block.rs

// Copyright 2021 The Grin Developers
//
// 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.

//! Blocks and blockheaders

use crate::consensus::{self, reward, REWARD};
use crate::core::committed::{self, Committed};
use crate::core::compact_block::CompactBlock;
use crate::core::hash::{DefaultHashable, Hash, Hashed, ZERO_HASH};
use crate::core::{
	pmmr, transaction, Commitment, Inputs, KernelFeatures, Output, Transaction, TransactionBody,
	TxKernel, Weighting,
};
use crate::global;
use crate::pow::{verify_size, Difficulty, Proof, ProofOfWork};
use crate::ser::{
	self, deserialize_default, serialize_default, PMMRable, Readable, Reader, Writeable, Writer,
};
use chrono::prelude::{DateTime, NaiveDateTime, Utc};
use chrono::Duration;
use keychain::{self, BlindingFactor};
use std::convert::TryInto;
use std::fmt;
use util::from_hex;
use util::{secp, static_secp_instance};

/// Errors thrown by Block validation
#[derive(Debug, Clone, Eq, PartialEq, thiserror::Error)]
pub enum Error {
	/// The sum of output minus input commitments does not
	/// match the sum of kernel commitments
	KernelSumMismatch,
	/// The total kernel sum on the block header is wrong
	InvalidTotalKernelSum,
	/// Same as above but for the coinbase part of a block, including reward
	CoinbaseSumMismatch,
	/// Restrict block total weight.
	TooHeavy,
	/// Block version is invalid for a given block height
	InvalidBlockVersion(HeaderVersion),
	/// Block time is invalid
	InvalidBlockTime,
	/// Invalid POW
	InvalidPow,
	/// Kernel not valid due to lock_height exceeding block header height
	KernelLockHeight(u64),
	/// NRD kernels are not valid prior to HF3.
	NRDKernelPreHF3,
	/// NRD kernels are not valid if disabled locally via "feature flag".
	NRDKernelNotEnabled,
	/// Underlying tx related error
	Transaction(transaction::Error),
	/// Underlying Secp256k1 error (signature validation or invalid public key
	/// typically)
	Secp(secp::Error),
	/// Underlying keychain related error
	Keychain(keychain::Error),
	/// Underlying Merkle proof error
	MerkleProof,
	/// Error when verifying kernel sums via committed trait.
	Committed(committed::Error),
	/// Validation error relating to cut-through.
	/// Specifically the tx is spending its own output, which is not valid.
	CutThrough,
	/// Underlying serialization error.
	Serialization(ser::Error),
	/// Other unspecified error condition
	Other(String),
}

impl From<committed::Error> for Error {
	fn from(e: committed::Error) -> Error {
		Error::Committed(e)
	}
}

impl From<transaction::Error> for Error {
	fn from(e: transaction::Error) -> Error {
		Error::Transaction(e)
	}
}

impl From<ser::Error> for Error {
	fn from(e: ser::Error) -> Error {
		Error::Serialization(e)
	}
}

impl From<secp::Error> for Error {
	fn from(e: secp::Error) -> Error {
		Error::Secp(e)
	}
}

impl From<keychain::Error> for Error {
	fn from(e: keychain::Error) -> Error {
		Error::Keychain(e)
	}
}

impl fmt::Display for Error {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		write!(f, "Block Error (display needs implementation")
	}
}

/// Header entry for storing in the header MMR.
/// Note: we hash the block header itself and maintain the hash in the entry.
/// This allows us to lookup the original header from the db as necessary.
#[derive(Debug)]
pub struct HeaderEntry {
	hash: Hash,
	timestamp: u64,
	total_difficulty: Difficulty,
	secondary_scaling: u32,
	is_secondary: bool,
}

impl Readable for HeaderEntry {
	fn read<R: Reader>(reader: &mut R) -> Result<HeaderEntry, ser::Error> {
		let hash = Hash::read(reader)?;
		let timestamp = reader.read_u64()?;
		let total_difficulty = Difficulty::read(reader)?;
		let secondary_scaling = reader.read_u32()?;

		// Using a full byte to represent the bool for now.
		let is_secondary = reader.read_u8()? != 0;

		Ok(HeaderEntry {
			hash,
			timestamp,
			total_difficulty,
			secondary_scaling,
			is_secondary,
		})
	}
}

impl Writeable for HeaderEntry {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		self.hash.write(writer)?;
		writer.write_u64(self.timestamp)?;
		self.total_difficulty.write(writer)?;
		writer.write_u32(self.secondary_scaling)?;

		// Using a full byte to represent the bool for now.
		if self.is_secondary {
			writer.write_u8(1)?;
		} else {
			writer.write_u8(0)?;
		}
		Ok(())
	}
}

impl Hashed for HeaderEntry {
	/// The hash of the underlying block.
	fn hash(&self) -> Hash {
		self.hash
	}
}

/// Some type safety around header versioning.
#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd, Serialize)]
pub struct HeaderVersion(pub u16);

impl From<HeaderVersion> for u16 {
	fn from(v: HeaderVersion) -> u16 {
		v.0
	}
}

impl Writeable for HeaderVersion {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		writer.write_u16(self.0)
	}
}

impl Readable for HeaderVersion {
	fn read<R: Reader>(reader: &mut R) -> Result<HeaderVersion, ser::Error> {
		let version = reader.read_u16()?;
		Ok(HeaderVersion(version))
	}
}

/// Block header, fairly standard compared to other blockchains.
#[derive(Clone, Debug, PartialEq, Serialize)]
pub struct BlockHeader {
	/// Version of the block
	pub version: HeaderVersion,
	/// Height of this block since the genesis block (height 0)
	pub height: u64,
	/// Hash of the block previous to this in the chain.
	pub prev_hash: Hash,
	/// Root hash of the header MMR at the previous header.
	pub prev_root: Hash,
	/// Timestamp at which the block was built.
	pub timestamp: DateTime<Utc>,
	/// Merklish root of all the commitments in the TxHashSet
	pub output_root: Hash,
	/// Merklish root of all range proofs in the TxHashSet
	pub range_proof_root: Hash,
	/// Merklish root of all transaction kernels in the TxHashSet
	pub kernel_root: Hash,
	/// Total accumulated sum of kernel offsets since genesis block.
	/// We can derive the kernel offset sum for *this* block from
	/// the total kernel offset of the previous block header.
	pub total_kernel_offset: BlindingFactor,
	/// Total size of the output MMR after applying this block
	pub output_mmr_size: u64,
	/// Total size of the kernel MMR after applying this block
	pub kernel_mmr_size: u64,
	/// Proof of work and related
	pub pow: ProofOfWork,
}
impl DefaultHashable for BlockHeader {}

impl Default for BlockHeader {
	fn default() -> BlockHeader {
		BlockHeader {
			version: HeaderVersion(1),
			height: 0,
			timestamp: DateTime::<Utc>::from_utc(NaiveDateTime::from_timestamp(0, 0), Utc),
			prev_hash: ZERO_HASH,
			prev_root: ZERO_HASH,
			output_root: ZERO_HASH,
			range_proof_root: ZERO_HASH,
			kernel_root: ZERO_HASH,
			total_kernel_offset: BlindingFactor::zero(),
			output_mmr_size: 0,
			kernel_mmr_size: 0,
			pow: ProofOfWork::default(),
		}
	}
}

impl PMMRable for BlockHeader {
	type E = HeaderEntry;

	fn as_elmt(&self) -> Self::E {
		HeaderEntry {
			hash: self.hash(),
			timestamp: self.timestamp.timestamp() as u64,
			total_difficulty: self.total_difficulty(),
			secondary_scaling: self.pow.secondary_scaling,
			is_secondary: self.pow.is_secondary(),
		}
	}

	// Size is hash + u64 + difficulty + u32 + u8.
	fn elmt_size() -> Option<u16> {
		const LEN: usize = Hash::LEN + 8 + Difficulty::LEN + 4 + 1;
		Some(LEN.try_into().unwrap())
	}
}

/// Serialization of a block header
impl Writeable for BlockHeader {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		if !writer.serialization_mode().is_hash_mode() {
			self.write_pre_pow(writer)?;
		}
		self.pow.write(writer)?;
		Ok(())
	}
}

fn read_block_header<R: Reader>(reader: &mut R) -> Result<BlockHeader, ser::Error> {
	let version = HeaderVersion::read(reader)?;
	let (height, timestamp) = ser_multiread!(reader, read_u64, read_i64);
	let prev_hash = Hash::read(reader)?;
	let prev_root = Hash::read(reader)?;
	let output_root = Hash::read(reader)?;
	let range_proof_root = Hash::read(reader)?;
	let kernel_root = Hash::read(reader)?;
	let total_kernel_offset = BlindingFactor::read(reader)?;
	let (output_mmr_size, kernel_mmr_size) = ser_multiread!(reader, read_u64, read_u64);
	let pow = ProofOfWork::read(reader)?;

	if timestamp > chrono::NaiveDate::MAX.and_hms(0, 0, 0).timestamp()
		|| timestamp < chrono::NaiveDate::MIN.and_hms(0, 0, 0).timestamp()
	{
		return Err(ser::Error::CorruptedData);
	}

	Ok(BlockHeader {
		version,
		height,
		timestamp: DateTime::<Utc>::from_utc(NaiveDateTime::from_timestamp(timestamp, 0), Utc),
		prev_hash,
		prev_root,
		output_root,
		range_proof_root,
		kernel_root,
		total_kernel_offset,
		output_mmr_size,
		kernel_mmr_size,
		pow,
	})
}

/// Deserialization of a block header
impl Readable for BlockHeader {
	fn read<R: Reader>(reader: &mut R) -> Result<BlockHeader, ser::Error> {
		read_block_header(reader)
	}
}

impl BlockHeader {
	/// Write the pre-hash portion of the header
	pub fn write_pre_pow<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		self.version.write(writer)?;
		ser_multiwrite!(
			writer,
			[write_u64, self.height],
			[write_i64, self.timestamp.timestamp()],
			[write_fixed_bytes, &self.prev_hash],
			[write_fixed_bytes, &self.prev_root],
			[write_fixed_bytes, &self.output_root],
			[write_fixed_bytes, &self.range_proof_root],
			[write_fixed_bytes, &self.kernel_root],
			[write_fixed_bytes, &self.total_kernel_offset],
			[write_u64, self.output_mmr_size],
			[write_u64, self.kernel_mmr_size]
		);
		Ok(())
	}

	/// Return the pre-pow, unhashed
	/// Let the cuck(at)oo miner/verifier handle the hashing
	/// for consistency with how this call is performed everywhere
	/// else
	pub fn pre_pow(&self) -> Vec<u8> {
		let mut header_buf = vec![];
		{
			let mut writer = ser::BinWriter::default(&mut header_buf);
			self.write_pre_pow(&mut writer).unwrap();
			self.pow.write_pre_pow(&mut writer).unwrap();
			writer.write_u64(self.pow.nonce).unwrap();
		}
		header_buf
	}

	/// Constructs a header given pre_pow string, nonce, and proof
	pub fn from_pre_pow_and_proof(
		pre_pow: String,
		nonce: u64,
		proof: Proof,
	) -> Result<Self, Error> {
		// Convert hex pre pow string
		let mut header_bytes =
			from_hex(&pre_pow).map_err(|e| Error::Serialization(ser::Error::HexError(e)))?;
		// Serialize and append serialized nonce and proof
		serialize_default(&mut header_bytes, &nonce)?;
		serialize_default(&mut header_bytes, &proof)?;

		// Deserialize header from constructed bytes
		Ok(deserialize_default(&mut &header_bytes[..])?)
	}

	/// Total number of outputs (spent and unspent) based on output MMR size committed to in this block.
	/// Note: *Not* the number of outputs in this block but total up to and including this block.
	/// The MMR size is the total number of hashes contained in the full MMR structure.
	/// We want the corresponding number of leaves in the MMR given the size.
	pub fn output_mmr_count(&self) -> u64 {
		pmmr::n_leaves(self.output_mmr_size)
	}

	/// Total number of kernels based on kernel MMR size committed to in this block.
	/// Note: *Not* the number of kernels in this block but total up to and including this block.
	/// The MMR size is the total number of hashes contained in the full MMR structure.
	/// We want the corresponding number of leaves in the MMR given the size.
	pub fn kernel_mmr_count(&self) -> u64 {
		pmmr::n_leaves(self.kernel_mmr_size)
	}

	/// Total difficulty accumulated by the proof of work on this header
	pub fn total_difficulty(&self) -> Difficulty {
		self.pow.total_difficulty
	}

	/// The "overage" to use when verifying the kernel sums.
	/// For a block header the overage is 0 - reward.
	pub fn overage(&self) -> i64 {
		(REWARD as i64).checked_neg().unwrap_or(0)
	}

	/// The "total overage" to use when verifying the kernel sums for a full
	/// chain state. For a full chain state this is 0 - (height * reward).
	pub fn total_overage(&self, genesis_had_reward: bool) -> i64 {
		let mut reward_count = self.height;
		if genesis_had_reward {
			reward_count += 1;
		}

		((reward_count * REWARD) as i64).checked_neg().unwrap_or(0)
	}

	/// Total kernel offset for the chain state up to and including this block.
	pub fn total_kernel_offset(&self) -> BlindingFactor {
		self.total_kernel_offset.clone()
	}
}

impl From<UntrustedBlockHeader> for BlockHeader {
	fn from(header: UntrustedBlockHeader) -> Self {
		header.0
	}
}

/// Block header which does lightweight validation as part of deserialization,
/// it supposed to be used when we can't trust the channel (eg network)
#[derive(Debug)]
pub struct UntrustedBlockHeader(BlockHeader);

/// Deserialization of an untrusted block header
impl Readable for UntrustedBlockHeader {
	fn read<R: Reader>(reader: &mut R) -> Result<UntrustedBlockHeader, ser::Error> {
		let header = read_block_header(reader)?;
		let ftl = global::get_future_time_limit();
		if header.timestamp > Utc::now() + Duration::seconds(ftl as i64) {
			// refuse blocks whose timestamp is too far in the future
			// this future_time_limit (FTL) is specified in grin-server.toml
			// TODO add warning in p2p code if local time is too different from peers
			error!(
				"block header {} validation error: block time is more than {} seconds in the future",
				header.hash(), ftl
			);
			return Err(ser::Error::CorruptedData);
		}

		// Check the block version before proceeding any further.
		// We want to do this here because blocks can be pretty large
		// and we want to halt processing as early as possible.
		// If we receive an invalid block version then the peer is not on our hard-fork.
		if !consensus::valid_header_version(header.height, header.version) {
			return Err(ser::Error::InvalidBlockVersion);
		}

		if !header.pow.is_primary() && !header.pow.is_secondary() {
			error!(
				"block header {} validation error: invalid edge bits",
				header.hash()
			);
			return Err(ser::Error::CorruptedData);
		}
		if let Err(e) = verify_size(&header) {
			error!(
				"block header {} validation error: invalid POW: {}",
				header.hash(),
				e
			);
			return Err(ser::Error::CorruptedData);
		}

		// Validate global output and kernel MMR sizes against upper bounds based on block height.
		let global_weight =
			TransactionBody::weight_by_iok(0, header.output_mmr_count(), header.kernel_mmr_count());
		if global_weight > global::max_block_weight() * (header.height + 1) {
			return Err(ser::Error::CorruptedData);
		}

		Ok(UntrustedBlockHeader(header))
	}
}

/// A block as expressed in the Mimblewimble protocol. The reward is
/// non-explicit, assumed to be deducible from block height (similar to
/// bitcoin's schedule) and expressed as a global transaction fee (added v.H),
/// additive to the total of fees ever collected.
#[derive(Debug, Clone, Serialize)]
pub struct Block {
	/// The header with metadata and commitments to the rest of the data
	pub header: BlockHeader,
	/// The body - inputs/outputs/kernels
	pub body: TransactionBody,
}

impl Hashed for Block {
	/// The hash of the underlying block.
	fn hash(&self) -> Hash {
		self.header.hash()
	}
}

/// Implementation of Writeable for a block, defines how to write the block to a
/// binary writer. Differentiates between writing the block for the purpose of
/// full serialization and the one of just extracting a hash.
impl Writeable for Block {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		self.header.write(writer)?;
		if !writer.serialization_mode().is_hash_mode() {
			self.body.write(writer)?;
		}
		Ok(())
	}
}

/// Implementation of Readable for a block, defines how to read a full block
/// from a binary stream.
impl Readable for Block {
	fn read<R: Reader>(reader: &mut R) -> Result<Block, ser::Error> {
		let header = BlockHeader::read(reader)?;
		let body = TransactionBody::read(reader)?;
		Ok(Block { header, body })
	}
}

/// Provides all information from a block that allows the calculation of total
/// Pedersen commitment.
impl Committed for Block {
	fn inputs_committed(&self) -> Vec<Commitment> {
		self.body.inputs_committed()
	}

	fn outputs_committed(&self) -> Vec<Commitment> {
		self.body.outputs_committed()
	}

	fn kernels_committed(&self) -> Vec<Commitment> {
		self.body.kernels_committed()
	}
}

/// Default properties for a block, everything zeroed out and empty vectors.
impl Default for Block {
	fn default() -> Block {
		Block {
			header: Default::default(),
			body: Default::default(),
		}
	}
}

impl Block {
	/// Builds a new block from the header of the previous block, a vector of
	/// transactions and the private key that will receive the reward. Checks
	/// that all transactions are valid and calculates the Merkle tree.
	///
	/// TODO - Move this somewhere where only tests will use it.
	/// *** Only used in tests. ***
	///
	#[warn(clippy::new_ret_no_self)]
	pub fn new(
		prev: &BlockHeader,
		txs: &[Transaction],
		difficulty: Difficulty,
		reward_output: (Output, TxKernel),
	) -> Result<Block, Error> {
		let mut block =
			Block::from_reward(prev, txs, reward_output.0, reward_output.1, difficulty)?;

		// Now set the pow on the header so block hashing works as expected.
		{
			let proof_size = global::proofsize();
			block.header.pow.proof = Proof::random(proof_size);
		}

		Ok(block)
	}

	/// Hydrate a block from a compact block.
	/// Note: caller must validate the block themselves, we do not validate it
	/// here.
	pub fn hydrate_from(cb: CompactBlock, txs: &[Transaction]) -> Result<Block, Error> {
		trace!("block: hydrate_from: {}, {} txs", cb.hash(), txs.len(),);

		let header = cb.header.clone();

		let mut inputs = vec![];
		let mut outputs = vec![];
		let mut kernels = vec![];

		// collect all the inputs, outputs and kernels from the txs
		for tx in txs {
			let tx_inputs: Vec<_> = tx.inputs().into();
			inputs.extend_from_slice(tx_inputs.as_slice());
			outputs.extend_from_slice(tx.outputs());
			kernels.extend_from_slice(tx.kernels());
		}

		// apply cut-through to our tx inputs and outputs
		let (inputs, outputs, _, _) = transaction::cut_through(&mut inputs, &mut outputs)?;

		let mut outputs = outputs.to_vec();
		let mut kernels = kernels.to_vec();

		// include the full outputs and kernels from the compact block
		outputs.extend_from_slice(cb.out_full());
		kernels.extend_from_slice(cb.kern_full());

		// Initialize a tx body and sort everything.
		let body = TransactionBody::init(inputs.into(), &outputs, &kernels, false)?;

		// Finally return the full block.
		// Note: we have not actually validated the block here,
		// caller must validate the block.
		Ok(Block { header, body })
	}

	/// Build a new empty block from a specified header
	pub fn with_header(header: BlockHeader) -> Block {
		Block {
			header,
			..Default::default()
		}
	}

	/// Builds a new block ready to mine from the header of the previous block,
	/// a vector of transactions and the reward information. Checks
	/// that all transactions are valid and calculates the Merkle tree.
	pub fn from_reward(
		prev: &BlockHeader,
		txs: &[Transaction],
		reward_out: Output,
		reward_kern: TxKernel,
		difficulty: Difficulty,
	) -> Result<Block, Error> {
		// A block is just a big transaction, aggregate and add the reward output
		// and reward kernel. At this point the tx is technically invalid but the
		// tx body is valid if we account for the reward (i.e. as a block).
		let agg_tx = transaction::aggregate(txs)?
			.with_output(reward_out)
			.with_kernel(reward_kern);

		// Now add the kernel offset of the previous block for a total
		let total_kernel_offset = committed::sum_kernel_offsets(
			vec![agg_tx.offset.clone(), prev.total_kernel_offset.clone()],
			vec![],
		)?;

		// Determine the height and associated version for the new header.
		let height = prev.height + 1;
		let version = consensus::header_version(height);

		let now = Utc::now().timestamp();
		let timestamp = DateTime::<Utc>::from_utc(NaiveDateTime::from_timestamp(now, 0), Utc);

		// Now build the block with all the above information.
		// Note: We have not validated the block here.
		// Caller must validate the block as necessary.
		let block = Block {
			header: BlockHeader {
				version,
				height,
				timestamp,
				prev_hash: prev.hash(),
				total_kernel_offset,
				pow: ProofOfWork {
					total_difficulty: difficulty + prev.pow.total_difficulty,
					..Default::default()
				},
				..Default::default()
			},
			body: agg_tx.into(),
		};
		Ok(block)
	}

	/// Consumes this block and returns a new block with the coinbase output
	/// and kernels added
	pub fn with_reward(mut self, reward_out: Output, reward_kern: TxKernel) -> Block {
		self.body.outputs = vec![reward_out];
		self.body.kernels = vec![reward_kern];
		self
	}

	/// Get inputs
	pub fn inputs(&self) -> Inputs {
		self.body.inputs()
	}

	/// Get outputs
	pub fn outputs(&self) -> &[Output] {
		&self.body.outputs()
	}

	/// Get kernels
	pub fn kernels(&self) -> &[TxKernel] {
		&self.body.kernels()
	}

	/// Sum of all fees (inputs less outputs) in the block
	pub fn total_fees(&self) -> u64 {
		self.body.fee()
	}

	/// "Lightweight" validation that we can perform quickly during read/deserialization.
	/// Subset of full validation that skips expensive verification steps, specifically -
	/// * rangeproof verification (on the body)
	/// * kernel signature verification (on the body)
	/// * coinbase sum verification
	/// * kernel sum verification
	pub fn validate_read(&self) -> Result<(), Error> {
		self.body.validate_read(Weighting::AsBlock)?;
		self.verify_kernel_lock_heights()?;
		Ok(())
	}

	fn block_kernel_offset(
		&self,
		prev_kernel_offset: BlindingFactor,
	) -> Result<BlindingFactor, Error> {
		let offset = if self.header.total_kernel_offset() == prev_kernel_offset {
			// special case when the sum hasn't changed (typically an empty block),
			// zero isn't a valid private key but it's a valid blinding factor
			BlindingFactor::zero()
		} else {
			committed::sum_kernel_offsets(
				vec![self.header.total_kernel_offset()],
				vec![prev_kernel_offset],
			)?
		};
		Ok(offset)
	}

	/// Validates all the elements in a block that can be checked without
	/// additional data. Includes commitment sums and kernels, Merkle
	/// trees, reward, etc.
	pub fn validate(&self, prev_kernel_offset: &BlindingFactor) -> Result<(), Error> {
		self.body.validate(Weighting::AsBlock)?;

		self.verify_kernel_lock_heights()?;
		self.verify_nrd_kernels_for_header_version()?;
		self.verify_coinbase()?;

		// take the kernel offset for this block (block offset minus previous) and
		// verify.body.outputs and kernel sums
		self.verify_kernel_sums(
			self.header.overage(),
			self.block_kernel_offset(prev_kernel_offset.clone())?,
		)?;

		Ok(())
	}

	/// Validate the coinbase.body.outputs generated by miners.
	/// Check the sum of coinbase-marked outputs match
	/// the sum of coinbase-marked kernels accounting for fees.
	pub fn verify_coinbase(&self) -> Result<(), Error> {
		let cb_outs = self
			.body
			.outputs
			.iter()
			.filter(|out| out.is_coinbase())
			.collect::<Vec<&Output>>();

		let cb_kerns = self
			.body
			.kernels
			.iter()
			.filter(|kernel| kernel.is_coinbase())
			.collect::<Vec<&TxKernel>>();

		{
			let secp = static_secp_instance();
			let secp = secp.lock();
			let over_commit = secp.commit_value(reward(self.total_fees()))?;

			let out_adjust_sum =
				secp.commit_sum(map_vec!(cb_outs, |x| x.commitment()), vec![over_commit])?;

			let kerns_sum = secp.commit_sum(cb_kerns.iter().map(|x| x.excess).collect(), vec![])?;

			// Verify the kernel sum equals the output sum accounting for block fees.
			if kerns_sum != out_adjust_sum {
				return Err(Error::CoinbaseSumMismatch);
			}
		}

		Ok(())
	}

	// Verify any absolute kernel lock heights.
	fn verify_kernel_lock_heights(&self) -> Result<(), Error> {
		for k in self.kernels() {
			// check we have no kernels with lock_heights greater than current height
			// no tx can be included in a block earlier than its lock_height
			if let KernelFeatures::HeightLocked { lock_height, .. } = k.features {
				if lock_height > self.header.height {
					return Err(Error::KernelLockHeight(lock_height));
				}
			}
		}
		Ok(())
	}

	// NRD kernels are not valid if the global feature flag is disabled.
	// NRD kernels were introduced in HF3 and are not valid for block version < 4.
	// Blocks prior to HF3 containing any NRD kernel(s) are invalid.
	fn verify_nrd_kernels_for_header_version(&self) -> Result<(), Error> {
		if self.kernels().iter().any(|k| k.is_nrd()) {
			if !global::is_nrd_enabled() {
				return Err(Error::NRDKernelNotEnabled);
			}
			if self.header.version < HeaderVersion(4) {
				return Err(Error::NRDKernelPreHF3);
			}
		}
		Ok(())
	}
}

impl From<UntrustedBlock> for Block {
	fn from(block: UntrustedBlock) -> Self {
		block.0
	}
}

/// Block which does lightweight validation as part of deserialization,
/// it supposed to be used when we can't trust the channel (eg network)
pub struct UntrustedBlock(Block);

/// Deserialization of an untrusted block header
impl Readable for UntrustedBlock {
	fn read<R: Reader>(reader: &mut R) -> Result<UntrustedBlock, ser::Error> {
		// we validate header here before parsing the body
		let header = UntrustedBlockHeader::read(reader)?;
		let body = TransactionBody::read(reader)?;

		// Now "lightweight" validation of the block.
		// Treat any validation issues as data corruption.
		// An example of this would be reading a block
		// that exceeded the allowed number of inputs.
		body.validate_read(Weighting::AsBlock).map_err(|e| {
			error!("read validation error: {}", e);
			ser::Error::CorruptedData
		})?;
		let block = Block {
			header: header.into(),
			body,
		};
		Ok(UntrustedBlock(block))
	}
}