Fantom-foundation/go-lachesis

// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package evmcore

import (
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/vm"
)

// DummyChain supports retrieving headers and consensus parameters from the
// current blockchain to be used during transaction processing.
type DummyChain interface {
    // GetHeader returns the hash corresponding to their hash.
    GetHeader(common.Hash, uint64) *EvmHeader
}

// NewEVMContext creates a new context for use in the EVM.
func NewEVMContext(msg Message, header *EvmHeader, chain DummyChain, author *common.Address) vm.Context {
    // If we don't have an explicit author (i.e. not mining), extract from the header
    var beneficiary common.Address
    if author == nil {
        beneficiary = header.Coinbase
    } else {
        beneficiary = *author
    }
    return vm.Context{
        CanTransfer: CanTransfer,
        Transfer:    Transfer,
        GetHash:     GetHashFn(header, chain),
        Origin:      msg.From(),
        Coinbase:    beneficiary,
        BlockNumber: new(big.Int).Set(header.Number),
        Time:        new(big.Int).SetUint64(uint64(header.Time.Unix())),
        Difficulty:  big.NewInt(1),
        GasLimit:    header.GasLimit,
        GasPrice:    new(big.Int).Set(msg.GasPrice()),
    }
}

// GetHashFn returns a GetHashFunc which retrieves header hashes by number
func GetHashFn(ref *EvmHeader, chain DummyChain) func(n uint64) common.Hash {
    // Cache will initially contain [refHash.parent],
    // Then fill up with [refHash.p, refHash.pp, refHash.ppp, ...]
    var cache []common.Hash

    return func(n uint64) common.Hash {
        // If there's no hash cache yet, make one
        if len(cache) == 0 {
            cache = append(cache, ref.ParentHash)
        }
        if idx := ref.Number.Uint64() - n - 1; idx < uint64(len(cache)) {
            return cache[idx]
        }
        // No luck in the cache, but we can start iterating from the last element we already know
        lastKnownHash := cache[len(cache)-1]
        lastKnownNumber := ref.Number.Uint64() - uint64(len(cache))

        for {
            header := chain.GetHeader(lastKnownHash, lastKnownNumber)
            if header == nil {
                break
            }
            cache = append(cache, header.ParentHash)
            lastKnownHash = header.ParentHash
            lastKnownNumber = header.Number.Uint64() - 1
            if n == lastKnownNumber {
                return lastKnownHash
            }
        }
        return common.Hash{}
    }
}

// CanTransfer checks whether there are enough funds in the address' account to make a transfer.
// This does not take the necessary gas in to account to make the transfer valid.
func CanTransfer(db vm.StateDB, addr common.Address, amount *big.Int) bool {
    return db.GetBalance(addr).Cmp(amount) >= 0
}

// Transfer subtracts amount from sender and adds amount to recipient using the given Db
func Transfer(db vm.StateDB, sender, recipient common.Address, amount *big.Int) {
    db.SubBalance(sender, amount)
    db.AddBalance(recipient, amount)
}