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package compression
import (
"context"
"io"
"github.com/containerd/containerd/content"
"github.com/containerd/containerd/images"
"github.com/klauspost/compress/zstd"
ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
)
func (c zstdType) Compress(ctx context.Context, comp Config) (compressorFunc Compressor, finalize Finalizer) {
return func(dest io.Writer, _ string) (io.WriteCloser, error) {
return zstdWriter(comp)(dest)
}, nil
}
func (c zstdType) Decompress(ctx context.Context, cs content.Store, desc ocispecs.Descriptor) (io.ReadCloser, error) {
return decompress(ctx, cs, desc)
}
func (c zstdType) NeedsConversion(ctx context.Context, cs content.Store, desc ocispecs.Descriptor) (bool, error) {
if !images.IsLayerType(desc.MediaType) {
return false, nil
}
ct, err := FromMediaType(desc.MediaType)
if err != nil {
return false, err
}
if ct == Zstd {
return false, nil
}
return true, nil
}
func (c zstdType) NeedsComputeDiffBySelf(comp Config) bool {
return true
}
func (c zstdType) OnlySupportOCITypes() bool {
return false
}
func (c zstdType) MediaType() string {
return ocispecs.MediaTypeImageLayerZstd
}
func (c zstdType) String() string {
return "zstd"
}
func zstdWriter(comp Config) func(io.Writer) (io.WriteCloser, error) {
return func(dest io.Writer) (io.WriteCloser, error) {
level := zstd.SpeedDefault
if comp.Level != nil {
level = toZstdEncoderLevel(*comp.Level)
}
return zstd.NewWriter(dest, zstd.WithEncoderLevel(level))
}
}
func toZstdEncoderLevel(level int) zstd.EncoderLevel {
// map zstd compression levels to go-zstd levels
// once we also have c based implementation move this to helper pkg
if level < 0 {
return zstd.SpeedDefault
} else if level < 3 {
return zstd.SpeedFastest
} else if level < 7 {
return zstd.SpeedDefault
} else if level < 9 {
return zstd.SpeedBetterCompression
}
return zstd.SpeedBestCompression
}
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