more refractoring, adding makefile for tests

Makefile

@@ -0,0 +1,8 @@
+test:
+	go test .
+
+dkim-proxy:
+	cd _examples && go get . && go build .
+
+testsum:
+	gotestsum --format testname

error.go

@@ -0,0 +1,22 @@
+package smtpd
+
+import (
+  "errors"
+  "fmt"
+)
+// Error represents an Error reported in the SMTP session.
+type Error struct {
+	Code    int    // The integer error code
+	Message string // The error message
+}
+
+// Error returns a string representation of the SMTP error
+func (e Error) Error() string { 
+  return fmt.Sprintf("%d %s", e.Code, e.Message) 
+}
+
+// ErrServerClosed is returned by the Server's Serve and ListenAndServe,
+// methods after a call to Shutdown.
+var ErrServerClosed = errors.New("smtp: Server closed")
+
+

session.go

@@ -160,4 +160,3 @@ func (session *session) close() {
 	session.conn.Close()
 }
 
-

smtpd.go

@@ -83,19 +83,6 @@ type Peer struct {
 	TLS        *tls.ConnectionState // TLS Connection details, if on TLS
 }
 
-// Error represents an Error reported in the SMTP session.
-type Error struct {
-	Code    int    // The integer error code
-	Message string // The error message
-}
-
-// Error returns a string representation of the SMTP error
-func (e Error) Error() string { return fmt.Sprintf("%d %s", e.Code, e.Message) }
-
-// ErrServerClosed is returned by the Server's Serve and ListenAndServe,
-// methods after a call to Shutdown.
-var ErrServerClosed = errors.New("smtp: Server closed")
-
 func (srv *Server) newSession(c net.Conn) (s *session) {
 
 	s = &session{