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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:
    *
    *   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.jboss.netty.handler.stream;
  
  import org.jboss.netty.buffer.ChannelBuffers;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelDownstreamHandler;
  import org.jboss.netty.channel.ChannelEvent;
  import org.jboss.netty.channel.ChannelFuture;
  import org.jboss.netty.channel.ChannelFutureListener;
  import org.jboss.netty.channel.ChannelHandler;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelPipeline;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.ChannelUpstreamHandler;
  import org.jboss.netty.channel.LifeCycleAwareChannelHandler;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.logging.InternalLogger;
  import org.jboss.netty.logging.InternalLoggerFactory;
  
  import java.io.IOException;
  import java.nio.channels.ClosedChannelException;
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import static org.jboss.netty.channel.Channels.*;
  
  /**
   * A {@link ChannelHandler} that adds support for writing a large data stream
   * asynchronously neither spending a lot of memory nor getting
   * {@link OutOfMemoryError}.  Large data streaming such as file
   * transfer requires complicated state management in a {@link ChannelHandler}
   * implementation.  {@link ChunkedWriteHandler} manages such complicated states
   * so that you can send a large data stream without difficulties.
   * <p>
   * To use {@link ChunkedWriteHandler} in your application, you have to insert
   * a new {@link ChunkedWriteHandler} instance:
   * <pre>
   * {@link ChannelPipeline} p = ...;
   * p.addLast("streamer", <b>new {@link ChunkedWriteHandler}()</b>);
   * p.addLast("handler", new MyHandler());
   * </pre>
   * Once inserted, you can write a {@link ChunkedInput} so that the
   * {@link ChunkedWriteHandler} can pick it up and fetch the content of the
   * stream chunk by chunk and write the fetched chunk downstream:
   * <pre>
   * {@link Channel} ch = ...;
   * ch.write(new {@link ChunkedFile}(new File("video.mkv"));
   * </pre>
   *
   * <h3>Sending a stream which generates a chunk intermittently</h3>
   *
   * Some {@link ChunkedInput} generates a chunk on a certain event or timing.
   * Such {@link ChunkedInput} implementation often returns {@code null} on
   * {@link ChunkedInput#nextChunk()}, resulting in the indefinitely suspended
   * transfer.  To resume the transfer when a new chunk is available, you have to
   * call {@link #resumeTransfer()}.
   * @apiviz.landmark
   * @apiviz.has org.jboss.netty.handler.stream.ChunkedInput oneway - - reads from
   */
  public class ChunkedWriteHandler
          implements ChannelUpstreamHandler, ChannelDownstreamHandler, LifeCycleAwareChannelHandler {
  
      private static final InternalLogger logger =
          InternalLoggerFactory.getInstance(ChunkedWriteHandler.class);
  
      private final Queue<MessageEvent> queue = new ConcurrentLinkedQueue<MessageEvent>();
  
      private volatile ChannelHandlerContext ctx;
      private final AtomicBoolean flush = new AtomicBoolean(false);
      private MessageEvent currentEvent;
      private volatile boolean flushNeeded;
  
      /**
       * Continues to fetch the chunks from the input.
       */
      public void resumeTransfer() {
          ChannelHandlerContext ctx = this.ctx;
          if (ctx == null) {
              return;
          }
  
          try {
              flush(ctx, false);
          } catch (Exception e) {
             if (logger.isWarnEnabled()) {
                 logger.warn("Unexpected exception while sending chunks.", e);
             }
         }
     }
 
     public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
             throws Exception {
         if (!(e instanceof MessageEvent)) {
             ctx.sendDownstream(e);
             return;
         }
 
         boolean offered = queue.offer((MessageEvent) e);
         assert offered;
 
         final Channel channel = ctx.getChannel();
         // call flush if the channel is writable or not connected. flush(..) will take care of the rest
 
         if (channel.isWritable() || !channel.isConnected()) {
             this.ctx = ctx;
             flush(ctx, false);
         }
     }
 
     public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)
             throws Exception {
         if (e instanceof ChannelStateEvent) {
             ChannelStateEvent cse = (ChannelStateEvent) e;
             switch (cse.getState()) {
             case INTEREST_OPS:
                 // Continue writing when the channel becomes writable.
                 flush(ctx, true);
                 break;
             case OPEN:
                 if (!Boolean.TRUE.equals(cse.getValue())) {
                     // Fail all pending writes
                     flush(ctx, true);
                 }
                 break;
             }
         }
         ctx.sendUpstream(e);
     }
 
     private void discard(ChannelHandlerContext ctx, boolean fireNow) {
         ClosedChannelException cause = null;
 
         for (;;) {
             MessageEvent currentEvent = this.currentEvent;
 
             if (this.currentEvent == null) {
                 currentEvent = queue.poll();
             } else {
                 this.currentEvent = null;
             }
 
             if (currentEvent == null) {
                 break;
             }
 
             Object m = currentEvent.getMessage();
             if (m instanceof ChunkedInput) {
                 closeInput((ChunkedInput) m);
             }
 
             // Trigger a ClosedChannelException
             if (cause == null) {
                 cause = new ClosedChannelException();
             }
             currentEvent.getFuture().setFailure(cause);
         }
 
         if (cause != null) {
             if (fireNow) {
                 fireExceptionCaught(ctx.getChannel(), cause);
             } else {
                 fireExceptionCaughtLater(ctx.getChannel(), cause);
             }
         }
     }
 
     private void flush(ChannelHandlerContext ctx, boolean fireNow) throws Exception {
         boolean acquired;
         final Channel channel = ctx.getChannel();
         boolean suspend = false;
         flushNeeded = true;
         // use CAS to see if the have flush already running, if so we don't need to take futher actions
         if (acquired = flush.compareAndSet(false, true)) {
             flushNeeded = false;
             try {
                 if (!channel.isConnected()) {
                     discard(ctx, fireNow);
                     return;
                 }
 
                 while (channel.isWritable()) {
                     if (currentEvent == null) {
                         currentEvent = queue.poll();
                     }
 
                     if (currentEvent == null) {
                         break;
                     }
 
                     if (currentEvent.getFuture().isDone()) {
                         // Skip the current request because the previous partial write
                         // attempt for the current request has been failed.
                         currentEvent = null;
                     } else {
                         final MessageEvent currentEvent = this.currentEvent;
                         Object m = currentEvent.getMessage();
                         if (m instanceof ChunkedInput) {
                             final ChunkedInput chunks = (ChunkedInput) m;
                             Object chunk;
                             boolean endOfInput;
                             try {
                                 chunk = chunks.nextChunk();
                                 endOfInput = chunks.isEndOfInput();
                                 if (chunk == null) {
                                     chunk = ChannelBuffers.EMPTY_BUFFER;
                                     // No need to suspend when reached at the end.
                                     suspend = !endOfInput;
                                 } else {
                                     suspend = false;
                                 }
                             } catch (Throwable t) {
                                 this.currentEvent = null;
 
                                 currentEvent.getFuture().setFailure(t);
                                 if (fireNow) {
                                     fireExceptionCaught(ctx, t);
                                 } else {
                                     fireExceptionCaughtLater(ctx, t);
                                 }
 
                                 closeInput(chunks);
                                 break;
                             }
 
                             if (suspend) {
                                 // ChunkedInput.nextChunk() returned null and it has
                                 // not reached at the end of input.  Let's wait until
                                 // more chunks arrive.  Nothing to write or notify.
                                 break;
                             } else {
                                 ChannelFuture writeFuture;
                                 if (endOfInput) {
                                     this.currentEvent = null;
                                     writeFuture = currentEvent.getFuture();
 
                                     // Register a listener which will close the input once the write
                                     // is complete. This is needed because the Chunk may have some
                                     // resource bound that can not be closed before its not written
                                     //
                                     // See https://github.com/netty/netty/issues/303
                                     writeFuture.addListener(new ChannelFutureListener() {
 
                                         public void operationComplete(ChannelFuture future) throws Exception {
                                             closeInput(chunks);
                                         }
                                     });
                                 } else {
                                     writeFuture = future(channel);
                                     writeFuture.addListener(new ChannelFutureListener() {
                                         public void operationComplete(ChannelFuture future) throws Exception {
                                             if (!future.isSuccess()) {
                                                 currentEvent.getFuture().setFailure(future.getCause());
                                                 closeInput((ChunkedInput) currentEvent.getMessage());
                                             }
                                         }
                                     });
                                 }
 
                                 write(
                                         ctx, writeFuture, chunk,
                                         currentEvent.getRemoteAddress());
                             }
                         } else {
                             this.currentEvent = null;
                             ctx.sendDownstream(currentEvent);
                         }
                     }
 
                     if (!channel.isConnected()) {
                         discard(ctx, fireNow);
                         return;
                     }
                 }
             } finally {
                 // mark the flush as done
                 flush.set(false);
             }
         }
 
         if (acquired && (!channel.isConnected() || channel.isWritable() && !queue.isEmpty() && !suspend
                 || flushNeeded)) {
             flush(ctx, fireNow);
         }
     }
 
     static void closeInput(ChunkedInput chunks) {
         try {
             chunks.close();
         } catch (Throwable t) {
             if (logger.isWarnEnabled()) {
                 logger.warn("Failed to close a chunked input.", t);
             }
         }
     }
 
     public void beforeAdd(ChannelHandlerContext ctx) throws Exception {
         // nothing to do
     }
 
     public void afterAdd(ChannelHandlerContext ctx) throws Exception {
         // nothing to do
     }
 
     public void beforeRemove(ChannelHandlerContext ctx) throws Exception {
         // try to flush again a last time.
         //
         // See #304
         flush(ctx, false);
     }
 
     // This method should not need any synchronization as the ChunkedWriteHandler will not receive any new events
     public void afterRemove(ChannelHandlerContext ctx) throws Exception {
         // Fail all MessageEvent's that are left. This is needed because otherwise we would never notify the
         // ChannelFuture and the registered FutureListener. See #304
         Throwable cause = null;
         boolean fireExceptionCaught = false;
 
         for (;;) {
             MessageEvent currentEvent = this.currentEvent;
 
             if (this.currentEvent == null) {
                 currentEvent = queue.poll();
             } else {
                 this.currentEvent = null;
             }
 
             if (currentEvent == null) {
                 break;
             }
 
             Object m = currentEvent.getMessage();
             if (m instanceof ChunkedInput) {
                 closeInput((ChunkedInput) m);
             }
 
             // Create exception
             if (cause == null) {
                 cause = new IOException("Unable to flush event, discarding");
             }
             currentEvent.getFuture().setFailure(cause);
             fireExceptionCaught = true;
         }
 
         if (fireExceptionCaught) {
             fireExceptionCaughtLater(ctx.getChannel(), cause);
         }
     }
 }