1 files changed, 139 insertions, 0 deletions
diff --git a/internal/smtpclient/client.go b/internal/smtpclient/client.go
new file mode 100644
index 0000000..e294323
--- /dev/null
+++ b/internal/smtpclient/client.go
@@ -0,0 +1,139 @@
+// 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
+}