Solved rot13 exercise

exercises/07-rot13/go.go

@@ -11,13 +11,21 @@ type rot13Reader struct {
 }
 
 func (r rot13Reader) Read(p []byte) (n int, err error) {
-    if len(p) == 0 {
-        return 0, nil
+	n, err = r.r.Read(p)
+	for i := range p[:n] {
+		p[i] = rot13(p[i])
+	}
+	return
+}
+
+func rot13(b byte) byte {
+	var a, z, A, Z byte = 'a', 'z', 'A', 'Z'
+    if a < b && b < z {
+        b = a + ((b - a + 13) % 26)
+    } else if A < b && b < Z {
+        b = A + ((b - A + 13) % 26)
     }
-    if r.i >= len(r.s) {
-        return 0, io.EOF
-    }
-    return
+	return b
 }
 
 func main() {