org.bitcoinj.core

Class CheckpointManager

java.lang.Object

org.bitcoinj.core.CheckpointManager

public class CheckpointManager
extends Object

Vends hard-coded StoredBlocks for blocks throughout the chain. Checkpoints serve two purposes:

1. 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.
2. They allow synchronization to the head of the chain for new wallets/users much faster than syncing all headers from the genesis block.

Checkpoints are used by the SPV BlockChain to initialize fresh SPVBlockStores. 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.

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.

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).

Field Summary

Fields

Modifier and Type	Field and Description
static BaseEncoding	BASE64
protected TreeMap<Long,StoredBlock>	checkpoints
protected Sha256Hash	dataHash
protected NetworkParameters	params

Constructor Summary

Constructors

Constructor and Description
CheckpointManager(NetworkParameters params, InputStream inputStream)

Method Summary

Modifier and Type	Method and Description
static void	checkpoint(NetworkParameters params, InputStream checkpoints, BlockStore store, long time) 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.
StoredBlock	getCheckpointBefore(long time) Returns a StoredBlock representing the last checkpoint before the given time, for example, normally you would want to know the checkpoint before the earliest wallet birthday.
Sha256Hash	getDataHash() Returns a hash of the concatenated checkpoint data.
int	numCheckpoints() Returns the number of checkpoints that were loaded.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

checkpoints

protected final TreeMap<Long,StoredBlock> checkpoints

params

protected final NetworkParameters params

dataHash

protected final Sha256Hash dataHash

BASE64

public static final BaseEncoding BASE64

Constructor Detail

CheckpointManager

public CheckpointManager(NetworkParameters params,
                         InputStream inputStream)
                  throws IOException

Throws:

IOException

Method Detail

getCheckpointBefore

public StoredBlock getCheckpointBefore(long time)

Returns a StoredBlock representing the last checkpoint before the given time, for example, normally you would want to know the checkpoint before the earliest wallet birthday.

numCheckpoints

public int numCheckpoints()

Returns the number of checkpoints that were loaded.

getDataHash

public Sha256Hash getDataHash()

Returns a hash of the concatenated checkpoint data.

checkpoint

public static void checkpoint(NetworkParameters params,
                              InputStream checkpoints,
                              BlockStore store,
                              long time)
                       throws IOException,
                              BlockStoreException

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.

Note that time is adjusted backwards by a week to account for possible clock drift in the block headers.

Throws:

IOException

BlockStoreException