/*
    * 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.codec.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelPromise;
  import io.netty.handler.codec.http2.Http2Stream.State;
  import io.netty.util.collection.IntObjectHashMap;
  import io.netty.util.collection.IntObjectMap;
  import io.netty.util.collection.IntObjectMap.PrimitiveEntry;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.concurrent.PromiseNotifier;
  import io.netty.util.internal.EmptyArrays;
  import io.netty.util.internal.UnstableApi;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Queue;
  import java.util.Set;
  
  import static io.netty.handler.codec.http2.Http2CodecUtil.CONNECTION_STREAM_ID;
  import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_MAX_RESERVED_STREAMS;
  import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
  import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
  import static io.netty.handler.codec.http2.Http2Error.REFUSED_STREAM;
  import static io.netty.handler.codec.http2.Http2Exception.closedStreamError;
  import static io.netty.handler.codec.http2.Http2Exception.connectionError;
  import static io.netty.handler.codec.http2.Http2Exception.streamError;
  import static io.netty.handler.codec.http2.Http2Stream.State.CLOSED;
  import static io.netty.handler.codec.http2.Http2Stream.State.HALF_CLOSED_LOCAL;
  import static io.netty.handler.codec.http2.Http2Stream.State.HALF_CLOSED_REMOTE;
  import static io.netty.handler.codec.http2.Http2Stream.State.IDLE;
  import static io.netty.handler.codec.http2.Http2Stream.State.OPEN;
  import static io.netty.handler.codec.http2.Http2Stream.State.RESERVED_LOCAL;
  import static io.netty.handler.codec.http2.Http2Stream.State.RESERVED_REMOTE;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  import static java.lang.Integer.MAX_VALUE;
  
  /**
   * Simple implementation of {@link Http2Connection}.
   */
  @UnstableApi
  public class DefaultHttp2Connection implements Http2Connection {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(DefaultHttp2Connection.class);
      // Fields accessed by inner classes
      final IntObjectMap<Http2Stream> streamMap = new IntObjectHashMap<Http2Stream>();
      final PropertyKeyRegistry propertyKeyRegistry = new PropertyKeyRegistry();
      final ConnectionStream connectionStream = new ConnectionStream();
      final DefaultEndpoint<Http2LocalFlowController> localEndpoint;
      final DefaultEndpoint<Http2RemoteFlowController> remoteEndpoint;
  
      /**
       * We chose a {@link List} over a {@link Set} to avoid allocating an {@link Iterator} objects when iterating over
       * the listeners.
       * <p>
       * Initial size of 4 because the default configuration currently has 3 listeners
       * (local/remote flow controller and {@link StreamByteDistributor}) and we leave room for 1 extra.
       * We could be more aggressive but the ArrayList resize will double the size if we are too small.
       */
      final List<Listener> listeners = new ArrayList<Listener>(4);
      final ActiveStreams activeStreams;
      Promise<Void> closePromise;
  
      /**
       * Creates a new connection with the given settings.
       * @param server whether or not this end-point is the server-side of the HTTP/2 connection.
       */
      public DefaultHttp2Connection(boolean server) {
          this(server, DEFAULT_MAX_RESERVED_STREAMS);
      }
  
      /**
       * Creates a new connection with the given settings.
       * @param server whether or not this end-point is the server-side of the HTTP/2 connection.
       * @param maxReservedStreams The maximum amount of streams which can exist in the reserved state for each endpoint.
       */
      public DefaultHttp2Connection(boolean server, int maxReservedStreams) {
         activeStreams = new ActiveStreams(listeners);
         // Reserved streams are excluded from the SETTINGS_MAX_CONCURRENT_STREAMS limit according to [1] and the RFC
         // doesn't define a way to communicate the limit on reserved streams. We rely upon the peer to send RST_STREAM
         // in response to any locally enforced limits being exceeded [2].
         // [1] https://tools.ietf.org/html/rfc7540#section-5.1.2
         // [2] https://tools.ietf.org/html/rfc7540#section-8.2.2
         localEndpoint = new DefaultEndpoint<Http2LocalFlowController>(server, server ? MAX_VALUE : maxReservedStreams);
         remoteEndpoint = new DefaultEndpoint<Http2RemoteFlowController>(!server, maxReservedStreams);
 
         // Add the connection stream to the map.
         streamMap.put(connectionStream.id(), connectionStream);
     }
 
     /**
      * Determine if {@link #close(Promise)} has been called and no more streams are allowed to be created.
      */
     final boolean isClosed() {
         return closePromise != null;
     }
 
     @Override
     public Future<Void> close(final Promise<Void> promise) {
         checkNotNull(promise, "promise");
         // Since we allow this method to be called multiple times, we must make sure that all the promises are notified
         // when all streams are removed and the close operation completes.
         if (closePromise != null) {
             if (closePromise == promise) {
                 // Do nothing
             } else if (promise instanceof ChannelPromise && ((ChannelFuture) closePromise).isVoid()) {
                 closePromise = promise;
             } else {
                 PromiseNotifier.cascade(closePromise, promise);
             }
         } else {
             closePromise = promise;
         }
         if (isStreamMapEmpty()) {
             promise.trySuccess(null);
             return promise;
         }
 
         Iterator<PrimitiveEntry<Http2Stream>> itr = streamMap.entries().iterator();
         // We must take care while iterating the streamMap as to not modify while iterating in case there are other code
         // paths iterating over the active streams.
         if (activeStreams.allowModifications()) {
             activeStreams.incrementPendingIterations();
             try {
                 while (itr.hasNext()) {
                     DefaultStream stream = (DefaultStream) itr.next().value();
                     if (stream.id() != CONNECTION_STREAM_ID) {
                         // If modifications of the activeStream map is allowed, then a stream close operation will also
                         // modify the streamMap. Pass the iterator in so that remove will be called to prevent
                         // concurrent modification exceptions.
                         stream.close(itr);
                     }
                 }
             } finally {
                 activeStreams.decrementPendingIterations();
             }
         } else {
             while (itr.hasNext()) {
                 Http2Stream stream = itr.next().value();
                 if (stream.id() != CONNECTION_STREAM_ID) {
                     // We are not allowed to make modifications, so the close calls will be executed after this
                     // iteration completes.
                     stream.close();
                 }
             }
         }
         return closePromise;
     }
 
     @Override
     public void addListener(Listener listener) {
         listeners.add(listener);
     }
 
     @Override
     public void removeListener(Listener listener) {
         listeners.remove(listener);
     }
 
     @Override
     public boolean isServer() {
         return localEndpoint.isServer();
     }
 
     @Override
     public Http2Stream connectionStream() {
         return connectionStream;
     }
 
     @Override
     public Http2Stream stream(int streamId) {
         return streamMap.get(streamId);
     }
 
     @Override
     public boolean streamMayHaveExisted(int streamId) {
         return remoteEndpoint.mayHaveCreatedStream(streamId) || localEndpoint.mayHaveCreatedStream(streamId);
     }
 
     @Override
     public int numActiveStreams() {
         return activeStreams.size();
     }
 
     @Override
     public Http2Stream forEachActiveStream(Http2StreamVisitor visitor) throws Http2Exception {
         return activeStreams.forEachActiveStream(visitor);
     }
 
     @Override
     public Endpoint<Http2LocalFlowController> local() {
         return localEndpoint;
     }
 
     @Override
     public Endpoint<Http2RemoteFlowController> remote() {
         return remoteEndpoint;
     }
 
     @Override
     public boolean goAwayReceived() {
         return localEndpoint.lastStreamKnownByPeer >= 0;
     }
 
     @Override
     public void goAwayReceived(final int lastKnownStream, long errorCode, ByteBuf debugData) throws Http2Exception {
         if (localEndpoint.lastStreamKnownByPeer() >= 0 && localEndpoint.lastStreamKnownByPeer() < lastKnownStream) {
             throw connectionError(PROTOCOL_ERROR, "lastStreamId MUST NOT increase. Current value: %d new value: %d",
                     localEndpoint.lastStreamKnownByPeer(), lastKnownStream);
         }
 
         localEndpoint.lastStreamKnownByPeer(lastKnownStream);
         for (int i = 0; i < listeners.size(); ++i) {
             try {
                 listeners.get(i).onGoAwayReceived(lastKnownStream, errorCode, debugData);
             } catch (Throwable cause) {
                 logger.error("Caught Throwable from listener onGoAwayReceived.", cause);
             }
         }
 
         closeStreamsGreaterThanLastKnownStreamId(lastKnownStream, localEndpoint);
     }
 
     @Override
     public boolean goAwaySent() {
         return remoteEndpoint.lastStreamKnownByPeer >= 0;
     }
 
     @Override
     public boolean goAwaySent(final int lastKnownStream, long errorCode, ByteBuf debugData) throws Http2Exception {
         if (remoteEndpoint.lastStreamKnownByPeer() >= 0) {
             // Protect against re-entrancy. Could happen if writing the frame fails, and error handling
             // treating this is a connection handler and doing a graceful shutdown...
             if (lastKnownStream == remoteEndpoint.lastStreamKnownByPeer()) {
                 return false;
             }
             if (lastKnownStream > remoteEndpoint.lastStreamKnownByPeer()) {
                 throw connectionError(PROTOCOL_ERROR, "Last stream identifier must not increase between " +
                                 "sending multiple GOAWAY frames (was '%d', is '%d').",
                         remoteEndpoint.lastStreamKnownByPeer(), lastKnownStream);
             }
         }
 
         remoteEndpoint.lastStreamKnownByPeer(lastKnownStream);
         for (int i = 0; i < listeners.size(); ++i) {
             try {
                 listeners.get(i).onGoAwaySent(lastKnownStream, errorCode, debugData);
             } catch (Throwable cause) {
                 logger.error("Caught Throwable from listener onGoAwaySent.", cause);
             }
         }
 
         closeStreamsGreaterThanLastKnownStreamId(lastKnownStream, remoteEndpoint);
         return true;
     }
 
     private void closeStreamsGreaterThanLastKnownStreamId(final int lastKnownStream,
                                                           final DefaultEndpoint<?> endpoint) throws Http2Exception {
         forEachActiveStream(new Http2StreamVisitor() {
             @Override
             public boolean visit(Http2Stream stream) {
                 if (stream.id() > lastKnownStream && endpoint.isValidStreamId(stream.id())) {
                     stream.close();
                 }
                 return true;
             }
         });
     }
 
     /**
      * Determine if {@link #streamMap} only contains the connection stream.
      */
     private boolean isStreamMapEmpty() {
         return streamMap.size() == 1;
     }
 
     /**
      * Remove a stream from the {@link #streamMap}.
      * @param stream the stream to remove.
      * @param itr an iterator that may be pointing to the stream during iteration and {@link Iterator#remove()} will be
      * used if non-{@code null}.
      */
     void removeStream(DefaultStream stream, Iterator<?> itr) {
         final boolean removed;
         if (itr == null) {
             removed = streamMap.remove(stream.id()) != null;
         } else {
             itr.remove();
             removed = true;
         }
 
         if (removed) {
             for (int i = 0; i < listeners.size(); i++) {
                 try {
                     listeners.get(i).onStreamRemoved(stream);
                 } catch (Throwable cause) {
                     logger.error("Caught Throwable from listener onStreamRemoved.", cause);
                 }
             }
 
             if (closePromise != null && isStreamMapEmpty()) {
                 closePromise.trySuccess(null);
             }
         }
     }
 
     static State activeState(int streamId, State initialState, boolean isLocal, boolean halfClosed)
             throws Http2Exception {
         switch (initialState) {
         case IDLE:
             return halfClosed ? isLocal ? HALF_CLOSED_LOCAL : HALF_CLOSED_REMOTE : OPEN;
         case RESERVED_LOCAL:
             return HALF_CLOSED_REMOTE;
         case RESERVED_REMOTE:
             return HALF_CLOSED_LOCAL;
         default:
             throw streamError(streamId, PROTOCOL_ERROR, "Attempting to open a stream in an invalid state: "
                     + initialState);
         }
     }
 
     void notifyHalfClosed(Http2Stream stream) {
         for (int i = 0; i < listeners.size(); i++) {
             try {
                 listeners.get(i).onStreamHalfClosed(stream);
             } catch (Throwable cause) {
                 logger.error("Caught Throwable from listener onStreamHalfClosed.", cause);
             }
         }
     }
 
     void notifyClosed(Http2Stream stream) {
         for (int i = 0; i < listeners.size(); i++) {
             try {
                 listeners.get(i).onStreamClosed(stream);
             } catch (Throwable cause) {
                 logger.error("Caught Throwable from listener onStreamClosed.", cause);
             }
         }
     }
 
     @Override
     public PropertyKey newKey() {
         return propertyKeyRegistry.newKey();
     }
 
     /**
      * Verifies that the key is valid and returns it as the internal {@link DefaultPropertyKey} type.
      *
      * @throws NullPointerException if the key is {@code null}.
      * @throws ClassCastException if the key is not of type {@link DefaultPropertyKey}.
      * @throws IllegalArgumentException if the key was not created by this connection.
      */
     final DefaultPropertyKey verifyKey(PropertyKey key) {
         return checkNotNull((DefaultPropertyKey) key, "key").verifyConnection(this);
     }
 
     /**
      * Simple stream implementation. Streams can be compared to each other by priority.
      */
     private class DefaultStream implements Http2Stream {
         private static final byte META_STATE_SENT_RST = 1;
         private static final byte META_STATE_SENT_HEADERS = 1 << 1;
         private static final byte META_STATE_SENT_TRAILERS = 1 << 2;
         private static final byte META_STATE_SENT_PUSHPROMISE = 1 << 3;
         private static final byte META_STATE_RECV_HEADERS = 1 << 4;
         private static final byte META_STATE_RECV_TRAILERS = 1 << 5;
         private final int id;
         private final long identity;
         private final PropertyMap properties = new PropertyMap();
         private State state;
         private byte metaState;
 
         DefaultStream(long identity, int id, State state) {
             this.identity = identity;
             this.id = id;
             this.state = state;
         }
 
         @Override
         public final int id() {
             return id;
         }
 
         @Override
         public final State state() {
             return state;
         }
 
         @Override
         public boolean isResetSent() {
             return (metaState & META_STATE_SENT_RST) != 0;
         }
 
         @Override
         public Http2Stream resetSent() {
             metaState |= META_STATE_SENT_RST;
             return this;
         }
 
         @Override
         public Http2Stream headersSent(boolean isInformational) {
             if (!isInformational) {
                 metaState |= isHeadersSent() ? META_STATE_SENT_TRAILERS : META_STATE_SENT_HEADERS;
             }
             return this;
         }
 
         @Override
         public boolean isHeadersSent() {
             return (metaState & META_STATE_SENT_HEADERS) != 0;
         }
 
         @Override
         public boolean isTrailersSent() {
             return (metaState & META_STATE_SENT_TRAILERS) != 0;
         }
 
         @Override
         public Http2Stream headersReceived(boolean isInformational) {
             if (!isInformational) {
                 metaState |= isHeadersReceived() ? META_STATE_RECV_TRAILERS : META_STATE_RECV_HEADERS;
             }
             return this;
         }
 
         @Override
         public boolean isHeadersReceived() {
             return (metaState & META_STATE_RECV_HEADERS) != 0;
         }
 
         @Override
         public boolean isTrailersReceived() {
             return (metaState & META_STATE_RECV_TRAILERS) != 0;
         }
 
         @Override
         public Http2Stream pushPromiseSent() {
             metaState |= META_STATE_SENT_PUSHPROMISE;
             return this;
         }
 
         @Override
         public boolean isPushPromiseSent() {
             return (metaState & META_STATE_SENT_PUSHPROMISE) != 0;
         }
 
         @Override
         public final <V> V setProperty(PropertyKey key, V value) {
             return properties.add(verifyKey(key), value);
         }
 
         @Override
         public final <V> V getProperty(PropertyKey key) {
             return properties.get(verifyKey(key));
         }
 
         @Override
         public final <V> V removeProperty(PropertyKey key) {
             return properties.remove(verifyKey(key));
         }
 
         @Override
         public Http2Stream open(boolean halfClosed) throws Http2Exception {
             state = activeState(id, state, isLocal(), halfClosed);
             final DefaultEndpoint<? extends Http2FlowController> endpoint = createdBy();
             if (!endpoint.canOpenStream()) {
                 throw connectionError(PROTOCOL_ERROR, "Maximum active streams violated for this endpoint: " +
                         endpoint.maxActiveStreams());
             }
 
             activate();
             return this;
         }
 
         void activate() {
             // If the stream is opened in a half-closed state, the headers must have either
             // been sent if this is a local stream, or received if it is a remote stream.
             if (state == HALF_CLOSED_LOCAL) {
                 headersSent(/*isInformational*/ false);
             } else if (state == HALF_CLOSED_REMOTE) {
                 headersReceived(/*isInformational*/ false);
             }
             activeStreams.activate(this);
         }
 
         Http2Stream close(Iterator<?> itr) {
             if (state == CLOSED) {
                 return this;
             }
 
             state = CLOSED;
 
             --createdBy().numStreams;
             activeStreams.deactivate(this, itr);
             return this;
         }
 
         @Override
         public Http2Stream close() {
             return close(null);
         }
 
         @Override
         public Http2Stream closeLocalSide() {
             switch (state) {
             case OPEN:
                 state = HALF_CLOSED_LOCAL;
                 notifyHalfClosed(this);
                 break;
             case HALF_CLOSED_LOCAL:
                 break;
             default:
                 close();
                 break;
             }
             return this;
         }
 
         @Override
         public Http2Stream closeRemoteSide() {
             switch (state) {
             case OPEN:
                 state = HALF_CLOSED_REMOTE;
                 notifyHalfClosed(this);
                 break;
             case HALF_CLOSED_REMOTE:
                 break;
             default:
                 close();
                 break;
             }
             return this;
         }
 
         DefaultEndpoint<? extends Http2FlowController> createdBy() {
             return localEndpoint.isValidStreamId(id) ? localEndpoint : remoteEndpoint;
         }
 
         final boolean isLocal() {
             return localEndpoint.isValidStreamId(id);
         }
 
         /**
          * Provides the lazy initialization for the {@link DefaultStream} data map.
          */
         private class PropertyMap {
             Object[] values = EmptyArrays.EMPTY_OBJECTS;
 
             <V> V add(DefaultPropertyKey key, V value) {
                 resizeIfNecessary(key.index);
                 @SuppressWarnings("unchecked")
                 V prevValue = (V) values[key.index];
                 values[key.index] = value;
                 return prevValue;
             }
 
             @SuppressWarnings("unchecked")
             <V> V get(DefaultPropertyKey key) {
                 if (key.index >= values.length) {
                     return null;
                 }
                 return (V) values[key.index];
             }
 
             @SuppressWarnings("unchecked")
             <V> V remove(DefaultPropertyKey key) {
                 V prevValue = null;
                 if (key.index < values.length) {
                     prevValue = (V) values[key.index];
                     values[key.index] = null;
                 }
                 return prevValue;
             }
 
             void resizeIfNecessary(int index) {
                 if (index >= values.length) {
                     values = Arrays.copyOf(values, propertyKeyRegistry.size());
                 }
             }
         }
 
         @Override
         public boolean equals(final Object obj) {
             return super.equals(obj);
         }
 
         @Override
         public int hashCode() {
             long value = identity;
             if (value == 0) {
                 return System.identityHashCode(this);
             }
             return (int) (value ^ (value >>> 32));
         }
     }
 
     /**
      * Stream class representing the connection, itself.
      */
     private final class ConnectionStream extends DefaultStream {
         ConnectionStream() {
             super(0, CONNECTION_STREAM_ID, IDLE);
         }
 
         @Override
         public boolean isResetSent() {
             return false;
         }
 
         @Override
         DefaultEndpoint<? extends Http2FlowController> createdBy() {
             return null;
         }
 
         @Override
         public Http2Stream resetSent() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream open(boolean halfClosed) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream close() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream closeLocalSide() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream closeRemoteSide() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream headersSent(boolean isInformational) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean isHeadersSent() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Http2Stream pushPromiseSent() {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean isPushPromiseSent() {
             throw new UnsupportedOperationException();
         }
     }
 
     /**
      * Simple endpoint implementation.
      */
     private final class DefaultEndpoint<F extends Http2FlowController> implements Endpoint<F> {
         private final boolean server;
         /**
          * This is an always increasing sequence number used to hash {@link DefaultStream} instances.
          */
         private long lastCreatedStreamIdentity;
         /**
          * The minimum stream ID allowed when creating the next stream. This only applies at the time the stream is
          * created. If the ID of the stream being created is less than this value, stream creation will fail. Upon
          * successful creation of a stream, this value is incremented to the next valid stream ID.
          */
         private int nextStreamIdToCreate;
         /**
          * Used for reservation of stream IDs. Stream IDs can be reserved in advance by applications before the streams
          * are actually created.  For example, applications may choose to buffer stream creation attempts as a way of
          * working around {@code SETTINGS_MAX_CONCURRENT_STREAMS}, in which case they will reserve stream IDs for each
          * buffered stream.
          */
         private int nextReservationStreamId;
         private int lastStreamKnownByPeer = -1;
         private boolean pushToAllowed;
         private F flowController;
         private int maxStreams;
         private int maxActiveStreams;
         private final int maxReservedStreams;
         // Fields accessed by inner classes
         int numActiveStreams;
         int numStreams;
 
         DefaultEndpoint(boolean server, int maxReservedStreams) {
             this.lastCreatedStreamIdentity = 0;
             this.server = server;
 
             // Determine the starting stream ID for this endpoint. Client-initiated streams
             // are odd and server-initiated streams are even. Zero is reserved for the
             // connection. Stream 1 is reserved client-initiated stream for responding to an
             // upgrade from HTTP 1.1.
             if (server) {
                 nextStreamIdToCreate = 2;
                 nextReservationStreamId = 0;
             } else {
                 nextStreamIdToCreate = 1;
                 // For manually created client-side streams, 1 is reserved for HTTP upgrade, so start at 3.
                 nextReservationStreamId = 1;
             }
 
             // Push is disallowed by default for servers and allowed for clients.
             pushToAllowed = !server;
             maxActiveStreams = MAX_VALUE;
             this.maxReservedStreams = checkPositiveOrZero(maxReservedStreams, "maxReservedStreams");
             updateMaxStreams();
         }
 
         @Override
         public int incrementAndGetNextStreamId() {
             return nextReservationStreamId >= 0 ? nextReservationStreamId += 2 : nextReservationStreamId;
         }
 
         private void incrementExpectedStreamId(int streamId) {
             if (streamId > nextReservationStreamId && nextReservationStreamId >= 0) {
                 nextReservationStreamId = streamId;
             }
             nextStreamIdToCreate = streamId + 2;
             ++numStreams;
         }
 
         @Override
         public boolean isValidStreamId(int streamId) {
             return streamId > 0 && server == ((streamId & 1) == 0);
         }
 
         @Override
         public boolean mayHaveCreatedStream(int streamId) {
             return isValidStreamId(streamId) && streamId <= lastStreamCreated();
         }
 
         @Override
         public boolean canOpenStream() {
             return numActiveStreams < maxActiveStreams;
         }
 
         @Override
         public DefaultStream createStream(int streamId, boolean halfClosed) throws Http2Exception {
             State state = activeState(streamId, IDLE, isLocal(), halfClosed);
 
             checkNewStreamAllowed(streamId, state);
 
             lastCreatedStreamIdentity++;
 
             // Create and initialize the stream.
             DefaultStream stream = new DefaultStream(lastCreatedStreamIdentity, streamId, state);
 
             incrementExpectedStreamId(streamId);
 
             addStream(stream);
 
             stream.activate();
             return stream;
         }
 
         @Override
         public boolean created(Http2Stream stream) {
             return stream instanceof DefaultStream && ((DefaultStream) stream).createdBy() == this;
         }
 
         @Override
         public boolean isServer() {
             return server;
         }
 
         @Override
         public DefaultStream reservePushStream(int streamId, Http2Stream parent) throws Http2Exception {
             if (parent == null) {
                 throw connectionError(PROTOCOL_ERROR, "Parent stream missing");
             }
             if (isLocal() ? !parent.state().localSideOpen() : !parent.state().remoteSideOpen()) {
                 throw connectionError(PROTOCOL_ERROR, "Stream %d is not open for sending push promise", parent.id());
             }
             if (!opposite().allowPushTo()) {
                 throw connectionError(PROTOCOL_ERROR, "Server push not allowed to opposite endpoint");
             }
             State state = isLocal() ? RESERVED_LOCAL : RESERVED_REMOTE;
             checkNewStreamAllowed(streamId, state);
 
             lastCreatedStreamIdentity++;
 
             // Create and initialize the stream.
             DefaultStream stream = new DefaultStream(lastCreatedStreamIdentity, streamId, state);
 
             incrementExpectedStreamId(streamId);
 
             // Register the stream.
             addStream(stream);
             return stream;
         }
 
         private void addStream(DefaultStream stream) {
             // Add the stream to the map and priority tree.
             streamMap.put(stream.id(), stream);
 
             // Notify the listeners of the event.
             for (int i = 0; i < listeners.size(); i++) {
                 try {
                     listeners.get(i).onStreamAdded(stream);
                 } catch (Throwable cause) {
                     logger.error("Caught Throwable from listener onStreamAdded.", cause);
                 }
             }
         }
 
         @Override
         public void allowPushTo(boolean allow) {
             if (allow && server) {
                 throw new IllegalArgumentException("Servers do not allow push");
             }
             pushToAllowed = allow;
         }
 
         @Override
         public boolean allowPushTo() {
             return pushToAllowed;
         }
 
         @Override
         public int numActiveStreams() {
             return numActiveStreams;
         }
 
         @Override
         public int maxActiveStreams() {
             return maxActiveStreams;
         }
 
         @Override
         public void maxActiveStreams(int maxActiveStreams) {
             this.maxActiveStreams = maxActiveStreams;
             updateMaxStreams();
         }
 
         @Override
         public int lastStreamCreated() {
             // Stream ids are always incremented by 2 so just subtract it. This is even ok in the case
             // of nextStreamIdToCreate overflown as it will just return the correct positive number.
             // Use max(...) to ensure we return the correct value for the case when its a client and no stream
             // was created yet.
             return Math.max(0, nextStreamIdToCreate - 2);
         }
 
         @Override
         public int lastStreamKnownByPeer() {
             return lastStreamKnownByPeer;
         }
 
         private void lastStreamKnownByPeer(int lastKnownStream) {
             lastStreamKnownByPeer = lastKnownStream;
         }
 
         @Override
         public F flowController() {
             return flowController;
         }
 
         @Override
         public void flowController(F flowController) {
             this.flowController = checkNotNull(flowController, "flowController");
         }
 
         @Override
         public Endpoint<? extends Http2FlowController> opposite() {
             return isLocal() ? remoteEndpoint : localEndpoint;
         }
 
         private void updateMaxStreams() {
             maxStreams = (int) Math.min(MAX_VALUE, (long) maxActiveStreams + maxReservedStreams);
         }
 
         private void checkNewStreamAllowed(int streamId, State state) throws Http2Exception {
             assert state != IDLE;
             if (lastStreamKnownByPeer >= 0 && streamId > lastStreamKnownByPeer) {
                 throw streamError(streamId, REFUSED_STREAM,
                         "Cannot create stream %d greater than Last-Stream-ID %d from GOAWAY.",
                         streamId, lastStreamKnownByPeer);
             }
             if (!isValidStreamId(streamId)) {
                 if (streamId < 0) {
                     throw new Http2NoMoreStreamIdsException();
                 }
                 throw connectionError(PROTOCOL_ERROR, "Request stream %d is not correct for %s connection", streamId,
                         server ? "server" : "client");
             }
             // This check must be after all id validated checks, but before the max streams check because it may be
             // recoverable to some degree for handling frames which can be sent on closed streams.
             if (streamId < nextStreamIdToCreate) {
                 throw closedStreamError(PROTOCOL_ERROR, "Request stream %d is behind the next expected stream %d",
                         streamId, nextStreamIdToCreate);
             }
             if (nextStreamIdToCreate <= 0) {
                 // We exhausted the stream id space that we can use. Let's signal this back but also signal that
                 // we still may want to process active streams.
                 throw new Http2Exception(REFUSED_STREAM, "Stream IDs are exhausted for this endpoint.",
                         Http2Exception.ShutdownHint.GRACEFUL_SHUTDOWN);
             }
             boolean isReserved = state == RESERVED_LOCAL || state == RESERVED_REMOTE;
             if (!isReserved && !canOpenStream() || isReserved && numStreams >= maxStreams) {
                 throw streamError(streamId, REFUSED_STREAM, "Maximum active streams violated for this endpoint: " +
                         (isReserved ? maxStreams : maxActiveStreams));
             }
             if (isClosed()) {
                 throw connectionError(INTERNAL_ERROR, "Attempted to create stream id %d after connection was closed",
                                       streamId);
             }
         }
 
         private boolean isLocal() {
             return this == localEndpoint;
         }
     }
 
     /**
      * Allows events which would modify the collection of active streams to be queued while iterating via {@link
      * #forEachActiveStream(Http2StreamVisitor)}.
      */
     interface Event {
         /**
          * Trigger the original intention of this event. Expect to modify the active streams list.
          * <p/>
          * If a {@link RuntimeException} object is thrown it will be logged and <strong>not propagated</strong>.
          * Throwing from this method is not supported and is considered a programming error.
          */
         void process();
     }
 
     /**
      * Manages the list of currently active streams.  Queues any {@link Event}s that would modify the list of
      * active streams in order to prevent modification while iterating.
      */
     private final class ActiveStreams {
         private final List<Listener> listeners;
         private final Queue<Event> pendingEvents = new ArrayDeque<Event>(4);
         private final Set<Http2Stream> streams = new LinkedHashSet<Http2Stream>();
         private int pendingIterations;
 
         ActiveStreams(List<Listener> listeners) {
             this.listeners = listeners;
         }
 
         public int size() {
             return streams.size();
         }
 
         public void activate(final DefaultStream stream) {
             if (allowModifications()) {
                 addToActiveStreams(stream);
             } else {
                 pendingEvents.add(new Event() {
                     @Override
                     public void process() {
                         addToActiveStreams(stream);
                     }
                 });
             }
         }
 
         public void deactivate(final DefaultStream stream, final Iterator<?> itr) {
             if (allowModifications() || itr != null) {
                 removeFromActiveStreams(stream, itr);
             } else {
                 pendingEvents.add(new Event() {
                     @Override
                     public void process() {
                         removeFromActiveStreams(stream, itr);
                     }
                 });
             }
         }
 
         public Http2Stream forEachActiveStream(Http2StreamVisitor visitor) throws Http2Exception {
             incrementPendingIterations();
             try {
                 for (Http2Stream stream : streams) {
                     if (!visitor.visit(stream)) {
                         return stream;
                     }
                 }
                 return null;
             } finally {
                 decrementPendingIterations();
             }
         }
 
         void addToActiveStreams(DefaultStream stream) {
             if (streams.add(stream)) {
                 // Update the number of active streams initiated by the endpoint.
                 stream.createdBy().numActiveStreams++;
 
                 for (int i = 0; i < listeners.size(); i++) {
                     try {
                         listeners.get(i).onStreamActive(stream);
                     } catch (Throwable cause) {
                         logger.error("Caught Throwable from listener onStreamActive.", cause);
                     }
                 }
             }
         }
 
         void removeFromActiveStreams(DefaultStream stream, Iterator<?> itr) {
             if (streams.remove(stream)) {
                 // Update the number of active streams initiated by the endpoint.
                 stream.createdBy().numActiveStreams--;
                 notifyClosed(stream);
             }
             removeStream(stream, itr);
         }
 
         boolean allowModifications() {
             return pendingIterations == 0;
         }
 
         void incrementPendingIterations() {
             ++pendingIterations;
         }
 
         void decrementPendingIterations() {
             --pendingIterations;
             if (allowModifications()) {
                 for (;;) {
                     Event event = pendingEvents.poll();
                     if (event == null) {
                         break;
                     }
                     try {
                         event.process();
                     } catch (Throwable cause) {
                         logger.error("Caught Throwable while processing pending ActiveStreams$Event.", cause);
                     }
                 }
             }
         }
     }
 
     /**
      * Implementation of {@link PropertyKey} that specifies the index position of the property.
      */
     final class DefaultPropertyKey implements PropertyKey {
         final int index;
 
         DefaultPropertyKey(int index) {
             this.index = index;
         }
 
         DefaultPropertyKey verifyConnection(Http2Connection connection) {
             if (connection != DefaultHttp2Connection.this) {
                 throw new IllegalArgumentException("Using a key that was not created by this connection");
             }
             return this;
         }
     }
 
     /**
      * A registry of all stream property keys known by this connection.
      */
     private final class PropertyKeyRegistry {
         /**
          * Initial size of 4 because the default configuration currently has 3 listeners
          * (local/remote flow controller and {@link StreamByteDistributor}) and we leave room for 1 extra.
          * We could be more aggressive but the ArrayList resize will double the size if we are too small.
          */
         final List<DefaultPropertyKey> keys = new ArrayList<DefaultPropertyKey>(4);
 
         /**
          * Registers a new property key.
          */
         DefaultPropertyKey newKey() {
             DefaultPropertyKey key = new DefaultPropertyKey(keys.size());
             keys.add(key);
             return key;
         }
 
         int size() {
             return keys.size();
         }
     }
 }