aboutsummaryrefslogtreecommitdiffstats
path: root/core/state_transition.go
blob: 6acc78479393126f17d5ae825c87fa2b4501e08a (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
// 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 core

import (
    "errors"
    "math/big"

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

var (
    Big0                         = big.NewInt(0)
    errInsufficientBalanceForGas = errors.New("insufficient balance to pay for gas")
)

/*
The State Transitioning Model

A state transition is a change made when a transaction is applied to the current world state
The state transitioning model does all all the necessary work to work out a valid new state root.

1) Nonce handling
2) Pre pay gas
3) Create a new state object if the recipient is \0*32
4) Value transfer
== If contract creation ==
  4a) Attempt to run transaction data
  4b) If valid, use result as code for the new state object
== end ==
5) Run Script section
6) Derive new state root
*/
type StateTransition struct {
    gp         *GasPool
    msg        Message
    gas        uint64
    gasPrice   *big.Int
    initialGas *big.Int
    value      *big.Int
    data       []byte
    state      vm.StateDB

    evm *vm.EVM
}

// Message represents a message sent to a contract.
type Message interface {
    From() common.Address
    //FromFrontier() (common.Address, error)
    To() *common.Address

    GasPrice() *big.Int
    Gas() *big.Int
    Value() *big.Int

    Nonce() uint64
    CheckNonce() bool
    Data() []byte
}

func MessageCreatesContract(msg Message) bool {
    return msg.To() == nil
}

// IntrinsicGas computes the 'intrinsic gas' for a message
// with the given data.
//
// TODO convert to uint64
func IntrinsicGas(data []byte, contractCreation, homestead bool) *big.Int {
    igas := new(big.Int)
    if contractCreation && homestead {
        igas.SetUint64(params.TxGasContractCreation)
    } else {
        igas.SetUint64(params.TxGas)
    }
    if len(data) > 0 {
        var nz int64
        for _, byt := range data {
            if byt != 0 {
                nz++
            }
        }
        m := big.NewInt(nz)
        m.Mul(m, new(big.Int).SetUint64(params.TxDataNonZeroGas))
        igas.Add(igas, m)
        m.SetInt64(int64(len(data)) - nz)
        m.Mul(m, new(big.Int).SetUint64(params.TxDataZeroGas))
        igas.Add(igas, m)
    }
    return igas
}

// NewStateTransition initialises and returns a new state transition object.
func NewStateTransition(evm *vm.EVM, msg Message, gp *GasPool) *StateTransition {
    return &StateTransition{
        gp:         gp,
        evm:        evm,
        msg:        msg,
        gasPrice:   msg.GasPrice(),
        initialGas: new(big.Int),
        value:      msg.Value(),
        data:       msg.Data(),
        state:      evm.StateDB,
    }
}

// ApplyMessage computes the new state by applying the given message
// against the old state within the environment.
//
// ApplyMessage returns the bytes returned by any EVM execution (if it took place),
// the gas used (which includes gas refunds) and an error if it failed. An error always
// indicates a core error meaning that the message would always fail for that particular
// state and would never be accepted within a block.
func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, *big.Int, error) {
    st := NewStateTransition(evm, msg, gp)

    ret, _, gasUsed, err := st.TransitionDb()
    return ret, gasUsed, err
}

func (self *StateTransition) from() vm.AccountRef {
    f := self.msg.From()
    if !self.state.Exist(f) {
        self.state.CreateAccount(f)
    }
    return vm.AccountRef(f)
}

func (self *StateTransition) to() vm.AccountRef {
    if self.msg == nil {
        return vm.AccountRef{}
    }
    to := self.msg.To()
    if to == nil {
        return vm.AccountRef{} // contract creation
    }

    reference := vm.AccountRef(*to)
    if !self.state.Exist(*to) {
        self.state.CreateAccount(*to)
    }
    return reference
}

func (self *StateTransition) useGas(amount uint64) error {
    if self.gas < amount {
        return vm.ErrOutOfGas
    }
    self.gas -= amount

    return nil
}

func (self *StateTransition) buyGas() error {
    mgas := self.msg.Gas()
    if mgas.BitLen() > 64 {
        return vm.ErrOutOfGas
    }

    mgval := new(big.Int).Mul(mgas, self.gasPrice)

    var (
        state  = self.state
        sender = self.from()
    )
    if state.GetBalance(sender.Address()).Cmp(mgval) < 0 {
        return errInsufficientBalanceForGas
    }
    if err := self.gp.SubGas(mgas); err != nil {
        return err
    }
    self.gas += mgas.Uint64()

    self.initialGas.Set(mgas)
    state.SubBalance(sender.Address(), mgval)
    return nil
}

func (self *StateTransition) preCheck() (err error) {
    msg := self.msg
    sender := self.from()

    // Make sure this transaction's nonce is correct
    if msg.CheckNonce() {
        if n := self.state.GetNonce(sender.Address()); n != msg.Nonce() {
            return NonceError(msg.Nonce(), n)
        }
    }

    // Pre-pay gas
    if err = self.buyGas(); err != nil {
        if IsGasLimitErr(err) {
            return err
        }
        return InvalidTxError(err)
    }

    return nil
}

// TransitionDb will transition the state by applying the current message and returning the result
// including the required gas for the operation as well as the used gas. It returns an error if it
// failed. An error indicates a consensus issue.
func (self *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *big.Int, err error) {
    if err = self.preCheck(); err != nil {
        return
    }
    msg := self.msg
    sender := self.from() // err checked in preCheck

    homestead := self.evm.ChainConfig().IsHomestead(self.evm.BlockNumber)
    contractCreation := MessageCreatesContract(msg)
    // Pay intrinsic gas
    // TODO convert to uint64
    intrinsicGas := IntrinsicGas(self.data, contractCreation, homestead)
    if intrinsicGas.BitLen() > 64 {
        return nil, nil, nil, InvalidTxError(vm.ErrOutOfGas)
    }

    if err = self.useGas(intrinsicGas.Uint64()); err != nil {
        return nil, nil, nil, InvalidTxError(err)
    }

    var (
        evm = self.evm
        // vm errors do not effect consensus and are therefor
        // not assigned to err, except for insufficient balance
        // error.
        vmerr error
    )
    if contractCreation {
        ret, _, self.gas, vmerr = evm.Create(sender, self.data, self.gas, self.value)
    } else {
        // Increment the nonce for the next transaction
        self.state.SetNonce(sender.Address(), self.state.GetNonce(sender.Address())+1)
        ret, self.gas, vmerr = evm.Call(sender, self.to().Address(), self.data, self.gas, self.value)
    }
    if vmerr != nil {
        glog.V(logger.Debug).Infoln("vm returned with error:", err)
        // The only possible consensus-error would be if there wasn't
        // sufficient balance to make the transfer happen. The first
        // balance transfer may never fail.
        if vmerr == vm.ErrInsufficientBalance {
            return nil, nil, nil, InvalidTxError(vmerr)
        }
    }

    requiredGas = new(big.Int).Set(self.gasUsed())

    self.refundGas()
    self.state.AddBalance(self.evm.Coinbase, new(big.Int).Mul(self.gasUsed(), self.gasPrice))

    return ret, requiredGas, self.gasUsed(), err
}

func (self *StateTransition) refundGas() {
    // Return eth for remaining gas to the sender account,
    // exchanged at the original rate.
    sender := self.from() // err already checked
    remaining := new(big.Int).Mul(new(big.Int).SetUint64(self.gas), self.gasPrice)
    self.state.AddBalance(sender.Address(), remaining)

    // Apply refund counter, capped to half of the used gas.
    uhalf := remaining.Div(self.gasUsed(), common.Big2)
    refund := common.BigMin(uhalf, self.state.GetRefund())
    self.gas += refund.Uint64()

    self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))

    // Also return remaining gas to the block gas counter so it is
    // available for the next transaction.
    self.gp.AddGas(new(big.Int).SetUint64(self.gas))
}

func (self *StateTransition) gasUsed() *big.Int {
    return new(big.Int).Sub(self.initialGas, new(big.Int).SetUint64(self.gas))
}