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package mailer
import (
"context"
"crypto/tls"
"errors"
"fmt"
"log/slog"
"net"
"net/smtp"
"strings"
"time"
)
type Message struct {
ID string
Recipient string
Subject string
Body string
}
type Queue interface {
ClaimMail(context.Context) (Message, bool, error)
MarkMailSent(context.Context, string) error
MarkMailFailed(context.Context, string, error) error
}
type SMTPConfig struct {
Address string
Username string
Password string
FromName string
FromAddress string
TLSMode string
DialTimeout time.Duration
}
type Sender struct {
config SMTPConfig
}
func NewSender(config SMTPConfig) (*Sender, error) {
if strings.TrimSpace(config.Address) == "" || strings.TrimSpace(config.FromAddress) == "" {
return nil, errors.New("SMTP address and from address are required")
}
if config.DialTimeout <= 0 {
config.DialTimeout = 10 * time.Second
}
return &Sender{config: config}, nil
}
func (s *Sender) Send(ctx context.Context, message Message) error {
host, _, err := net.SplitHostPort(s.config.Address)
if err != nil {
return fmt.Errorf("parse SMTP address: %w", err)
}
dialer := net.Dialer{Timeout: s.config.DialTimeout}
var conn net.Conn
if s.config.TLSMode == "tls" {
conn, err = tls.DialWithDialer(&dialer, "tcp", s.config.Address, &tls.Config{MinVersion: tls.VersionTLS12, ServerName: host})
} else {
conn, err = dialer.DialContext(ctx, "tcp", s.config.Address)
}
if err != nil {
return fmt.Errorf("connect SMTP: %w", err)
}
defer conn.Close()
client, err := smtp.NewClient(conn, host)
if err != nil {
return fmt.Errorf("open SMTP client: %w", err)
}
defer client.Close()
if s.config.TLSMode == "starttls" {
if ok, _ := client.Extension("STARTTLS"); !ok {
return errors.New("SMTP server does not support required STARTTLS")
}
if err := client.StartTLS(&tls.Config{MinVersion: tls.VersionTLS12, ServerName: host}); err != nil {
return fmt.Errorf("start SMTP TLS: %w", err)
}
}
if s.config.Username != "" {
if ok, _ := client.Extension("AUTH"); !ok {
return errors.New("SMTP server does not support authentication")
}
if err := client.Auth(smtp.PlainAuth("", s.config.Username, s.config.Password, host)); err != nil {
return fmt.Errorf("authenticate SMTP: %w", err)
}
}
if err := client.Mail(s.config.FromAddress); err != nil {
return fmt.Errorf("set SMTP sender: %w", err)
}
if err := client.Rcpt(message.Recipient); err != nil {
return fmt.Errorf("set SMTP recipient: %w", err)
}
w, err := client.Data()
if err != nil {
return fmt.Errorf("start SMTP body: %w", err)
}
from := s.config.FromAddress
if name := cleanHeader(s.config.FromName); name != "" {
from = fmt.Sprintf("%s <%s>", name, s.config.FromAddress)
}
body := strings.ReplaceAll(message.Body, "\r\n", "\n")
body = strings.ReplaceAll(body, "\n", "\r\n")
_, writeErr := fmt.Fprintf(w, "From: %s\r\nTo: %s\r\nSubject: %s\r\nMIME-Version: 1.0\r\nContent-Type: text/plain; charset=UTF-8\r\nContent-Transfer-Encoding: 8bit\r\n\r\n%s\r\n",
from, cleanHeader(message.Recipient), cleanHeader(message.Subject), body)
closeErr := w.Close()
if writeErr != nil {
return fmt.Errorf("write SMTP body: %w", writeErr)
}
if closeErr != nil {
return fmt.Errorf("finish SMTP body: %w", closeErr)
}
if err := client.Quit(); err != nil {
return fmt.Errorf("finish SMTP session: %w", err)
}
return nil
}
func cleanHeader(value string) string {
value = strings.ReplaceAll(value, "\r", "")
return strings.ReplaceAll(value, "\n", "")
}
type Worker struct {
queue Queue
sender *Sender
logger *slog.Logger
}
func NewWorker(queue Queue, sender *Sender, logger *slog.Logger) *Worker {
if logger == nil {
logger = slog.Default()
}
return &Worker{queue: queue, sender: sender, logger: logger}
}
func (w *Worker) Run(ctx context.Context) {
ticker := time.NewTicker(3 * time.Second)
defer ticker.Stop()
for {
w.drain(ctx)
select {
case <-ctx.Done():
return
case <-ticker.C:
}
}
}
func (w *Worker) drain(ctx context.Context) {
for i := 0; i < 20 && ctx.Err() == nil; i++ {
message, ok, err := w.queue.ClaimMail(ctx)
if err != nil {
w.logger.Warn("mail_outbox_claim_failed", "error", err)
return
}
if !ok {
return
}
if err := w.sender.Send(ctx, message); err != nil {
_ = w.queue.MarkMailFailed(ctx, message.ID, err)
w.logger.Warn("mail_delivery_failed", "message_id", message.ID, "error", err)
continue
}
if err := w.queue.MarkMailSent(ctx, message.ID); err != nil {
w.logger.Warn("mail_outbox_complete_failed", "message_id", message.ID, "error", err)
}
}
}
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