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// Package smtpclient sends classic RFC 5322 messages to mail2news gateways.
package smtpclient
import (
"crypto/tls"
"errors"
"fmt"
"net"
"net/mail"
"net/smtp"
"strings"
"time"
"golang.org/x/net/proxy"
)
type Config struct {
Host string
Port string
Mode string
Username string
Password string
InsecureSkipVerify bool
ProxyType string
ProxyAddress string
Timeout time.Duration
}
func Send(cfg Config, from string, recipients []string, message []byte) error {
if err := validate(cfg, from, recipients); err != nil {
return err
}
timeout := cfg.Timeout
if timeout <= 0 {
timeout = 30 * time.Second
}
target := net.JoinHostPort(cfg.Host, cfg.Port)
dialer := &net.Dialer{Timeout: timeout, KeepAlive: 30 * time.Second}
var conn net.Conn
var err error
if strings.EqualFold(cfg.ProxyType, "SOCKS5") {
socks, proxyErr := proxy.SOCKS5("tcp", cfg.ProxyAddress, nil, dialer)
if proxyErr != nil {
return fmt.Errorf("configure SMTP SOCKS5 proxy: %w", proxyErr)
}
conn, err = socks.Dial("tcp", target)
} else {
conn, err = dialer.Dial("tcp", target)
}
if err != nil {
return fmt.Errorf("connect SMTP server: %w", err)
}
defer conn.Close()
tlsConfig := &tls.Config{ServerName: cfg.Host, MinVersion: tls.VersionTLS12, InsecureSkipVerify: cfg.InsecureSkipVerify} // #nosec G402, explicit user opt-in
if strings.EqualFold(cfg.Mode, "TLS") {
tlsConn := tls.Client(conn, tlsConfig)
if err := tlsConn.Handshake(); err != nil {
return fmt.Errorf("SMTP TLS handshake: %w", err)
}
conn = tlsConn
}
client, err := smtp.NewClient(conn, cfg.Host)
if err != nil {
return fmt.Errorf("initialize SMTP client: %w", err)
}
defer client.Close()
if strings.EqualFold(cfg.Mode, "STARTTLS") {
if ok, _ := client.Extension("STARTTLS"); !ok {
return errors.New("SMTP server does not advertise STARTTLS")
}
if err := client.StartTLS(tlsConfig); err != nil {
return fmt.Errorf("SMTP STARTTLS: %w", err)
}
}
if cfg.Username != "" {
state, ok := client.TLSConnectionState()
if !ok || !state.HandshakeComplete {
return errors.New("SMTP authentication requires TLS")
}
if err := client.Auth(smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)); err != nil {
return fmt.Errorf("SMTP authentication: %w", err)
}
}
if err := client.Mail(from); err != nil {
return fmt.Errorf("SMTP MAIL FROM: %w", err)
}
for _, recipient := range recipients {
if err := client.Rcpt(recipient); err != nil {
return fmt.Errorf("SMTP RCPT TO: %w", err)
}
}
writer, err := client.Data()
if err != nil {
return fmt.Errorf("SMTP DATA: %w", err)
}
if _, err := writer.Write(message); err != nil {
_ = writer.Close()
return fmt.Errorf("write SMTP message: %w", err)
}
if err := writer.Close(); err != nil {
return fmt.Errorf("finish SMTP message: %w", err)
}
return client.Quit()
}
func validate(cfg Config, from string, recipients []string) error {
if strings.TrimSpace(cfg.Host) == "" || strings.TrimSpace(cfg.Port) == "" {
return errors.New("SMTP host and port are required")
}
if cfg.Mode != "" && cfg.Mode != "TLS" && cfg.Mode != "STARTTLS" {
return errors.New("SMTP mode must be cleartext, TLS or STARTTLS")
}
if cfg.ProxyType != "DIRECT" && cfg.ProxyType != "SOCKS5" {
return errors.New("SMTP proxy type must be DIRECT or SOCKS5")
}
if strings.HasSuffix(strings.ToLower(cfg.Host), ".onion") && cfg.ProxyType != "SOCKS5" {
return errors.New(".onion SMTP server requires SOCKS5")
}
if cfg.ProxyType == "SOCKS5" {
if _, _, err := net.SplitHostPort(cfg.ProxyAddress); err != nil {
return fmt.Errorf("invalid SMTP SOCKS5 address: %w", err)
}
}
if cfg.Username != "" && cfg.Mode == "" {
return errors.New("SMTP authentication requires TLS or STARTTLS")
}
if _, err := mail.ParseAddress(from); err != nil {
return fmt.Errorf("invalid SMTP sender: %w", err)
}
if len(recipients) == 0 {
return errors.New("at least one SMTP recipient is required")
}
for _, recipient := range recipients {
if _, err := mail.ParseAddress(recipient); err != nil {
return fmt.Errorf("invalid SMTP recipient: %w", err)
}
}
return nil
}
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