/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.handler.ipfilter;
  
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.util.internal.PlatformDependent;
  
  import java.net.SocketAddress;
  
  /**
   * This class provides the functionality to either accept or reject new {@link Channel}s
   * based on their IP address.
   * <p>
   * You should inherit from this class if you would like to implement your own IP-based filter. Basically you have to
   * implement {@link #accept(ChannelHandlerContext, SocketAddress)} to decided whether you want to accept or reject
   * a connection from the remote address.
   * <p>
   * Furthermore overriding {@link #channelRejected(ChannelHandlerContext, SocketAddress)} gives you the
   * flexibility to respond to rejected (denied) connections. If you do not want to send a response, just have it return
   * null.  Take a look at {@link RuleBasedIpFilter} for details.
   */
  public abstract class AbstractRemoteAddressFilter<T extends SocketAddress> extends ChannelInboundHandlerAdapter {
  
      @Override
      public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
          handleNewChannel(ctx);
          ctx.fireChannelRegistered();
      }
  
      @Override
      public void channelActive(ChannelHandlerContext ctx) throws Exception {
          if (!handleNewChannel(ctx)) {
              throw new IllegalStateException("cannot determine to accept or reject a channel: " + ctx.channel());
          } else {
              ctx.fireChannelActive();
          }
      }
  
      private boolean handleNewChannel(ChannelHandlerContext ctx) throws Exception {
          @SuppressWarnings("unchecked")
          T remoteAddress = (T) ctx.channel().remoteAddress();
  
          // If the remote address is not available yet, defer the decision.
          if (remoteAddress == null) {
              return false;
          }
  
          // Evaluate the decision before removing this handler from the pipeline, so that if accept(...) throws,
          // the channel is closed instead of silently continuing through the rest of the pipeline unfiltered.
          boolean accepted;
          try {
              accepted = accept(ctx, remoteAddress);
          } catch (Throwable cause) {
              ctx.close();
              PlatformDependent.throwException(cause);
              return true;
          }
  
          // No need to keep this handler in the pipeline anymore because the decision has been made.
          // Also, this will prevent the subsequent events from being handled by this handler.
          ctx.pipeline().remove(this);
  
          if (accepted) {
              channelAccepted(ctx, remoteAddress);
          } else {
              ChannelFuture rejectedFuture = channelRejected(ctx, remoteAddress);
              if (rejectedFuture != null) {
                  rejectedFuture.addListener(ChannelFutureListener.CLOSE);
              } else {
                  ctx.close();
              }
          }
  
          return true;
      }
  
      /**
       * This method is called immediately after a {@link io.netty.channel.Channel} gets registered.
       *
       * @return Return true if connections from this IP address and port should be accepted. False otherwise.
       */
      protected abstract boolean accept(ChannelHandlerContext ctx, T remoteAddress) throws Exception;
 
     /**
      * This method is called if {@code remoteAddress} gets accepted by
      * {@link #accept(ChannelHandlerContext, SocketAddress)}.  You should override it if you would like to handle
      * (e.g. respond to) accepted addresses.
      */
     @SuppressWarnings("UnusedParameters")
     protected void channelAccepted(ChannelHandlerContext ctx, T remoteAddress) { }
 
     /**
      * This method is called if {@code remoteAddress} gets rejected by
      * {@link #accept(ChannelHandlerContext, SocketAddress)}.  You should override it if you would like to handle
      * (e.g. respond to) rejected addresses.
      *
      * @return A {@link ChannelFuture} if you perform I/O operations, so that
      *         the {@link Channel} can be closed once it completes. Null otherwise.
      */
     @SuppressWarnings("UnusedParameters")
     protected ChannelFuture channelRejected(ChannelHandlerContext ctx, T remoteAddress) {
         return null;
     }
 }