/**
* 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.
*/
package com.google.devcoin.core;
import com.google.devcoin.utils.Threading;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Collections;
import java.util.List;
import java.util.Random;
/**
* Represents a single transaction broadcast that we are performing. A broadcast occurs after a new transaction is created
* (typically by a {@link Wallet} and needs to be sent to the network. A broadcast can succeed or fail. A success is
* defined as seeing the transaction be announced by peers via inv messages, thus indicating their acceptance. A failure
* is defined as not reaching acceptance within a timeout period, or getting an explicit error message from peers
* indicating that the transaction was not acceptable (this isn't currently implemented in v0.8 of the network protocol
* but should be coming in 0.9).
*/
public class TransactionBroadcast {
private static final Logger log = LoggerFactory.getLogger(TransactionBroadcast.class);
private final SettableFuture<Transaction> future = SettableFuture.create();
private final PeerGroup peerGroup;
private final Transaction tx;
private int minConnections;
private int numWaitingFor, numToBroadcastTo;
// Used for the peers permutation: unit tests replace this to make themselves deterministic.
@VisibleForTesting static Random random = new Random();
private Transaction pinnedTx;
public TransactionBroadcast(PeerGroup peerGroup, Transaction tx) {
this.peerGroup = peerGroup;
this.tx = tx;
this.minConnections = Math.max(1, peerGroup.getMinBroadcastConnections());
}
public ListenableFuture<Transaction> future() {
return future;
}
public void setMinConnections(int minConnections) {
this.minConnections = minConnections;
}
public ListenableFuture<Transaction> broadcast() {
log.info("Waiting for {} peers required for broadcast ...", minConnections);
ListenableFuture<PeerGroup> peerAvailabilityFuture = peerGroup.waitForPeers(minConnections);
peerAvailabilityFuture.addListener(new EnoughAvailablePeers(), Threading.SAME_THREAD);
return future;
}
private class EnoughAvailablePeers implements Runnable {
public void run() {
// We now have enough connected peers to send the transaction.
// This can be called immediately if we already have enough. Otherwise it'll be called from a peer
// thread.
// We will send the tx simultaneously to half the connected peers and wait to hear back from at least half
// of the other half, i.e., with 4 peers connected we will send the tx to 2 randomly chosen peers, and then
// wait for it to show up on one of the other two. This will be taken as sign of network acceptance. As can
// be seen, 4 peers is probably too little - it doesn't taken many broken peers for tx propagation to have
// a big effect.
List<Peer> peers = peerGroup.getConnectedPeers(); // snapshots
// We intern the tx here so we are using a canonical version of the object (as it's unfortunately mutable).
pinnedTx = peerGroup.getMemoryPool().intern(tx);
// Prepare to send the transaction by adding a listener that'll be called when confidence changes.
// Only bother with this if we might actually hear back:
if (minConnections > 1)
pinnedTx.getConfidence().addEventListener(new ConfidenceChange());
// Satoshis code sends an inv in this case and then lets the peer request the tx data. We just
// blast out the TX here for a couple of reasons. Firstly it's simpler: in the case where we have
// just a single connection we don't have to wait for getdata to be received and handled before
// completing the future in the code immediately below. Secondly, it's faster. The reason the
// Satoshi client sends an inv is privacy - it means you can't tell if the peer originated the
// transaction or not. However, we are not a fully validating node and this is advertised in
// our version message, as SPV nodes cannot relay it doesn't give away any additional information
// to skip the inv here - we wouldn't send invs anyway.
int numConnected = peers.size();
numToBroadcastTo = (int) Math.max(1, Math.round(Math.ceil(peers.size() / 2.0)));
numWaitingFor = (int) Math.ceil((peers.size() - numToBroadcastTo) / 2.0);
Collections.shuffle(peers, random);
peers = peers.subList(0, numToBroadcastTo);
log.info("broadcastTransaction: We have {} peers, adding {} to the memory pool and sending to {} peers, will wait for {}: {}",
new Object[] { numConnected, tx.getHashAsString(), numToBroadcastTo, numWaitingFor, Joiner.on(",").join(peers) });
for (Peer peer : peers) {
try {
peer.sendMessage(pinnedTx);
// We don't record the peer as having seen the tx in the memory pool because we want to track only
// how many peers announced to us.
} catch (Exception e) {
log.error("Caught exception sending to {}", peer, e);
}
}
// If we've been limited to talk to only one peer, we can't wait to hear back because the
// remote peer won't tell us about transactions we just announced to it for obvious reasons.
// So we just have to assume we're done, at that point. This happens when we're not given
// any peer discovery source and the user just calls connectTo() once.
if (minConnections == 1) {
future.set(pinnedTx);
}
}
}
private class ConfidenceChange implements TransactionConfidence.Listener {
public void onConfidenceChanged(Transaction tx, ChangeReason reason) {
// The number of peers that announced this tx has gone up.
final TransactionConfidence conf = tx.getConfidence();
int numSeenPeers = conf.numBroadcastPeers();
boolean mined = tx.getAppearsInHashes() != null;
log.info("broadcastTransaction: {}: TX {} seen by {} peers{}", new Object[] { reason, pinnedTx.getHashAsString(),
numSeenPeers, mined ? " and mined" : "" });
if (numSeenPeers >= numWaitingFor || mined) {
// We've seen the min required number of peers announce the transaction, or it was included
// in a block. Normally we'd expect to see it fully propagate before it gets mined, but
// it can be that a block is solved very soon after broadcast, and it's also possible that
// due to version skew and changes in the relay rules our transaction is not going to
// fully propagate yet can get mined anyway.
//
// Note that we can't wait for the current number of connected peers right now because we
// could have added more peers after the broadcast took place, which means they won't
// have seen the transaction. In future when peers sync up their memory pools after they
// connect we could come back and change this.
//
// We're done! It's important that the PeerGroup lock is not held (by this thread) at this
// point to avoid triggering inversions when the Future completes.
log.info("broadcastTransaction: {} complete", pinnedTx.getHashAsString());
tx.getConfidence().removeEventListener(this);
future.set(pinnedTx); // RE-ENTRANCY POINT
}
}
}
}