lib.rs

// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of Open Ethereum.

// Open Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Open Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Open Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use std::cmp;
use std::collections::BTreeMap;
use std::path::Path;
use std::sync::Arc;

use block_reward::{self, BlockRewardContract, RewardKind};
use common_types::{
	BlockNumber,
	header::Header,
	engines::{
		EthashSeal,
		OptimizeFor,
		params::CommonParams,
	},
	errors::{BlockError, EthcoreError as Error},
	snapshot::Snapshotting,
};
use engine::Engine;
use ethereum_types::{H256, U256};
use ethash::{self, quick_get_difficulty, slow_hash_block_number, EthashManager};
use keccak_hash::KECCAK_EMPTY_LIST_RLP;
use log::trace;
use machine::{
	ExecutedBlock,
	Machine,
};
use unexpected::{OutOfBounds, Mismatch};

/// Number of blocks in an ethash snapshot.
// make dependent on difficulty increment divisor?
const SNAPSHOT_BLOCKS: u64 = 5000;
/// Maximum number of blocks allowed in an ethash snapshot.
const MAX_SNAPSHOT_BLOCKS: u64 = 30000;

/// Ethash params.
#[derive(Debug, PartialEq)]
pub struct EthashParams {
	/// Minimum difficulty.
	pub minimum_difficulty: U256,
	/// Difficulty bound divisor.
	pub difficulty_bound_divisor: U256,
	/// Difficulty increment divisor.
	pub difficulty_increment_divisor: u64,
	/// Metropolis difficulty increment divisor.
	pub metropolis_difficulty_increment_divisor: u64,
	/// Block duration.
	pub duration_limit: u64,
	/// Homestead transition block number.
	pub homestead_transition: u64,
	/// Transition block for a change of difficulty params (currently just bound_divisor).
	pub difficulty_hardfork_transition: u64,
	/// Difficulty param after the difficulty transition.
	pub difficulty_hardfork_bound_divisor: U256,
	/// Block on which there is no additional difficulty from the exponential bomb.
	pub bomb_defuse_transition: u64,
	/// Number of first block where EIP-100 rules begin.
	pub eip100b_transition: u64,
	/// Total block number for one ECIP-1017 era.
	pub ecip1017_era_rounds: u64,
	/// Block reward in base units.
	pub block_reward: BTreeMap<BlockNumber, U256>,
	/// EXPIP-2 block height
	pub expip2_transition: u64,
	/// EXPIP-2 duration limit
	pub expip2_duration_limit: u64,
	/// Block reward contract transition block.
	pub block_reward_contract_transition: u64,
	/// Block reward contract.
	pub block_reward_contract: Option<BlockRewardContract>,
	/// Difficulty bomb delays.
	pub difficulty_bomb_delays: BTreeMap<BlockNumber, BlockNumber>,
	/// Block to transition to progpow
	pub progpow_transition: u64,
}

impl From<ethjson::spec::EthashParams> for EthashParams {
	fn from(p: ethjson::spec::EthashParams) -> Self {
		EthashParams {
			minimum_difficulty: p.minimum_difficulty.into(),
			difficulty_bound_divisor: p.difficulty_bound_divisor.into(),
			difficulty_increment_divisor: p.difficulty_increment_divisor.map_or(10, Into::into),
			metropolis_difficulty_increment_divisor: p.metropolis_difficulty_increment_divisor.map_or(9, Into::into),
			duration_limit: p.duration_limit.map_or(0, Into::into),
			homestead_transition: p.homestead_transition.map_or(0, Into::into),
			difficulty_hardfork_transition: p.difficulty_hardfork_transition.map_or(u64::max_value(), Into::into),
			difficulty_hardfork_bound_divisor: p.difficulty_hardfork_bound_divisor.map_or(p.difficulty_bound_divisor.into(), Into::into),
			bomb_defuse_transition: p.bomb_defuse_transition.map_or(u64::max_value(), Into::into),
			eip100b_transition: p.eip100b_transition.map_or(u64::max_value(), Into::into),
			ecip1017_era_rounds: p.ecip1017_era_rounds.map_or(u64::max_value(), Into::into),
			block_reward: p.block_reward.map_or_else(
				|| {
					let mut ret = BTreeMap::new();
					ret.insert(0, U256::zero());
					ret
				},
				|reward| {
					match reward {
						ethjson::spec::BlockReward::Single(reward) => {
							let mut ret = BTreeMap::new();
							ret.insert(0, reward.into());
							ret
						},
						ethjson::spec::BlockReward::Multi(multi) => {
							multi.into_iter()
								.map(|(block, reward)| (block.into(), reward.into()))
								.collect()
						},
					}
				}),
			expip2_transition: p.expip2_transition.map_or(u64::max_value(), Into::into),
			expip2_duration_limit: p.expip2_duration_limit.map_or(30, Into::into),
			progpow_transition: p.progpow_transition.map_or(u64::max_value(), Into::into),
			block_reward_contract_transition: p.block_reward_contract_transition.map_or(0, Into::into),
			block_reward_contract: match (p.block_reward_contract_code, p.block_reward_contract_address) {
				(Some(code), _) => Some(BlockRewardContract::new_from_code(Arc::new(code.into()))),
				(_, Some(address)) => Some(BlockRewardContract::new_from_address(address.into())),
				(None, None) => None,
			},
			difficulty_bomb_delays: p.difficulty_bomb_delays.unwrap_or_default().into_iter()
				.map(|(block, delay)| (block.into(), delay.into()))
				.collect()
		}
	}
}

/// Engine using Ethash proof-of-work consensus algorithm, suitable for Ethereum
/// mainnet chains in the Olympic, Frontier and Homestead eras.
pub struct Ethash {
	ethash_params: EthashParams,
	pow: Arc<EthashManager>,
	machine: Machine,
}

impl Ethash {
	/// Create a new instance of Ethash engine
	pub fn new<T: Into<Option<OptimizeFor>>>(
		cache_dir: &Path,
		ethash_params: EthashParams,
		machine: Machine,
		optimize_for: T,
	) -> Self {
		let progpow_transition = ethash_params.progpow_transition;

		Ethash {
			ethash_params,
			machine,
			pow: Arc::new(EthashManager::new(
				cache_dir.as_ref(),
				optimize_for.into(),
				progpow_transition
			)),
		}
	}
}

fn verify_block_unordered(pow: &Arc<EthashManager>, header: &Header) -> Result<(), Error> {
	let seal = EthashSeal::parse_seal(header.seal())?;

	let result = pow.compute_light(
		header.number(),
		&header.bare_hash().0,
		seal.nonce.to_low_u64_be()
	);
	let mix = H256(result.mix_hash);
	let difficulty = ethash::boundary_to_difficulty(&H256(result.value));
	trace!(target: "miner", "num: {num}, seed: {seed}, h: {h}, non: {non}, mix: {mix}, res: {res}",
	       num = header.number() as u64,
	       seed = H256(slow_hash_block_number(header.number() as u64)),
	       h = header.bare_hash(),
	       non = seal.nonce.to_low_u64_be(),
	       mix = H256(result.mix_hash),
	       res = H256(result.value));
	if mix != seal.mix_hash {
		return Err(From::from(BlockError::MismatchedH256SealElement(Mismatch {
			expected: mix,
			found: seal.mix_hash
		})));
	}
	if &difficulty < header.difficulty() {
		return Err(From::from(BlockError::InvalidProofOfWork(OutOfBounds {
			min: Some(*header.difficulty()),
			max: None,
			found: difficulty
		})));
	}
	Ok(())
}


// TODO [rphmeier]
//
// for now, this is different than Ethash's own epochs, and signal
// "consensus epochs".
// in this sense, `Ethash` is epochless: the same `EpochVerifier` can be used
// for any block in the chain.
// in the future, we might move the Ethash epoch
// caching onto this mechanism as well.
struct EpochVerifier {
	pow: Arc<EthashManager>
}

impl engine::EpochVerifier for EpochVerifier {
	fn verify_heavy(&self, header: &Header) -> Result<(), Error> {
		verify_block_unordered(&self.pow, header)
	}
}

impl Engine for Ethash {
	fn name(&self) -> &str { "Ethash" }

	fn machine(&self) -> &Machine { &self.machine }

	// Two fields - nonce and mix.
	fn seal_fields(&self, _header: &Header) -> usize { 2 }

	/// Additional engine-specific information for the user/developer concerning `header`.
	fn extra_info(&self, header: &Header) -> BTreeMap<String, String> {
		let mut engine_info = BTreeMap::new();
		if let Ok(seal) = EthashSeal::parse_seal(header.seal()) {
			engine_info.insert("nonce".to_string(), format!("{:#x}", seal.nonce));
			engine_info.insert("mixHash".to_string(), format!("{:#x}", seal.mix_hash));
		}
		engine_info
	}

	fn maximum_uncle_count(&self, _block: BlockNumber) -> usize { 2 }

	fn maximum_gas_limit(&self) -> Option<U256> { Some(0x7fff_ffff_ffff_ffff_u64.into()) }

	/// Apply the block reward on finalisation of the block.
	/// This assumes that all uncles are valid uncles (i.e. of at least one generation before the current).
	fn on_close_block(&self, block: &mut ExecutedBlock, _parent_header: &Header) -> Result<(), Error> {
		use std::ops::Shr;

		let author = *block.header.author();
		let number = block.header.number();

		let rewards = match self.ethash_params.block_reward_contract {
			Some(ref c) if number >= self.ethash_params.block_reward_contract_transition => {
				let mut beneficiaries = Vec::new();

				beneficiaries.push((author, RewardKind::Author));
				for u in &block.uncles {
					let uncle_author = u.author();
					beneficiaries.push((*uncle_author, RewardKind::uncle(number, u.number())));
				}

				let mut call = engine::default_system_or_code_call(&self.machine, block);

				let rewards = c.reward(beneficiaries, &mut call)?;
				rewards.into_iter().map(|(author, amount)| (author, RewardKind::External, amount)).collect()
			},
			_ => {
				let mut rewards = Vec::new();

				let (_, reward) = self.ethash_params.block_reward.iter()
					.rev()
					.find(|&(block, _)| *block <= number)
					.expect("Current block's reward is not found; this indicates a chain config error; qed");
				let reward = *reward;

				// Applies ECIP-1017 eras.
				let eras_rounds = self.ethash_params.ecip1017_era_rounds;
				let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, reward, number);

				//let n_uncles = LiveBlock::uncles(&*block).len();
				let n_uncles = block.uncles.len();

				// Bestow block rewards.
				let result_block_reward = reward + reward.shr(5) * U256::from(n_uncles);

				rewards.push((author, RewardKind::Author, result_block_reward));

				// Bestow uncle rewards.
				for u in &block.uncles {
					let uncle_author = u.author();
					let result_uncle_reward = if eras == 0 {
						(reward * U256::from(8 + u.number() - number)).shr(3)
					} else {
						reward.shr(5)
					};

					rewards.push((*uncle_author, RewardKind::uncle(number, u.number()), result_uncle_reward));
				}

				rewards
			},
		};

		block_reward::apply_block_rewards(&rewards, block, &self.machine)
	}

	#[cfg(not(feature = "miner-debug"))]
	fn verify_local_seal(&self, header: &Header) -> Result<(), Error> {
		self.verify_block_basic(header)
			.and_then(|_| self.verify_block_unordered(header))
	}

	#[cfg(feature = "miner-debug")]
	fn verify_local_seal(&self, _header: &Header) -> Result<(), Error> {
		warn!("Skipping seal verification, running in miner testing mode.");
		Ok(())
	}

	fn verify_block_basic(&self, header: &Header) -> Result<(), Error> {
		// check the seal fields.
		let seal = EthashSeal::parse_seal(header.seal())?;

		// TODO: consider removing these lines.
		let min_difficulty = self.ethash_params.minimum_difficulty;
		if header.difficulty() < &min_difficulty {
			return Err(From::from(BlockError::DifficultyOutOfBounds(OutOfBounds {
				min: Some(min_difficulty),
				max: None,
				found: *header.difficulty(),
			})))
		}

		let difficulty = ethash::boundary_to_difficulty(&H256(quick_get_difficulty(
			&header.bare_hash().0,
			seal.nonce.to_low_u64_be(),
			&seal.mix_hash.0,
			header.number() >= self.ethash_params.progpow_transition
		)));

		if &difficulty < header.difficulty() {
			return Err(From::from(BlockError::InvalidProofOfWork(OutOfBounds {
				min: Some(*header.difficulty()),
				max: None,
				found: difficulty
			})));
		}

		Ok(())
	}

	fn verify_block_unordered(&self, header: &Header) -> Result<(), Error> {
		verify_block_unordered(&self.pow, header)
	}

	fn verify_block_family(&self, header: &Header, parent: &Header) -> Result<(), Error> {
		// we should not calculate difficulty for genesis blocks
		if header.number() == 0 {
			return Err(From::from(BlockError::RidiculousNumber(OutOfBounds {
				min: Some(1),
				max: None,
				found: header.number()
			})));
		}

		// Check difficulty is correct given the two timestamps.
		let expected_difficulty = self.calculate_difficulty(header, parent);
		if header.difficulty() != &expected_difficulty {
			return Err(From::from(BlockError::InvalidDifficulty(Mismatch {
				expected: expected_difficulty,
				found: *header.difficulty()
			})))
		}

		Ok(())
	}

	fn epoch_verifier<'a>(&self, _header: &Header, _proof: &'a [u8]) -> engine::ConstructedVerifier<'a> {
		let v = EpochVerifier{pow: self.pow.clone()};
		engine::ConstructedVerifier::Trusted(Box::new(v))
	}

	fn populate_from_parent(&self, header: &mut Header, parent: &Header) {
		let difficulty = self.calculate_difficulty(header, parent);
		header.set_difficulty(difficulty);
	}

	fn snapshot_mode(&self) -> Snapshotting {
		Snapshotting::PoW {
			blocks: SNAPSHOT_BLOCKS,
			max_restore_blocks: MAX_SNAPSHOT_BLOCKS
		}
	}

	fn params(&self) -> &CommonParams { self.machine.params() }
}

impl Ethash {
	fn calculate_difficulty(&self, header: &Header, parent: &Header) -> U256 {
		const EXP_DIFF_PERIOD: u64 = 100_000;
		if header.number() == 0 {
			panic!("Can't calculate genesis block difficulty");
		}

		let parent_has_uncles = parent.uncles_hash() != &KECCAK_EMPTY_LIST_RLP;

		let min_difficulty = self.ethash_params.minimum_difficulty;

		let difficulty_hardfork = header.number() >= self.ethash_params.difficulty_hardfork_transition;
		let difficulty_bound_divisor = if difficulty_hardfork {
			self.ethash_params.difficulty_hardfork_bound_divisor
		} else {
			self.ethash_params.difficulty_bound_divisor
		};

		let expip2_hardfork = header.number() >= self.ethash_params.expip2_transition;
		let duration_limit = if expip2_hardfork {
			self.ethash_params.expip2_duration_limit
		} else {
			self.ethash_params.duration_limit
		};

		let frontier_limit = self.ethash_params.homestead_transition;

		let mut target = if header.number() < frontier_limit {
			if header.timestamp() >= parent.timestamp() + duration_limit {
				*parent.difficulty() - (*parent.difficulty() / difficulty_bound_divisor)
			} else {
				*parent.difficulty() + (*parent.difficulty() / difficulty_bound_divisor)
			}
		} else {
			trace!(target: "ethash", "Calculating difficulty parent.difficulty={}, header.timestamp={}, parent.timestamp={}", parent.difficulty(), header.timestamp(), parent.timestamp());
			//block_diff = parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99)
			let (increment_divisor, threshold) = if header.number() < self.ethash_params.eip100b_transition {
				(self.ethash_params.difficulty_increment_divisor, 1)
			} else if parent_has_uncles {
				(self.ethash_params.metropolis_difficulty_increment_divisor, 2)
			} else {
				(self.ethash_params.metropolis_difficulty_increment_divisor, 1)
			};

			let diff_inc = (header.timestamp() - parent.timestamp()) / increment_divisor;
			if diff_inc <= threshold {
				*parent.difficulty() + *parent.difficulty() / difficulty_bound_divisor * U256::from(threshold - diff_inc)
			} else {
				let multiplier: U256 = cmp::min(diff_inc - threshold, 99).into();
				parent.difficulty().saturating_sub(
					*parent.difficulty() / difficulty_bound_divisor * multiplier
				)
			}
		};
		target = cmp::max(min_difficulty, target);
		if header.number() < self.ethash_params.bomb_defuse_transition {
				let mut number = header.number();
				let original_number = number;
				for (block, delay) in &self.ethash_params.difficulty_bomb_delays {
					if original_number >= *block {
						number = number.saturating_sub(*delay);
					}
				}
				let period = (number / EXP_DIFF_PERIOD) as usize;
				if period > 1 {
					target = cmp::max(min_difficulty, target + (U256::from(1) << (period - 2)));
				}
		}
		target
	}
}


/// Calculates the number of eras and reward
///
/// # Panics
///
/// This function will panic if `era_rounds` is less than `2`
fn ecip1017_eras_block_reward(era_rounds: u64, mut reward: U256, block_number: u64) -> (u64, U256) {
	// NOTE(niklasad1): all numbers is divisible by 1, it will cause the if below
	// to succeed except for the first block. Thus, `era_rounds - 1 == 0` and cause `divide by zero`
	assert!(era_rounds > 1, "ecip1017EraRounds must be bigger than 1");
	let eras = if block_number != 0 && block_number % era_rounds == 0 {
		block_number / era_rounds - 1
	} else {
		block_number / era_rounds
	};
	let mut divi = U256::from(1);
	for _ in 0..eras {
		reward = reward * U256::from(4);
		divi = divi * U256::from(5);
	}
	reward = reward / divi;
	(eras, reward)
}

#[cfg(test)]
mod tests {
	use std::str::FromStr;
	use std::sync::Arc;
	use std::collections::BTreeMap;

	use common_types::{
		header::Header,
		errors::{BlockError, EthcoreError as Error}
	};
	use engine::Engine;
	use ethereum_types::{H64, H256, U256, Address};
	use ethcore::{
		block::*,
		test_helpers::get_temp_state_db,
	};
	use rlp;
	use spec::{new_ropsten, new_mcip3_test, new_homestead_test_machine, Spec};
	use tempfile::TempDir;

	use super::{Ethash, EthashParams, ecip1017_eras_block_reward};

	fn test_spec() -> Spec {
		let tempdir = TempDir::new().unwrap();
		new_ropsten(&tempdir.path())
	}

	fn get_default_ethash_params() -> EthashParams {
		EthashParams {
			minimum_difficulty: U256::from(131072),
			difficulty_bound_divisor: U256::from(2048),
			difficulty_increment_divisor: 10,
			metropolis_difficulty_increment_divisor: 9,
			homestead_transition: 1150000,
			duration_limit: 13,
			block_reward: {
				let mut ret = BTreeMap::new();
				ret.insert(0, 0.into());
				ret
			},
			difficulty_hardfork_transition: u64::max_value(),
			difficulty_hardfork_bound_divisor: U256::from(0),
			bomb_defuse_transition: u64::max_value(),
			eip100b_transition: u64::max_value(),
			ecip1017_era_rounds: u64::max_value(),
			expip2_transition: u64::max_value(),
			expip2_duration_limit: 30,
			block_reward_contract: None,
			block_reward_contract_transition: 0,
			difficulty_bomb_delays: BTreeMap::new(),
			progpow_transition: u64::max_value(),
		}
	}

	#[test]
	fn on_close_block() {
		let spec = test_spec();
		let engine = &*spec.engine;
		let genesis_header = spec.genesis_header();
		let db = spec.ensure_db_good(get_temp_state_db(), &Default::default()).unwrap();
		let last_hashes = Arc::new(vec![genesis_header.hash()]);
		let b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, Address::zero(), (3141562.into(), 31415620.into()), vec![], false).unwrap();
		let b = b.close().unwrap();
		assert_eq!(b.state.balance(&Address::zero()).unwrap(), U256::from_str("4563918244f40001").unwrap());
	}

	#[test]
	fn has_valid_ecip1017_eras_block_reward() {
		let eras_rounds = 5000000;

		let start_reward: U256 = "4563918244F40000".parse().unwrap();

		let block_number = 0;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(0, eras);
		assert_eq!(U256::from_str("4563918244F40000").unwrap(), reward);

		let block_number = 5000000;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(0, eras);
		assert_eq!(U256::from_str("4563918244F40000").unwrap(), reward);

		let block_number = 10000000;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(1, eras);
		assert_eq!(U256::from_str("3782DACE9D900000").unwrap(), reward);

		let block_number = 20000000;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(3, eras);
		assert_eq!(U256::from_str("2386F26FC1000000").unwrap(), reward);

		let block_number = 80000000;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(15, eras);
		assert_eq!(U256::from_str("271000000000000").unwrap(), reward);

		let block_number = 250000000;
		let (eras, reward) = ecip1017_eras_block_reward(eras_rounds, start_reward, block_number);
		assert_eq!(49, eras);
		assert_eq!(U256::from_str("51212FFBAF0A").unwrap(), reward);
	}

	#[test]
	fn on_close_block_with_uncle() {
		let spec = test_spec();
		let engine = &*spec.engine;
		let genesis_header = spec.genesis_header();
		let db = spec.ensure_db_good(get_temp_state_db(), &Default::default()).unwrap();
		let last_hashes = Arc::new(vec![genesis_header.hash()]);
		let mut b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, Address::zero(), (3141562.into(), 31415620.into()), vec![], false).unwrap();
		let mut uncle = Header::new();
		let uncle_author = Address::from_str("ef2d6d194084c2de36e0dabfce45d046b37d1106").unwrap();
		uncle.set_author(uncle_author);
		b.push_uncle(uncle).unwrap();

		let b = b.close().unwrap();
		assert_eq!(b.state.balance(&Address::zero()).unwrap(), "478eae0e571ba001".into());
		assert_eq!(b.state.balance(&uncle_author).unwrap(), "3cb71f51fc558000".into());
	}

	#[test]
	fn has_valid_mcip3_era_block_rewards() {
		let spec = new_mcip3_test();
		let engine = &*spec.engine;
		let genesis_header = spec.genesis_header();
		let db = spec.ensure_db_good(get_temp_state_db(), &Default::default()).unwrap();
		let last_hashes = Arc::new(vec![genesis_header.hash()]);
		let b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, Address::zero(), (3141562.into(), 31415620.into()), vec![], false).unwrap();
		let b = b.close().unwrap();

		let ubi_contract = Address::from_str("00efdd5883ec628983e9063c7d969fe268bbf310").unwrap();
		let dev_contract = Address::from_str("00756cf8159095948496617f5fb17ed95059f536").unwrap();
		assert_eq!(b.state.balance(&Address::zero()).unwrap(), U256::from_str("d8d726b7177a80000").unwrap());
		assert_eq!(b.state.balance(&ubi_contract).unwrap(), U256::from_str("2b5e3af16b1880000").unwrap());
		assert_eq!(b.state.balance(&dev_contract).unwrap(), U256::from_str("c249fdd327780000").unwrap());
	}

	#[test]
	fn has_valid_metadata() {
		let engine = test_spec().engine;
		assert_eq!(engine.name(), "Ethash");
	}

	#[test]
	fn can_return_schedule() {
		let engine = test_spec().engine;
		let schedule = engine.schedule(10000000);
		assert!(schedule.stack_limit > 0);

		let schedule = engine.schedule(100);
		assert!(schedule.have_delegate_call);
	}

	#[test]
	fn can_do_seal_verification_fail() {
		let engine = test_spec().engine;
		let header: Header = Header::default();

		let verify_result = engine.verify_block_basic(&header);

		match verify_result {
			Err(Error::Block(BlockError::InvalidSealArity(_))) => {},
			Err(_) => { panic!("should be block seal-arity mismatch error (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_do_difficulty_verification_fail() {
		let engine = test_spec().engine;
		let mut header: Header = Header::default();
		header.set_seal(vec![rlp::encode(&H256::zero()), rlp::encode(&H64::zero())]);

		let verify_result = engine.verify_block_basic(&header);

		match verify_result {
			Err(Error::Block(BlockError::DifficultyOutOfBounds(_))) => {},
			Err(_) => { panic!("should be block difficulty error (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_do_proof_of_work_verification_fail() {
		let engine = test_spec().engine;
		let mut header: Header = Header::default();
		header.set_seal(vec![rlp::encode(&H256::zero()), rlp::encode(&H64::zero())]);
		header.set_difficulty(U256::from_str("ffffffffffffffffffffffffffffffffffffffffffffaaaaaaaaaaaaaaaaaaaa").unwrap());

		let verify_result = engine.verify_block_basic(&header);

		match verify_result {
			Err(Error::Block(BlockError::InvalidProofOfWork(_))) => {},
			Err(_) => { panic!("should be invalid proof of work error (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_do_seal_unordered_verification_fail() {
		let engine = test_spec().engine;
		let header = Header::default();

		let verify_result = engine.verify_block_unordered(&header);

		match verify_result {
			Err(Error::Block(BlockError::InvalidSealArity(_))) => {},
			Err(_) => { panic!("should be block seal-arity mismatch error (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_do_seal_unordered_verification_fail2() {
		let engine = test_spec().engine;
		let mut header = Header::default();
		header.set_seal(vec![vec![], vec![]]);

		let verify_result = engine.verify_block_unordered(&header);
		// rlp error, shouldn't panic
		assert!(verify_result.is_err());
	}

	#[test]
	fn can_do_seal256_verification_fail() {
		let engine = test_spec().engine;
		let mut header: Header = Header::default();
		header.set_seal(vec![rlp::encode(&H256::zero()), rlp::encode(&H64::zero())]);
		let verify_result = engine.verify_block_unordered(&header);

		match verify_result {
			Err(Error::Block(BlockError::MismatchedH256SealElement(_))) => {},
			Err(_) => { panic!("should be invalid 256-bit seal fail (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_do_proof_of_work_unordered_verification_fail() {
		let engine = test_spec().engine;
		let mut header: Header = Header::default();
		header.set_seal(vec![rlp::encode(&H256::from_str("b251bd2e0283d0658f2cadfdc8ca619b5de94eca5742725e2e757dd13ed7503d").unwrap()), rlp::encode(&H64::zero())]);
		header.set_difficulty(U256::from_str("ffffffffffffffffffffffffffffffffffffffffffffaaaaaaaaaaaaaaaaaaaa").unwrap());

		let verify_result = engine.verify_block_unordered(&header);

		match verify_result {
			Err(Error::Block(BlockError::InvalidProofOfWork(_))) => {},
			Err(_) => { panic!("should be invalid proof-of-work fail (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_verify_block_family_genesis_fail() {
		let engine = test_spec().engine;
		let header: Header = Header::default();
		let parent_header: Header = Header::default();

		let verify_result = engine.verify_block_family(&header, &parent_header);

		match verify_result {
			Err(Error::Block(BlockError::RidiculousNumber(_))) => {},
			Err(_) => { panic!("should be invalid block number fail (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn can_verify_block_family_difficulty_fail() {
		let engine = test_spec().engine;
		let mut header: Header = Header::default();
		header.set_number(2);
		let mut parent_header: Header = Header::default();
		parent_header.set_number(1);

		let verify_result = engine.verify_block_family(&header, &parent_header);

		match verify_result {
			Err(Error::Block(BlockError::InvalidDifficulty(_))) => {},
			Err(_) => { panic!("should be invalid difficulty fail (got {:?})", verify_result); },
			_ => { panic!("Should be error, got Ok"); },
		}
	}

	#[test]
	fn difficulty_frontier() {
		let machine = new_homestead_test_machine();
		let ethparams = get_default_ethash_params();
		let tempdir = TempDir::new().unwrap();
		let ethash = Ethash::new(tempdir.path(), ethparams, machine, None);

		let mut parent_header = Header::default();
		parent_header.set_number(1000000);
		parent_header.set_difficulty(U256::from_str("b69de81a22b").unwrap());
		parent_header.set_timestamp(1455404053);
		let mut header = Header::default();
		header.set_number(parent_header.number() + 1);
		header.set_timestamp(1455404058);

		let difficulty = ethash.calculate_difficulty(&header, &parent_header);
		assert_eq!(U256::from_str("b6b4bbd735f").unwrap(), difficulty);
	}

	#[test]
	fn difficulty_homestead() {
		let machine = new_homestead_test_machine();
		let ethparams = get_default_ethash_params();
		let tempdir = TempDir::new().unwrap();
		let ethash = Ethash::new(tempdir.path(), ethparams, machine, None);

		let mut parent_header = Header::default();
		parent_header.set_number(1500000);
		parent_header.set_difficulty(U256::from_str("1fd0fd70792b").unwrap());
		parent_header.set_timestamp(1463003133);
		let mut header = Header::default();
		header.set_number(parent_header.number() + 1);
		header.set_timestamp(1463003177);

		let difficulty = ethash.calculate_difficulty(&header, &parent_header);
		assert_eq!(U256::from_str("1fc50f118efe").unwrap(), difficulty);
	}

	#[test]
	fn difficulty_max_timestamp() {
		let machine = new_homestead_test_machine();
		let ethparams = get_default_ethash_params();
		let tempdir = TempDir::new().unwrap();
		let ethash = Ethash::new(tempdir.path(), ethparams, machine, None);

		let mut parent_header = Header::default();
		parent_header.set_number(1000000);
		parent_header.set_difficulty(U256::from_str("b69de81a22b").unwrap());
		parent_header.set_timestamp(1455404053);
		let mut header = Header::default();
		header.set_number(parent_header.number() + 1);
		header.set_timestamp(u64::max_value());

		let difficulty = ethash.calculate_difficulty(&header, &parent_header);
		assert_eq!(U256::from(12543204905719u64), difficulty);
	}

	#[test]
	fn test_extra_info() {
		let machine = new_homestead_test_machine();
		let ethparams = get_default_ethash_params();
		let tempdir = TempDir::new().unwrap();
		let ethash = Ethash::new(tempdir.path(), ethparams, machine, None);
		let mut header = Header::default();
		header.set_seal(vec![rlp::encode(&H256::from_str("b251bd2e0283d0658f2cadfdc8ca619b5de94eca5742725e2e757dd13ed7503d").unwrap()), rlp::encode(&H64::zero())]);
		let info = ethash.extra_info(&header);
		assert_eq!(info["nonce"], "0x0000000000000000");
		assert_eq!(info["mixHash"], "0xb251bd2e0283d0658f2cadfdc8ca619b5de94eca5742725e2e757dd13ed7503d");
	}
}