/**
* 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.store.BlockStore;
import com.google.devcoin.store.BlockStoreException;
import com.google.devcoin.store.FullPrunedBlockStore;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import java.util.Map;
import java.util.TreeMap;
import static com.google.common.base.Preconditions.*;
/**
* <p>Vends hard-coded {@link StoredBlock}s for blocks throughout the chain. Checkpoints serve two purposes:</p>
* <ol>
* <li>They act as a safety mechanism against huge re-orgs that could rewrite large chunks of history, thus
* constraining the block chain to be a consensus mechanism only for recent parts of the timeline.</li>
* <li>They allow synchronization to the head of the chain for new wallets/users much faster than syncing all
* headers from the genesis block.</li>
* </ol>
*
* <p>Checkpoints are used by the SPV {@link BlockChain} to initialize fresh
* {@link com.google.devcoin.store.SPVBlockStore}s. They are not used by fully validating mode, which instead has a
* different concept of checkpoints that are used to hard-code the validity of blocks that violate BIP30 (duplicate
* coinbase transactions). Those "checkpoints" can be found in NetworkParameters.</p>
*
* <p>The file format consists of the string "CHECKPOINTS 1", followed by a uint32 containing the number of signatures
* to read. The value may not be larger than 256 (so it could have been a byte but isn't for historical reasons).
* If the number of signatures is larger than zero, each 65 byte ECDSA secp256k1 signature then follows. The signatures
* sign the hash of all bytes that follow the last signature.</p>
*
* <p>After the signatures come an int32 containing the number of checkpoints in the file. Then each checkpoint follows
* one after the other. A checkpoint is 12 bytes for the total work done field, 4 bytes for the height, 80 bytes
* for the block header and then 1 zero byte at the end (i.e. number of transactions in the block: always zero).</p>
*/
public class CheckpointManager {
private static final Logger log = LoggerFactory.getLogger(CheckpointManager.class);
private static final int MAX_SIGNATURES = 256;
// Map of block header time to data.
protected final TreeMap<Long, StoredBlock> checkpoints = new TreeMap<Long, StoredBlock>();
protected final NetworkParameters params;
protected final Sha256Hash dataHash;
public CheckpointManager(NetworkParameters params, InputStream inputStream) throws IOException {
this.params = checkNotNull(params);
checkNotNull(inputStream);
DataInputStream dis = null;
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
DigestInputStream digestInputStream = new DigestInputStream(inputStream, digest);
dis = new DataInputStream(digestInputStream);
digestInputStream.on(false);
String magic = "CHECKPOINTS 1";
byte[] header = new byte[magic.length()];
dis.readFully(header);
if (!Arrays.equals(header, magic.getBytes("US-ASCII")))
throw new IOException("Header bytes did not match expected version");
int numSignatures = checkPositionIndex(dis.readInt(), MAX_SIGNATURES, "Num signatures out of range");
for (int i = 0; i < numSignatures; i++) {
byte[] sig = new byte[65];
dis.readFully(sig);
// TODO: Do something with the signature here.
}
digestInputStream.on(true);
int numCheckpoints = dis.readInt();
checkState(numCheckpoints > 0);
final int size = StoredBlock.COMPACT_SERIALIZED_SIZE;
ByteBuffer buffer = ByteBuffer.allocate(size);
for (int i = 0; i < numCheckpoints; i++) {
if (dis.read(buffer.array(), 0, size) < size)
throw new IOException("Incomplete read whilst loading checkpoints.");
StoredBlock block = StoredBlock.deserializeCompact(params, buffer);
buffer.position(0);
checkpoints.put(block.getHeader().getTimeSeconds(), block);
}
dataHash = new Sha256Hash(digest.digest());
log.info("Read {} checkpoints, hash is {}", checkpoints.size(), dataHash);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e); // Cannot happen.
} catch (ProtocolException e) {
throw new IOException(e);
} finally {
if (dis != null) dis.close();
inputStream.close();
}
}
/**
* Returns a {@link StoredBlock} representing the last checkpoint before the given time, for example, normally
* you would want to know the checkpoint before the earliest wallet birthday.
*/
public StoredBlock getCheckpointBefore(long time) {
try {
checkArgument(time > params.getGenesisBlock().getTimeSeconds());
// This is thread safe because the map never changes after creation.
Map.Entry<Long, StoredBlock> entry = checkpoints.floorEntry(time);
if (entry != null) return entry.getValue();
Block genesis = params.getGenesisBlock().cloneAsHeader();
return new StoredBlock(genesis, genesis.getWork(), 0);
} catch (VerificationException e) {
throw new RuntimeException(e); // Cannot happen.
}
}
/** Returns the number of checkpoints that were loaded. */
public int numCheckpoints() {
return checkpoints.size();
}
/** Returns a hash of the concatenated checkpoint data. */
public Sha256Hash getDataHash() {
return dataHash;
}
/**
* <p>Convenience method that creates a CheckpointManager, loads the given data, gets the checkpoint for the given
* time, then inserts it into the store and sets that to be the chain head. Useful when you have just created
* a new store from scratch and want to use configure it all in one go.</p>
*
* <p>Note that time is adjusted backwards by a week to account for possible clock drift in the block headers.</p>
*/
public static void checkpoint(NetworkParameters params, InputStream checkpoints, BlockStore store, long time)
throws IOException, BlockStoreException {
checkNotNull(params);
checkNotNull(store);
checkArgument(!(store instanceof FullPrunedBlockStore), "You cannot use checkpointing with a full store.");
time -= 86400 * 7;
BufferedInputStream stream = new BufferedInputStream(checkpoints);
CheckpointManager manager = new CheckpointManager(params, stream);
StoredBlock checkpoint = manager.getCheckpointBefore(time);
store.put(checkpoint);
store.setChainHead(checkpoint);
}
}