smtpSender.Send() now automatically redials in case of a timeout

smtp.go

@@ -110,7 +110,7 @@ func (d *Dialer) Dial() (SendCloser, error) {
 		}
 	}
 
-	return &smtpSender{c}, nil
+	return &smtpSender{c, d}, nil
 }
 
 func (d *Dialer) tlsConfig() *tls.Config {
@@ -138,10 +138,21 @@ func (d *Dialer) DialAndSend(m ...*Message) error {
 
 type smtpSender struct {
 	smtpClient
+	d *Dialer
 }
 
 func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 	if err := c.Mail(from); err != nil {
+		if err == io.EOF {
+			// This is probably due to a timeout, so reconnect and try again.
+			sc, derr := c.d.Dial()
+			if derr == nil {
+				if s, ok := sc.(*smtpSender); ok {
+					*c = *s
+					return c.Send(from, to, msg)
+				}
+			}
+		}
 		return err
 	}
 

smtp_test.go

@@ -115,12 +115,35 @@ func TestDialerNoAuth(t *testing.T) {
 	})
 }
 
+func TestDialerTimeout(t *testing.T) {
+	d := &Dialer{
+		Host: testHost,
+		Port: testPort,
+	}
+	testSendMailTimeout(t, d, []string{
+		"Extension STARTTLS",
+		"StartTLS",
+		"Mail " + testFrom,
+		"Extension STARTTLS",
+		"StartTLS",
+		"Mail " + testFrom,
+		"Rcpt " + testTo1,
+		"Rcpt " + testTo2,
+		"Data",
+		"Write message",
+		"Close writer",
+		"Quit",
+		"Close",
+	})
+}
+
 type mockClient struct {
 	t       *testing.T
 	i       int
 	want    []string
 	addr    string
 	config  *tls.Config
+	timeout bool
 }
 
 func (c *mockClient) Hello(localName string) error {
@@ -149,6 +172,10 @@ func (c *mockClient) Auth(a smtp.Auth) error {
 
 func (c *mockClient) Mail(from string) error {
 	c.do("Mail " + from)
+	if c.timeout {
+		c.timeout = false
+		return io.EOF
+	}
 	return nil
 }
 
@@ -204,11 +231,20 @@ func (w *mockWriter) Close() error {
 }
 
 func testSendMail(t *testing.T, d *Dialer, want []string) {
+	doTestSendMail(t, d, want, false)
+}
+
+func testSendMailTimeout(t *testing.T, d *Dialer, want []string) {
+	doTestSendMail(t, d, want, true)
+}
+
+func doTestSendMail(t *testing.T, d *Dialer, want []string, timeout bool) {
 	testClient := &mockClient{
 		t:       t,
 		want:    want,
 		addr:    addr(d.Host, d.Port),
 		config:  d.TLSConfig,
+		timeout: timeout,
 	}
 
 	netDial = func(network, address string) (net.Conn, error) {