feat: Move mail system to shared

2026-07-28 09:50:46 +01:00
parent 5e326335af
commit a232c74990
49 changed files with 1206 additions and 706 deletions
@@ -0,0 +1,241 @@
+// Package mail is the one email system for every Vantage service.
+//
+// It owns three things that used to exist in three copies: the SMTP
+// conversation (including the 465-implicit-TLS case that net/smtp gets wrong),
+// the RFC 5322 envelope, and the rendered look of a Vantage email. Callers see
+// only typed Send* methods — nobody outside this package builds a subject line,
+// a MIME part or a colour.
+package mail
+
+import (
+	"crypto/rand"
+	"crypto/tls"
+	"encoding/hex"
+	"fmt"
+	"mime"
+	"mime/multipart"
+	"net"
+	"net/smtp"
+	"net/textproto"
+	"os"
+	"strings"
+	"time"
+)
+
+// timeout bounds the whole SMTP conversation. Without it a mail server that
+// accepts the connection and then stalls holds an HTTP request open until the
+// client gives up — and admin's signup rollback runs on that request's context.
+const timeout = 15 * time.Second
+
+// Sender is a configured SMTP destination. It is a value, not a singleton:
+// server/internal/notify builds one per notification channel from data in
+// Mongo, while admin and sitesvc build one at boot.
+type Sender struct {
+	Host     string
+	Port     string
+	From     string
+	Username string
+	Password string
+
+	// PublicURL is the browser origin used to build links in messages that
+	// carry one (verification, invitations). Empty is fine for senders that
+	// never send those, such as a monitor notification channel.
+	PublicURL string
+}
+
+// FromEnv reads the standard SMTP_* variables. Used by services configured
+// straight from the environment; admin builds its Sender from its own config
+// struct instead.
+func FromEnv() Sender {
+	return Sender{
+		Host:     os.Getenv("SMTP_HOST"),
+		Port:     envOr("SMTP_PORT", "587"),
+		Username: os.Getenv("SMTP_USERNAME"),
+		Password: os.Getenv("SMTP_PASSWORD"),
+		From:     os.Getenv("SMTP_FROM"),
+	}
+}
+
+func envOr(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+// Enabled reports whether this Sender can deliver anything at all. Callers
+// check it to degrade politely rather than logging a failure per message.
+func (s Sender) Enabled() bool { return s.Host != "" && s.From != "" }
+
+// message is one rendered email, ready to be put on the wire.
+type message struct {
+	To      string // one address, or a comma-separated list
+	ReplyTo string
+	Subject string
+	HTML    string
+	Text    string
+}
+
+// sendTemplate renders name against data and delivers the result.
+func (s Sender) sendTemplate(to, replyTo, name string, data any) error {
+	m, err := render(name, data)
+	if err != nil {
+		return fmt.Errorf("mail: render %s: %w", name, err)
+	}
+	m.To = to
+	m.ReplyTo = replyTo
+	return s.send(m)
+}
+
+// send delivers one message.
+//
+// Port 465 is implicit TLS: the server expects a TLS handshake immediately, so
+// the connection is wrapped BEFORE any SMTP is spoken. Every other port gets
+// plaintext then STARTTLS if offered. net/smtp.SendMail only does the latter,
+// which is why it fails against a 465 mail server — that bug silently stopped
+// every admin email from being delivered once already.
+func (s Sender) send(m message) error {
+	if !s.Enabled() {
+		return fmt.Errorf("smtp: not configured")
+	}
+	rcpts := recipients(m.To)
+	if len(rcpts) == 0 {
+		return fmt.Errorf("smtp: no recipient")
+	}
+
+	addr := net.JoinHostPort(s.Host, s.Port)
+	conn, err := net.DialTimeout("tcp", addr, timeout)
+	if err != nil {
+		return fmt.Errorf("smtp: dial %s: %w", addr, err)
+	}
+	_ = conn.SetDeadline(time.Now().Add(timeout))
+
+	if s.Port == "465" {
+		conn = tls.Client(conn, &tls.Config{ServerName: s.Host})
+	}
+
+	client, err := smtp.NewClient(conn, s.Host)
+	if err != nil {
+		conn.Close()
+		return fmt.Errorf("smtp: client: %w", err)
+	}
+	defer client.Close()
+
+	if s.Port != "465" {
+		if ok, _ := client.Extension("STARTTLS"); ok {
+			if err := client.StartTLS(&tls.Config{ServerName: s.Host}); err != nil {
+				return fmt.Errorf("smtp: starttls: %w", err)
+			}
+		}
+	}
+
+	if s.Username != "" {
+		if err := client.Auth(smtp.PlainAuth("", s.Username, s.Password, s.Host)); err != nil {
+			return fmt.Errorf("smtp: auth: %w", err)
+		}
+	}
+
+	if err := client.Mail(s.From); err != nil {
+		return fmt.Errorf("smtp: mail from: %w", err)
+	}
+	for _, rcpt := range rcpts {
+		if err := client.Rcpt(rcpt); err != nil {
+			return fmt.Errorf("smtp: rcpt %s: %w", rcpt, err)
+		}
+	}
+
+	body, err := s.envelope(m)
+	if err != nil {
+		return fmt.Errorf("smtp: build message: %w", err)
+	}
+
+	w, err := client.Data()
+	if err != nil {
+		return fmt.Errorf("smtp: data: %w", err)
+	}
+	if _, err := w.Write(body); err != nil {
+		return fmt.Errorf("smtp: write: %w", err)
+	}
+	if err := w.Close(); err != nil {
+		return fmt.Errorf("smtp: close data: %w", err)
+	}
+	return client.Quit()
+}
+
+func recipients(to string) []string {
+	parts := strings.Split(to, ",")
+	out := make([]string, 0, len(parts))
+	for _, p := range parts {
+		if p = strings.TrimSpace(p); p != "" {
+			out = append(out, p)
+		}
+	}
+	return out
+}
+
+// envelope builds the RFC 5322 message as multipart/alternative.
+//
+// Date and Message-ID are not decoration: a message without them is scored as
+// spam by most filters, which is its own way of "the email never arrived". A
+// text part is sent beside every HTML one for the same reason, and because a
+// client that refuses HTML should not receive a blank message. Header values
+// are stripped of CR and LF so a crafted instance name cannot inject headers.
+func (s Sender) envelope(m message) ([]byte, error) {
+	var parts strings.Builder
+	w := multipart.NewWriter(&parts)
+
+	textPart, err := w.CreatePart(textproto.MIMEHeader{
+		"Content-Type": {"text/plain; charset=utf-8"},
+	})
+	if err != nil {
+		return nil, err
+	}
+	if _, err := textPart.Write([]byte(m.Text)); err != nil {
+		return nil, err
+	}
+
+	htmlPart, err := w.CreatePart(textproto.MIMEHeader{
+		"Content-Type": {"text/html; charset=utf-8"},
+	})
+	if err != nil {
+		return nil, err
+	}
+	if _, err := htmlPart.Write([]byte(m.HTML)); err != nil {
+		return nil, err
+	}
+
+	if err := w.Close(); err != nil {
+		return nil, err
+	}
+
+	var b strings.Builder
+	b.WriteString("From: " + sanitizeHeader(s.From) + "\r\n")
+	b.WriteString("To: " + sanitizeHeader(m.To) + "\r\n")
+	if m.ReplyTo != "" {
+		b.WriteString("Reply-To: " + sanitizeHeader(m.ReplyTo) + "\r\n")
+	}
+	b.WriteString("Date: " + time.Now().Format(time.RFC1123Z) + "\r\n")
+	b.WriteString("Message-ID: " + messageID(s.From) + "\r\n")
+	b.WriteString("Subject: " + mime.QEncoding.Encode("utf-8", sanitizeHeader(m.Subject)) + "\r\n")
+	b.WriteString("MIME-Version: 1.0\r\n")
+	b.WriteString("Content-Type: multipart/alternative; boundary=" + w.Boundary() + "\r\n")
+	b.WriteString("\r\n")
+	b.WriteString(parts.String())
+	return []byte(b.String()), nil
+}
+
+func messageID(from string) string {
+	domain := "vantage.local"
+	if at := strings.LastIndex(from, "@"); at >= 0 && at < len(from)-1 {
+		domain = strings.Trim(from[at+1:], "<> ")
+	}
+	var buf [16]byte
+	if _, err := rand.Read(buf[:]); err != nil {
+		return fmt.Sprintf("<%d@%s>", time.Now().UnixNano(), domain)
+	}
+	return fmt.Sprintf("<%s@%s>", hex.EncodeToString(buf[:]), domain)
+}
+
+func sanitizeHeader(v string) string {
+	return strings.NewReplacer("\r", " ", "\n", " ").Replace(v)
+}