1 files changed, 122 insertions, 0 deletions
diff --git a/mailer.go b/mailer.go
new file mode 100644
index 0000000..cb687c9
--- /dev/null
+++ b/mailer.go
@@ -0,0 +1,122 @@
+// SPDX-FileCopyrightText: © 2020 Grégoire Duchêne <gduchene@awhk.org>
+// SPDX-License-Identifier: ISC
+
+package main
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"fmt"
+	"log"
+	"net"
+	"net/smtp"
+	"text/template"
+	"time"
+
+	"go.awhk.org/fwdsms/pkg/twilio"
+)
+
+type email struct {
+	from, to string
+	body     []byte
+}
+
+type mailer struct {
+	auth                      smtp.Auth
+	hostname                  string
+	sms                       <-chan twilio.SMS
+	tmplFrom, tmplTo, tmplMsg *template.Template
+}
+
+func (m *mailer) sendEmail(e email) error {
+	dialer := &net.Dialer{Timeout: time.Second}
+	conn, err := tls.DialWithDialer(dialer, "tcp", m.hostname, nil)
+	if err != nil {
+		return err
+	}
+	if err := conn.SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
+		log.Printf("Failed to set the SMTP connection deadline: %s.", err)
+	}
+	h, _, _ := net.SplitHostPort(m.hostname)
+	c, err := smtp.NewClient(conn, h)
+	if err != nil {
+		conn.Close()
+		return err
+	}
+	defer c.Close()
+	if err := c.Auth(m.auth); err != nil {
+		return err
+	}
+
+	if err := c.Mail(e.from); err != nil {
+		return err
+	}
+	if err := c.Rcpt(e.to); err != nil {
+		return err
+	}
+	w, err := c.Data()
+	if err != nil {
+		return err
+	}
+	if _, err := w.Write(e.body); err != nil {
+		return err
+	}
+	if err = w.Close(); err != nil {
+		return nil
+	}
+	return c.Quit()
+}
+
+func (m *mailer) newEmail(sms twilio.SMS) email {
+	var from, to, msg bytes.Buffer
+	if err := m.tmplFrom.Execute(&from, sms); err != nil {
+		log.Printf("Failed to apply a template: %v.", err)
+	}
+	if err := m.tmplTo.Execute(&to, sms); err != nil {
+		log.Printf("Failed to apply a template: %v.", err)
+	}
+	if err := m.tmplMsg.Execute(&msg, sms); err != nil {
+		log.Printf("Failed to apply a template: %v.", err)
+	}
+	return email{from.String(), to.String(), msg.Bytes()}
+}
+
+func (m *mailer) start(ctx context.Context) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case sms := <-m.sms:
+			if err := m.sendEmail(m.newEmail(sms)); err != nil {
+				log.Printf("Failed to send email: %v.", err)
+			}
+		}
+	}
+}
+
+func newMailer(cfg *Config, sms <-chan twilio.SMS) *mailer {
+	if cfg.Message.From == "" {
+		log.Fatal("Missing From field.")
+	}
+	if cfg.Message.To == "" {
+		log.Fatal("Missing To field.")
+	}
+	if cfg.Message.Subject == "" {
+		log.Fatal("Missing Subject field.")
+	}
+	if cfg.Message.Template == "" {
+		log.Fatal("Missing Template field.")
+	}
+	tmplMsg := fmt.Sprintf("From: %s\r\nTo: %s\r\nSubject: %s\r\n\r\n%s\r\n",
+		cfg.Message.From, cfg.Message.To, cfg.Message.Subject, cfg.Message.Template)
+	host, _, _ := net.SplitHostPort(cfg.SMTP.Address)
+	return &mailer{
+		auth:     smtp.PlainAuth("", cfg.SMTP.Username, cfg.SMTP.Password, host),
+		hostname: cfg.SMTP.Address,
+		sms:      sms,
+		tmplFrom: template.Must(template.New("from").Parse(cfg.Message.From)),
+		tmplTo:   template.Must(template.New("to").Parse(cfg.Message.To)),
+		tmplMsg:  template.Must(template.New("message").Parse(tmplMsg)),
+	}
+}