/*
 * Copyright (c) 2015, 2020, 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
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package jdk.internal.net.http;

import java.io.IOException;
import java.lang.System.Logger.Level;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.Flow;
import java.util.stream.Collectors;
import jdk.internal.net.http.common.FlowTube;
import jdk.internal.net.http.common.Logger;
import jdk.internal.net.http.common.Utils;

Http 1.1 connection pool.
/**
 * Http 1.1 connection pool.
 */
final class ConnectionPool {

    static final long KEEP_ALIVE = Utils.getIntegerNetProperty(
            "jdk.httpclient.keepalive.timeout", 1200); // seconds
    static final long MAX_POOL_SIZE = Utils.getIntegerNetProperty(
            "jdk.httpclient.connectionPoolSize", 0); // unbounded
    final Logger debug = Utils.getDebugLogger(this::dbgString, Utils.DEBUG);

    // Pools of idle connections

    private final HashMap<CacheKey,LinkedList<HttpConnection>> plainPool;
    private final HashMap<CacheKey,LinkedList<HttpConnection>> sslPool;
    private final ExpiryList expiryList;
    private final String dbgTag; // used for debug
    boolean stopped;

    
Entries in connection pool are keyed by destination address and/or
proxy address:
case 1: plain TCP not via proxy (destination only)
case 2: plain TCP via proxy (proxy only)
case 3: SSL not via proxy (destination only)
case 4: SSL over tunnel (destination and proxy)
/**
     * Entries in connection pool are keyed by destination address and/or
     * proxy address:
     * case 1: plain TCP not via proxy (destination only)
     * case 2: plain TCP via proxy (proxy only)
     * case 3: SSL not via proxy (destination only)
     * case 4: SSL over tunnel (destination and proxy)
     */
    static class CacheKey {
        final InetSocketAddress proxy;
        final InetSocketAddress destination;

        CacheKey(InetSocketAddress destination, InetSocketAddress proxy) {
            this.proxy = proxy;
            this.destination = destination;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            final CacheKey other = (CacheKey) obj;
            if (!Objects.equals(this.proxy, other.proxy)) {
                return false;
            }
            if (!Objects.equals(this.destination, other.destination)) {
                return false;
            }
            return true;
        }

        @Override
        public int hashCode() {
            return Objects.hash(proxy, destination);
        }
    }

    ConnectionPool(long clientId) {
        this("ConnectionPool("+clientId+")");
    }

    
There should be one of these per HttpClient.
/**
     * There should be one of these per HttpClient.
     */
    private ConnectionPool(String tag) {
        dbgTag = tag;
        plainPool = new HashMap<>();
        sslPool = new HashMap<>();
        expiryList = new ExpiryList();
    }

    final String dbgString() {
        return dbgTag;
    }

    synchronized void start() {
        assert !stopped : "Already stopped";
    }

    static CacheKey cacheKey(InetSocketAddress destination,
                             InetSocketAddress proxy)
    {
        return new CacheKey(destination, proxy);
    }

    synchronized HttpConnection getConnection(boolean secure,
                                              InetSocketAddress addr,
                                              InetSocketAddress proxy) {
        if (stopped) return null;
        // for plain (unsecure) proxy connection the destination address is irrelevant.
        addr = secure || proxy == null ? addr : null;
        CacheKey key = new CacheKey(addr, proxy);
        HttpConnection c = secure ? findConnection(key, sslPool)
                                  : findConnection(key, plainPool);
        //System.out.println ("getConnection returning: " + c);
        assert c == null || c.isSecure() == secure;
        return c;
    }

    
Returns the connection to the pool.
/**
     * Returns the connection to the pool.
     */
    void returnToPool(HttpConnection conn) {
        returnToPool(conn, Instant.now(), KEEP_ALIVE);
    }

    // Called also by whitebox tests
    void returnToPool(HttpConnection conn, Instant now, long keepAlive) {

        assert (conn instanceof PlainHttpConnection) || conn.isSecure()
            : "Attempting to return unsecure connection to SSL pool: "
                + conn.getClass();

        // Don't call registerCleanupTrigger while holding a lock,
        // but register it before the connection is added to the pool,
        // since we don't want to trigger the cleanup if the connection
        // is not in the pool.
        CleanupTrigger cleanup = registerCleanupTrigger(conn);

        // it's possible that cleanup may have been called.
        HttpConnection toClose = null;
        synchronized(this) {
            if (cleanup.isDone()) {
                return;
            } else if (stopped) {
                conn.close();
                return;
            }
            if (MAX_POOL_SIZE > 0 && expiryList.size() >= MAX_POOL_SIZE) {
                toClose = expiryList.removeOldest();
                if (toClose != null) removeFromPool(toClose);
            }
            if (conn instanceof PlainHttpConnection) {
                putConnection(conn, plainPool);
            } else {
                assert conn.isSecure();
                putConnection(conn, sslPool);
            }
            expiryList.add(conn, now, keepAlive);
        }
        if (toClose != null) {
            if (debug.on()) {
                debug.log("Maximum pool size reached: removing oldest connection %s",
                          toClose.dbgString());
            }
            close(toClose);
        }
        //System.out.println("Return to pool: " + conn);
    }

    private CleanupTrigger registerCleanupTrigger(HttpConnection conn) {
        // Connect the connection flow to a pub/sub pair that will take the
        // connection out of the pool and close it if anything happens
        // while the connection is sitting in the pool.
        CleanupTrigger cleanup = new CleanupTrigger(conn);
        FlowTube flow = conn.getConnectionFlow();
        if (debug.on()) debug.log("registering %s", cleanup);
        flow.connectFlows(cleanup, cleanup);
        return cleanup;
    }

    private HttpConnection
    findConnection(CacheKey key,
                   HashMap<CacheKey,LinkedList<HttpConnection>> pool) {
        LinkedList<HttpConnection> l = pool.get(key);
        if (l == null || l.isEmpty()) {
            return null;
        } else {
            HttpConnection c = l.removeFirst();
            expiryList.remove(c);
            return c;
        }
    }

    /* called from cache cleaner only  */
    private boolean
    removeFromPool(HttpConnection c,
                   HashMap<CacheKey,LinkedList<HttpConnection>> pool) {
        //System.out.println("cacheCleaner removing: " + c);
        assert Thread.holdsLock(this);
        CacheKey k = c.cacheKey();
        List<HttpConnection> l = pool.get(k);
        if (l == null || l.isEmpty()) {
            pool.remove(k);
            return false;
        }
        return l.remove(c);
    }

    private void
    putConnection(HttpConnection c,
                  HashMap<CacheKey,LinkedList<HttpConnection>> pool) {
        CacheKey key = c.cacheKey();
        LinkedList<HttpConnection> l = pool.get(key);
        if (l == null) {
            l = new LinkedList<>();
            pool.put(key, l);
        }
        l.add(c);
    }

    
Purge expired connection and return the number of milliseconds
in which the next connection is scheduled to expire.
If no connections are scheduled to be purged return 0.
Returns:
the delay in milliseconds in which the next connection will
        expire./**
     * Purge expired connection and return the number of milliseconds
     * in which the next connection is scheduled to expire.
     * If no connections are scheduled to be purged return 0.
     * @return the delay in milliseconds in which the next connection will
     *         expire.
     */
    long purgeExpiredConnectionsAndReturnNextDeadline() {
        if (!expiryList.purgeMaybeRequired()) return 0;
        return purgeExpiredConnectionsAndReturnNextDeadline(Instant.now());
    }

    // Used for whitebox testing
    long purgeExpiredConnectionsAndReturnNextDeadline(Instant now) {
        long nextPurge = 0;

        // We may be in the process of adding new elements
        // to the expiry list - but those elements will not
        // have outlast their keep alive timer yet since we're
        // just adding them.
        if (!expiryList.purgeMaybeRequired()) return nextPurge;

        List<HttpConnection> closelist;
        synchronized (this) {
            closelist = expiryList.purgeUntil(now);
            for (HttpConnection c : closelist) {
                if (c instanceof PlainHttpConnection) {
                    boolean wasPresent = removeFromPool(c, plainPool);
                    assert wasPresent;
                } else {
                    boolean wasPresent = removeFromPool(c, sslPool);
                    assert wasPresent;
                }
            }
            nextPurge = now.until(
                    expiryList.nextExpiryDeadline().orElse(now),
                    ChronoUnit.MILLIS);
        }
        closelist.forEach(this::close);
        return nextPurge;
    }

    private void close(HttpConnection c) {
        try {
            c.close();
        } catch (Throwable e) {} // ignore
    }

    void stop() {
        List<HttpConnection> closelist = Collections.emptyList();
        try {
            synchronized (this) {
                stopped = true;
                closelist = expiryList.stream()
                    .map(e -> e.connection)
                    .collect(Collectors.toList());
                expiryList.clear();
                plainPool.clear();
                sslPool.clear();
            }
        } finally {
            closelist.forEach(this::close);
        }
    }

    static final class ExpiryEntry {
        final HttpConnection connection;
        final Instant expiry; // absolute time in seconds of expiry time
        ExpiryEntry(HttpConnection connection, Instant expiry) {
            this.connection = connection;
            this.expiry = expiry;
        }
    }

    
Manages a LinkedList of sorted ExpiryEntry. The entry with the closer
deadline is at the tail of the list, and the entry with the farther
deadline is at the head. In the most common situation, new elements
will need to be added at the head (or close to it), and expired elements
will need to be purged from the tail.
/**
     * Manages a LinkedList of sorted ExpiryEntry. The entry with the closer
     * deadline is at the tail of the list, and the entry with the farther
     * deadline is at the head. In the most common situation, new elements
     * will need to be added at the head (or close to it), and expired elements
     * will need to be purged from the tail.
     */
    private static final class ExpiryList {
        private final LinkedList<ExpiryEntry> list = new LinkedList<>();
        private volatile boolean mayContainEntries;

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

        // A loosely accurate boolean whose value is computed
        // at the end of each operation performed on ExpiryList;
        // Does not require synchronizing on the ConnectionPool.
        boolean purgeMaybeRequired() {
            return mayContainEntries;
        }

        // Returns the next expiry deadline
        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        Optional<Instant> nextExpiryDeadline() {
            if (list.isEmpty()) return Optional.empty();
            else return Optional.of(list.getLast().expiry);
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        HttpConnection removeOldest() {
            ExpiryEntry entry = list.pollLast();
            return entry == null ? null : entry.connection;
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        void add(HttpConnection conn) {
            add(conn, Instant.now(), KEEP_ALIVE);
        }

        // Used by whitebox test.
        void add(HttpConnection conn, Instant now, long keepAlive) {
            Instant then = now.truncatedTo(ChronoUnit.SECONDS)
                    .plus(keepAlive, ChronoUnit.SECONDS);

            // Elements with the farther deadline are at the head of
            // the list. It's more likely that the new element will
            // have the farthest deadline, and will need to be inserted
            // at the head of the list, so we're using an ascending
            // list iterator to find the right insertion point.
            ListIterator<ExpiryEntry> li = list.listIterator();
            while (li.hasNext()) {
                ExpiryEntry entry = li.next();

                if (then.isAfter(entry.expiry)) {
                    li.previous();
                    // insert here
                    li.add(new ExpiryEntry(conn, then));
                    mayContainEntries = true;
                    return;
                }
            }
            // last (or first) element of list (the last element is
            // the first when the list is empty)
            list.add(new ExpiryEntry(conn, then));
            mayContainEntries = true;
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        void remove(HttpConnection c) {
            if (c == null || list.isEmpty()) return;
            ListIterator<ExpiryEntry> li = list.listIterator();
            while (li.hasNext()) {
                ExpiryEntry e = li.next();
                if (e.connection.equals(c)) {
                    li.remove();
                    mayContainEntries = !list.isEmpty();
                    return;
                }
            }
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool.
        // Purge all elements whose deadline is before now (now included).
        List<HttpConnection> purgeUntil(Instant now) {
            if (list.isEmpty()) return Collections.emptyList();

            List<HttpConnection> closelist = new ArrayList<>();

            // elements with the closest deadlines are at the tail
            // of the queue, so we're going to use a descending iterator
            // to remove them, and stop when we find the first element
            // that has not expired yet.
            Iterator<ExpiryEntry> li = list.descendingIterator();
            while (li.hasNext()) {
                ExpiryEntry entry = li.next();
                // use !isAfter instead of isBefore in order to
                // remove the entry if its expiry == now
                if (!entry.expiry.isAfter(now)) {
                    li.remove();
                    HttpConnection c = entry.connection;
                    closelist.add(c);
                } else break; // the list is sorted
            }
            mayContainEntries = !list.isEmpty();
            return closelist;
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        java.util.stream.Stream<ExpiryEntry> stream() {
            return list.stream();
        }

        // should only be called while holding a synchronization
        // lock on the ConnectionPool
        void clear() {
            list.clear();
            mayContainEntries = false;
        }
    }

    // Remove a connection from the pool.
    // should only be called while holding a synchronization
    // lock on the ConnectionPool
    private void removeFromPool(HttpConnection c) {
        assert Thread.holdsLock(this);
        if (c instanceof PlainHttpConnection) {
            removeFromPool(c, plainPool);
        } else {
            assert c.isSecure() : "connection " + c + " is not secure!";
            removeFromPool(c, sslPool);
        }
    }

    // Used by tests
    synchronized boolean contains(HttpConnection c) {
        final CacheKey key = c.cacheKey();
        List<HttpConnection> list;
        if ((list = plainPool.get(key)) != null) {
            if (list.contains(c)) return true;
        }
        if ((list = sslPool.get(key)) != null) {
            if (list.contains(c)) return true;
        }
        return false;
    }

    void cleanup(HttpConnection c, Throwable error) {
        if (debug.on())
            debug.log("%s : ConnectionPool.cleanup(%s)",
                    String.valueOf(c.getConnectionFlow()), error);
        synchronized(this) {
            removeFromPool(c);
            expiryList.remove(c);
        }
        c.close();
    }

    
An object that subscribes to the flow while the connection is in
the pool. Anything that comes in will cause the connection to be closed
and removed from the pool.
/**
     * An object that subscribes to the flow while the connection is in
     * the pool. Anything that comes in will cause the connection to be closed
     * and removed from the pool.
     */
    private final class CleanupTrigger implements
            FlowTube.TubeSubscriber, FlowTube.TubePublisher,
            Flow.Subscription {

        private final HttpConnection connection;
        private volatile boolean done;

        public CleanupTrigger(HttpConnection connection) {
            this.connection = connection;
        }

        public boolean isDone() { return done;}

        private void triggerCleanup(Throwable error) {
            done = true;
            cleanup(connection, error);
        }

        @Override public void request(long n) {}
        @Override public void cancel() {}

        @Override
        public void onSubscribe(Flow.Subscription subscription) {
            subscription.request(1);
        }
        @Override
        public void onError(Throwable error) { triggerCleanup(error); }
        @Override
        public void onComplete() { triggerCleanup(null); }
        @Override
        public void onNext(List<ByteBuffer> item) {
            triggerCleanup(new IOException("Data received while in pool"));
        }

        @Override
        public void subscribe(Flow.Subscriber<? super List<ByteBuffer>> subscriber) {
            subscriber.onSubscribe(this);
        }

        @Override
        public String toString() {
            return "CleanupTrigger(" + connection.getConnectionFlow() + ")";
        }
    }
}