Add default ports and fallback behavior for SSL and TLS

client.go

@@ -20,9 +20,15 @@ import (
 
 // Defaults
 const (
-	// DefaultPort is the default connection port cto the SMTP server
+	// DefaultPort is the default connection port to the SMTP server
 	DefaultPort = 25
 
+	// DefaultPortSSL is the default connection port for SSL/TLS to the SMTP server
+	DefaultPortSSL = 465
+
+	// DefaultPortTLS is the default connection port for STARTTLS to the SMTP server
+	DefaultPortTLS = 587
+
 	// DefaultTimeout is the default connection timeout
 	DefaultTimeout = time.Second * 15
 
@@ -105,14 +111,15 @@ type Client struct {
 	// HELO/EHLO string for the greeting the target SMTP server
 	helo string
 
-	// Hostname of the target SMTP server cto connect cto
+	// Hostname of the target SMTP server to connect to
 	host string
 
 	// pass is the corresponding SMTP AUTH password
 	pass string
 
-	// Port of the SMTP server cto connect cto
-	port int
+	// Port of the SMTP server to connect to
+	port         int
+	fallbackPort int
 
 	// sa is a pointer to smtp.Auth
 	sa smtp.Auth
@@ -246,13 +253,27 @@ func WithTimeout(t time.Duration) Option {
 }
 
 // WithSSL tells the client to use a SSL/TLS connection
+//
+// Deprecated: use WithSSLPort instead.
 func WithSSL() Option {
 	return func(c *Client) error {
 		c.ssl = true
 		return nil
 	}
 }
 
+// WithSSLPort tells the client to use a SSL/TLS connection.
+// It automatically sets the port to 465.
+//
+// When the SSL connection fails and fallback is set to true,
+// the client will attempt to connect on port 25 using plaintext.
+func WithSSLPort(fb bool) Option {
+	return func(c *Client) error {
+		c.SetSSLPort(true, fb)
+		return nil
+	}
+}
+
 // WithDebugLog tells the client to log incoming and outgoing messages of the SMTP client
 // to StdErr
 func WithDebugLog() Option {
@@ -282,13 +303,29 @@ func WithHELO(h string) Option {
 }
 
 // WithTLSPolicy tells the client to use the provided TLSPolicy
+//
+// Deprecated: use WithTLSPortPolicy instead.
 func WithTLSPolicy(p TLSPolicy) Option {
 	return func(c *Client) error {
 		c.tlspolicy = p
 		return nil
 	}
 }
 
+// WithTLSPortPolicy tells the client to use the provided TLSPolicy,
+// The correct port is automatically set.
+//
+// Port 587 is used for TLSMandatory and TLSOpportunistic.
+// If the connection fails with TLSOpportunistic,
+// a plaintext connection is attempted on port 25 as a fallback.
+// NoTLS will allways use port 25.
+func WithTLSPortPolicy(p TLSPolicy) Option {
+	return func(c *Client) error {
+		c.SetTLSPortPolicy(p)
+		return nil
+	}
+}
+
 // WithTLSConfig tells the client to use the provided *tls.Config
 func WithTLSConfig(co *tls.Config) Option {
 	return func(c *Client) error {
@@ -430,11 +467,52 @@ func (c *Client) SetTLSPolicy(p TLSPolicy) {
 	c.tlspolicy = p
 }
 
+// SetTLSPortPolicy overrides the current TLSPolicy with the given TLSPolicy
+// value. The correct port is automatically set.
+//
+// Port 587 is used for TLSMandatory and TLSOpportunistic.
+// If the connection fails with TLSOpportunistic, a plaintext connection is
+// attempted on port 25 as a fallback.
+// NoTLS will allways use port 25.
+func (c *Client) SetTLSPortPolicy(p TLSPolicy) {
+	c.port = DefaultPortTLS
+
+	if p == TLSOpportunistic {
+		c.fallbackPort = DefaultPort
+	}
+	if p == NoTLS {
+		c.port = DefaultPort
+	}
+
+	c.tlspolicy = p
+}
+
 // SetSSL tells the Client wether to use SSL or not
 func (c *Client) SetSSL(s bool) {
 	c.ssl = s
 }
 
+// SetSSLPort tells the Client wether or not to use SSL and fallback.
+// The correct port is automatically set.
+//
+// Port 465 is used when SSL set (true).
+// Port 25 is used when SSL is unset (false).
+// When the SSL connection fails and fb is set to true,
+// the client will attempt to connect on port 25 using plaintext.
+func (c *Client) SetSSLPort(ssl bool, fb bool) {
+	c.port = DefaultPort
+	if ssl {
+		c.port = DefaultPortSSL
+	}
+
+	c.fallbackPort = 0
+	if fb {
+		c.fallbackPort = DefaultPort
+	}
+
+	c.ssl = ssl
+}
+
 // SetDebugLog tells the Client whether debug logging is enabled or not
 func (c *Client) SetDebugLog(v bool) {
 	c.dl = v
@@ -507,6 +585,10 @@ func (c *Client) DialWithContext(pc context.Context) error {
 	}
 	var err error
 	c.co, err = c.dialContextFunc(ctx, "tcp", c.ServerAddr())
+	if err != nil && c.fallbackPort != 0 {
+		// TODO: should we somehow log or append the previous error?
+		c.co, err = c.dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
+	}
 	if err != nil {
 		return err
 	}
@@ -606,6 +688,12 @@ func (c *Client) checkConn() error {
 	return nil
 }
 
+// serverFallbackAddr returns the currently set combination of hostname
+// and fallback port.
+func (c *Client) serverFallbackAddr() string {
+	return fmt.Sprintf("%s:%d", c.host, c.fallbackPort)
+}
+
 // tls tries to make sure that the STARTTLS requirements are satisfied
 func (c *Client) tls() error {
 	if c.co == nil {

client_test.go

@@ -89,9 +89,12 @@ func TestNewClientWithOptions(t *testing.T) {
 		{"WithTimeout()", WithTimeout(time.Second * 5), false},
 		{"WithTimeout()", WithTimeout(-10), true},
 		{"WithSSL()", WithSSL(), false},
+		{"WithSSLPort(false)", WithSSLPort(false), false},
+		{"WithSSLPort(true)", WithSSLPort(true), false},
 		{"WithHELO()", WithHELO(host), false},
 		{"WithHELO(); helo is empty", WithHELO(""), true},
 		{"WithTLSPolicy()", WithTLSPolicy(TLSOpportunistic), false},
+		{"WithTLSPortPolicy()", WithTLSPortPolicy(TLSOpportunistic), false},
 		{"WithTLSConfig()", WithTLSConfig(&tls.Config{}), false},
 		{"WithTLSConfig(); config is nil", WithTLSConfig(nil), true},
 		{"WithSMTPAuth()", WithSMTPAuth(SMTPAuthLogin), false},
@@ -235,6 +238,42 @@ func TestWithTLSPolicy(t *testing.T) {
 	}
 }
 
+// TestWithTLSPortPolicy tests the WithTLSPortPolicy() option for the NewClient() method
+func TestWithTLSPortPolicy(t *testing.T) {
+	tests := []struct {
+		name     string
+		value    TLSPolicy
+		want     string
+		wantPort int
+		fbPort   int
+		sf       bool
+	}{
+		{"Policy: TLSMandatory", TLSMandatory, TLSMandatory.String(), 587, 0, false},
+		{"Policy: TLSOpportunistic", TLSOpportunistic, TLSOpportunistic.String(), 587, 25, false},
+		{"Policy: NoTLS", NoTLS, NoTLS.String(), 25, 0, false},
+		{"Policy: Invalid", -1, "UnknownPolicy", 587, 0, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c, err := NewClient(DefaultHost, WithTLSPortPolicy(tt.value))
+			if err != nil && !tt.sf {
+				t.Errorf("failed to create new client: %s", err)
+				return
+			}
+			if c.tlspolicy.String() != tt.want {
+				t.Errorf("failed to set TLSPortPolicy. Want: %s, got: %s", tt.want, c.tlspolicy)
+			}
+			if c.port != tt.wantPort {
+				t.Errorf("failed to set TLSPortPolicy, wanted port: %d, got: %d", tt.wantPort, c.port)
+			}
+			if c.fallbackPort != tt.fbPort {
+				t.Errorf("failed to set TLSPortPolicy, wanted fallbakc port: %d, got: %d", tt.fbPort,
+					c.fallbackPort)
+			}
+		})
+	}
+}
+
 // TestSetTLSPolicy tests the SetTLSPolicy() method for the Client object
 func TestSetTLSPolicy(t *testing.T) {
 	tests := []struct {
@@ -312,6 +351,42 @@ func TestSetSSL(t *testing.T) {
 	}
 }
 
+// TestSetSSLPort tests the Client.SetSSLPort method
+func TestClient_SetSSLPort(t *testing.T) {
+	tests := []struct {
+		name   string
+		value  bool
+		fb     bool
+		port   int
+		fbPort int
+	}{
+		{"SSL: on, fb: off", true, false, 465, 0},
+		{"SSL: on, fb: on", true, true, 465, 25},
+		{"SSL: off, fb: off", false, false, 25, 0},
+		{"SSL: off, fb: on", false, true, 25, 25},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c, err := NewClient(DefaultHost)
+			if err != nil {
+				t.Errorf("failed to create new client: %s", err)
+				return
+			}
+			c.SetSSLPort(tt.value, tt.fb)
+			if c.ssl != tt.value {
+				t.Errorf("failed to set SSL setting. Got: %t, want: %t", c.ssl, tt.value)
+			}
+			if c.port != tt.port {
+				t.Errorf("failed to set SSLPort, wanted port: %d, got: %d", c.port, tt.port)
+			}
+			if c.fallbackPort != tt.fbPort {
+				t.Errorf("failed to set SSLPort, wanted fallback port: %d, got: %d", c.fallbackPort,
+					tt.fbPort)
+			}
+		})
+	}
+}
+
 // TestSetUsername tests the SetUsername method for the Client object
 func TestSetUsername(t *testing.T) {
 	tests := []struct {
@@ -550,6 +625,38 @@ func TestClient_DialWithContext(t *testing.T) {
 	}
 }
 
+// TestClient_DialWithContext_Fallback tests the Client.DialWithContext method with the fallback
+// port functionality
+func TestClient_DialWithContext_Fallback(t *testing.T) {
+	c, err := getTestConnection(true)
+	if err != nil {
+		t.Skipf("failed to create test client: %s. Skipping tests", err)
+	}
+	c.SetTLSPortPolicy(TLSOpportunistic)
+	c.port = 999
+	ctx := context.Background()
+	if err := c.DialWithContext(ctx); err != nil {
+		t.Errorf("failed to dial with context: %s", err)
+		return
+	}
+	if c.co == nil {
+		t.Errorf("DialWithContext didn't fail but no connection found.")
+	}
+	if c.sc == nil {
+		t.Errorf("DialWithContext didn't fail but no SMTP client found.")
+	}
+	if err := c.Close(); err != nil {
+		t.Errorf("failed to close connection: %s", err)
+	}
+
+	c.port = 999
+	c.fallbackPort = 999
+	if err = c.DialWithContext(ctx); err == nil {
+		t.Error("dial with context was supposed to fail, but didn't")
+		return
+	}
+}
+
 // TestClient_DialWithContext_Debug tests the DialWithContext method for the Client object with debug
 // logging enabled on the SMTP client
 func TestClient_DialWithContext_Debug(t *testing.T) {