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    /*
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// TODO: test peer with segwit

package org.bitcoinj.core;

import com.google.common.base.*;
import com.google.common.base.Objects;
import org.bitcoinj.core.listeners.*;
import org.bitcoinj.net.StreamConnection;
import org.bitcoinj.store.BlockStore;
import org.bitcoinj.store.BlockStoreException;
import org.bitcoinj.utils.ListenerRegistration;
import org.bitcoinj.utils.Threading;
import org.bitcoinj.wallet.Wallet;

import com.google.common.collect.Lists;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import net.jcip.annotations.GuardedBy;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nullable;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

/**
 * 
    A Peer handles the high level communication with a Bitcoin node, extending a {@link PeerSocketHandler} which
 * handles low-level message (de)serialization.
    
 *
 * 
    Note that timeouts are handled by the extended
 * {@link org.bitcoinj.net.AbstractTimeoutHandler} and timeout is automatically disabled (using
 * {@link org.bitcoinj.net.AbstractTimeoutHandler#setTimeoutEnabled(boolean)}) once the version
 * handshake completes.
    
 */
public class Peer extends PeerSocketHandler {
    private static final Logger log = LoggerFactory.getLogger(Peer.class);

    protected final ReentrantLock lock = Threading.lock("peer");

    private final NetworkParameters params;
    private final AbstractBlockChain blockChain;
    private final Context context;

    private final CopyOnWriteArrayList> blocksDownloadedEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> chainDownloadStartedEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> connectedEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> disconnectedEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> getDataEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> preMessageReceivedEventListeners
        = new CopyOnWriteArrayList<>();
    private final CopyOnWriteArrayList> onTransactionEventListeners
        = new CopyOnWriteArrayList<>();
    // Whether to try and download blocks and transactions from this peer. Set to false by PeerGroup if not the
    // primary peer. This is to avoid redundant work and concurrency problems with downloading the same chain
    // in parallel.
    private volatile boolean vDownloadData;
    // The version data to announce to the other side of the connections we make: useful for setting our "user agent"
    // equivalent and other things.
    private final VersionMessage versionMessage;
    // Maximum depth up to which pending transaction dependencies are downloaded, or 0 for disabled.
    private volatile int vDownloadTxDependencyDepth;
    // How many block messages the peer has announced to us. Peers only announce blocks that attach to their best chain
    // so we can use this to calculate the height of the peers chain, by adding it to the initial height in the version
    // message. This method can go wrong if the peer re-orgs onto a shorter (but harder) chain, however, this is rare.
    private final AtomicInteger blocksAnnounced = new AtomicInteger();
    // Each wallet added to the peer will be notified of downloaded transaction data.
    private final CopyOnWriteArrayList wallets;
    // A time before which we only download block headers, after that point we download block bodies.
    @GuardedBy("lock") private long fastCatchupTimeSecs;
    // Whether we are currently downloading headers only or block bodies. Starts at true. If the fast catchup time is
    // set AND our best block is before that date, switch to false until block headers beyond that point have been
    // received at which point it gets set to true again. This isn't relevant unless vDownloadData is true.
    @GuardedBy("lock") private boolean downloadBlockBodies = true;
    // Whether to request filtered blocks instead of full blocks if the protocol version allows for them.
    @GuardedBy("lock") private boolean useFilteredBlocks = false;
    // The current Bloom filter set on the connection, used to tell the remote peer what transactions to send us.
    private volatile BloomFilter vBloomFilter;
    // The last filtered block we received, we're waiting to fill it out with transactions.
    private FilteredBlock currentFilteredBlock = null;
    // How many filtered blocks have been received during the lifetime of this connection. Used to decide when to
    // refresh the server-side side filter by sending a new one (it degrades over time as false positives are added
    // on the remote side, see BIP 37 for a discussion of this).
    // TODO: Is this still needed? It should not be since the auto FP tracking logic was added.
    private int filteredBlocksReceived;
    // If non-null, we should discard incoming filtered blocks because we ran out of keys and are awaiting a new filter
    // to be calculated by the PeerGroup. The discarded block hashes should be added here so we can re-request them
    // once we've recalculated and resent a new filter.
    @GuardedBy("lock") @Nullable private List awaitingFreshFilter;
    // How frequently to refresh the filter. This should become dynamic in future and calculated depending on the
    // actual false positive rate. For now a good value was determined empirically around January 2013.
    private static final int RESEND_BLOOM_FILTER_BLOCK_COUNT = 25000;
    // Keeps track of things we requested internally with getdata but didn't receive yet, so we can avoid re-requests.
    // It's not quite the same as getDataFutures, as this is used only for getdatas done as part of downloading
    // the chain and so is lighter weight (we just keep a bunch of hashes not futures).
    //
    // It is important to avoid a nasty edge case where we can end up with parallel chain downloads proceeding
    // simultaneously if we were to receive a newly solved block whilst parts of the chain are streaming to us.
    private final HashSet pendingBlockDownloads = new HashSet<>();
    // Keep references to TransactionConfidence objects for transactions that were announced by a remote peer, but
    // which we haven't downloaded yet. These objects are de-duplicated by the TxConfidenceTable class.
    // Once the tx is downloaded (by some peer), the Transaction object that is created will have a reference to
    // the confidence object held inside it, and it's then up to the event listeners that receive the Transaction
    // to keep it pinned to the root set if they care about this data.
    @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
    private final HashSet pendingTxDownloads = new HashSet<>();
    // The lowest version number we're willing to accept. Lower than this will result in an immediate disconnect.
    private volatile int vMinProtocolVersion;
    // When an API user explicitly requests a block or transaction from a peer, the InventoryItem is put here
    // whilst waiting for the response. Is not used for downloads Peer generates itself.
    private static class GetDataRequest {
        public GetDataRequest(Sha256Hash hash, SettableFuture future) {
            this.hash = hash;
            this.future = future;
        }
        final Sha256Hash hash;
        final SettableFuture future;
    }
    // TODO: The types/locking should be rationalised a bit.
    private final CopyOnWriteArrayList getDataFutures;
    @GuardedBy("getAddrFutures") private final LinkedList> getAddrFutures;
    @Nullable @GuardedBy("lock") private LinkedList> getutxoFutures;

    // Outstanding pings against this peer and how long the last one took to complete.
    private final ReentrantLock lastPingTimesLock = new ReentrantLock();
    @GuardedBy("lastPingTimesLock") private long[] lastPingTimes = null;
    private final CopyOnWriteArrayList pendingPings;
    private static final int PING_MOVING_AVERAGE_WINDOW = 20;

    private volatile VersionMessage vPeerVersionMessage;

    // A settable future which completes (with this) when the connection is open
    private final SettableFuture connectionOpenFuture = SettableFuture.create();
    private final SettableFuture outgoingVersionHandshakeFuture = SettableFuture.create();
    private final SettableFuture incomingVersionHandshakeFuture = SettableFuture.create();
    private final ListenableFuture versionHandshakeFuture = Futures.transform(
            Futures.allAsList(outgoingVersionHandshakeFuture, incomingVersionHandshakeFuture),
            new Function, Peer>() {

                @Override
                @Nullable
                public Peer apply(@Nullable List peers) {
                    checkNotNull(peers);
                    checkState(peers.size() == 2 && peers.get(0) == peers.get(1));
                    return peers.get(0);
                }
            });

    /**
     * 
    Construct a peer that reads/writes from the given block chain.
    
     *
     * 
    Note that this does NOT make a connection to the given remoteAddress, it only creates a handler for a
     * connection. If you want to create a one-off connection, create a Peer and pass it to
     * {@link org.bitcoinj.net.NioClientManager#openConnection(java.net.SocketAddress, StreamConnection)}
     * or
     * {@link org.bitcoinj.net.NioClient#NioClient(java.net.SocketAddress, StreamConnection, int)}.
    
     *
     * 
    The remoteAddress provided should match the remote address of the peer which is being connected to, and is
     * used to keep track of which peers relayed transactions and offer more descriptive logging.
    
     */
    public Peer(NetworkParameters params, VersionMessage ver, @Nullable AbstractBlockChain chain, PeerAddress remoteAddress) {
        this(params, ver, remoteAddress, chain);
    }

    /**
     * 
    Construct a peer that reads/writes from the given block chain. Transactions stored in a {@link org.bitcoinj.core.TxConfidenceTable}
     * will have their confidence levels updated when a peer announces it, to reflect the greater likelyhood that
     * the transaction is valid.
    
     *
     * 
    Note that this does NOT make a connection to the given remoteAddress, it only creates a handler for a
     * connection. If you want to create a one-off connection, create a Peer and pass it to
     * {@link org.bitcoinj.net.NioClientManager#openConnection(java.net.SocketAddress, StreamConnection)}
     * or
     * {@link org.bitcoinj.net.NioClient#NioClient(java.net.SocketAddress, StreamConnection, int)}.
    
     *
     * 
    The remoteAddress provided should match the remote address of the peer which is being connected to, and is
     * used to keep track of which peers relayed transactions and offer more descriptive logging.
    
     */
    public Peer(NetworkParameters params, VersionMessage ver, PeerAddress remoteAddress,
                @Nullable AbstractBlockChain chain) {
        this(params, ver, remoteAddress, chain, Integer.MAX_VALUE);
    }

    /**
     * 
    Construct a peer that reads/writes from the given block chain. Transactions stored in a {@link org.bitcoinj.core.TxConfidenceTable}
     * will have their confidence levels updated when a peer announces it, to reflect the greater likelyhood that
     * the transaction is valid.
    
     *
     * 
    Note that this does NOT make a connection to the given remoteAddress, it only creates a handler for a
     * connection. If you want to create a one-off connection, create a Peer and pass it to
     * {@link org.bitcoinj.net.NioClientManager#openConnection(java.net.SocketAddress, StreamConnection)}
     * or
     * {@link org.bitcoinj.net.NioClient#NioClient(java.net.SocketAddress, StreamConnection, int)}.
    
     *
     * 
    The remoteAddress provided should match the remote address of the peer which is being connected to, and is
     * used to keep track of which peers relayed transactions and offer more descriptive logging.
    
     */
    public Peer(NetworkParameters params, VersionMessage ver, PeerAddress remoteAddress,
                @Nullable AbstractBlockChain chain, int downloadTxDependencyDepth) {
        super(params, remoteAddress);
        this.params = Preconditions.checkNotNull(params);
        this.versionMessage = Preconditions.checkNotNull(ver);
        this.vDownloadTxDependencyDepth = chain != null ? downloadTxDependencyDepth : 0;
        this.blockChain = chain;  // Allowed to be null.
        this.vDownloadData = chain != null;
        this.getDataFutures = new CopyOnWriteArrayList<>();
        this.getAddrFutures = new LinkedList<>();
        this.fastCatchupTimeSecs = params.getGenesisBlock().getTimeSeconds();
        this.pendingPings = new CopyOnWriteArrayList<>();
        this.vMinProtocolVersion = params.getProtocolVersionNum(NetworkParameters.ProtocolVersion.PONG);
        this.wallets = new CopyOnWriteArrayList<>();
        this.context = Context.get();

        this.versionHandshakeFuture.addListener(new Runnable() {
            @Override
            public void run() {
                versionHandshakeComplete();
            }
        }, Threading.SAME_THREAD);
    }

    /**
     * 
    Construct a peer that reads/writes from the given chain. Automatically creates a VersionMessage for you from
     * the given software name/version strings, which should be something like "MySimpleTool", "1.0" and which will tell
     * the remote node to relay transaction inv messages before it has received a filter.
    
     *
     * 
    Note that this does NOT make a connection to the given remoteAddress, it only creates a handler for a
     * connection. If you want to create a one-off connection, create a Peer and pass it to
     * {@link org.bitcoinj.net.NioClientManager#openConnection(java.net.SocketAddress, StreamConnection)}
     * or
     * {@link org.bitcoinj.net.NioClient#NioClient(java.net.SocketAddress, StreamConnection, int)}.
    
     *
     * 
    The remoteAddress provided should match the remote address of the peer which is being connected to, and is
     * used to keep track of which peers relayed transactions and offer more descriptive logging.
    
     */
    public Peer(NetworkParameters params, AbstractBlockChain blockChain, PeerAddress peerAddress, String thisSoftwareName, String thisSoftwareVersion) {
        this(params, new VersionMessage(params, blockChain.getBestChainHeight()), blockChain, peerAddress);
        this.versionMessage.appendToSubVer(thisSoftwareName, thisSoftwareVersion, null);
    }

    /** Deprecated: use the more specific event handler methods instead */
    @Deprecated @SuppressWarnings("deprecation")
    public void addEventListener(AbstractPeerEventListener listener) {
        addBlocksDownloadedEventListener(Threading.USER_THREAD, listener);
        addChainDownloadStartedEventListener(Threading.USER_THREAD, listener);
        addConnectedEventListener(Threading.USER_THREAD, listener);
        addDisconnectedEventListener(Threading.USER_THREAD, listener);
        addGetDataEventListener(Threading.USER_THREAD, listener);
        addOnTransactionBroadcastListener(Threading.USER_THREAD, listener);
        addPreMessageReceivedEventListener(Threading.USER_THREAD, listener);
    }

    /** Deprecated: use the more specific event handler methods instead */
    @Deprecated
    public void addEventListener(AbstractPeerEventListener listener, Executor executor) {
        addBlocksDownloadedEventListener(executor, listener);
        addChainDownloadStartedEventListener(executor, listener);
        addConnectedEventListener(executor, listener);
        addDisconnectedEventListener(executor, listener);
        addGetDataEventListener(executor, listener);
        addOnTransactionBroadcastListener(executor, listener);
        addPreMessageReceivedEventListener(executor, listener);
    }

    /** Deprecated: use the more specific event handler methods instead */
    @Deprecated
    public void removeEventListener(AbstractPeerEventListener listener) {
        removeBlocksDownloadedEventListener(listener);
        removeChainDownloadStartedEventListener(listener);
        removeConnectedEventListener(listener);
        removeDisconnectedEventListener(listener);
        removeGetDataEventListener(listener);
        removeOnTransactionBroadcastListener(listener);
        removePreMessageReceivedEventListener(listener);
    }

    /** Registers a listener that is invoked when new blocks are downloaded. */
    public void addBlocksDownloadedEventListener(BlocksDownloadedEventListener listener) {
        addBlocksDownloadedEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is invoked when new blocks are downloaded. */
    public void addBlocksDownloadedEventListener(Executor executor, BlocksDownloadedEventListener listener) {
        blocksDownloadedEventListeners.add(new ListenerRegistration(listener, executor));
    }

    /** Registers a listener that is invoked when a blockchain downloaded starts. */
    public void addChainDownloadStartedEventListener(ChainDownloadStartedEventListener listener) {
        addChainDownloadStartedEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is invoked when a blockchain downloaded starts. */
    public void addChainDownloadStartedEventListener(Executor executor, ChainDownloadStartedEventListener listener) {
        chainDownloadStartedEventListeners.add(new ListenerRegistration(listener, executor));
    }

    /** Registers a listener that is invoked when a peer is connected. */
    public void addConnectedEventListener(PeerConnectedEventListener listener) {
        addConnectedEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is invoked when a peer is connected. */
    public void addConnectedEventListener(Executor executor, PeerConnectedEventListener listener) {
        connectedEventListeners.add(new ListenerRegistration(listener, executor));
    }

    /** Registers a listener that is invoked when a peer is disconnected. */
    public void addDisconnectedEventListener(PeerDisconnectedEventListener listener) {
        addDisconnectedEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is invoked when a peer is disconnected. */
    public void addDisconnectedEventListener(Executor executor, PeerDisconnectedEventListener listener) {
        disconnectedEventListeners.add(new ListenerRegistration(listener, executor));
    }

    /** Registers a listener that is called when messages are received. */
    public void addGetDataEventListener(GetDataEventListener listener) {
        addGetDataEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is called when messages are received. */
    public void addGetDataEventListener(Executor executor, GetDataEventListener listener) {
        getDataEventListeners.add(new ListenerRegistration<>(listener, executor));
    }

    /** Registers a listener that is called when a transaction is broadcast across the network */
    public void addOnTransactionBroadcastListener(OnTransactionBroadcastListener listener) {
        addOnTransactionBroadcastListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is called when a transaction is broadcast across the network */
    public void addOnTransactionBroadcastListener(Executor executor, OnTransactionBroadcastListener listener) {
        onTransactionEventListeners.add(new ListenerRegistration<>(listener, executor));
    }

    /** Registers a listener that is called immediately before a message is received */
    public void addPreMessageReceivedEventListener(PreMessageReceivedEventListener listener) {
        addPreMessageReceivedEventListener(Threading.USER_THREAD, listener);
    }

    /** Registers a listener that is called immediately before a message is received */
    public void addPreMessageReceivedEventListener(Executor executor, PreMessageReceivedEventListener listener) {
        preMessageReceivedEventListeners.add(new ListenerRegistration<>(listener, executor));
    }

    public boolean removeBlocksDownloadedEventListener(BlocksDownloadedEventListener listener) {
        return ListenerRegistration.removeFromList(listener, blocksDownloadedEventListeners);
    }

    public boolean removeChainDownloadStartedEventListener(ChainDownloadStartedEventListener listener) {
        return ListenerRegistration.removeFromList(listener, chainDownloadStartedEventListeners);
    }

    public boolean removeConnectedEventListener(PeerConnectedEventListener listener) {
        return ListenerRegistration.removeFromList(listener, connectedEventListeners);
    }

    public boolean removeDisconnectedEventListener(PeerDisconnectedEventListener listener) {
        return ListenerRegistration.removeFromList(listener, disconnectedEventListeners);
    }

    public boolean removeGetDataEventListener(GetDataEventListener listener) {
        return ListenerRegistration.removeFromList(listener, getDataEventListeners);
    }

    public boolean removeOnTransactionBroadcastListener(OnTransactionBroadcastListener listener) {
        return ListenerRegistration.removeFromList(listener, onTransactionEventListeners);
    }

    public boolean removePreMessageReceivedEventListener(PreMessageReceivedEventListener listener) {
        return ListenerRegistration.removeFromList(listener, preMessageReceivedEventListeners);
    }

    @Override
    public String toString() {
        PeerAddress addr = getAddress();
        // if null, it's a user-provided NetworkConnection object
        return addr == null ? "Peer()" : addr.toString();
    }

    @Override
    protected void timeoutOccurred() {
        super.timeoutOccurred();
        if (!connectionOpenFuture.isDone()) {
            connectionClosed();  // Invoke the event handlers to tell listeners e.g. PeerGroup that we never managed to connect.
        }
    }

    @Override
    public void connectionClosed() {
        for (final ListenerRegistration registration : disconnectedEventListeners) {
            registration.executor.execute(new Runnable() {
                @Override
                public void run() {
                    registration.listener.onPeerDisconnected(Peer.this, 0);
                }
            });
        }
    }

    @Override
    public void connectionOpened() {
        // Announce ourselves. This has to come first to connect to clients beyond v0.3.20.2 which wait to hear
        // from us until they send their version message back.
        PeerAddress address = getAddress();
        log.info("Announcing to {} as: {}", address == null ? "Peer" : address.toSocketAddress(), versionMessage.subVer);
        sendMessage(versionMessage);
        connectionOpenFuture.set(this);
        // When connecting, the remote peer sends us a version message with various bits of
        // useful data in it. We need to know the peer protocol version before we can talk to it.
    }

    /**
     * Provides a ListenableFuture that can be used to wait for the socket to connect.  A socket connection does not
     * mean that protocol handshake has occurred.
     */
    public ListenableFuture getConnectionOpenFuture() {
        return connectionOpenFuture;
    }

    public ListenableFuture getVersionHandshakeFuture() {
        return versionHandshakeFuture;
    }

    @Override
    protected void processMessage(Message m) throws Exception {
        // Allow event listeners to filter the message stream. Listeners are allowed to drop messages by
        // returning null.
        for (ListenerRegistration registration : preMessageReceivedEventListeners) {
            // Skip any listeners that are supposed to run in another thread as we don't want to block waiting
            // for it, which might cause circular deadlock.
            if (registration.executor == Threading.SAME_THREAD) {
                m = registration.listener.onPreMessageReceived(this, m);
                if (m == null) break;
            }
        }
        if (m == null) return;

        // If we are in the middle of receiving transactions as part of a filtered block push from the remote node,
        // and we receive something that's not a transaction, then we're done.
        if (currentFilteredBlock != null && !(m instanceof Transaction)) {
            endFilteredBlock(currentFilteredBlock);
            currentFilteredBlock = null;
        }

        // No further communication is possible until version handshake is complete.
        if (!(m instanceof VersionMessage || m instanceof VersionAck
                || (versionHandshakeFuture.isDone() && !versionHandshakeFuture.isCancelled())))
            throw new ProtocolException(
                    "Received " + m.getClass().getSimpleName() + " before version handshake is complete.");

        if (m instanceof Ping) {
            processPing((Ping) m);
        } else if (m instanceof Pong) {
            processPong((Pong) m);
        } else if (m instanceof NotFoundMessage) {
            // This is sent to us when we did a getdata on some transactions that aren't in the peers memory pool.
            // Because NotFoundMessage is a subclass of InventoryMessage, the test for it must come before the next.
            processNotFoundMessage((NotFoundMessage) m);
        } else if (m instanceof InventoryMessage) {
            processInv((InventoryMessage) m);
        } else if (m instanceof Block) {
            processBlock((Block) m);
        } else if (m instanceof FilteredBlock) {
            startFilteredBlock((FilteredBlock) m);
        } else if (m instanceof Transaction) {
            processTransaction((Transaction) m);
        } else if (m instanceof GetDataMessage) {
            processGetData((GetDataMessage) m);
        } else if (m instanceof AddressMessage) {
            // We don't care about addresses of the network right now. But in future,
            // we should save them in the wallet so we don't put too much load on the seed nodes and can
            // properly explore the network.
            processAddressMessage((AddressMessage) m);
        } else if (m instanceof HeadersMessage) {
            processHeaders((HeadersMessage) m);
        } else if (m instanceof AlertMessage) {
            processAlert((AlertMessage) m);
        } else if (m instanceof VersionMessage) {
            processVersionMessage((VersionMessage) m);
        } else if (m instanceof VersionAck) {
            processVersionAck((VersionAck) m);
        } else if (m instanceof UTXOsMessage) {
            processUTXOMessage((UTXOsMessage) m);
        } else if (m instanceof RejectMessage) {
            log.error("{} {}: Received {}", this, getPeerVersionMessage().subVer, m);
        } else {
            log.warn("{}: Received unhandled message: {}", this, m);
        }
    }

    protected void processUTXOMessage(UTXOsMessage m) {
        SettableFuture future = null;
        lock.lock();
        try {
            if (getutxoFutures != null)
                future = getutxoFutures.pollFirst();
        } finally {
            lock.unlock();
        }
        if (future != null)
            future.set(m);
    }

    private void processAddressMessage(AddressMessage m) {
        SettableFuture future;
        synchronized (getAddrFutures) {
            future = getAddrFutures.poll();
            if (future == null)  // Not an addr message we are waiting for.
                return;
        }
        future.set(m);
    }

    private void processVersionMessage(VersionMessage m) throws ProtocolException {
        if (vPeerVersionMessage != null)
            throw new ProtocolException("Got two version messages from peer");
        vPeerVersionMessage = m;
        // Switch to the new protocol version.
        long peerTime = vPeerVersionMessage.time * 1000;
        log.info("{}: Got version={}, subVer='{}', services=0x{}, time={}, blocks={}",
                this,
                vPeerVersionMessage.clientVersion,
                vPeerVersionMessage.subVer,
                vPeerVersionMessage.localServices,
                String.format(Locale.US, "%tF %tT", peerTime, peerTime),
                vPeerVersionMessage.bestHeight);
        // bitcoinj is a client mode implementation. That means there's not much point in us talking to other client
        // mode nodes because we can't download the data from them we need to find/verify transactions. Some bogus
        // implementations claim to have a block chain in their services field but then report a height of zero, filter
        // them out here.
        if (!vPeerVersionMessage.hasBlockChain() ||
                (!params.allowEmptyPeerChain() && vPeerVersionMessage.bestHeight == 0)) {
            // Shut down the channel gracefully.
            log.info("{}: Peer does not have a copy of the block chain.", this);
            close();
            return;
        }
        if ((vPeerVersionMessage.localServices
                & VersionMessage.NODE_BITCOIN_CASH) == VersionMessage.NODE_BITCOIN_CASH) {
            log.info("{}: Peer follows an incompatible block chain.", this);
            // Shut down the channel gracefully.
            close();
            return;
        }
        if (vPeerVersionMessage.bestHeight < 0)
            // In this case, it's a protocol violation.
            throw new ProtocolException("Peer reports invalid best height: " + vPeerVersionMessage.bestHeight);
        // Now it's our turn ...
        // Send an ACK message stating we accept the peers protocol version.
        sendMessage(new VersionAck());
        log.debug("{}: Incoming version handshake complete.", this);
        incomingVersionHandshakeFuture.set(this);
    }

    private void processVersionAck(VersionAck m) throws ProtocolException {
        if (vPeerVersionMessage == null) {
            throw new ProtocolException("got a version ack before version");
        }
        if (outgoingVersionHandshakeFuture.isDone()) {
            throw new ProtocolException("got more than one version ack");
        }
        log.debug("{}: Outgoing version handshake complete.", this);
        outgoingVersionHandshakeFuture.set(this);
    }

    private void versionHandshakeComplete() {
        log.debug("{}: Handshake complete.", this);
        setTimeoutEnabled(false);
        for (final ListenerRegistration registration : connectedEventListeners) {
            registration.executor.execute(new Runnable() {
                @Override
                public void run() {
                    registration.listener.onPeerConnected(Peer.this, 1);
                }
            });
        }
        // We check min version after onPeerConnected as channel.close() will
        // call onPeerDisconnected, and we should probably call onPeerConnected first.
        final int version = vMinProtocolVersion;
        if (vPeerVersionMessage.clientVersion < version) {
            log.warn("Connected to a peer speaking protocol version {} but need {}, closing",
                    vPeerVersionMessage.clientVersion, version);
            close();
        }
    }

    protected void startFilteredBlock(FilteredBlock m) {
        // Filtered blocks come before the data that they refer to, so stash it here and then fill it out as
        // messages stream in. We'll call endFilteredBlock when a non-tx message arrives (eg, another
        // FilteredBlock) or when a tx that isn't needed by that block is found. A ping message is sent after
        // a getblocks, to force the non-tx message path.
        currentFilteredBlock = m;
        // Potentially refresh the server side filter. Because the remote node adds hits back into the filter
        // to save round-tripping back through us, the filter degrades over time as false positives get added,
        // triggering yet more false positives. We refresh it every so often to get the FP rate back down.
        filteredBlocksReceived++;
        if (filteredBlocksReceived % RESEND_BLOOM_FILTER_BLOCK_COUNT == RESEND_BLOOM_FILTER_BLOCK_COUNT - 1) {
            sendMessage(vBloomFilter);
        }
    }

    protected void processNotFoundMessage(NotFoundMessage m) {
        // This is received when we previously did a getdata but the peer couldn't find what we requested in it's
        // memory pool. Typically, because we are downloading dependencies of a relevant transaction and reached
        // the bottom of the dependency tree (where the unconfirmed transactions connect to transactions that are
        // in the chain).
        //
        // We go through and cancel the pending getdata futures for the items we were told weren't found.
        for (GetDataRequest req : getDataFutures) {
            for (InventoryItem item : m.getItems()) {
                if (item.hash.equals(req.hash)) {
                    log.info("{}: Bottomed out dep tree at {}", this, req.hash);
                    req.future.cancel(true);
                    getDataFutures.remove(req);
                    break;
                }
            }
        }
    }

    protected void processAlert(AlertMessage m) {
        try {
            if (m.isSignatureValid()) {
                log.debug("Received alert from peer {}: {}", this, m.getStatusBar());
            } else {
                log.debug("Received alert with invalid signature from peer {}: {}", this, m.getStatusBar());
            }
        } catch (Throwable t) {
            // Signature checking can FAIL on Android platforms before Gingerbread apparently due to bugs in their
            // BigInteger implementations! See https://github.com/bitcoinj/bitcoinj/issues/526 for discussion. As
            // alerts are just optional and not that useful, we just swallow the error here.
            log.error("Failed to check signature: bug in platform libraries?", t);
        }
    }

    protected void processHeaders(HeadersMessage m) throws ProtocolException {
        // Runs in network loop thread for this peer.
        //
        // This method can run if a peer just randomly sends us a "headers" message (should never happen), or more
        // likely when we've requested them as part of chain download using fast catchup. We need to add each block to
        // the chain if it pre-dates the fast catchup time. If we go past it, we can stop processing the headers and
        // request the full blocks from that point on instead.
        boolean downloadBlockBodies;
        long fastCatchupTimeSecs;

        lock.lock();
        try {
            if (blockChain == null) {
                // Can happen if we are receiving unrequested data, or due to programmer error.
                log.warn("Received headers when Peer is not configured with a chain.");
                return;
            }
            fastCatchupTimeSecs = this.fastCatchupTimeSecs;
            downloadBlockBodies = this.downloadBlockBodies;
        } finally {
            lock.unlock();
        }

        try {
            checkState(!downloadBlockBodies, toString());
            for (int i = 0; i < m.getBlockHeaders().size(); i++) {
                Block header = m.getBlockHeaders().get(i);
                // Process headers until we pass the fast catchup time, or are about to catch up with the head
                // of the chain - always process the last block as a full/filtered block to kick us out of the
                // fast catchup mode (in which we ignore new blocks).
                boolean passedTime = header.getTimeSeconds() >= fastCatchupTimeSecs;
                boolean reachedTop = blockChain.getBestChainHeight() >= vPeerVersionMessage.bestHeight;
                if (!passedTime && !reachedTop) {
                    if (!vDownloadData) {
                        // Not download peer anymore, some other peer probably became better.
                        log.info("Lost download peer status, throwing away downloaded headers.");
                        return;
                    }
                    if (blockChain.add(header)) {
                        // The block was successfully linked into the chain. Notify the user of our progress.
                        invokeOnBlocksDownloaded(header, null);
                    } else {
                        // This block is unconnected - we don't know how to get from it back to the genesis block yet.
                        // That must mean that the peer is buggy or malicious because we specifically requested for
                        // headers that are part of the best chain.
                        throw new ProtocolException("Got unconnected header from peer: " + header.getHashAsString());
                    }
                } else {
                    lock.lock();
                    try {
                        log.info(
                                "Passed the fast catchup time ({}) at height {}, discarding {} headers and requesting full blocks",
                                Utils.dateTimeFormat(fastCatchupTimeSecs * 1000), blockChain.getBestChainHeight() + 1,
                                m.getBlockHeaders().size() - i);
                        this.downloadBlockBodies = true;
                        // Prevent this request being seen as a duplicate.
                        this.lastGetBlocksBegin = Sha256Hash.ZERO_HASH;
                        blockChainDownloadLocked(Sha256Hash.ZERO_HASH);
                    } finally {
                        lock.unlock();
                    }
                    return;
                }
            }
            // We added all headers in the message to the chain. Request some more if we got up to the limit, otherwise
            // we are at the end of the chain.
            if (m.getBlockHeaders().size() >= HeadersMessage.MAX_HEADERS) {
                lock.lock();
                try {
                    blockChainDownloadLocked(Sha256Hash.ZERO_HASH);
                } finally {
                    lock.unlock();
                }
            }
        } catch (VerificationException e) {
            log.warn("Block header verification failed", e);
        } catch (PrunedException e) {
            // Unreachable when in SPV mode.
            throw new RuntimeException(e);
        }
    }

    protected void processGetData(GetDataMessage getdata) {
        log.info("{}: Received getdata message: {}", getAddress(), getdata.toString());
        ArrayList items = new ArrayList<>();
        for (ListenerRegistration registration : getDataEventListeners) {
            if (registration.executor != Threading.SAME_THREAD) continue;
            List listenerItems = registration.listener.getData(this, getdata);
            if (listenerItems == null) continue;
            items.addAll(listenerItems);
        }
        if (items.isEmpty()) {
            return;
        }
        log.info("{}: Sending {} items gathered from listeners to peer", getAddress(), items.size());
        for (Message item : items) {
            sendMessage(item);
        }
    }

    protected void processTransaction(final Transaction tx) throws VerificationException {
        // Check a few basic syntax issues to ensure the received TX isn't nonsense.
        tx.verify();
        lock.lock();
        try {
            log.debug("{}: Received tx {}", getAddress(), tx.getHashAsString());
            // Label the transaction as coming in from the P2P network (as opposed to being created by us, direct import,
            // etc). This helps the wallet decide how to risk analyze it later.
            //
            // Additionally, by invoking tx.getConfidence(), this tx now pins the confidence data into the heap, meaning
            // we can stop holding a reference to the confidence object ourselves. It's up to event listeners on the
            // Peer to stash the tx object somewhere if they want to keep receiving updates about network propagation
            // and so on.
            TransactionConfidence confidence = tx.getConfidence();
            confidence.setSource(TransactionConfidence.Source.NETWORK);
            pendingTxDownloads.remove(confidence);
            if (maybeHandleRequestedData(tx)) {
                return;
            }
            if (currentFilteredBlock != null) {
                if (!currentFilteredBlock.provideTransaction(tx)) {
                    // Got a tx that didn't fit into the filtered block, so we must have received everything.
                    endFilteredBlock(currentFilteredBlock);
                    currentFilteredBlock = null;
                }
                // Don't tell wallets or listeners about this tx as they'll learn about it when the filtered block is
                // fully downloaded instead.
                return;
            }
            // It's a broadcast transaction. Tell all wallets about this tx so they can check if it's relevant or not.
            for (final Wallet wallet : wallets) {
                try {
                    if (wallet.isPendingTransactionRelevant(tx)) {
                        if (vDownloadTxDependencyDepth > 0) {
                            // This transaction seems interesting to us, so let's download its dependencies. This has
                            // several purposes: we can check that the sender isn't attacking us by engaging in protocol
                            // abuse games, like depending on a time-locked transaction that will never confirm, or
                            // building huge chains of unconfirmed transactions (again - so they don't confirm and the
                            // money can be taken back with a Finney attack). Knowing the dependencies also lets us
                            // store them in a serialized wallet so we always have enough data to re-announce to the
                            // network and get the payment into the chain, in case the sender goes away and the network
                            // starts to forget.
                            //
                            // TODO: Not all the above things are implemented.
                            //
                            // Note that downloading of dependencies can end up walking around 15 minutes back even
                            // through transactions that have confirmed, as getdata on the remote peer also checks
                            // relay memory not only the mempool. Unfortunately we have no way to know that here. In
                            // practice it should not matter much.
                            Futures.addCallback(downloadDependencies(tx), new FutureCallback>() {
                                @Override
                                public void onSuccess(List dependencies) {
                                    try {
                                        log.info("{}: Dependency download complete!", getAddress());
                                        wallet.receivePending(tx, dependencies);
                                    } catch (VerificationException e) {
                                        log.error("{}: Wallet failed to process pending transaction {}", getAddress(), tx.getHash());
                                        log.error("Error was: ", e);
                                        // Not much more we can do at this point.
                                    }
                                }

                                @Override
                                public void onFailure(Throwable throwable) {
                                    log.error("Could not download dependencies of tx {}", tx.getHashAsString());
                                    log.error("Error was: ", throwable);
                                    // Not much more we can do at this point.
                                }
                            });
                        } else {
                            wallet.receivePending(tx, null);
                        }
                    }
                } catch (VerificationException e) {
                    log.error("Wallet failed to verify tx", e);
                    // Carry on, listeners may still want to know.
                }
            }
        } finally {
            lock.unlock();
        }
        // Tell all listeners about this tx so they can decide whether to keep it or not. If no listener keeps a
        // reference around then the memory pool will forget about it after a while too because it uses weak references.
        for (final ListenerRegistration registration : onTransactionEventListeners) {
            registration.executor.execute(new Runnable() {
                @Override
                public void run() {
                    registration.listener.onTransaction(Peer.this, tx);
                }
            });
        }
    }

    /**
     * 
    Returns a future that wraps a list of all transactions that the given transaction depends on, recursively.
     * Only transactions in peers memory pools are included; the recursion stops at transactions that are in the
     * current best chain. So it doesn't make much sense to provide a tx that was already in the best chain and
     * a precondition checks this.
    
     *
     * 
    For example, if tx has 2 inputs that connect to transactions A and B, and transaction B is unconfirmed and
     * has one input connecting to transaction C that is unconfirmed, and transaction C connects to transaction D
     * that is in the chain, then this method will return either {B, C} or {C, B}. No ordering is guaranteed.
    
     *
     * 
    This method is useful for apps that want to learn about how long an unconfirmed transaction might take
     * to confirm, by checking for unexpectedly time locked transactions, unusually deep dependency trees or fee-paying
     * transactions that depend on unconfirmed free transactions.
    
     *
     * 
    Note that dependencies downloaded this way will not trigger the onTransaction method of event listeners.
    
     */
    public ListenableFuture> downloadDependencies(Transaction tx) {
        TransactionConfidence.ConfidenceType txConfidence = tx.getConfidence().getConfidenceType();
        Preconditions.checkArgument(txConfidence != TransactionConfidence.ConfidenceType.BUILDING);
        log.info("{}: Downloading dependencies of {}", getAddress(), tx.getHashAsString());
        final LinkedList results = new LinkedList<>();
        // future will be invoked when the entire dependency tree has been walked and the results compiled.
        final ListenableFuture future = downloadDependenciesInternal(vDownloadTxDependencyDepth, 0, tx,
                new Object(), results);
        final SettableFuture> resultFuture = SettableFuture.create();
        Futures.addCallback(future, new FutureCallback() {
            @Override
            public void onSuccess(Object ignored) {
                resultFuture.set(results);
            }

            @Override
            public void onFailure(Throwable throwable) {
                resultFuture.setException(throwable);
            }
        });
        return resultFuture;
    }

    // The marker object in the future returned is the same as the parameter. It is arbitrary and can be anything.
    protected ListenableFuture downloadDependenciesInternal(final int maxDepth, final int depth,
            final Transaction tx, final Object marker, final List results) {

        final SettableFuture resultFuture = SettableFuture.create();
        final Sha256Hash rootTxHash = tx.getHash();
        // We want to recursively grab its dependencies. This is so listeners can learn important information like
        // whether a transaction is dependent on a timelocked transaction or has an unexpectedly deep dependency tree
        // or depends on a no-fee transaction.

        // We may end up requesting transactions that we've already downloaded and thrown away here.
        Set needToRequest = new CopyOnWriteArraySet<>();
        for (TransactionInput input : tx.getInputs()) {
            // There may be multiple inputs that connect to the same transaction.
            needToRequest.add(input.getOutpoint().getHash());
        }
        lock.lock();
        try {
            // Build the request for the missing dependencies.
            List> futures = Lists.newArrayList();
            GetDataMessage getdata = new GetDataMessage(params);
            if (needToRequest.size() > 1)
                log.info("{}: Requesting {} transactions for depth {} dep resolution", getAddress(), needToRequest.size(), depth + 1);
            for (Sha256Hash hash : needToRequest) {
                if (vPeerVersionMessage.isWitnessSupported())
                    getdata.addWitnessTransaction(hash);
                else
                    getdata.addTransaction(hash);
                GetDataRequest req = new GetDataRequest(hash, SettableFuture.create());
                futures.add(req.future);
                getDataFutures.add(req);
            }
            ListenableFuture> successful = Futures.successfulAsList(futures);
            Futures.addCallback(successful, new FutureCallback>() {
                @Override
                public void onSuccess(List transactions) {
                    // Once all transactions either were received, or we know there are no more to come ...
                    // Note that transactions will contain "null" for any positions that weren't successful.
                    List> childFutures = Lists.newLinkedList();
                    for (Transaction tx : transactions) {
                        if (tx == null) continue;
                        log.info("{}: Downloaded dependency of {}: {}", getAddress(), rootTxHash, tx.getHashAsString());
                        results.add(tx);
                        // Now recurse into the dependencies of this transaction too.
                        if (depth + 1 < maxDepth)
                            childFutures.add(downloadDependenciesInternal(maxDepth, depth + 1, tx, marker, results));
                    }
                    if (childFutures.size() == 0) {
                        // Short-circuit: we're at the bottom of this part of the tree.
                        resultFuture.set(marker);
                    } else {
                        // There are some children to download. Wait until it's done (and their children and their
                        // children...) to inform the caller that we're finished.
                        Futures.addCallback(Futures.successfulAsList(childFutures), new FutureCallback>() {
                            @Override
                            public void onSuccess(List objects) {
                                resultFuture.set(marker);
                            }

                            @Override
                            public void onFailure(Throwable throwable) {
                                resultFuture.setException(throwable);
                            }
                        });
                    }
                }

                @Override
                public void onFailure(Throwable throwable) {
                    resultFuture.setException(throwable);
                }
            });
            // Start the operation.
            sendMessage(getdata);
        } catch (Exception e) {
            log.error("{}: Couldn't send getdata in downloadDependencies({})", this, tx.getHash(), e);
            resultFuture.setException(e);
            return resultFuture;
        } finally {
            lock.unlock();
        }
        return resultFuture;
    }

    protected void processBlock(Block m) {
        if (log.isDebugEnabled()) {
            log.debug("{}: Received broadcast block {}", getAddress(), m.getHashAsString());
        }
        // Was this block requested by getBlock()?
        if (maybeHandleRequestedData(m)) return;
        if (blockChain == null) {
            log.debug("Received block but was not configured with an AbstractBlockChain");
            return;
        }
        // Did we lose download peer status after requesting block data?
        if (!vDownloadData) {
            log.debug("{}: Received block we did not ask for: {}", getAddress(), m.getHashAsString());
            return;
        }
        pendingBlockDownloads.remove(m.getHash());
        try {
            // Otherwise it's a block sent to us because the peer thought we needed it, so add it to the block chain.
            if (blockChain.add(m)) {
                // The block was successfully linked into the chain. Notify the user of our progress.
                invokeOnBlocksDownloaded(m, null);
            } else {
                // This block is an orphan - we don't know how to get from it back to the genesis block yet. That
                // must mean that there are blocks we are missing, so do another getblocks with a new block locator
                // to ask the peer to send them to us. This can happen during the initial block chain download where
                // the peer will only send us 500 at a time and then sends us the head block expecting us to request
                // the others.
                //
                // We must do two things here:
                // (1) Request from current top of chain to the oldest ancestor of the received block in the orphan set
                // (2) Filter out duplicate getblock requests (done in blockChainDownloadLocked).
                //
                // The reason for (1) is that otherwise if new blocks were solved during the middle of chain download
                // we'd do a blockChainDownloadLocked() on the new best chain head, which would cause us to try and grab the
                // chain twice (or more!) on the same connection! The block chain would filter out the duplicates but
                // only at a huge speed penalty. By finding the orphan root we ensure every getblocks looks the same
                // no matter how many blocks are solved, and therefore that the (2) duplicate filtering can work.
                //
                // We only do this if we are not currently downloading headers. If we are then we don't want to kick
                // off a request for lots more headers in parallel.
                lock.lock();
                try {
                    if (downloadBlockBodies) {
                        final Block orphanRoot = checkNotNull(blockChain.getOrphanRoot(m.getHash()));
                        blockChainDownloadLocked(orphanRoot.getHash());
                    } else {
                        log.info("Did not start chain download on solved block due to in-flight header download.");
                    }
                } finally {
                    lock.unlock();
                }
            }
        } catch (VerificationException e) {
            // We don't want verification failures to kill the thread.
            log.warn("{}: Block verification failed", getAddress(), e);
        } catch (PrunedException e) {
            // Unreachable when in SPV mode.
            throw new RuntimeException(e);
        }
    }

    // TODO: Fix this duplication.
    protected void endFilteredBlock(FilteredBlock m) {
        if (log.isDebugEnabled())
            log.debug("{}: Received broadcast filtered block {}", getAddress(), m.getHash().toString());
        if (!vDownloadData) {
            log.debug("{}: Received block we did not ask for: {}", getAddress(), m.getHash().toString());
            return;
        }
        if (blockChain == null) {
            log.debug("Received filtered block but was not configured with an AbstractBlockChain");
            return;
        }
        // Note that we currently do nothing about peers which maliciously do not include transactions which
        // actually match our filter or which simply do not send us all the transactions we need: it can be fixed
        // by cross-checking peers against each other.
        pendingBlockDownloads.remove(m.getBlockHeader().getHash());
        try {
            // It's a block sent to us because the peer thought we needed it, so maybe add it to the block chain.
            // The FilteredBlock m here contains a list of hashes, and may contain Transaction objects for a subset
            // of the hashes (those that were sent to us by the remote peer). Any hashes that haven't had a tx
            // provided in processTransaction are ones that were announced to us previously via an 'inv' so the
            // assumption is we have already downloaded them and either put them in the wallet, or threw them away
            // for being false positives.
            //
            // TODO: Fix the following protocol race.
            // It is possible for this code to go wrong such that we miss a confirmation. If the remote peer announces
            // a relevant transaction via an 'inv' and then it immediately announces the block that confirms
            // the tx before we had a chance to download it+its dependencies and provide them to the wallet, then we
            // will add the block to the chain here without the tx being in the wallet and thus it will miss its
            // confirmation and become stuck forever. The fix is to notice that there's a pending getdata for a tx
            // that appeared in this block and delay processing until it arrived ... it's complicated by the fact that
            // the data may be requested by a different peer to this one.

            // Ask each wallet attached to the peer/blockchain if this block exhausts the list of data items
            // (keys/addresses) that were used to calculate the previous filter. If so, then it's possible this block
            // is only partial. Check for discarding first so we don't check for exhaustion on blocks we already know
            // we're going to discard, otherwise redundant filters might end up being queued and calculated.
            lock.lock();
            try {
                if (awaitingFreshFilter != null) {
                    log.info("Discarding block {} because we're still waiting for a fresh filter", m.getHash());
                    // We must record the hashes of blocks we discard because you cannot do getblocks twice on the same
                    // range of blocks and get an inv both times, due to the codepath in Bitcoin Core hitting
                    // CPeer::PushInventory() which checks CPeer::setInventoryKnown and thus deduplicates.
                    awaitingFreshFilter.add(m.getHash());
                    return;   // Chain download process is restarted via a call to setBloomFilter.
                } else if (checkForFilterExhaustion(m)) {
                    // Yes, so we must abandon the attempt to process this block and any further blocks we receive,
                    // then wait for the Bloom filter to be recalculated, sent to this peer and for the peer to acknowledge
                    // that the new filter is now in use (which we have to simulate with a ping/pong), and then we can
                    // safely restart the chain download with the new filter that contains a new set of lookahead keys.
                    log.info("Bloom filter exhausted whilst processing block {}, discarding", m.getHash());
                    awaitingFreshFilter = new LinkedList<>();
                    awaitingFreshFilter.add(m.getHash());
                    awaitingFreshFilter.addAll(blockChain.drainOrphanBlocks());
                    return;   // Chain download process is restarted via a call to setBloomFilter.
                }
            } finally {
                lock.unlock();
            }

            if (blockChain.add(m)) {
                // The block was successfully linked into the chain. Notify the user of our progress.
                invokeOnBlocksDownloaded(m.getBlockHeader(), m);
            } else {
                // This block is an orphan - we don't know how to get from it back to the genesis block yet. That
                // must mean that there are blocks we are missing, so do another getblocks with a new block locator
                // to ask the peer to send them to us. This can happen during the initial block chain download where
                // the peer will only send us 500 at a time and then sends us the head block expecting us to request
                // the others.
                //
                // We must do two things here:
                // (1) Request from current top of chain to the oldest ancestor of the received block in the orphan set
                // (2) Filter out duplicate getblock requests (done in blockChainDownloadLocked).
                //
                // The reason for (1) is that otherwise if new blocks were solved during the middle of chain download
                // we'd do a blockChainDownloadLocked() on the new best chain head, which would cause us to try and grab the
                // chain twice (or more!) on the same connection! The block chain would filter out the duplicates but
                // only at a huge speed penalty. By finding the orphan root we ensure every getblocks looks the same
                // no matter how many blocks are solved, and therefore that the (2) duplicate filtering can work.
                lock.lock();
                try {
                    final Block orphanRoot = checkNotNull(blockChain.getOrphanRoot(m.getHash()));
                    blockChainDownloadLocked(orphanRoot.getHash());
                } finally {
                    lock.unlock();
                }
            }
        } catch (VerificationException e) {
            // We don't want verification failures to kill the thread.
            log.warn("{}: FilteredBlock verification failed", getAddress(), e);
        } catch (PrunedException e) {
            // We pruned away some of the data we need to properly handle this block. We need to request the needed
            // data from the remote peer and fix things. Or just give up.
            // TODO: Request e.getHash() and submit it to the block store before any other blocks
            throw new RuntimeException(e);
        }
    }

    private boolean checkForFilterExhaustion(FilteredBlock m) {
        boolean exhausted = false;
        for (Wallet wallet : wallets) {
            exhausted |= wallet.checkForFilterExhaustion(m);
        }
        return exhausted;
    }

    private boolean maybeHandleRequestedData(Message m) {
        boolean found = false;
        Sha256Hash hash = m.getHash();
        for (GetDataRequest req : getDataFutures) {
            if (hash.equals(req.hash)) {
                req.future.set(m);
                getDataFutures.remove(req);
                found = true;
                // Keep going in case there are more.
            }
        }
        return found;
    }

    private void invokeOnBlocksDownloaded(final Block block, @Nullable final FilteredBlock fb) {
        // It is possible for the peer block height difference to be negative when blocks have been solved and broadcast
        // since the time we first connected to the peer. However, it's weird and unexpected to receive a callback
        // with negative "blocks left" in this case, so we clamp to zero so the API user doesn't have to think about it.
        final int blocksLeft = Math.max(0, (int) vPeerVersionMessage.bestHeight - checkNotNull(blockChain).getBestChainHeight());
        for (final ListenerRegistration registration : blocksDownloadedEventListeners) {
            registration.executor.execute(new Runnable() {
                @Override
                public void run() {
                    registration.listener.onBlocksDownloaded(Peer.this, block, fb, blocksLeft);
                }
            });
        }
    }

    protected void processInv(InventoryMessage inv) {
        List items = inv.getItems();

        // Separate out the blocks and transactions, we'll handle them differently
        List transactions = new LinkedList<>();
        List blocks = new LinkedList<>();

        for (InventoryItem item : items) {
            switch (item.type) {
                case Transaction:
                    transactions.add(item);
                    break;
                case Block:
                    blocks.add(item);
                    break;
                default:
                    throw new IllegalStateException("Not implemented: " + item.type);
            }
        }

        final boolean downloadData = this.vDownloadData;

        if (transactions.size() == 0 && blocks.size() == 1) {
            // Single block announcement. If we're downloading the chain this is just a tickle to make us continue
            // (the block chain download protocol is very implicit and not well thought out). If we're not downloading
            // the chain then this probably means a new block was solved and the peer believes it connects to the best
            // chain, so count it. This way getBestChainHeight() can be accurate.
            if (downloadData && blockChain != null) {
                if (!blockChain.isOrphan(blocks.get(0).hash)) {
                    blocksAnnounced.incrementAndGet();
                }
            } else {
                blocksAnnounced.incrementAndGet();
            }
        }

        GetDataMessage getdata = new GetDataMessage(params);

        Iterator it = transactions.iterator();
        while (it.hasNext()) {
            InventoryItem item = it.next();
            // Only download the transaction if we are the first peer that saw it be advertised. Other peers will also
            // see it be advertised in inv packets asynchronously, they co-ordinate via the memory pool. We could
            // potentially download transactions faster by always asking every peer for a tx when advertised, as remote
            // peers run at different speeds. However to conserve bandwidth on mobile devices we try to only download a
            // transaction once. This means we can miss broadcasts if the peer disconnects between sending us an inv and
            // sending us the transaction: currently we'll never try to re-fetch after a timeout.
            //
            // The line below can trigger confidence listeners.
            TransactionConfidence conf = context.getConfidenceTable().seen(item.hash, this.getAddress());
            if (conf.numBroadcastPeers() > 1) {
                // Some other peer already announced this so don't download.
                it.remove();
            } else if (conf.getSource().equals(TransactionConfidence.Source.SELF)) {
                // We created this transaction ourselves, so don't download.
                it.remove();
            } else {
                log.debug("{}: getdata on tx {}", getAddress(), item.hash);
                getdata.addItem(vPeerVersionMessage.isWitnessSupported() ? item.toWitnessItem() : item);
                // Register with the garbage collector that we care about the confidence data for a while.
                pendingTxDownloads.add(conf);
            }
        }

        // If we are requesting filteredblocks we have to send a ping after the getdata so that we have a clear
        // end to the final FilteredBlock's transactions (in the form of a pong) sent to us
        boolean pingAfterGetData = false;

        lock.lock();
        try {
            if (blocks.size() > 0 && downloadData && blockChain != null) {
                // Ideally, we'd only ask for the data here if we actually needed it. However that can imply a lot of
                // disk IO to figure out what we've got. Normally peers will not send us inv for things we already have
                // so we just re-request it here, and if we get duplicates the block chain / wallet will filter them out.
                for (InventoryItem item : blocks) {
                    if (blockChain.isOrphan(item.hash) && downloadBlockBodies) {
                        // If an orphan was re-advertised, ask for more blocks unless we are not currently downloading
                        // full block data because we have a getheaders outstanding.
                        final Block orphanRoot = checkNotNull(blockChain.getOrphanRoot(item.hash));
                        blockChainDownloadLocked(orphanRoot.getHash());
                    } else {
                        // Don't re-request blocks we already requested. Normally this should not happen. However there is
                        // an edge case: if a block is solved and we complete the inv<->getdata<->block<->getblocks cycle
                        // whilst other parts of the chain are streaming in, then the new getblocks request won't match the
                        // previous one: whilst the stopHash is the same (because we use the orphan root), the start hash
                        // will be different and so the getblocks req won't be dropped as a duplicate. We'll end up
                        // requesting a subset of what we already requested, which can lead to parallel chain downloads
                        // and other nastyness. So we just do a quick removal of redundant getdatas here too.
                        //
                        // Note that as of June 2012 Bitcoin Core won't actually ever interleave blocks pushed as
                        // part of chain download with newly announced blocks, so it should always be taken care of by
                        // the duplicate check in blockChainDownloadLocked(). But Bitcoin Core may change in future so
                        // it's better to be safe here.
                        if (!pendingBlockDownloads.contains(item.hash)) {
                            if (vPeerVersionMessage.isBloomFilteringSupported() && useFilteredBlocks) {
                                getdata.addFilteredBlock(item.hash);
                                pingAfterGetData = true;
                            } else {
                                getdata.addItem(vPeerVersionMessage.isWitnessSupported() ? item.toWitnessItem() : item);
                            }
                            pendingBlockDownloads.add(item.hash);
                        }
                    }
                }
                // If we're downloading the chain, doing a getdata on the last block we were told about will cause the
                // peer to advertize the head block to us in a single-item inv. When we download THAT, it will be an
                // orphan block, meaning we'll re-enter blockChainDownloadLocked() to trigger another getblocks between the
                // current best block we have and the orphan block. If more blocks arrive in the meantime they'll also
                // become orphan.
            }
        } finally {
            lock.unlock();
        }

        if (!getdata.getItems().isEmpty()) {
            // This will cause us to receive a bunch of block or tx messages.
            sendMessage(getdata);
        }

        if (pingAfterGetData)
            sendMessage(new Ping((long) (Math.random() * Long.MAX_VALUE)));
    }

    /**
     * Asks the connected peer for the block of the given hash, and returns a future representing the answer.
     * If you want the block right away and don't mind waiting for it, just call .get() on the result. Your thread
     * will block until the peer answers.
     */
    @SuppressWarnings("unchecked")
    // The 'unchecked conversion' warning being suppressed here comes from the sendSingleGetData() formally returning
    // ListenableFuture instead of ListenableFuture. This is okay as sendSingleGetData() actually returns
    // ListenableFuture in this context. Note that sendSingleGetData() is also used for Transactions.
    public ListenableFuture getBlock(Sha256Hash blockHash) {
        // This does not need to be locked.
        log.info("Request to fetch block {}", blockHash);
        GetDataMessage getdata = new GetDataMessage(params);
        if (vPeerVersionMessage.isWitnessSupported())
            getdata.addWitnessBlock(blockHash);
        else
            getdata.addBlock(blockHash);
        return sendSingleGetData(getdata);
    }

    /**
     * Asks the connected peer for the given transaction from its memory pool. Transactions in the chain cannot be
     * retrieved this way because peers don't have a transaction ID to transaction-pos-on-disk index, and besides,
     * in future many peers will delete old transaction data they don't need.
     */
    @SuppressWarnings("unchecked")
    // The 'unchecked conversion' warning being suppressed here comes from the sendSingleGetData() formally returning
    // ListenableFuture instead of ListenableFuture. This is okay as sendSingleGetData() actually returns
    // ListenableFuture in this context. Note that sendSingleGetData() is also used for Blocks.
    public ListenableFuture getPeerMempoolTransaction(Sha256Hash hash) {
        // This does not need to be locked.
        // TODO: Unit test this method.
        log.info("Request to fetch peer mempool tx  {}", hash);
        GetDataMessage getdata = new GetDataMessage(params);
        if (vPeerVersionMessage.isWitnessSupported())
            getdata.addWitnessTransaction(hash);
        else
            getdata.addTransaction(hash);
        return sendSingleGetData(getdata);
    }

    /** Sends a getdata with a single item in it. */
    private ListenableFuture sendSingleGetData(GetDataMessage getdata) {
        // This does not need to be locked.
        Preconditions.checkArgument(getdata.getItems().size() == 1);
        GetDataRequest req = new GetDataRequest(getdata.getItems().get(0).hash, SettableFuture.create());
        getDataFutures.add(req);
        sendMessage(getdata);
        return req.future;
    }

    /** Sends a getaddr request to the peer and returns a future that completes with the answer once the peer has replied. */
    public ListenableFuture getAddr() {
        SettableFuture future = SettableFuture.create();
        synchronized (getAddrFutures) {
            getAddrFutures.add(future);
        }
        sendMessage(new GetAddrMessage(params));
        return future;
    }

    /**
     * When downloading the block chain, the bodies will be skipped for blocks created before the given date. Any
     * transactions relevant to the wallet will therefore not be found, but if you know your wallet has no such
     * transactions it doesn't matter and can save a lot of bandwidth and processing time. Note that the times of blocks
     * isn't known until their headers are available and they are requested in chunks, so some headers may be downloaded
     * twice using this scheme, but this optimization can still be a large win for newly created wallets.
     *
     * @param secondsSinceEpoch Time in seconds since the epoch or 0 to reset to always downloading block bodies.
     */
    public void setDownloadParameters(long secondsSinceEpoch, boolean useFilteredBlocks) {
        lock.lock();
        try {
            if (secondsSinceEpoch == 0) {
                fastCatchupTimeSecs = params.getGenesisBlock().getTimeSeconds();
                downloadBlockBodies = true;
            } else {
                fastCatchupTimeSecs = secondsSinceEpoch;
                // If the given time is before the current chains head block time, then this has no effect (we already
                // downloaded everything we need).
                if (blockChain != null && fastCatchupTimeSecs > blockChain.getChainHead().getHeader().getTimeSeconds())
                    downloadBlockBodies = false;
            }
            this.useFilteredBlocks = useFilteredBlocks;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Links the given wallet to this peer. If you have multiple peers, you should use a {@link PeerGroup} to manage
     * them and use the {@link PeerGroup#addWallet(Wallet)} method instead of registering the wallet with each peer
     * independently, otherwise the wallet will receive duplicate notifications.
     */
    public void addWallet(Wallet wallet) {
        wallets.add(wallet);
    }

    /** Unlinks the given wallet from peer. See {@link Peer#addWallet(Wallet)}. */
    public void removeWallet(Wallet wallet) {
        wallets.remove(wallet);
    }

    // Keep track of the last request we made to the peer in blockChainDownloadLocked so we can avoid redundant and harmful
    // getblocks requests.
    @GuardedBy("lock")
    private Sha256Hash lastGetBlocksBegin, lastGetBlocksEnd;

    @GuardedBy("lock")
    private void blockChainDownloadLocked(Sha256Hash toHash) {
        checkState(lock.isHeldByCurrentThread());
        // The block chain download process is a bit complicated. Basically, we start with one or more blocks in a
        // chain that we have from a previous session. We want to catch up to the head of the chain BUT we don't know
        // where that chain is up to or even if the top block we have is even still in the chain - we
        // might have got ourselves onto a fork that was later resolved by the network.
        //
        // To solve this, we send the peer a block locator which is just a list of block hashes. It contains the
        // blocks we know about, but not all of them, just enough of them so the peer can figure out if we did end up
        // on a fork and if so, what the earliest still valid block we know about is likely to be.
        //
        // Once it has decided which blocks we need, it will send us an inv with up to 500 block messages. We may
        // have some of them already if we already have a block chain and just need to catch up. Once we request the
        // last block, if there are still more to come it sends us an "inv" containing only the hash of the head
        // block.
        //
        // That causes us to download the head block but then we find (in processBlock) that we can't connect
        // it to the chain yet because we don't have the intermediate blocks. So we rerun this function building a
        // new block locator describing where we're up to.
        //
        // The getblocks with the new locator gets us another inv with another bunch of blocks. We download them once
        // again. This time when the peer sends us an inv with the head block, we already have it so we won't download
        // it again - but we recognize this case as special and call back into blockChainDownloadLocked to continue the
        // process.
        //
        // So this is a complicated process but it has the advantage that we can download a chain of enormous length
        // in a relatively stateless manner and with constant memory usage.
        //
        // All this is made more complicated by the desire to skip downloading the bodies of blocks that pre-date the
        // 'fast catchup time', which is usually set to the creation date of the earliest key in the wallet. Because
        // we know there are no transactions using our keys before that date, we need only the headers. To do that we
        // use the "getheaders" command. Once we find we've gone past the target date, we throw away the downloaded
        // headers and then request the blocks from that point onwards. "getheaders" does not send us an inv, it just
        // sends us the data we requested in a "headers" message.

        // TODO: Block locators should be abstracted out rather than special cased here.
        List blockLocator = new ArrayList<>(51);
        // For now we don't do the exponential thinning as suggested here:
        //
        //   https://en.bitcoin.it/wiki/Protocol_specification#getblocks
        //
        // This is because it requires scanning all the block chain headers, which is very slow. Instead we add the top
        // 100 block headers. If there is a re-org deeper than that, we'll end up downloading the entire chain. We
        // must always put the genesis block as the first entry.
        BlockStore store = checkNotNull(blockChain).getBlockStore();
        StoredBlock chainHead = blockChain.getChainHead();
        Sha256Hash chainHeadHash = chainHead.getHeader().getHash();
        // Did we already make this request? If so, don't do it again.
        if (Objects.equal(lastGetBlocksBegin, chainHeadHash) && Objects.equal(lastGetBlocksEnd, toHash)) {
            log.info("blockChainDownloadLocked({}): ignoring duplicated request: {}", toHash, chainHeadHash);
            for (Sha256Hash hash : pendingBlockDownloads)
                log.info("Pending block download: {}", hash);
            log.info(Throwables.getStackTraceAsString(new Throwable()));
            return;
        }
        if (log.isDebugEnabled())
            log.debug("{}: blockChainDownloadLocked({}) current head = {}",
                    this, toHash, chainHead.getHeader().getHashAsString());
        StoredBlock cursor = chainHead;
        for (int i = 100; cursor != null && i > 0; i--) {
            blockLocator.add(cursor.getHeader().getHash());
            try {
                cursor = cursor.getPrev(store);
            } catch (BlockStoreException e) {
                log.error("Failed to walk the block chain whilst constructing a locator");
                throw new RuntimeException(e);
            }
        }
        // Only add the locator if we didn't already do so. If the chain is < 50 blocks we already reached it.
        if (cursor != null)
            blockLocator.add(params.getGenesisBlock().getHash());

        // Record that we requested this range of blocks so we can filter out duplicate requests in the event of a
        // block being solved during chain download.
        lastGetBlocksBegin = chainHeadHash;
        lastGetBlocksEnd = toHash;

        if (downloadBlockBodies) {
            GetBlocksMessage message = new GetBlocksMessage(params, blockLocator, toHash);
            sendMessage(message);
        } else {
            // Downloading headers for a while instead of full blocks.
            GetHeadersMessage message = new GetHeadersMessage(params, blockLocator, toHash);
            sendMessage(message);
        }
    }

    /**
     * Starts an asynchronous download of the block chain. The chain download is deemed to be complete once we've
     * downloaded the same number of blocks that the peer advertised having in its version handshake message.
     */
    public void startBlockChainDownload() {
        setDownloadData(true);
        // TODO: peer might still have blocks that we don't have, and even have a heavier
        // chain even if the chain block count is lower.
        final int blocksLeft = getPeerBlockHeightDifference();
        if (blocksLeft >= 0) {
            for (final ListenerRegistration registration : chainDownloadStartedEventListeners) {
                registration.executor.execute(new Runnable() {
                    @Override
                    public void run() {
                        registration.listener.onChainDownloadStarted(Peer.this, blocksLeft);
                    }
                });
            }
            // When we just want as many blocks as possible, we can set the target hash to zero.
            lock.lock();
            try {
                blockChainDownloadLocked(Sha256Hash.ZERO_HASH);
            } finally {
                lock.unlock();
            }
        }
    }

    private class PendingPing {
        // The future that will be invoked when the pong is heard back.
        public SettableFuture future;
        // The random nonce that lets us tell apart overlapping pings/pongs.
        public final long nonce;
        // Measurement of the time elapsed.
        public final long startTimeMsec;

        public PendingPing(long nonce) {
            future = SettableFuture.create();
            this.nonce = nonce;
            startTimeMsec = Utils.currentTimeMillis();
        }

        public void complete() {
            if (!future.isDone()) {
                Long elapsed = Utils.currentTimeMillis() - startTimeMsec;
                Peer.this.addPingTimeData(elapsed);
                log.debug("{}: ping time is {} msec", Peer.this.toString(), elapsed);
                future.set(elapsed);
            }
        }
    }

    /** Adds a ping time sample to the averaging window. */
    private void addPingTimeData(long sample) {
        lastPingTimesLock.lock();
        try {
            if (lastPingTimes == null) {
                lastPingTimes = new long[PING_MOVING_AVERAGE_WINDOW];
                // Initialize the averaging window to the first sample.
                Arrays.fill(lastPingTimes, sample);
            } else {
                // Shift all elements backwards by one.
                System.arraycopy(lastPingTimes, 1, lastPingTimes, 0, lastPingTimes.length - 1);
                // And append the new sample to the end.
                lastPingTimes[lastPingTimes.length - 1] = sample;
            }
        } finally {
            lastPingTimesLock.unlock();
        }
    }

    /**
     * Sends the peer a ping message and returns a future that will be invoked when the pong is received back.
     * The future provides a number which is the number of milliseconds elapsed between the ping and the pong.
     * Once the pong is received the value returned by {@link org.bitcoinj.core.Peer#getLastPingTime()} is
     * updated.
     * @throws ProtocolException if the peer version is too low to support measurable pings.
     */
    public ListenableFuture ping() throws ProtocolException {
        return ping((long) (Math.random() * Long.MAX_VALUE));
    }

    protected ListenableFuture ping(long nonce) throws ProtocolException {
        final VersionMessage ver = vPeerVersionMessage;
        if (!ver.isPingPongSupported())
            throw new ProtocolException("Peer version is too low for measurable pings: " + ver);
        PendingPing pendingPing = new PendingPing(nonce);
        pendingPings.add(pendingPing);
        sendMessage(new Ping(pendingPing.nonce));
        return pendingPing.future;
    }

    /**
     * Returns the elapsed time of the last ping/pong cycle. If {@link org.bitcoinj.core.Peer#ping()} has never
     * been called or we did not hear back the "pong" message yet, returns {@link Long#MAX_VALUE}.
     */
    public long getLastPingTime() {
        lastPingTimesLock.lock();
        try {
            if (lastPingTimes == null)
                return Long.MAX_VALUE;
            return lastPingTimes[lastPingTimes.length - 1];
        } finally {
            lastPingTimesLock.unlock();
        }
    }

    /**
     * Returns a moving average of the last N ping/pong cycles. If {@link org.bitcoinj.core.Peer#ping()} has never
     * been called or we did not hear back the "pong" message yet, returns {@link Long#MAX_VALUE}. The moving average
     * window is 5 buckets.
     */
    public long getPingTime() {
        lastPingTimesLock.lock();
        try {
            if (lastPingTimes == null)
                return Long.MAX_VALUE;
            long sum = 0;
            for (long i : lastPingTimes) sum += i;
            return (long)((double) sum / lastPingTimes.length);
        } finally {
            lastPingTimesLock.unlock();
        }
    }

    private void processPing(Ping m) {
        if (m.hasNonce())
            sendMessage(new Pong(m.getNonce()));
    }

    protected void processPong(Pong m) {
        // Iterates over a snapshot of the list, so we can run unlocked here.
        for (PendingPing ping : pendingPings) {
            if (m.getNonce() == ping.nonce) {
                pendingPings.remove(ping);
                // This line may trigger an event listener that re-runs ping().
                ping.complete();
                return;
            }
        }
    }

    /**
     * Returns the difference between our best chain height and the peers, which can either be positive if we are
     * behind the peer, or negative if the peer is ahead of us.
     */
    public int getPeerBlockHeightDifference() {
        checkNotNull(blockChain, "No block chain configured");
        // Chain will overflow signed int blocks in ~41,000 years.
        int chainHeight = (int) getBestHeight();
        // chainHeight should not be zero/negative because we shouldn't have given the user a Peer that is to another
        // client-mode node, nor should it be unconnected. If that happens it means the user overrode us somewhere or
        // there is a bug in the peer management code.
        checkState(params.allowEmptyPeerChain() || chainHeight > 0, "Connected to peer with zero/negative chain height", chainHeight);
        return chainHeight - blockChain.getBestChainHeight();
    }

    private boolean isNotFoundMessageSupported() {
        return vPeerVersionMessage.clientVersion >= NotFoundMessage.MIN_PROTOCOL_VERSION;
    }

    /**
     * Returns true if this peer will try and download things it is sent in "inv" messages. Normally you only need
     * one peer to be downloading data. Defaults to true.
     */
    public boolean isDownloadData() {
        return vDownloadData;
    }

    /**
     * If set to false, the peer won't try and fetch blocks and transactions it hears about. Normally, only one
     * peer should download missing blocks. Defaults to true. Changing this value from false to true may trigger
     * a request to the remote peer for the contents of its memory pool, if Bloom filtering is active.
     */
    public void setDownloadData(boolean downloadData) {
        this.vDownloadData = downloadData;
    }

    /** Returns version data announced by the remote peer. */
    public VersionMessage getPeerVersionMessage() {
        return vPeerVersionMessage;
    }

    /** Returns version data we announce to our remote peers. */
    public VersionMessage getVersionMessage() {
        return versionMessage;
    }

    /**
     * @return the height of the best chain as claimed by peer: sum of its ver announcement and blocks announced since.
     */
    public long getBestHeight() {
        return vPeerVersionMessage.bestHeight + blocksAnnounced.get();
    }

    /**
     * The minimum P2P protocol version that is accepted. If the peer speaks a protocol version lower than this, it
     * will be disconnected.
     * @return true if the peer was disconnected as a result
     */
    public boolean setMinProtocolVersion(int minProtocolVersion) {
        this.vMinProtocolVersion = minProtocolVersion;
        VersionMessage ver = getPeerVersionMessage();
        if (ver != null && ver.clientVersion < minProtocolVersion) {
            log.warn("{}: Disconnecting due to new min protocol version {}, got: {}", this, minProtocolVersion, ver.clientVersion);
            close();
            return true;
        }
        return false;
    }

    /**
     * 
    Sets a Bloom filter on this connection. This will cause the given {@link BloomFilter} object to be sent to the
     * remote peer and if either a memory pool has been set using the constructor or the
     * vDownloadData property is true, a {@link MemoryPoolMessage} is sent as well to trigger downloading of any
     * pending transactions that may be relevant.
    
     *
     * 
    The Peer does not automatically request filters from any wallets added using {@link Peer#addWallet(Wallet)}.
     * This is to allow callers to avoid redundantly recalculating the same filter repeatedly when using multiple peers
     * and multiple wallets together.
    
     *
     * 
    Therefore, you should not use this method if your app uses a {@link PeerGroup}. It is called for you.
    
     *
     * 
    If the remote peer doesn't support Bloom filtering, then this call is ignored. Once set you presently cannot
     * unset a filter, though the underlying p2p protocol does support it.
    
     */
    public void setBloomFilter(BloomFilter filter) {
        setBloomFilter(filter, true);
    }

    /**
     * 
    Sets a Bloom filter on this connection. This will cause the given {@link BloomFilter} object to be sent to the
     * remote peer and if requested, a {@link MemoryPoolMessage} is sent as well to trigger downloading of any
     * pending transactions that may be relevant.
    
     *
     * 
    The Peer does not automatically request filters from any wallets added using {@link Peer#addWallet(Wallet)}.
     * This is to allow callers to avoid redundantly recalculating the same filter repeatedly when using multiple peers
     * and multiple wallets together.
    
     *
     * 
    Therefore, you should not use this method if your app uses a {@link PeerGroup}. It is called for you.
    
     *
     * 
    If the remote peer doesn't support Bloom filtering, then this call is ignored. Once set you presently cannot
     * unset a filter, though the underlying p2p protocol does support it.
    
     */
    public void setBloomFilter(BloomFilter filter, boolean andQueryMemPool) {
        checkNotNull(filter, "Clearing filters is not currently supported");
        final VersionMessage ver = vPeerVersionMessage;
        if (ver == null || !ver.isBloomFilteringSupported())
            return;
        vBloomFilter = filter;
        log.debug("{}: Sending Bloom filter{}", this, andQueryMemPool ? " and querying mempool" : "");
        sendMessage(filter);
        if (andQueryMemPool)
            sendMessage(new MemoryPoolMessage());
        maybeRestartChainDownload();
    }

    private void maybeRestartChainDownload() {
        lock.lock();
        try {
            if (awaitingFreshFilter == null)
                return;
            if (!vDownloadData) {
                // This branch should be harmless but I want to know how often it happens in reality.
                log.warn("Lost download peer status whilst awaiting fresh filter.");
                return;
            }
            // Ping/pong to wait for blocks that are still being streamed to us to finish being downloaded and
            // discarded.
            ping().addListener(new Runnable() {
                @Override
                public void run() {
                    lock.lock();
                    checkNotNull(awaitingFreshFilter);
                    GetDataMessage getdata = new GetDataMessage(params);
                    for (Sha256Hash hash : awaitingFreshFilter)
                        getdata.addFilteredBlock(hash);
                    awaitingFreshFilter = null;
                    lock.unlock();

                    log.info("Restarting chain download");
                    sendMessage(getdata);
                    // TODO: This bizarre ping-after-getdata hack probably isn't necessary.
                    // It's to ensure we know when the end of a filtered block stream of txns is, but we should just be
                    // able to match txns with the merkleblock. Ask Matt why it's written this way.
                    sendMessage(new Ping((long) (Math.random() * Long.MAX_VALUE)));
                }
            }, Threading.SAME_THREAD);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns the last {@link BloomFilter} set by {@link Peer#setBloomFilter(BloomFilter)}. Bloom filters tell
     * the remote node what transactions to send us, in a compact manner.
     */
    public BloomFilter getBloomFilter() {
        return vBloomFilter;
    }

    /**
     * Sends a query to the remote peer asking for the unspent transaction outputs (UTXOs) for the given outpoints,
     * with the memory pool included. The result should be treated only as a hint: it's possible for the returned
     * outputs to be fictional and not exist in any transaction, and it's possible for them to be spent the moment
     * after the query returns. Most peers do not support this request. You will need to connect to Bitcoin XT
     * peers if you want this to work.
     *
     * @throws ProtocolException if this peer doesn't support the protocol.
     */
    public ListenableFuture getUTXOs(List outPoints) {
        return getUTXOs(outPoints, true);
    }

    /**
     * Sends a query to the remote peer asking for the unspent transaction outputs (UTXOs) for the given outpoints.
     * The result should be treated only as a hint: it's possible for the returned outputs to be fictional and not
     * exist in any transaction, and it's possible for them to be spent the moment after the query returns.
     * Most peers do not support this request. You will need to connect to Bitcoin XT peers if you want
     * this to work.
     *
     * @param includeMempool If true (the default) the results take into account the contents of the memory pool too.
     * @throws ProtocolException if this peer doesn't support the protocol.
     */
    public ListenableFuture getUTXOs(List outPoints, boolean includeMempool) {
        lock.lock();
        try {
            VersionMessage peerVer = getPeerVersionMessage();
            if (peerVer.clientVersion < GetUTXOsMessage.MIN_PROTOCOL_VERSION)
                throw new ProtocolException("Peer does not support getutxos protocol version");
            if ((peerVer.localServices & GetUTXOsMessage.SERVICE_FLAGS_REQUIRED) != GetUTXOsMessage.SERVICE_FLAGS_REQUIRED)
                throw new ProtocolException("Peer does not support getutxos protocol flag: find Bitcoin XT nodes.");
            SettableFuture future = SettableFuture.create();
            // Add to the list of in flight requests.
            if (getutxoFutures == null)
                getutxoFutures = new LinkedList<>();
            getutxoFutures.add(future);
            sendMessage(new GetUTXOsMessage(params, outPoints, includeMempool));
            return future;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns true if this peer will use getdata/notfound messages to walk backwards through transaction dependencies
     * before handing the transaction off to the wallet. The wallet can do risk analysis on pending/recent transactions
     * to try and discover if a pending tx might be at risk of double spending.
     */
    public boolean isDownloadTxDependencies() {
        return vDownloadTxDependencyDepth > 0;
    }

    /**
     * Sets if this peer will use getdata/notfound messages to walk backwards through transaction dependencies
     * before handing the transaction off to the wallet. The wallet can do risk analysis on pending/recent transactions
     * to try and discover if a pending tx might be at risk of double spending.
     */
    public void setDownloadTxDependencies(boolean enable) {
        vDownloadTxDependencyDepth = enable ? Integer.MAX_VALUE : 0;
    }

    /**
     * Sets if this peer will use getdata/notfound messages to walk backwards through transaction dependencies
     * before handing the transaction off to the wallet. The wallet can do risk analysis on pending/recent transactions
     * to try and discover if a pending tx might be at risk of double spending.
     */
    public void setDownloadTxDependencies(int depth) {
        vDownloadTxDependencyDepth = depth;
    }
}
    
    
    
    

    




    
    
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