cache: Implement RangeOption #1825

lib/readers/limited.go

@@ -0,0 +1,22 @@
+package readers
+
+import "io"
+
+// LimitedReadCloser adds io.Closer to io.LimitedReader.  Create one with NewLimitedReadCloser
+type LimitedReadCloser struct {
+	*io.LimitedReader
+	io.Closer
+}
+
+// NewLimitedReadCloser returns a LimitedReadCloser wrapping rc to
+// limit it to reading limit bytes. If limit == 0 then it does not
+// wrap rc, it just returns it.
+func NewLimitedReadCloser(rc io.ReadCloser, limit int64) (lrc io.ReadCloser) {
+	if limit == 0 {
+		return rc
+	}
+	return &LimitedReadCloser{
+		LimitedReader: &io.LimitedReader{R: rc, N: limit},
+		Closer:        rc,
+	}
+}