Package org.bitcoinj.core

Class CheckpointManager

  • public class CheckpointManager
extends java.lang.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 Detail

      • checkpoints

        protected final java.util.TreeMap<java.time.Instant,​StoredBlock> checkpoints

      • BASE64

        public static final com.google.common.io.BaseEncoding BASE64

    • Constructor Detail

      • CheckpointManager

        public CheckpointManager​(NetworkParameters params)
                  throws java.io.IOException
        Loads the default checkpoints bundled with bitcoinj
        Throws:
        java.io.IOException

      • CheckpointManager

        public CheckpointManager​(NetworkParameters params,
                         @Nullable
                         java.io.InputStream inputStream)
                  throws java.io.IOException
        Loads the checkpoints from the given stream
        Throws:
        java.io.IOException

    • Method Detail

      • openStream

        public static java.io.InputStream openStream​(NetworkParameters params)
        Returns a checkpoints stream pointing to inside the bitcoinj JAR

      • getCheckpointBefore

        public StoredBlock getCheckpointBefore​(java.time.Instant 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,
                              java.io.InputStream checkpoints,
                              BlockStore store,
                              java.time.Instant time)
                       throws java.io.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:
        java.io.IOException
        BlockStoreException