path: root/core/vm/contract.go

// 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 vm

import (
    "math/big"

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

// ContractRef is a reference to the contract's backing object
type ContractRef interface {
    Address() common.Address
}

// AccountRef implements ContractRef.
//
// Account references are used during EVM initialisation and
// it's primary use is to fetch addresses. Removing this object
// proves difficult because of the cached jump destinations which
// are fetched from the parent contract (i.e. the caller), which
// is a ContractRef.
type AccountRef common.Address

// Address casts AccountRef to a Address
func (ar AccountRef) Address() common.Address { return (common.Address)(ar) }

// Contract represents an ethereum contract in the state database. It contains
// the contract code, calling arguments. Contract implements ContractRef
type Contract struct {
    // CallerAddress is the result of the caller which initialised this
    // contract. However when the "call method" is delegated this value
    // needs to be initialised to that of the caller's caller.
    CallerAddress common.Address
    caller        ContractRef
    self          ContractRef

    jumpdests destinations // result of JUMPDEST analysis.

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

    Gas   uint64
    value *big.Int

    Args []byte

    DelegateCall bool
}

// NewContract returns a new contract environment for the execution of EVM.
func NewContract(caller ContractRef, object ContractRef, value *big.Int, gas uint64) *Contract {
    c := &Contract{CallerAddress: caller.Address(), 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
    // ensures a value is set
    c.value = value

    return c
}

// AsDelegate sets the contract to be a delegate call and returns the current
// contract (for chaining calls)
func (c *Contract) AsDelegate() *Contract {
    c.DelegateCall = true
    // NOTE: caller must, at all times be a contract. It should never happen
    // that caller is something other than a Contract.
    parent := c.caller.(*Contract)
    c.CallerAddress = parent.CallerAddress
    c.value = parent.value

    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
}

// Caller returns the caller of the contract.
//
// Caller will recursively call caller when the contract is a delegate
// call, including that of caller's caller.
func (c *Contract) Caller() common.Address {
    return c.CallerAddress
}

// UseGas attempts the use gas and subtracts it and returns true on success
func (c *Contract) UseGas(gas uint64) (ok bool) {
    if c.Gas < gas {
        return false
    }
    c.Gas -= gas
    return true
}

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

// Value returns the contracts value (sent to it from it's caller)
func (c *Contract) Value() *big.Int {
    return c.value
}

// SetCode sets the code to the contract
func (c *Contract) SetCode(hash common.Hash, code []byte) {
    c.Code = code
    c.CodeHash = hash
}

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