chunked: use a limitWriter instead of LimitReader

so we can use the WriteTo interface offered by the zstd library.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/chunked/storage_linux.go

@@ -785,20 +785,43 @@ func (c *chunkedDiffer) prepareCompressedStreamToFile(compression compressedFile
 	return nil
 }
 
+func limitWriter(r io.Writer, n int64) io.Writer { return &LimitedWriter{r, n} }
+
+type LimitedWriter struct {
+	W io.Writer // underlying writer
+	N int64  // max bytes remaining
+}
+
+func (l *LimitedWriter) Write(p []byte) (n int, err error) {
+	if l.N <= 0 {
+		return len(p), nil
+	}
+	pp := p
+	if int64(len(p)) > l.N {
+		pp = p[0:l.N]
+	}
+	n, err = l.W.Write(pp)
+	l.N -= int64(n)
+	if l.N == 0 {
+		return len(p), nil
+	}
+	return
+}
+
 func (c *chunkedDiffer) appendCompressedStreamToFile(compression compressedFileType, destFile *destinationFile, reader io.Reader, size int64) (err error) {
+	l := limitWriter(destFile.to, size)
 	switch compression {
 	case fileTypeZstdChunked:
 		defer c.zstdReader.Reset(nil)
-		if _, err := io.CopyBuffer(destFile.to, io.LimitReader(c.zstdReader, size), c.copyBuffer); err != nil {
-			return err
-		}
+
+		_, err := c.zstdReader.WriteTo(l)
+		return err
 	case fileTypeEstargz:
-		if _, err := io.CopyBuffer(destFile.to, io.LimitReader(c.gzipReader, size), c.copyBuffer); err != nil {
-			return err
-		}
 		defer c.gzipReader.Close()
+		_, err := c.gzipReader.WriteTo(l)
+		return err
 	case fileTypeNoCompression:
-		_, err := io.CopyBuffer(destFile.to, io.LimitReader(reader, size), c.copyBuffer)
+		_, err := io.CopyBuffer(l, reader, c.copyBuffer)
 		if err != nil {
 			return err
 		}