notification: smtp channel

internal/notification/smtp.go

@@ -0,0 +1,140 @@
+package notification
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	"net/smtp"
+	"strings"
+	"time"
+)
+
+// SMTPConfig holds the configuration for an SMTP notification channel.
+type SMTPConfig struct {
+	Host       string `json:"host"`
+	Port       int    `json:"port"`
+	Encryption string `json:"encryption"` // "starttls" | "tls" | "none"
+	Username   string `json:"username"`
+	Password   string `json:"password"`
+	From       string `json:"from"`
+	To         string `json:"to"`
+}
+
+// SMTPChannel delivers alert notifications via plain-text email.
+type SMTPChannel struct {
+	cfg SMTPConfig
+	// messageIDDomain holds the public base hostname of restic-manager so
+	// Message-IDs include a stable right-hand-side. Falls back to
+	// "restic-manager.local" when unset.
+	messageIDDomain string
+}
+
+// NewSMTPChannel builds an SMTP channel. messageIDDomain comes from
+// cfg.Cfg.BaseURL — caller passes it through.
+func NewSMTPChannel(cfg SMTPConfig, messageIDDomain string) *SMTPChannel {
+	if messageIDDomain == "" {
+		messageIDDomain = "restic-manager.local"
+	}
+	return &SMTPChannel{cfg: cfg, messageIDDomain: messageIDDomain}
+}
+
+// Kind returns "smtp".
+func (c *SMTPChannel) Kind() string { return "smtp" }
+
+// Send delivers the payload as a plain-text email via SMTP.
+// Returns (250, latency, nil) on success.
+func (c *SMTPChannel) Send(ctx context.Context, p Payload) (int, time.Duration, error) {
+	t0 := time.Now()
+	addr := fmt.Sprintf("%s:%d", c.cfg.Host, c.cfg.Port)
+
+	// Dial respects ctx (we use net.Dialer).
+	dialer := &net.Dialer{Timeout: 10 * time.Second}
+	rawConn, err := dialer.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: dial %s: %w", addr, err)
+	}
+
+	var client *smtp.Client
+	switch strings.ToLower(c.cfg.Encryption) {
+	case "tls":
+		conn := tls.Client(rawConn, &tls.Config{ServerName: c.cfg.Host, MinVersion: tls.VersionTLS12})
+		client, err = smtp.NewClient(conn, c.cfg.Host)
+	case "starttls", "":
+		client, err = smtp.NewClient(rawConn, c.cfg.Host)
+		if err == nil {
+			err = client.StartTLS(&tls.Config{ServerName: c.cfg.Host, MinVersion: tls.VersionTLS12})
+		}
+	case "none":
+		client, err = smtp.NewClient(rawConn, c.cfg.Host)
+	default:
+		_ = rawConn.Close()
+		return 0, time.Since(t0), fmt.Errorf("smtp: unknown encryption %q", c.cfg.Encryption)
+	}
+	if err != nil {
+		_ = rawConn.Close()
+		return 0, time.Since(t0), fmt.Errorf("smtp: handshake: %w", err)
+	}
+	defer func() { _ = client.Quit() }()
+
+	if c.cfg.Username != "" {
+		auth := smtp.PlainAuth("", c.cfg.Username, c.cfg.Password, c.cfg.Host)
+		if err := client.Auth(auth); err != nil {
+			return 0, time.Since(t0), fmt.Errorf("smtp: auth: %w", err)
+		}
+	}
+
+	if err := client.Mail(extractAddr(c.cfg.From)); err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: MAIL FROM: %w", err)
+	}
+	if err := client.Rcpt(c.cfg.To); err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: RCPT TO: %w", err)
+	}
+	wc, err := client.Data()
+	if err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: DATA: %w", err)
+	}
+	msg := buildEmailBody(c.cfg, c.messageIDDomain, p)
+	if _, err := wc.Write(msg); err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: write: %w", err)
+	}
+	if err := wc.Close(); err != nil {
+		return 0, time.Since(t0), fmt.Errorf("smtp: close DATA: %w", err)
+	}
+
+	return 250, time.Since(t0), nil
+}
+
+// extractAddr pulls the bare email out of a "Name <addr@host>" form.
+func extractAddr(s string) string {
+	if i, j := strings.LastIndex(s, "<"), strings.LastIndex(s, ">"); i >= 0 && j > i {
+		return s[i+1 : j]
+	}
+	return s
+}
+
+// buildEmailBody assembles the RFC 5322 message bytes per the spec.
+// Plain text only; subject hardcoded.
+func buildEmailBody(cfg SMTPConfig, msgIDDomain string, p Payload) []byte {
+	var b strings.Builder
+	b.WriteString("From: " + cfg.From + "\r\n")
+	b.WriteString("To: " + cfg.To + "\r\n")
+	b.WriteString(fmt.Sprintf("Subject: [restic-manager] [%s] %s: %s\r\n", p.Severity, p.HostName, p.Kind))
+	b.WriteString("Date: " + p.RaisedAt.UTC().Format(time.RFC1123Z) + "\r\n")
+	b.WriteString("Message-ID: <" + p.AlertID + "@" + msgIDDomain + ">\r\n")
+	b.WriteString("MIME-Version: 1.0\r\n")
+	b.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
+	b.WriteString("\r\n")
+	b.WriteString(p.Message + "\r\n\r\n")
+	b.WriteString("—\r\n")
+	b.WriteString("Raised at: " + p.RaisedAt.UTC().Format(time.RFC3339) + "\r\n")
+	b.WriteString("Severity:  " + p.Severity + "\r\n")
+	b.WriteString("Host:      " + p.HostName + "\r\n")
+	b.WriteString("Kind:      " + p.Kind + "\r\n")
+	if p.Link != "" {
+		b.WriteString("\r\nOpen in restic-manager:\r\n")
+		b.WriteString(p.Link + "\r\n")
+	}
+	b.WriteString("\r\n(This message was sent by restic-manager. Acknowledge or resolve in the UI.)\r\n")
+	return []byte(b.String())
+}