feat: add headless mode support for SSH -N connections

- use s.lifecycle.GetConnection().Wait() to block until SSH connection closes
- Prevent premature session closure in headless mode

In headless mode (ssh -N), there's no channel interaction to block on,
so the session would immediately return and close. Now blocking on
conn.Wait() keeps the session alive until the client disconnects.

session/session.go

@@ -9,6 +9,7 @@ import (
 	"tunnel_pls/session/interaction"
 	"tunnel_pls/session/lifecycle"
 	"tunnel_pls/session/slug"
+	"tunnel_pls/types"
 
 	"golang.org/x/crypto/ssh"
 )
@@ -87,31 +88,56 @@ func (s *SSHSession) Detail() Detail {
 }
 
 func (s *SSHSession) Start() error {
-	channel := <-s.sshReqChannel
-	ch, reqs, err := channel.Accept()
-	if err != nil {
-		log.Printf("failed to accept channel: %v", err)
-		return err
+	var channel ssh.NewChannel
+	var ok bool
+	select {
+	case channel, ok = <-s.sshReqChannel:
+		if !ok {
+			log.Println("Forwarding request channel closed")
+			return nil
+		}
+		ch, reqs, err := channel.Accept()
+		if err != nil {
+			log.Printf("failed to accept channel: %v", err)
+			return err
+		}
+		go s.HandleGlobalRequest(reqs)
+
+		s.lifecycle.SetChannel(ch)
+		s.interaction.SetChannel(ch)
+		s.interaction.SetMode(types.INTERACTIVE)
+	case <-time.After(500 * time.Millisecond):
+		s.interaction.SetMode(types.HEADLESS)
 	}
-	go s.HandleGlobalRequest(reqs)
 
 	tcpipReq := s.waitForTCPIPForward()
 	if tcpipReq == nil {
-		_, err := ch.Write([]byte(fmt.Sprintf("Port forwarding request not received. Ensure you ran the correct command with -R flag. Example: ssh %s -p %s -R 80:localhost:3000", config.Getenv("DOMAIN", "localhost"), config.Getenv("PORT", "2200"))))
+		err := s.interaction.Send(fmt.Sprintf("Port forwarding request not received. Ensure you ran the correct command with -R flag. Example: ssh %s -p %s -R 80:localhost:3000", config.Getenv("DOMAIN", "localhost"), config.Getenv("PORT", "2200")))
 		if err != nil {
 			return err
 		}
-		if err := s.lifecycle.Close(); err != nil {
+		if err = s.lifecycle.Close(); err != nil {
 			log.Printf("failed to close session: %v", err)
 		}
 		return fmt.Errorf("no forwarding Request")
 	}
 
-	s.lifecycle.SetChannel(ch)
-	s.interaction.SetChannel(ch)
+	if (s.interaction.GetMode() == types.HEADLESS && config.Getenv("MODE", "standalone") == "standalone") || s.lifecycle.GetUser() == "UNAUTHORIZED" {
+		if err := tcpipReq.Reply(false, nil); err != nil {
+			log.Printf("cannot reply to tcpip req: %s\n", err)
+			return err
+		}
+		if err := s.lifecycle.Close(); err != nil {
+			log.Printf("failed to close session: %v", err)
+			return err
+		}
+		return nil
+	}
 
 	s.HandleTCPIPForward(tcpipReq)
+	s.interaction.Start()
 
+	s.lifecycle.GetConnection().Wait()
 	if err := s.lifecycle.Close(); err != nil {
 		log.Printf("failed to close session: %v", err)
 		return err