core, core/state, trie: EIP158, reprice & skip empty account write

This commit implements EIP158 part 1, 2, 3 & 4

1. If an account is empty it's no longer written to the trie. An empty
  account is defined as (balance=0, nonce=0, storage=0, code=0).
2. Delete an empty account if it's touched
3. An empty account is redefined as either non-existent or empty.
4. Zero value calls and zero value suicides no longer consume the 25k
  reation costs.

params: moved core/config to params

Signed-off-by: Jeffrey Wilcke <jeffrey@ethereum.org>

5 files changed, 38 insertions, 18 deletions

diff --git a/core/state/state_object.go b/core/state/state_object.go
index edb073173..2b5dfea7d 100644
--- a/core/state/state_object.go
+++ b/core/state/state_object.go
@@ -91,6 +91,11 @@ type StateObject struct {
 	onDirty   func(addr common.Address) // Callback method to mark a state object newly dirty
 }
 
+// empty returns whether the account is considered empty.
+func (s *StateObject) empty() bool {
+	return s.data.Nonce == 0 && s.data.Balance.BitLen() == 0 && bytes.Equal(s.data.CodeHash, emptyCodeHash)
+}
+
 // Account is the Ethereum consensus representation of accounts.
 // These objects are stored in the main account trie.
 type Account struct {
@@ -221,8 +226,12 @@ func (self *StateObject) CommitTrie(db trie.Database, dbw trie.DatabaseWriter) e
 	return err
 }
 
+// AddBalance removes amount from c's balance.
+// It is used to add funds to the destination account of a transfer.
 func (c *StateObject) AddBalance(amount *big.Int) {
-	if amount.Cmp(common.Big0) == 0 {
+	// EIP158: We must check emptiness for the objects such that the account
+	// clearing (0,0,0 objects) can take effect.
+	if amount.Cmp(common.Big0) == 0 && !c.empty() {
 		return
 	}
 	c.SetBalance(new(big.Int).Add(c.Balance(), amount))
@@ -232,6 +241,8 @@ func (c *StateObject) AddBalance(amount *big.Int) {
 	}
 }
 
+// SubBalance removes amount from c's balance.
+// It is used to remove funds from the origin account of a transfer.
 func (c *StateObject) SubBalance(amount *big.Int) {
 	if amount.Cmp(common.Big0) == 0 {
 		return
diff --git a/core/state/state_test.go b/core/state/state_test.go
index f188bc271..435d1d829 100644
--- a/core/state/state_test.go
+++ b/core/state/state_test.go
@@ -48,7 +48,7 @@ func (s *StateSuite) TestDump(c *checker.C) {
 	// write some of them to the trie
 	s.state.updateStateObject(obj1)
 	s.state.updateStateObject(obj2)
-	s.state.Commit()
+	s.state.Commit(false)
 
 	// check that dump contains the state objects that are in trie
 	got := string(s.state.Dump())
@@ -100,7 +100,7 @@ func TestNull(t *testing.T) {
 	//value := common.FromHex("0x823140710bf13990e4500136726d8b55")
 	var value common.Hash
 	state.SetState(address, common.Hash{}, value)
-	state.Commit()
+	state.Commit(false)
 	value = state.GetState(address, common.Hash{})
 	if !common.EmptyHash(value) {
 		t.Errorf("expected empty hash. got %x", value)
@@ -160,7 +160,7 @@ func TestSnapshot2(t *testing.T) {
 	so0.deleted = false
 	state.setStateObject(so0)
 
-	root, _ := state.Commit()
+	root, _ := state.Commit(false)
 	state.Reset(root)
 
 	// and one with deleted == true
diff --git a/core/state/statedb.go b/core/state/statedb.go
index ae106e03b..1c4af0295 100644
--- a/core/state/statedb.go
+++ b/core/state/statedb.go
@@ -213,6 +213,13 @@ func (self *StateDB) Exist(addr common.Address) bool {
 	return self.GetStateObject(addr) != nil
 }
 
+// Empty returns whether the state object is either non-existant
+// or empty according to the EIP161 specification (balance = nonce = code = 0)
+func (self *StateDB) Empty(addr common.Address) bool {
+	so := self.GetStateObject(addr)
+	return so == nil || so.empty()
+}
+
 func (self *StateDB) GetAccount(addr common.Address) vm.Account {
 	return self.GetStateObject(addr)
 }
@@ -516,10 +523,10 @@ func (self *StateDB) GetRefund() *big.Int {
 // IntermediateRoot computes the current root hash of the state trie.
 // It is called in between transactions to get the root hash that
 // goes into transaction receipts.
-func (s *StateDB) IntermediateRoot() common.Hash {
+func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 	for addr, _ := range s.stateObjectsDirty {
 		stateObject := s.stateObjects[addr]
-		if stateObject.suicided {
+		if stateObject.suicided || (deleteEmptyObjects && stateObject.empty()) {
 			s.deleteStateObject(stateObject)
 		} else {
 			stateObject.updateRoot(s.db)
@@ -553,17 +560,17 @@ func (s *StateDB) DeleteSuicides() {
 }
 
 // Commit commits all state changes to the database.
-func (s *StateDB) Commit() (root common.Hash, err error) {
-	root, batch := s.CommitBatch()
+func (s *StateDB) Commit(deleteEmptyObjects bool) (root common.Hash, err error) {
+	root, batch := s.CommitBatch(deleteEmptyObjects)
 	return root, batch.Write()
 }
 
 // CommitBatch commits all state changes to a write batch but does not
 // execute the batch. It is used to validate state changes against
 // the root hash stored in a block.
-func (s *StateDB) CommitBatch() (root common.Hash, batch ethdb.Batch) {
+func (s *StateDB) CommitBatch(deleteEmptyObjects bool) (root common.Hash, batch ethdb.Batch) {
 	batch = s.db.NewBatch()
-	root, _ = s.commit(batch)
+	root, _ = s.commit(batch, deleteEmptyObjects)
 
 	glog.V(logger.Debug).Infof("Trie cache stats: %d misses, %d unloads", trie.CacheMisses(), trie.CacheUnloads())
 	return root, batch
@@ -575,16 +582,18 @@ func (s *StateDB) clearJournalAndRefund() {
 	s.refund = new(big.Int)
 }
 
-func (s *StateDB) commit(dbw trie.DatabaseWriter) (root common.Hash, err error) {
+func (s *StateDB) commit(dbw trie.DatabaseWriter, deleteEmptyObjects bool) (root common.Hash, err error) {
 	defer s.clearJournalAndRefund()
 
 	// Commit objects to the trie.
 	for addr, stateObject := range s.stateObjects {
-		if stateObject.suicided {
+		_, isDirty := s.stateObjectsDirty[addr]
+		switch {
+		case stateObject.suicided || (isDirty && deleteEmptyObjects && stateObject.empty()):
 			// If the object has been removed, don't bother syncing it
 			// and just mark it for deletion in the trie.
 			s.deleteStateObject(stateObject)
-		} else if _, ok := s.stateObjectsDirty[addr]; ok {
+		case isDirty:
 			// Write any contract code associated with the state object
 			if stateObject.code != nil && stateObject.dirtyCode {
 				if err := dbw.Put(stateObject.CodeHash(), stateObject.code); err != nil {
diff --git a/core/state/statedb_test.go b/core/state/statedb_test.go
index 5d041c740..a44818b7c 100644
--- a/core/state/statedb_test.go
+++ b/core/state/statedb_test.go
@@ -51,7 +51,7 @@ func TestUpdateLeaks(t *testing.T) {
 		if i%3 == 0 {
 			state.SetCode(addr, []byte{i, i, i, i, i})
 		}
-		state.IntermediateRoot()
+		state.IntermediateRoot(false)
 	}
 	// Ensure that no data was leaked into the database
 	for _, key := range db.Keys() {
@@ -86,7 +86,7 @@ func TestIntermediateLeaks(t *testing.T) {
 		modify(transState, common.Address{byte(i)}, i, 0)
 	}
 	// Write modifications to trie.
-	transState.IntermediateRoot()
+	transState.IntermediateRoot(false)
 
 	// Overwrite all the data with new values in the transient database.
 	for i := byte(0); i < 255; i++ {
@@ -95,10 +95,10 @@ func TestIntermediateLeaks(t *testing.T) {
 	}
 
 	// Commit and cross check the databases.
-	if _, err := transState.Commit(); err != nil {
+	if _, err := transState.Commit(false); err != nil {
 		t.Fatalf("failed to commit transition state: %v", err)
 	}
-	if _, err := finalState.Commit(); err != nil {
+	if _, err := finalState.Commit(false); err != nil {
 		t.Fatalf("failed to commit final state: %v", err)
 	}
 	for _, key := range finalDb.Keys() {
diff --git a/core/state/sync_test.go b/core/state/sync_test.go
index f5390d80f..8111320e6 100644
--- a/core/state/sync_test.go
+++ b/core/state/sync_test.go
@@ -60,7 +60,7 @@ func makeTestState() (ethdb.Database, common.Hash, []*testAccount) {
 		state.updateStateObject(obj)
 		accounts = append(accounts, acc)
 	}
-	root, _ := state.Commit()
+	root, _ := state.Commit(false)
 
 	// Return the generated state
 	return db, root, accounts