines
3.4 KiB
Go
137 lines
3.4 KiB
Go
package compression
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import (
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"bytes"
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"context"
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"io"
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"github.com/containerd/containerd/content"
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"github.com/containerd/containerd/images"
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digest "github.com/opencontainers/go-digest"
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ocispec "github.com/opencontainers/image-spec/specs-go/v1"
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"github.com/pkg/errors"
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"github.com/sirupsen/logrus"
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)
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// Type represents compression type for blob data.
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type Type int
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const (
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// Uncompressed indicates no compression.
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Uncompressed Type = iota
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// Gzip is used for blob data.
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Gzip
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// UnknownCompression means not supported yet.
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UnknownCompression Type = -1
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)
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var Default = Gzip
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func (ct Type) String() string {
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switch ct {
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case Uncompressed:
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return "uncompressed"
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case Gzip:
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return "gzip"
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default:
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return "unknown"
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}
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}
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// DetectLayerMediaType returns media type from existing blob data.
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func DetectLayerMediaType(ctx context.Context, cs content.Store, id digest.Digest, oci bool) (string, error) {
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ra, err := cs.ReaderAt(ctx, ocispec.Descriptor{Digest: id})
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if err != nil {
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return "", err
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}
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defer ra.Close()
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ct, err := detectCompressionType(content.NewReader(ra))
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if err != nil {
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return "", err
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}
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switch ct {
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case Uncompressed:
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if oci {
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return ocispec.MediaTypeImageLayer, nil
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}
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return images.MediaTypeDockerSchema2Layer, nil
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case Gzip:
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if oci {
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return ocispec.MediaTypeImageLayerGzip, nil
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}
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return images.MediaTypeDockerSchema2LayerGzip, nil
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default:
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return "", errors.Errorf("failed to detect layer %v compression type", id)
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}
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}
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// detectCompressionType detects compression type from real blob data.
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func detectCompressionType(cr io.Reader) (Type, error) {
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var buf [10]byte
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var n int
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var err error
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if n, err = cr.Read(buf[:]); err != nil && err != io.EOF {
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// Note: we'll ignore any io.EOF error because there are some
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// odd cases where the layer.tar file will be empty (zero bytes)
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// and we'll just treat it as a non-compressed stream and that
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// means just create an empty layer.
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//
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// See issue docker/docker#18170
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return UnknownCompression, err
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}
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for c, m := range map[Type][]byte{
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Gzip: {0x1F, 0x8B, 0x08},
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} {
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if n < len(m) {
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continue
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}
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if bytes.Equal(m, buf[:len(m)]) {
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return c, nil
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}
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}
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return Uncompressed, nil
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}
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var toDockerLayerType = map[string]string{
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ocispec.MediaTypeImageLayer: images.MediaTypeDockerSchema2Layer,
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images.MediaTypeDockerSchema2Layer: images.MediaTypeDockerSchema2Layer,
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ocispec.MediaTypeImageLayerGzip: images.MediaTypeDockerSchema2LayerGzip,
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images.MediaTypeDockerSchema2LayerGzip: images.MediaTypeDockerSchema2LayerGzip,
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}
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var toOCILayerType = map[string]string{
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ocispec.MediaTypeImageLayer: ocispec.MediaTypeImageLayer,
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images.MediaTypeDockerSchema2Layer: ocispec.MediaTypeImageLayer,
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ocispec.MediaTypeImageLayerGzip: ocispec.MediaTypeImageLayerGzip,
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images.MediaTypeDockerSchema2LayerGzip: ocispec.MediaTypeImageLayerGzip,
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}
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func convertLayerMediaType(mediaType string, oci bool) string {
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var converted string
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if oci {
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converted = toOCILayerType[mediaType]
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} else {
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converted = toDockerLayerType[mediaType]
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}
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if converted == "" {
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logrus.Warnf("unhandled conversion for mediatype %q", mediaType)
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return mediaType
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}
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return converted
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}
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func ConvertAllLayerMediaTypes(oci bool, descs ...ocispec.Descriptor) []ocispec.Descriptor {
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var converted []ocispec.Descriptor
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for _, desc := range descs {
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desc.MediaType = convertLayerMediaType(desc.MediaType, oci)
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converted = append(converted, desc)
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}
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return converted
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}
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