http://netty.io/netty-all/: Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers and clients. (The Netty Project) 
/*
 * 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 static io.netty.handler.codec.http2.Http2CodecUtil.CONNECTION_STREAM_ID;
import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_WINDOW_SIZE;
import static io.netty.handler.codec.http2.Http2CodecUtil.MAX_INITIAL_WINDOW_SIZE;
import static io.netty.handler.codec.http2.Http2CodecUtil.MIN_INITIAL_WINDOW_SIZE;
import static io.netty.handler.codec.http2.Http2Error.FLOW_CONTROL_ERROR;
import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
import static io.netty.handler.codec.http2.Http2Exception.connectionError;
import static io.netty.handler.codec.http2.Http2Exception.streamError;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static java.lang.Math.max;
import static java.lang.Math.min;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.http2.Http2Exception.CompositeStreamException;
import io.netty.handler.codec.http2.Http2Exception.StreamException;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.UnstableApi;


Basic implementation of Http2LocalFlowController. 

This class is NOT thread safe. The assumption is all methods must be invoked from a single thread. Typically this thread is the event loop thread for the ChannelHandlerContext managed by this class. 
/**
 * Basic implementation of {@link Http2LocalFlowController}.
 * <p>
 * This class is <strong>NOT</strong> thread safe. The assumption is all methods must be invoked from a single thread.
 * Typically this thread is the event loop thread for the {@link ChannelHandlerContext} managed by this class.
 */
@UnstableApi
public class DefaultHttp2LocalFlowController implements Http2LocalFlowController {
    
The default ratio of window size to initial window size below which a WINDOW_UPDATE is sent to expand the window. 
/**
     * The default ratio of window size to initial window size below which a {@code WINDOW_UPDATE}
     * is sent to expand the window.
     */
    public static final float DEFAULT_WINDOW_UPDATE_RATIO = 0.5f;

    private final Http2Connection connection;
    private final Http2Connection.PropertyKey stateKey;
    private Http2FrameWriter frameWriter;
    private ChannelHandlerContext ctx;
    private float windowUpdateRatio;
    private int initialWindowSize = DEFAULT_WINDOW_SIZE;

    public DefaultHttp2LocalFlowController(Http2Connection connection) {
        this(connection, DEFAULT_WINDOW_UPDATE_RATIO, false);
    }

    
Constructs a controller with the given settings.

Params:
  • connection – the connection state.
  • windowUpdateRatio – the window percentage below which to send a WINDOW_UPDATE.
  • autoRefillConnectionWindow – if true, effectively disables the connection window in the flow control algorithm as they will always refill automatically without requiring the application to consume the bytes. When enabled, the maximum bytes you must be prepared to queue is proportional to maximum number of concurrent streams * the initial window
size per stream (SETTINGS_MAX_CONCURRENT_STREAMS
SETTINGS_INITIAL_WINDOW_SIZE).
/**
     * Constructs a controller with the given settings.
     *
     * @param connection the connection state.
     * @param windowUpdateRatio the window percentage below which to send a {@code WINDOW_UPDATE}.
     * @param autoRefillConnectionWindow if {@code true}, effectively disables the connection window
     * in the flow control algorithm as they will always refill automatically without requiring the
     * application to consume the bytes. When enabled, the maximum bytes you must be prepared to
     * queue is proportional to {@code maximum number of concurrent streams * the initial window
     * size per stream}
     * (<a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_CONCURRENT_STREAMS</a>
     * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_INITIAL_WINDOW_SIZE</a>).
     */
    public DefaultHttp2LocalFlowController(Http2Connection connection,
                                           float windowUpdateRatio,
                                           boolean autoRefillConnectionWindow) {
        this.connection = checkNotNull(connection, "connection");
        windowUpdateRatio(windowUpdateRatio);

        // Add a flow state for the connection.
        stateKey = connection.newKey();
        FlowState connectionState = autoRefillConnectionWindow ?
                new AutoRefillState(connection.connectionStream(), initialWindowSize) :
                new DefaultState(connection.connectionStream(), initialWindowSize);
        connection.connectionStream().setProperty(stateKey, connectionState);

        // Register for notification of new streams.
        connection.addListener(new Http2ConnectionAdapter() {
            @Override
            public void onStreamAdded(Http2Stream stream) {
                // Unconditionally used the reduced flow control state because it requires no object allocation
                // and the DefaultFlowState will be allocated in onStreamActive.
                stream.setProperty(stateKey, REDUCED_FLOW_STATE);
            }

            @Override
            public void onStreamActive(Http2Stream stream) {
                // Need to be sure the stream's initial window is adjusted for SETTINGS
                // frames which may have been exchanged while it was in IDLE
                stream.setProperty(stateKey, new DefaultState(stream, initialWindowSize));
            }

            @Override
            public void onStreamClosed(Http2Stream stream) {
                try {
                    // When a stream is closed, consume any remaining bytes so that they
                    // are restored to the connection window.
                    FlowState state = state(stream);
                    int unconsumedBytes = state.unconsumedBytes();
                    if (ctx != null && unconsumedBytes > 0) {
                        connectionState().consumeBytes(unconsumedBytes);
                        state.consumeBytes(unconsumedBytes);
                    }
                } catch (Http2Exception e) {
                    PlatformDependent.throwException(e);
                } finally {
                    // Unconditionally reduce the amount of memory required for flow control because there is no
                    // object allocation costs associated with doing so and the stream will not have any more
                    // local flow control state to keep track of anymore.
                    stream.setProperty(stateKey, REDUCED_FLOW_STATE);
                }
            }
        });
    }

    @Override
    public DefaultHttp2LocalFlowController frameWriter(Http2FrameWriter frameWriter) {
        this.frameWriter = checkNotNull(frameWriter, "frameWriter");
        return this;
    }

    @Override
    public void channelHandlerContext(ChannelHandlerContext ctx) {
        this.ctx = checkNotNull(ctx, "ctx");
    }

    @Override
    public void initialWindowSize(int newWindowSize) throws Http2Exception {
        assert ctx == null || ctx.executor().inEventLoop();
        int delta = newWindowSize - initialWindowSize;
        initialWindowSize = newWindowSize;

        WindowUpdateVisitor visitor = new WindowUpdateVisitor(delta);
        connection.forEachActiveStream(visitor);
        visitor.throwIfError();
    }

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

    @Override
    public int windowSize(Http2Stream stream) {
        return state(stream).windowSize();
    }

    @Override
    public int initialWindowSize(Http2Stream stream) {
        return state(stream).initialWindowSize();
    }

    @Override
    public void incrementWindowSize(Http2Stream stream, int delta) throws Http2Exception {
        assert ctx != null && ctx.executor().inEventLoop();
        FlowState state = state(stream);
        // Just add the delta to the stream-specific initial window size so that the next time the window
        // expands it will grow to the new initial size.
        state.incrementInitialStreamWindow(delta);
        state.writeWindowUpdateIfNeeded();
    }

    @Override
    public boolean consumeBytes(Http2Stream stream, int numBytes) throws Http2Exception {
        assert ctx != null && ctx.executor().inEventLoop();
        if (numBytes < 0) {
            throw new IllegalArgumentException("numBytes must not be negative");
        }
        if (numBytes == 0) {
            return false;
        }

        // Streams automatically consume all remaining bytes when they are closed, so just ignore
        // if already closed.
        if (stream != null && !isClosed(stream)) {
            if (stream.id() == CONNECTION_STREAM_ID) {
                throw new UnsupportedOperationException("Returning bytes for the connection window is not supported");
            }

            boolean windowUpdateSent = connectionState().consumeBytes(numBytes);
            windowUpdateSent |= state(stream).consumeBytes(numBytes);
            return windowUpdateSent;
        }
        return false;
    }

    @Override
    public int unconsumedBytes(Http2Stream stream) {
        return state(stream).unconsumedBytes();
    }

    private static void checkValidRatio(float ratio) {
        if (Double.compare(ratio, 0.0) <= 0 || Double.compare(ratio, 1.0) >= 0) {
            throw new IllegalArgumentException("Invalid ratio: " + ratio);
        }
    }

    
The window update ratio is used to determine when a window update must be sent. If the ratio
of bytes processed since the last update has meet or exceeded this ratio then a window update will
be sent. This is the global window update ratio that will be used for new streams.

Params:
  • ratio – the ratio to use when checking if a WINDOW_UPDATE is determined necessary for new streams.
Throws:
/**
     * The window update ratio is used to determine when a window update must be sent. If the ratio
     * of bytes processed since the last update has meet or exceeded this ratio then a window update will
     * be sent. This is the global window update ratio that will be used for new streams.
     * @param ratio the ratio to use when checking if a {@code WINDOW_UPDATE} is determined necessary for new streams.
     * @throws IllegalArgumentException If the ratio is out of bounds (0, 1).
     */
    public void windowUpdateRatio(float ratio) {
        assert ctx == null || ctx.executor().inEventLoop();
        checkValidRatio(ratio);
        windowUpdateRatio = ratio;
    }

    
The window update ratio is used to determine when a window update must be sent. If the ratio
of bytes processed since the last update has meet or exceeded this ratio then a window update will
be sent. This is the global window update ratio that will be used for new streams.

/**
     * The window update ratio is used to determine when a window update must be sent. If the ratio
     * of bytes processed since the last update has meet or exceeded this ratio then a window update will
     * be sent. This is the global window update ratio that will be used for new streams.
     */
    public float windowUpdateRatio() {
        return windowUpdateRatio;
    }

    
The window update ratio is used to determine when a window update must be sent. If the ratio of bytes processed since the last update has meet or exceeded this ratio then a window update will be sent. This window update ratio will only be applied to streamId. 
 Note it is the responsibly of the caller to ensure that the the initial SETTINGS frame is sent before this is called. It would be considered a Http2Error.PROTOCOL_ERROR if a WINDOW_UPDATE was generated by this method before the initial SETTINGS frame is sent. 
Params:
  • stream – the stream for which ratio applies to.
  • ratio – the ratio to use when checking if a WINDOW_UPDATE is determined necessary.
Throws:
  • Http2Exception – If a protocol-error occurs while generating WINDOW_UPDATE frames
/**
     * The window update ratio is used to determine when a window update must be sent. If the ratio
     * of bytes processed since the last update has meet or exceeded this ratio then a window update will
     * be sent. This window update ratio will only be applied to {@code streamId}.
     * <p>
     * Note it is the responsibly of the caller to ensure that the the
     * initial {@code SETTINGS} frame is sent before this is called. It would
     * be considered a {@link Http2Error#PROTOCOL_ERROR} if a {@code WINDOW_UPDATE}
     * was generated by this method before the initial {@code SETTINGS} frame is sent.
     * @param stream the stream for which {@code ratio} applies to.
     * @param ratio the ratio to use when checking if a {@code WINDOW_UPDATE} is determined necessary.
     * @throws Http2Exception If a protocol-error occurs while generating {@code WINDOW_UPDATE} frames
     */
    public void windowUpdateRatio(Http2Stream stream, float ratio) throws Http2Exception {
        assert ctx != null && ctx.executor().inEventLoop();
        checkValidRatio(ratio);
        FlowState state = state(stream);
        state.windowUpdateRatio(ratio);
        state.writeWindowUpdateIfNeeded();
    }

    
The window update ratio is used to determine when a window update must be sent. If the ratio of bytes processed since the last update has meet or exceeded this ratio then a window update will be sent. This window update ratio will only be applied to streamId. 
Throws:
  • Http2Exception – If no stream corresponding to stream could be found.
/**
     * The window update ratio is used to determine when a window update must be sent. If the ratio
     * of bytes processed since the last update has meet or exceeded this ratio then a window update will
     * be sent. This window update ratio will only be applied to {@code streamId}.
     * @throws Http2Exception If no stream corresponding to {@code stream} could be found.
     */
    public float windowUpdateRatio(Http2Stream stream) throws Http2Exception {
        return state(stream).windowUpdateRatio();
    }

    @Override
    public void receiveFlowControlledFrame(Http2Stream stream, ByteBuf data, int padding,
            boolean endOfStream) throws Http2Exception {
        assert ctx != null && ctx.executor().inEventLoop();
        int dataLength = data.readableBytes() + padding;

        // Apply the connection-level flow control
        FlowState connectionState = connectionState();
        connectionState.receiveFlowControlledFrame(dataLength);

        if (stream != null && !isClosed(stream)) {
            // Apply the stream-level flow control
            FlowState state = state(stream);
            state.endOfStream(endOfStream);
            state.receiveFlowControlledFrame(dataLength);
        } else if (dataLength > 0) {
            // Immediately consume the bytes for the connection window.
            connectionState.consumeBytes(dataLength);
        }
    }

    private FlowState connectionState() {
        return connection.connectionStream().getProperty(stateKey);
    }

    private FlowState state(Http2Stream stream) {
        return stream.getProperty(stateKey);
    }

    private static boolean isClosed(Http2Stream stream) {
        return stream.state() == Http2Stream.State.CLOSED;
    }

    
Flow control state that does autorefill of the flow control window when the data is
received.

/**
     * Flow control state that does autorefill of the flow control window when the data is
     * received.
     */
    private final class AutoRefillState extends DefaultState {
        public AutoRefillState(Http2Stream stream, int initialWindowSize) {
            super(stream, initialWindowSize);
        }

        @Override
        public void receiveFlowControlledFrame(int dataLength) throws Http2Exception {
            super.receiveFlowControlledFrame(dataLength);
            // Need to call the super to consume the bytes, since this.consumeBytes does nothing.
            super.consumeBytes(dataLength);
        }

        @Override
        public boolean consumeBytes(int numBytes) throws Http2Exception {
            // Do nothing, since the bytes are already consumed upon receiving the data.
            return false;
        }
    }

    
Flow control window state for an individual stream.

/**
     * Flow control window state for an individual stream.
     */
    private class DefaultState implements FlowState {
        private final Http2Stream stream;

        
The actual flow control window that is decremented as soon as DATA arrives. 
/**
         * The actual flow control window that is decremented as soon as {@code DATA} arrives.
         */
        private int window;

        
A view of window that is used to determine when to send WINDOW_UPDATE frames. Decrementing this window for received DATA frames is delayed until the application has indicated that the data has been fully processed. This prevents sending a WINDOW_UPDATE until the number of processed bytes drops below the threshold. 
/**
         * A view of {@link #window} that is used to determine when to send {@code WINDOW_UPDATE}
         * frames. Decrementing this window for received {@code DATA} frames is delayed until the
         * application has indicated that the data has been fully processed. This prevents sending
         * a {@code WINDOW_UPDATE} until the number of processed bytes drops below the threshold.
         */
        private int processedWindow;

        
This is what is used to determine how many bytes need to be returned relative to processedWindow. Each stream has their own initial window size. 
/**
         * This is what is used to determine how many bytes need to be returned relative to {@link #processedWindow}.
         * Each stream has their own initial window size.
         */
        private int initialStreamWindowSize;

        
This is used to determine when processedWindow is sufficiently far away from initialStreamWindowSize such that a WINDOW_UPDATE should be sent. Each stream has their own window update ratio. 
/**
         * This is used to determine when {@link #processedWindow} is sufficiently far away from
         * {@link #initialStreamWindowSize} such that a {@code WINDOW_UPDATE} should be sent.
         * Each stream has their own window update ratio.
         */
        private float streamWindowUpdateRatio;

        private int lowerBound;
        private boolean endOfStream;

        public DefaultState(Http2Stream stream, int initialWindowSize) {
            this.stream = stream;
            window(initialWindowSize);
            streamWindowUpdateRatio = windowUpdateRatio;
        }

        @Override
        public void window(int initialWindowSize) {
            assert ctx == null || ctx.executor().inEventLoop();
            window = processedWindow = initialStreamWindowSize = initialWindowSize;
        }

        @Override
        public int windowSize() {
            return window;
        }

        @Override
        public int initialWindowSize() {
            return initialStreamWindowSize;
        }

        @Override
        public void endOfStream(boolean endOfStream) {
            this.endOfStream = endOfStream;
        }

        @Override
        public float windowUpdateRatio() {
            return streamWindowUpdateRatio;
        }

        @Override
        public void windowUpdateRatio(float ratio) {
            assert ctx == null || ctx.executor().inEventLoop();
            streamWindowUpdateRatio = ratio;
        }

        @Override
        public void incrementInitialStreamWindow(int delta) {
            // Clip the delta so that the resulting initialStreamWindowSize falls within the allowed range.
            int newValue = (int) min(MAX_INITIAL_WINDOW_SIZE,
                    max(MIN_INITIAL_WINDOW_SIZE, initialStreamWindowSize + (long) delta));
            delta = newValue - initialStreamWindowSize;

            initialStreamWindowSize += delta;
        }

        @Override
        public void incrementFlowControlWindows(int delta) throws Http2Exception {
            if (delta > 0 && window > MAX_INITIAL_WINDOW_SIZE - delta) {
                throw streamError(stream.id(), FLOW_CONTROL_ERROR,
                        "Flow control window overflowed for stream: %d", stream.id());
            }

            window += delta;
            processedWindow += delta;
            lowerBound = delta < 0 ? delta : 0;
        }

        @Override
        public void receiveFlowControlledFrame(int dataLength) throws Http2Exception {
            assert dataLength >= 0;

            // Apply the delta. Even if we throw an exception we want to have taken this delta into account.
            window -= dataLength;

            // Window size can become negative if we sent a SETTINGS frame that reduces the
            // size of the transfer window after the peer has written data frames.
            // The value is bounded by the length that SETTINGS frame decrease the window.
            // This difference is stored for the connection when writing the SETTINGS frame
            // and is cleared once we send a WINDOW_UPDATE frame.
            if (window < lowerBound) {
                throw streamError(stream.id(), FLOW_CONTROL_ERROR,
                        "Flow control window exceeded for stream: %d", stream.id());
            }
        }

        private void returnProcessedBytes(int delta) throws Http2Exception {
            if (processedWindow - delta < window) {
                throw streamError(stream.id(), INTERNAL_ERROR,
                        "Attempting to return too many bytes for stream %d", stream.id());
            }
            processedWindow -= delta;
        }

        @Override
        public boolean consumeBytes(int numBytes) throws Http2Exception {
            // Return the bytes processed and update the window.
            returnProcessedBytes(numBytes);
            return writeWindowUpdateIfNeeded();
        }

        @Override
        public int unconsumedBytes() {
            return processedWindow - window;
        }

        @Override
        public boolean writeWindowUpdateIfNeeded() throws Http2Exception {
            if (endOfStream || initialStreamWindowSize <= 0) {
                return false;
            }

            int threshold = (int) (initialStreamWindowSize * streamWindowUpdateRatio);
            if (processedWindow <= threshold) {
                writeWindowUpdate();
                return true;
            }
            return false;
        }

        
Called to perform a window update for this stream (or connection). Updates the window size back
to the size of the initial window and sends a window update frame to the remote endpoint.

/**
         * Called to perform a window update for this stream (or connection). Updates the window size back
         * to the size of the initial window and sends a window update frame to the remote endpoint.
         */
        private void writeWindowUpdate() throws Http2Exception {
            // Expand the window for this stream back to the size of the initial window.
            int deltaWindowSize = initialStreamWindowSize - processedWindow;
            try {
                incrementFlowControlWindows(deltaWindowSize);
            } catch (Throwable t) {
                throw connectionError(INTERNAL_ERROR, t,
                        "Attempting to return too many bytes for stream %d", stream.id());
            }

            // Send a window update for the stream/connection.
            frameWriter.writeWindowUpdate(ctx, stream.id(), deltaWindowSize, ctx.newPromise());
        }
    }

    
The local flow control state for a single stream that is not in a state where flow controlled frames cannot
be exchanged.

/**
     * The local flow control state for a single stream that is not in a state where flow controlled frames cannot
     * be exchanged.
     */
    private static final FlowState REDUCED_FLOW_STATE = new FlowState() {

        @Override
        public int windowSize() {
            return 0;
        }

        @Override
        public int initialWindowSize() {
            return 0;
        }

        @Override
        public void window(int initialWindowSize) {
            throw new UnsupportedOperationException();
        }

        @Override
        public void incrementInitialStreamWindow(int delta) {
            // This operation needs to be supported during the initial settings exchange when
            // the peer has not yet acknowledged this peer being activated.
        }

        @Override
        public boolean writeWindowUpdateIfNeeded() throws Http2Exception {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean consumeBytes(int numBytes) throws Http2Exception {
            return false;
        }

        @Override
        public int unconsumedBytes() {
            return 0;
        }

        @Override
        public float windowUpdateRatio() {
            throw new UnsupportedOperationException();
        }

        @Override
        public void windowUpdateRatio(float ratio) {
            throw new UnsupportedOperationException();
        }

        @Override
        public void receiveFlowControlledFrame(int dataLength) throws Http2Exception {
            throw new UnsupportedOperationException();
        }

        @Override
        public void incrementFlowControlWindows(int delta) throws Http2Exception {
            // This operation needs to be supported during the initial settings exchange when
            // the peer has not yet acknowledged this peer being activated.
        }

        @Override
        public void endOfStream(boolean endOfStream) {
            throw new UnsupportedOperationException();
        }
    };

    
An abstraction which provides specific extensions used by local flow control.

/**
     * An abstraction which provides specific extensions used by local flow control.
     */
    private interface FlowState {

        int windowSize();

        int initialWindowSize();

        void window(int initialWindowSize);

        
Increment the initial window size for this stream.

Params:
  • delta – The amount to increase the initial window size by.
/**
         * Increment the initial window size for this stream.
         * @param delta The amount to increase the initial window size by.
         */
        void incrementInitialStreamWindow(int delta);

        
Updates the flow control window for this stream if it is appropriate.

Returns:true if WINDOW_UPDATE was written, false otherwise.
/**
         * Updates the flow control window for this stream if it is appropriate.
         *
         * @return true if {@code WINDOW_UPDATE} was written, false otherwise.
         */
        boolean writeWindowUpdateIfNeeded() throws Http2Exception;

        
Indicates that the application has consumed numBytes from the connection or stream and is ready to receive more data. 
Params:
  • numBytes – the number of bytes to be returned to the flow control window.
Throws:
Returns:true if WINDOW_UPDATE was written, false otherwise.
/**
         * Indicates that the application has consumed {@code numBytes} from the connection or stream and is
         * ready to receive more data.
         *
         * @param numBytes the number of bytes to be returned to the flow control window.
         * @return true if {@code WINDOW_UPDATE} was written, false otherwise.
         * @throws Http2Exception
         */
        boolean consumeBytes(int numBytes) throws Http2Exception;

        int unconsumedBytes();

        float windowUpdateRatio();

        void windowUpdateRatio(float ratio);

        
A flow control event has occurred and we should decrement the amount of available bytes for this stream.

Params:
  • dataLength – The amount of data to for which this stream is no longer eligible to use for flow control.
Throws:
  • Http2Exception – If too much data is used relative to how much is available.
/**
         * A flow control event has occurred and we should decrement the amount of available bytes for this stream.
         * @param dataLength The amount of data to for which this stream is no longer eligible to use for flow control.
         * @throws Http2Exception If too much data is used relative to how much is available.
         */
        void receiveFlowControlledFrame(int dataLength) throws Http2Exception;

        
Increment the windows which are used to determine many bytes have been processed.

Params:
  • delta – The amount to increment the window by.
Throws:
/**
         * Increment the windows which are used to determine many bytes have been processed.
         * @param delta The amount to increment the window by.
         * @throws Http2Exception if integer overflow occurs on the window.
         */
        void incrementFlowControlWindows(int delta) throws Http2Exception;

        void endOfStream(boolean endOfStream);
    }

    
Provides a means to iterate over all active streams and increment the flow control windows.

/**
     * Provides a means to iterate over all active streams and increment the flow control windows.
     */
    private final class WindowUpdateVisitor implements Http2StreamVisitor {
        private CompositeStreamException compositeException;
        private final int delta;

        public WindowUpdateVisitor(int delta) {
            this.delta = delta;
        }

        @Override
        public boolean visit(Http2Stream stream) throws Http2Exception {
            try {
                // Increment flow control window first so state will be consistent if overflow is detected.
                FlowState state = state(stream);
                state.incrementFlowControlWindows(delta);
                state.incrementInitialStreamWindow(delta);
            } catch (StreamException e) {
                if (compositeException == null) {
                    compositeException = new CompositeStreamException(e.error(), 4);
                }
                compositeException.add(e);
            }
            return true;
        }

        public void throwIfError() throws CompositeStreamException {
            if (compositeException != null) {
                throw compositeException;
            }
        }
    }
}