Adding upstream version 3.5.1.

Signed-off-by: Daniel Baumann <daniel@debian.org>

gz.go

@@ -0,0 +1,76 @@
+package archiver
+
+import (
+	"fmt"
+	"io"
+	"path/filepath"
+
+	"github.com/klauspost/compress/gzip"
+	"github.com/klauspost/pgzip"
+)
+
+// Gz facilitates gzip compression.
+type Gz struct {
+	CompressionLevel int
+	SingleThreaded   bool
+}
+
+// Compress reads in, compresses it, and writes it to out.
+func (gz *Gz) Compress(in io.Reader, out io.Writer) error {
+	var w io.WriteCloser
+	var err error
+	if gz.SingleThreaded {
+		w, err = gzip.NewWriterLevel(out, gz.CompressionLevel)
+	} else {
+		w, err = pgzip.NewWriterLevel(out, gz.CompressionLevel)
+	}
+	if err != nil {
+		return err
+	}
+	defer w.Close()
+	_, err = io.Copy(w, in)
+	return err
+}
+
+// Decompress reads in, decompresses it, and writes it to out.
+func (gz *Gz) Decompress(in io.Reader, out io.Writer) error {
+	var r io.ReadCloser
+	var err error
+	if gz.SingleThreaded {
+		r, err = gzip.NewReader(in)
+	} else {
+		r, err = pgzip.NewReader(in)
+	}
+	if err != nil {
+		return err
+	}
+	defer r.Close()
+	_, err = io.Copy(out, r)
+	return err
+}
+
+// CheckExt ensures the file extension matches the format.
+func (gz *Gz) CheckExt(filename string) error {
+	if filepath.Ext(filename) != ".gz" {
+		return fmt.Errorf("filename must have a .gz extension")
+	}
+	return nil
+}
+
+func (gz *Gz) String() string { return "gz" }
+
+// NewGz returns a new, default instance ready to be customized and used.
+func NewGz() *Gz {
+	return &Gz{
+		CompressionLevel: gzip.DefaultCompression,
+	}
+}
+
+// Compile-time checks to ensure type implements desired interfaces.
+var (
+	_ = Compressor(new(Gz))
+	_ = Decompressor(new(Gz))
+)
+
+// DefaultGz is a default instance that is conveniently ready to use.
+var DefaultGz = NewGz()