mocked_host.hpp

// EVMC: Ethereum Client-VM Connector API.
// Copyright 2019 The EVMC Authors.
// Licensed under the Apache License, Version 2.0.
#pragma once

#include <evmc/evmc.hpp>
#include <algorithm>
#include <cassert>
#include <string>
#include <map>
#include <unordered_map>
#include <vector>

namespace evmc
{
/// Extended value (with original value and access flag) for account storage.
struct StorageValue
{
    /// The current storage value.
    bytes32 current;

    /// The original storage value.
    bytes32 original;

    /// Is the storage key cold or warm.
    evmc_access_status access_status = EVMC_ACCESS_COLD;

    /// Default constructor.
    StorageValue() noexcept = default;

    /// Constructor sets the current and original to the same value. Optional access status.
    StorageValue(const bytes32& _value,  // NOLINT(hicpp-explicit-conversions)
                 evmc_access_status _access_status = EVMC_ACCESS_COLD) noexcept
      : current{_value}, original{_value}, access_status{_access_status}
    {}

    /// Constructor with original value and optional access status
    StorageValue(const bytes32& _value,
                 const bytes32& _original,
                 evmc_access_status _access_status = EVMC_ACCESS_COLD) noexcept
      : current{_value}, original{_original}, access_status{_access_status}
    {}
};

/// Mocked account.
struct MockedAccount
{
    /// The account nonce.
    int nonce = 0;

    /// The account code.
    bytes code;

    /// The code hash. Can be a value not related to the actual code.
    bytes32 codehash;

    /// The account balance.
    uint256be balance;

    /// The account storage map.
    std::map<bytes32, StorageValue> storage;

    /// The account transient storage.
    std::unordered_map<bytes32, bytes32> transient_storage;

    /// Helper method for setting balance by numeric type.
    void set_balance(uint64_t x) noexcept
    {
        balance = uint256be{};
        for (std::size_t i = 0; i < sizeof(x); ++i)
            balance.bytes[sizeof(balance) - 1 - i] = static_cast<uint8_t>(x >> (8 * i));
    }
};

/// Mocked EVMC Host implementation.
class MockedHost : public Host
{
public:
    /// LOG record.
    struct log_record
    {
        /// The address of the account which created the log.
        address creator;

        /// The data attached to the log.
        bytes data;

        /// The log topics.
        std::vector<bytes32> topics;

        /// Equal operator.
        bool operator==(const log_record& other) const noexcept
        {
            return creator == other.creator && data == other.data && topics == other.topics;
        }
    };

    /// The set of all accounts in the Host, organized by their addresses.
    std::unordered_map<address, MockedAccount> accounts;

    /// The EVMC transaction context to be returned by get_tx_context().
    evmc_tx_context tx_context = {};

    /// The block header hash value to be returned by get_block_hash().
    bytes32 block_hash = {};

    /// The call result to be returned by the call() method.
    evmc_result call_result = {};

    /// The record of all block numbers for which get_block_hash() was called.
    mutable std::vector<int64_t> recorded_blockhashes;

    /// The record of all account accesses.
    mutable std::vector<address> recorded_account_accesses;

    /// The maximum number of entries in recorded_account_accesses record.
    /// This is arbitrary value useful in fuzzing when we don't want the record to explode.
    static constexpr auto max_recorded_account_accesses = 200;

    /// The record of all call messages requested in the call() method.
    std::vector<evmc_message> recorded_calls;

    /// The maximum number of entries in recorded_calls record.
    /// This is arbitrary value useful in fuzzing when we don't want the record to explode.
    static constexpr auto max_recorded_calls = 100;

    /// The record of all LOGs passed to the emit_log() method.
    std::vector<log_record> recorded_logs;

    /// The record of all SELFDESTRUCTs from the selfdestruct() method
    /// as a map selfdestructed_address => [beneficiary1, beneficiary2, ...].
    std::unordered_map<address, std::vector<address>> recorded_selfdestructs;

private:
    /// The copy of call inputs for the recorded_calls record.
    std::vector<bytes> m_recorded_calls_inputs;

    /// Record an account access.
    /// @param addr  The address of the accessed account.
    void record_account_access(const address& addr) const
    {
        if (recorded_account_accesses.empty())
            recorded_account_accesses.reserve(max_recorded_account_accesses);

        if (recorded_account_accesses.size() < max_recorded_account_accesses)
            recorded_account_accesses.emplace_back(addr);
    }

public:
    /// Returns true if an account exists (EVMC Host method).
    bool account_exists(const address& addr) const noexcept override
    {
        record_account_access(addr);
        return accounts.count(addr) != 0;
    }

    /// Get the account's storage value at the given key (EVMC Host method).
    bytes32 get_storage(const address& addr, const bytes32& key) const noexcept override
    {
        record_account_access(addr);

        const auto account_iter = accounts.find(addr);
        if (account_iter == accounts.end())
            return {};

        const auto storage_iter = account_iter->second.storage.find(key);
        if (storage_iter != account_iter->second.storage.end())
            return storage_iter->second.current;
        return {};
    }

    /// Set the account's storage value (EVMC Host method).
    evmc_storage_status set_storage(const address& addr,
                                    const bytes32& key,
                                    const bytes32& value) noexcept override
    {
        record_account_access(addr);

        // Get the reference to the storage entry value.
        // This will create the account in case it was not present.
        // This is convenient for unit testing and standalone EVM execution to preserve the
        // storage values after the execution terminates.
        auto& s = accounts[addr].storage[key];

        // Follow the EIP-2200 specification as closely as possible.
        // https://eips.ethereum.org/EIPS/eip-2200
        // Warning: this is not the most efficient implementation. The storage status can be
        // figured out by combining only 4 checks:
        // - original != current (dirty)
        // - original == value (restored)
        // - current != 0
        // - value != 0
        const auto status = [&original = s.original, &current = s.current, &value]() {
            // Clause 1 is irrelevant:
            // 1. "If gasleft is less than or equal to gas stipend,
            //    fail the current call frame with ‘out of gas’ exception"

            // 2. "If current value equals new value (this is a no-op)"
            if (current == value)
            {
                // "SLOAD_GAS is deducted"
                return EVMC_STORAGE_ASSIGNED;
            }
            // 3. "If current value does not equal new value"
            else
            {
                // 3.1. "If original value equals current value
                //      (this storage slot has not been changed by the current execution context)"
                if (original == current)
                {
                    // 3.1.1 "If original value is 0"
                    if (is_zero(original))
                    {
                        // "SSTORE_SET_GAS is deducted"
                        return EVMC_STORAGE_ADDED;
                    }
                    // 3.1.2 "Otherwise"
                    else
                    {
                        // "SSTORE_RESET_GAS gas is deducted"
                        auto st = EVMC_STORAGE_MODIFIED;

                        // "If new value is 0"
                        if (is_zero(value))
                        {
                            // "add SSTORE_CLEARS_SCHEDULE gas to refund counter"
                            st = EVMC_STORAGE_DELETED;
                        }

                        return st;
                    }
                }
                // 3.2. "If original value does not equal current value
                //      (this storage slot is dirty),
                //      SLOAD_GAS gas is deducted.
                //      Apply both of the following clauses."
                else
                {
                    // Because we need to apply "both following clauses"
                    // we first collect information which clause is triggered
                    // then assign status code to combination of these clauses.
                    enum
                    {
                        None = 0,
                        RemoveClearsSchedule = 1 << 0,
                        AddClearsSchedule = 1 << 1,
                        RestoredBySet = 1 << 2,
                        RestoredByReset = 1 << 3,
                    };
                    int triggered_clauses = None;

                    // 3.2.1. "If original value is not 0"
                    if (!is_zero(original))
                    {
                        // 3.2.1.1. "If current value is 0"
                        if (is_zero(current))
                        {
                            // "(also means that new value is not 0)"
                            assert(!is_zero(value));
                            // "remove SSTORE_CLEARS_SCHEDULE gas from refund counter"
                            triggered_clauses |= RemoveClearsSchedule;
                        }
                        // 3.2.1.2. "If new value is 0"
                        if (is_zero(value))
                        {
                            // "(also means that current value is not 0)"
                            assert(!is_zero(current));
                            // "add SSTORE_CLEARS_SCHEDULE gas to refund counter"
                            triggered_clauses |= AddClearsSchedule;
                        }
                    }

                    // 3.2.2. "If original value equals new value (this storage slot is reset)"
                    // Except: we use term 'storage slot restored'.
                    if (original == value)
                    {
                        // 3.2.2.1. "If original value is 0"
                        if (is_zero(original))
                        {
                            // "add SSTORE_SET_GAS - SLOAD_GAS to refund counter"
                            triggered_clauses |= RestoredBySet;
                        }
                        // 3.2.2.2. "Otherwise"
                        else
                        {
                            // "add SSTORE_RESET_GAS - SLOAD_GAS gas to refund counter"
                            triggered_clauses |= RestoredByReset;
                        }
                    }

                    switch (triggered_clauses)
                    {
                    case RemoveClearsSchedule:
                        return EVMC_STORAGE_DELETED_ADDED;
                    case AddClearsSchedule:
                        return EVMC_STORAGE_MODIFIED_DELETED;
                    case RemoveClearsSchedule | RestoredByReset:
                        return EVMC_STORAGE_DELETED_RESTORED;
                    case RestoredBySet:
                        return EVMC_STORAGE_ADDED_DELETED;
                    case RestoredByReset:
                        return EVMC_STORAGE_MODIFIED_RESTORED;
                    case None:
                        return EVMC_STORAGE_ASSIGNED;
                    default:
                        assert(false);  // Other combinations are impossible.
                        return evmc_storage_status{};
                    }
                }
            }
        }();

        s.current = value;  // Finally update the current storage value.
        return status;
    }

    /// Get the account's balance (EVMC Host method).
    uint256be get_balance(const address& addr) const noexcept override
    {
        record_account_access(addr);
        const auto it = accounts.find(addr);
        if (it == accounts.end())
            return {};

        return it->second.balance;
    }

    /// Get the account's code size (EVMC host method).
    size_t get_code_size(const address& addr) const noexcept override
    {
        record_account_access(addr);
        const auto it = accounts.find(addr);
        if (it == accounts.end())
            return 0;
        return it->second.code.size();
    }

    /// Get the account's code hash (EVMC host method).
    bytes32 get_code_hash(const address& addr) const noexcept override
    {
        record_account_access(addr);
        const auto it = accounts.find(addr);
        if (it == accounts.end())
            return {};
        return it->second.codehash;
    }

    /// Copy the account's code to the given buffer (EVMC host method).
    size_t copy_code(const address& addr,
                     size_t code_offset,
                     uint8_t* buffer_data,
                     size_t buffer_size) const noexcept override
    {
        record_account_access(addr);
        const auto it = accounts.find(addr);
        if (it == accounts.end())
            return 0;

        const auto& code = it->second.code;

        if (code_offset >= code.size())
            return 0;

        const auto n = std::min(buffer_size, code.size() - code_offset);

        if (n > 0)
            std::copy_n(&code[code_offset], n, buffer_data);
        return n;
    }

    /// Selfdestruct the account (EVMC host method).
    bool selfdestruct(const address& addr, const address& beneficiary) noexcept override
    {
        record_account_access(addr);
        auto& beneficiaries = recorded_selfdestructs[addr];
        beneficiaries.emplace_back(beneficiary);
        return beneficiaries.size() == 1;
    }

    /// Call/create other contract (EVMC host method).
    Result call(const evmc_message& msg) noexcept override
    {
        record_account_access(msg.recipient);

        if (recorded_calls.empty())
        {
            recorded_calls.reserve(max_recorded_calls);
            m_recorded_calls_inputs.reserve(max_recorded_calls);  // Iterators will not invalidate.
        }

        if (recorded_calls.size() < max_recorded_calls)
        {
            recorded_calls.emplace_back(msg);
            auto& call_msg = recorded_calls.back();
            if (call_msg.input_size > 0)
            {
                m_recorded_calls_inputs.emplace_back(call_msg.input_data, call_msg.input_size);
                const auto& input_copy = m_recorded_calls_inputs.back();
                call_msg.input_data = input_copy.data();
            }
        }
        return Result{call_result};
    }

    /// Get transaction context (EVMC host method).
    evmc_tx_context get_tx_context() const noexcept override { return tx_context; }

    /// Get the block header hash (EVMC host method).
    bytes32 get_block_hash(int64_t block_number) const noexcept override
    {
        recorded_blockhashes.emplace_back(block_number);
        return block_hash;
    }

    /// Emit LOG (EVMC host method).
    void emit_log(const address& addr,
                  const uint8_t* data,
                  size_t data_size,
                  const bytes32 topics[],
                  size_t topics_count) noexcept override
    {
        recorded_logs.push_back({addr, {data, data_size}, {topics, topics + topics_count}});
    }

    /// Record an account access.
    ///
    /// This method is required by EIP-2929 introduced in ::EVMC_BERLIN. It will record the account
    /// access in MockedHost::recorded_account_accesses and return previous access status.
    /// This methods returns ::EVMC_ACCESS_WARM for known addresses of precompiles.
    /// The EIP-2929 specifies that evmc_message::sender and evmc_message::recipient are always
    /// ::EVMC_ACCESS_WARM. Therefore, you should init the MockedHost with:
    ///
    ///     mocked_host.access_account(msg.sender);
    ///     mocked_host.access_account(msg.recipient);
    ///
    /// The same way you can mock transaction access list (EIP-2930) for account addresses.
    ///
    /// @param addr  The address of the accessed account.
    /// @returns     The ::EVMC_ACCESS_WARM if the account has been accessed before,
    ///              the ::EVMC_ACCESS_COLD otherwise.
    evmc_access_status access_account(const address& addr) noexcept override
    {
        // Check if the address have been already accessed.
        const auto already_accessed =
            std::find(recorded_account_accesses.begin(), recorded_account_accesses.end(), addr) !=
            recorded_account_accesses.end();

        record_account_access(addr);

        // Accessing precompiled contracts is always warm.
        if (addr >= 0x0000000000000000000000000000000000000001_address &&
            addr <= 0x0000000000000000000000000000000000000009_address)
            return EVMC_ACCESS_WARM;

        return already_accessed ? EVMC_ACCESS_WARM : EVMC_ACCESS_COLD;
    }

    /// Access the account's storage value at the given key.
    ///
    /// This method is required by EIP-2929 introduced in ::EVMC_BERLIN. In records
    /// that the given account's storage key has been access and returns the
    /// previous access status. To mock storage access list (EIP-2930), you can
    /// pre-init account's storage values with the ::EVMC_ACCESS_WARM flag:
    ///
    ///     mocked_host.accounts[msg.recipient].storage[key] = {value,
    ///     EVMC_ACCESS_WARM};
    ///
    /// @param addr  The account address.
    /// @param key   The account's storage key.
    /// @return      The ::EVMC_ACCESS_WARM if the storage key has been accessed before,
    ///              the ::EVMC_ACCESS_COLD otherwise.
    evmc_access_status access_storage(const address& addr, const bytes32& key) noexcept override
    {
        auto& value = accounts[addr].storage[key];
        const auto access_status = value.access_status;
        value.access_status = EVMC_ACCESS_WARM;
        return access_status;
    }

    /// Get account's transient storage.
    ///
    /// @param addr  The account address.
    /// @param key   The account's transient storage key.
    /// @return      The transient storage value. Null value in case the account does not exist.
    bytes32 get_transient_storage(const address& addr, const bytes32& key) const noexcept override
    {
        record_account_access(addr);

        const auto account_iter = accounts.find(addr);
        if (account_iter == accounts.end())
            return {};

        const auto storage_iter = account_iter->second.transient_storage.find(key);
        if (storage_iter != account_iter->second.transient_storage.end())
            return storage_iter->second;
        return {};
    }

    /// Set account's transient storage.
    ///
    /// @param addr   The account address.
    /// @param key    The account's transient storage key.
    /// @param value  The value to be stored.
    void set_transient_storage(const address& addr,
                               const bytes32& key,
                               const bytes32& value) noexcept override
    {
        record_account_access(addr);
        accounts[addr].transient_storage[key] = value;
    }
};
}  // namespace evmc