core, core/state: move gas tracking out of core/state

The amount of gas available for tx execution was tracked in the
StateObject representing the coinbase account. This commit makes the gas
counter a separate type in package core, which avoids unintended
consequences of intertwining the counter with state logic.

core/block_processor.go

@@ -58,16 +58,31 @@ type BlockProcessor struct {
 	eventMux *event.TypeMux
 }
 
-// TODO: type GasPool big.Int
-//
-// GasPool is implemented by state.StateObject. This is a historical
-// coincidence. Gas tracking should move out of StateObject.
-
 // GasPool tracks the amount of gas available during
 // execution of the transactions in a block.
-type GasPool interface {
-	AddGas(gas, price *big.Int)
-	SubGas(gas, price *big.Int) error
+// The zero value is a pool with zero gas available.
+type GasPool big.Int
+
+// AddGas makes gas available for execution.
+func (gp *GasPool) AddGas(amount *big.Int) *GasPool {
+	i := (*big.Int)(gp)
+	i.Add(i, amount)
+	return gp
+}
+
+// SubGas deducts the given amount from the pool if enough gas is
+// available and returns an error otherwise.
+func (gp *GasPool) SubGas(amount *big.Int) error {
+	i := (*big.Int)(gp)
+	if i.Cmp(amount) < 0 {
+		return &GasLimitErr{Have: new(big.Int).Set(i), Want: amount}
+	}
+	i.Sub(i, amount)
+	return nil
+}
+
+func (gp *GasPool) String() string {
+	return (*big.Int)(gp).String()
 }
 
 func NewBlockProcessor(db ethdb.Database, pow pow.PoW, blockchain *BlockChain, eventMux *event.TypeMux) *BlockProcessor {
@@ -82,8 +97,10 @@ func NewBlockProcessor(db ethdb.Database, pow pow.PoW, blockchain *BlockChain, e
 }
 
 func (sm *BlockProcessor) TransitionState(statedb *state.StateDB, parent, block *types.Block, transientProcess bool) (receipts types.Receipts, err error) {
-	gp := statedb.GetOrNewStateObject(block.Coinbase())
-	gp.SetGasLimit(block.GasLimit())
+	gp := new(GasPool).AddGas(block.GasLimit())
+	if glog.V(logger.Core) {
+		glog.Infof("%x: gas (+ %v)", block.Coinbase(), gp)
+	}
 
 	// Process the transactions on to parent state
 	receipts, err = sm.ApplyTransactions(gp, statedb, block, block.Transactions(), transientProcess)
@@ -94,7 +111,7 @@ func (sm *BlockProcessor) TransitionState(statedb *state.StateDB, parent, block
 	return receipts, nil
 }
 
-func (self *BlockProcessor) ApplyTransaction(gp GasPool, statedb *state.StateDB, header *types.Header, tx *types.Transaction, usedGas *big.Int, transientProcess bool) (*types.Receipt, *big.Int, error) {
+func (self *BlockProcessor) ApplyTransaction(gp *GasPool, statedb *state.StateDB, header *types.Header, tx *types.Transaction, usedGas *big.Int, transientProcess bool) (*types.Receipt, *big.Int, error) {
 	_, gas, err := ApplyMessage(NewEnv(statedb, self.bc, tx, header), tx, gp)
 	if err != nil {
 		return nil, nil, err
@@ -128,7 +145,7 @@ func (self *BlockProcessor) BlockChain() *BlockChain {
 	return self.bc
 }
 
-func (self *BlockProcessor) ApplyTransactions(gp GasPool, statedb *state.StateDB, block *types.Block, txs types.Transactions, transientProcess bool) (types.Receipts, error) {
+func (self *BlockProcessor) ApplyTransactions(gp *GasPool, statedb *state.StateDB, block *types.Block, txs types.Transactions, transientProcess bool) (types.Receipts, error) {
 	var (
 		receipts      types.Receipts
 		totalUsedGas  = big.NewInt(0)

core/chain_makers.go

@@ -54,7 +54,7 @@ type BlockGen struct {
 	header  *types.Header
 	statedb *state.StateDB
 
-	coinbase *state.StateObject
+	gasPool  *GasPool
 	txs      []*types.Transaction
 	receipts []*types.Receipt
 	uncles   []*types.Header
@@ -63,15 +63,14 @@ type BlockGen struct {
 // SetCoinbase sets the coinbase of the generated block.
 // It can be called at most once.
 func (b *BlockGen) SetCoinbase(addr common.Address) {
-	if b.coinbase != nil {
+	if b.gasPool != nil {
 		if len(b.txs) > 0 {
 			panic("coinbase must be set before adding transactions")
 		}
 		panic("coinbase can only be set once")
 	}
 	b.header.Coinbase = addr
-	b.coinbase = b.statedb.GetOrNewStateObject(addr)
-	b.coinbase.SetGasLimit(b.header.GasLimit)
+	b.gasPool = new(GasPool).AddGas(b.header.GasLimit)
 }
 
 // SetExtra sets the extra data field of the generated block.
@@ -88,10 +87,10 @@ func (b *BlockGen) SetExtra(data []byte) {
 // added. Notably, contract code relying on the BLOCKHASH instruction
 // will panic during execution.
 func (b *BlockGen) AddTx(tx *types.Transaction) {
-	if b.coinbase == nil {
+	if b.gasPool == nil {
 		b.SetCoinbase(common.Address{})
 	}
-	_, gas, err := ApplyMessage(NewEnv(b.statedb, nil, tx, b.header), tx, b.coinbase)
+	_, gas, err := ApplyMessage(NewEnv(b.statedb, nil, tx, b.header), tx, b.gasPool)
 	if err != nil {
 		panic(err)
 	}

core/error.go

@@ -188,3 +188,16 @@ func IsBadHashError(err error) bool {
 	_, ok := err.(BadHashError)
 	return ok
 }
+
+type GasLimitErr struct {
+	Have, Want *big.Int
+}
+
+func IsGasLimitErr(err error) bool {
+	_, ok := err.(*GasLimitErr)
+	return ok
+}
+
+func (err *GasLimitErr) Error() string {
+	return fmt.Sprintf("GasLimit reached. Have %d gas, transaction requires %d", err.Have, err.Want)
+}

core/state/state_object.go

@@ -75,11 +75,6 @@ type StateObject struct {
 	// Cached storage (flushed when updated)
 	storage Storage
 
-	// Total gas pool is the total amount of gas currently
-	// left if this object is the coinbase. Gas is directly
-	// purchased of the coinbase.
-	gasPool *big.Int
-
 	// Mark for deletion
 	// When an object is marked for deletion it will be delete from the trie
 	// during the "update" phase of the state transition
@@ -89,10 +84,9 @@ type StateObject struct {
 }
 
 func NewStateObject(address common.Address, db ethdb.Database) *StateObject {
-	object := &StateObject{db: db, address: address, balance: new(big.Int), gasPool: new(big.Int), dirty: true}
+	object := &StateObject{db: db, address: address, balance: new(big.Int), dirty: true}
 	object.trie, _ = trie.NewSecure(common.Hash{}, db)
 	object.storage = make(Storage)
-	object.gasPool = new(big.Int)
 	return object
 }
 
@@ -121,7 +115,6 @@ func NewStateObjectFromBytes(address common.Address, data []byte, db ethdb.Datab
 	object.codeHash = extobject.CodeHash
 	object.trie = trie
 	object.storage = make(map[string]common.Hash)
-	object.gasPool = new(big.Int)
 	object.code, _ = db.Get(extobject.CodeHash)
 	return object
 }
@@ -209,36 +202,9 @@ func (c *StateObject) St() Storage {
 	return c.storage
 }
 
-//
-// Gas setters and getters
-//
-
 // Return the gas back to the origin. Used by the Virtual machine or Closures
 func (c *StateObject) ReturnGas(gas, price *big.Int) {}
 
-func (self *StateObject) SetGasLimit(gasLimit *big.Int) {
-	self.gasPool = new(big.Int).Set(gasLimit)
-	self.dirty = true
-
-	if glog.V(logger.Core) {
-		glog.Infof("%x: gas (+ %v)", self.Address(), self.gasPool)
-	}
-}
-
-func (self *StateObject) SubGas(gas, price *big.Int) error {
-	if self.gasPool.Cmp(gas) < 0 {
-		return GasLimitError(self.gasPool, gas)
-	}
-	self.gasPool.Sub(self.gasPool, gas)
-	self.dirty = true
-	return nil
-}
-
-func (self *StateObject) AddGas(gas, price *big.Int) {
-	self.gasPool.Add(self.gasPool, gas)
-	self.dirty = true
-}
-
 func (self *StateObject) Copy() *StateObject {
 	stateObject := NewStateObject(self.Address(), self.db)
 	stateObject.balance.Set(self.balance)
@@ -248,7 +214,6 @@ func (self *StateObject) Copy() *StateObject {
 	stateObject.code = common.CopyBytes(self.code)
 	stateObject.initCode = common.CopyBytes(self.initCode)
 	stateObject.storage = self.storage.Copy()
-	stateObject.gasPool.Set(self.gasPool)
 	stateObject.remove = self.remove
 	stateObject.dirty = self.dirty
 	stateObject.deleted = self.deleted

core/state/state_test.go

@@ -138,7 +138,6 @@ func TestSnapshot2(t *testing.T) {
 	so0 := state.GetStateObject(stateobjaddr0)
 	so0.balance = big.NewInt(42)
 	so0.nonce = 43
-	so0.gasPool = big.NewInt(44)
 	so0.code = []byte{'c', 'a', 'f', 'e'}
 	so0.codeHash = so0.CodeHash()
 	so0.remove = true
@@ -150,7 +149,6 @@ func TestSnapshot2(t *testing.T) {
 	so1 := state.GetStateObject(stateobjaddr1)
 	so1.balance = big.NewInt(52)
 	so1.nonce = 53
-	so1.gasPool = big.NewInt(54)
 	so1.code = []byte{'c', 'a', 'f', 'e', '2'}
 	so1.codeHash = so1.CodeHash()
 	so1.remove = true
@@ -207,9 +205,6 @@ func compareStateObjects(so0, so1 *StateObject, t *testing.T) {
 		}
 	}
 
-	if so0.gasPool.Cmp(so1.gasPool) != 0 {
-		t.Fatalf("GasPool mismatch: have %v, want %v", so0.gasPool, so1.gasPool)
-	}
 	if so0.remove != so1.remove {
 		t.Fatalf("Remove mismatch: have %v, want %v", so0.remove, so1.remove)
 	}

core/state_transition.go

@@ -21,31 +21,31 @@ import (
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/core/state"
 	"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"
 )
 
 /*
- * 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 / buy gas of the coinbase (miner)
- * 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
- */
+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
+	gp            *GasPool
 	msg           Message
 	gas, gasPrice *big.Int
 	initialGas    *big.Int
@@ -94,7 +94,7 @@ func IntrinsicGas(data []byte) *big.Int {
 	return igas
 }
 
-func ApplyMessage(env vm.Environment, msg Message, gp GasPool) ([]byte, *big.Int, error) {
+func ApplyMessage(env vm.Environment, msg Message, gp *GasPool) ([]byte, *big.Int, error) {
 	var st = StateTransition{
 		gp:         gp,
 		env:        env,
@@ -158,7 +158,7 @@ func (self *StateTransition) buyGas() error {
 	if sender.Balance().Cmp(mgval) < 0 {
 		return fmt.Errorf("insufficient ETH for gas (%x). Req %v, has %v", sender.Address().Bytes()[:4], mgval, sender.Balance())
 	}
-	if err = self.gp.SubGas(mgas, self.gasPrice); err != nil {
+	if err = self.gp.SubGas(mgas); err != nil {
 		return err
 	}
 	self.addGas(mgas)
@@ -180,9 +180,9 @@ func (self *StateTransition) preCheck() (err error) {
 		return NonceError(msg.Nonce(), n)
 	}
 
-	// Pre-pay gas / Buy gas of the coinbase account
+	// Pre-pay gas
 	if err = self.buyGas(); err != nil {
-		if state.IsGasLimitErr(err) {
+		if IsGasLimitErr(err) {
 			return err
 		}
 		return InvalidTxError(err)
@@ -246,17 +246,21 @@ func (self *StateTransition) transitionDb() (ret []byte, usedGas *big.Int, err e
 }
 
 func (self *StateTransition) refundGas() {
+	// Return eth for remaining gas to the sender account,
+	// exchanged at the original rate.
 	sender, _ := self.from() // err already checked
-	// Return remaining gas
 	remaining := new(big.Int).Mul(self.gas, self.gasPrice)
 	sender.AddBalance(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.Add(self.gas, refund)
 	self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))
 
-	self.gp.AddGas(self.gas, self.gasPrice)
+	// Also return remaining gas to the block gas counter so it is
+	// available for the next transaction.
+	self.gp.AddGas(self.gas)
 }
 
 func (self *StateTransition) gasUsed() *big.Int {