content: /**
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   * <p>
   * http://www.apache.org/licenses/LICENSE-2.0
   * <p>
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.atlas.web.filters;
  
  import org.apache.atlas.web.service.ActiveInstanceState;
  import org.apache.atlas.web.service.ServiceState;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.springframework.stereotype.Component;
  import org.springframework.web.util.UriUtils;
  
  import javax.inject.Inject;
  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.ws.rs.HttpMethod;
  import javax.ws.rs.core.HttpHeaders;
  
  import java.io.IOException;
  
  /**
   * A servlet {@link Filter} that redirects web requests from a passive Atlas server instance to an active one.
   *
   * All requests to an active instance pass through. Requests received by a passive instance are redirected
   * by identifying the currently active server. Requests to servers which are in transition are returned with
   * an error SERVICE_UNAVAILABLE. Identification of this state is carried out using
   * {@link ServiceState} and {@link ActiveInstanceState}.
   */
  @Component
  public class ActiveServerFilter implements Filter {
      private static final Logger LOG = LoggerFactory.getLogger(ActiveServerFilter.class);
  
      private static final String MIGRATION_STATUS_STATIC_PAGE = "migration-status.html";
  
      private final String[]            adminUriNotFiltered = {"/admin/export", "/admin/import", "/admin/importfile", "/admin/audits",
              "/admin/purge", "/admin/expimp/audit", "/admin/metrics", "/admin/server", "/admin/audit/", "admin/tasks",
              "/admin/debug/metrics", "/admin/audits/ageout", "admin/async/import", "admin/async/import/status"};
      private final ActiveInstanceState activeInstanceState;
      private final ServiceState        serviceState;
  
      @Inject
      public ActiveServerFilter(ActiveInstanceState activeInstanceState, ServiceState serviceState) {
          this.activeInstanceState = activeInstanceState;
          this.serviceState        = serviceState;
      }
  
      @Override
      public void init(FilterConfig filterConfig) throws ServletException {
          LOG.info("ActiveServerFilter initialized");
      }
  
      /**
       * Determines if this Atlas server instance is passive and redirects to active if so.
       *
       * @param servletRequest Request object from which the URL and other parameters are determined.
       * @param servletResponse Response object to handle the redirect.
       * @param filterChain Chain to pass through requests if the instance is Active.
       * @throws IOException
       * @throws ServletException
       */
      @Override
      public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
          if (isFilteredURI(servletRequest)) {
              if (LOG.isDebugEnabled()) {
                  LOG.debug("Is a filtered URI: {}. Passing request downstream.", ((HttpServletRequest) servletRequest).getRequestURI());
              }
  
              filterChain.doFilter(servletRequest, servletResponse);
          } else if (isInstanceActive()) {
              LOG.debug("Active. Passing request downstream");
  
              filterChain.doFilter(servletRequest, servletResponse);
          } else if (serviceState.isInstanceInTransition()) {
              HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
  
              LOG.error("Instance in transition. Service may not be ready to return a result");
  
              httpServletResponse.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
          } else if (serviceState.isInstanceInMigration()) {
              if (isRootURI(servletRequest)) {
                  handleMigrationRedirect(servletRequest, servletResponse);
              }
  
              HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
  
              LOG.error("Instance in migration. Service may not be ready to return a result");
  
              httpServletResponse.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
          } else {
              HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
              String              activeServerAddress = activeInstanceState.getActiveServerAddress();
  
              if (activeServerAddress == null) {
                  LOG.error("Could not retrieve active server address as it is null. Cannot redirect request {}", ((HttpServletRequest) servletRequest).getRequestURI());
  
                  httpServletResponse.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
              } else {
                  handleRedirect((HttpServletRequest) servletRequest, httpServletResponse, activeServerAddress);
              }
          }
      }
  
      @Override
      public void destroy() {
      }
  
      boolean isInstanceActive() {
          return serviceState.getState() == ServiceState.ServiceStateValue.ACTIVE;
      }
  
      private boolean isFilteredURI(ServletRequest servletRequest) {
          HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
          String             requestURI         = httpServletRequest.getRequestURI();
  
          if (requestURI.contains("/admin/")) {
              for (String s : adminUriNotFiltered) {
                  if (requestURI.contains(s)) {
                      LOG.trace("URL not supported in HA mode: {}", requestURI);
  
                      return false;
                  }
              }
  
              return true;
          } else {
              return false;
          }
      }
  
      private boolean isRootURI(ServletRequest servletRequest) {
          HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
          String             requestURI         = httpServletRequest.getRequestURI();
  
          return requestURI.equals("/");
      }
  
      private void handleMigrationRedirect(ServletRequest servletRequest, ServletResponse servletResponse) throws IOException {
          HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
          HttpServletRequest  httpServletRequest  = (HttpServletRequest) servletRequest;
          String              redirectLocation    = httpServletRequest.getRequestURL() + MIGRATION_STATUS_STATIC_PAGE;
  
          if (isUnsafeHttpMethod(httpServletRequest)) {
              httpServletResponse.setHeader(HttpHeaders.LOCATION, redirectLocation);
              httpServletResponse.setStatus(HttpServletResponse.SC_TEMPORARY_REDIRECT);
          } else {
              httpServletResponse.sendRedirect(redirectLocation);
          }
      }
  
      private void handleRedirect(HttpServletRequest servletRequest, HttpServletResponse httpServletResponse, String activeServerAddress) throws IOException {
          String requestURI  = servletRequest.getRequestURI();
          String queryString = servletRequest.getQueryString();
  
          if (queryString != null && (!queryString.isEmpty())) {
              //Decoding the queryString from UI to avoid partial encoding issue and re-encoding.
              String decodedQueryString = UriUtils.decode(queryString, "UTF-8");
              queryString = UriUtils.encodeQuery(decodedQueryString, "UTF-8");
          }
  
          if ((queryString != null) && (!queryString.isEmpty())) {
              requestURI += "?" + queryString;
          }
  
          if (requestURI == null) {
              requestURI = "/";
          }
  
          String redirectLocation = activeServerAddress + requestURI;
  
          LOG.info("Not active. Redirecting to {}", redirectLocation);
  
          // A POST/PUT/DELETE require special handling by sending HTTP 307 instead of the regular 301/302.
          // Reference: http://stackoverflow.com/questions/2068418/whats-the-difference-between-a-302-and-a-307-redirect
          if (isUnsafeHttpMethod(servletRequest)) {
              httpServletResponse.setHeader(HttpHeaders.LOCATION, redirectLocation);
              httpServletResponse.setStatus(HttpServletResponse.SC_TEMPORARY_REDIRECT);
          } else {
              httpServletResponse.sendRedirect(redirectLocation);
          }
      }
  
      private boolean isUnsafeHttpMethod(HttpServletRequest httpServletRequest) {
          String method = httpServletRequest.getMethod();
  
          return (method.equals(HttpMethod.POST)) || (method.equals(HttpMethod.PUT)) || (method.equals(HttpMethod.DELETE));
      }
  }
  