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/*
 * Copyright 2014 the original author or authors.
 *
 * Licensed 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 ratpack.server.internal;

import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.handler.codec.http.*;
import io.netty.handler.ssl.SslHandler;
import io.netty.handler.stream.ChunkedNioStream;
import io.netty.util.AttributeKey;
import io.netty.util.ReferenceCountUtil;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import ratpack.api.Nullable;
import ratpack.exec.Blocking;
import ratpack.file.internal.ResponseTransmitter;
import ratpack.func.Action;
import ratpack.handling.RequestOutcome;
import ratpack.handling.internal.DefaultRequestOutcome;
import ratpack.handling.internal.DoubleTransmissionException;
import ratpack.http.Request;
import ratpack.http.SentResponse;
import ratpack.http.internal.*;

import java.io.FileInputStream;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;

public class DefaultResponseTransmitter implements ResponseTransmitter {

  static final AttributeKey ATTRIBUTE_KEY = AttributeKey.valueOf(DefaultResponseTransmitter.class.getName());

  private final static Logger LOGGER = LoggerFactory.getLogger(DefaultResponseTransmitter.class);
  private static final Runnable NOOP_RUNNABLE = () -> {
  };
  private static final ChannelFutureListener CHANNEL_READ = f -> f.channel().read();

  private final AtomicBoolean transmitted;
  private final Channel channel;
  private final Request ratpackRequest;
  private final HttpHeaders responseHeaders;
  private final RequestBodyAccumulator requestBodyAccumulator;
  private final boolean isSsl;

  private List> outcomeListeners;

  private boolean isKeepAlive;
  private Instant stopTime;

  private Runnable onWritabilityChanged = NOOP_RUNNABLE;

  public DefaultResponseTransmitter(AtomicBoolean transmitted, Channel channel, HttpRequest nettyRequest, Request ratpackRequest, HttpHeaders responseHeaders, @Nullable RequestBodyAccumulator requestBodyAccumulator) {
    this.transmitted = transmitted;
    this.channel = channel;
    this.ratpackRequest = ratpackRequest;
    this.responseHeaders = responseHeaders;
    this.requestBodyAccumulator = requestBodyAccumulator;
    this.isKeepAlive = HttpUtil.isKeepAlive(nettyRequest);
    this.isSsl = channel.pipeline().get(SslHandler.class) != null;
  }

  @SuppressWarnings("deprecation")
  private ChannelFuture pre(HttpResponseStatus responseStatus) {
    if (transmitted.compareAndSet(false, true)) {
      stopTime = Instant.now();

      if (requestBodyAccumulator != null && !requestBodyAccumulator.isComplete()) {
        responseHeaders.set(HttpHeaderNames.CONNECTION, HttpHeaderValues.CLOSE);
        isKeepAlive = false;
      } else if (responseHeaders.contains(HttpHeaderNames.CONNECTION, HttpHeaderValues.CLOSE, true)) {
        isKeepAlive = false;
      }

      HttpResponse headersResponse = new CustomHttpResponse(responseStatus, responseHeaders);

      if (isKeepAlive) {
        headersResponse.headers().set(HttpHeaderConstants.CONNECTION, HttpHeaderConstants.KEEP_ALIVE);
      }

      if (channel.isOpen()) {
        return channel.writeAndFlush(headersResponse).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
      } else {
        return null;
      }
    } else {
      String msg = "attempt at double transmission for: " + ratpackRequest.getRawUri();
      LOGGER.warn(msg, new DoubleTransmissionException(msg));
      return null;
    }
  }

  @Override
  public void transmit(HttpResponseStatus responseStatus, ByteBuf body) {
    transmit(responseStatus, new DefaultHttpContent(body), true);
  }

  private void transmit(final HttpResponseStatus responseStatus, Object body, boolean sendLastHttpContent) {
    ChannelFuture channelFuture = pre(responseStatus);
    if (channelFuture == null) {
      ReferenceCountUtil.release(body);
      return;
    }

    channelFuture.addListener(future -> {
      if (channel.isOpen()) {
        if (sendLastHttpContent) {
          channel.write(body);
          post(responseStatus);
        } else {
          post(responseStatus, channel.writeAndFlush(body));
        }
      } else {
        ReferenceCountUtil.release(body);
      }
    });
  }

  @Override
  public void transmit(HttpResponseStatus status, Path file) {
    String sizeString = responseHeaders.getAsString(HttpHeaderConstants.CONTENT_LENGTH);
    long size = sizeString == null ? 0 : Long.parseLong(sizeString);
    boolean compress = !responseHeaders.contains(HttpHeaderConstants.CONTENT_ENCODING, HttpHeaderConstants.IDENTITY, true);

    if (!isSsl && !compress && file.getFileSystem().equals(FileSystems.getDefault())) {
      Blocking.get(() -> new FileInputStream(file.toFile()).getChannel()).then(fileChannel -> {
        FileRegion defaultFileRegion = new DefaultFileRegion(fileChannel, 0, size);
        transmit(status, defaultFileRegion, true);
      });
    } else {
      Blocking.get(() ->
          Files.newByteChannel(file)
      ).then(fileChannel ->
          transmit(status, new HttpChunkedInput(new ChunkedNioStream(fileChannel)), false)
      );
    }
  }

  @Override
  public Subscriber transmitter(HttpResponseStatus responseStatus) {
    return new Subscriber() {
      private Subscription subscription;
      private final AtomicBoolean done = new AtomicBoolean();

      private final ChannelFutureListener cancelOnFailure = future -> {
        if (!done.get()) {
          if (!future.isSuccess()) {
            cancel();
          }
        }
      };

      private void cancel() {
        if (done.compareAndSet(false, true)) {
          subscription.cancel();
          post(responseStatus);
        }
      }

      @Override
      public void onSubscribe(Subscription subscription) {
        if (subscription == null) {
          throw new NullPointerException("'subscription' is null");
        }
        if (this.subscription != null) {
          subscription.cancel();
          return;
        }

        this.subscription = subscription;

        onWritabilityChanged = () -> {
          if (channel.isWritable() && !done.get()) {
            this.subscription.request(1);
          }
        };

        ChannelFuture channelFuture = pre(responseStatus);
        if (channelFuture == null) {
          subscription.cancel();
          notifyListeners(responseStatus, channel.close());
        } else {
          channelFuture.addListener(cancelOnFailure);
          if (channel.isWritable()) {
            this.subscription.request(1);
          }
        }
      }

      @Override
      public void onNext(ByteBuf o) {
        if (channel.isOpen()) {
          channel.writeAndFlush(new DefaultHttpContent(o)).addListener(cancelOnFailure);
          if (channel.isWritable()) {
            subscription.request(1);
          }
        } else {
          cancel();
        }
      }

      @Override
      public void onError(Throwable t) {
        if (t == null) {
          throw new NullPointerException("error is null");
        }
        LOGGER.warn("Exception thrown transmitting stream", t);
        if (done.compareAndSet(false, true)) {
          post(responseStatus);
        }
      }

      @Override
      public void onComplete() {
        if (done.compareAndSet(false, true)) {
          post(responseStatus);
        }
      }
    };
  }

  private void post(HttpResponseStatus responseStatus) {
    post(responseStatus, channel.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT));
  }

  private void post(HttpResponseStatus responseStatus, ChannelFuture lastContentFuture) {
    if (channel.isOpen()) {
      if (isKeepAlive) {
        lastContentFuture.addListener(CHANNEL_READ);
      } else {
        lastContentFuture.addListener(ChannelFutureListener.CLOSE);
      }
      notifyListeners(responseStatus, lastContentFuture);
    } else {
      notifyListeners(responseStatus, channel.newSucceededFuture());
    }
  }

  private void notifyListeners(final HttpResponseStatus responseStatus, ChannelFuture future) {
    if (outcomeListeners != null) {
      future.addListener(ignore -> {
        channel.attr(ATTRIBUTE_KEY).remove();
        SentResponse sentResponse = new DefaultSentResponse(new NettyHeadersBackedHeaders(responseHeaders), new DefaultStatus(responseStatus));
        RequestOutcome requestOutcome = new DefaultRequestOutcome(ratpackRequest, sentResponse, stopTime);
        for (Action outcomeListener : outcomeListeners) {
          try {
            outcomeListener.execute(requestOutcome);
          } catch (Exception e) {
            LOGGER.warn("request outcome listener " + outcomeListener + " threw exception", e);
          }
        }
      });
    }
  }

  public void writabilityChanged() {
    onWritabilityChanged.run();
  }

  @Override
  public void addOutcomeListener(Action action) {
    if (outcomeListeners == null) {
      outcomeListeners = new ArrayList<>(1);
    }
    outcomeListeners.add(action);
  }

  @Override
  public void forceCloseConnection() {
    responseHeaders.set(HttpHeaderNames.CONNECTION, HttpHeaderValues.CLOSE);
  }
}