path: root/vm/context.go

package vm

import (
    "math"
    "math/big"

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

type ContextRef interface {
    ReturnGas(*big.Int, *big.Int)
    Address() []byte
    SetCode([]byte)
}

type Context struct {
    caller ContextRef
    object ContextRef
    Code   []byte

    Gas, UsedGas, Price *big.Int

    Args []byte
}

// Create a new context for the given data items
func NewContext(caller ContextRef, object ContextRef, code []byte, gas, price *big.Int) *Context {
    c := &Context{caller: caller, object: object, Code: code, Args: nil}

    // 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)
    // 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
}

func (c *Context) GetOp(n uint64) OpCode {
    return OpCode(c.GetByte(n))
}

func (c *Context) GetByte(n uint64) byte {
    if n < uint64(len(c.Code)) {
        return c.Code[n]
    }

    return 0
}

func (c *Context) GetBytes(x, y int) []byte {
    return c.GetRangeValue(uint64(x), uint64(y))
}

func (c *Context) GetRangeValue(x, size uint64) []byte {
    x = uint64(math.Min(float64(x), float64(len(c.Code))))
    y := uint64(math.Min(float64(x+size), float64(len(c.Code))))

    return ethutil.LeftPadBytes(c.Code[x:y], int(size))
}

func (c *Context) GetCode(x, size uint64) []byte {
    x = uint64(math.Min(float64(x), float64(len(c.Code))))
    y := uint64(math.Min(float64(x+size), float64(len(c.Code))))

    return ethutil.RightPadBytes(c.Code[x:y], int(size))
}

func (c *Context) Return(ret []byte) []byte {
    // Return the remaining gas to the caller
    c.caller.ReturnGas(c.Gas, c.Price)

    return ret
}

/*
 * Gas functions
 */
func (c *Context) UseGas(gas *big.Int) bool {
    if c.Gas.Cmp(gas) < 0 {
        return false
    }

    // Sub the amount of gas from the remaining
    c.Gas.Sub(c.Gas, gas)
    c.UsedGas.Add(c.UsedGas, gas)

    return true
}

// Implement the caller interface
func (c *Context) ReturnGas(gas, price *big.Int) {
    // Return the gas to the context
    c.Gas.Add(c.Gas, gas)
    c.UsedGas.Sub(c.UsedGas, gas)
}

/*
 * Set / Get
 */
func (c *Context) Address() []byte {
    return c.object.Address()
}

func (self *Context) SetCode(code []byte) {
    self.Code = code
}