hsd/lib/blockchain/chain.js

Cryptocurrency bike-shed

/*!
 * chain.js - blockchain management for hsd
 * Copyright (c) 2017-2018, Christopher Jeffrey (MIT License).
 * https://github.com/handshake-org/hsd
 */

'use strict';

const assert = require('bsert');
const path = require('path');
const AsyncEmitter = require('bevent');
const Logger = require('blgr');
const {Lock} = require('bmutex');
const LRU = require('blru');
const {BufferMap, BufferSet} = require('buffer-map');
const Network = require('../protocol/network');
const ChainDB = require('./chaindb');
const common = require('./common');
const consensus = require('../protocol/consensus');
const rules = require('../covenants/rules');
const NameState = require('../covenants/namestate');
const util = require('../utils/util');
const ChainEntry = require('./chainentry');
const CoinView = require('../coins/coinview');
const Script = require('../script/script');
const {VerifyError} = require('../protocol/errors');
const {OwnershipProof} = require('../covenants/ownership');
const AirdropProof = require('../primitives/airdropproof');
const {CriticalError} = require('../errors');
const thresholdStates = common.thresholdStates;
const scanActions = common.scanActions;
const {states} = NameState;

const {
  VERIFY_COVENANTS_HARDENED,
  VERIFY_COVENANTS_LOCKUP
} = rules.nameFlags;

/** @typedef {import('../types').Hash} Hash */
/** @typedef {import('../types').LockFlags} LockFlags */
/** @typedef {import('@handshake-org/bfilter').BloomFilter} BloomFilter */
/** @typedef {import('../primitives/block')} Block */
/** @typedef {import('../primitives/tx')} TX */
/** @typedef {import('../primitives/txmeta')} TXMeta */
/** @typedef {import('../primitives/outpoint')} Outpoint */
/** @typedef {import('../primitives/coin')} Coin */
/** @typedef {import('../primitives/address')} Address */
/** @typedef {import('../coins/coinentry')} CoinEntry */

/**
 * Blockchain
 * @alias module:blockchain.Chain
 * @property {ChainDB} db
 * @property {ChainEntry?} tip
 * @property {Number} height
 * @property {DeploymentState} state
 */

class Chain extends AsyncEmitter {
  /**
   * Create a blockchain.
   * @constructor
   * @param {Object} options
   */

  constructor(options) {
    super();

    this.opened = false;
    this.options = new ChainOptions(options);

    this.network = this.options.network;
    this.logger = this.options.logger.context('chain');
    this.workers = this.options.workers;

    this.db = new ChainDB(this.options);

    this.locker = new Lock(true, BufferMap);
    this.invalid = new LRU(5000, null, BufferMap);
    this.state = new DeploymentState(this.network.genesis.hash);

    this.tip = new ChainEntry();
    this.height = -1;
    this.synced = false;

    this.orphanMap = new BufferMap();
    this.orphanPrev = new BufferMap();
  }

  /**
   * Open the chain, wait for the database to load.
   * @returns {Promise<void>}
   */

  async open() {
    assert(!this.opened, 'Chain is already open.');
    this.opened = true;

    this.logger.info('Chain is loading.');

    if (this.options.checkpoints)
      this.logger.info('Checkpoints are enabled.');

    await this.db.open();

    const tip = await this.db.getTip();

    assert(tip);

    this.tip = tip;
    this.height = tip.height;

    this.logger.info('Chain Height: %d', tip.height);

    this.logger.memory();

    const state = await this.getDeploymentState();

    this.setDeploymentState(state);

    if (!this.options.spv) {
      const sync = await this.tryCompact();

      if (sync)
        await this.syncTree();
    }

    this.logger.memory();

    this.emit('tip', tip);

    this.maybeSync();
  }

  /**
   * Close the chain, wait for the database to close.
   * @returns {Promise<void>}
   */

  async close() {
    assert(this.opened, 'Chain is not open.');
    this.opened = false;
    return this.db.close();
  }

  /**
   * Get compaction heights.
   * @returns {Promise<Object>}
   */

  async getCompactionHeights() {
    if (this.options.spv)
      return null;

    const {keepBlocks} = this.network.block;
    const {compactionHeight} = await this.db.getTreeState();
    const {compactTreeInitInterval} = this.options;
    const compactFrom = compactionHeight + keepBlocks + compactTreeInitInterval;

    return {
      compactionHeight,
      compactFrom
    };
  }

  /**
   * Check if we need to compact tree data.
   * @returns {Promise<Boolean>} - Should we sync
   */

  async tryCompact() {
    if (this.options.spv)
      return false;

    if (!this.options.compactTreeOnInit)
      return true;

    const {txStart} = this.network;
    const {keepBlocks} = this.network.block;
    const startFrom = txStart + keepBlocks;

    if (this.height <= startFrom)
      return true;

    const {compactFrom} = await this.getCompactionHeights();

    if (compactFrom > this.height) {
      this.logger.debug(
        `Tree will compact when restarted after height ${compactFrom}.`);
      return true;
    }

    // Compact tree calls syncTree so we don't want to rerun it.
    await this.compactTree();
    return false;
  }

  /**
   * Sync tree state.
   */

  async syncTree() {
    this.logger.info('Synchronizing Tree with block history...');

    // Current state of the tree, loaded from chain database and
    // injected in chainDB.open(). It should be in the most
    // recently-committed state, which should have been at the last
    // tree interval. We might also need to recover from a
    // failed compactTree() operation. Either way, there might have been
    // new blocks added to the chain since then.
    const currentRoot = this.db.treeRoot();

    // We store commit height for the tree in the tree state.
    // commitHeight is the height of the block that committed tree root.
    // Note that the block at commitHeight has different tree root.
    const treeState = await this.db.getTreeState();
    const {commitHeight} = treeState;

    // sanity check
    if (commitHeight < this.height) {
      const entry = await this.db.getEntryByHeight(commitHeight + 1);
      assert(entry.treeRoot.equals(treeState.treeRoot));
      assert(entry.treeRoot.equals(currentRoot));
    }

    // Replay all blocks since the last tree interval to rebuild
    // the `txn` which is the in-memory delta between tree interval commitments.
    for (let height = commitHeight + 1; height <= this.height; height++) {
      const entry = await this.db.getEntryByHeight(height);
      assert(entry);

      const block = await this.db.getBlock(entry.hash);
      assert(block);

      const state = await this.readDeploymentState(entry);
      assert(state);

      const view = new CoinView();

      for (const tx of block.txs)
        await this.verifyCovenants(tx, view, height, state.nameFlags);

      // If the chain replay crosses a tree interval, it will commit
      // and write to disk in saveNames(), resetting the `txn` like usual.
      await this.db.saveNames(view, entry, false);
    }

    this.logger.info('Synchronized Tree Root: %x.', this.db.txn.rootHash());
  }

  /**
   * Perform all necessary contextual verification on a block.
   * @private
   * @param {Block} block
   * @param {ChainEntry} prev
   * @param {Number} flags
   * @returns {Promise<Array>} - [CoinView, DeploymentState]
   */

  async verifyContext(block, prev, flags) {
    // Initial non-contextual verification.
    const state = await this.verify(block, prev, flags);

    // Skip everything if we're in SPV mode.
    if (this.options.spv) {
      const view = new CoinView();
      return [view, state];
    }

    // Skip everything if we're using checkpoints.
    if (this.isHistorical(prev)) {
      const view = await this.updateInputs(block, prev, state);
      return [view, state];
    }

    // Verify scripts, spend and add coins.
    const view = await this.verifyInputs(block, prev, state);

    return [view, state];
  }

  /**
   * Perform all necessary contextual verification
   * on a block, without POW check.
   * @param {Block} block
   * @returns {Promise<Array>} - [CoinView, DeploymentState]
   */

  async verifyBlock(block) {
    const unlock = await this.locker.lock();
    try {
      return await this._verifyBlock(block);
    } finally {
      unlock();
    }
  }

  /**
   * Perform all necessary contextual verification
   * on a block, without POW check (no lock).
   * @private
   * @param {Block} block
   * @returns {Promise<Array>} - [CoinView, DeploymentState]
   */

  async _verifyBlock(block) {
    const flags = common.DEFAULT_FLAGS & ~common.flags.VERIFY_POW;
    return this.verifyContext(block, this.tip, flags);
  }

  /**
   * Test whether the hash is in the main chain.
   * @param {Hash} hash
   * @returns {Promise<Boolean>}
   */

  isMainHash(hash) {
    return this.db.isMainHash(hash);
  }

  /**
   * Test whether the entry is in the main chain.
   * @param {ChainEntry} entry
   * @returns {Promise<Boolean>}
   */

  isMainChain(entry) {
    return this.db.isMainChain(entry);
  }

  /**
   * Get ancestor by `height`.
   * @param {ChainEntry} entry
   * @param {Number} height
   * @returns {Promise<ChainEntry?>}
   */

  getAncestor(entry, height) {
    return this.db.getAncestor(entry, height);
  }

  /**
   * Get previous entry.
   * @param {ChainEntry} entry
   * @returns {Promise<ChainEntry?>}
   */

  getPrevious(entry) {
    return this.db.getPrevious(entry);
  }

  /**
   * Get previous cached entry.
   * @param {ChainEntry} entry
   * @returns {ChainEntry?}
   */

  getPrevCache(entry) {
    return this.db.getPrevCache(entry);
  }

  /**
   * Get next entry.
   * @param {ChainEntry} entry
   * @returns {Promise<ChainEntry?>}
   */

  getNext(entry) {
    return this.db.getNext(entry);
  }

  /**
   * Get next entry.
   * @param {ChainEntry} entry
   * @returns {Promise<ChainEntry?>}
   */

  getNextEntry(entry) {
    return this.db.getNextEntry(entry);
  }

  /**
   * Calculate median time past.
   * @param {ChainEntry} prev
   * @returns {Promise<Number>}
   */

  async getMedianTime(prev) {
    const timespan = consensus.MEDIAN_TIMESPAN;
    const median = [];

    let entry = prev;

    for (let i = 0; i < timespan && entry; i++) {
      median.push(entry.time);

      const cache = this.getPrevCache(entry);

      if (cache)
        entry = cache;
      else
        entry = await this.getPrevious(entry);
    }

    median.sort(cmp);

    return median[median.length >>> 1];
  }

  /**
   * Test whether the entry is potentially
   * an ancestor of a checkpoint.
   * @param {ChainEntry} prev
   * @returns {Boolean}
   */

  isHistorical(prev) {
    if (this.options.checkpoints) {
      if (prev.height + 1 <= this.network.lastCheckpoint)
        return true;
    }
    return false;
  }

  /**
   * Test whether the height is potentially
   * an ancestor of a checkpoint.
   * @param {Number} height
   * @returns {Boolean}
   */

  isHistoricalHeight(height) {
    if (this.options.checkpoints) {
      if (height <= this.network.lastCheckpoint)
        return true;
    }
    return false;
  }

  /**
   * Contextual verification for a block, including
   * version deployments (IsSuperMajority), versionbits,
   * coinbase height, finality checks.
   * @private
   * @param {Block} block
   * @param {ChainEntry} prev
   * @param {Number} flags
   * @returns {Promise<DeploymentState>}
   */

  async verify(block, prev, flags) {
    assert(typeof flags === 'number');

    // Extra sanity check.
    if (!block.prevBlock.equals(prev.hash))
      throw new VerifyError(block, 'invalid', 'bad-prevblk', 0);

    // Verify a checkpoint if there is one.
    const hash = block.hash();
    if (!this.verifyCheckpoint(prev, hash)) {
      throw new VerifyError(block,
        'checkpoint',
        'checkpoint mismatch',
        100);
    }

    // Skip everything when using checkpoints.
    // We can do this safely because every
    // block in between each checkpoint was
    // validated outside in the header chain.
    if (this.isHistorical(prev)) {
      // Check merkle root.
      if (flags & common.flags.VERIFY_BODY) {
        assert(typeof block.createMerkleRoot === 'function');

        const root = block.createMerkleRoot();

        if (!block.merkleRoot.equals(root)) {
          throw new VerifyError(block,
            'invalid',
            'bad-txnmrklroot',
            100,
            true);
        }

        const witnessRoot = block.createWitnessRoot();

        if (!block.witnessRoot.equals(witnessRoot)) {
          throw new VerifyError(block,
            'invalid',
            'bad-witnessroot',
            100,
            true);
        }

        flags &= ~common.flags.VERIFY_BODY;
      }
    }

    // Non-contextual checks.
    if (flags & common.flags.VERIFY_BODY) {
      const [valid, reason, score] = block.checkBody();

      if (!valid)
        throw new VerifyError(block, 'invalid', reason, score, true);
    }

    // Check name DoS limits.
    const set = new BufferSet();

    let opens = 0;
    let updates = 0;
    let renewals = 0;

    for (let i = 0; i < block.txs.length; i++) {
      const tx = block.txs[i];

      opens += rules.countOpens(tx);

      if (opens > consensus.MAX_BLOCK_OPENS) {
        throw new VerifyError(block,
          'invalid',
          'bad-blk-opens',
          100);
      }

      updates += rules.countUpdates(tx);

      if (updates > consensus.MAX_BLOCK_UPDATES) {
        throw new VerifyError(block,
          'invalid',
          'bad-blk-updates',
          100);
      }

      renewals += rules.countRenewals(tx);

      if (renewals > consensus.MAX_BLOCK_RENEWALS) {
        throw new VerifyError(block,
          'invalid',
          'bad-blk-renewals',
          100);
      }

      // Certain covenants can only be used once per name per block
      if (rules.hasNames(tx, set)) {
        throw new VerifyError(block,
          'invalid',
          'bad-blk-names',
          100);
      }

      rules.addNames(tx, set);
    }

    // Ensure the POW is what we expect.
    const bits = await this.getTarget(block.time, prev);

    if (block.bits !== bits) {
      this.logger.debug(
        'Bad diffbits: 0x%s != 0x%s',
        util.hex32(block.bits),
        util.hex32(bits));

      throw new VerifyError(block,
        'invalid',
        'bad-diffbits',
        100);
    }

    // Ensure the timestamp is correct.
    const mtp = await this.getMedianTime(prev);

    if (block.time <= mtp) {
      throw new VerifyError(block,
        'invalid',
        'time-too-old',
        0);
    }

    // Check timestamp against adj-time+2hours.
    // If this fails we may be able to accept
    // the block later.
    if (block.time > this.network.now() + 2 * 60 * 60) {
      throw new VerifyError(block,
        'invalid',
        'time-too-new',
        0,
        true);
    }

    // Skip all blocks in spv mode once
    // we've verified the network target.
    if (this.options.spv)
      return this.state;

    // Calculate height of current block.
    const height = prev.height + 1;

    // Get the new deployment state.
    const state = await this.getDeployments(block.time, prev);

    // Transactions must be finalized with
    // regards to nSequence and nLockTime.
    for (let i = 1; i < block.txs.length; i++) {
      const tx = block.txs[i];
      if (!tx.isFinal(height, mtp)) {
        throw new VerifyError(block,
          'invalid',
          'bad-txns-nonfinal',
          10);
      }
    }

    // Make sure the height contained
    // in the coinbase is correct.
    if (block.getCoinbaseHeight() !== height) {
      throw new VerifyError(block,
        'invalid',
        'bad-cb-height',
        100);
    }

    const cb = block.txs[0];

    for (let i = 1; i < cb.inputs.length; i++) {
      const {witness} = cb.inputs[i];

      if (witness.items.length !== 1) {
        throw new VerifyError(block,
          'invalid',
          'bad-witness-size',
          100);
      }

      if (i >= cb.outputs.length) {
        throw new VerifyError(block,
          'invalid',
          'bad-output',
          100);
      }

      const output = cb.outputs[i];

      // Airdrop proof.
      if (!output.covenant.isClaim()) {
        // Disable airdrop claims if airstop is activated
        if (state.hasAirstop) {
          throw new VerifyError(block,
            'invalid',
            'bad-airdrop-disabled',
            100);
        }

        let proof;
        try {
          proof = AirdropProof.decode(witness.items[0]);
        } catch (e) {
          throw new VerifyError(block,
            'invalid',
            'bad-airdrop-format',
            100);
        }

        if (!proof.isSane()) {
          throw new VerifyError(block,
            'invalid',
            'bad-airdrop-sanity',
            100);
        }

        if (prev.height + 1 >= this.network.goosigStop) {
          const key = proof.getKey();

          if (!key) {
            throw new VerifyError(block,
              'invalid',
              'bad-airdrop-proof',
              100);
          }

          if (key.isGoo()) {
            throw new VerifyError(block,
              'invalid',
              'bad-goosig-disabled',
              100);
          }
        }

        // Note: GooSig RSA 1024 is possible to
        // crack as well, but in order to make
        // it safe we would need to include a
        // commitment to the key size (bad).
        // We may have to just disallow <2048
        // bit for mainnet.
        if (state.hasHardening()) {
          if (proof.isWeak()) {
            throw new VerifyError(block,
              'invalid',
              'bad-airdrop-sanity',
              10);
          }
        }

        continue;
      }

      // DNSSEC ownership proof.
      let proof;
      try {
        proof = OwnershipProof.decode(witness.items[0]);
      } catch (e) {
        throw new VerifyError(block,
          'invalid',
          'bad-dnssec-format',
          100);
      }

      // Verify times.
      if (!proof.verifyTimes(prev.time)) {
        throw new VerifyError(block,
          'invalid',
          'bad-dnssec-times',
          10);
      }
    }

    return state;
  }

  /**
   * Check all deployments on a chain.
   * @param {Number} time
   * @param {ChainEntry} prev
   * @returns {Promise<DeploymentState>}
   */

  async getDeployments(time, prev) {
    const deployments = this.network.deployments;
    const state = new DeploymentState(prev.hash);

    // Disable RSA-1024.
    if (await this.isActive(prev, deployments.hardening))
      state.nameFlags |= rules.nameFlags.VERIFY_COVENANTS_HARDENED;

    // Disable ICANN, TOP100 and CUSTOM TLDs from getting auctioned.
    if (await this.isActive(prev, deployments.icannlockup))
      state.nameFlags |= rules.nameFlags.VERIFY_COVENANTS_LOCKUP;

    // Disable airdrop claims.
    if (await this.isActive(prev, deployments.airstop))
      state.hasAirstop = true;

    return state;
  }

  /**
   * Set a new deployment state.
   * @param {DeploymentState} state
   */

  setDeploymentState(state) {
    if (this.options.checkpoints && this.height < this.network.lastCheckpoint) {
      this.state = state;
      return;
    }

    if (!this.state.hasHardening() && state.hasHardening())
      this.logger.warning('RSA hardening has been activated.');

    if (this.height === this.network.deflationHeight)
      this.logger.warning('Name claim deflation has been activated.');

    if (!this.state.hasICANNLockup() && state.hasICANNLockup())
      this.logger.warning('ICANN lockup has been activated.');

    if (!this.state.hasAirstop && state.hasAirstop)
      this.logger.warning('Airdrop claims has been disabled.');

    this.state = state;
  }

  /**
   * Spend and update inputs (checkpoints only).
   * @private
   * @param {Block} block
   * @param {ChainEntry} prev
   * @param {DeploymentState} state
   * @returns {Promise<CoinView>}
   */

  async updateInputs(block, prev, state) {
    const view = new CoinView();
    const height = prev.height + 1;

    assert(block.treeRoot.equals(this.db.treeRoot()));

    for (let i = 0; i < block.txs.length; i++) {
      const tx = block.txs[i];

      if (i === 0) {
        assert(view.bits.spend(this.db.field, tx));
      } else {
        assert(await view.spendInputs(this.db, tx),
          'BUG: Spent inputs in historical data!');
      }

      await this.verifyCovenants(tx, view, height, state.nameFlags);

      view.addTX(tx, height);
    }

    return view;
  }

  /**
   * Check block transactions for all things pertaining
   * to inputs. This function is important because it is
   * what actually fills the coins into the block. This
   * function will check the block reward, the sigops,
   * the tx values, and execute and verify the scripts (it
   * will attempt to do this on the worker pool). If
   * `checkpoints` is enabled, it will skip verification
   * for historical data.
   * @private
   * @see TX#verifyInputs
   * @see TX#verify
   * @param {Block} block
   * @param {ChainEntry} prev
   * @param {DeploymentState} state
   * @returns {Promise<CoinView>}
   */

  async verifyInputs(block, prev, state) {
    const network = this.network;
    const view = new CoinView();
    const height = prev.height + 1;
    const interval = network.halvingInterval;

    let sigops = 0;
    let reward = 0;

    // Check the name tree root.
    if (!block.treeRoot.equals(this.db.treeRoot())) {
      throw new VerifyError(block,
        'invalid',
        'bad-tree-root',
        100);
    }

    // Check all transactions
    for (let i = 0; i < block.txs.length; i++) {
      const tx = block.txs[i];

      // Ensure tx is not double spending an output.
      if (i === 0) {
        if (!view.bits.spend(this.db.field, tx)) {
          throw new VerifyError(block,
            'invalid',
            'bad-txns-bits-missingorspent',
            100);
        }
      } else {
        if (!await view.spendInputs(this.db, tx)) {
          throw new VerifyError(block,
            'invalid',
            'bad-txns-inputs-missingorspent',
            100);
        }

        // Verify sequence locks.
        const valid = await this.verifyLocks(prev, tx, view, state.lockFlags);

        if (!valid) {
          throw new VerifyError(block,
            'invalid',
            'bad-txns-nonfinal',
            100);
        }
      }

      // Count sigops.
      sigops += tx.getSigops(view);

      if (sigops > consensus.MAX_BLOCK_SIGOPS) {
        throw new VerifyError(block,
          'invalid',
          'bad-blk-sigops',
          100);
      }

      // Contextual sanity checks.
      const [fee, reason, score] = tx.checkInputs(view, height, network);

      if (fee === -1) {
        throw new VerifyError(block,
          'invalid',
          reason,
          score);
      }

      reward += fee;

      if (reward > consensus.MAX_MONEY) {
        throw new VerifyError(block,
          'invalid',
          'bad-cb-amount',
          100);
      }

      // Verify covenants.
      await this.verifyCovenants(tx, view, height, state.nameFlags);

      // Add new coins.
      view.addTX(tx, height);
    }

    // Make sure the miner isn't trying to conjure more coins.
    reward += consensus.getReward(height, interval);

    if (block.getClaimed() > reward) {
      throw new VerifyError(block,
        'invalid',
        'bad-cb-amount',
        0);
    }

    // Push onto verification queue.
    const jobs = [];
    for (let i = 0; i < block.txs.length; i++) {
      const tx = block.txs[i];
      jobs.push(tx.verifyAsync(view, state.flags, this.workers));
    }

    // Verify all txs in parallel.
    const results = await Promise.all(jobs);

    for (const result of results) {
      if (!result) {
        throw new VerifyError(block,
          'invalid',
          'mandatory-script-verify-flag-failed',
          100);
      }
    }

    return view;
  }

  /**
   * Get main chain height for hash.
   * @param {Hash} hash
   * @returns {Promise<Number>}
   */

  async getMainHeight(hash) {
    const entry = await this.db.getEntry(hash);

    if (!entry)
      return -1;

    // Must be the current chain.
    if (!await this.db.isMainChain(entry))
      return -1;

    return entry.height;
  }

  /**
   * Verify a renewal.
   * @param {Hash} hash
   * @param {Number} height
   * @returns {Promise<Boolean>}
   */

  async verifyRenewal(hash, height) {
    assert(Buffer.isBuffer(hash));
    assert((height >>> 0) === height);

    // Cannot renew yet.
    if (height < this.network.names.renewalMaturity)
      return true;

    // We require renewals to commit to a block
    // within the past 6 months, to prove that
    // the user still owns the key. This prevents
    // people from presigning thousands of years
    // worth of renewals. The block must be at
    // least 400 blocks back to prevent the
    // possibility of a reorg invalidating the
    // covenant.

    const entry = await this.db.getEntry(hash);

    if (!entry)
      return false;

    // Must be the current chain.
    if (!await this.db.isMainChain(entry))
      return false;

    // Make sure it's a mature block (unlikely to be reorgd).
    if (entry.height > height - this.network.names.renewalMaturity)
      return false;

    // Block committed to must be
    // no older than a 6 months.
    if (entry.height < height - this.network.names.renewalPeriod)
      return false;

    return true;
  }

  /**
   * Verify covenants.
   * @param {TX} tx
   * @param {CoinView} view
   * @param {Number} height
   * @param {Number} nameFlags
   */

  async verifyCovenants(tx, view, height, nameFlags) {
    assert(tx);
    assert(view instanceof CoinView);
    assert((height >>> 0) === height);
    assert(typeof nameFlags === 'number');

    const {types} = rules;
    const network = this.network;

    for (let i = 0; i < tx.outputs.length; i++) {
      const output = tx.outputs[i];
      const {covenant} = output;

      if (!covenant.isName())
        continue;

      // BID and REDEEM covenants to do not update NameState.
      // Therefore, if we are still inside checkpoints we can simply
      // assume these covenants are valid without checking anything,
      // or even getting and decoding the NameState from the tree.
      // We could skip checks for ALL covenant types under checkpoints,
      // but since the other types modify the NameState we still
      // need to get the data, and the checks themselves are cheap.
      if (this.isHistoricalHeight(height)) {
        if (covenant.isBid() || covenant.isRedeem())
          continue;
      }

      const nameHash = covenant.getHash(0);
      const start = covenant.getU32(1);
      const ns = await view.getNameState(this.db, nameHash);

      if (ns.isNull()) {
        if (!covenant.isClaim() && !covenant.isOpen())
          throw new Error('Database inconsistency.');

        const name = covenant.get(2);
        ns.set(name, height);
      }

      // Check for name expiration/revocation.
      // Note that claimed names never expire
      // before the reservation period ends.
      // However, they _can_ be revoked.
      ns.maybeExpire(height, network);

      // Calculate the current state.
      const state = ns.state(height, network);

      // none -> claim
      if (covenant.isClaim()) {
        const flags = covenant.getU8(3);
        const weak = (flags & 1) !== 0;

        // Claims can be re-redeemed any time
        // before registration. This is required
        // in order for our emergency soft-forks
        // to truly behave as _soft_ forks. Once
        // re-redeemed, the locktime resets and
        // they re-enter the LOCKED state. Note
        // that a newer claim invalidates the
        // old output by committing to a higher
        // height (will fail with nonlocal).
        const valid = state === states.OPENING
                   || state === states.LOCKED
                   || (state === states.CLOSED && !ns.registered);

        if (!valid) {
          throw new VerifyError(tx,
            'invalid',
            'bad-claim-state',
            100);
        }

        // Can only claim reserved names.
        // Once a reserved name is revoked,
        // it is no longer claimable.
        if (ns.expired || !rules.isReserved(nameHash, height, network)) {
          throw new VerifyError(tx,
            'invalid',
            'bad-claim-notreserved',
            100);
        }

        // Once the fork is active, we reject
        // any weak algorithms (i.e. RSA-1024).
        // Any future emergency soft-forks should
        // also be included below this check.
        if ((nameFlags & VERIFY_COVENANTS_HARDENED) && weak) {
          throw new VerifyError(tx,
            'invalid',
            'bad-claim-algorithm',
            100);
        }

        // Check commitment hash.
        const block = covenant.getHash(4);
        const claimed = await this.getMainHeight(block);

        // Implicitly checks for `-1`.
        if (claimed !== covenant.getU32(5)) {
          throw new VerifyError(tx,
            'invalid',
            'bad-claim-commit-height',
            100);
        }

        // Implicitly disallows the genesis block.
        if (claimed <= ns.claimed) {
          throw new VerifyError(tx,
            'invalid',
            'bad-claim-commit-hash',
            100);
        }

        assert(claimed >= 1);

        // Handle inflation-fixing soft-fork.
        if (height >= network.deflationHeight) {
          const {claimFrequency} = network.names;

          // Require claim height to be 1 on
          // initial claims. This makes some
          // non-contextual verification easier.
          if (ns.owner.isNull()) {
            if (claimed !== 1) {
              throw new VerifyError(tx,
                'invalid',
                'bad-claim-height',
                0);
            }
          }

          // Limit the frequency of re-claims.
          if (!ns.owner.isNull() && height < ns.height + claimFrequency) {
            throw new VerifyError(tx,
              'invalid',
              'bad-claim-frequency',
              0);
          }

          // Allow replacement, but require the
          // same fee, which is then miner-burned.
          if (!ns.owner.isNull()) {
            const coin = await this.getCoin(ns.owner.hash, ns.owner.index);

            if (!coin || output.value !== coin.value) {
              throw new VerifyError(tx,
                'invalid',
                'bad-claim-value',
                0);
            }
          }
        }

        ns.setHeight(height);
        ns.setRenewal(height);
        ns.setClaimed(claimed);
        ns.setValue(0);
        ns.setOwner(tx.outpoint(i));
        ns.setHighest(0);
        ns.setWeak(weak);

        continue;
      }

      assert(!tx.isCoinbase());

      // none/redeem/open -> open
      if (covenant.isOpen()) {
        if (state !== states.OPENING) {
          throw new VerifyError(tx,
            'invalid',
            'bad-open-state',
            100);
        }

        // Only one open transaction can ever exist.
        if (ns.height !== height) {
          throw new VerifyError(tx,
            'invalid',
            'bad-open-multiple',
            100);
        }

        // Cannot bid on a reserved name.
        if (!ns.expired && rules.isReserved(nameHash, height, network)) {
          throw new VerifyError(tx,
            'invalid',
            'bad-open-reserved',
            100);
        }

        // Make sure locked up names are not opened if ICANN LOCKUP has
        // activated.
        const isLockUpActive = nameFlags & VERIFY_COVENANTS_LOCKUP;
        if (isLockUpActive && rules.isLockedUp(nameHash, height, network)) {
          throw new VerifyError(tx,
            'invalid',
            'bad-open-lockedup',
            100);
        }

        // On mainnet, names are released on a
        // weekly basis for the first year.
        if (!rules.hasRollout(nameHash, height, network)) {
          throw new VerifyError(tx,
            'invalid',
            'bad-open-rollout',
            100);
        }

        continue;
      }

      // none/redeem/open -> bid
      if (covenant.isBid()) {
        if (state !== states.BIDDING) {
          throw new VerifyError(tx,
            'invalid',
            'bad-bid-state',
            100);
        }

        if (start !== ns.height) {
          throw new VerifyError(tx,
            'invalid',
            'bad-bid-height',
            100);
        }

        continue;
      }

      assert(i < tx.inputs.length);

      const {prevout} = tx.inputs[i];

      switch (covenant.type) {
        // bid -> reveal
        case types.REVEAL: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-reveal-nonlocal',
              100);
          }

          // Early reveals? No.
          if (state !== states.REVEAL) {
            throw new VerifyError(tx,
              'invalid',
              'bad-reveal-state',
              100);
          }

          if (ns.owner.isNull() || output.value > ns.highest) {
            ns.setValue(ns.highest);
            ns.setOwner(tx.outpoint(i));
            ns.setHighest(output.value);
          } else if (output.value > ns.value) {
            ns.setValue(output.value);
          }

          break;
        }

        // reveal -> redeem
        case types.REDEEM: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-redeem-nonlocal',
              100);
          }

          // Allow participants to get their
          // money out, even in a revoked state.
          if (state < states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-redeem-state',
              100);
          }

          // Must be the loser in order
          // to redeem the money now.
          if (prevout.equals(ns.owner)) {
            throw new VerifyError(tx,
              'invalid',
              'bad-redeem-owner',
              100);
          }

          break;
        }

        // claim/reveal -> register
        case types.REGISTER: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-register-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-register-state',
              100);
          }

          const data = covenant.get(2);
          const hash = covenant.getHash(3);

          // Verify block hash for renewal.
          if (!await this.verifyRenewal(hash, height)) {
            throw new VerifyError(tx,
              'invalid',
              'bad-register-renewal',
              100);
          }

          // Must be the winner in
          // order to redeem the name.
          if (!prevout.equals(ns.owner)) {
            throw new VerifyError(tx,
              'invalid',
              'bad-register-owner',
              100);
          }

          // Must match the second highest bid.
          if (output.value !== ns.value) {
            throw new VerifyError(tx,
              'invalid',
              'bad-register-value',
              100);
          }

          // For claimed names: if the keys used in
          // the proof were somehow compromised, the
          // name becomes locked until the reservation
          // period ends. Note that this is the same
          // code path that can be used for emergency
          // soft-forks in the case that a large name
          // registrar's keys are compromised.
          if (ns.isClaimable(height, network)) {
            // Soft-fork #1 (RSA hardening).
            if ((nameFlags & VERIFY_COVENANTS_HARDENED) && ns.weak) {
              throw new VerifyError(tx,
                'invalid',
                'bad-register-state',
                100);
            }

            // Emergency soft-forks go here.
            // Use only to prevent sky from falling.
            //
            // A vision for an emergency soft-fork:
            //
            // 1. A list of compromised DNSKEYs are collected
            //    out of band.
            // 2. The chain is scanned on first boot in order
            //    to find proofs which are vulnerable. The
            //    relevant names are marked as such.
            //    - Pruned nodes and nodes without witness
            //      data will unfortunately need to re-sync.
            // 3. Any proof published before the flag day
            //    is also marked in this way if it contains
            //    a vulnerable key.
            // 4. At soft-fork activation, the "vulnerable"
            //    check will take place here. This function
            //    should return true for any name that was
            //    redeemed with a vulnerable key.
            //
            // To future generations:
            // PUT THE VULNERABLE KEY CHECK HERE!
          }

          ns.setRegistered(true);
          ns.setOwner(tx.outpoint(i));

          if (data.length > 0)
            ns.setData(data);

          ns.setRenewal(height);

          break;
        }

        // update/renew/register/finalize -> update
        case types.UPDATE: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-update-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-update-state',
              100);
          }

          const data = covenant.get(2);

          ns.setOwner(tx.outpoint(i));

          if (data.length > 0)
            ns.setData(data);

          ns.setTransfer(0);

          break;
        }

        // update/renew/register/finalize -> renew
        case types.RENEW: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-renewal-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-renewal-state',
              100);
          }

          const hash = covenant.getHash(2);

          if (height < ns.renewal + network.names.treeInterval) {
            throw new VerifyError(tx,
              'invalid',
              'bad-renewal-premature',
              100);
          }

          if (!await this.verifyRenewal(hash, height)) {
            throw new VerifyError(tx,
              'invalid',
              'bad-renewal',
              100);
          }

          ns.setOwner(tx.outpoint(i));
          ns.setTransfer(0);
          ns.setRenewal(height);
          ns.setRenewals(ns.renewals + 1);

          break;
        }

        // update/renew/register/finalize -> transfer
        case types.TRANSFER: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-transfer-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-transfer-state',
              100);
          }

          ns.setOwner(tx.outpoint(i));

          assert(ns.transfer === 0);
          ns.setTransfer(height);

          break;
        }

        // transfer -> finalize
        case types.FINALIZE: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-finalize-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-finalize-state',
              100);
          }

          assert(ns.transfer !== 0);
          assert(network.names.transferLockup >= network.names.treeInterval);

          if (height < ns.transfer + network.names.transferLockup) {
            throw new VerifyError(tx,
              'invalid',
              'bad-finalize-maturity',
              100);
          }

          const flags = covenant.getU8(3);
          const weak = (flags & 1) !== 0;
          const claimed = covenant.getU32(4);
          const renewals = covenant.getU32(5);
          const hash = covenant.getHash(6);

          if (weak !== ns.weak
              || claimed !== ns.claimed
              || renewals !== ns.renewals) {
            throw new VerifyError(tx,
              'invalid',
              'bad-finalize-statetransfer',
              100);
          }

          if (!await this.verifyRenewal(hash, height)) {
            throw new VerifyError(tx,
              'invalid',
              'bad-finalize-renewal',
              100);
          }

          ns.setOwner(tx.outpoint(i));
          ns.setTransfer(0);
          ns.setRenewal(height);
          ns.setRenewals(ns.renewals + 1);

          break;
        }

        // register/update/renew/transfer/finalize -> revoke
        case types.REVOKE: {
          if (start !== ns.height) {
            throw new VerifyError(tx,
              'invalid',
              'bad-revoke-nonlocal',
              100);
          }

          if (state !== states.CLOSED) {
            throw new VerifyError(tx,
              'invalid',
              'bad-revoke-state',
              100);
          }

          assert(ns.revoked === 0);
          ns.setRevoked(height);
          ns.setTransfer(0);
          ns.setData(null);

          break;
        }

        default: {
          assert.fail('Invalid covenant type.');
          break;
        }
      }
    }

    return;
  }

  /**
   * Find the block at which a fork ocurred.
   * @private
   * @param {ChainEntry} fork - The current chain.
   * @param {ChainEntry} longer - The competing chain.
   * @returns {Promise<ChainEntry>}
   */

  async findFork(fork, longer) {
    while (!fork.hash.equals(longer.hash)) {
      while (longer.height > fork.height) {
        longer = await this.getPrevious(longer);
        if (!longer)
          throw new Error('No previous entry for new tip.');
      }

      if (fork.hash.equals(longer.hash))
        return fork;

      fork = await this.getPrevious(fork);

      if (!fork)
        throw new Error('No previous entry for old tip.');
    }

    return fork;
  }

  /**
   * Reorganize the blockchain (connect and disconnect inputs).
   * Called when a competing chain with a higher chainwork
   * is received.
   * @private
   * @param {ChainEntry} competitor - The competing chain's tip.
   * @returns {Promise<ChainEntry>} - Fork block.
   */

  async reorganize(competitor) {
    const tip = this.tip;
    const fork = await this.findFork(tip, competitor);

    assert(fork, 'No free space or data corruption.');

    // Blocks to disconnect.
    const disconnect = [];
    let entry = tip;
    while (!entry.hash.equals(fork.hash)) {
      disconnect.push(entry);
      entry = await this.getPrevious(entry);
      assert(entry);
    }

    // Blocks to connect.
    const connect = [];
    entry = competitor;
    while (!entry.hash.equals(fork.hash)) {
      connect.push(entry);
      entry = await this.getPrevious(entry);
      assert(entry);
    }

    // Disconnect blocks/txs.
    for (let i = 0; i < disconnect.length; i++) {
      const entry = disconnect[i];
      await this.disconnect(entry);
    }

    // Connect blocks/txs.
    // We don't want to connect the new tip here.
    // That will be done outside in setBestChain.
    for (let i = connect.length - 1; i >= 1; i--) {
      const entry = connect[i];

      try {
        await this.reconnect(entry);
      } catch (err) {
        if (err.type === 'VerifyError') {
          if (!err.malleated) {
            while (i--)
              this.setInvalid(connect[i].hash);
          }

          if (this.tip.chainwork.lte(tip.chainwork))
            await this.unreorganize(fork, tip);
        }

        throw err;
      }
    }

    this.logger.warning(
      'Chain reorganization: old=%x(%d) new=%x(%d)',
      tip.hash,
      tip.height,
      competitor.hash,
      competitor.height
    );

    await this.emitAsync('reorganize', tip, competitor, fork);

    return fork;
  }

  /**
   * Revert a failed reorganization.
   * @private
   * @param {ChainEntry} fork - The common ancestor.
   * @param {ChainEntry} last - The previous valid tip.
   * @returns {Promise}
   */

  async unreorganize(fork, last) {
    const tip = this.tip;

    // Blocks to disconnect.
    const disconnect = [];
    let entry = tip;
    while (!entry.hash.equals(fork.hash)) {
      disconnect.push(entry);
      entry = await this.getPrevious(entry);
      assert(entry);
    }

    // Blocks to connect.
    const connect = [];
    entry = last;
    while (!entry.hash.equals(fork.hash)) {
      connect.push(entry);
      entry = await this.getPrevious(entry);
      assert(entry);
    }

    // Disconnect blocks/txs.
    for (let i = 0; i < disconnect.length; i++) {
      const entry = disconnect[i];
      await this.disconnect(entry);
    }

    // Connect blocks/txs.
    for (let i = connect.length - 1; i >= 0; i--) {
      const entry = connect[i];
      await this.reconnect(entry);
    }

    this.logger.warning(
      'Chain un-reorganization: old=%x(%d) new=%x(%d)',
      tip.hash,
      tip.height,
      last.hash,
      last.height
    );

    // Treat as a reorganize event.
    await this.emitAsync('reorganize', tip, last, fork);
  }

  /**
   * Reorganize the blockchain for SPV. This
   * will reset the chain to the fork block.
   * @private
   * @param {ChainEntry} competitor - The competing chain's tip.
   * @returns {Promise}
   */

  async reorganizeSPV(competitor) {
    const tip = this.tip;
    const fork = await this.findFork(tip, competitor);

    assert(fork, 'No free space or data corruption.');

    // Buffer disconnected blocks.
    const disconnect = [];
    let entry = tip;
    while (!entry.hash.equals(fork.hash)) {
      disconnect.push(entry);
      entry = await this.getPrevious(entry);
      assert(entry);
    }

    // Reset the main chain back
    // to the fork block, causing
    // us to redownload the blocks
    // on the new main chain.
    await this._reset(fork.hash, false);

    // Emit disconnection events now that
    // the chain has successfully reset.
    for (const entry of disconnect) {
      const headers = entry.toHeaders();
      const view = new CoinView();
      await this.emitAsync('disconnect', entry, headers, view);
    }

    this.logger.warning(
      'SPV reorganization: old=%x(%d) new=%x(%d)',
      tip.hash,
      tip.height,
      competitor.hash,
      competitor.height
    );

    this.logger.warning(
      'Chain replay from height %d necessary.',
      fork.height);

    return this.emitAsync('reorganize', tip, competitor, fork);
  }

  /**
   * Disconnect an entry from the chain (updates the tip).
   * @param {ChainEntry} entry
   * @returns {Promise}
   */

  async disconnect(entry) {
    let block = await this.getBlock(entry.hash);

    if (!block) {
      if (!this.options.spv)
        throw new Error('Block not found.');
      block = entry.toHeaders();
    }

    const prev = await this.getPrevious(entry);
    const view = await this.db.disconnect(entry, block);

    assert(prev);

    this.tip = prev;
    this.height = prev.height;

    this.emit('tip', prev);

    return this.emitAsync('disconnect', entry, block, view);
  }

  /**
   * Reconnect an entry to the chain (updates the tip).
   * This will do contextual-verification on the block
   * (necessary because we cannot validate the inputs
   * in alternate chains when they come in).
   * @param {ChainEntry} entry
   * @returns {Promise}
   */

  async reconnect(entry) {
    const flags = common.flags.VERIFY_NONE;

    let block = await this.getBlock(entry.hash);

    if (!block) {
      if (!this.options.spv)
        throw new Error('Block not found.');
      block = entry.toHeaders();
    }

    const prev = await this.getPrevious(entry);
    assert(prev);

    let view, state;
    try {
      [view, state] = await this.verifyContext(block, prev, flags);
    } catch (err) {
      if (err.type === 'VerifyError') {
        if (!err.malleated)
          this.setInvalid(entry.hash);
        this.logger.warning(
          'Tried to reconnect invalid block: %x (%d).',
          entry.hash, entry.height);
      }
      throw err;
    }

    await this.db.reconnect(entry, block, view);

    this.tip = entry;
    this.height = entry.height;
    this.setDeploymentState(state);

    this.emit('tip', entry);
    this.emit('reconnect', entry, block);

    if ((entry.height % this.network.names.treeInterval) === 0)
      this.emit('tree commit', this.db.tree.rootHash(), entry, block);

    return this.emitAsync('connect', entry, block, view);
  }

  /**
   * Set the best chain. This is called on every incoming
   * block with greater chainwork than the current tip.
   * @private
   * @param {ChainEntry} entry
   * @param {Block} block
   * @param {ChainEntry} prev
   * @param {Number} flags
   * @returns {Promise}
   */

  async setBestChain(entry, block, prev, flags) {
    const tip = this.tip;

    let fork = null;

    // A higher fork has arrived.
    // Time to reorganize the chain.
    if (!entry.prevBlock.equals(this.tip.hash)) {
      try {
        // Do as much verification
        // as we can before reorganizing.
        await this.verify(block, prev, flags);
      } catch (err) {
        if (err.type === 'VerifyError') {
          if (!err.malleated)
            this.setInvalid(entry.hash);

          this.logger.warning(
            'Tried to connect invalid block: %x (%d).',
            entry.hash,