Contract accounting removal (#2230)

* first partial implementation * update rent allowance * fmt Co-Authored-By: thiolliere <gui.thiolliere@gmail.com> * remove comments * reward surcharge claims * remove rent allowance in param + code_hash changed * Fix bug * fix tests * fmt * impl getter setter rent allowance * fmt Co-Authored-By: thiolliere <gui.thiolliere@gmail.com> * comments * doc + be->le * doc * doc * fix improve fast return * renamings * rename + COMPLEXITY * COMPLEXITY * add test * etrinsic claim surcharge delay configurable * comment addressed * move and rewrite of pay_rent * remove child trie * fmt * use derive * arithmetic operation * fix * fix storage root + checked_mul + test * WIP: test * WIP * add tests and fix * fmt * typo and doc suggestions Co-Authored-By: thiolliere <gui.thiolliere@gmail.com> * WIP * address some comments divide tests + some docs * use br_table * remove unused function * Bump the runtime version * insert_with * Add some comments. * Refactor * Shuffle and fix comments * More comment fixes. * dues limited * Add comment * Handicap * Docs. * Apply suggestions from code review Co-Authored-By: pepyakin <s.pepyakin@gmail.com> * Coalesce block_passed in a block * Fix build * Paid → Ok * match → if * Imrpove handicap description
2026-06-11 04:51:09 +00:00 · 2019-04-30 09:41:33 +02:00
parent f14580535e
commit c7d9ca379d
12 changed files with 1040 additions and 133 deletions
@@ -159,7 +159,7 @@ impl<H: Hasher> Externalities<H> for TestExternalities<H> where H::Out: Ord + He
 	}

 	fn child_storage_root(&mut self, _storage_key: ChildStorageKey<H>) -> Vec<u8> {
-		unimplemented!()
+		vec![]
 	}

 	fn storage_changes_root(&mut self, parent: H::Out, parent_num: u64) -> Option<H::Out> {
@@ -152,6 +152,12 @@ fn staging_testnet_config_genesis() -> GenesisConfig {
 			burn: Permill::from_percent(50),
 		}),
 		contract: Some(ContractConfig {
+			signed_claim_handicap: 2,
+			rent_byte_price: 4,
+			rent_deposit_offset: 1000,
+			storage_size_offset: 8,
+			surcharge_reward: 150,
+			tombstone_deposit: 16,
 			transaction_base_fee: 1 * CENTS,
 			transaction_byte_fee: 10 * MILLICENTS,
 			transfer_fee: 1 * CENTS,
@@ -239,6 +245,12 @@ pub fn testnet_genesis(
 	const ENDOWMENT: u128 = 1 << 20;

 	let mut contract_config = ContractConfig {
+		signed_claim_handicap: 2,
+		rent_byte_price: 4,
+		rent_deposit_offset: 1000,
+		storage_size_offset: 8,
+		surcharge_reward: 150,
+		tombstone_deposit: 16,
 		transaction_base_fee: 1,
 		transaction_byte_fee: 0,
 		transfer_fee: 0,
@@ -745,7 +745,13 @@ mod tests {

 		runtime_io::with_externalities(&mut t, || {
 			// Verify that the contract constructor worked well and code of TRANSFER contract is actually deployed.
-			assert_eq!(&contract::CodeHashOf::<Runtime>::get(addr).unwrap(), &transfer_ch);
+			assert_eq!(
+				&contract::ContractInfoOf::<Runtime>::get(addr)
+					.and_then(|c| c.get_alive())
+					.unwrap()
+					.code_hash,
+				&transfer_ch
+			);
 		});
 	}

@@ -59,7 +59,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
 	spec_version: 67,
-	impl_version: 67,
+	impl_version: 68,
 	apis: RUNTIME_API_VERSIONS,
 };

@@ -85,7 +85,7 @@ execution contexts operate on the AccountDb. All changes are flushed into underl

 Today `AccountDb` is implemented as a cascade of overlays with the direct storage at the bottom. Each overlay is represented by a `Map`. On a commit from an overlay to an overlay, maps are merged. On commit from an overlay to the bottommost `AccountDb` all changes are flushed to the storage. On revert, the overlay is just discarded.

-## get_storage, get_code, get_balance
+## get_storage, get_code_hash, get_rent_allowance, get_balance, contract_exists

 These functions check the local cache for a requested value and, if it is there, the value is returned. Otherwise, these functions will ask an underlying `AccountDb`  for the value. This means that the number of lookups is proportional to the depth of the overlay cascade. If the value can't be found before reaching the bottommost `AccountDb`, then a DB read will be performed (in case `get_balance` the function `free_balance` will be invoked).

@@ -95,7 +95,7 @@ These functions return an owned value as its result, so memory usage depends on

 **complexity**: The memory complexity is proportional to the size of the value. The computational complexity is proportional to the depth of the overlay cascade and the size of the value; the cost is dominated by the DB read though.

-## set_storage, set_code, set_balance
+## set_storage, set_balance, set_rent_allowance

 These functions only modify the local `Map`.

@@ -105,6 +105,12 @@ While these functions only modify the local `Map`, if changes made by them are c

 **complexity**: Each lookup has a logarithmical computing time to the number of already inserted entries. No additional memory is required.

+## create_contract
+
+Calls `contract_exists` and if it doesn't exist, do not modify the local `Map` similarly to `set_rent_allowance`.
+
+**complexity**: The computational complexity is proportional to the depth of the overlay cascade and the size of the value; the cost is dominated by the DB read though. No additional memory is required.
+
 ## commit

 In this function, all cached values will be inserted into the underlying `AccountDb` or into the storage.
@@ -327,3 +333,25 @@ This function copies slice of data from the scratch buffer to the sandbox memory
 1. Storing a specified slice of the scratch buffer into the sandbox memory (see sandboxing memory set)

 **complexity**: The computing complexity of this function is proportional to the length of the slice. No additional memory is required.
+
+## ext_set_rent_allowance
+
+This function receives the following argument:
+
+- `value` buffer of a marshaled `Balance`,
+
+It consists of the following steps:
+
+1. Loading `value` buffer from the sandbox memory and then decoding it.
+2. Invoking `set_rent_allowance` AccountDB function.
+
+**complexity**: Complexity is proportional to the size of the `value`. This function induces a DB write of size proportional to the `value` size (if flushed to the storage), so should be priced accordingly.
+
+## ext_rent_allowance
+
+It consists of the following steps:
+
+1. Invoking `get_rent_allowance` AccountDB function.
+2. Serializing the rent allowance of the current contract into the scratch buffer.
+
+**complexity**: Assuming that the rent allowance is of constant size, this function has constant complexity.
@@ -16,21 +16,28 @@

 //! Auxilliaries to help with managing partial changes to accounts state.

-use super::{CodeHash, CodeHashOf, Trait, TrieId, AccountInfoOf, BalanceOf, AccountInfo, TrieIdGenerator};
+use super::{
+	AliveContractInfo, BalanceOf, CodeHash, ContractInfo, ContractInfoOf, Module, Trait, TrieId,
+	TrieIdGenerator,
+};
 use crate::exec::StorageKey;
-use system;
 use rstd::cell::RefCell;
 use rstd::collections::btree_map::{BTreeMap, Entry};
 use rstd::prelude::*;
 use runtime_io::blake2_256;
 use runtime_primitives::traits::Zero;
-use srml_support::{StorageMap, traits::{UpdateBalanceOutcome,
-	SignedImbalance, Currency, Imbalance}, storage::child};
+use srml_support::traits::{Currency, Imbalance, SignedImbalance, UpdateBalanceOutcome};
+use srml_support::{storage::child, StorageMap};
+use system;

+// Note: we don't provide Option<Contract> because we can't create
+// the trie_id in the overlay, thus we provide an overlay on the fields
+// specifically.
 pub struct ChangeEntry<T: Trait> {
 	balance: Option<BalanceOf<T>>,
-	/// In the case the outer option is None, the code_hash remains untouched, while providing `Some(None)` signifies a removing of the code in question
-	code: Option<Option<CodeHash<T>>>,
+	/// If None, the code_hash remains untouched.
+	code_hash: Option<CodeHash<T>>,
+	rent_allowance: Option<BalanceOf<T>>,
 	storage: BTreeMap<StorageKey, Option<Vec<u8>>>,
 }

@@ -38,8 +45,9 @@ pub struct ChangeEntry<T: Trait> {
 impl<T: Trait> Default for ChangeEntry<T> {
 	fn default() -> Self {
 		ChangeEntry {
+			rent_allowance: Default::default(),
 			balance: Default::default(),
-			code: Default::default(),
+			code_hash: Default::default(),
 			storage: Default::default(),
 		}
 	}
@@ -51,10 +59,15 @@ pub trait AccountDb<T: Trait> {
 	/// Account is used when overlayed otherwise trie_id must be provided.
 	/// This is for performance reason.
 	///
-	/// Trie id can be None iff account doesn't have an associated trie id in <AccountInfoOf<T>>.
+	/// Trie id is None iff account doesn't have an associated trie id in <ContractInfoOf<T>>.
 	/// Because DirectAccountDb bypass the lookup for this association.
 	fn get_storage(&self, account: &T::AccountId, trie_id: Option<&TrieId>, location: &StorageKey) -> Option<Vec<u8>>;
-	fn get_code(&self, account: &T::AccountId) -> Option<CodeHash<T>>;
+	/// If account has an alive contract then return the code hash associated.
+	fn get_code_hash(&self, account: &T::AccountId) -> Option<CodeHash<T>>;
+	/// If account has an alive contract then return the rent allowance associated.
+	fn get_rent_allowance(&self, account: &T::AccountId) -> Option<BalanceOf<T>>;
+	/// Returns false iff account has no alive contract nor tombstone.
+	fn contract_exists(&self, account: &T::AccountId) -> bool;
 	fn get_balance(&self, account: &T::AccountId) -> BalanceOf<T>;

 	fn commit(&mut self, change_set: ChangeSet<T>);
@@ -65,8 +78,14 @@ impl<T: Trait> AccountDb<T> for DirectAccountDb {
 	fn get_storage(&self, _account: &T::AccountId, trie_id: Option<&TrieId>, location: &StorageKey) -> Option<Vec<u8>> {
 		trie_id.and_then(|id| child::get_raw(id, &blake2_256(location)))
 	}
-	fn get_code(&self, account: &T::AccountId) -> Option<CodeHash<T>> {
-		<CodeHashOf<T>>::get(account)
+	fn get_code_hash(&self, account: &T::AccountId) -> Option<CodeHash<T>> {
+		<ContractInfoOf<T>>::get(account).and_then(|i| i.as_alive().map(|i| i.code_hash))
+	}
+	fn get_rent_allowance(&self, account: &T::AccountId) -> Option<BalanceOf<T>> {
+		<ContractInfoOf<T>>::get(account).and_then(|i| i.as_alive().map(|i| i.rent_allowance))
+	}
+	fn contract_exists(&self, account: &T::AccountId) -> bool {
+		<ContractInfoOf<T>>::exists(account)
 	}
 	fn get_balance(&self, account: &T::AccountId) -> BalanceOf<T> {
 		T::Currency::free_balance(account)
@@ -84,42 +103,58 @@ impl<T: Trait> AccountDb<T> for DirectAccountDb {
 					continue;
 				}
 			}
-			if changed.code.is_some() || !changed.storage.is_empty() {
-				let mut info = if !<AccountInfoOf<T>>::exists(&address) {
-					let info = AccountInfo {
-						trie_id: <T as Trait>::TrieIdGenerator::trie_id(&address),
-						storage_size: 0,
-					};
-					<AccountInfoOf<T>>::insert(&address, &info);
-					info
-				} else {
-					<AccountInfoOf<T>>::get(&address).unwrap()
+
+			if changed.code_hash.is_some()
+				|| changed.rent_allowance.is_some()
+				|| !changed.storage.is_empty()
+			{
+				let old_info = match <ContractInfoOf<T>>::get(&address) {
+					Some(ContractInfo::Alive(alive)) => Some(alive),
+					None => None,
+					// Cannot commit changes to tombstone contract
+					Some(ContractInfo::Tombstone(_)) => continue,
 				};

-				if let Some(code) = changed.code {
-					if let Some(code) = code {
-						<CodeHashOf<T>>::insert(&address, code);
-					} else {
-						<CodeHashOf<T>>::remove(&address);
+				let mut new_info = if let Some(info) = old_info.clone() {
+					info
+				} else if let Some(code_hash) = changed.code_hash {
+					AliveContractInfo::<T> {
+						code_hash,
+						storage_size: <Module<T>>::storage_size_offset(),
+						trie_id: <T as Trait>::TrieIdGenerator::trie_id(&address),
+						deduct_block: <system::Module<T>>::block_number(),
+						rent_allowance: <BalanceOf<T>>::zero(),
 					}
+				} else {
+					// No contract exist and no code_hash provided
+					continue;
+				};
+
+				if let Some(rent_allowance) = changed.rent_allowance {
+					new_info.rent_allowance = rent_allowance;
+				}
+
+				if let Some(code_hash) = changed.code_hash {
+					new_info.code_hash = code_hash;
 				}

-				let mut new_storage_size = info.storage_size;
 				for (k, v) in changed.storage.into_iter() {
-					if let Some(value) = child::get_raw(&info.trie_id[..], &blake2_256(&k)) {
-						new_storage_size -= value.len() as u64;
+					if let Some(value) = child::get_raw(&new_info.trie_id[..], &blake2_256(&k)) {
+						new_info.storage_size -= value.len() as u64;
 					}
 					if let Some(value) = v {
-						new_storage_size += value.len() as u64;
-						child::put_raw(&info.trie_id[..], &blake2_256(&k), &value[..]);
+						new_info.storage_size += value.len() as u64;
+						child::put_raw(&new_info.trie_id[..], &blake2_256(&k), &value[..]);
 					} else {
-						child::kill(&info.trie_id[..], &blake2_256(&k));
+						child::kill(&new_info.trie_id[..], &blake2_256(&k));
 					}
 				}

-				if new_storage_size != info.storage_size {
-					info.storage_size = new_storage_size;
-					<AccountInfoOf<T>>::insert(&address, info);
+				if old_info
+					.map(|old_info| old_info != new_info)
+					.unwrap_or(true)
+				{
+					<ContractInfoOf<T>>::insert(&address, ContractInfo::Alive(new_info));
 				}
 			}
 		}
@@ -140,9 +175,7 @@ pub struct OverlayAccountDb<'a, T: Trait + 'a> {
 	underlying: &'a AccountDb<T>,
 }
 impl<'a, T: Trait> OverlayAccountDb<'a, T> {
-	pub fn new(
-		underlying: &'a AccountDb<T>,
-	) -> OverlayAccountDb<'a, T> {
+	pub fn new(underlying: &'a AccountDb<T>) -> OverlayAccountDb<'a, T> {
 		OverlayAccountDb {
 			local: RefCell::new(ChangeSet::new()),
 			underlying,
@@ -166,12 +199,31 @@ impl<'a, T: Trait> OverlayAccountDb<'a, T> {
 			.insert(location, value);
 	}

-	pub fn set_code(&mut self, account: &T::AccountId, code: Option<CodeHash<T>>) {
+	/// Return an error if contract already exists (either if it is alive or tombstone)
+	pub fn create_contract(
+		&mut self,
+		account: &T::AccountId,
+		code_hash: CodeHash<T>,
+	) -> Result<(), &'static str> {
+		if self.contract_exists(account) {
+			return Err("Alive contract or tombstone already exists");
+		}
+
+		let mut local = self.local.borrow_mut();
+		let contract = local.entry(account.clone()).or_insert_with(|| Default::default());
+
+		contract.code_hash = Some(code_hash);
+		contract.rent_allowance = Some(<BalanceOf<T>>::zero());
+
+		Ok(())
+	}
+	/// Assume contract exists
+	pub fn set_rent_allowance(&mut self, account: &T::AccountId, rent_allowance: BalanceOf<T>) {
 		self.local
 			.borrow_mut()
 			.entry(account.clone())
 			.or_insert(Default::default())
-			.code = Some(code);
+			.rent_allowance = Some(rent_allowance);
 	}
 	pub fn set_balance(&mut self, account: &T::AccountId, balance: BalanceOf<T>) {
 		self.local
@@ -191,12 +243,26 @@ impl<'a, T: Trait> AccountDb<T> for OverlayAccountDb<'a, T> {
 			.cloned()
 			.unwrap_or_else(|| self.underlying.get_storage(account, trie_id, location))
 	}
-	fn get_code(&self, account: &T::AccountId) -> Option<CodeHash<T>> {
+	fn get_code_hash(&self, account: &T::AccountId) -> Option<CodeHash<T>> {
 		self.local
 			.borrow()
 			.get(account)
-			.and_then(|a| a.code.clone())
-			.unwrap_or_else(|| self.underlying.get_code(account))
+			.and_then(|changes| changes.code_hash)
+			.or_else(|| self.underlying.get_code_hash(account))
+	}
+	fn get_rent_allowance(&self, account: &T::AccountId) -> Option<BalanceOf<T>> {
+		self.local
+			.borrow()
+			.get(account)
+			.and_then(|changes| changes.rent_allowance)
+			.or_else(|| self.underlying.get_rent_allowance(account))
+	}
+	fn contract_exists(&self, account: &T::AccountId) -> bool {
+		self.local
+			.borrow()
+			.get(account)
+			.map(|a| a.code_hash.is_some())
+			.unwrap_or_else(|| self.underlying.contract_exists(account))
 	}
 	fn get_balance(&self, account: &T::AccountId) -> BalanceOf<T> {
 		self.local
@@ -212,12 +278,9 @@ impl<'a, T: Trait> AccountDb<T> for OverlayAccountDb<'a, T> {
 			match local.entry(address) {
 				Entry::Occupied(e) => {
 					let mut value = e.into_mut();
-					if changed.balance.is_some() {
-						value.balance = changed.balance;
-					}
-					if changed.code.is_some() {
-						value.code = changed.code;
-					}
+					value.balance = changed.balance.or(value.balance);
+					value.code_hash = changed.code_hash.or(value.code_hash);
+					value.rent_allowance = changed.rent_allowance.or(value.rent_allowance);
 					value.storage.extend(changed.storage.into_iter());
 				}
 				Entry::Vacant(e) => {
@@ -14,7 +14,8 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate. If not, see <http://www.gnu.org/licenses/>.

-use super::{CodeHash, Config, ContractAddressFor, Event, RawEvent, Trait, TrieId, BalanceOf, AccountInfoOf};
+use super::{CodeHash, Config, ContractAddressFor, Event, RawEvent, Trait,
+	TrieId, BalanceOf, ContractInfoOf};
 use crate::account_db::{AccountDb, DirectAccountDb, OverlayAccountDb};
 use crate::gas::{GasMeter, Token, approx_gas_for_balance};

@@ -107,6 +108,12 @@ pub trait Ext {

 	/// Deposit an event.
 	fn deposit_event(&mut self, data: Vec<u8>);
+
+	/// Set rent allowance of the contract
+	fn set_rent_allowance(&mut self, rent_allowance: BalanceOf<Self::T>);
+
+	/// Rent allowance of the contract
+	fn rent_allowance(&self) -> BalanceOf<Self::T>;
 }

 /// Loader is a companion of the `Vm` trait. It loads an appropriate abstract
@@ -249,7 +256,8 @@ where
 	/// The specified `origin` address will be used as `sender` for
 	pub fn top_level(origin: T::AccountId, cfg: &'a Config<T>, vm: &'a V, loader: &'a L) -> Self {
 		ExecutionContext {
-			self_trie_id: <AccountInfoOf<T>>::get(&origin).map(|s| s.trie_id),
+			self_trie_id: <ContractInfoOf<T>>::get(&origin)
+				.and_then(|i| i.as_alive().map(|i| i.trie_id.clone())),
 			self_account: origin,
 			overlay: OverlayAccountDb::<T>::new(&DirectAccountDb),
 			depth: 0,
@@ -263,7 +271,8 @@ where

 	fn nested(&self, overlay: OverlayAccountDb<'a, T>, dest: T::AccountId) -> Self {
 		ExecutionContext {
-			self_trie_id: <AccountInfoOf<T>>::get(&dest).map(|s| s.trie_id),
+			self_trie_id: <ContractInfoOf<T>>::get(&dest)
+				.and_then(|i| i.as_alive().map(|i| i.trie_id.clone())),
 			self_account: dest,
 			overlay,
 			depth: self.depth + 1,
@@ -295,7 +304,11 @@ where
 			return Err("not enough gas to pay base call fee");
 		}

-		let dest_code_hash = self.overlay.get_code(&dest);
+		// Assumption: pay_rent doesn't collide with overlay because
+		// pay_rent will be done on first call and dest contract and balance
+		// cannot be changed before the first call
+		crate::rent::pay_rent::<T>(&dest);
+
 		let mut output_data = Vec::new();

 		let (change_set, events, calls) = {
@@ -315,7 +328,7 @@ where
 				)?;
 			}

-			if let Some(dest_code_hash) = dest_code_hash {
+			if let Some(dest_code_hash) = self.overlay.get_code_hash(&dest) {
 				let executable = self.loader.load_main(&dest_code_hash)?;
 				output_data = self
 					.vm
@@ -369,15 +382,11 @@ where
 			&self.self_account,
 		);

-		if self.overlay.get_code(&dest).is_some() {
-			// It should be enough to check only the code.
-			return Err("contract already exists");
-		}
-
 		let (change_set, events, calls) = {
 			let mut overlay = OverlayAccountDb::new(&self.overlay);
-				
-			overlay.set_code(&dest, Some(code_hash.clone()));
+
+			overlay.create_contract(&dest, code_hash.clone())?;
+
 			let mut nested = self.nested(overlay, dest.clone());

 			// Send funds unconditionally here. If the `endowment` is below existential_deposit
@@ -625,6 +634,15 @@ where
 	fn deposit_event(&mut self, data: Vec<u8>) {
 		self.ctx.events.push(RawEvent::Contract(self.ctx.self_account.clone(), data));
 	}
+
+	fn set_rent_allowance(&mut self, rent_allowance: BalanceOf<T>) {
+		self.ctx.overlay.set_rent_allowance(&self.ctx.self_account, rent_allowance)
+	}
+
+	fn rent_allowance(&self) -> BalanceOf<T> {
+		self.ctx.overlay.get_rent_allowance(&self.ctx.self_account)
+			.unwrap_or(<BalanceOf<T>>::zero()) // Must never be triggered actually
+	}
 }

 /// These tests exercise the executive layer.
@@ -763,7 +781,7 @@ mod tests {
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&BOB, Some(exec_ch));
+			ctx.overlay.create_contract(&BOB, exec_ch).unwrap();

 			assert_matches!(
 				ctx.call(BOB, value, &mut gas_meter, &data, EmptyOutputBuf::new()),
@@ -998,7 +1016,7 @@ mod tests {
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(origin, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&BOB, Some(return_ch));
+			ctx.overlay.create_contract(&BOB, return_ch).unwrap();

 			let result = ctx.call(
 				dest,
@@ -1026,7 +1044,7 @@ mod tests {
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&BOB, Some(input_data_ch));
+			ctx.overlay.create_contract(&BOB, input_data_ch).unwrap();

 			let result = ctx.call(
 				BOB,
@@ -1038,7 +1056,7 @@ mod tests {
 			assert_matches!(result, Ok(_));
 		});

-		// This one tests passing the input data into a contract via call.
+		// This one tests passing the input data into a contract via instantiate.
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
@@ -1085,7 +1103,7 @@ mod tests {
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&BOB, Some(recurse_ch));
+			ctx.overlay.create_contract(&BOB, recurse_ch).unwrap();

 			let result = ctx.call(
 				BOB,
@@ -1132,8 +1150,8 @@ mod tests {
 			let cfg = Config::preload();

 			let mut ctx = ExecutionContext::top_level(origin, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&dest, Some(bob_ch));
-			ctx.overlay.set_code(&CHARLIE, Some(charlie_ch));
+			ctx.overlay.create_contract(&dest, bob_ch).unwrap();
+			ctx.overlay.create_contract(&CHARLIE, charlie_ch).unwrap();

 			let result = ctx.call(
 				dest,
@@ -1175,8 +1193,8 @@ mod tests {
 		with_externalities(&mut ExtBuilder::default().build(), || {
 			let cfg = Config::preload();
 			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
-			ctx.overlay.set_code(&BOB, Some(bob_ch));
-			ctx.overlay.set_code(&CHARLIE, Some(charlie_ch));
+			ctx.overlay.create_contract(&BOB, bob_ch).unwrap();
+			ctx.overlay.create_contract(&CHARLIE, charlie_ch).unwrap();

 			let result = ctx.call(
 				BOB,
@@ -1242,7 +1260,7 @@ mod tests {

 				// Check that the newly created account has the expected code hash and
 				// there are instantiation event.
-				assert_eq!(ctx.overlay.get_code(&created_contract_address).unwrap(), dummy_ch);
+				assert_eq!(ctx.overlay.get_code_hash(&created_contract_address).unwrap(), dummy_ch);
 				assert_eq!(&ctx.events, &[
 					RawEvent::Transfer(ALICE, created_contract_address, 100),
 					RawEvent::Instantiated(ALICE, created_contract_address),
@@ -1283,7 +1301,7 @@ mod tests {
 				let cfg = Config::preload();
 				let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
 				ctx.overlay.set_balance(&ALICE, 1000);
-				ctx.overlay.set_code(&BOB, Some(creator_ch));
+				ctx.overlay.create_contract(&BOB, creator_ch).unwrap();

 				assert_matches!(
 					ctx.call(BOB, 20, &mut GasMeter::<Test>::with_limit(1000, 1), &[], EmptyOutputBuf::new()),
@@ -1294,7 +1312,7 @@ mod tests {

 				// Check that the newly created account has the expected code hash and
 				// there are instantiation event.
-				assert_eq!(ctx.overlay.get_code(&created_contract_address).unwrap(), dummy_ch);
+				assert_eq!(ctx.overlay.get_code_hash(&created_contract_address).unwrap(), dummy_ch);
 				assert_eq!(&ctx.events, &[
 					RawEvent::Transfer(ALICE, BOB, 20),
 					RawEvent::Transfer(BOB, created_contract_address, 15),
@@ -1334,7 +1352,7 @@ mod tests {
 				let cfg = Config::preload();
 				let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
 				ctx.overlay.set_balance(&ALICE, 1000);
-				ctx.overlay.set_code(&BOB, Some(creator_ch));
+				ctx.overlay.create_contract(&BOB, creator_ch).unwrap();

 				assert_matches!(
 					ctx.call(BOB, 20, &mut GasMeter::<Test>::with_limit(1000, 1), &[], EmptyOutputBuf::new()),
@@ -1349,4 +1367,29 @@ mod tests {
 			}
 		);
 	}
+
+	#[test]
+	fn rent_allowance() {
+		let vm = MockVm::new();
+		let mut loader = MockLoader::empty();
+		let rent_allowance_ch = loader.insert(|ctx| {
+			assert_eq!(ctx.ext.rent_allowance(), 0);
+			ctx.ext.set_rent_allowance(10);
+			assert_eq!(ctx.ext.rent_allowance(), 10);
+			VmExecResult::Ok
+		});
+
+		with_externalities(&mut ExtBuilder::default().build(), || {
+			let cfg = Config::preload();
+			let mut ctx = ExecutionContext::top_level(ALICE, &cfg, &vm, &loader);
+
+			let result = ctx.instantiate(
+				0,
+				&mut GasMeter::<Test>::with_limit(10000, 1),
+				&rent_allowance_ch,
+				&[],
+			);
+			assert_matches!(result, Ok(_));
+		});
+	}
 }
@@ -83,6 +83,7 @@ mod gas;
 mod account_db;
 mod exec;
 mod wasm;
+mod rent;

 #[cfg(test)]
 mod tests;
@@ -96,7 +97,7 @@ use substrate_primitives::crypto::UncheckedFrom;
 use rstd::prelude::*;
 use rstd::marker::PhantomData;
 use parity_codec::{Codec, Encode, Decode};
-use runtime_primitives::traits::{Hash, As, SimpleArithmetic,Bounded, StaticLookup};
+use runtime_primitives::traits::{Hash, As, SimpleArithmetic, Bounded, StaticLookup, Zero};
 use srml_support::dispatch::{Result, Dispatchable};
 use srml_support::{Parameter, StorageMap, StorageValue, decl_module, decl_event, decl_storage, storage::child};
 use srml_support::traits::{OnFreeBalanceZero, OnUnbalanced, Currency};
@@ -117,14 +118,94 @@ pub trait ComputeDispatchFee<Call, Balance> {
 	fn compute_dispatch_fee(call: &Call) -> Balance;
 }

-#[derive(Encode,Decode,Clone,Debug)]
+/// Information for managing an acocunt and its sub trie abstraction.
+/// This is the required info to cache for an account
+#[derive(Encode, Decode)]
+pub enum ContractInfo<T: Trait> {
+	Alive(AliveContractInfo<T>),
+	Tombstone(TombstoneContractInfo<T>),
+}
+
+impl<T: Trait> ContractInfo<T> {
+	/// If contract is alive then return some alive info
+	pub fn get_alive(self) -> Option<AliveContractInfo<T>> {
+		if let ContractInfo::Alive(alive) = self {
+			Some(alive)
+		} else {
+			None
+		}
+	}
+	/// If contract is alive then return some reference to alive info
+	pub fn as_alive(&self) -> Option<&AliveContractInfo<T>> {
+		if let ContractInfo::Alive(ref alive) = self {
+			Some(alive)
+		} else {
+			None
+		}
+	}
+	/// If contract is alive then return some mutable reference to alive info
+	pub fn as_alive_mut(&mut self) -> Option<&mut AliveContractInfo<T>> {
+		if let ContractInfo::Alive(ref mut alive) = self {
+			Some(alive)
+		} else {
+			None
+		}
+	}
+
+	/// If contract is tombstone then return some alive info
+	pub fn get_tombstone(self) -> Option<TombstoneContractInfo<T>> {
+		if let ContractInfo::Tombstone(tombstone) = self {
+			Some(tombstone)
+		} else {
+			None
+		}
+	}
+	/// If contract is tombstone then return some reference to tombstone info
+	pub fn as_tombstone(&self) -> Option<&TombstoneContractInfo<T>> {
+		if let ContractInfo::Tombstone(ref tombstone) = self {
+			Some(tombstone)
+		} else {
+			None
+		}
+	}
+	/// If contract is tombstone then return some mutable reference to tombstone info
+	pub fn as_tombstone_mut(&mut self) -> Option<&mut TombstoneContractInfo<T>> {
+		if let ContractInfo::Tombstone(ref mut tombstone) = self {
+			Some(tombstone)
+		} else {
+			None
+		}
+	}
+}
+
+pub type AliveContractInfo<T> = RawAliveContractInfo<CodeHash<T>, BalanceOf<T>, <T as system::Trait>::BlockNumber>;
+
 /// Information for managing an account and its sub trie abstraction.
 /// This is the required info to cache for an account.
-pub struct AccountInfo {
-	/// Unique ID for the subtree encoded as a byte.
+// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
+#[derive(Encode, Decode, Clone, PartialEq, Eq)]
+pub struct RawAliveContractInfo<CodeHash, Balance, BlockNumber> {
+	/// Unique ID for the subtree encoded as a bytes vector.
 	pub trie_id: TrieId,
 	/// The size of stored value in octet.
 	pub storage_size: u64,
+	/// The code associated with a given account.
+	pub code_hash: CodeHash,
+	pub rent_allowance: Balance,
+	pub deduct_block: BlockNumber,
+}
+
+#[derive(Encode, Decode)]
+pub struct TombstoneContractInfo<T: Trait>(T::Hash);
+
+impl<T: Trait> TombstoneContractInfo<T> {
+	fn new(storage_root: Vec<u8>, storage_size: u64, code_hash: CodeHash<T>) -> Self {
+		let mut buf = Vec::new();
+		storage_root.using_encoded(|encoded| buf.extend_from_slice(encoded));
+		storage_size.using_encoded(|encoded| buf.extend_from_slice(encoded));
+		buf.extend_from_slice(code_hash.as_ref());
+		TombstoneContractInfo(T::Hashing::hash(&buf[..]))
+	}
 }

 /// Get a trie id (trie id must be unique and collision resistant depending upon its context).
@@ -384,6 +465,39 @@ decl_module! {
 			result.map(|_| ())
 		}

+		/// Allows block producers to claim a small reward for evicting a contract. If a block producer
+		/// fails to do so, a regular users will be allowed to claim the reward.
+		///
+		/// If contract is not evicted as a result of this call, no actions are taken and
+		/// the sender is not eligible for the reward.
+		fn claim_surcharge(origin, dest: T::AccountId, aux_sender: Option<T::AccountId>) {
+			let origin = origin.into();
+			let (signed, rewarded) = match origin {
+				Some(system::RawOrigin::Signed(ref account)) if aux_sender.is_none() => {
+					(true, account)
+				},
+				Some(system::RawOrigin::Inherent) if aux_sender.is_some() => {
+					(false, aux_sender.as_ref().expect("checked above"))
+				},
+				_ => return Err("Invalid surcharge claim: origin must be signed or \
+								inherent and auxiliary sender only provided on inherent")
+			};
+
+			// Add some advantage for block producers (who send unsigned extrinsics) by
+			// adding a handicap: for signed extrinsics we use a slightly older block number
+			// for the eviction check. This can be viewed as if we pushed regular users back in past.
+			let handicap = if signed {
+				<Module<T>>::signed_claim_handicap()
+			} else {
+				Zero::zero()
+			};
+
+			// If poking the contract has lead to eviction of the contract, give out the rewards.
+			if rent::try_evict::<T>(&dest, handicap) == rent::RentOutcome::Evicted {
+				T::Currency::deposit_into_existing(rewarded, Self::surcharge_reward())?;
+			}
+		}
+
 		fn on_finalize() {
 			<GasSpent<T>>::kill();
 		}
@@ -420,6 +534,29 @@ decl_event! {

 decl_storage! {
 	trait Store for Module<T: Trait> as Contract {
+		/// Number of block delay an extrinsic claim surcharge has.
+		///
+		/// When claim surchage is called by an extrinsic the rent is checked
+		/// for current_block - delay
+		SignedClaimHandicap get(signed_claim_handicap) config(): T::BlockNumber;
+		/// The minimum amount required to generate a tombstone.
+		TombstoneDeposit get(tombstone_deposit) config(): BalanceOf<T>;
+		/// Size of a contract at the time of creation. This is a simple way to ensure
+		/// that empty contracts eventually gets deleted.
+		StorageSizeOffset get(storage_size_offset) config(): u64;
+		/// Price of a byte of storage per one block interval. Should be greater than 0.
+		RentByteFee get(rent_byte_price) config(): BalanceOf<T>;
+		/// The amount of funds a contract should deposit in order to offset
+		/// the cost of one byte.
+		///
+		/// Let's suppose the deposit is 1,000 EDG/byte and the rent is 1 EDG/byte/day, then a contract
+		/// with 1,000,000 EDG that uses 1,000 bytes of storage would pay no rent.
+		/// But if the balance reduced to 500,000 EDG and the storage stayed the same at 1,000,
+		/// then it would pay 500 EDG/day.
+		RentDepositOffset get(rent_deposit_offset) config(): BalanceOf<T>;
+		/// Reward that is received by the party whose touch has led
+		/// to removal of a contract.
+		SurchargeReward get(surcharge_reward) config(): BalanceOf<T>;
 		/// The fee required to make a transfer.
 		TransferFee get(transfer_fee) config(): BalanceOf<T>;
 		/// The fee required to create an account.
@@ -444,8 +581,6 @@ decl_storage! {
 		GasSpent get(gas_spent): T::Gas;
 		/// Current cost schedule for contracts.
 		CurrentSchedule get(current_schedule) config(): Schedule<T::Gas> = Schedule::default();
-		/// The code associated with a given account.
-		pub CodeHashOf: map T::AccountId => Option<CodeHash<T>>;
 		/// A mapping from an original code hash to the original code, untouched by instrumentation.
 		pub PristineCode: map CodeHash<T> => Option<Vec<u8>>;
 		/// A mapping between an original code hash and instrumented wasm code, ready for execution.
@@ -453,14 +588,16 @@ decl_storage! {
 		/// The subtrie counter.
 		pub AccountCounter: u64 = 0;
 		/// The code associated with a given account.
-		pub AccountInfoOf: map T::AccountId => Option<AccountInfo>;
+		pub ContractInfoOf: map T::AccountId => Option<ContractInfo<T>>;
 	}
 }

 impl<T: Trait> OnFreeBalanceZero<T::AccountId> for Module<T> {
 	fn on_free_balance_zero(who: &T::AccountId) {
-		<CodeHashOf<T>>::remove(who);
-		<AccountInfoOf<T>>::get(who).map(|info| child::kill_storage(&info.trie_id));
+		if let Some(ContractInfo::Alive(info)) = <ContractInfoOf<T>>::get(who) {
+			child::kill_storage(&info.trie_id);
+		}
+		<ContractInfoOf<T>>::remove(who);
 	}
 }

@@ -0,0 +1,190 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate. If not, see <http://www.gnu.org/licenses/>.
+
+use crate::{BalanceOf, ContractInfo, ContractInfoOf, Module, TombstoneContractInfo, Trait};
+use runtime_primitives::traits::{As, Bounded, CheckedDiv, CheckedMul, Saturating, Zero};
+use srml_support::traits::{Currency, ExistenceRequirement, Imbalance, WithdrawReason};
+use srml_support::StorageMap;
+
+#[derive(PartialEq, Eq, Copy, Clone)]
+#[must_use]
+pub enum RentOutcome {
+	/// Exempted from rent iff:
+	/// * rent is offset completely by the `rent_deposit_offset`,
+	/// * or rent has already been paid for this block number,
+	/// * or account doesn't have a contract,
+	/// * or account has a tombstone.
+	Exempted,
+	/// Evicted iff:
+	/// * rent exceed rent allowance,
+	/// * or can't withdraw the rent,
+	/// * or go below subsistence threshold.
+	Evicted,
+	/// The outstanding dues were paid or were able to be paid.
+	Ok,
+}
+
+/// Evict and optionally pay dues (or check account can pay them otherwise) at the current
+/// block number (modulo `handicap`, read on).
+///
+/// `pay_rent` gives an ability to pay or skip paying rent.
+/// `handicap` gives a way to check or pay the rent up to a moment in the past instead
+/// of current block.
+///
+/// NOTE: This function acts eagerly, all modification are committed into the storage.
+fn try_evict_or_and_pay_rent<T: Trait>(
+	account: &T::AccountId,
+	handicap: T::BlockNumber,
+	pay_rent: bool,
+) -> RentOutcome {
+	let contract = match <ContractInfoOf<T>>::get(account) {
+		None | Some(ContractInfo::Tombstone(_)) => return RentOutcome::Exempted,
+		Some(ContractInfo::Alive(contract)) => contract,
+	};
+
+	// How much block has passed since the last deduction for the contract.
+	let blocks_passed = {
+		// Calculate an effective block number, i.e. after adjusting for handicap.
+		let effective_block_number = <system::Module<T>>::block_number().saturating_sub(handicap);
+		let n = effective_block_number.saturating_sub(contract.deduct_block);
+		if n.is_zero() {
+			// Rent has already been paid
+			return RentOutcome::Exempted;
+		}
+		n
+	};
+
+	let balance = T::Currency::free_balance(account);
+
+	// An amount of funds to charge per block for storage taken up by the contract.
+	let fee_per_block = {
+		let free_storage = balance
+			.checked_div(&<Module<T>>::rent_deposit_offset())
+			.unwrap_or(<BalanceOf<T>>::sa(0));
+
+		let effective_storage_size =
+			<BalanceOf<T>>::sa(contract.storage_size).saturating_sub(free_storage);
+
+		effective_storage_size
+			.checked_mul(&<Module<T>>::rent_byte_price())
+			.unwrap_or(<BalanceOf<T>>::max_value())
+	};
+
+	if fee_per_block.is_zero() {
+		// The rent deposit offset reduced the fee to 0. This means that the contract
+		// gets the rent for free.
+		return RentOutcome::Exempted;
+	}
+
+	// The minimal amount of funds required for a contract not to be evicted.
+	let subsistence_threshold = T::Currency::minimum_balance() + <Module<T>>::tombstone_deposit();
+
+	let dues = fee_per_block
+		.checked_mul(&<BalanceOf<T>>::sa(blocks_passed.as_()))
+		.unwrap_or(<BalanceOf<T>>::max_value());
+
+	let dues_limited = dues.min(contract.rent_allowance);
+	let rent_allowance_exceeded = dues > contract.rent_allowance;
+	let is_below_subsistence = balance < subsistence_threshold;
+	let go_below_subsistence = balance.saturating_sub(dues_limited) < subsistence_threshold;
+	let can_withdraw_rent = T::Currency::ensure_can_withdraw(
+		account,
+		dues_limited,
+		WithdrawReason::Fee,
+		balance.saturating_sub(dues_limited),
+	)
+	.is_ok();
+
+	if !rent_allowance_exceeded && can_withdraw_rent && !go_below_subsistence {
+		// Collect dues
+
+		if pay_rent {
+			let imbalance = T::Currency::withdraw(
+				account,
+				dues,
+				WithdrawReason::Fee,
+				ExistenceRequirement::KeepAlive,
+			)
+			.expect(
+				"Withdraw has been checked above;
+				go_below_subsistence is false and subsistence > existencial_deposit;
+				qed",
+			);
+
+			<ContractInfoOf<T>>::mutate(account, |contract| {
+				contract
+					.as_mut()
+					.and_then(|c| c.as_alive_mut())
+					.expect("Dead or inexistent account has been exempt above; qed")
+					.rent_allowance -= imbalance.peek(); // rent_allowance is not exceeded
+			})
+		}
+
+		RentOutcome::Ok
+	} else {
+		// Evict
+
+		if can_withdraw_rent && !go_below_subsistence {
+			T::Currency::withdraw(
+				account,
+				dues,
+				WithdrawReason::Fee,
+				ExistenceRequirement::KeepAlive,
+			)
+			.expect("Can withdraw and don't go below subsistence");
+		} else if !is_below_subsistence {
+			T::Currency::make_free_balance_be(account, subsistence_threshold);
+		} else {
+			T::Currency::make_free_balance_be(account, <BalanceOf<T>>::zero());
+		}
+
+		if !is_below_subsistence {
+			// The contract has funds above subsistence deposit and that means it can afford to
+			// leave tombstone.
+
+			// Note: this operation is heavy.
+			let child_storage_root = runtime_io::child_storage_root(&contract.trie_id);
+
+			let tombstone = TombstoneContractInfo::new(
+				child_storage_root,
+				contract.storage_size,
+				contract.code_hash,
+			);
+			<ContractInfoOf<T>>::insert(account, ContractInfo::Tombstone(tombstone));
+			runtime_io::kill_child_storage(&contract.trie_id);
+		}
+
+		RentOutcome::Evicted
+	}
+}
+
+/// Make account paying the rent for the current block number
+///
+/// NOTE: This function acts eagerly.
+pub fn pay_rent<T: Trait>(account: &T::AccountId) {
+	let _ = try_evict_or_and_pay_rent::<T>(account, Zero::zero(), true);
+}
+
+/// Evict the account if it should be evicted at the given block number.
+///
+/// `handicap` gives a way to check or pay the rent up to a moment in the past instead
+/// of current block. E.g. if the contract is going to be evicted at the current block,
+/// `handicap=1` can defer the eviction for 1 block.
+///
+/// NOTE: This function acts eagerly.
+pub fn try_evict<T: Trait>(account: &T::AccountId, handicap: T::BlockNumber) -> RentOutcome {
+	try_evict_or_and_pay_rent::<T>(account, handicap, false)
+}
@@ -19,27 +19,28 @@

 #![allow(unused)]

-use runtime_io::with_externalities;
-use runtime_primitives::testing::{Digest, DigestItem, H256, Header, UintAuthorityId};
-use runtime_primitives::traits::{BlakeTwo256, IdentityLookup};
-use runtime_primitives::BuildStorage;
-use runtime_io;
-use srml_support::{storage::child, StorageMap, assert_ok, impl_outer_event, impl_outer_dispatch,
-	impl_outer_origin, traits::Currency};
-use substrate_primitives::Blake2Hasher;
-use system::{self, Phase, EventRecord};
-use {wabt, balances, consensus};
-use hex_literal::hex;
-use assert_matches::assert_matches;
+use crate::account_db::{AccountDb, DirectAccountDb, OverlayAccountDb};
 use crate::{
-	ContractAddressFor, GenesisConfig, Module, RawEvent,
-	Trait, ComputeDispatchFee, TrieIdGenerator, TrieId,
-	AccountInfo, AccountInfoOf, TrieIdFromParentCounter
+	ComputeDispatchFee, ContractAddressFor, ContractInfo, ContractInfoOf, GenesisConfig, Module,
+	RawAliveContractInfo, RawEvent, Trait, TrieId, TrieIdFromParentCounter, TrieIdGenerator,
+};
+use assert_matches::assert_matches;
+use hex_literal::*;
+use parity_codec::{Decode, Encode, KeyedVec};
+use runtime_io;
+use runtime_io::with_externalities;
+use runtime_primitives::testing::{Digest, DigestItem, Header, UintAuthorityId, H256};
+use runtime_primitives::traits::{As, BlakeTwo256, IdentityLookup};
+use runtime_primitives::BuildStorage;
+use srml_support::{
+	assert_ok, impl_outer_dispatch, impl_outer_event, impl_outer_origin, storage::child,
+	traits::Currency, StorageMap,
 };
-use substrate_primitives::storage::well_known_keys;
-use parity_codec::{Encode, Decode, KeyedVec};
 use std::sync::atomic::{AtomicUsize, Ordering};
-use crate::account_db::{DirectAccountDb, OverlayAccountDb, AccountDb};
+use substrate_primitives::storage::well_known_keys;
+use substrate_primitives::Blake2Hasher;
+use system::{self, EventRecord, Phase};
+use {balances, consensus, wabt};

 mod contract {
 	// Re-export contents of the root. This basically
@@ -206,8 +207,14 @@ impl ExtBuilder {
 		);
 		t.extend(
 			GenesisConfig::<Test> {
-				transaction_base_fee: 0,
-				transaction_byte_fee: 0,
+				signed_claim_handicap: 2,
+				rent_byte_price: 4,
+				rent_deposit_offset: 10_000,
+				storage_size_offset: 8,
+				surcharge_reward: 150,
+				tombstone_deposit: 16,
+				transaction_base_fee: 2,
+				transaction_byte_fee: 6,
 				transfer_fee: self.transfer_fee,
 				creation_fee: self.creation_fee,
 				contract_fee: 21,
@@ -231,13 +238,7 @@ fn refunds_unused_gas() {
 	with_externalities(&mut ExtBuilder::default().build(), || {
 		Balances::deposit_creating(&0, 100_000_000);

-		assert_ok!(Contract::call(
-			Origin::signed(0),
-			1,
-			0,
-			100_000,
-			Vec::new()
-		));
+		assert_ok!(Contract::call(Origin::signed(0), 1, 0, 100_000, Vec::new()));

 		assert_eq!(Balances::free_balance(&0), 100_000_000 - (2 * 135));
 	});
@@ -256,10 +257,13 @@ fn account_removal_removes_storage() {
 			// Set up two accounts with free balance above the existential threshold.
 			{
 				Balances::deposit_creating(&1, 110);
-				AccountInfoOf::<Test>::insert(1, &AccountInfo {
+				ContractInfoOf::<Test>::insert(1, &ContractInfo::Alive(RawAliveContractInfo {
 					trie_id: trie_id1.clone(),
-					storage_size: 0,
-				});
+					storage_size: Contract::storage_size_offset(),
+					deduct_block: System::block_number(),
+					code_hash: H256::repeat_byte(1),
+					rent_allowance: 40,
+				}));

 				let mut overlay = OverlayAccountDb::<Test>::new(&DirectAccountDb);
 				overlay.set_storage(&1, key1.clone(), Some(b"1".to_vec()));
@@ -267,10 +271,13 @@ fn account_removal_removes_storage() {
 				DirectAccountDb.commit(overlay.into_change_set());

 				Balances::deposit_creating(&2, 110);
-				AccountInfoOf::<Test>::insert(2, &AccountInfo {
+				ContractInfoOf::<Test>::insert(2, &ContractInfo::Alive(RawAliveContractInfo {
 					trie_id: trie_id2.clone(),
-					storage_size: 0,
-				});
+					storage_size: Contract::storage_size_offset(),
+					deduct_block: System::block_number(),
+					code_hash: H256::repeat_byte(2),
+					rent_allowance: 40,
+				}));

 				let mut overlay = OverlayAccountDb::<Test>::new(&DirectAccountDb);
 				overlay.set_storage(&2, key1.clone(), Some(b"3".to_vec()));
@@ -287,7 +294,6 @@ fn account_removal_removes_storage() {
 			// Verify that all entries from account 1 is removed, while
 			// entries from account 2 is in place.
 			{
-				// let a: <Test as system::Trait>::AccountId = 1;
 				assert!(<AccountDb<Test>>::get_storage(&DirectAccountDb, &1, Some(&trie_id1), key1).is_none());
 				assert!(<AccountDb<Test>>::get_storage(&DirectAccountDb, &1, Some(&trie_id1), key2).is_none());

@@ -342,11 +348,7 @@ fn instantiate_and_call_and_deposit_event() {
 		|| {
 			Balances::deposit_creating(&ALICE, 1_000_000);

-			assert_ok!(Contract::put_code(
-				Origin::signed(ALICE),
-				100_000,
-				wasm,
-			));
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));

 			// Check at the end to get hash on error easily
 			let creation = Contract::create(
@@ -387,7 +389,7 @@ fn instantiate_and_call_and_deposit_event() {
 			]);

 			assert_ok!(creation);
-			assert!(AccountInfoOf::<Test>::exists(BOB));
+			assert!(ContractInfoOf::<Test>::exists(BOB));
 		},
 	);
 }
@@ -424,11 +426,7 @@ fn dispatch_call() {
 		|| {
 			Balances::deposit_creating(&ALICE, 1_000_000);

-			assert_ok!(Contract::put_code(
-				Origin::signed(ALICE),
-				100_000,
-				wasm,
-			));
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));

 			// Let's keep this assert even though it's redundant. If you ever need to update the
 			// wasm source this test will fail and will show you the actual hash.
@@ -506,3 +504,399 @@ fn dispatch_call() {
 		},
 	);
 }
+
+const CODE_SET_RENT: &str = r#"
+(module
+	(import "env" "ext_dispatch_call" (func $ext_dispatch_call (param i32 i32)))
+	(import "env" "ext_set_storage" (func $ext_set_storage (param i32 i32 i32 i32)))
+	(import "env" "ext_set_rent_allowance" (func $ext_set_rent_allowance (param i32 i32)))
+	(import "env" "ext_input_size" (func $ext_input_size (result i32)))
+	(import "env" "ext_input_copy" (func $ext_input_copy (param i32 i32 i32)))
+	(import "env" "memory" (memory 1 1))
+
+	;; insert a value of 4 bytes into storage
+	(func $call_0
+		(call $ext_set_storage
+			(i32.const 1)
+			(i32.const 1)
+			(i32.const 0)
+			(i32.const 4)
+		)
+	)
+
+	;; remove the value inserted by call_1
+	(func $call_1
+		(call $ext_set_storage
+			(i32.const 1)
+			(i32.const 0)
+			(i32.const 0)
+			(i32.const 0)
+		)
+	)
+
+	;; transfer 50 to ALICE
+	(func $call_2
+		(call $ext_dispatch_call
+			(i32.const 8)
+			(i32.const 11)
+		)
+	)
+
+	;; do nothing
+	(func $call_else)
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	;; Dispatch the call according to input size
+	(func (export "call")
+		(local $input_size i32)
+		(set_local $input_size
+			(call $ext_input_size)
+		)
+		(block $IF_ELSE
+			(block $IF_2
+				(block $IF_1
+					(block $IF_0
+						(br_table $IF_0 $IF_1 $IF_2 $IF_ELSE
+							(get_local $input_size)
+						)
+						(unreachable)
+					)
+					(call $call_0)
+					return
+				)
+				(call $call_1)
+				return
+			)
+			(call $call_2)
+			return
+		)
+		(call $call_else)
+	)
+
+	;; Set into storage a 4 bytes value
+	;; Set call set_rent_allowance with input
+	(func (export "deploy")
+		(local $input_size i32)
+		(call $ext_set_storage
+			(i32.const 0)
+			(i32.const 1)
+			(i32.const 0)
+			(i32.const 4)
+		)
+		(set_local $input_size
+			(call $ext_input_size)
+		)
+		(call $ext_input_copy
+			(i32.const 0)
+			(i32.const 0)
+			(get_local $input_size)
+		)
+		(call $ext_set_rent_allowance
+			(i32.const 0)
+			(get_local $input_size)
+		)
+	)
+
+	;; Encoding of 10 in balance
+	(data (i32.const 0) "\28")
+
+	;; Encoding of call transfer 50 to CHARLIE
+	(data (i32.const 8) "\00\00\03\00\00\00\00\00\00\00\C8")
+)
+"#;
+const HASH_SET_RENT: [u8; 32] = hex!("a51c2a6f3f68936d4ae9abdb93b28eedcbd0f6f39770e168f9025f0c1e7094ef");
+
+
+/// Input data for each call in set_rent code
+mod call {
+	pub fn set_storage_4_byte() -> Vec<u8> { vec![] }
+	pub fn remove_storage_4_byte() -> Vec<u8> { vec![0] }
+	pub fn transfer() -> Vec<u8> { vec![0, 0] }
+	pub fn null() -> Vec<u8> { vec![0, 0, 0] }
+}
+
+/// Test correspondance of set_rent code and its hash.
+/// Also test that encoded extrinsic in code correspond to the correct transfer
+#[test]
+fn set_rent_hash_and_code() {
+	// This test can fail due to the encoding changes. In case it becomes too annoying
+	// let's rewrite so as we use this module controlled call or we serialize it in runtime.
+	let encoded = parity_codec::Encode::encode(&Call::Balances(balances::Call::transfer(CHARLIE, 50)));
+	assert_eq!(&encoded[..], &hex!("00000300000000000000C8")[..]);
+
+	let wasm = wabt::wat2wasm(CODE_SET_RENT).unwrap();
+
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));
+
+			// If you ever need to update the wasm source this test will fail and will show you the actual hash.
+			assert_eq!(System::events(), vec![
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(0),
+					event: MetaEvent::balances(balances::RawEvent::NewAccount(1, 1_000_000)),
+				},
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(0),
+					event: MetaEvent::contract(RawEvent::CodeStored(HASH_SET_RENT.into())),
+				},
+			]);
+		}
+	);
+}
+
+#[test]
+fn storage_size() {
+	let wasm = wabt::wat2wasm(CODE_SET_RENT).unwrap();
+
+	// Storage size
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				30_000,
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(1_000u64).encode() // rent allowance
+			));
+			let bob_contract = super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap();
+			assert_eq!(bob_contract.storage_size, Contract::storage_size_offset() + 4);
+
+			assert_ok!(Contract::call(Origin::signed(ALICE), BOB, 0, 100_000, call::set_storage_4_byte()));
+			let bob_contract = super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap();
+			assert_eq!(bob_contract.storage_size, Contract::storage_size_offset() + 4 + 4);
+
+			assert_ok!(Contract::call(Origin::signed(ALICE), BOB, 0, 100_000, call::remove_storage_4_byte()));
+			let bob_contract = super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap();
+			assert_eq!(bob_contract.storage_size, Contract::storage_size_offset() + 4);
+		}
+	);
+}
+
+#[test]
+fn deduct_blocks() {
+	let wasm = wabt::wat2wasm(CODE_SET_RENT).unwrap();
+
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				30_000,
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(1_000u64).encode() // rent allowance
+			));
+
+			// Check creation
+			let bob_contract = super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap();
+			assert_eq!(bob_contract.rent_allowance, 1_000);
+
+			// Advance 4 blocks
+			System::initialize(&5, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent through call
+			assert_ok!(Contract::call(Origin::signed(ALICE), BOB, 0, 100_000, call::null()));
+
+			// Check result
+			let rent = (8 + 4 - 3) // storage size = size_offset + deploy_set_storage - deposit_offset
+				* 4 // rent byte price
+				* 4; // blocks to rent
+			let bob_contract = super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap();
+			assert_eq!(bob_contract.rent_allowance, 1_000 - rent);
+			assert_eq!(Balances::free_balance(BOB), 30_000 - rent);
+		}
+	);
+}
+
+#[test]
+fn call_contract_removals() {
+	removals(|| Contract::call(Origin::signed(ALICE), BOB, 0, 100_000, call::null()).is_ok());
+}
+
+#[test]
+fn inherent_claim_surcharge_contract_removals() {
+	removals(|| Contract::claim_surcharge(Origin::INHERENT, BOB, Some(ALICE)).is_ok());
+}
+
+#[test]
+fn signed_claim_surcharge_contract_removals() {
+	removals(|| Contract::claim_surcharge(Origin::signed(ALICE), BOB, None).is_ok());
+}
+
+#[test]
+fn claim_surcharge_malus() {
+	// Test surcharge malus for inherent
+	claim_surcharge(4, || Contract::claim_surcharge(Origin::INHERENT, BOB, Some(ALICE)).is_ok(), true);
+	claim_surcharge(3, || Contract::claim_surcharge(Origin::INHERENT, BOB, Some(ALICE)).is_ok(), true);
+	claim_surcharge(2, || Contract::claim_surcharge(Origin::INHERENT, BOB, Some(ALICE)).is_ok(), true);
+	claim_surcharge(1, || Contract::claim_surcharge(Origin::INHERENT, BOB, Some(ALICE)).is_ok(), false);
+
+	// Test surcharge malus for signed
+	claim_surcharge(4, || Contract::claim_surcharge(Origin::signed(ALICE), BOB, None).is_ok(), true);
+	claim_surcharge(3, || Contract::claim_surcharge(Origin::signed(ALICE), BOB, None).is_ok(), false);
+	claim_surcharge(2, || Contract::claim_surcharge(Origin::signed(ALICE), BOB, None).is_ok(), false);
+	claim_surcharge(1, || Contract::claim_surcharge(Origin::signed(ALICE), BOB, None).is_ok(), false);
+}
+
+/// Claim surcharge with the given trigger_call at the given blocks.
+/// if removes is true then assert that the contract is a tombstonedead
+fn claim_surcharge(blocks: u64, trigger_call: impl Fn() -> bool, removes: bool) {
+	let wasm = wabt::wat2wasm(CODE_SET_RENT).unwrap();
+
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				100,
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(1_000u64).encode() // rent allowance
+			));
+
+			// Advance blocks
+			System::initialize(&blocks, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent through call
+			assert!(trigger_call());
+
+			if removes {
+				assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_tombstone().is_some());
+			} else {
+				assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().is_some());
+			}
+		}
+	);
+}
+
+/// Test for all kind of removals for the given trigger:
+/// * if balance is reached and balance > subsistence threshold
+/// * if allowance is exceeded
+/// * if balance is reached and balance < subsistence threshold
+fn removals(trigger_call: impl Fn() -> bool) {
+	let wasm = wabt::wat2wasm(CODE_SET_RENT).unwrap();
+
+	// Balance reached and superior to subsistence threshold
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm.clone()));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				100,
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(1_000u64).encode() // rent allowance
+			));
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert_eq!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap().rent_allowance, 1_000);
+
+			// Advance blocks
+			System::initialize(&10, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent through call
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_tombstone().is_some());
+
+			// Advance blocks
+			System::initialize(&20, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_tombstone().is_some());
+		}
+	);
+
+	// Allowance exceeded
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm.clone()));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				1_000,
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(100u64).encode() // rent allowance
+			));
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert_eq!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap().rent_allowance, 100);
+
+			// Advance blocks
+			System::initialize(&10, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent through call
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_tombstone().is_some());
+
+			// Advance blocks
+			System::initialize(&20, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_tombstone().is_some());
+		}
+	);
+
+	// Balance reached and inferior to subsistence threshold
+	with_externalities(
+		&mut ExtBuilder::default().existential_deposit(50).build(),
+		|| {
+			// Create
+			Balances::deposit_creating(&ALICE, 1_000_000);
+			assert_ok!(Contract::put_code(Origin::signed(ALICE), 100_000, wasm.clone()));
+			assert_ok!(Contract::create(
+				Origin::signed(ALICE),
+				50+Balances::minimum_balance(),
+				100_000, HASH_SET_RENT.into(),
+				<Test as balances::Trait>::Balance::sa(1_000u64).encode() // rent allowance
+			));
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert_eq!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap().rent_allowance, 1_000);
+
+			// Transfer funds
+			assert_ok!(Contract::call(Origin::signed(ALICE), BOB, 0, 100_000, call::transfer()));
+			assert_eq!(super::ContractInfoOf::<Test>::get(BOB).unwrap().get_alive().unwrap().rent_allowance, 1_000);
+
+			// Advance blocks
+			System::initialize(&10, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent through call
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).is_none());
+
+			// Advance blocks
+			System::initialize(&20, &[0u8; 32].into(), &[0u8; 32].into());
+
+			// Trigger rent must have no effect
+			assert!(trigger_call());
+			assert!(super::ContractInfoOf::<Test>::get(BOB).is_none());
+		}
+	);
+}
@@ -200,6 +200,7 @@ mod tests {
 	#[derive(Default)]
 	pub struct MockExt {
 		storage: HashMap<StorageKey, Vec<u8>>,
+		rent_allowance: u64,
 		creates: Vec<CreateEntry>,
 		transfers: Vec<TransferEntry>,
 		dispatches: Vec<DispatchEntry>,
@@ -281,6 +282,14 @@ mod tests {
 		fn deposit_event(&mut self, data: Vec<u8>) {
 			self.events.push(data)
 		}
+
+		fn set_rent_allowance(&mut self, rent_allowance: u64) {
+			self.rent_allowance = rent_allowance;
+		}
+
+		fn rent_allowance(&self) -> u64 {
+			self.rent_allowance
+		}
 	}

 	fn execute<E: Ext>(
@@ -629,6 +629,31 @@ define_env!(Env, <E: Ext>,
 		Ok(())
 	},

+	// Set rent allowance of the contract
+	//
+	// - value_ptr: a pointer to the buffer with value, how much to allow for rent
+	//   Should be decodable as a `T::Balance`. Traps otherwise.
+	// - value_len: length of the value buffer.
+	ext_set_rent_allowance(ctx, value_ptr: u32, value_len: u32) => {
+		let value = {
+			let value_buf = read_sandbox_memory(ctx, value_ptr, value_len)?;
+			BalanceOf::<<E as Ext>::T>::decode(&mut &value_buf[..])
+				.ok_or_else(|| sandbox::HostError)?
+		};
+		ctx.ext.set_rent_allowance(value);
+
+		Ok(())
+	},
+
+	// Stores the rent allowance into the scratch buffer.
+	//
+	// The data is encoded as T::Balance. The current contents of the scratch buffer are overwritten.
+	ext_rent_allowance(ctx) => {
+		ctx.scratch_buf = ctx.ext.rent_allowance().encode();
+
+		Ok(())
+	},
+
 	// Prints utf8 encoded string from the data buffer.
 	// Only available on `--dev` chains.
 	// This function may be removed at any time, superseded by a more general contract debugging feature.