refactor(countrw): move to iout

iout/null_reader.go

@@ -0,0 +1,18 @@
+package iout
+
+import "io"
+
+type nullReader struct{}
+
+func NewNullReader() io.Reader {
+	return &nullReader{}
+}
+
+func (*nullReader) Read(p []byte) (n int, err error) {
+	for b := range p {
+		p[b] = 0
+	}
+	return len(p), nil
+}
+
+var _ io.Reader = (*nullReader)(nil)