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   /*
    * Copyright 2012 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.channel.socket.nio;
  
  import io.netty.channel.ChannelException;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOption;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.util.internal.SocketUtils;
  import io.netty.channel.nio.AbstractNioMessageChannel;
  import io.netty.channel.socket.DefaultServerSocketChannelConfig;
  import io.netty.channel.socket.ServerSocketChannelConfig;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.SuppressJava6Requirement;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.io.IOException;
  import java.net.InetSocketAddress;
  import java.net.ServerSocket;
  import java.net.SocketAddress;
  import java.nio.channels.SelectionKey;
  import java.nio.channels.ServerSocketChannel;
  import java.nio.channels.SocketChannel;
  import java.nio.channels.spi.SelectorProvider;
  import java.util.List;
  import java.util.Map;
  
  /**
   * A {@link io.netty.channel.socket.ServerSocketChannel} implementation which uses
   * NIO selector based implementation to accept new connections.
   */
  public class NioServerSocketChannel extends AbstractNioMessageChannel
                               implements io.netty.channel.socket.ServerSocketChannel {
  
      private static final ChannelMetadata METADATA = new ChannelMetadata(false, 16);
      private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioServerSocketChannel.class);
  
      private static ServerSocketChannel newSocket(SelectorProvider provider) {
          try {
              /**
               *  Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
               *  {@link SelectorProvider#provider()} which is called by each ServerSocketChannel.open() otherwise.
               *
               *  See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.
               */
              return provider.openServerSocketChannel();
          } catch (IOException e) {
              throw new ChannelException(
                      "Failed to open a server socket.", e);
          }
      }
  
      private final ServerSocketChannelConfig config;
  
      /**
       * Create a new instance
       */
      public NioServerSocketChannel() {
          this(newSocket(DEFAULT_SELECTOR_PROVIDER));
      }
  
      /**
       * Create a new instance using the given {@link SelectorProvider}.
       */
      public NioServerSocketChannel(SelectorProvider provider) {
          this(newSocket(provider));
      }
  
      /**
       * Create a new instance using the given {@link ServerSocketChannel}.
       */
      public NioServerSocketChannel(ServerSocketChannel channel) {
          super(null, channel, SelectionKey.OP_ACCEPT);
          config = new NioServerSocketChannelConfig(this, javaChannel().socket());
      }
  
      @Override
      public InetSocketAddress localAddress() {
          return (InetSocketAddress) super.localAddress();
      }
  
      @Override
      public ChannelMetadata metadata() {
         return METADATA;
     }
 
     @Override
     public ServerSocketChannelConfig config() {
         return config;
     }
 
     @Override
     public boolean isActive() {
         // As java.nio.ServerSocketChannel.isBound() will continue to return true even after the channel was closed
         // we will also need to check if it is open.
         return isOpen() && javaChannel().socket().isBound();
     }
 
     @Override
     public InetSocketAddress remoteAddress() {
         return null;
     }
 
     @Override
     protected ServerSocketChannel javaChannel() {
         return (ServerSocketChannel) super.javaChannel();
     }
 
     @Override
     protected SocketAddress localAddress0() {
         return SocketUtils.localSocketAddress(javaChannel().socket());
     }
 
     @SuppressJava6Requirement(reason = "Usage guarded by java version check")
     @Override
     protected void doBind(SocketAddress localAddress) throws Exception {
         if (PlatformDependent.javaVersion() >= 7) {
             javaChannel().bind(localAddress, config.getBacklog());
         } else {
             javaChannel().socket().bind(localAddress, config.getBacklog());
         }
     }
 
     @Override
     protected void doClose() throws Exception {
         javaChannel().close();
     }
 
     @Override
     protected int doReadMessages(List<Object> buf) throws Exception {
         SocketChannel ch = SocketUtils.accept(javaChannel());
 
         try {
             if (ch != null) {
                 buf.add(new NioSocketChannel(this, ch));
                 return 1;
             }
         } catch (Throwable t) {
             logger.warn("Failed to create a new channel from an accepted socket.", t);
 
             try {
                 ch.close();
             } catch (Throwable t2) {
                 logger.warn("Failed to close a socket.", t2);
             }
         }
 
         return 0;
     }
 
     // Unnecessary stuff
     @Override
     protected boolean doConnect(
             SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
         throw new UnsupportedOperationException();
     }
 
     @Override
     protected void doFinishConnect() throws Exception {
         throw new UnsupportedOperationException();
     }
 
     @Override
     protected SocketAddress remoteAddress0() {
         return null;
     }
 
     @Override
     protected void doDisconnect() throws Exception {
         throw new UnsupportedOperationException();
     }
 
     @Override
     protected boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception {
         throw new UnsupportedOperationException();
     }
 
     @Override
     protected final Object filterOutboundMessage(Object msg) throws Exception {
         throw new UnsupportedOperationException();
     }
 
     private final class NioServerSocketChannelConfig extends DefaultServerSocketChannelConfig {
         private NioServerSocketChannelConfig(NioServerSocketChannel channel, ServerSocket javaSocket) {
             super(channel, javaSocket);
         }
 
         @Override
         protected void autoReadCleared() {
             clearReadPending();
         }
 
         @Override
         public <T> boolean setOption(ChannelOption<T> option, T value) {
             if (PlatformDependent.javaVersion() >= 7 && option instanceof NioChannelOption) {
                 return NioChannelOption.setOption(jdkChannel(), (NioChannelOption<T>) option, value);
             }
             return super.setOption(option, value);
         }
 
         @Override
         public <T> T getOption(ChannelOption<T> option) {
             if (PlatformDependent.javaVersion() >= 7 && option instanceof NioChannelOption) {
                 return NioChannelOption.getOption(jdkChannel(), (NioChannelOption<T>) option);
             }
             return super.getOption(option);
         }
 
         @Override
         public Map<ChannelOption<?>, Object> getOptions() {
             if (PlatformDependent.javaVersion() >= 7) {
                 return getOptions(super.getOptions(), NioChannelOption.getOptions(jdkChannel()));
             }
             return super.getOptions();
         }
 
         private ServerSocketChannel jdkChannel() {
             return ((NioServerSocketChannel) channel).javaChannel();
         }
     }
 
     // Override just to to be able to call directly via unit tests.
     @Override
     protected boolean closeOnReadError(Throwable cause) {
         return super.closeOnReadError(cause);
     }
 }