// any time the server needs access to the dataset, it gets a "GuardedDataset" which allows us to
  // add caching
  // optionally, a session may be established, which allows us to reserve the dataset for that
  // session.
  protected GuardedDataset getDataset(ReqState preq) throws Exception {
    HttpServletRequest req = preq.getRequest();
    String reqPath = preq.getDataSet();

    // see if the client wants sessions
    boolean acceptSession = false;
    String s = req.getHeader("X-Accept-Session");
    if (s != null && s.equalsIgnoreCase("true") && allowSessions) acceptSession = true;

    HttpSession session = null;
    if (acceptSession) {
      // see if theres already a session established, create one if not
      session = req.getSession();
      if (!session.isNew()) {
        GuardedDataset gdataset = (GuardedDataset) session.getAttribute(reqPath);
        if (null != gdataset) {
          if (debugSession)
            System.out.printf(" found gdataset %s in session %s %n", reqPath, session.getId());
          if (log.isDebugEnabled())
            log.debug(" found gdataset " + gdataset + " in session " + session.getId());
          return gdataset;
        }
      }
    }

    NetcdfFile ncd = DatasetHandler.getNetcdfFile(req, preq.getResponse(), reqPath);
    if (null == ncd) return null;

    GuardedDataset gdataset = new GuardedDatasetCacheAndClone(reqPath, ncd, acceptSession);
    // GuardedDataset gdataset = new GuardedDatasetImpl(reqPath, ncd, acceptSession);

    if (acceptSession) {
      String cookiePath = req.getRequestURI();
      String suffix = "." + preq.getRequestSuffix();
      if (cookiePath.endsWith(suffix)) // snip off the suffix
      cookiePath = cookiePath.substring(0, cookiePath.length() - suffix.length());
      session.setAttribute(reqPath, gdataset);
      session.setAttribute(CookieFilter.SESSION_PATH, cookiePath);
      // session.setAttribute("dataset", ncd.getLocation());  // for UsageValve
      // session.setMaxInactiveInterval(30); // 30 second timeout !!
      if (debugSession)
        System.out.printf(
            " added gdataset %s in session %s cookiePath %s %n",
            reqPath, session.getId(), cookiePath);
      if (log.isDebugEnabled())
        log.debug(" added gdataset " + gdataset + " in session " + session.getId());
    } /* else {
        session = req.getSession();
        session.setAttribute("dataset", ncd.getLocation()); // for UsageValve
      } */

    return gdataset;
  }
  private void doClose(ReqState rs) throws Exception {
    HttpServletResponse response = rs.getResponse();
    HttpServletRequest request = rs.getRequest();
    String reqPath = rs.getDataSet();
    HttpSession session = request.getSession();
    session.removeAttribute(reqPath); // work done in the listener

    response.setHeader("XDODS-Server", getServerVersion()); // needed by client

    /* if (path.endsWith(".close")) {
      closeSession(request, response);
      response.setContentLength(0);
      log.info("doGet(): " + UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_OK, 0));
      return;

    }

    // so we need to worry about deleting sessions?
    session.invalidate();  */
  }
  public void doGetHTML(ReqState rs) throws Exception {
    HttpServletResponse response = rs.getResponse();
    HttpServletRequest request = rs.getRequest();
    GuardedDataset ds = null;
    try {
      ds = getDataset(rs);
      if (ds == null) return;

      response.setHeader("XDODS-Server", getServerVersion());
      response.setContentType("text/html");
      response.setHeader("Content-Description", "dods-form");

      // Utilize the getDDS() method to get	a parsed and populated DDS
      // for this server.
      ServerDDS myDDS = ds.getDDS();
      DAS das = ds.getDAS();
      GetHTMLInterfaceHandler2 di = new GetHTMLInterfaceHandler2();
      di.sendDataRequestForm(request, response, rs.getDataSet(), myDDS, das);

    } finally { // release lock if needed
      if (ds != null) ds.release();
    }
  }
  public void doGet(HttpServletRequest request, HttpServletResponse response) {
    log.info("doGet(): " + UsageLog.setupRequestContext(request));
    // System.out.printf("opendap doGet: req=%s%n%s%n", ServletUtil.getRequest(request),
    // ServletUtil.showRequestDetail(this, request));

    String path = null;

    ReqState rs = getRequestState(request, response);

    try {
      path = request.getPathInfo();
      log.debug("doGet path={}", path);

      if (thredds.servlet.Debug.isSet("showRequestDetail"))
        log.debug(ServletUtil.showRequestDetail(this, request));

      if (path == null) {
        log.info(
            "doGet(): "
                + UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_NOT_FOUND, -1));
        response.sendError(HttpServletResponse.SC_NOT_FOUND);
        return;
      }

      if (baseURI == null) { // first time, set baseURI
        URI reqURI = ServletUtil.getRequestURI(request);
        // Build base URI from request (rather than hard-coding "/thredds/dodsC/").
        String baseUriString = request.getContextPath() + request.getServletPath() + "/";
        baseURI = reqURI.resolve(baseUriString);
        log.debug("doGet(): baseURI was set = {}", baseURI);
      }

      if (path.endsWith("latest.xml")) {
        DataRootHandler.getInstance().processReqForLatestDataset(this, request, response);
        return;
      }

      // Redirect all catalog requests at the root level.
      if (path.equals("/") || path.equals("/catalog.html") || path.equals("/catalog.xml")) {
        ServletUtil.sendPermanentRedirect(ServletUtil.getContextPath() + path, request, response);
        return;
      }

      // Make sure catalog requests match a dataRoot before trying to handle.
      if (path.endsWith("/") || path.endsWith("/catalog.html") || path.endsWith("/catalog.xml")) {
        if (!DataRootHandler.getInstance().hasDataRootMatch(path)) {
          log.info(
              "doGet(): "
                  + UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_NOT_FOUND, -1));
          response.sendError(HttpServletResponse.SC_NOT_FOUND);
          return;
        }

        if (!DataRootHandler.getInstance().processReqForCatalog(request, response))
          log.error(
              "doGet(): "
                  + UsageLog.closingMessageForRequestContext(
                      ServletUtil.STATUS_FORWARD_FAILURE, -1));

        return;
      }

      if (rs != null) {
        String dataSet = rs.getDataSet();
        String requestSuffix = rs.getRequestSuffix();

        if ((dataSet == null) || dataSet.equals("/") || dataSet.equals("")) {
          doGetDIR(rs);
        } else if (requestSuffix.equalsIgnoreCase("blob")) {
          doGetBLOB(rs);
        } else if (requestSuffix.equalsIgnoreCase("close")) {
          doClose(rs);
        } else if (requestSuffix.equalsIgnoreCase("dds")) {
          doGetDDS(rs);
        } else if (requestSuffix.equalsIgnoreCase("das")) {
          doGetDAS(rs);
        } else if (requestSuffix.equalsIgnoreCase("ddx")) {
          doGetDDX(rs);
        } else if (requestSuffix.equalsIgnoreCase("dods")) {
          doGetDAP2Data(rs);
        } else if (requestSuffix.equalsIgnoreCase("asc")
            || requestSuffix.equalsIgnoreCase("ascii")) {
          doGetASC(rs);
        } else if (requestSuffix.equalsIgnoreCase("info")) {
          doGetINFO(rs);
        } else if (requestSuffix.equalsIgnoreCase("html")
            || requestSuffix.equalsIgnoreCase("htm")) {
          doGetHTML(rs);
        } else if (requestSuffix.equalsIgnoreCase("ver")
            || requestSuffix.equalsIgnoreCase("version")
            || dataSet.equalsIgnoreCase("/version")
            || dataSet.equalsIgnoreCase("/version/")) {
          doGetVER(rs);
        } else if (dataSet.equalsIgnoreCase("/help")
            || dataSet.equalsIgnoreCase("/help/")
            || dataSet.equalsIgnoreCase("/" + requestSuffix)
            || requestSuffix.equalsIgnoreCase("help")) {
          doGetHELP(rs);
        } else {
          sendErrorResponse(response, HttpServletResponse.SC_BAD_REQUEST, "Unrecognized request");
          return;
        }

      } else {
        sendErrorResponse(response, HttpServletResponse.SC_BAD_REQUEST, "Unrecognized request");
        return;
      }

      log.info(UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_OK, -1));

      // plain ol' 404
    } catch (FileNotFoundException e) {
      sendErrorResponse(response, HttpServletResponse.SC_NOT_FOUND, e.getMessage());

      // DAP2Exception bad url
    } catch (BadURLException e) {
      log.info(UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_BAD_REQUEST, -1));
      response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
      dap2ExceptionHandler(e, rs);

      // all other DAP2Exception
    } catch (DAP2Exception de) {
      int status =
          (de.getErrorCode() == DAP2Exception.NO_SUCH_FILE)
              ? HttpServletResponse.SC_NOT_FOUND
              : HttpServletResponse.SC_BAD_REQUEST;
      if ((de.getErrorCode() != DAP2Exception.NO_SUCH_FILE) && (de.getErrorMessage() != null))
        log.debug(de.getErrorMessage());
      log.info(UsageLog.closingMessageForRequestContext(status, -1));
      response.setStatus(status);
      dap2ExceptionHandler(de, rs);

      // parsing, usually the CE
    } catch (ParseException pe) {
      log.info(UsageLog.closingMessageForRequestContext(HttpServletResponse.SC_BAD_REQUEST, -1));
      response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
      parseExceptionHandler(pe, response);

      // 403 - request too big
    } catch (UnsupportedOperationException e) {
      sendErrorResponse(response, HttpServletResponse.SC_FORBIDDEN, e.getMessage());

    } catch (java.net.SocketException e) {
      log.info("SocketException: " + e.getMessage(), e);
      log.info(UsageLog.closingMessageForRequestContext(ServletUtil.STATUS_CLIENT_ABORT, -1));

    } catch (IOException e) {
      String eName =
          e.getClass().getName(); // dont want compile time dependency on ClientAbortException
      if (eName.equals("org.apache.catalina.connector.ClientAbortException")) {
        log.debug("ClientAbortException: " + e.getMessage());
        log.info(UsageLog.closingMessageForRequestContext(ServletUtil.STATUS_CLIENT_ABORT, -1));
        return;
      }

      log.error("path= " + path, e);
      sendErrorResponse(response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e.getMessage());

      // everything else
    } catch (Throwable t) {
      log.error("path= " + path, t);
      t.printStackTrace();
      sendErrorResponse(response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, t.getMessage());
    }
  }