Set gas limit according to TxPermission.blockGasLimit.

ethcore/call-contract/src/call_contract.rs

@@ -18,12 +18,18 @@
 
 use bytes::Bytes;
 use ethereum_types::Address;
+use types::header::Header;
 use types::ids::BlockId;
 
 /// Provides `call_contract` method
 pub trait CallContract {
 	/// Like `call`, but with various defaults. Designed to be used for calling contracts.
 	fn call_contract(&self, id: BlockId, address: Address, data: Bytes) -> Result<Bytes, String>;
+
+	/// Makes a constant call to a contract, at the beginning of the block corresponding to the given header, i.e. with
+	/// the EVM state after the block's parent, but with the new header's block number. Fails if the parent is not in
+	/// the database.
+	fn call_contract_before(&self, header: &Header, address: Address, data: Bytes) -> Result<Bytes, String>;
 }
 
 /// Provides information on a blockchain service and it's registry

ethcore/private-tx/src/key_server_keys.rs

@@ -160,6 +160,10 @@ mod tests {
 
 	impl CallContract for DummyRegistryClient {
 		fn call_contract(&self, _id: BlockId, _address: Address, _data: Bytes) -> Result<Bytes, String> { Ok(vec![]) }
+
+		fn call_contract_before(&self, _header: &Header, _address: Address, _data: Bytes) -> Result<Bytes, String> {
+			Ok(vec![])
+		}
 	}
 
 	#[test]
@@ -170,4 +174,4 @@ mod tests {
 		keys_data.update_acl_contract();
 		assert_eq!(keys_data.keys_acl_contract.read().unwrap(), key.address());
 	}
-}
+}

ethcore/res/contracts/block_gas_limit.json

@@ -0,0 +1,16 @@
+[
+	{
+		"constant": true,
+		"inputs": [],
+		"name": "blockGasLimit",
+		"outputs": [
+			{
+				"name": "",
+				"type": "uint256"
+			}
+		],
+		"payable": false,
+		"stateMutability": "view",
+		"type": "function"
+	}
+]

ethcore/src/client/client.rs

@@ -1456,6 +1456,49 @@ impl CallContract for Client {
 			.map_err(|e| format!("{:?}", e))
 			.map(|executed| executed.output)
 	}
+
+	fn call_contract_before(&self, header: &Header, address: Address, data: Bytes) -> Result<Bytes, String> {
+		let db = self.state_db.read().boxed_clone();
+
+		// early exit for pruned blocks
+		if db.is_pruned() && self.pruning_info().earliest_state > header.number() {
+			return Err(CallError::StatePruned.to_string());
+		}
+
+		let parent = self.chain.read().block_header_data(header.parent_hash()).ok_or_else(|| {
+			error!(target: "client", "Failed to call contract at {:?}'s child", header.parent_hash());
+			format!("Failed to call contract at {:?}'s child", header.parent_hash())
+		})?;
+		let root = parent.state_root();
+		let nonce = self.engine.account_start_nonce(header.number());
+		let mut state = State::from_existing(db, root, nonce, self.factories.clone())
+			.map_err(|_| CallError::StatePruned.to_string())?;
+
+		let from = Address::default();
+		let transaction = transaction::Transaction {
+			nonce: state.nonce(&from).unwrap_or_else(|_| self.engine.account_start_nonce(0)),
+			action: Action::Call(address),
+			gas: U256::from(50_000_000),
+			gas_price: U256::default(),
+			value: U256::default(),
+			data,
+		}.fake_sign(from);
+
+		let env_info = EnvInfo {
+			number: header.number(),
+			author: header.author().clone(),
+			timestamp: header.timestamp(),
+			difficulty: header.difficulty().clone(),
+			last_hashes: self.build_last_hashes(&parent.hash()),
+			gas_used: U256::default(),
+			gas_limit: U256::max_value(),
+		};
+		let machine = self.engine.machine();
+
+		Self::do_virtual_call(&machine, &env_info, &mut state, &transaction, Default::default())
+			.map_err(|e| format!("{:?}", e))
+			.map(|executed| executed.output)
+	}
 }
 
 impl ImportBlock for Client {

ethcore/src/client/test_client.rs

@@ -523,6 +523,10 @@ impl BlockInfo for TestBlockChainClient {
 
 impl CallContract for TestBlockChainClient {
 	fn call_contract(&self, _id: BlockId, _address: Address, _data: Bytes) -> Result<Bytes, String> { Ok(vec![]) }
+
+	fn call_contract_before(&self, _header: &Header, _address: Address, _data: Bytes) -> Result<Bytes, String> {
+		Ok(vec![])
+	}
 }
 
 impl TransactionInfo for TestBlockChainClient {

ethcore/src/engines/authority_round/mod.rs

@@ -32,7 +32,8 @@ use engines::{Engine, Seal, SealingState, EngineError, ConstructedVerifier};
 use engines::block_reward;
 use engines::block_reward::{BlockRewardContract, RewardKind};
 use error::{Error, ErrorKind, BlockError};
-use ethjson::{spec::StepDuration};
+use ethabi::FunctionOutputDecoder;
+use ethjson::{self, spec::StepDuration};
 use machine::{AuxiliaryData, Call, EthereumMachine};
 use hash::keccak;
 use super::signer::EngineSigner;
@@ -53,6 +54,8 @@ use unexpected::{Mismatch, OutOfBounds};
 #[cfg(not(time_checked_add))]
 use time_utils::CheckedSystemTime;
 
+use_contract!(block_gas_limit, "res/contracts/block_gas_limit.json");
+
 mod finality;
 mod randomness;
 pub(crate) mod util;
@@ -1107,6 +1110,14 @@ impl Engine<EthereumMachine> for AuthorityRound {
 
 		let score = calculate_score(parent_step, current_step, current_empty_steps_len);
 		header.set_difficulty(score);
+		if let Some(gas_limit) = self.gas_limit_override(header) {
+			trace!(target: "engine", "Setting gas limit to {} for block {}.", gas_limit, header.number());
+			let parent_gas_limit = *parent.gas_limit();
+			header.set_gas_limit(gas_limit);
+			if parent_gas_limit != gas_limit {
+				info!(target: "engine", "Block gas limit was changed from {} to {}.", parent_gas_limit, gas_limit);
+			}
+		}
 	}
 
 	fn sealing_state(&self) -> SealingState {
@@ -1783,6 +1794,36 @@ impl Engine<EthereumMachine> for AuthorityRound {
 
 		finalized.into_iter().map(AncestryAction::MarkFinalized).collect()
 	}
+
+	fn gas_limit_override(&self, header: &Header) -> Option<U256> {
+		let (_, &address) = self.machine.params().block_gas_limit_contract.range(..=header.number()).last()?;
+
+		let client = match self.client.read().as_ref().and_then(|weak| weak.upgrade()) {
+			Some(client) => client,
+			None => {
+				debug!(target: "engine", "Unable to prepare block: missing client ref.");
+				return None;
+			}
+		};
+		let full_client = match client.as_full_client() {
+			Some(full_client) => full_client,
+			None => {
+				debug!(target: "engine", "Failed to upgrade to BlockchainClient.");
+				return None;
+			}
+		};
+
+		let (data, decoder) = block_gas_limit::functions::block_gas_limit::call();
+		let value = full_client.call_contract_before(header, address, data).map_err(|err| {
+			error!(target: "engine", "Failed to call blockGasLimit. Not changing the block gas limit. {:?}", err);
+		}).ok()?;
+		if value.is_empty() {
+			debug!(target: "engine", "blockGasLimit returned nothing. Not changing the block gas limit.");
+			None
+		} else {
+			decoder.decode(&value).ok()
+		}
+	}
 }
 
 #[cfg(test)]

ethcore/src/engines/mod.rs

@@ -457,6 +457,12 @@ pub trait Engine<M: Machine>: Sync + Send {
 
 	/// Check whether the given new block is the best block, after finalization check.
 	fn fork_choice(&self, new: &M::ExtendedHeader, best: &M::ExtendedHeader) -> ForkChoice;
+
+	/// Overrides the block gas limit. Whenever this returns `Some` for a header, the next block's gas limit must be
+	/// exactly that value.
+	fn gas_limit_override(&self, _header: &Header) -> Option<U256> {
+		None
+	}
 }
 
 /// Check whether a given block is the best block based on the default total difficulty rule.

ethcore/src/machine.rs

@@ -108,6 +108,11 @@ impl EthereumMachine {
 	pub fn ethash_extensions(&self) -> Option<&EthashExtensions> {
 		self.ethash_extensions.as_ref()
 	}
+
+	/// Get a reference to the transaction filter, if present.
+	pub fn tx_filter(&self) -> Option<&Arc<TransactionFilter>> {
+		self.tx_filter.as_ref()
+	}
 }
 
 impl EthereumMachine {

ethcore/src/spec/spec.rs

@@ -79,6 +79,8 @@ pub struct CommonParams {
 	pub subprotocol_name: String,
 	/// Minimum gas limit.
 	pub min_gas_limit: U256,
+	/// The address of a contract that determines the block gas limit.
+	pub block_gas_limit_contract: BTreeMap<BlockNumber, Address>,
 	/// Fork block to check.
 	pub fork_block: Option<(BlockNumber, H256)>,
 	/// EIP150 transition block number.
@@ -243,6 +245,7 @@ impl From<ethjson::spec::Params> for CommonParams {
 			},
 			subprotocol_name: p.subprotocol_name.unwrap_or_else(|| "eth".to_owned()),
 			min_gas_limit: p.min_gas_limit.into(),
+			block_gas_limit_contract: p.block_gas_limit_contract.map(|bglc| bglc.into()).unwrap_or_default(),
 			fork_block: if let (Some(n), Some(h)) = (p.fork_block, p.fork_hash) {
 				Some((n.into(), h.into()))
 			} else {

ethcore/src/tx_filter.rs

@@ -64,6 +64,11 @@ impl TransactionFilter {
 		)
 	}
 
+	/// Get a reference to the contract address.
+	pub fn contract_address(&self) -> &Address {
+		&self.contract_address
+	}
+
 	/// Check if transaction is allowed at given block.
 	pub fn transaction_allowed<C: BlockInfo + CallContract>(&self, parent_hash: &H256, block_number: BlockNumber, transaction: &SignedTransaction, client: &C) -> bool {
 		if block_number < self.transition_block { return true; }

ethcore/src/verification/verification.rs

@@ -283,13 +283,21 @@ pub fn verify_header_params(header: &Header, engine: &EthEngine, is_full: bool,
 	if header.gas_used() > header.gas_limit() {
 		return Err(From::from(BlockError::TooMuchGasUsed(OutOfBounds { max: Some(*header.gas_limit()), min: None, found: *header.gas_used() })));
 	}
-	let min_gas_limit = engine.params().min_gas_limit;
-	if header.gas_limit() < &min_gas_limit {
-		return Err(From::from(BlockError::InvalidGasLimit(OutOfBounds { min: Some(min_gas_limit), max: None, found: *header.gas_limit() })));
-	}
-	if let Some(limit) = engine.maximum_gas_limit() {
-		if header.gas_limit() > &limit {
-			return Err(From::from(::error::BlockError::InvalidGasLimit(OutOfBounds { min: None, max: Some(limit), found: *header.gas_limit() })));
+	if let Some(gas_limit) = engine.gas_limit_override(header) {
+		if *header.gas_limit() != gas_limit {
+			return Err(From::from(BlockError::InvalidGasLimit(
+				OutOfBounds { min: Some(gas_limit), max: Some(gas_limit), found: *header.gas_limit() }
+			)));
+		}
+	} else {
+		let min_gas_limit = engine.params().min_gas_limit;
+		if header.gas_limit() < &min_gas_limit {
+			return Err(From::from(BlockError::InvalidGasLimit(OutOfBounds { min: Some(min_gas_limit), max: None, found: *header.gas_limit() })));
+		}
+		if let Some(limit) = engine.maximum_gas_limit() {
+			if header.gas_limit() > &limit {
+				return Err(From::from(::error::BlockError::InvalidGasLimit(OutOfBounds { min: None, max: Some(limit), found: *header.gas_limit() })));
+			}
 		}
 	}
 	let maximum_extra_data_size = engine.maximum_extra_data_size();
@@ -325,13 +333,11 @@ pub fn verify_header_params(header: &Header, engine: &EthEngine, is_full: bool,
 	Ok(())
 }
 
-/// Check header parameters agains parent header.
+/// Check header parameters against parent header.
 fn verify_parent(header: &Header, parent: &Header, engine: &EthEngine) -> Result<(), Error> {
 	assert!(header.parent_hash().is_zero() || &parent.hash() == header.parent_hash(),
 			"Parent hash should already have been verified; qed");
 
-	let gas_limit_divisor = engine.params().gas_limit_bound_divisor;
-
 	if !engine.is_timestamp_valid(header.timestamp(), parent.timestamp()) {
 		let now = SystemTime::now();
 		let min = now.checked_add(Duration::from_secs(parent.timestamp().saturating_add(1)))
@@ -348,11 +354,14 @@ fn verify_parent(header: &Header, parent: &Header, engine: &EthEngine) -> Result
 		return Err(BlockError::RidiculousNumber(OutOfBounds { min: Some(1), max: None, found: header.number() }).into());
 	}
 
-	let parent_gas_limit = *parent.gas_limit();
-	let min_gas = parent_gas_limit - parent_gas_limit / gas_limit_divisor;
-	let max_gas = parent_gas_limit + parent_gas_limit / gas_limit_divisor;
-	if header.gas_limit() <= &min_gas || header.gas_limit() >= &max_gas {
-		return Err(From::from(BlockError::InvalidGasLimit(OutOfBounds { min: Some(min_gas), max: Some(max_gas), found: *header.gas_limit() })));
+	if engine.gas_limit_override(header).is_none() {
+		let gas_limit_divisor = engine.params().gas_limit_bound_divisor;
+		let parent_gas_limit = *parent.gas_limit();
+		let min_gas = parent_gas_limit - parent_gas_limit / gas_limit_divisor;
+		let max_gas = parent_gas_limit + parent_gas_limit / gas_limit_divisor;
+		if header.gas_limit() <= &min_gas || header.gas_limit() >= &max_gas {
+			return Err(From::from(BlockError::InvalidGasLimit(OutOfBounds { min: Some(min_gas), max: Some(max_gas), found: *header.gas_limit() })));
+		}
 	}
 
 	Ok(())

json/src/spec/params.rs

@@ -16,6 +16,9 @@
 
 //! Spec params deserialization.
 
+use std::collections::BTreeMap;
+use std::iter;
+use ethereum_types::H160;
 use uint::{self, Uint};
 use hash::{H256, Address};
 use bytes::Bytes;
@@ -31,6 +34,8 @@ pub struct Params {
 	pub maximum_extra_data_size: Uint,
 	/// Minimum gas limit.
 	pub min_gas_limit: Uint,
+	/// The address of a contract that determines the block gas limit.
+	pub block_gas_limit_contract: Option<BlockGasLimitContract>,
 
 	/// Network id.
 	#[serde(rename = "networkID")]
@@ -126,12 +131,36 @@ pub struct Params {
 	pub kip6_transition: Option<Uint>,
 }
 
+/// A contract that determines block gas limits can be configured either as a single address, or as a map, assigning
+/// to each starting block number the contract address that should be used from that block on.
+#[derive(Debug, PartialEq, Deserialize)]
+#[serde(deny_unknown_fields, untagged)]
+pub enum BlockGasLimitContract {
+	/// A single address for a block gas limit contract.
+	Single(Address),
+	/// A map from block numbers to the contract addresses that should be used for the gas limit after that block.
+	Transitions(BTreeMap<Uint, Address>),
+}
+
+impl From<BlockGasLimitContract> for BTreeMap<u64, H160> {
+	fn from(contract: BlockGasLimitContract) -> Self {
+		match contract {
+			BlockGasLimitContract::Single(Address(addr)) => iter::once((0, addr)).collect(),
+			BlockGasLimitContract::Transitions(transitions) => {
+				transitions.into_iter().map(|(Uint(block), Address(addr))| (block.into(), addr)).collect()
+			}
+		}
+	}
+}
+
 #[cfg(test)]
 mod tests {
+	use std::str::FromStr;
 	use serde_json;
 	use uint::Uint;
-	use ethereum_types::U256;
-	use spec::params::Params;
+	use ethereum_types::{U256, H160};
+	use hash::Address;
+	use spec::params::{BlockGasLimitContract, Params};
 
 	#[test]
 	fn params_deserialization() {
@@ -144,7 +173,11 @@ mod tests {
 			"accountStartNonce": "0x01",
 			"gasLimitBoundDivisor": "0x20",
 			"maxCodeSize": "0x1000",
-			"wasmActivationTransition": "0x1010"
+			"wasmActivationTransition": "0x1010",
+			"blockGasLimitContract": {
+				"10": "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+				"20": "0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"
+			}
 		}"#;
 
 		let deserialized: Params = serde_json::from_str(s).unwrap();