revm_handler/

handler.rs

use crate::{
    evm::FrameTr,
    execution,
    post_execution::{self, build_result_gas},
    pre_execution::{self, apply_eip7702_auth_list},
    validation, EvmTr, FrameResult, ItemOrResult,
};
use context::{
    result::{ExecutionResult, FromStringError},
    LocalContextTr,
};
use context_interface::{
    context::{take_error, ContextError},
    result::{HaltReasonTr, InvalidHeader, InvalidTransaction, ResultGas},
    Cfg, ContextTr, Database, JournalTr, Transaction,
};
use interpreter::{interpreter_action::FrameInit, Gas, InitialAndFloorGas, SharedMemory};
use primitives::U256;

/// Trait for errors that can occur during EVM execution.
///
/// This trait represents the minimal error requirements for EVM execution,
/// ensuring that all necessary error types can be converted into the handler's error type.
pub trait EvmTrError<EVM: EvmTr>:
    From<InvalidTransaction>
    + From<InvalidHeader>
    + From<<<EVM::Context as ContextTr>::Db as Database>::Error>
    + From<ContextError<<<EVM::Context as ContextTr>::Db as Database>::Error>>
    + FromStringError
{
}

impl<
        EVM: EvmTr,
        T: From<InvalidTransaction>
            + From<InvalidHeader>
            + From<<<EVM::Context as ContextTr>::Db as Database>::Error>
            + From<ContextError<<<EVM::Context as ContextTr>::Db as Database>::Error>>
            + FromStringError,
    > EvmTrError<EVM> for T
{
}

/// The main implementation of Ethereum Mainnet transaction execution.
///
/// The [`Handler::run`] method serves as the entry point for execution and provides
/// out-of-the-box support for executing Ethereum mainnet transactions.
///
/// This trait allows EVM variants to customize execution logic by implementing
/// their own method implementations.
///
/// The handler logic consists of four phases:
///   * Validation - Validates tx/block/config fields and loads caller account and validates initial gas requirements and
///     balance checks.
///   * Pre-execution - Loads and warms accounts, deducts initial gas
///   * Execution - Executes the main frame loop, delegating to [`EvmTr`] for creating and running call frames.
///   * Post-execution - Calculates final refunds, validates gas floor, reimburses caller,
///     and rewards beneficiary
///
///
/// The [`Handler::catch_error`] method handles cleanup of intermediate state if an error
/// occurs during execution.
///
/// # Returns
///
/// Returns execution status, error, gas spend and logs. State change is not returned and it is
/// contained inside Context Journal. This setup allows multiple transactions to be chain executed.
///
/// To finalize the execution and obtain changed state, call [`JournalTr::finalize`] function.
pub trait Handler {
    /// The EVM type containing Context, Instruction, and Precompiles implementations.
    type Evm: EvmTr<
        Context: ContextTr<Journal: JournalTr, Local: LocalContextTr>,
        Frame: FrameTr<FrameInit = FrameInit, FrameResult = FrameResult>,
    >;
    /// The error type returned by this handler.
    type Error: EvmTrError<Self::Evm>;
    /// The halt reason type included in the output
    type HaltReason: HaltReasonTr;

    /// The main entry point for transaction execution.
    ///
    /// This method calls [`Handler::run_without_catch_error`] and if it returns an error,
    /// calls [`Handler::catch_error`] to handle the error and cleanup.
    ///
    /// The [`Handler::catch_error`] method ensures intermediate state is properly cleared.
    ///
    /// # Error handling
    ///
    /// In case of error, the journal can be in an inconsistent state and should be cleared by calling
    /// [`JournalTr::discard_tx`] method or dropped.
    ///
    /// # Returns
    ///
    /// Returns execution result, error, gas spend and logs.
    #[inline]
    fn run(
        &mut self,
        evm: &mut Self::Evm,
    ) -> Result<ExecutionResult<Self::HaltReason>, Self::Error> {
        // Run inner handler and catch all errors to handle cleanup.
        match self.run_without_catch_error(evm) {
            Ok(output) => Ok(output),
            Err(e) => self.catch_error(evm, e),
        }
    }

    /// Runs the system call.
    ///
    /// System call is a special transaction where caller is a [`crate::SYSTEM_ADDRESS`]
    ///
    /// It is used to call a system contracts and it skips all the `validation` and `pre-execution` and most of `post-execution` phases.
    /// For example it will not deduct the caller or reward the beneficiary.
    ///
    /// State changs can be obtained by calling [`JournalTr::finalize`] method from the [`EvmTr::Context`].
    ///
    /// # Error handling
    ///
    /// By design system call should not fail and should always succeed.
    /// In case of an error (If fetching account/storage on rpc fails), the journal can be in an inconsistent
    /// state and should be cleared by calling [`JournalTr::discard_tx`] method or dropped.
    #[inline]
    fn run_system_call(
        &mut self,
        evm: &mut Self::Evm,
    ) -> Result<ExecutionResult<Self::HaltReason>, Self::Error> {
        // dummy values that are not used.
        let init_and_floor_gas = InitialAndFloorGas::new(0, 0);
        // call execution and than output.
        match self
            .execution(evm, &init_and_floor_gas)
            .and_then(|exec_result| {
                // System calls have no intrinsic gas; build ResultGas from frame result.
                let gas = exec_result.gas();
                let result_gas = build_result_gas(gas, init_and_floor_gas);
                self.execution_result(evm, exec_result, result_gas)
            }) {
            out @ Ok(_) => out,
            Err(e) => self.catch_error(evm, e),
        }
    }

    /// Called by [`Handler::run`] to execute the core handler logic.
    ///
    /// Executes the four phases in sequence: [Handler::validate],
    /// [Handler::pre_execution], [Handler::execution], [Handler::post_execution].
    ///
    /// Returns any errors without catching them or calling [`Handler::catch_error`].
    #[inline]
    fn run_without_catch_error(
        &mut self,
        evm: &mut Self::Evm,
    ) -> Result<ExecutionResult<Self::HaltReason>, Self::Error> {
        let mut init_and_floor_gas = self.validate(evm)?;
        let eip7702_refund = self.pre_execution(evm, &mut init_and_floor_gas)?;
        // Regular refund is returned from pre_execution after state gas split is applied
        let eip7702_regular_refund = eip7702_refund as i64;

        let mut exec_result = self.execution(evm, &init_and_floor_gas)?;
        let result_gas = self.post_execution(
            evm,
            &mut exec_result,
            init_and_floor_gas,
            eip7702_regular_refund,
        )?;

        // Prepare the output
        self.execution_result(evm, exec_result, result_gas)
    }

    /// Validates the execution environment and transaction parameters.
    ///
    /// Calculates initial and floor gas requirements and verifies they are covered by the gas limit.
    ///
    /// Validation against state is done later in pre-execution phase in deduct_caller function.
    #[inline]
    fn validate(&self, evm: &mut Self::Evm) -> Result<InitialAndFloorGas, Self::Error> {
        self.validate_env(evm)?;
        self.validate_initial_tx_gas(evm)
    }

    /// Prepares the EVM state for execution.
    ///
    /// Loads the beneficiary account (EIP-3651: Warm COINBASE) and all accounts/storage from the access list (EIP-2929).
    ///
    /// Deducts the maximum possible fee from the caller's balance.
    ///
    /// For EIP-7702 transactions, applies the authorization list and delegates successful authorizations.
    /// Returns the gas refund amount from EIP-7702. Authorizations are applied before execution begins.
    #[inline]
    fn pre_execution(
        &self,
        evm: &mut Self::Evm,
        init_and_floor_gas: &mut InitialAndFloorGas,
    ) -> Result<u64, Self::Error> {
        self.validate_against_state_and_deduct_caller(evm)?;
        self.load_accounts(evm)?;

        let gas = self.apply_eip7702_auth_list(evm, init_and_floor_gas)?;
        Ok(gas)
    }

    /// Creates and executes the initial frame, then processes the execution loop.
    ///
    /// Always calls [Handler::last_frame_result] to handle returned gas from the call.
    #[inline]
    fn execution(
        &mut self,
        evm: &mut Self::Evm,
        init_and_floor_gas: &InitialAndFloorGas,
    ) -> Result<FrameResult, Self::Error> {
        // Deduct regular initial gas from the transaction gas limit.
        // State gas is handled separately via the reservoir.
        let gas_limit = evm.ctx().tx().gas_limit() - init_and_floor_gas.initial_regular_gas();
        // Create first frame action
        // Note: first_frame_input now handles state gas deduction from the reservoir
        let first_frame_input = self.first_frame_input(evm, gas_limit, init_and_floor_gas)?;

        // Run execution loop
        let mut frame_result = self.run_exec_loop(evm, first_frame_input)?;

        // Handle last frame result
        self.last_frame_result(evm, &mut frame_result)?;
        Ok(frame_result)
    }

    /// Handles the final steps of transaction execution.
    ///
    /// Calculates final refunds and validates the gas floor (EIP-7623) to ensure minimum gas is spent.
    /// After EIP-7623, at least floor gas must be consumed.
    ///
    /// Reimburses unused gas to the caller and rewards the beneficiary with transaction fees.
    /// The effective gas price determines rewards, with the base fee being burned.
    ///
    /// Finally, finalizes output by returning the journal state and clearing internal state
    /// for the next execution.
    #[inline]
    fn post_execution(
        &self,
        evm: &mut Self::Evm,
        exec_result: &mut FrameResult,
        init_and_floor_gas: InitialAndFloorGas,
        eip7702_gas_refund: i64,
    ) -> Result<ResultGas, Self::Error> {
        // Calculate final refund and add EIP-7702 refund to gas.
        self.refund(evm, exec_result, eip7702_gas_refund);

        // Build ResultGas from the final gas state
        // This includes all necessary fields and gas values.
        let result_gas = post_execution::build_result_gas(exec_result.gas(), init_and_floor_gas);

        // Ensure gas floor is met and minimum floor gas is spent.
        // if `cfg.is_eip7623_disabled` is true, floor gas will be set to zero
        self.eip7623_check_gas_floor(evm, exec_result, init_and_floor_gas);
        // Return unused gas to caller
        self.reimburse_caller(evm, exec_result)?;
        // Pay transaction fees to beneficiary
        self.reward_beneficiary(evm, exec_result)?;
        // Build ResultGas from the final gas state
        Ok(result_gas)
    }

    /* VALIDATION */

    /// Validates block, transaction and configuration fields.
    ///
    /// Performs all validation checks that can be done without loading state.
    /// For example, verifies transaction gas limit is below block gas limit.
    #[inline]
    fn validate_env(&self, evm: &mut Self::Evm) -> Result<(), Self::Error> {
        validation::validate_env(evm.ctx())
    }

    /// Calculates initial gas costs based on transaction type and input data.
    ///
    /// Includes additional costs for access list and authorization list.
    ///
    /// Verifies the initial cost does not exceed the transaction gas limit.
    #[inline]
    fn validate_initial_tx_gas(
        &self,
        evm: &mut Self::Evm,
    ) -> Result<InitialAndFloorGas, Self::Error> {
        let ctx = evm.ctx_ref();
        let gas = validation::validate_initial_tx_gas(
            ctx.tx(),
            ctx.cfg().spec().into(),
            ctx.cfg().is_eip7623_disabled(),
            ctx.cfg().is_amsterdam_eip8037_enabled(),
            ctx.cfg().tx_gas_limit_cap(),
        )?;

        Ok(gas)
    }

    /* PRE EXECUTION */

    /// Loads access list and beneficiary account, marking them as warm in the [`context::Journal`].
    #[inline]
    fn load_accounts(&self, evm: &mut Self::Evm) -> Result<(), Self::Error> {
        pre_execution::load_accounts(evm)
    }

    /// Processes the authorization list, validating authority signatures, nonces and chain IDs.
    /// Applies valid authorizations to accounts.
    ///
    /// Returns the gas refund amount specified by EIP-7702.
    #[inline]
    fn apply_eip7702_auth_list(
        &self,
        evm: &mut Self::Evm,
        init_and_floor_gas: &mut InitialAndFloorGas,
    ) -> Result<u64, Self::Error> {
        apply_eip7702_auth_list(evm.ctx_mut(), init_and_floor_gas)
    }

    /// Deducts the maximum possible fee from caller's balance.
    ///
    /// If cfg.is_balance_check_disabled, this method will add back enough funds to ensure that
    /// the caller's balance is at least tx.value() before returning. Note that the amount of funds
    /// added back in this case may exceed the maximum fee.
    ///
    /// Unused fees are returned to caller after execution completes.
    #[inline]
    fn validate_against_state_and_deduct_caller(
        &self,
        evm: &mut Self::Evm,
    ) -> Result<(), Self::Error> {
        pre_execution::validate_against_state_and_deduct_caller(evm.ctx())
    }

    /* EXECUTION */

    /// Creates initial frame input using transaction parameters, gas limit and configuration.
    #[inline]
    fn first_frame_input(
        &mut self,
        evm: &mut Self::Evm,
        mut gas_limit: u64,
        init_and_floor_gas: &InitialAndFloorGas,
    ) -> Result<FrameInit, Self::Error> {
        let ctx = evm.ctx_mut();
        let mut memory = SharedMemory::new_with_buffer(ctx.local().shared_memory_buffer().clone());
        memory.set_memory_limit(ctx.cfg().memory_limit());

        // For the first frame, determine the reservoir and cap gas_limit to the regular gas budget.
        //
        // EIP-8037 reservoir model:
        //   execution_gas = tx.gas_limit - intrinsic_gas  (= gas_limit parameter)
        //   regular_gas_budget = min(execution_gas, TX_MAX_GAS_LIMIT - intrinsic_gas)
        //   reservoir = execution_gas - regular_gas_budget
        //
        // On mainnet (state gas disabled), reservoir = 0 and gas_limit is unchanged.
        let execution_gas = gas_limit;
        // System calls pass init_and_floor_gas with all zeros and should not be
        // subject to the TX_MAX_GAS_LIMIT cap.
        let regular_gas_cap = if init_and_floor_gas.initial_total_gas == 0 {
            u64::MAX
        } else if ctx.cfg().is_amsterdam_eip8037_enabled() {
            ctx.cfg()
                .tx_gas_limit_cap()
                .saturating_sub(init_and_floor_gas.initial_regular_gas())
        } else {
            ctx.cfg().tx_gas_limit_cap()
        };
        gas_limit = core::cmp::min(gas_limit, regular_gas_cap);
        let reservoir_remaining_gas = execution_gas - gas_limit;

        let mut frame_input = execution::create_init_frame(ctx, gas_limit)?;
        frame_input.set_reservoir(reservoir_remaining_gas);

        // Deduct initial state gas from the reservoir. When the reservoir is
        // insufficient (e.g. gas_limit < TX_MAX_GAS_LIMIT), the deficit is
        // charged from the regular gas budget (reducing frame gas_limit).
        let initial_state_gas = init_and_floor_gas.initial_state_gas;
        if initial_state_gas > 0 {
            let reservoir = frame_input.reservoir();
            if reservoir >= initial_state_gas {
                frame_input.set_reservoir(reservoir - initial_state_gas);
            } else {
                let deficit = initial_state_gas - reservoir;
                frame_input.set_reservoir(0);
                frame_input.reduce_gas_limit(deficit);
            }
        }

        // EIP-7702 state gas refund for existing authorities goes directly to
        // the reservoir. In the Python spec, set_delegation adds this refund to
        // state_gas_reservoir so it stays as state gas (not regular gas).
        let eip7702_refund = init_and_floor_gas.eip7702_reservoir_refund;
        if eip7702_refund > 0 {
            frame_input.set_reservoir(frame_input.reservoir() + eip7702_refund);
        }

        Ok(FrameInit {
            depth: 0,
            memory,
            frame_input,
        })
    }

    /// Processes the result of the initial call and handles returned gas.
    #[inline]
    fn last_frame_result(
        &mut self,
        evm: &mut Self::Evm,
        frame_result: &mut <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
    ) -> Result<(), Self::Error> {
        let instruction_result = frame_result.interpreter_result().result;
        let gas = frame_result.gas_mut();
        let remaining = gas.remaining();
        let refunded = gas.refunded();
        let reservoir = gas.reservoir();
        let state_gas_spent = gas.state_gas_spent();

        // Spend the gas limit. Gas is reimbursed when the tx returns successfully.
        *gas = Gas::new_spent(evm.ctx().tx().gas_limit());

        if instruction_result.is_ok_or_revert() {
            // Return unused regular gas. Reservoir is handled separately via state_gas_spent.
            gas.erase_cost(remaining);
        }

        if instruction_result.is_ok() {
            gas.record_refund(refunded);
        }

        // Reservoir handling at the top-level frame:
        // - On success: use the frame's final reservoir as-is, state gas was consumed.
        // - On revert/halt: restore state gas spent back to the reservoir,
        //   because state changes are rolled back so state gas should be refunded.
        //
        // Note: eth devnet3 does NOT do this — it ignores state_gas_spent and
        // unconditionally sets gas.set_reservoir(reservoir) regardless of the
        // instruction_result kind. This is a bug in the devnet3 spec.
        if instruction_result.is_ok() {
            gas.set_state_gas_spent(state_gas_spent);
            gas.set_reservoir(reservoir);
        } else {
            // State changes rolled back, so no execution state gas was consumed.
            gas.set_state_gas_spent(0);
            gas.set_reservoir(reservoir + state_gas_spent);
        }

        Ok(())
    }

    /* FRAMES */

    /// Executes the main frame processing loop.
    ///
    /// This loop manages the frame stack, processing each frame until execution completes.
    /// For each iteration:
    /// 1. Calls the current frame
    /// 2. Handles the returned frame input or result
    /// 3. Creates new frames or propagates results as needed
    #[inline]
    fn run_exec_loop(
        &mut self,
        evm: &mut Self::Evm,
        first_frame_input: <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameInit,
    ) -> Result<FrameResult, Self::Error> {
        let res = evm.frame_init(first_frame_input)?;

        if let ItemOrResult::Result(frame_result) = res {
            return Ok(frame_result);
        }

        loop {
            let call_or_result = evm.frame_run()?;

            let result = match call_or_result {
                ItemOrResult::Item(init) => {
                    match evm.frame_init(init)? {
                        ItemOrResult::Item(_) => {
                            continue;
                        }
                        // Do not pop the frame since no new frame was created
                        ItemOrResult::Result(result) => result,
                    }
                }
                ItemOrResult::Result(result) => result,
            };

            if let Some(result) = evm.frame_return_result(result)? {
                return Ok(result);
            }
        }
    }

    /* POST EXECUTION */

    /// Validates that the minimum gas floor requirements are satisfied.
    ///
    /// Ensures that at least the floor gas amount has been consumed during execution.
    #[inline]
    fn eip7623_check_gas_floor(
        &self,
        _evm: &mut Self::Evm,
        exec_result: &mut <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
        init_and_floor_gas: InitialAndFloorGas,
    ) {
        post_execution::eip7623_check_gas_floor(exec_result.gas_mut(), init_and_floor_gas)
    }

    /// Calculates the final gas refund amount, including any EIP-7702 refunds.
    #[inline]
    fn refund(
        &self,
        evm: &mut Self::Evm,
        exec_result: &mut <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
        eip7702_refund: i64,
    ) {
        let spec = evm.ctx().cfg().spec().into();
        post_execution::refund(spec, exec_result.gas_mut(), eip7702_refund)
    }

    /// Returns unused gas costs to the transaction sender's account.
    #[inline]
    fn reimburse_caller(
        &self,
        evm: &mut Self::Evm,
        exec_result: &mut <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
    ) -> Result<(), Self::Error> {
        post_execution::reimburse_caller(evm.ctx(), exec_result.gas(), U256::ZERO)
            .map_err(From::from)
    }

    /// Transfers transaction fees to the block beneficiary's account.
    #[inline]
    fn reward_beneficiary(
        &self,
        evm: &mut Self::Evm,
        exec_result: &mut <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
    ) -> Result<(), Self::Error> {
        post_execution::reward_beneficiary(evm.ctx(), exec_result.gas()).map_err(From::from)
    }

    /// Processes the final execution output.
    ///
    /// This method, retrieves the final state from the journal, converts internal results to the external output format.
    /// Internal state is cleared and EVM is prepared for the next transaction.
    #[inline]
    fn execution_result(
        &mut self,
        evm: &mut Self::Evm,
        result: <<Self::Evm as EvmTr>::Frame as FrameTr>::FrameResult,
        result_gas: ResultGas,
    ) -> Result<ExecutionResult<Self::HaltReason>, Self::Error> {
        take_error::<Self::Error, _>(evm.ctx().error())?;

        let exec_result = post_execution::output(evm.ctx(), result, result_gas);

        // commit transaction
        evm.ctx().journal_mut().commit_tx();
        evm.ctx().local_mut().clear();
        evm.frame_stack().clear();

        Ok(exec_result)
    }

    /// Handles cleanup when an error occurs during execution.
    ///
    /// Ensures the journal state is properly cleared before propagating the error.
    /// On happy path journal is cleared in [`Handler::execution_result`] method.
    #[inline]
    fn catch_error(
        &self,
        evm: &mut Self::Evm,
        error: Self::Error,
    ) -> Result<ExecutionResult<Self::HaltReason>, Self::Error> {
        // clean up local context. Initcode cache needs to be discarded.
        evm.ctx().local_mut().clear();
        evm.ctx().journal_mut().discard_tx();
        evm.frame_stack().clear();
        Err(error)
    }
}