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|
package smtpclient
import (
"bufio"
"context"
"crypto/tls"
"fmt"
"io"
"net"
"net/textproto"
"strings"
"time"
)
type DialContextFunc func(ctx context.Context, network, address string) (net.Conn, error)
type Config struct {
Host string
Port int
Recipient string
EnvelopeFrom string
HELO string
TLSServerName string
RequireTLS bool
ImplicitTLS bool
Timeout time.Duration
DryRun bool
}
type Client struct {
cfg Config
dial DialContextFunc
}
type Message struct {
EnvelopeFrom string
Raw string
}
func New(cfg Config, dial DialContextFunc) *Client {
return &Client{cfg: cfg, dial: dial}
}
func (c *Client) Send(ctx context.Context, msg Message) error {
if c.cfg.DryRun {
return nil
}
if c.dial == nil {
c.dial = (&net.Dialer{}).DialContext
}
timeout := c.cfg.Timeout
if timeout <= 0 {
timeout = 90 * time.Second
}
ctx, cancel := context.WithTimeout(ctx, timeout)
defer cancel()
addr := net.JoinHostPort(c.cfg.Host, fmt.Sprintf("%d", c.cfg.Port))
conn, err := c.dial(ctx, "tcp", addr)
if err != nil {
return fmt.Errorf("dial smtp: %w", err)
}
defer conn.Close()
if deadline, ok := ctx.Deadline(); ok {
_ = conn.SetDeadline(deadline)
}
if c.cfg.ImplicitTLS {
tlsConn := tls.Client(conn, &tls.Config{
ServerName: c.cfg.TLSServerName,
MinVersion: tls.VersionTLS12,
})
if err := tlsConn.HandshakeContext(ctx); err != nil {
return fmt.Errorf("implicit tls handshake: %w", err)
}
conn = tlsConn
}
session := newSession(conn)
if _, _, err := session.read(220); err != nil {
return fmt.Errorf("smtp greeting: %w", err)
}
if err := session.ehlo(c.cfg.HELO); err != nil {
return err
}
if c.cfg.RequireTLS && !c.cfg.ImplicitTLS {
if _, _, err := session.cmd(220, "STARTTLS\r\n"); err != nil {
return fmt.Errorf("starttls: %w", err)
}
tlsConn := tls.Client(conn, &tls.Config{
ServerName: c.cfg.TLSServerName,
MinVersion: tls.VersionTLS12,
})
if err := tlsConn.HandshakeContext(ctx); err != nil {
return fmt.Errorf("tls handshake: %w", err)
}
session = newSession(tlsConn)
if err := session.ehlo(c.cfg.HELO); err != nil {
return err
}
}
envelopeFrom := sanitizeEnvelope(c.cfg.EnvelopeFrom)
if envelopeFrom == "" {
envelopeFrom = sanitizeEnvelope(msg.EnvelopeFrom)
}
if _, _, err := session.cmd(250, "MAIL FROM:<%s>\r\n", envelopeFrom); err != nil {
return fmt.Errorf("mail from rejected: %w", err)
}
if _, _, err := session.cmd(250, "RCPT TO:<%s>\r\n", sanitizeEnvelope(c.cfg.Recipient)); err != nil {
return fmt.Errorf("rcpt to rejected: %w", err)
}
if _, _, err := session.cmd(354, "DATA\r\n"); err != nil {
return fmt.Errorf("data rejected: %w", err)
}
if err := writeSMTPData(session.w, msg.Raw); err != nil {
return err
}
if _, _, err := session.read(250); err != nil {
return fmt.Errorf("message rejected: %w", err)
}
_, _, _ = session.cmd(221, "QUIT\r\n")
return nil
}
type session struct {
conn net.Conn
tp *textproto.Reader
w *bufio.Writer
}
func newSession(conn net.Conn) *session {
reader := bufio.NewReader(conn)
return &session{
conn: conn,
tp: textproto.NewReader(reader),
w: bufio.NewWriter(conn),
}
}
func (s *session) ehlo(helo string) error {
if helo == "" {
helo = "n2usenet.local"
}
if _, _, err := s.cmd(250, "EHLO %s\r\n", sanitizeAtom(helo)); err != nil {
if _, _, heloErr := s.cmd(250, "HELO %s\r\n", sanitizeAtom(helo)); heloErr != nil {
return fmt.Errorf("ehlo failed: %w", err)
}
}
return nil
}
func (s *session) cmd(expect int, format string, args ...any) (int, string, error) {
if _, err := fmt.Fprintf(s.w, format, args...); err != nil {
return 0, "", err
}
if err := s.w.Flush(); err != nil {
return 0, "", err
}
return s.read(expect)
}
func (s *session) read(expect int) (int, string, error) {
code, msg, err := s.tp.ReadResponse(expect)
if err != nil {
return code, msg, err
}
return code, msg, nil
}
func writeSMTPData(w *bufio.Writer, raw string) error {
raw = strings.ReplaceAll(raw, "\r\n", "\n")
raw = strings.ReplaceAll(raw, "\r", "\n")
for _, line := range strings.Split(raw, "\n") {
if strings.HasPrefix(line, ".") {
line = "." + line
}
if _, err := io.WriteString(w, line+"\r\n"); err != nil {
return fmt.Errorf("write smtp data: %w", err)
}
}
if _, err := io.WriteString(w, ".\r\n"); err != nil {
return fmt.Errorf("write smtp terminator: %w", err)
}
if err := w.Flush(); err != nil {
return fmt.Errorf("flush smtp data: %w", err)
}
return nil
}
func sanitizeEnvelope(v string) string {
v = strings.TrimSpace(v)
v = strings.ReplaceAll(v, "\r", "")
v = strings.ReplaceAll(v, "\n", "")
v = strings.Trim(v, "<>")
return v
}
func sanitizeAtom(v string) string {
v = strings.TrimSpace(v)
v = strings.ReplaceAll(v, "\r", "")
v = strings.ReplaceAll(v, "\n", "")
if v == "" {
return "n2usenet.local"
}
return v
}
|
