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gRPC: Netty
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/*
 * Copyright 2015, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *    * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *
 *    * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package io.grpc.netty;

import static io.netty.handler.codec.http2.Http2CodecUtil.getEmbeddedHttp2Exception;
import static java.util.concurrent.TimeUnit.SECONDS;

import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.http2.Http2ConnectionDecoder;
import io.netty.handler.codec.http2.Http2ConnectionEncoder;
import io.netty.handler.codec.http2.Http2ConnectionHandler;
import io.netty.handler.codec.http2.Http2Exception;
import io.netty.handler.codec.http2.Http2Settings;
import io.netty.handler.codec.http2.Http2Stream;

/**
 * Base class for all Netty gRPC handlers. This class standardizes exception handling (always
 * shutdown the connection) as well as sending the initial connection window at startup.
 */
abstract class AbstractNettyHandler extends Http2ConnectionHandler {
  private static long GRACEFUL_SHUTDOWN_TIMEOUT = SECONDS.toMillis(5);
  private int initialConnectionWindow;
  private ChannelHandlerContext ctx;

  AbstractNettyHandler(Http2ConnectionDecoder decoder,
                       Http2ConnectionEncoder encoder,
                       Http2Settings initialSettings) {
    super(decoder, encoder, initialSettings);

    // Set the timeout for graceful shutdown.
    gracefulShutdownTimeoutMillis(GRACEFUL_SHUTDOWN_TIMEOUT);

    // Extract the connection window from the settings if it was set.
    this.initialConnectionWindow = initialSettings.initialWindowSize() == null ? -1 :
            initialSettings.initialWindowSize();
  }

  @Override
  public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
    this.ctx = ctx;
    // Sends the connection preface if we haven't already.
    super.handlerAdded(ctx);
    sendInitialConnectionWindow();
  }

  @Override
  public void channelActive(ChannelHandlerContext ctx) throws Exception {
    // Sends connection preface if we haven't already.
    super.channelActive(ctx);
    sendInitialConnectionWindow();
  }

  @Override
  public final void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
    Http2Exception embedded = getEmbeddedHttp2Exception(cause);
    if (embedded == null) {
      // There was no embedded Http2Exception, assume it's a connection error. Subclasses are
      // responsible for storing the appropriate status and shutting down the connection.
      onError(ctx, cause);
    } else {
      super.exceptionCaught(ctx, cause);
    }
  }

  protected final ChannelHandlerContext ctx() {
    return ctx;
  }

  /**
   * Sends initial connection window to the remote endpoint if necessary.
   */
  private void sendInitialConnectionWindow() throws Http2Exception {
    if (ctx.channel().isActive() && initialConnectionWindow > 0) {
      Http2Stream connectionStream = connection().connectionStream();
      int currentSize = connection().local().flowController().windowSize(connectionStream);
      int delta = initialConnectionWindow - currentSize;
      decoder().flowController().incrementWindowSize(connectionStream, delta);
      initialConnectionWindow = -1;
      ctx.flush();
    }
  }
}