Added support for sending with relay hosts

smtp/client.go

@@ -0,0 +1,107 @@
+package smtp
+
+import (
+	"crypto/tls"
+	"io"
+	"net/smtp"
+	"strings"
+
+	"gitlab.com/etke.cc/go/logger"
+	"gitlab.com/etke.cc/go/trysmtp"
+)
+
+type MailSender interface {
+	Send(from string, to string, data string) error
+}
+
+type Client struct {
+	config *RelayConfig
+	log    *logger.Logger
+}
+
+func newClient(cfg *RelayConfig, log *logger.Logger) Client {
+	return Client{
+		config: cfg,
+		log:    log,
+	}
+}
+
+func (c Client) Send(from string, to string, data string) error {
+	c.log.Debug("Sending email from %s to %s", from, to)
+	conn, err := c.createSmtpClient(from, to)
+	if conn == nil {
+		c.log.Error("cannot connect to SMTP server of %s: %v", to, err)
+		return err
+	}
+	if err != nil {
+		c.log.Warn("connection to the SMTP server of %s returned the following non-fatal error(-s): %v", err)
+	}
+	defer conn.Close()
+
+	var w io.WriteCloser
+	w, err = conn.Data()
+	if err != nil {
+		c.log.Error("cannot send DATA command: %v", err)
+		return err
+	}
+	defer w.Close()
+	c.log.Debug("sending DATA:\n%s", data)
+	_, err = strings.NewReader(data).WriteTo(w)
+	if err != nil {
+		c.log.Debug("cannot write DATA: %v", err)
+		return err
+	}
+
+	c.log.Debug("email has been sent")
+	return nil
+}
+
+func (c *Client) createSmtpClient(from string, to string) (*smtp.Client, error) {
+	if c.config.Host != "" {
+		return c.createDirectClient(from, to)
+	}
+
+	return trysmtp.Connect(from, to)
+}
+
+func (c *Client) createDirectClient(from string, to string) (*smtp.Client, error) {
+	localname := strings.SplitN(from, "@", 2)[1]
+	target := c.config.Host + ":" + c.config.Port
+	conn, err := smtp.Dial(target)
+
+	if err != nil {
+		return nil, err
+	}
+
+	err = conn.Hello(localname)
+	if err != nil {
+		return nil, err
+	}
+
+	if ok, _ := conn.Extension("STARTTLS"); ok {
+		config := &tls.Config{ServerName: c.config.Host}
+		conn.StartTLS(config) //nolint:errcheck // if it doesn't work - we can't do anything anyway
+	}
+
+	if c.config.Usename != "" {
+		err = conn.Auth(smtp.PlainAuth("", c.config.Usename, c.config.Password, c.config.Host))
+		if err != nil {
+			conn.Close()
+			return nil, err
+		}
+	}
+
+	err = conn.Mail(from)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	err = conn.Rcpt(to)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	return conn, nil
+}