path: root/core/vm/contract.go

// Copyright 2014 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 vm

import (
    "math/big"

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

// ContractRef is a reference to the contract's backing object
type ContractRef interface {
    ReturnGas(*big.Int, *big.Int)
    Address() common.Address
    SetCode([]byte)
}

// Contract represents an ethereum contract in the state database. It contains
// the the contract code, calling arguments. Contract implements ContractReg
type Contract struct {
    caller ContractRef
    self   ContractRef

    jumpdests destinations // result of JUMPDEST analysis.

    Code     []byte
    Input    []byte
    CodeAddr *common.Address

    value, Gas, UsedGas, Price *big.Int

    Args []byte
}

// Create a new context for the given data items.
func NewContract(caller ContractRef, object ContractRef, value, gas, price *big.Int) *Contract {
    c := &Contract{caller: caller, self: object, Args: nil}

    if parent, ok := caller.(*Contract); ok {
        // Reuse JUMPDEST analysis from parent context if available.
        c.jumpdests = parent.jumpdests
    } else {
        c.jumpdests = make(destinations)
    }

    // Gas should be a pointer so it can safely be reduced through the run
    // This pointer will be off the state transition
    c.Gas = gas //new(big.Int).Set(gas)
    c.value = new(big.Int).Set(value)
    // In most cases price and value are pointers to transaction objects
    // and we don't want the transaction's values to change.
    c.Price = new(big.Int).Set(price)
    c.UsedGas = new(big.Int)

    return c
}

// GetOp returns the n'th element in the contract's byte array
func (c *Contract) GetOp(n uint64) OpCode {
    return OpCode(c.GetByte(n))
}

// GetByte returns the n'th byte in the contract's byte array
func (c *Contract) GetByte(n uint64) byte {
    if n < uint64(len(c.Code)) {
        return c.Code[n]
    }

    return 0
}

// Return returns the given ret argument and returns any remaining gas to the
// caller
func (c *Contract) Return(ret []byte) []byte {
    // Return the remaining gas to the caller
    c.caller.ReturnGas(c.Gas, c.Price)

    return ret
}

// UseGas attempts the use gas and subtracts it and returns true on success
func (c *Contract) UseGas(gas *big.Int) (ok bool) {
    ok = useGas(c.Gas, gas)
    if ok {
        c.UsedGas.Add(c.UsedGas, gas)
    }
    return
}

// ReturnGas adds the given gas back to itself.
func (c *Contract) ReturnGas(gas, price *big.Int) {
    // Return the gas to the context
    c.Gas.Add(c.Gas, gas)
    c.UsedGas.Sub(c.UsedGas, gas)
}

// Address returns the contracts address
func (c *Contract) Address() common.Address {
    return c.self.Address()
}

// SetCode sets the code to the contract
func (self *Contract) SetCode(code []byte) {
    self.Code = code
}

// SetCallCode sets the code of the contract and address of the backing data
// object
func (self *Contract) SetCallCode(addr *common.Address, code []byte) {
    self.Code = code
    self.CodeAddr = addr
}