Image encryption/decryption support in skopeo

Signed-off-by: Harshal Patil <harshal.patil@in.ibm.com>
Signed-off-by: Brandon Lum <lumjjb@gmail.com>

vendor/github.com/klauspost/compress/zstd/encoder_options.go

@@ -1,6 +1,7 @@
 package zstd
 
 import (
+	"errors"
 	"fmt"
 	"runtime"
 	"strings"
@@ -18,6 +19,7 @@ type encoderOptions struct {
 	blockSize  int
 	windowSize int
 	level      EncoderLevel
+	fullZero   bool
 }
 
 func (o *encoderOptions) setDefault() {
@@ -63,6 +65,30 @@ func WithEncoderConcurrency(n int) EOption {
 	}
 }
 
+// WithWindowSize will set the maximum allowed back-reference distance.
+// The value must be a power of two between WindowSizeMin and WindowSizeMax.
+// A larger value will enable better compression but allocate more memory and,
+// for above-default values, take considerably longer.
+// The default value is determined by the compression level.
+func WithWindowSize(n int) EOption {
+	return func(o *encoderOptions) error {
+		switch {
+		case n < MinWindowSize:
+			return fmt.Errorf("window size must be at least %d", MinWindowSize)
+		case n > MaxWindowSize:
+			return fmt.Errorf("window size must be at most %d", MaxWindowSize)
+		case (n & (n - 1)) != 0:
+			return errors.New("window size must be a power of 2")
+		}
+
+		o.windowSize = n
+		if o.blockSize > o.windowSize {
+			o.blockSize = o.windowSize
+		}
+		return nil
+	}
+}
+
 // WithEncoderPadding will add padding to all output so the size will be a multiple of n.
 // This can be used to obfuscate the exact output size or make blocks of a certain size.
 // The contents will be a skippable frame, so it will be invisible by the decoder.
@@ -166,6 +192,16 @@ func WithEncoderLevel(l EncoderLevel) EOption {
 	}
 }
 
+// WithZeroFrames will encode 0 length input as full frames.
+// This can be needed for compatibility with zstandard usage,
+// but is not needed for this package.
+func WithZeroFrames(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.fullZero = b
+		return nil
+	}
+}
+
 // WithSingleSegment will set the "single segment" flag when EncodeAll is used.
 // If this flag is set, data must be regenerated within a single continuous memory segment.
 // In this case, Window_Descriptor byte is skipped, but Frame_Content_Size is necessarily present.