/*
 * 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:
 *
 * 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 io.netty.handler.codec.http2;

import io.netty.buffer.ByteBuf;
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.UnaryPromiseNotifier;
import io.netty.util.internal.EmptyArrays;
import io.netty.util.internal.PlatformDependent;
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 Http2Connection. /**
 * 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 List over a Set to avoid allocating an Iterator objects when iterating over the listeners. 
 Initial size of 4 because the default configuration currently has 3 listeners (local/remote flow controller and 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. /**
     * 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.
Params:
server – whether or not this end-point is the server-side of the HTTP/2 connection./**
     * 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.
Params:
server – whether or not this end-point is the server-side of the HTTP/2 connection.
maxReservedStreams – The maximum amount of streams which can exist in the reserved state for each endpoint./**
     * 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 close(Promise<Void>) has been called and no more streams are allowed to be created. /**
     * 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) && ((ChannelPromise) closePromise).isVoid()) {
                closePromise = promise;
            } else {
                closePromise.addListener(new UnaryPromiseNotifier<Void>(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) {
        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);
            }
        }

        try {
            forEachActiveStream(new Http2StreamVisitor() {
                @Override
                public boolean visit(Http2Stream stream) {
                    if (stream.id() > lastKnownStream && localEndpoint.isValidStreamId(stream.id())) {
                        stream.close();
                    }
                    return true;
                }
            });
        } catch (Http2Exception e) {
            PlatformDependent.throwException(e);
        }
    }

    @Override
    public boolean goAwaySent() {
        return remoteEndpoint.lastStreamKnownByPeer >= 0;
    }

    @Override
    public void goAwaySent(final int lastKnownStream, long errorCode, ByteBuf debugData) {
        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);
            }
        }

        try {
            forEachActiveStream(new Http2StreamVisitor() {
                @Override
                public boolean visit(Http2Stream stream) {
                    if (stream.id() > lastKnownStream && remoteEndpoint.isValidStreamId(stream.id())) {
                        stream.close();
                    }
                    return true;
                }
            });
        } catch (Http2Exception e) {
            PlatformDependent.throwException(e);
        }
    }

    
Determine if streamMap only contains the connection stream. /**
     * Determine if {@link #streamMap} only contains the connection stream.
     */
    private boolean isStreamMapEmpty() {
        return streamMap.size() == 1;
    }

    
Remove a stream from the streamMap. 
Params:
stream – the stream to remove.
itr – an iterator that may be pointing to the stream during iteration and Iterator.remove() will be used if non-null./**
     * 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 DefaultPropertyKey type. 
Throws:
NullPointerException – if the key is null.
ClassCastException – if the key is not of type DefaultPropertyKey.
IllegalArgumentException – if the key was not created by this connection./**
     * 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.
/**
     * 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 PropertyMap properties = new PropertyMap();
        private State state;
        private byte metaState;

        DefaultStream(int id, State state) {
            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);
            if (!createdBy().canOpenStream()) {
                throw connectionError(PROTOCOL_ERROR, "Maximum active streams violated for this endpoint.");
            }

            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 DefaultStream data map. /**
         * 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());
                }
            }
        }
    }

    
Stream class representing the connection, itself.
/**
     * Stream class representing the connection, itself.
     */
    private final class ConnectionStream extends DefaultStream {
        ConnectionStream() {
            super(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.
/**
     * Simple endpoint implementation.
     */
    private final class DefaultEndpoint<F extends Http2FlowController> implements Endpoint<F> {
        private final boolean server;
        
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.
/**
         * 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 SETTINGS_MAX_CONCURRENT_STREAMS, in which case they will reserve stream IDs for each buffered stream. /**
         * 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 = true;
        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.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);

            // Create and initialize the stream.
            DefaultStream stream = new DefaultStream(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);

            // Create and initialize the stream.
            DefaultStream stream = new DefaultStream(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() {
            return nextStreamIdToCreate > 1 ? nextStreamIdToCreate - 2 : 0;
        }

        @Override
        public int lastStreamKnownByPeer() {
            return lastStreamKnownByPeer;
        }

        private void lastStreamKnownByPeer(int lastKnownStream) {
            this.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 (goAwayReceived() && streamId > localEndpoint.lastStreamKnownByPeer()) {
                throw connectionError(PROTOCOL_ERROR, "Cannot create stream %d since this endpoint has received a " +
                                                      "GOAWAY frame with last stream id %d.", streamId,
                                                      localEndpoint.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) {
                throw connectionError(REFUSED_STREAM, "Stream IDs are exhausted for this endpoint.");
            }
            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.");
            }
            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 DefaultHttp2Connection.forEachActiveStream(Http2StreamVisitor). /**
     * 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.
 If a RuntimeException object is thrown it will be logged and not propagated.
Throwing from this method is not supported and is considered a programming error.
/**
         * 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 Events that would modify the list of active streams in order to prevent modification while iterating. /**
     * 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;

        public 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 PropertyKey that specifies the index position of the property. /**
     * 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.
/**
     * 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 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. /**
         * 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.
/**
         * Registers a new property key.
         */
        DefaultPropertyKey newKey() {
            DefaultPropertyKey key = new DefaultPropertyKey(keys.size());
            keys.add(key);
            return key;
        }

        int size() {
            return keys.size();
        }
    }
}