DefaultEndpoint Class — netty Architecture

Source Code

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java lines 694–950

    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;
        }