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Contracts: seal0::balance should return the free balance #1254

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42 changes: 42 additions & 0 deletions substrate/frame/contracts/fixtures/balance.wat
Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
(module
(import "seal0" "seal_balance" (func $seal_balance (param i32 i32)))
(import "env" "memory" (memory 1 1))

;; [0, 8) reserved for $seal_balance output

;; [8, 16) length of the buffer for $seal_balance
(data (i32.const 8) "\08")

;; [16, inf) zero initialized

(func $assert (param i32)
(block $ok
(br_if $ok
(get_local 0)
)
(unreachable)
)
)

(func (export "deploy"))

(func (export "call")
(call $seal_balance (i32.const 0) (i32.const 8))

;; Balance should be encoded as a u64.
(call $assert
(i32.eq
(i32.load (i32.const 8))
(i32.const 8)
)
)

;; Assert the free balance to be zero.
(call $assert
(i64.eq
(i64.load (i32.const 0))
(i64.const 0)
)
)
)
)
35 changes: 30 additions & 5 deletions substrate/frame/contracts/fixtures/drain.wat
Original file line number Diff line number Diff line change
@@ -1,14 +1,20 @@
(module
(import "seal0" "seal_balance" (func $seal_balance (param i32 i32)))
(import "seal0" "seal_minimum_balance" (func $seal_minimum_balance (param i32 i32)))
(import "seal0" "seal_transfer" (func $seal_transfer (param i32 i32 i32 i32) (result i32)))
(import "env" "memory" (memory 1 1))

;; [0, 8) reserved for $seal_balance output

;; [8, 16) length of the buffer
;; [8, 16) length of the buffer for $seal_balance
(data (i32.const 8) "\08")

;; [16, inf) zero initialized
;; [16, 24) reserved for $seal_minimum_balance

;; [24, 32) length of the buffer for $seal_minimum_balance
(data (i32.const 24) "\08")

;; [32, inf) zero initialized

(func $assert (param i32)
(block $ok
Expand All @@ -33,13 +39,32 @@
)
)

;; Try to self-destruct by sending full balance to the 0 address.
;; Get the minimum balance.
(call $seal_minimum_balance (i32.const 16) (i32.const 24))

;; Minimum balance should be encoded as a u64.
(call $assert
(i32.eq
(i32.load (i32.const 24))
(i32.const 8)
)
)

;; Make the transferred value exceed the balance by adding the minimum balance.
(i64.store (i32.const 0)
(i64.add
(i64.load (i32.const 0))
(i64.load (i32.const 16))
)
)
Comment on lines +53 to +59
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isn't it simpler not to modify the fixture but to add ED to the transferred balance?

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Hmm, not sure what you mean, this does add the ED to the transferred balance. How would I do that without modifying the fixture?

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@xermicus xermicus Aug 29, 2023

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I mean the fixture is broken, given seal_balance should only return free balance: It tries to send away all free balance but expects the transfer to fail. Which should never fail. Hence we need to modify it anyways.


;; Try to self-destruct by sending more balance to the 0 address.
;; The call will fail because a contract transfer has a keep alive requirement
(call $assert
(i32.eq
(call $seal_transfer
(i32.const 16) ;; Pointer to destination address
(i32.const 32) ;; Length of destination address
(i32.const 32) ;; Pointer to destination address
(i32.const 48) ;; Length of destination address
(i32.const 0) ;; Pointer to the buffer with value to transfer
(i32.const 8) ;; Length of the buffer with value to transfer
)
Expand Down
8 changes: 6 additions & 2 deletions substrate/frame/contracts/src/exec.rs
Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ use frame_support::{
storage::{with_transaction, TransactionOutcome},
traits::{
fungible::{Inspect, Mutate},
tokens::Preservation,
tokens::{Fortitude, Preservation},
Contains, OriginTrait, Randomness, Time,
},
weights::Weight,
Expand Down Expand Up @@ -1368,7 +1368,11 @@ where
}

fn balance(&self) -> BalanceOf<T> {
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@pgherveou pgherveou Aug 29, 2023

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good catch, looks like this is a regression from paritytech/substrate#14020

 	fn balance(&self) -> BalanceOf<T> {
-		T::Currency::free_balance(&self.top_frame().account_id)
+		T::Currency::balance(&self.top_frame().account_id)
 	}

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Those are different traits. On the Currency trait (before) we had free_balance. But on the new trait Inspect it is just balance which also doesn't include holds or freezes.

T::Currency::balance(&self.top_frame().account_id)
T::Currency::reducible_balance(
&self.top_frame().account_id,
Preservation::Preserve,
Fortitude::Polite,
)
}

fn value_transferred(&self) -> BalanceOf<T> {
Expand Down
50 changes: 50 additions & 0 deletions substrate/frame/contracts/src/tests.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5891,3 +5891,53 @@ fn root_cannot_instantiate() {
);
});
}

#[test]
fn balance_api_returns_free_balance() {
let (wasm, _code_hash) = compile_module::<Test>("balance").unwrap();
ExtBuilder::default().existential_deposit(200).build().execute_with(|| {
let _ = <Test as Config>::Currency::set_balance(&ALICE, 1_000_000);

// Instantiate the BOB contract without any extra balance.
let addr = Contracts::bare_instantiate(
ALICE,
0,
GAS_LIMIT,
None,
Code::Upload(wasm.to_vec()),
vec![],
vec![],
DebugInfo::Skip,
CollectEvents::Skip,
)
.result
.unwrap()
.account_id;

let value = 0;
// Call BOB which makes it call the balance runtime API.
// The contract code asserts that the returned balance is 0.
assert_ok!(Contracts::call(
RuntimeOrigin::signed(ALICE),
addr.clone(),
value,
GAS_LIMIT,
None,
vec![]
));

let value = 1;
// Calling with value will trap the contract.
assert_err_ignore_postinfo!(
Contracts::call(
RuntimeOrigin::signed(ALICE),
addr.clone(),
value,
GAS_LIMIT,
None,
vec![]
),
<Error<Test>>::ContractTrapped
);
});
}