website/app/internal/mail/send.go

package mail

import (
	"bytes"
	"crypto/tls"
	"fmt"
	"net"
	"net/smtp"
	"strings"
)

// ContactEmail sends a contact form message via the configured SMTP relay.
func (c Config) ContactEmail(name, replyTo, message string) error {
	subject := fmt.Sprintf("Contact form: %s", name)
	var body bytes.Buffer
	body.WriteString(fmt.Sprintf("Name: %s\n", name))
	body.WriteString(fmt.Sprintf("Email: %s\n\n", replyTo))
	body.WriteString(message)

	return c.send(subject, body.String(), replyTo)
}

func (c Config) send(subject, body, replyTo string) error {
	addr := fmt.Sprintf("%s:%d", c.Host, c.Port)

	var msg bytes.Buffer
	msg.WriteString(fmt.Sprintf("From: %s\r\n", c.From))
	msg.WriteString(fmt.Sprintf("To: %s\r\n", c.To))
	if replyTo != "" {
		msg.WriteString(fmt.Sprintf("Reply-To: %s\r\n", replyTo))
	}
	msg.WriteString(fmt.Sprintf("Subject: %s\r\n", subject))
	msg.WriteString("MIME-Version: 1.0\r\n")
	msg.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
	msg.WriteString("\r\n")
	msg.WriteString(body)

	raw := msg.Bytes()
	from := extractAddr(c.From)

	var auth smtp.Auth
	if c.User != "" {
		auth = smtp.PlainAuth("", c.User, c.Password, c.Host)
	}

	switch c.tlsMode() {
	case "plain":
		return smtp.SendMail(addr, auth, from, []string{c.To}, raw)
	case "tls":
		return c.sendTLS(addr, auth, from, raw)
	default:
		return c.sendStartTLS(addr, auth, from, raw)
	}
}

func (c Config) tlsMode() string {
	switch strings.ToLower(c.TLS) {
	case "plain", "tls":
		return strings.ToLower(c.TLS)
	}
	if c.Port == 465 {
		return "tls"
	}
	if c.Port == 25 {
		return "plain"
	}
	return "starttls"
}

func (c Config) sendStartTLS(addr string, auth smtp.Auth, from string, raw []byte) error {
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		return err
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, c.Host)
	if err != nil {
		return err
	}
	defer client.Close()

	if ok, _ := client.Extension("STARTTLS"); ok {
		if err := client.StartTLS(&tls.Config{ServerName: c.Host}); err != nil {
			return err
		}
	}

	if auth != nil {
		if ok, _ := client.Extension("AUTH"); ok {
			if err := client.Auth(auth); err != nil {
				return err
			}
		}
	}

	if err := client.Mail(from); err != nil {
		return err
	}
	if err := client.Rcpt(c.To); err != nil {
		return err
	}
	w, err := client.Data()
	if err != nil {
		return err
	}
	if _, err := w.Write(raw); err != nil {
		return err
	}
	if err := w.Close(); err != nil {
		return err
	}
	return client.Quit()
}

func (c Config) sendTLS(addr string, auth smtp.Auth, from string, raw []byte) error {
	conn, err := tls.Dial("tcp", addr, &tls.Config{ServerName: c.Host})
	if err != nil {
		return err
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, c.Host)
	if err != nil {
		return err
	}
	defer client.Close()

	if auth != nil {
		if ok, _ := client.Extension("AUTH"); ok {
			if err := client.Auth(auth); err != nil {
				return err
			}
		}
	}

	if err := client.Mail(from); err != nil {
		return err
	}
	if err := client.Rcpt(c.To); err != nil {
		return err
	}
	w, err := client.Data()
	if err != nil {
		return err
	}
	if _, err := w.Write(raw); err != nil {
		return err
	}
	if err := w.Close(); err != nil {
		return err
	}
	return client.Quit()
}

func extractAddr(from string) string {
	if i := strings.Index(from, "<"); i >= 0 {
		if j := strings.Index(from[i:], ">"); j > 0 {
			return strings.TrimSpace(from[i+1 : i+j])
		}
	}
	return strings.TrimSpace(from)
}