fix(server): SMTP dispatch dial timeout + implicit/STARTTLS handling

server/internal/notify/smtp.go

@@ -1,15 +1,25 @@
 package notify
 
 import (
+	"crypto/tls"
 	"fmt"
+	"net"
 	"net/smtp"
 	"strings"
+	"time"
 
 	"github.com/mrhid6/vantage/server/internal/models"
 )
 
+const smtpTimeout = 15 * time.Second
+
 // dispatchSMTP sends the alert as a plain-text email. Config keys: host, port,
-// username, password, from, to. Auth is skipped when username is empty.
+// username, password, from, to. Auth is skipped when username is empty. Port 465
+// uses implicit TLS; other ports use STARTTLS when the server advertises it.
+//
+// It dials with a timeout and sets a connection deadline so an unreachable or
+// misconfigured SMTP host fails fast instead of hanging the request until the OS
+// TCP timeout (which resets the upstream proxy connection).
 func dispatchSMTP(ch models.NotificationChannel, ev Event) error {
 	host := ch.Config["host"]
 	port := ch.Config["port"]
@@ -19,6 +29,56 @@ func dispatchSMTP(ch models.NotificationChannel, ev Event) error {
 		return fmt.Errorf("smtp: missing host/port/from/to")
 	}
 
+	addr := net.JoinHostPort(host, port)
+	conn, err := net.DialTimeout("tcp", addr, smtpTimeout)
+	if err != nil {
+		return fmt.Errorf("smtp: dial %s: %w", addr, err)
+	}
+	_ = conn.SetDeadline(time.Now().Add(smtpTimeout))
+
+	// Implicit TLS on 465; otherwise start plain and upgrade via STARTTLS.
+	if port == "465" {
+		conn = tls.Client(conn, &tls.Config{ServerName: host})
+	}
+
+	c, err := smtp.NewClient(conn, host)
+	if err != nil {
+		conn.Close()
+		return fmt.Errorf("smtp: client: %w", err)
+	}
+	defer c.Close()
+
+	if port != "465" {
+		if ok, _ := c.Extension("STARTTLS"); ok {
+			if err := c.StartTLS(&tls.Config{ServerName: host}); err != nil {
+				return fmt.Errorf("smtp: starttls: %w", err)
+			}
+		}
+	}
+
+	if user := ch.Config["username"]; user != "" {
+		if err := c.Auth(smtp.PlainAuth("", user, ch.Config["password"], host)); err != nil {
+			return fmt.Errorf("smtp: auth: %w", err)
+		}
+	}
+
+	recipients := strings.Split(to, ",")
+	for i := range recipients {
+		recipients[i] = strings.TrimSpace(recipients[i])
+	}
+
+	if err := c.Mail(from); err != nil {
+		return fmt.Errorf("smtp: mail from: %w", err)
+	}
+	for _, rcpt := range recipients {
+		if rcpt == "" {
+			continue
+		}
+		if err := c.Rcpt(rcpt); err != nil {
+			return fmt.Errorf("smtp: rcpt %s: %w", rcpt, err)
+		}
+	}
+
 	title := ev.title()
 	msg := strings.Join([]string{
 		"From: " + from,
@@ -32,14 +92,15 @@ func dispatchSMTP(ch models.NotificationChannel, ev Event) error {
 		"Time: " + ev.Time.String(),
 	}, "\r\n")
 
-	var auth smtp.Auth
-	if user := ch.Config["username"]; user != "" {
-		auth = smtp.PlainAuth("", user, ch.Config["password"], host)
+	w, err := c.Data()
+	if err != nil {
+		return fmt.Errorf("smtp: data: %w", err)
 	}
-	addr := host + ":" + port
-	recipients := strings.Split(to, ",")
-	for i := range recipients {
-		recipients[i] = strings.TrimSpace(recipients[i])
+	if _, err := w.Write([]byte(msg)); err != nil {
+		return fmt.Errorf("smtp: write: %w", err)
 	}
-	return smtp.SendMail(addr, auth, from, recipients, []byte(msg))
+	if err := w.Close(); err != nil {
+		return fmt.Errorf("smtp: close data: %w", err)
+	}
+	return c.Quit()
 }