java/12 : java.net.http/jdk/internal/net/http/common/SSLFlowDelegate.java

SSLFlowDelegate
https://openjdk.java.net/
GPLv2 + Classpath Exception
/*
 * Copyright (c) 2017, 2019, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 */

package jdk.internal.net.http.common;

import jdk.internal.net.http.common.SubscriberWrapper.SchedulingAction;

import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLEngineResult;
import javax.net.ssl.SSLEngineResult.HandshakeStatus;
import javax.net.ssl.SSLEngineResult.Status;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
import java.io.IOException;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.Flow;
import java.util.concurrent.Flow.Subscriber;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Consumer;
import java.util.function.IntBinaryOperator;

Implements SSL using two SubscriberWrappers.
 Constructor takes two Flow.Subscribers: one that receives the network
data (after it has been encrypted by SSLFlowDelegate) data, and one that
receives the application data (before it has been encrypted by SSLFlowDelegate).
 Methods upstreamReader() and upstreamWriter() return the corresponding
Flow.Subscribers containing Flows for the encrypted/decrypted upstream data.
See diagram below.
 How Flow.Subscribers are used in this class, and where they come from:

--------->  data flow direction
                        +------------------+
       upstreamWriter   |                  | downWriter
       ---------------> |                  | ------------>
 obtained from this     |                  | supplied to constructor
                        | SSLFlowDelegate  |
       downReader       |                  | upstreamReader
       <--------------- |                  | <--------------
supplied to constructor |                  | obtained from this
                        +------------------+
Errors are reported to the downReader Flow.Subscriber
 
/**
 * Implements SSL using two SubscriberWrappers.
 *
 * <p> Constructor takes two Flow.Subscribers: one that receives the network
 * data (after it has been encrypted by SSLFlowDelegate) data, and one that
 * receives the application data (before it has been encrypted by SSLFlowDelegate).
 *
 * <p> Methods upstreamReader() and upstreamWriter() return the corresponding
 * Flow.Subscribers containing Flows for the encrypted/decrypted upstream data.
 * See diagram below.
 *
 * <p> How Flow.Subscribers are used in this class, and where they come from:
 * <pre>
 * {@code
 *
 *
 *
 * --------->  data flow direction
 *
 *
 *                         +------------------+
 *        upstreamWriter   |                  | downWriter
 *        ---------------> |                  | ------------>
 *  obtained from this     |                  | supplied to constructor
 *                         | SSLFlowDelegate  |
 *        downReader       |                  | upstreamReader
 *        <--------------- |                  | <--------------
 * supplied to constructor |                  | obtained from this
 *                         +------------------+
 *
 * Errors are reported to the downReader Flow.Subscriber
 *
 * }
 * </pre>
 */
public class SSLFlowDelegate {

    final Logger debug =
            Utils.getDebugLogger(this::dbgString, Utils.DEBUG);

    private static final ByteBuffer SENTINEL = Utils.EMPTY_BYTEBUFFER;
    private static final ByteBuffer HS_TRIGGER = ByteBuffer.allocate(0);
    // When handshake is in progress trying to wrap may produce no bytes.
    private static final ByteBuffer NOTHING = ByteBuffer.allocate(0);
    private static final String monProp = Utils.getProperty("jdk.internal.httpclient.monitorFlowDelegate");
    private static final boolean isMonitored =
            monProp != null && (monProp.isEmpty() || monProp.equalsIgnoreCase("true"));

    final Executor exec;
    final Reader reader;
    final Writer writer;
    final SSLEngine engine;
    final String tubeName; // hack
    final CompletableFuture<String> alpnCF; // completes on initial handshake
    final Monitorable monitor = isMonitored ? this::monitor : null; // prevent GC until SSLFD is stopped
    volatile boolean close_notify_received;
    final CompletableFuture<Void> readerCF;
    final CompletableFuture<Void> writerCF;
    final CompletableFuture<Void> stopCF;
    final Consumer<ByteBuffer> recycler;
    static AtomicInteger scount = new AtomicInteger(1);
    final int id;

    Creates an SSLFlowDelegate fed from two Flow.Subscribers. Each Flow.Subscriber requires an associated CompletableFuture for errors that need to be signaled from downstream to upstream. /**
     * Creates an SSLFlowDelegate fed from two Flow.Subscribers. Each
     * Flow.Subscriber requires an associated {@link CompletableFuture}
     * for errors that need to be signaled from downstream to upstream.
     */
    public SSLFlowDelegate(SSLEngine engine,
                           Executor exec,
                           Subscriber<? super List<ByteBuffer>> downReader,
                           Subscriber<? super List<ByteBuffer>> downWriter)
    {
        this(engine, exec, null, downReader, downWriter);
    }

    Creates an SSLFlowDelegate fed from two Flow.Subscribers. Each Flow.Subscriber requires an associated CompletableFuture for errors that need to be signaled from downstream to upstream. /**
     * Creates an SSLFlowDelegate fed from two Flow.Subscribers. Each
     * Flow.Subscriber requires an associated {@link CompletableFuture}
     * for errors that need to be signaled from downstream to upstream.
     */
    public SSLFlowDelegate(SSLEngine engine,
            Executor exec,
            Consumer<ByteBuffer> recycler,
            Subscriber<? super List<ByteBuffer>> downReader,
            Subscriber<? super List<ByteBuffer>> downWriter)
        {
        this.id = scount.getAndIncrement();
        this.tubeName = String.valueOf(downWriter);
        this.recycler = recycler;
        this.reader = new Reader();
        this.writer = new Writer();
        this.engine = engine;
        this.exec = exec;
        this.handshakeState = new AtomicInteger(NOT_HANDSHAKING);
        this.readerCF = reader.completion();
        this.writerCF = reader.completion();
        readerCF.exceptionally(this::stopOnError);
        writerCF.exceptionally(this::stopOnError);
        this.stopCF = CompletableFuture.allOf(reader.completion(), writer.completion())
            .thenRun(this::normalStop);
        this.alpnCF = new MinimalFuture<>();

        // connect the Reader to the downReader and the
        // Writer to the downWriter.
        connect(downReader, downWriter);

        if (isMonitored) Monitor.add(monitor);
    }

    Returns true if the SSLFlowDelegate has detected a TLS
close_notify from the server.
Returns: true, if a close_notify was detected./**
     * Returns true if the SSLFlowDelegate has detected a TLS
     * close_notify from the server.
     * @return true, if a close_notify was detected.
     */
    public boolean closeNotifyReceived() {
        return close_notify_received;
    }

    Connects the read sink (downReader) to the SSLFlowDelegate Reader,
and the write sink (downWriter) to the SSLFlowDelegate Writer.
Called from within the constructor. Overwritten by SSLTube.
Params: downReader –  The left hand side read sink (typically, the
                   HttpConnection read subscriber).
downWriter –  The right hand side write sink (typically
                   the SocketTube write subscriber)./**
     * Connects the read sink (downReader) to the SSLFlowDelegate Reader,
     * and the write sink (downWriter) to the SSLFlowDelegate Writer.
     * Called from within the constructor. Overwritten by SSLTube.
     *
     * @param downReader  The left hand side read sink (typically, the
     *                    HttpConnection read subscriber).
     * @param downWriter  The right hand side write sink (typically
     *                    the SocketTube write subscriber).
     */
    void connect(Subscriber<? super List<ByteBuffer>> downReader,
                 Subscriber<? super List<ByteBuffer>> downWriter) {
        this.reader.subscribe(downReader);
        this.writer.subscribe(downWriter);
    }

   Returns a CompletableFuture which completes after
the initial handshake completes, and which contains the negotiated
alpn.
/**
    * Returns a CompletableFuture<String> which completes after
    * the initial handshake completes, and which contains the negotiated
    * alpn.
    */
    public CompletableFuture<String> alpn() {
        return alpnCF;
    }

    private void setALPN() {
        // Handshake is finished. So, can retrieve the ALPN now
        if (alpnCF.isDone())
            return;
        String alpn = engine.getApplicationProtocol();
        if (debug.on()) debug.log("setALPN = %s", alpn);
        alpnCF.complete(alpn);
    }

    public String monitor() {
        StringBuilder sb = new StringBuilder();
        sb.append("SSL: id ").append(id);
        sb.append(" ").append(dbgString());
        sb.append(" HS state: " + states(handshakeState));
        sb.append(" Engine state: " + engine.getHandshakeStatus().toString());
        if (stateList != null) {
            sb.append(" LL : ");
            for (String s : stateList) {
                sb.append(s).append(" ");
            }
        }
        sb.append("\r\n");
        sb.append("Reader:: ").append(reader.toString());
        sb.append("\r\n");
        sb.append("Writer:: ").append(writer.toString());
        sb.append("\r\n===================================");
        return sb.toString();
    }

    protected SchedulingAction enterReadScheduling() {
        return SchedulingAction.CONTINUE;
    }


    Processing function for incoming data. Pass it thru SSLEngine.unwrap().
Any decrypted buffers returned to be passed downstream.
Status codes:
    NEED_UNWRAP: do nothing. Following incoming data will contain
                 any required handshake data
    NEED_WRAP: call writer.addData() with empty buffer
    NEED_TASK: delegate task to executor
    BUFFER_OVERFLOW: allocate larger output buffer. Repeat unwrap
    BUFFER_UNDERFLOW: keep buffer and wait for more data
    OK: return generated buffers.
Upstream subscription strategy is to try and keep no more than
TARGET_BUFSIZE bytes in readBuf
/**
     * Processing function for incoming data. Pass it thru SSLEngine.unwrap().
     * Any decrypted buffers returned to be passed downstream.
     * Status codes:
     *     NEED_UNWRAP: do nothing. Following incoming data will contain
     *                  any required handshake data
     *     NEED_WRAP: call writer.addData() with empty buffer
     *     NEED_TASK: delegate task to executor
     *     BUFFER_OVERFLOW: allocate larger output buffer. Repeat unwrap
     *     BUFFER_UNDERFLOW: keep buffer and wait for more data
     *     OK: return generated buffers.
     *
     * Upstream subscription strategy is to try and keep no more than
     * TARGET_BUFSIZE bytes in readBuf
     */
    final class Reader extends SubscriberWrapper implements FlowTube.TubeSubscriber {
        // Maximum record size is 16k.
        // Because SocketTube can feeds us up to 3 16K buffers,
        // then setting this size to 16K means that the readBuf
        // can store up to 64K-1 (16K-1 + 3*16K)
        static final int TARGET_BUFSIZE = 16 * 1024;

        final SequentialScheduler scheduler;
        volatile ByteBuffer readBuf;
        volatile boolean completing;
        final Object readBufferLock = new Object();
        final Logger debugr = Utils.getDebugLogger(this::dbgString, Utils.DEBUG);

        private final class ReaderDownstreamPusher implements Runnable {
            @Override
            public void run() {
                processData();
            }
        }

        Reader() {
            super();
            scheduler = SequentialScheduler.synchronizedScheduler(
                    new ReaderDownstreamPusher());
            this.readBuf = ByteBuffer.allocate(1024);
            readBuf.limit(0); // keep in read mode
        }

        @Override
        public boolean supportsRecycling() {
            return recycler != null;
        }

        protected SchedulingAction enterScheduling() {
            return enterReadScheduling();
        }

        public final String dbgString() {
            return "SSL Reader(" + tubeName + ")";
        }

        entry point for buffers delivered from upstream Subscriber
/**
         * entry point for buffers delivered from upstream Subscriber
         */
        @Override
        public void incoming(List<ByteBuffer> buffers, boolean complete) {
            if (debugr.on())
                debugr.log("Adding %d bytes to read buffer",
                        Utils.remaining(buffers));
            addToReadBuf(buffers, complete);
            scheduler.runOrSchedule(exec);
        }

        @Override
        public String toString() {
            return "READER: " + super.toString() + ", readBuf: " + readBuf.toString()
                    + ", count: " + count.toString() + ", scheduler: "
                    + (scheduler.isStopped() ? "stopped" : "running")
                    + ", status: " + lastUnwrapStatus
                    + ", handshakeState: " + handshakeState.get()
                    + ", engine: " + engine.getHandshakeStatus();
        }

        private void reallocReadBuf() {
            int sz = readBuf.capacity();
            ByteBuffer newb = ByteBuffer.allocate(sz * 2);
            readBuf.flip();
            Utils.copy(readBuf, newb);
            readBuf = newb;
        }

        @Override
        protected long upstreamWindowUpdate(long currentWindow, long downstreamQsize) {
            if (readBuf.remaining() > TARGET_BUFSIZE) {
                if (debugr.on())
                    debugr.log("readBuf has more than TARGET_BUFSIZE: %d",
                            readBuf.remaining());
                return 0;
            } else {
                return super.upstreamWindowUpdate(currentWindow, downstreamQsize);
            }
        }

        // readBuf is kept ready for reading outside of this method
        private void addToReadBuf(List<ByteBuffer> buffers, boolean complete) {
            assert Utils.remaining(buffers) > 0 || buffers.isEmpty();
            synchronized (readBufferLock) {
                for (ByteBuffer buf : buffers) {
                    readBuf.compact();
                    while (readBuf.remaining() < buf.remaining())
                        reallocReadBuf();
                    readBuf.put(buf);
                    readBuf.flip();
                    // should be safe to call inside lock
                    // since the only implementation
                    // offers the buffer to an unbounded queue.
                    // WARNING: do not touch buf after this point!
                    if (recycler != null) recycler.accept(buf);
                }
                if (complete) {
                    this.completing = complete;
                    minBytesRequired = 0;
                }
            }
        }

        void schedule() {
            scheduler.runOrSchedule(exec);
        }

        void stop() {
            if (debugr.on()) debugr.log("stop");
            scheduler.stop();
        }

        AtomicInteger count = new AtomicInteger(0);

        // minimum number of bytes required to call unwrap.
        // Usually this is 0, unless there was a buffer underflow.
        // In this case we need to wait for more bytes than what
        // we had before calling unwrap() again.
        volatile int minBytesRequired;

        // work function where it all happens
        final void processData() {
            try {
                if (debugr.on())
                    debugr.log("processData:"
                            + " readBuf remaining:" + readBuf.remaining()
                            + ", state:" + states(handshakeState)
                            + ", engine handshake status:" + engine.getHandshakeStatus());
                int len;
                boolean complete = false;
                while (readBuf.remaining() > (len = minBytesRequired)) {
                    boolean handshaking = false;
                    try {
                        EngineResult result;
                        synchronized (readBufferLock) {
                            complete = this.completing;
                            if (debugr.on()) debugr.log("Unwrapping: %s", readBuf.remaining());
                            // Unless there is a BUFFER_UNDERFLOW, we should try to
                            // unwrap any number of bytes. Set minBytesRequired to 0:
                            // we only need to do that if minBytesRequired is not already 0.
                            len = len > 0 ? minBytesRequired = 0 : len;
                            result = unwrapBuffer(readBuf);
                            len = readBuf.remaining();
                            if (debugr.on()) {
                                debugr.log("Unwrapped: result: %s", result.result);
                                debugr.log("Unwrapped: consumed: %s", result.bytesConsumed());
                            }
                        }
                        if (result.bytesProduced() > 0) {
                            if (debugr.on())
                                debugr.log("sending %d", result.bytesProduced());
                            count.addAndGet(result.bytesProduced());
                            outgoing(result.destBuffer, false);
                        }
                        if (result.status() == Status.BUFFER_UNDERFLOW) {
                            if (debugr.on()) debugr.log("BUFFER_UNDERFLOW");
                            // not enough data in the read buffer...
                            // no need to try to unwrap again unless we get more bytes
                            // than minBytesRequired = len in the read buffer.
                            synchronized (readBufferLock) {
                                minBytesRequired = len;
                                // more bytes could already have been added...
                                assert readBuf.remaining() >= len;
                                // check if we have received some data, and if so
                                // we can just re-spin the loop
                                if (readBuf.remaining() > len) continue;
                                else if (this.completing) {
                                    if (debug.on()) {
                                        debugr.log("BUFFER_UNDERFLOW with EOF," +
                                                " %d bytes non decrypted.", len);
                                    }
                                    // The channel won't send us any more data, and
                                    // we are in underflow: we need to fail.
                                    throw new IOException("BUFFER_UNDERFLOW with EOF, "
                                            + len + " bytes non decrypted.");
                                }
                            }
                            // request more data and return.
                            requestMore();
                            return;
                        }
                        if (complete && result.status() == Status.CLOSED) {
                            if (debugr.on()) debugr.log("Closed: completing");
                            outgoing(Utils.EMPTY_BB_LIST, true);
                            // complete ALPN if not yet completed
                            setALPN();
                            return;
                        }
                        if (result.handshaking()) {
                            handshaking = true;
                            if (debugr.on()) debugr.log("handshaking");
                            if (doHandshake(result, READER)) continue; // need unwrap
                            else break; // doHandshake will have triggered the write scheduler if necessary
                        } else {
                            if (trySetALPN()) {
                                resumeActivity();
                            }
                        }
                    } catch (IOException ex) {
                        errorCommon(ex);
                        handleError(ex);
                        return;
                    }
                    if (handshaking && !complete)
                        return;
                }
                if (!complete) {
                    synchronized (readBufferLock) {
                        complete = this.completing && !readBuf.hasRemaining();
                    }
                }
                if (complete) {
                    if (debugr.on()) debugr.log("completing");
                    // Complete the alpnCF, if not already complete, regardless of
                    // whether or not the ALPN is available, there will be no more
                    // activity.
                    setALPN();
                    outgoing(Utils.EMPTY_BB_LIST, true);
                }
            } catch (Throwable ex) {
                errorCommon(ex);
                handleError(ex);
            }
        }

        private volatile Status lastUnwrapStatus;
        EngineResult unwrapBuffer(ByteBuffer src) throws IOException {
            ByteBuffer dst = getAppBuffer();
            int len = src.remaining();
            while (true) {
                SSLEngineResult sslResult = engine.unwrap(src, dst);
                switch (lastUnwrapStatus = sslResult.getStatus()) {
                    case BUFFER_OVERFLOW:
                        // may happen if app size buffer was changed, or if
                        // our 'adaptiveBufferSize' guess was too small for
                        // the current payload. In that case, update the
                        // value of applicationBufferSize, and allocate a
                        // buffer of that size, which we are sure will be
                        // big enough to decode whatever needs to be
                        // decoded. We will later update adaptiveBufferSize
                        // in OK: below.
                        int appSize = applicationBufferSize =
                                engine.getSession().getApplicationBufferSize();
                        ByteBuffer b = ByteBuffer.allocate(appSize + dst.position());
                        dst.flip();
                        b.put(dst);
                        dst = b;
                        break;
                    case CLOSED:
                        assert dst.position() == 0;
                        return doClosure(new EngineResult(sslResult));
                    case BUFFER_UNDERFLOW:
                        // handled implicitly by compaction/reallocation of readBuf
                        assert dst.position() == 0;
                        return new EngineResult(sslResult);
                    case OK:
                        int size = dst.position();
                        if (debug.on()) {
                            debugr.log("Decoded " + size + " bytes out of " + len
                                    + " into buffer of " + dst.capacity()
                                    + " remaining to decode: " + src.remaining());
                        }
                        // if the record payload was bigger than what was originally
                        // allocated, then sets the adaptiveAppBufferSize to size
                        // and we will use that new size as a guess for the next app
                        // buffer.
                        if (size > adaptiveAppBufferSize) {
                            adaptiveAppBufferSize = ((size + 7) >>> 3) << 3;
                        }
                        dst.flip();
                        return new EngineResult(sslResult, dst);
                }
            }
        }
    }

    public interface Monitorable {
        public String getInfo();
    }

    public static class Monitor extends Thread {
        final List<WeakReference<Monitorable>> list;
        final List<FinalMonitorable> finalList;
        final ReferenceQueue<Monitorable> queue = new ReferenceQueue<>();
        static Monitor themon;

        static {
            themon = new Monitor();
            themon.start(); // uncomment to enable Monitor
        }

        // An instance used to temporarily store the
        // last observable state of a monitorable object.
        // When Monitor.remove(o) is called, we replace
        // 'o' with a FinalMonitorable whose reference
        // will be enqueued after the last observable state
        // has been printed.
        final class FinalMonitorable implements Monitorable {
            final String finalState;
            FinalMonitorable(Monitorable o) {
                finalState = o.getInfo();
                finalList.add(this);
            }
            @Override
            public String getInfo() {
                finalList.remove(this);
                return finalState;
            }
        }

        Monitor() {
            super("Monitor");
            setDaemon(true);
            list = Collections.synchronizedList(new LinkedList<>());
            finalList = new ArrayList<>(); // access is synchronized on list above
        }

        void addTarget(Monitorable o) {
            list.add(new WeakReference<>(o, queue));
        }
        void removeTarget(Monitorable o) {
            // It can take a long time for GC to clean up references.
            // Calling Monitor.remove() early helps removing noise from the
            // logs/
            synchronized (list) {
                Iterator<WeakReference<Monitorable>> it = list.iterator();
                while (it.hasNext()) {
                    Monitorable m = it.next().get();
                    if (m == null) it.remove();
                    if (o == m) {
                        it.remove();
                        break;
                    }
                }
                FinalMonitorable m = new FinalMonitorable(o);
                addTarget(m);
                Reference.reachabilityFence(m);
            }
        }

        public static void add(Monitorable o) {
            themon.addTarget(o);
        }
        public static void remove(Monitorable o) {
            themon.removeTarget(o);
        }

        @Override
        public void run() {
            System.out.println("Monitor starting");
            try {
                while (true) {
                    Thread.sleep(20 * 1000);
                    synchronized (list) {
                        Reference<? extends Monitorable> expired;
                        while ((expired = queue.poll()) != null) list.remove(expired);
                        for (WeakReference<Monitorable> ref : list) {
                            Monitorable o = ref.get();
                            if (o == null) continue;
                            if (o instanceof FinalMonitorable) {
                                ref.enqueue();
                            }
                            System.out.println(o.getInfo());
                            System.out.println("-------------------------");
                        }
                    }
                    System.out.println("--o-o-o-o-o-o-o-o-o-o-o-o-o-o-");
                }
            } catch (InterruptedException e) {
                System.out.println("Monitor exiting with " + e);
            }
        }
    }

    Processing function for outgoing data. Pass it thru SSLEngine.wrap()
Any encrypted buffers generated are passed downstream to be written.
Status codes:
    NEED_UNWRAP: call reader.addData() with empty buffer
    NEED_WRAP: call addData() with empty buffer
    NEED_TASK: delegate task to executor
    BUFFER_OVERFLOW: allocate larger output buffer. Repeat wrap
    BUFFER_UNDERFLOW: shouldn't happen on writing side
    OK: return generated buffers
/**
     * Processing function for outgoing data. Pass it thru SSLEngine.wrap()
     * Any encrypted buffers generated are passed downstream to be written.
     * Status codes:
     *     NEED_UNWRAP: call reader.addData() with empty buffer
     *     NEED_WRAP: call addData() with empty buffer
     *     NEED_TASK: delegate task to executor
     *     BUFFER_OVERFLOW: allocate larger output buffer. Repeat wrap
     *     BUFFER_UNDERFLOW: shouldn't happen on writing side
     *     OK: return generated buffers
     */
    class Writer extends SubscriberWrapper {
        final SequentialScheduler scheduler;
        // queues of buffers received from upstream waiting
        // to be processed by the SSLEngine
        final List<ByteBuffer> writeList;
        final Logger debugw =  Utils.getDebugLogger(this::dbgString, Utils.DEBUG);
        volatile boolean completing;
        boolean completed; // only accessed in processData

        class WriterDownstreamPusher extends SequentialScheduler.CompleteRestartableTask {
            @Override public void run() { processData(); }
        }

        Writer() {
            super();
            writeList = Collections.synchronizedList(new LinkedList<>());
            scheduler = new SequentialScheduler(new WriterDownstreamPusher());
        }

        @Override
        protected void incoming(List<ByteBuffer> buffers, boolean complete) {
            assert complete ? buffers == Utils.EMPTY_BB_LIST : true;
            assert buffers != Utils.EMPTY_BB_LIST ? complete == false : true;
            if (complete) {
                if (debugw.on()) debugw.log("adding SENTINEL");
                completing = true;
                writeList.add(SENTINEL);
            } else {
                writeList.addAll(buffers);
            }
            if (debugw.on())
                debugw.log("added " + buffers.size()
                           + " (" + Utils.remaining(buffers)
                           + " bytes) to the writeList");
            scheduler.runOrSchedule();
        }

        public final String dbgString() {
            return "SSL Writer(" + tubeName + ")";
        }

        protected void onSubscribe() {
            if (debugw.on()) debugw.log("onSubscribe initiating handshaking");
            addData(HS_TRIGGER);  // initiates handshaking
        }

        void schedule() {
            scheduler.runOrSchedule();
        }

        void stop() {
            if (debugw.on()) debugw.log("stop");
            scheduler.stop();
        }

        @Override
        public boolean closing() {
            return closeNotifyReceived();
        }

        private boolean isCompleting() {
            return completing;
        }

        @Override
        protected long upstreamWindowUpdate(long currentWindow, long downstreamQsize) {
            if (writeList.size() > 10)
                return 0;
            else
                return super.upstreamWindowUpdate(currentWindow, downstreamQsize);
        }

        private boolean hsTriggered() {
            synchronized(writeList) {
                for (ByteBuffer b : writeList)
                    if (b == HS_TRIGGER)
                        return true;
                return false;
            }
        }

        void triggerWrite() {
            synchronized (writeList) {
                if (writeList.isEmpty()) {
                    writeList.add(HS_TRIGGER);
                }
            }
            scheduler.runOrSchedule();
        }

        private void processData() {
            boolean completing = isCompleting();

            try {
                if (debugw.on())
                    debugw.log("processData, writeList remaining:"
                                + Utils.remaining(writeList) + ", hsTriggered:"
                                + hsTriggered() + ", needWrap:" + needWrap());

                while (Utils.remaining(writeList) > 0 || hsTriggered() || needWrap()) {
                    ByteBuffer[] outbufs = writeList.toArray(Utils.EMPTY_BB_ARRAY);
                    EngineResult result = wrapBuffers(outbufs);
                    if (debugw.on())
                        debugw.log("wrapBuffer returned %s", result.result);

                    if (result.status() == Status.CLOSED) {
                        if (!upstreamCompleted) {
                            upstreamCompleted = true;
                            upstreamSubscription.cancel();
                            // complete ALPN if not yet completed
                            setALPN();
                        }
                        if (result.bytesProduced() <= 0)
                            return;

                        if (!completing && !completed) {
                            completing = this.completing = true;
                            // There could still be some outgoing data in outbufs.
                            writeList.add(SENTINEL);
                        }
                    }

                    boolean handshaking = false;
                    if (result.handshaking()) {
                        if (debugw.on()) debugw.log("handshaking");
                        doHandshake(result, WRITER);  // ok to ignore return
                        handshaking = true;
                    } else {
                        if (trySetALPN()) {
                            resumeActivity();
                        }
                    }
                    cleanList(writeList); // tidy up the source list
                    sendResultBytes(result);
                    if (handshaking) {
                        if (!completing && needWrap()) {
                            continue;
                        } else {
                            return;
                        }
                    }
                }
                if (completing && Utils.remaining(writeList) == 0) {
                    if (!completed) {
                        completed = true;
                        writeList.clear();
                        outgoing(Utils.EMPTY_BB_LIST, true);
                    }
                    return;
                }
                if (writeList.isEmpty() && needWrap()) {
                    writer.addData(HS_TRIGGER);
                }
            } catch (Throwable ex) {
                errorCommon(ex);
                handleError(ex);
            }
        }

        // The SSLEngine insists on being given a buffer that is at least
        // SSLSession.getPacketBufferSize() long (usually 16K). If given
        // a smaller buffer it will go in BUFFER_OVERFLOW, even if it only
        // has 6 bytes to wrap. Typical usage shows that for GET we
        // usually produce an average of ~ 100 bytes.
        // To avoid wasting space, and because allocating and zeroing
        // 16K buffers for encoding 6 bytes is costly, we are reusing the
        // same writeBuffer to interact with SSLEngine.wrap().
        // If the SSLEngine produces less than writeBuffer.capacity() / 2,
        // then we copy off the bytes to a smaller buffer that we send
        // downstream. Otherwise, we send the writeBuffer downstream
        // and will allocate a new one next time.
        volatile ByteBuffer writeBuffer;
        private volatile Status lastWrappedStatus;
        @SuppressWarnings("fallthrough")
        EngineResult wrapBuffers(ByteBuffer[] src) throws SSLException {
            long len = Utils.remaining(src);
            if (debugw.on())
                debugw.log("wrapping " + len + " bytes");

            ByteBuffer dst = writeBuffer;
            if (dst == null) dst = writeBuffer = getNetBuffer();
            assert dst.position() == 0 : "buffer position is " + dst.position();
            assert dst.hasRemaining() : "buffer has no remaining space: capacity=" + dst.capacity();

            while (true) {
                SSLEngineResult sslResult = engine.wrap(src, dst);
                if (debugw.on()) debugw.log("SSLResult: " + sslResult);
                switch (lastWrappedStatus = sslResult.getStatus()) {
                    case BUFFER_OVERFLOW:
                        // Shouldn't happen. We allocated buffer with packet size
                        // get it again if net buffer size was changed
                        if (debugw.on()) debugw.log("BUFFER_OVERFLOW");
                        int netSize = packetBufferSize
                                = engine.getSession().getPacketBufferSize();
                        ByteBuffer b = writeBuffer = ByteBuffer.allocate(netSize + dst.position());
                        dst.flip();
                        b.put(dst);
                        dst = b;
                        break; // try again
                    case CLOSED:
                        if (debugw.on()) debugw.log("CLOSED");
                        // fallthrough. There could be some remaining data in dst.
                        // CLOSED will be handled by the caller.
                    case OK:
                        final ByteBuffer dest;
                        if (dst.position() == 0) {
                            dest = NOTHING; // can happen if handshake is in progress
                        } else if (dst.position() < dst.capacity() / 2) {
                            // less than half the buffer was used.
                            // copy off the bytes to a smaller buffer, and keep
                            // the writeBuffer for next time.
                            dst.flip();
                            dest = Utils.copyAligned(dst);
                            dst.clear();
                        } else {
                            // more than half the buffer was used.
                            // just send that buffer downstream, and we will
                            // get a new writeBuffer next time it is needed.
                            dst.flip();
                            dest = dst;
                            writeBuffer = null;
                        }
                        if (debugw.on())
                            debugw.log("OK => produced: %d bytes into %d, not wrapped: %d",
                                       dest.remaining(),  dest.capacity(), Utils.remaining(src));
                        return new EngineResult(sslResult, dest);
                    case BUFFER_UNDERFLOW:
                        // Shouldn't happen.  Doesn't returns when wrap()
                        // underflow handled externally
                        // assert false : "Buffer Underflow";
                        if (debug.on()) debug.log("BUFFER_UNDERFLOW");
                        return new EngineResult(sslResult);
                    default:
                        if (debugw.on())
                            debugw.log("result: %s", sslResult.getStatus());
                        assert false : "result:" + sslResult.getStatus();
                }
            }
        }

        private boolean needWrap() {
            return engine.getHandshakeStatus() == HandshakeStatus.NEED_WRAP;
        }

        private void sendResultBytes(EngineResult result) {
            if (result.bytesProduced() > 0) {
                if (debugw.on())
                    debugw.log("Sending %d bytes downstream",
                               result.bytesProduced());
                outgoing(result.destBuffer, false);
            }
        }

        @Override
        public String toString() {
            return "WRITER: " + super.toString()
                    + ", writeList size: " + Integer.toString(writeList.size())
                    + ", scheduler: " + (scheduler.isStopped() ? "stopped" : "running")
                    + ", status: " + lastWrappedStatus;
                    //" writeList: " + writeList.toString();
        }
    }

    private void handleError(Throwable t) {
        if (debug.on()) debug.log("handleError", t);
        readerCF.completeExceptionally(t);
        writerCF.completeExceptionally(t);
        // no-op if already completed
        alpnCF.completeExceptionally(t);
        reader.stop();
        writer.stop();
    }

    boolean stopped;

    private synchronized void normalStop() {
        if (stopped)
            return;
        stopped = true;
        reader.stop();
        writer.stop();
        // make sure the alpnCF is completed.
        if (!alpnCF.isDone()) {
            Throwable alpn = new SSLHandshakeException(
                    "Connection closed before successful ALPN negotiation");
            alpnCF.completeExceptionally(alpn);
        }
        if (isMonitored) Monitor.remove(monitor);
    }

    private Void stopOnError(Throwable error) {
        // maybe log, etc
        // ensure the ALPN is completed
        // We could also do this in SSLTube.SSLSubscriberWrapper
        // onError/onComplete - with the caveat that the ALP CF
        // would get completed externally. Doing it here keeps
        // it all inside SSLFlowDelegate.
        if (!alpnCF.isDone()) {
            alpnCF.completeExceptionally(error);
        }
        normalStop();
        return null;
    }

    private void cleanList(List<ByteBuffer> l) {
        synchronized (l) {
            Iterator<ByteBuffer> iter = l.iterator();
            while (iter.hasNext()) {
                ByteBuffer b = iter.next();
                if (!b.hasRemaining() && b != SENTINEL) {
                    iter.remove();
                }
            }
        }
    }

    States for handshake. We avoid races when accessing/updating the AtomicInt
because updates always schedule an additional call to both the read()
and write() functions.
/**
     * States for handshake. We avoid races when accessing/updating the AtomicInt
     * because updates always schedule an additional call to both the read()
     * and write() functions.
     */
    private static final int NOT_HANDSHAKING = 0;
    private static final int HANDSHAKING = 1;

    // Bit flags
    // a thread is currently executing tasks
    private static final int DOING_TASKS = 4;
    // a thread wants to execute tasks, while another thread is executing
    private static final int REQUESTING_TASKS = 8;
    private static final int TASK_BITS = 12; // Both bits

    private static final int READER = 1;
    private static final int WRITER = 2;

    private static String states(AtomicInteger state) {
        int s = state.get();
        StringBuilder sb = new StringBuilder();
        int x = s & ~TASK_BITS;
        switch (x) {
            case NOT_HANDSHAKING:
                sb.append(" NOT_HANDSHAKING ");
                break;
            case HANDSHAKING:
                sb.append(" HANDSHAKING ");
                break;
            default:
                throw new InternalError();
        }
        if ((s & DOING_TASKS) > 0)
            sb.append("|DOING_TASKS");
        if ((s & REQUESTING_TASKS) > 0)
            sb.append("|REQUESTING_TASKS");
        return sb.toString();
    }

    private void resumeActivity() {
        reader.schedule();
        writer.schedule();
    }

    final AtomicInteger handshakeState;
    final ConcurrentLinkedQueue<String> stateList =
            debug.on() ? new ConcurrentLinkedQueue<>() : null;

    // Atomically executed to update task bits. Sets either DOING_TASKS or REQUESTING_TASKS
    // depending on previous value
    private static final IntBinaryOperator REQUEST_OR_DO_TASKS = (current, ignored) -> {
        if ((current & DOING_TASKS) == 0)
            return DOING_TASKS | (current & HANDSHAKING);
        else
            return DOING_TASKS | REQUESTING_TASKS | (current & HANDSHAKING);
    };

    // Atomically executed to update task bits. Sets DOING_TASKS if REQUESTING was set
    // clears bits if not.
    private static final IntBinaryOperator FINISH_OR_DO_TASKS = (current, ignored) -> {
        if ((current & REQUESTING_TASKS) != 0)
            return DOING_TASKS | (current & HANDSHAKING);
        // clear both bits
        return (current & HANDSHAKING);
    };

    private boolean doHandshake(EngineResult r, int caller) {
        // unconditionally sets the HANDSHAKING bit, while preserving task bits
        handshakeState.getAndAccumulate(0, (current, unused) -> HANDSHAKING | (current & TASK_BITS));
        if (stateList != null && debug.on()) {
            stateList.add(r.handshakeStatus().toString());
            stateList.add(Integer.toString(caller));
        }
        switch (r.handshakeStatus()) {
            case NEED_TASK:
                int s = handshakeState.accumulateAndGet(0, REQUEST_OR_DO_TASKS);
                if ((s & REQUESTING_TASKS) > 0) { // someone else is or will do tasks
                    return false;
                }

                if (debug.on()) debug.log("obtaining and initiating task execution");
                List<Runnable> tasks = obtainTasks();
                executeTasks(tasks);
                return false;  // executeTasks will resume activity
            case NEED_WRAP:
                if (caller == READER) {
                    writer.triggerWrite();
                    return false;
                }
                break;
            case NEED_UNWRAP:
            case NEED_UNWRAP_AGAIN:
                // do nothing else
                // receiving-side data will trigger unwrap
                if (caller == WRITER) {
                    reader.schedule();
                    return false;
                }
                break;
            default:
                throw new InternalError("Unexpected handshake status:"
                                        + r.handshakeStatus());
        }
        return true;
    }

    private List<Runnable> obtainTasks() {
        List<Runnable> l = new ArrayList<>();
        Runnable r;
        while ((r = engine.getDelegatedTask()) != null) {
            l.add(r);
        }
        return l;
    }

    private void executeTasks(List<Runnable> tasks) {
        exec.execute(() -> {
            try {
                List<Runnable> nextTasks = tasks;
                if (debug.on()) debug.log("#tasks to execute: " + Integer.toString(nextTasks.size()));
                do {
                    nextTasks.forEach(Runnable::run);
                    if (engine.getHandshakeStatus() == HandshakeStatus.NEED_TASK) {
                        nextTasks = obtainTasks();
                    } else {
                        int s = handshakeState.accumulateAndGet(0, FINISH_OR_DO_TASKS);
                        if ((s & DOING_TASKS) != 0) {
                            if (debug.on()) debug.log("re-running tasks (B)");
                            nextTasks = obtainTasks();
                            continue;
                        }
                        break;
                    }
                } while (true);
                if (debug.on()) debug.log("finished task execution");
                HandshakeStatus hs = engine.getHandshakeStatus();
                if (hs == HandshakeStatus.FINISHED || hs == HandshakeStatus.NOT_HANDSHAKING) {
                    // We're no longer handshaking, try setting ALPN
                    trySetALPN();
                }
                resumeActivity();
            } catch (Throwable t) {
                handleError(t);
            }
        });
    }

    boolean trySetALPN() {
        // complete ALPN CF if needed.
        if ((handshakeState.getAndSet(NOT_HANDSHAKING) & ~DOING_TASKS) == HANDSHAKING) {
            applicationBufferSize = engine.getSession().getApplicationBufferSize();
            packetBufferSize = engine.getSession().getPacketBufferSize();
            setALPN();
            return true;
        }
        return false;
    }

    // FIXME: acknowledge a received CLOSE request from peer
    EngineResult doClosure(EngineResult r) throws IOException {
        if (debug.on())
            debug.log("doClosure(%s): %s [isOutboundDone: %s, isInboundDone: %s]",
                      r.result, engine.getHandshakeStatus(),
                      engine.isOutboundDone(), engine.isInboundDone());
        if (engine.getHandshakeStatus() == HandshakeStatus.NEED_WRAP) {
            // we have received TLS close_notify and need to send
            // an acknowledgement back. We're calling doHandshake
            // to finish the close handshake.
            if (engine.isInboundDone() && !engine.isOutboundDone()) {
                if (debug.on()) debug.log("doClosure: close_notify received");
                close_notify_received = true;
                if (!writer.scheduler.isStopped()) {
                    doHandshake(r, READER);
                } else {
                    // We have received closed notify, but we
                    // won't be able to send the acknowledgement.
                    // Nothing more will come from the socket either,
                    // so mark the reader as completed.
                    synchronized (reader.readBufferLock) {
                        reader.completing = true;
                    }
                }
            }
        }
        return r;
    }

    Returns the upstream Flow.Subscriber of the reading (incoming) side.
This flow must be given the encrypted data read from upstream (eg socket)
before it is decrypted.
/**
     * Returns the upstream Flow.Subscriber of the reading (incoming) side.
     * This flow must be given the encrypted data read from upstream (eg socket)
     * before it is decrypted.
     */
    public Flow.Subscriber<List<ByteBuffer>> upstreamReader() {
        return reader;
    }

    Returns the upstream Flow.Subscriber of the writing (outgoing) side.
This flow contains the plaintext data before it is encrypted.
/**
     * Returns the upstream Flow.Subscriber of the writing (outgoing) side.
     * This flow contains the plaintext data before it is encrypted.
     */
    public Flow.Subscriber<List<ByteBuffer>> upstreamWriter() {
        return writer;
    }

    public boolean resumeReader() {
        return reader.signalScheduling();
    }

    public void resetReaderDemand() {
        reader.resetDownstreamDemand();
    }

    static class EngineResult {
        final SSLEngineResult result;
        final ByteBuffer destBuffer;

        // normal result
        EngineResult(SSLEngineResult result) {
            this(result, null);
        }

        EngineResult(SSLEngineResult result, ByteBuffer destBuffer) {
            this.result = result;
            this.destBuffer = destBuffer;
        }

        boolean handshaking() {
            HandshakeStatus s = result.getHandshakeStatus();
            return s != HandshakeStatus.FINISHED
                   && s != HandshakeStatus.NOT_HANDSHAKING
                   && result.getStatus() != Status.CLOSED;
        }

        boolean needUnwrap() {
            HandshakeStatus s = result.getHandshakeStatus();
            return s == HandshakeStatus.NEED_UNWRAP;
        }


        int bytesConsumed() {
            return result.bytesConsumed();
        }

        int bytesProduced() {
            return result.bytesProduced();
        }

        SSLEngineResult.HandshakeStatus handshakeStatus() {
            return result.getHandshakeStatus();
        }

        SSLEngineResult.Status status() {
            return result.getStatus();
        }
    }

    // The maximum network buffer size negotiated during
    // the handshake. Usually 16K.
    volatile int packetBufferSize;
    final ByteBuffer getNetBuffer() {
        int netSize = packetBufferSize;
        if (netSize <= 0) {
            packetBufferSize = netSize = engine.getSession().getPacketBufferSize();
        }
        return ByteBuffer.allocate(netSize);
    }

    // The maximum application buffer size negotiated during
    // the handshake. Usually close to 16K.
    volatile int applicationBufferSize;
    // Despite of the maximum applicationBufferSize negotiated
    // above, TLS records usually have a much smaller payload.
    // The adaptativeAppBufferSize records the max payload
    // ever decoded, and we use that as a guess for how big
    // a buffer we will need for the next payload.
    // This avoids allocating and zeroing a 16K buffer for
    // nothing...
    volatile int adaptiveAppBufferSize;
    final ByteBuffer getAppBuffer() {
        int appSize = applicationBufferSize;
        if (appSize <= 0) {
            applicationBufferSize = appSize
                    = engine.getSession().getApplicationBufferSize();
        }
        int size = adaptiveAppBufferSize;
        if (size <= 0) {
            size = 512; // start with 512 this is usually enough for handshaking / headers
        } else if (size > appSize) {
            size = appSize;
        }
        // will cause a BUFFER_OVERFLOW if not big enough, but
        // that's OK.
        return ByteBuffer.allocate(size);
    }

    final String dbgString() {
        return "SSLFlowDelegate(" + tubeName + ")";
    }
}
/

java/ 12/ java.net.http/jdk/internal/net/http/common/SSLFlowDelegate.java
