[client,management] Rewrite the SSH feature (#4015)

client/ssh/detection/detection.go

@@ -0,0 +1,99 @@
+package detection
+
+import (
+	"bufio"
+	"context"
+	"net"
+	"strconv"
+	"strings"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	// ServerIdentifier is the base response for NetBird SSH servers
+	ServerIdentifier = "NetBird-SSH-Server"
+	// ProxyIdentifier is the base response for NetBird SSH proxy
+	ProxyIdentifier = "NetBird-SSH-Proxy"
+	// JWTRequiredMarker is appended to responses when JWT is required
+	JWTRequiredMarker = "NetBird-JWT-Required"
+
+	// Timeout is the timeout for SSH server detection
+	Timeout = 5 * time.Second
+)
+
+type ServerType string
+
+const (
+	ServerTypeNetBirdJWT   ServerType = "netbird-jwt"
+	ServerTypeNetBirdNoJWT ServerType = "netbird-no-jwt"
+	ServerTypeRegular      ServerType = "regular"
+)
+
+// Dialer provides network connection capabilities
+type Dialer interface {
+	DialContext(ctx context.Context, network, address string) (net.Conn, error)
+}
+
+// RequiresJWT checks if the server type requires JWT authentication
+func (s ServerType) RequiresJWT() bool {
+	return s == ServerTypeNetBirdJWT
+}
+
+// ExitCode returns the exit code for the detect command
+func (s ServerType) ExitCode() int {
+	switch s {
+	case ServerTypeNetBirdJWT:
+		return 0
+	case ServerTypeNetBirdNoJWT:
+		return 1
+	case ServerTypeRegular:
+		return 2
+	default:
+		return 2
+	}
+}
+
+// DetectSSHServerType detects SSH server type using the provided dialer
+func DetectSSHServerType(ctx context.Context, dialer Dialer, host string, port int) (ServerType, error) {
+	targetAddr := net.JoinHostPort(host, strconv.Itoa(port))
+
+	conn, err := dialer.DialContext(ctx, "tcp", targetAddr)
+	if err != nil {
+		log.Debugf("SSH connection failed for detection: %v", err)
+		return ServerTypeRegular, nil
+	}
+	defer conn.Close()
+
+	if err := conn.SetReadDeadline(time.Now().Add(Timeout)); err != nil {
+		log.Debugf("set read deadline: %v", err)
+		return ServerTypeRegular, nil
+	}
+
+	reader := bufio.NewReader(conn)
+	serverBanner, err := reader.ReadString('\n')
+	if err != nil {
+		log.Debugf("read SSH banner: %v", err)
+		return ServerTypeRegular, nil
+	}
+
+	serverBanner = strings.TrimSpace(serverBanner)
+	log.Debugf("SSH server banner: %s", serverBanner)
+
+	if !strings.HasPrefix(serverBanner, "SSH-") {
+		log.Debugf("Invalid SSH banner")
+		return ServerTypeRegular, nil
+	}
+
+	if !strings.Contains(serverBanner, ServerIdentifier) {
+		log.Debugf("Server banner does not contain identifier '%s'", ServerIdentifier)
+		return ServerTypeRegular, nil
+	}
+
+	if strings.Contains(serverBanner, JWTRequiredMarker) {
+		return ServerTypeNetBirdJWT, nil
+	}
+
+	return ServerTypeNetBirdNoJWT, nil
+}