/*
 * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.net.URI;
import javax.net.ssl.SSLSession;
import javax.net.ssl.SSLSocket;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.concurrent.ExecutorService;
import java.util.function.Consumer;

import jdk.incubator.http.internal.common.ByteBufferReference;
import jdk.incubator.http.internal.frame.FramesDecoder;

import jdk.incubator.http.internal.common.BufferHandler;
import jdk.incubator.http.internal.common.HttpHeadersImpl;
import jdk.incubator.http.internal.common.Queue;
import jdk.incubator.http.internal.frame.*;
import jdk.incubator.http.internal.hpack.Decoder;
import jdk.incubator.http.internal.hpack.DecodingCallback;
import jdk.incubator.http.internal.hpack.Encoder;
import static jdk.incubator.http.internal.frame.SettingsFrame.HEADER_TABLE_SIZE;

/**
 * Represents one HTTP2 connection, either plaintext upgraded from HTTP/1.1
 * or HTTPS opened using "h2" ALPN.
 */
public class Http2TestServerConnection {
    final Http2TestServer server;
    @SuppressWarnings({"rawtypes","unchecked"})
    final Map<Integer, Queue> streams; // input q per stream
    final HashSet<Integer> pushStreams;
    final Queue<Http2Frame> outputQ;
    volatile int nextstream;
    final Socket socket;
    final InputStream is;
    final OutputStream os;
    volatile Encoder hpackOut;
    volatile Decoder hpackIn;
    volatile SettingsFrame clientSettings;
    final SettingsFrame serverSettings;
    final ExecutorService exec;
    final boolean secure;
    volatile boolean stopping;
    volatile int nextPushStreamId = 2;

    final static ByteBuffer EMPTY_BUFFER = ByteBuffer.allocate(0);
    final static byte[] EMPTY_BARRAY = new byte[0];

    final static byte[] clientPreface = "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n".getBytes();

    Http2TestServerConnection(Http2TestServer server, Socket socket) throws IOException {
        System.err.println("TestServer: New connection from " + socket);
        this.server = server;
        this.streams = Collections.synchronizedMap(new HashMap<>());
        this.outputQ = new Queue<>();
        this.socket = socket;
        this.serverSettings = SettingsFrame.getDefaultSettings();
        this.exec = server.exec;
        this.secure = server.secure;
        this.pushStreams = new HashSet<>();
        is = new BufferedInputStream(socket.getInputStream());
        os = new BufferedOutputStream(socket.getOutputStream());
    }

    void close() {
        streams.forEach((i, q) -> {
            q.close();
        });
        stopping = true;
        try {
            socket.close();
            // TODO: put a reset on each stream
        } catch (IOException e) {
        }
    }

    private void readPreface() throws IOException {
        int len = clientPreface.length;
        byte[] bytes = new byte[len];
        is.readNBytes(bytes, 0, len);
        if (Arrays.compare(clientPreface, bytes) != 0) {
            throw new IOException("Invalid preface: " + new String(bytes, 0, len));
        }
    }

    String doUpgrade() throws IOException {
        String upgrade = readHttp1Request();
        String h2c = getHeader(upgrade, "Upgrade");
        if (h2c == null || !h2c.equals("h2c")) {
            System.err.println("Server:HEADERS: " + upgrade);
            throw new IOException("Bad upgrade 1 " + h2c);
        }

        sendHttp1Response(101, "Switching Protocols", "Connection", "Upgrade",
                "Upgrade", "h2c");

        sendSettingsFrame();
        readPreface();

        String clientSettingsString = getHeader(upgrade, "HTTP2-Settings");
        clientSettings = getSettingsFromString(clientSettingsString);

        return upgrade;
    }

    /**
     * Decodes the given, Client, settings payload provided in base64 HTTP1
     * header value.
     */
    private SettingsFrame getSettingsFromString(String s) throws IOException {
        Base64.Decoder decoder = Base64.getUrlDecoder();
        byte[] payload = decoder.decode(s);
        ByteBuffer bb1 = ByteBuffer.wrap(payload);
        // simulate header of Settings Frame
        ByteBuffer bb0 = ByteBuffer.wrap(
                new byte[] {0, 0, (byte)payload.length, 4, 0, 0, 0, 0, 0});
        List<Http2Frame> frames = new ArrayList<>();
        FramesDecoder reader = new FramesDecoder(frames::add);
        reader.decode(ByteBufferReference.of(bb0));
        reader.decode(ByteBufferReference.of(bb1));
        if (frames.size()!=1)
            throw new IOException("Expected 1 frame got "+frames.size()) ;
        Http2Frame frame = frames.get(0);
        if (!(frame instanceof SettingsFrame))
            throw new IOException("Expected SettingsFrame");
        return (SettingsFrame)frame;
    }

    void run() throws Exception {
        String upgrade = null;
        if (!secure) {
            upgrade = doUpgrade();
        } else {
            readPreface();
            sendSettingsFrame(true);
            clientSettings = (SettingsFrame) readFrame();
            if (clientSettings.getFlag(SettingsFrame.ACK)) {
                // we received the ack to our frame first
                clientSettings = (SettingsFrame) readFrame();
            }
            nextstream = 1;
        }

        System.out.println("ServerSettings: " + serverSettings);
        System.out.println("ClientSettings: " + clientSettings);

        hpackOut = new Encoder(serverSettings.getParameter(HEADER_TABLE_SIZE));
        hpackIn = new Decoder(clientSettings.getParameter(HEADER_TABLE_SIZE));

        if (!secure) {
            createPrimordialStream(upgrade);
            nextstream = 3;
        }

        exec.submit(this::readLoop);
        exec.submit(this::writeLoop);
    }

    static class BufferPool implements BufferHandler {

        public void setMinBufferSize(int size) {
        }

        @Override
        public ByteBuffer getBuffer() {
            int size = 32 * 1024;
            return ByteBuffer.allocate(size);
        }

        @Override
        public void returnBuffer(ByteBuffer buffer) {
        }
    }

    private void writeFrame(Http2Frame frame) throws IOException {
        ByteBufferReference[] refs = new FramesEncoder().encodeFrame(frame);
        //System.err.println("TestServer: Writing frame " + frame.toString());
        int c = 0;
        for (ByteBufferReference ref : refs) {
            ByteBuffer buf = ref.get();
            byte[] ba = buf.array();
            int start = buf.arrayOffset() + buf.position();
            c += buf.remaining();
            os.write(ba, start, buf.remaining());
        }
        os.flush();
        //System.err.printf("TestServer: wrote %d bytes\n", c);
    }

    void handleStreamReset(ResetFrame resetFrame) throws IOException {
        // TODO: cleanup
        throw new IOException("Stream reset");
    }

    private void handleCommonFrame(Http2Frame f) throws IOException {
        if (f instanceof SettingsFrame) {
            SettingsFrame sf = (SettingsFrame) f;
            if (sf.getFlag(SettingsFrame.ACK)) // ignore
            {
                return;
            }
            // otherwise acknowledge it
            clientSettings = sf;
            SettingsFrame frame = new SettingsFrame();
            frame.setFlag(SettingsFrame.ACK);
            frame.streamid(0);
            outputQ.put(frame);
            return;
        }
        //System.err.println("TestServer: Received ---> " + f.toString());
        throw new UnsupportedOperationException("Not supported yet.");
    }

    void sendWindowUpdates(int len, int streamid) throws IOException {
        if (len == 0)
            return;
        WindowUpdateFrame wup = new WindowUpdateFrame(streamid, len);
        outputQ.put(wup);
        wup = new WindowUpdateFrame(0 , len);
        outputQ.put(wup);
    }

    HttpHeadersImpl decodeHeaders(List<HeaderFrame> frames) {
        HttpHeadersImpl headers = new HttpHeadersImpl();

        DecodingCallback cb = (name, value) -> {
            headers.addHeader(name.toString(), value.toString());
        };

        for (HeaderFrame frame : frames) {
            ByteBufferReference[] buffers = frame.getHeaderBlock();
            for (ByteBufferReference buffer : buffers) {
                hpackIn.decode(buffer.get(), false, cb);
            }
        }
        hpackIn.decode(EMPTY_BUFFER, true, cb);
        return headers;
    }

    String getRequestLine(String request) {
        int eol = request.indexOf(CRLF);
        return request.substring(0, eol);
    }

    String getHeaders(String request) {
        int start = request.indexOf(CRLF);
        int end = request.indexOf(CRLFCRLF);
        if (start == -1 || end == -1) {
            throw new RuntimeException("Malformed request");
        }
        return request.substring(start,end);
    }

    void addHeaders(String headers, HttpHeadersImpl hdrs) {
        String[] hh = headers.split(CRLF);
        for (String header : hh) {
            int colon = header.indexOf(':');
            if (colon == -1)
                continue;
            String name = header.substring(0, colon);
            String value = header.substring(colon+1);
            while (value.startsWith(" "))
                value = value.substring(1);
            hdrs.addHeader(name, value);
        }
    }

    // First stream (1) comes from a plaintext HTTP/1.1 request
    @SuppressWarnings({"rawtypes","unchecked"})
    void createPrimordialStream(String request) throws IOException {
        HttpHeadersImpl headers = new HttpHeadersImpl();
        String requestLine = getRequestLine(request);
        String[] tokens = requestLine.split(" ");
        if (!tokens[2].equals("HTTP/1.1")) {
            throw new IOException("bad request line");
        }
        URI uri = null;
        try {
            uri = new URI(tokens[1]);
        } catch (URISyntaxException e) {
            throw new IOException(e);
        }
        String host = getHeader(request, "Host");
        if (host == null) {
            throw new IOException("missing Host");
        }

        headers.setHeader(":method", tokens[0]);
        headers.setHeader(":scheme", "http"); // always in this case
        headers.setHeader(":authority", host);
        headers.setHeader(":path", uri.getPath());
        Queue q = new Queue();
        String body = getRequestBody(request);
        addHeaders(getHeaders(request), headers);
        headers.setHeader("Content-length", Integer.toString(body.length()));

        addRequestBodyToQueue(body, q);
        streams.put(1, q);
        exec.submit(() -> {
            handleRequest(headers, q, 1, true /*complete request has been read*/);
        });
    }

    // all other streams created here
    @SuppressWarnings({"rawtypes","unchecked"})
    void createStream(HeaderFrame frame) throws IOException {
        List<HeaderFrame> frames = new LinkedList<>();
        frames.add(frame);
        int streamid = frame.streamid();
        if (streamid != nextstream) {
            throw new IOException("unexpected stream id");
        }
        nextstream += 2;

        boolean endStream = false;
        if (frame.getFlag(HeaderFrame.END_STREAM)) {
            endStream = true;
        }

        while (!frame.getFlag(HeaderFrame.END_HEADERS)) {
            Http2Frame f = readFrame();
            if (!(f instanceof HeaderFrame)) {
                handleCommonFrame(f); // should only be error frames
            } else {
                frame = (HeaderFrame) f;
                if (frame.getFlag(HeaderFrame.END_STREAM)) {
                    endStream = true;
                }
                frames.add(frame);
            }
        }
        boolean endStreamReceived = endStream;
        HttpHeadersImpl headers = decodeHeaders(frames);
        Queue q = new Queue();
        streams.put(streamid, q);
        exec.submit(() -> {
            handleRequest(headers, q, streamid, endStreamReceived);
        });
    }

    // runs in own thread. Handles request from start to finish. Incoming frames
    // for this stream/request delivered on Q

    @SuppressWarnings({"rawtypes","unchecked"})
    void handleRequest(HttpHeadersImpl headers,
                       Queue queue,
                       int streamid,
                       boolean endStreamReceived)
    {
        String method = headers.firstValue(":method").orElse("");
        //System.out.println("method = " + method);
        String path = headers.firstValue(":path").orElse("");
        //System.out.println("path = " + path);
        String scheme = headers.firstValue(":scheme").orElse("");
        //System.out.println("scheme = " + scheme);
        String authority = headers.firstValue(":authority").orElse("");
        //System.out.println("authority = " + authority);
        System.err.printf("TestServer: %s %s\n", method, path);
        HttpHeadersImpl rspheaders = new HttpHeadersImpl();
        int winsize = clientSettings.getParameter(
                        SettingsFrame.INITIAL_WINDOW_SIZE);
        //System.err.println ("Stream window size = " + winsize);

        final InputStream bis;
        if (endStreamReceived) {
            bis = NullInputStream.INSTANCE;
        } else {
            bis = new BodyInputStream(queue, streamid, this);
        }
        try (bis;
             BodyOutputStream bos = new BodyOutputStream(streamid, winsize, this))
        {
            String us = scheme + "://" + authority + path;
            URI uri = new URI(us);
            boolean pushAllowed = clientSettings.getParameter(SettingsFrame.ENABLE_PUSH) == 1;
            Http2TestExchange exchange = new Http2TestExchange(streamid, method,
                    headers, rspheaders, uri, bis, getSSLSession(),
                    bos, this, pushAllowed);

            // give to user
            Http2Handler handler = server.getHandlerFor(uri.getPath());
            handler.handle(exchange);

            // everything happens in the exchange from here. Hopefully will
            // return though.
        } catch (Throwable e) {
            System.err.println("TestServer: handleRequest exception: " + e);
            e.printStackTrace();
        }
    }

    private SSLSession getSSLSession() {
        if (! (socket instanceof SSLSocket))
            return null;
        SSLSocket ssl = (SSLSocket)socket;
        return ssl.getSession();
    }
    // Runs in own thread

    @SuppressWarnings({"rawtypes","unchecked"})
    void readLoop() {
        try {
            while (!stopping) {
                Http2Frame frame = readFrame();
                //System.err.printf("TestServer: received frame %s\n", frame);
                int stream = frame.streamid();
                if (stream == 0) {
                    if (frame.type() == WindowUpdateFrame.TYPE) {
                        WindowUpdateFrame wup = (WindowUpdateFrame) frame;
                        updateConnectionWindow(wup.getUpdate());
                    } else {
                        // other common frame types
                        handleCommonFrame(frame);
                    }
                } else {
                    Queue q = streams.get(stream);
                    if (frame.type() == HeadersFrame.TYPE) {
                        if (q != null) {
                            System.err.println("HEADERS frame for existing stream! Error.");
                            // TODO: close connection
                            continue;
                        } else {
                            createStream((HeadersFrame) frame);
                        }
                    } else {
                        if (q == null && !pushStreams.contains(stream)) {
                            System.err.printf("Non Headers frame received with"+
                                " non existing stream (%d) ", frame.streamid());
                            System.err.println(frame);
                            continue;
                        }
                        if (frame.type() == WindowUpdateFrame.TYPE) {
                            WindowUpdateFrame wup = (WindowUpdateFrame) frame;
                            synchronized (updaters) {
                                Consumer<Integer> r = updaters.get(stream);
                                r.accept(wup.getUpdate());
                            }
                        } else {
                            q.put(frame);
                        }
                    }
                }
            }
        } catch (Throwable e) {
            if (!stopping) {
                System.err.println("Http server reader thread shutdown");
                e.printStackTrace();
            }
            close();
        }
    }

    ByteBufferReference[] encodeHeaders(HttpHeadersImpl headers) {
        List<ByteBuffer> buffers = new LinkedList<>();

        ByteBuffer buf = getBuffer();
        boolean encoded;
        for (Map.Entry<String, List<String>> entry : headers.map().entrySet()) {
            List<String> values = entry.getValue();
            String key = entry.getKey().toLowerCase();
            for (String value : values) {
                do {
                    hpackOut.header(key, value);
                    encoded = hpackOut.encode(buf);
                    if (!encoded) {
                        buf.flip();
                        buffers.add(buf);
                        buf = getBuffer();
                    }
                } while (!encoded);
            }
        }
        buf.flip();
        buffers.add(buf);
        return ByteBufferReference.toReferences(buffers.toArray(bbarray));
    }

    static void closeIgnore(Closeable c) {
        try {
            c.close();
        } catch (IOException e) {}
    }

    // Runs in own thread
    void writeLoop() {
        try {
            while (!stopping) {
                Http2Frame frame = outputQ.take();
                if (frame instanceof ResponseHeaders) {
                    ResponseHeaders rh = (ResponseHeaders)frame;
                    HeadersFrame hf = new HeadersFrame(rh.streamid(), rh.getFlags(), encodeHeaders(rh.headers));
                    writeFrame(hf);
                } else if (frame instanceof OutgoingPushPromise) {
                    handlePush((OutgoingPushPromise)frame);
                } else
                    writeFrame(frame);
            }
            System.err.println("TestServer: Connection writer stopping");
        } catch (Throwable e) {
            e.printStackTrace();
            /*close();
            if (!stopping) {
                e.printStackTrace();
                System.err.println("TestServer: writeLoop exception: " + e);
            }*/
        }
    }

    private void handlePush(OutgoingPushPromise op) throws IOException {
        int promisedStreamid = nextPushStreamId;
        PushPromiseFrame pp = new PushPromiseFrame(op.parentStream, HeaderFrame.END_HEADERS, promisedStreamid, encodeHeaders(op.headers), 0);
        pushStreams.add(promisedStreamid);
        nextPushStreamId += 2;
        pp.streamid(op.parentStream);
        writeFrame(pp);
        final InputStream ii = op.is;
        final BodyOutputStream oo = new BodyOutputStream(
                promisedStreamid,
                clientSettings.getParameter(
                        SettingsFrame.INITIAL_WINDOW_SIZE), this);
        oo.goodToGo();
        exec.submit(() -> {
            try {
                ResponseHeaders oh = getPushResponse(promisedStreamid);
                outputQ.put(oh);
                ii.transferTo(oo);
            } catch (Throwable ex) {
                System.err.printf("TestServer: pushing response error: %s\n",
                        ex.toString());
            } finally {
                closeIgnore(ii);
                closeIgnore(oo);
            }
        });

    }

    // returns a minimal response with status 200
    // that is the response to the push promise just sent
    private ResponseHeaders getPushResponse(int streamid) {
        HttpHeadersImpl h = new HttpHeadersImpl();
        h.addHeader(":status", "200");
        ResponseHeaders oh = new ResponseHeaders(h);
        oh.streamid(streamid);
        oh.setFlag(HeaderFrame.END_HEADERS);
        return oh;
    }

    private ByteBuffer getBuffer() {
        return ByteBuffer.allocate(8 * 1024);
    }

    private Http2Frame readFrame() throws IOException {
        byte[] buf = new byte[9];
        if (is.readNBytes(buf, 0, 9) != 9)
            throw new IOException("readFrame: connection closed");
        int len = 0;
        for (int i = 0; i < 3; i++) {
            int n = buf[i] & 0xff;
            //System.err.println("n = " + n);
            len = (len << 8) + n;
        }
        byte[] rest = new byte[len];
        int n = is.readNBytes(rest, 0, len);
        if (n != len)
            throw new IOException("Error reading frame");
        List<Http2Frame> frames = new ArrayList<>();
        FramesDecoder reader = new FramesDecoder(frames::add);
        reader.decode(ByteBufferReference.of(ByteBuffer.wrap(buf)));
        reader.decode(ByteBufferReference.of(ByteBuffer.wrap(rest)));
        if (frames.size()!=1)
            throw new IOException("Expected 1 frame got "+frames.size()) ;

        return frames.get(0);
    }

    void sendSettingsFrame() throws IOException {
        sendSettingsFrame(false);
    }

    void sendSettingsFrame(boolean now) throws IOException {
        if (now) {
            writeFrame(serverSettings);
        } else {
            outputQ.put(serverSettings);
        }
    }

    String readUntil(String end) throws IOException {
        int number = end.length();
        int found = 0;
        StringBuilder sb = new StringBuilder();
        while (found < number) {
            char expected = end.charAt(found);
            int c = is.read();
            if (c == -1) {
                throw new IOException("Connection closed");
            }
            char c0 = (char) c;
            sb.append(c0);
            if (c0 != expected) {
                found = 0;
                continue;
            }
            found++;
        }
        return sb.toString();
    }

    private int getContentLength(String headers) {
        return getIntHeader(headers, "Content-length");
    }

    private int getIntHeader(String headers, String name) {
        String val = getHeader(headers, name);
        if (val == null) {
            return -1;
        }
        return Integer.parseInt(val);
    }

    private String getHeader(String headers, String name) {
        String headers1 = headers.toLowerCase(); // not efficient
        name = CRLF + name.toLowerCase();
        int start = headers1.indexOf(name);
        if (start == -1) {
            return null;
        }
        start += 2;
        int end = headers1.indexOf(CRLF, start);
        String line = headers.substring(start, end);
        start = line.indexOf(':');
        if (start == -1) {
            return null;
        }
        return line.substring(start + 1).trim();
    }

    final static String CRLF = "\r\n";
    final static String CRLFCRLF = "\r\n\r\n";

    String readHttp1Request() throws IOException {
        String headers = readUntil(CRLF + CRLF);
        int clen = getContentLength(headers);
        // read the content.
        byte[] buf = new byte[clen];
        is.readNBytes(buf, 0, clen);
        String body = new String(buf, StandardCharsets.US_ASCII);
        return headers + body;
    }

    void sendHttp1Response(int code, String msg, String... headers) throws IOException {
        StringBuilder sb = new StringBuilder();
        sb.append("HTTP/1.1 ")
                .append(code)
                .append(' ')
                .append(msg)
                .append(CRLF);
        int numheaders = headers.length;
        for (int i = 0; i < numheaders; i += 2) {
            sb.append(headers[i])
                    .append(": ")
                    .append(headers[i + 1])
                    .append(CRLF);
        }
        sb.append(CRLF);
        String s = sb.toString();
        os.write(s.getBytes("US-ASCII"));
        os.flush();
    }

    private void unexpectedFrame(Http2Frame frame) {
        System.err.println("OOPS. Unexpected");
        assert false;
    }

    final static ByteBuffer[] bbarray = new ByteBuffer[0];

    // wrapper around a BlockingQueue that throws an exception when it's closed
    // Each stream has one of these

    String getRequestBody(String request) {
        int bodystart = request.indexOf(CRLF+CRLF);
        String body;
        if (bodystart == -1)
            body = "";
        else
            body = request.substring(bodystart+4);
        return body;
    }

    @SuppressWarnings({"rawtypes","unchecked"})
    void addRequestBodyToQueue(String body, Queue q) throws IOException {
        ByteBuffer buf = ByteBuffer.wrap(body.getBytes(StandardCharsets.US_ASCII));
        DataFrame df = new DataFrame(1, DataFrame.END_STREAM, ByteBufferReference.of(buf));
        // only used for primordial stream
        q.put(df);
    }

    // window updates done in main reader thread because they may
    // be used to unblock BodyOutputStreams waiting for WUPs

    HashMap<Integer,Consumer<Integer>> updaters = new HashMap<>();

    void registerStreamWindowUpdater(int streamid, Consumer<Integer> r) {
        synchronized(updaters) {
            updaters.put(streamid, r);
        }
    }

    int sendWindow = 64 * 1024 - 1; // connection level send window

    /**
     * BodyOutputStreams call this to get the connection window first.
     *
     * @param amount
     */
    synchronized void obtainConnectionWindow(int amount) throws InterruptedException {
       while (amount > 0) {
           int n = Math.min(amount, sendWindow);
           amount -= n;
           sendWindow -= n;
           if (amount > 0)
               wait();
       }
    }

    synchronized void updateConnectionWindow(int amount) {
        sendWindow += amount;
        notifyAll();
    }

    // simplified output headers class. really just a type safe container
    // for the hashmap.

    static class ResponseHeaders extends Http2Frame {
        HttpHeadersImpl headers;

        ResponseHeaders(HttpHeadersImpl headers) {
            super(0, 0);
            this.headers = headers;
        }

    }

    static class NullInputStream extends InputStream {
       static final NullInputStream INSTANCE = new NullInputStream();
       private NullInputStream() {}
       public int read()      { return -1; }
       public int available() { return 0;  }
   }
}