WIP: client: use standard port when setting SSL/TLS

client.go

@@ -19,9 +19,15 @@ 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
 
@@ -107,8 +113,9 @@ type Client struct {
  // 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
@@ -236,13 +243,27 @@ 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(fallback bool) Option {
+ return func(c *Client) error {
+ c.SetSSLPort(true, fallback)
+ return nil
+ }
+}
+
 // WithDebugLog tells the client to log incoming and outgoing messages of the SMTP client
 // to StdErr
 func WithDebugLog() Option {
@@ -264,13 +285,29 @@ 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 {
@@ -394,6 +431,12 @@ func (c *Client) TLSPolicy() string {
  return c.tlspolicy.String()
 }
 
+// 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)
+}
+
 // ServerAddr returns the currently set combination of hostname and port
 func (c *Client) ServerAddr() string {
  return fmt.Sprintf("%s:%d", c.host, c.port)
@@ -404,11 +447,54 @@ func (c *Client) SetTLSPolicy(p TLSPolicy) {
  c.tlspolicy = p
 }
 
+// SetTLSPolicy 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 fallback is set to true,
+// the client will attempt to connect on port 25 using plaintext.
+func (c *Client) SetSSLPort(ssl bool, fallback bool) {
+ if ssl {
+ c.port = DefaultPortSSL
+ } else {
+ c.port = DefaultPort
+ }
+
+ if fallback {
+ c.fallbackPort = DefaultPort
+ } else {
+ c.fallbackPort = 0
+ }
+
+ c.ssl = ssl
+}
+
 // SetDebugLog tells the Client whether debug logging is enabled or not
 func (c *Client) SetDebugLog(v bool) {
  c.dl = v
@@ -473,6 +559,14 @@ func (c *Client) DialWithContext(pc context.Context) error {
  if !c.ssl {
  c.co, err = nd.DialContext(ctx, "tcp", c.ServerAddr())
  }
+
+ if err != nil && c.fallbackPort != 0 {
+ ctx, cfn := context.WithTimeout(pc, c.cto)
+ defer cfn()
+
+ // TODO: should we somehow log or append the previous error?
+ c.co, err = nd.DialContext(ctx, "tcp", c.serverFallbackAddr())
+ }
  if err != nil {
  return err
  }