兄弟连区块链教程以太坊源码分析core-state源码分析，2018年下半年，区块链行业正逐渐褪去发展之初的浮躁、回归理性，表面上看相关人才需求与身价似乎正在回落。但事实上，正是初期泡沫的渐退，让人们更多的关注点放在了区块链真正的技术之上。
## statedb.go
stateDB用来存储以太坊中关于merkle trie的所有内容。 StateDB负责缓存和存储嵌套状态。 这是检索合约和账户的一般查询界面：
数据结构
type StateDB struct {
db Database // 后端的数据库
trie Trie // trie树 main account trie
// This map holds 'live' objects, which will get modified while processing a state transition.
// 下面的Map用来存储当前活动的对象，这些对象在状态转换的时候会被修改。
// stateObjects 用来缓存对象
// stateObjectsDirty用来缓存被修改过的对象。
stateObjects map[common.Address]*stateObject
stateObjectsDirty map[common.Address]struct{}
// DB error.
// State objects are used by the consensus core and VM which are
// unable to deal with database-level errors. Any error that occurs
// during a database read is memoized here and will eventually be returned
// by StateDB.Commit.
dbErr error
// The refund counter, also used by state transitioning.
// refund计数器。 暂时还不清楚功能。
refund *big.Int
thash, bhash common.Hash //当前的transaction hash 和block hash
txIndex int // 当前的交易的index
logs map[common.Hash][]*types.Log // 日志 key是交易的hash值
logSize uint
preimages map[common.Hash][]byte // EVM计算的 SHA3->byte[]的映射关系
// Journal of state modifications. This is the backbone of
// Snapshot and RevertToSnapshot.
// 状态修改日志。 这是Snapshot和RevertToSnapshot的支柱。
journal journal
validRevisions []revision
nextRevisionId int
lock sync.Mutex
}
构造函数
// 一般的用法 statedb, _ := state.New(common.Hash{}, state.NewDatabase(db))
// Create a new state from a given trie
func New(root common.Hash, db Database) (*StateDB, error) {
tr, err := db.OpenTrie(root)
if err != nil {
return nil, err
}
return &StateDB{
db: db,
trie: tr,
stateObjects: make(map[common.Address]*stateObject),
stateObjectsDirty: make(map[common.Address]struct{}),
refund: new(big.Int),
logs: make(map[common.Hash][]*types.Log),
preimages: make(map[common.Hash][]byte),
}, nil
}
### 对于Log的处理
state提供了Log的处理，这比较意外，因为Log实际上是存储在区块链中的，并没有存储在state trie中, state提供Log的处理， 使用了基于下面的几个函数。 奇怪的是暂时没看到如何删除logs里面的信息，如果不删除的话，应该会越积累越多。 TODO logs 删除
Prepare函数，在交易执行开始被执行。
AddLog函数，在交易执行过程中被VM执行。添加日志。同时把日志和交易关联起来，添加部分交易的信息。
GetLogs函数，交易完成取走。
// Prepare sets the current transaction hash and index and block hash which is
// used when the EVM emits new state logs.
func (self *StateDB) Prepare(thash, bhash common.Hash, ti int) {
self.thash = thash
self.bhash = bhash
self.txIndex = ti
}
func (self *StateDB) AddLog(log *types.Log) {
self.journal = append(self.journal, addLogChange{txhash: self.thash})
log.TxHash = self.thash
log.BlockHash = self.bhash
log.TxIndex = uint(self.txIndex)
log.Index = self.logSize
self.logs[self.thash] = append(self.logs[self.thash], log)
self.logSize++
}
func (self *StateDB) GetLogs(hash common.Hash) []*types.Log {
return self.logs[hash]
}
func (self *StateDB) Logs() []*types.Log {
var logs []*types.Log
for _, lgs := range self.logs {
logs = append(logs, lgs...)
}
return logs
}
### stateObject处理
getStateObject,首先从缓存里面获取，如果没有就从trie树里面获取，并加载到缓存。
// Retrieve a state object given my the address. Returns nil if not found.
func (self *StateDB) getStateObject(addr common.Address) (stateObject *stateObject) {
// Prefer 'live' objects.
if obj := self.stateObjects[addr]; obj != nil {
if obj.deleted {
return nil
}
return obj
}
// Load the object from the database.
enc, err := self.trie.TryGet(addr[:])
if len(enc) == 0 {
self.setError(err)
return nil
}
var data Account
if err := rlp.DecodeBytes(enc, &data); err != nil {
log.Error("Failed to decode state object", "addr", addr, "err", err)
return nil
}
// Insert into the live set.
obj := newObject(self, addr, data, self.MarkStateObjectDirty)
self.setStateObject(obj)
return obj
}
MarkStateObjectDirty， 设置一个stateObject为Dirty。 直接往stateObjectDirty对应的地址插入一个空结构体。
// MarkStateObjectDirty adds the specified object to the dirty map to avoid costly
// state object cache iteration to find a handful of modified ones.
func (self *StateDB) MarkStateObjectDirty(addr common.Address) {
self.stateObjectsDirty[addr] = struct{}{}
}
### 快照和回滚功能
Snapshot可以创建一个快照， 然后通过 RevertToSnapshot可以回滚到哪个状态，这个功能是通过journal来做到的。 每一步的修改都会往journal里面添加一个undo日志。 如果需要回滚只需要执行undo日志就行了。
// Snapshot returns an identifier for the current revision of the state.
func (self *StateDB) Snapshot() int {
id := self.nextRevisionId
self.nextRevisionId++
self.validRevisions = append(self.validRevisions, revision{id, len(self.journal)})
return id
}
// RevertToSnapshot reverts all state changes made since the given revision.
func (self *StateDB) RevertToSnapshot(revid int) {
// Find the snapshot in the stack of valid snapshots.
idx := sort.Search(len(self.validRevisions), func(i int) bool {
return self.validRevisions[i].id >= revid
})
if idx == len(self.validRevisions) || self.validRevisions[idx].id != revid {
panic(fmt.Errorf("revision id %v cannot be reverted", revid))
}
snapshot := self.validRevisions[idx].journalIndex
// Replay the journal to undo changes.
for i := len(self.journal) - 1; i >= snapshot; i-- {
self.journal[i].undo(self)
}
self.journal = self.journal[:snapshot]
// Remove invalidated snapshots from the stack.
self.validRevisions = self.validRevisions[:idx]
}
### 获取中间状态的 root hash值
IntermediateRoot 用来计算当前的state trie的root的hash值。这个方法会在交易执行的过程中被调用。会被存入 transaction receipt
Finalise方法会调用update方法把存放在cache层的修改写入到trie数据库里面。 但是这个时候还没有写入底层的数据库。 还没有调用commit，数据还在内存里面，还没有落地成文件。
// Finalise finalises the state by removing the self destructed objects
// and clears the journal as well as the refunds.
func (s *StateDB) Finalise(deleteEmptyObjects bool) {
for addr := range s.stateObjectsDirty {
stateObject := s.stateObjects[addr]
if stateObject.suicided || (deleteEmptyObjects && stateObject.empty()) {
s.deleteStateObject(stateObject)
} else {
stateObject.updateRoot(s.db)
s.updateStateObject(stateObject)
}
}
// Invalidate journal because reverting across transactions is not allowed.
s.clearJournalAndRefund()
}
// 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(deleteEmptyObjects bool) common.Hash {
s.Finalise(deleteEmptyObjects)
return s.trie.Hash()
}
### commit方法
CommitTo用来提交更改。
// CommitTo writes the state to the given database.
func (s *StateDB) CommitTo(dbw trie.DatabaseWriter, deleteEmptyObjects bool) (root common.Hash, err error) {
defer s.clearJournalAndRefund()
// Commit objects to the trie.
for addr, stateObject := range s.stateObjects {
_, 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)
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 {
return common.Hash{}, err
}
stateObject.dirtyCode = false
}
// Write any storage changes in the state object to its storage trie.
if err := stateObject.CommitTrie(s.db, dbw); err != nil {
return common.Hash{}, err
}
// Update the object in the main account trie.
s.updateStateObject(stateObject)
}
delete(s.stateObjectsDirty, addr)
}
// Write trie changes.
root, err = s.trie.CommitTo(dbw)
log.Debug("Trie cache stats after commit", "misses", trie.CacheMisses(), "unloads", trie.CacheUnloads())
return root, err
}
### 总结
state包提供了用户和合约的状态管理的功能。 管理了状态和合约的各种状态转换。 cache， trie， 数据库。 日志和回滚功能。
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