/**
 * 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
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.falcon.security;

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 java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Filter that resolves the requester hostname.
 */
public class HostnameFilter implements Filter {
    private static final Logger LOG = LoggerFactory.getLogger(HostnameFilter.class);

    static final ThreadLocal<String> HOSTNAME_TL = new ThreadLocal<>();

    /**
     * Initializes the filter.
     *
     * @param config filter configuration.
     *
     * @throws javax.servlet.ServletException thrown if the filter could not be initialized.
     */
    @Override
    public void init(FilterConfig config) throws ServletException {
    }

    /**
     * Resolves the requester hostname and delegates the request to the chain.
     * <p>
     * The requester hostname is available via the {@link #get} method.
     *
     * @param request servlet request.
     * @param response servlet response.
     * @param chain filter chain.
     *
     * @throws java.io.IOException thrown if an IO error occurs.
     * @throws ServletException thrown if a servlet error occurs.
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
        try {
            String hostname;
            try {
                String address = request.getRemoteAddr();
                if (address != null) {
                    hostname = InetAddress.getByName(address).getCanonicalHostName();
                } else {
                    LOG.warn("Request remote address is NULL");
                    hostname = "???";
                }
            } catch (UnknownHostException ex) {
                LOG.warn("Request remote address could not be resolved, {}", ex.toString(), ex);
                hostname = "???";
            }
            HOSTNAME_TL.set(hostname);
            chain.doFilter(request, response);
        } finally {
            HOSTNAME_TL.remove();
        }
    }

    /**
     * Returns the requester hostname.
     *
     * @return the requester hostname.
     */
    public static String get() {
        return HOSTNAME_TL.get();
    }

    /**
     * Destroys the filter.
     * <p>
     * This implementation is a NOP.
     */
    @Override
    public void destroy() {
    }
}