Europa debugging example

Duplicate topics#

checkout ink! to commit 8e8fe09565ca6d2fad7701d68ff13f12deda7eed.

$ cd ink$ git checkout 8e8fe09565ca6d2fad7701d68ff13f12deda7eed -b tmp

Change the value to 0_u128 in the Transfer event under ink/examples/erc20/lib.rs:L90.

#[ink(constructor)]pub fn new(initial_supply: Balance) -> Self {     //...     Self::env().emit_event(Transfer {        from: None,        to: Some(caller),        // change this from `initial_supply` to `0_u128`        value: 0_u128.into() // initial_supply,     });     instance}

Execute cargo +nightly contract build --debug to compile the contract.
Use Redspot or Polkadot/Substrate Portal to deploy the contract.

Note erc20.wasm must be used here instead of erc20-opt.wasm, otherwise the wasm backtrace cannot be printed normally.

During the deployment process, you will encounter DuplicateTopics and the Europa log looks like:

1: NestedRuntime {    #...    env_trace: [        seal_input(Some(0xd183512b0)),        #...            seal_deposit_event((Some([0x45726332303a3a5472616e736....]), None)),    ],    trap_reason: TrapReason::SupervisorError(DispatchError::Module { index: 5, error: 23, message: Some("DuplicateTopics") }),    wasm_error: Error::WasmiExecution(Trap(Trap { kind: Host(DummyHostError) }))        wasm backtrace:         |  ink_env::engine::on_chain::ext::deposit_event[1623]        |  ink_env::engine::on_chain::impls::<impl ink_env::backend::TypedEnvBackend for ink_env::engine::on_chain::EnvInstance>::emit_event[1564]        |  ink_env::api::emit_event::{{closure}}[1563]        |  <ink_env::engine::on_chain::EnvInstance as ink_env::engine::OnInstance>::on_instance[1562]        |  ink_env::api::emit_event[1561]        |  erc20::erc20::_::<impl ink_lang::events::EmitEvent<erc20::erc20::Erc20> for ink_lang::env_access::EnvAccess<<erc20::erc20::Erc20 as ink_lang::env_access::ContractEnv>::Env>>::emit_event[1685]        # ...        # ...        |  deploy[1691]        ╰─><unknown>[2385]    ,    nest: [],}

The last record in env_trace is seal_deposit_event, not seal_return. If the contract is executed normally, the last record should be seal_return.
The second parameter of seal_deposit_event is None, which means that the host_function is not executed normally. For more details, please refer to the relevant implementation.
Combined with wasm backtrace, you can see that the top of the stack is deposit_event.

In summary, it can be concluded that the error occurred in the host_function of seal_deposit_event.

Inconsistent balance types#

Assuming that the balance on the chain is defined as u64, and the balance in ink! is defined as u128, an ordinary erc20 contract is deployed.

When reading total_supply, the log content in Europa looks like:

1: NestedRuntime {    ext_result: [failed] ExecError { error: DispatchError::Module { index: 5, error: 17, message: Some("ContractTrapped") }, origin: ErrorOrigin::Caller },    caller: 0000000000000000000000000000000000000000000000000000000000000000 (5C4hrfjw...),    self_account: 2fe715301c9609c0c5ab75b24f2d8ad7dbe9671d7aebfeed80ed8963bc017955 (5D9Wkfa3...),    selector: 0xdb6375a8,    args: None,    value: 0,    gas_limit: 4999999999999,    gas_left: 4999865113466,    env_trace: [        seal_value_transferred(Some(0x0000000000000000)),    ],    wasm_error: Error::WasmiExecution(Trap(Trap { kind: Unreachable }))            wasm backtrace:            |  core::panicking::panic_fmt.48[1956]            |  core::result::unwrap_failed[1057]            |  core::result::Result<T,E>::expect[1060]            |  ink_lang::dispatcher::deny_payment[1878]            |  call[1906]            ╰─><unknown>[2614]    ,    nest: [],}

When calling tranfer, the log in Europa looks like:

1: NestedRuntime {    ext_result: [failed] ExecError { error: DispatchError::Module { index: 5, error: 17, message: Some("ContractTrapped") }, origin: ErrorOrigin::Caller },    caller: 0000000000000000000000000000000000000000000000000000000000000000 (5C4hrfjw...),    self_account: 2fe715301c9609c0c5ab75b24f2d8ad7dbe9671d7aebfeed80ed8963bc017955 (5D9Wkfa3...),    selector: 0xdb6375a8,    args: None,    value: 0,    gas_limit: 4999999999999,    gas_left: 4999865113466,    env_trace: [        seal_value_transferred(Some(0x0000000000000000)),    ],    wasm_error: Error::WasmiExecution(Trap(Trap { kind: Unreachable }))            wasm backtrace:            |  core::panicking::panic_fmt.48[1956]            |  core::result::unwrap_failed[1057]            |  core::result::Result<T,E>::expect[1060]            |  ink_lang::dispatcher::deny_payment[1878]            |  call[1906]            ╰─><unknown>[2614]    ,    nest: [],}

It can be found that whether it is a read operation or a write operation, there will be a call -> deny_payment -> expect call process. The reason is that in ink!, there are the following codes.

#[no_mangle]fn call() -> u32 {    if true {     ::ink_lang::deny_payment::<<Erc20 as ::ink_lang::ContractEnv>::Env>()                    .expect("caller transferred value even though all ink! message deny payments")    }    ::ink_lang::DispatchRetCode::from(        <Erc20 as ::ink_lang::DispatchUsingMode>::dispatch_using_mode(            ::ink_lang::DispatchMode::Call,        ),    )    .to_u32()}pub fn deny_payment<E>() -> Result<()>where    E: Environment,{    let transferred = ink_env::transferred_balance::<E>()        .expect("encountered error while querying transferred balance");    if transferred != <E as Environment>::Balance::from(0u32) {        return Err(DispatchError::PaidUnpayableMessage)    }    Ok(())}

In ink!, the timing of expect is different for off_chain and on_chain. In off_chain, it is because ink_env::transferred_balance::<E>() cannot be decoded correctly. In on_chain,deny_payment returns Error due totransferred!=0, and expect appears in call.It can be seen that the current ink! in off_chain and on_chain is not exactly the same for some situations, causing debugging troubles.