refactor: Start implementation of public API

internal/counters/read_write.go

@@ -0,0 +1,31 @@
+package counters
+
+import "io"
+
+type CounterReader struct {
+	Reader io.Reader
+
+	BytesRead int
+}
+
+func (r *CounterReader) Read(p []byte) (n int, err error) {
+	n, err = r.Reader.Read(p)
+
+	r.BytesRead += n
+
+	return n, err
+}
+
+type CounterWriter struct {
+	Writer io.Writer
+
+	BytesRead int
+}
+
+func (w *CounterWriter) Write(p []byte) (n int, err error) {
+	n, err = w.Writer.Write(p)
+
+	w.BytesRead += n
+
+	return n, err
+}