move implementation to internal/ directory (#828)

internal/util/bytecounter/bytecounter_readcloser.go

@@ -0,0 +1,42 @@
+package bytecounter
+
+import (
+	"io"
+	"sync/atomic"
+)
+
+// ReadCloser wraps an io.ReadCloser, reimplementing
+// its interface and counting the bytes written to during copying.
+type ReadCloser interface {
+	io.ReadCloser
+	Count() uint64
+}
+
+// NewReadCloser wraps rc.
+func NewReadCloser(rc io.ReadCloser) ReadCloser {
+	return &readCloser{rc, 0}
+}
+
+type readCloser struct {
+	rc    io.ReadCloser
+	count uint64
+}
+
+func (r *readCloser) Count() uint64 {
+	return atomic.LoadUint64(&r.count)
+}
+
+var _ io.ReadCloser = &readCloser{}
+
+func (r *readCloser) Close() error {
+	return r.rc.Close()
+}
+
+func (r *readCloser) Read(p []byte) (int, error) {
+	n, err := r.rc.Read(p)
+	if n < 0 {
+		panic("expecting n >= 0")
+	}
+	atomic.AddUint64(&r.count, uint64(n))
+	return n, err
+}