Refactor SMTP client functions to improve modularity

Refactor `DialWithContext` to delegate client creation to `SMTPClientFromDialWithContext`. Add new methods `SendWithSMTPClient`, `CloseWithSMTPClient`, and `ResetWithSMTPClient` to handle specific actions on `smtp.Client`. Simplify `auth`, `sendSingleMsg`, and `tls` methods by passing client as parameters.

client.go

@@ -142,9 +142,6 @@ type (
 		// host is the hostname of the SMTP server we are connecting to.
 		host string
 
-		// isEncrypted indicates wether the Client connection is encrypted or not.
-		isEncrypted bool
-
 		// logAuthData indicates whether authentication-related data should be logged.
 		logAuthData bool
 
@@ -931,62 +928,131 @@ func (c *Client) SetLogAuthData(logAuth bool) {
 // Returns:
 //   - An error if the connection to the SMTP server fails or any subsequent command fails.
 func (c *Client) DialWithContext(dialCtx context.Context) error {
-	c.mutex.Lock()
+	client, err := c.SMTPClientFromDialWithContext(dialCtx)
-	defer c.mutex.Unlock()
-
-	ctx, cancel := context.WithDeadline(dialCtx, time.Now().Add(c.connTimeout))
-	defer cancel()
-
-	if c.dialContextFunc == nil {
-		netDialer := net.Dialer{}
-		c.dialContextFunc = netDialer.DialContext
-
-		if c.useSSL {
-			tlsDialer := tls.Dialer{NetDialer: &netDialer, Config: c.tlsconfig}
-			c.isEncrypted = true
-			c.dialContextFunc = tlsDialer.DialContext
-		}
-	}
-	connection, err := c.dialContextFunc(ctx, "tcp", c.ServerAddr())
-	if err != nil && c.fallbackPort != 0 {
-		// TODO: should we somehow log or append the previous error?
-		connection, err = c.dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
-	}
 	if err != nil {
 		return err
 	}
+	c.mutex.Lock()
+	c.smtpClient = client
+	c.mutex.Unlock()
+	/*
+		ctx, cancel := context.WithDeadline(dialCtx, time.Now().Add(c.connTimeout))
+		defer cancel()
+
+		isEncrypted := false
+		if c.dialContextFunc == nil {
+			netDialer := net.Dialer{}
+			c.dialContextFunc = netDialer.DialContext
+
+			if c.useSSL {
+				tlsDialer := tls.Dialer{NetDialer: &netDialer, Config: c.tlsconfig}
+				isEncrypted = true
+				c.dialContextFunc = tlsDialer.DialContext
+			}
+		}
+		connection, err := c.dialContextFunc(ctx, "tcp", c.ServerAddr())
+		if err != nil && c.fallbackPort != 0 {
+			// TODO: should we somehow log or append the previous error?
+			connection, err = c.dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
+		}
+		if err != nil {
+			return err
+		}
+
+		client, err := smtp.NewClient(connection, c.host)
+		if err != nil {
+			return err
+		}
+		if client == nil {
+			return fmt.Errorf("SMTP client is nil")
+		}
+		c.smtpClient = client
+
+		if c.logger != nil {
+			c.smtpClient.SetLogger(c.logger)
+		}
+		if c.useDebugLog {
+			c.smtpClient.SetDebugLog(true)
+		}
+		if c.logAuthData {
+			c.smtpClient.SetLogAuthData()
+		}
+		if err = c.smtpClient.Hello(c.helo); err != nil {
+			return err
+		}
+
+		if err = c.tls(c.smtpClient, &isEncrypted); err != nil {
+			return err
+		}
+
+		if err = c.auth(c.smtpClient, isEncrypted); err != nil {
+			return err
+		}
+
+	*/
+
+	return nil
+}
+
+// SMTPClientFromDialWithContext is similar to DialWithContext but instead of storing the smtp.Client
+// on the Client it will return the smtp.Client instead.
+func (c *Client) SMTPClientFromDialWithContext(ctxDial context.Context) (*smtp.Client, error) {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+
+	ctx, cancel := context.WithDeadline(ctxDial, time.Now().Add(c.connTimeout))
+	defer cancel()
+
+	isEncrypted := false
+	dialContextFunc := c.dialContextFunc
+	if c.dialContextFunc == nil {
+		netDialer := net.Dialer{}
+		dialContextFunc = netDialer.DialContext
+		if c.useSSL {
+			tlsDialer := tls.Dialer{NetDialer: &netDialer, Config: c.tlsconfig}
+			isEncrypted = true
+			dialContextFunc = tlsDialer.DialContext
+		}
+	}
+	connection, err := dialContextFunc(ctx, "tcp", c.ServerAddr())
+	if err != nil && c.fallbackPort != 0 {
+		// TODO: should we somehow log or append the previous error?
+		connection, err = dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
+	}
+	if err != nil {
+		return nil, err
+	}
 
 	client, err := smtp.NewClient(connection, c.host)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	if client == nil {
-		return fmt.Errorf("SMTP client is nil")
+		return nil, fmt.Errorf("SMTP client is nil")
 	}
-	c.smtpClient = client
 
 	if c.logger != nil {
-		c.smtpClient.SetLogger(c.logger)
+		client.SetLogger(c.logger)
 	}
 	if c.useDebugLog {
-		c.smtpClient.SetDebugLog(true)
+		client.SetDebugLog(true)
 	}
 	if c.logAuthData {
-		c.smtpClient.SetLogAuthData()
+		client.SetLogAuthData()
 	}
-	if err = c.smtpClient.Hello(c.helo); err != nil {
+	if err = client.Hello(c.helo); err != nil {
-		return err
+		return nil, err
 	}
 
-	if err = c.tls(); err != nil {
+	if err = c.tls(client, &isEncrypted); err != nil {
-		return err
+		return nil, err
 	}
 
-	if err = c.auth(); err != nil {
+	if err = c.auth(client, isEncrypted); err != nil {
-		return err
+		return nil, err
 	}
 
-	return nil
+	return client, nil
 }
 
 // Close terminates the connection to the SMTP server, returning an error if the disconnection
@@ -999,10 +1065,14 @@ func (c *Client) DialWithContext(dialCtx context.Context) error {
 // Returns:
 //   - An error if the disconnection fails; otherwise, returns nil.
 func (c *Client) Close() error {
-	if c.smtpClient == nil || !c.smtpClient.HasConnection() {
+	return c.CloseWithSMTPClient(c.smtpClient)
+}
+
+func (c *Client) CloseWithSMTPClient(client *smtp.Client) error {
+	if client == nil || !client.HasConnection() {
 		return nil
 	}
-	if err := c.smtpClient.Quit(); err != nil {
+	if err := client.Quit(); err != nil {
 		return fmt.Errorf("failed to close SMTP client: %w", err)
 	}
 
@@ -1018,10 +1088,14 @@ func (c *Client) Close() error {
 // Returns:
 //   - An error if the connection check fails or if sending the RSET command fails; otherwise, returns nil.
 func (c *Client) Reset() error {
-	if err := c.checkConn(); err != nil {
+	return c.ResetWithSMTPClient(c.smtpClient)
+}
+
+func (c *Client) ResetWithSMTPClient(client *smtp.Client) error {
+	if err := c.checkConn(client); err != nil {
 		return err
 	}
-	if err := c.smtpClient.Reset(); err != nil {
+	if err := client.Reset(); err != nil {
 		return fmt.Errorf("failed to send RSET to SMTP client: %w", err)
 	}
 
@@ -1061,19 +1135,20 @@ func (c *Client) DialAndSend(messages ...*Msg) error {
 //   - An error if the connection fails, if sending the messages fails, or if closing the
 //     connection fails; otherwise, returns nil.
 func (c *Client) DialAndSendWithContext(ctx context.Context, messages ...*Msg) error {
-	c.sendMutex.Lock()
+	//c.sendMutex.Lock()
-	defer c.sendMutex.Unlock()
+	//defer c.sendMutex.Unlock()
-	if err := c.DialWithContext(ctx); err != nil {
+	client, err := c.SMTPClientFromDialWithContext(ctx)
+	if err != nil {
 		return fmt.Errorf("dial failed: %w", err)
 	}
 	defer func() {
-		_ = c.Close()
+		_ = c.CloseWithSMTPClient(client)
 	}()
 
-	if err := c.Send(messages...); err != nil {
+	if err := c.SendWithSMTPClient(client, messages...); err != nil {
 		return fmt.Errorf("send failed: %w", err)
 	}
-	if err := c.Close(); err != nil {
+	if err := c.CloseWithSMTPClient(client); err != nil {
 		return fmt.Errorf("failed to close connection: %w", err)
 	}
 	return nil
@@ -1098,16 +1173,17 @@ func (c *Client) DialAndSendWithContext(ctx context.Context, messages ...*Msg) e
 // Returns:
 //   - An error if the connection check fails, if no supported authentication method is found,
 //     or if the authentication process fails.
-func (c *Client) auth() error {
+func (c *Client) auth(client *smtp.Client, isEnc bool) error {
+	var smtpAuth smtp.Auth
 	if c.smtpAuth == nil && c.smtpAuthType != SMTPAuthNoAuth {
-		hasSMTPAuth, smtpAuthType := c.smtpClient.Extension("AUTH")
+		hasSMTPAuth, smtpAuthType := client.Extension("AUTH")
 		if !hasSMTPAuth {
 			return fmt.Errorf("server does not support SMTP AUTH")
 		}
 
 		authType := c.smtpAuthType
 		if c.smtpAuthType == SMTPAuthAutoDiscover {
-			discoveredType, err := c.authTypeAutoDiscover(smtpAuthType)
+			discoveredType, err := c.authTypeAutoDiscover(smtpAuthType, isEnc)
 			if err != nil {
 				return err
 			}
@@ -1119,74 +1195,74 @@ func (c *Client) auth() error {
 			if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
 				return ErrPlainAuthNotSupported
 			}
-			c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, false)
+			smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, false)
 		case SMTPAuthPlainNoEnc:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
 				return ErrPlainAuthNotSupported
 			}
-			c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, true)
+			smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, true)
 		case SMTPAuthLogin:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
 				return ErrLoginAuthNotSupported
 			}
-			c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, false)
+			smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, false)
 		case SMTPAuthLoginNoEnc:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
 				return ErrLoginAuthNotSupported
 			}
-			c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, true)
+			smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, true)
 		case SMTPAuthCramMD5:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthCramMD5)) {
 				return ErrCramMD5AuthNotSupported
 			}
-			c.smtpAuth = smtp.CRAMMD5Auth(c.user, c.pass)
+			smtpAuth = smtp.CRAMMD5Auth(c.user, c.pass)
 		case SMTPAuthXOAUTH2:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthXOAUTH2)) {
 				return ErrXOauth2AuthNotSupported
 			}
-			c.smtpAuth = smtp.XOAuth2Auth(c.user, c.pass)
+			smtpAuth = smtp.XOAuth2Auth(c.user, c.pass)
 		case SMTPAuthSCRAMSHA1:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthSCRAMSHA1)) {
 				return ErrSCRAMSHA1AuthNotSupported
 			}
-			c.smtpAuth = smtp.ScramSHA1Auth(c.user, c.pass)
+			smtpAuth = smtp.ScramSHA1Auth(c.user, c.pass)
 		case SMTPAuthSCRAMSHA256:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthSCRAMSHA256)) {
 				return ErrSCRAMSHA256AuthNotSupported
 			}
-			c.smtpAuth = smtp.ScramSHA256Auth(c.user, c.pass)
+			smtpAuth = smtp.ScramSHA256Auth(c.user, c.pass)
 		case SMTPAuthSCRAMSHA1PLUS:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthSCRAMSHA1PLUS)) {
 				return ErrSCRAMSHA1PLUSAuthNotSupported
 			}
-			tlsConnState, err := c.smtpClient.GetTLSConnectionState()
+			tlsConnState, err := client.GetTLSConnectionState()
 			if err != nil {
 				return err
 			}
-			c.smtpAuth = smtp.ScramSHA1PlusAuth(c.user, c.pass, tlsConnState)
+			smtpAuth = smtp.ScramSHA1PlusAuth(c.user, c.pass, tlsConnState)
 		case SMTPAuthSCRAMSHA256PLUS:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthSCRAMSHA256PLUS)) {
 				return ErrSCRAMSHA256PLUSAuthNotSupported
 			}
-			tlsConnState, err := c.smtpClient.GetTLSConnectionState()
+			tlsConnState, err := client.GetTLSConnectionState()
 			if err != nil {
 				return err
 			}
-			c.smtpAuth = smtp.ScramSHA256PlusAuth(c.user, c.pass, tlsConnState)
+			smtpAuth = smtp.ScramSHA256PlusAuth(c.user, c.pass, tlsConnState)
 		default:
 			return fmt.Errorf("unsupported SMTP AUTH type %q", c.smtpAuthType)
 		}
 	}
 
-	if c.smtpAuth != nil {
+	if smtpAuth != nil {
-		if err := c.smtpClient.Auth(c.smtpAuth); err != nil {
+		if err := client.Auth(smtpAuth); err != nil {
 			return fmt.Errorf("SMTP AUTH failed: %w", err)
 		}
 	}
 	return nil
 }
 
-func (c *Client) authTypeAutoDiscover(supported string) (SMTPAuthType, error) {
+func (c *Client) authTypeAutoDiscover(supported string, isEnc bool) (SMTPAuthType, error) {
 	if supported == "" {
 		return "", ErrNoSupportedAuthDiscovered
 	}
@@ -1194,7 +1270,7 @@ func (c *Client) authTypeAutoDiscover(supported string) (SMTPAuthType, error) {
 		SMTPAuthSCRAMSHA256PLUS, SMTPAuthSCRAMSHA256, SMTPAuthSCRAMSHA1PLUS, SMTPAuthSCRAMSHA1,
 		SMTPAuthXOAUTH2, SMTPAuthCramMD5, SMTPAuthPlain, SMTPAuthLogin,
 	}
-	if !c.isEncrypted {
+	if !isEnc {
 		preferList = []SMTPAuthType{SMTPAuthSCRAMSHA256, SMTPAuthSCRAMSHA1, SMTPAuthXOAUTH2, SMTPAuthCramMD5}
 	}
 	mechs := strings.Split(supported, " ")
@@ -1231,13 +1307,13 @@ func sliceContains(slice []string, item string) bool {
 //
 // Returns:
 //   - An error if any part of the sending process fails; otherwise, returns nil.
-func (c *Client) sendSingleMsg(message *Msg) error {
+func (c *Client) sendSingleMsg(client *smtp.Client, message *Msg) error {
-	c.mutex.Lock()
+	c.mutex.RLock()
-	defer c.mutex.Unlock()
+	defer c.mutex.RUnlock()
-	escSupport, _ := c.smtpClient.Extension("ENHANCEDSTATUSCODES")
+	escSupport, _ := client.Extension("ENHANCEDSTATUSCODES")
 
 	if message.encoding == NoEncoding {
-		if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
+		if ok, _ := client.Extension("8BITMIME"); !ok {
 			return &SendError{Reason: ErrNoUnencoded, isTemp: false, affectedMsg: message}
 		}
 	}
@@ -1260,16 +1336,16 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 
 	if c.requestDSN {
 		if c.dsnReturnType != "" {
-			c.smtpClient.SetDSNMailReturnOption(string(c.dsnReturnType))
+			client.SetDSNMailReturnOption(string(c.dsnReturnType))
 		}
 	}
-	if err = c.smtpClient.Mail(from); err != nil {
+	if err = client.Mail(from); err != nil {
 		retError := &SendError{
 			Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err),
 			affectedMsg: message, errcode: errorCode(err),
 			enhancedStatusCode: enhancedStatusCode(err, escSupport),
 		}
-		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+		if resetSendErr := client.Reset(); resetSendErr != nil {
 			retError.errlist = append(retError.errlist, resetSendErr)
 		}
 		return retError
@@ -1279,9 +1355,9 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 	rcptSendErr.errlist = make([]error, 0)
 	rcptSendErr.rcpt = make([]string, 0)
 	rcptNotifyOpt := strings.Join(c.dsnRcptNotifyType, ",")
-	c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
+	client.SetDSNRcptNotifyOption(rcptNotifyOpt)
 	for _, rcpt := range rcpts {
-		if err = c.smtpClient.Rcpt(rcpt); err != nil {
+		if err = client.Rcpt(rcpt); err != nil {
 			rcptSendErr.Reason = ErrSMTPRcptTo
 			rcptSendErr.errlist = append(rcptSendErr.errlist, err)
 			rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
@@ -1292,12 +1368,12 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 		}
 	}
 	if hasError {
-		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+		if resetSendErr := client.Reset(); resetSendErr != nil {
 			rcptSendErr.errlist = append(rcptSendErr.errlist, resetSendErr)
 		}
 		return rcptSendErr
 	}
-	writer, err := c.smtpClient.Data()
+	writer, err := client.Data()
 	if err != nil {
 		return &SendError{
 			Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err),
@@ -1322,7 +1398,7 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 	}
 	message.isDelivered = true
 
-	if err = c.Reset(); err != nil {
+	if err = c.ResetWithSMTPClient(client); err != nil {
 		return &SendError{
 			Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err),
 			affectedMsg: message, errcode: errorCode(err),
@@ -1344,21 +1420,24 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 // Returns:
 //   - An error if there is no active connection, if the NOOP command fails, or if extending
 //     the deadline fails; otherwise, returns nil.
-func (c *Client) checkConn() error {
+func (c *Client) checkConn(client *smtp.Client) error {
-	if c.smtpClient == nil {
+	if client == nil {
 		return ErrNoActiveConnection
 	}
-	if !c.smtpClient.HasConnection() {
+	if !client.HasConnection() {
 		return ErrNoActiveConnection
 	}
 
-	if !c.noNoop {
+	c.mutex.RLock()
-		if err := c.smtpClient.Noop(); err != nil {
+	noNoop := c.noNoop
+	c.mutex.RUnlock()
+	if !noNoop {
+		if err := client.Noop(); err != nil {
 			return ErrNoActiveConnection
 		}
 	}
 
-	if err := c.smtpClient.UpdateDeadline(c.connTimeout); err != nil {
+	if err := client.UpdateDeadline(c.connTimeout); err != nil {
 		return ErrDeadlineExtendFailed
 	}
 	return nil
@@ -1405,10 +1484,10 @@ func (c *Client) setDefaultHelo() error {
 // Returns:
 //   - An error if there is no active connection, if STARTTLS is required but not supported,
 //     or if there are issues during the TLS handshake; otherwise, returns nil.
-func (c *Client) tls() error {
+func (c *Client) tls(client *smtp.Client, isEnc *bool) error {
 	if !c.useSSL && c.tlspolicy != NoTLS {
 		hasStartTLS := false
-		extension, _ := c.smtpClient.Extension("STARTTLS")
+		extension, _ := client.Extension("STARTTLS")
 		if c.tlspolicy == TLSMandatory {
 			hasStartTLS = true
 			if !extension {
@@ -1422,21 +1501,21 @@ func (c *Client) tls() error {
 			}
 		}
 		if hasStartTLS {
-			if err := c.smtpClient.StartTLS(c.tlsconfig); err != nil {
+			if err := client.StartTLS(c.tlsconfig); err != nil {
 				return err
 			}
 		}
-		tlsConnState, err := c.smtpClient.GetTLSConnectionState()
+		tlsConnState, err := client.GetTLSConnectionState()
 		if err != nil {
 			switch {
 			case errors.Is(err, smtp.ErrNonTLSConnection):
-				c.isEncrypted = false
+				*isEnc = false
 				return nil
 			default:
 				return fmt.Errorf("failed to get TLS connection state: %w", err)
 			}
 		}
-		c.isEncrypted = tlsConnState.HandshakeComplete
+		*isEnc = tlsConnState.HandshakeComplete
 	}
 	return nil
 }

client_120.go

@@ -9,6 +9,8 @@ package mail
 
 import (
 	"errors"
+
+	"github.com/wneessen/go-mail/smtp"
 )
 
 // Send attempts to send one or more Msg using the Client connection to the SMTP server.
@@ -27,11 +29,15 @@ import (
 // Returns:
 //   - An error that aggregates any SendErrors encountered during the sending process; otherwise, returns nil.
 func (c *Client) Send(messages ...*Msg) (returnErr error) {
+	return c.SendWithSMTPClient(c.smtpClient, messages...)
+}
+
+func (c *Client) SendWithSMTPClient(client *smtp.Client, messages ...*Msg) (returnErr error) {
 	escSupport := false
-	if c.smtpClient != nil {
+	if client != nil {
-		escSupport, _ = c.smtpClient.Extension("ENHANCEDSTATUSCODES")
+		escSupport, _ = client.Extension("ENHANCEDSTATUSCODES")
 	}
-	if err := c.checkConn(); err != nil {
+	if err := c.checkConn(client); err != nil {
 		returnErr = &SendError{
 			Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err),
 			errcode: errorCode(err), enhancedStatusCode: enhancedStatusCode(err, escSupport),
@@ -45,7 +51,7 @@ func (c *Client) Send(messages ...*Msg) (returnErr error) {
 	}()
 
 	for id, message := range messages {
-		if sendErr := c.sendSingleMsg(message); sendErr != nil {
+		if sendErr := c.sendSingleMsg(client, message); sendErr != nil {
 			messages[id].sendError = sendErr
 			errs = append(errs, sendErr)
 		}