ETH源码阅读(获得一个地址的余额getBalance)

1. 执行

命令：

eth.getBalance("0xd4C3b95bf0bbF0Fd0087062125dD572114DeD44F")

执行结果：

0

2. UML图

UML

3.流程图

流程图

4. 代码流程

go-ethereum/internal/ethapi/api.go

func (s *PublicBlockChainAPI) GetBalance(ctx context.Context, address common.Address, blockNr rpc.BlockNumber) (*big.Int, error) {
    state, _, err := s.b.StateAndHeaderByNumber(ctx, blockNr)   //4.1
    if state == nil || err != nil {
        return nil, err
    }
    b := state.GetBalance(address)  //4.2  state：StateDB
    return b, state.Error()
}

4.1. StateAndHeaderByNumber

go-ethereum/eth/api_backend.go (blockNr: -1)

func (b *EthAPIBackend) StateAndHeaderByNumber(ctx context.Context, blockNr rpc.BlockNumber) (*state.StateDB, *types.Header, error) {
    // Pending state is only known by the miner
    if blockNr == rpc.PendingBlockNumber {
        block, state := b.eth.miner.Pending()
        return state, block.Header(), nil
    }
    // Otherwise resolve the block number and return its state
    header, err := b.HeaderByNumber(ctx, blockNr)        //3.1.1
    if header == nil || err != nil {
        return nil, nil, err
    }
    stateDb, err := b.eth.BlockChain().StateAt(header.Root) //3.1.2
    return stateDb, header, err
}

4.1.1 HeaderByNumber

Ethereum -> *core.BlockChain -> currentBlock -> Header
go-ethereum/eth/api_backend.go

func (b *EthAPIBackend) HeaderByNumber(ctx context.Context, blockNr rpc.BlockNumber) (*types.Header, error) {
    // Pending block is only known by the miner
    if blockNr == rpc.PendingBlockNumber {
        block := b.eth.miner.PendingBlock()
        return block.Header(), nil
    }
    // Otherwise resolve and return the block
    if blockNr == rpc.LatestBlockNumber {    //blockNr: -1
        return b.eth.blockchain.CurrentBlock().Header(), nil  //获得 Header
    }
    return b.eth.blockchain.GetHeaderByNumber(uint64(blockNr)), nil
}

4.1.2 StateAt

go-ethereum/core/blockchain.go

// StateAt returns a new mutable state based on a particular point in time.
func (bc *BlockChain) StateAt(root common.Hash) (*state.StateDB, error) {
    return state.New(root, bc.stateCache) //3.1.2.1
}

4.1.2.1 New

go-ethereum/core/state/statedb.go

// 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{}),
        logs:              make(map[common.Hash][]*types.Log),
        preimages:         make(map[common.Hash][]byte),
        journal:           newJournal(),
    }, nil
}

4.2. GetBalance

获得stateObject，通过stateObject获得balance

go-ethereum/core/state/statedb.go

// Retrieve the balance from the given address or 0 if object not found
func (self *StateDB) GetBalance(addr common.Address) *big.Int {
    stateObject := self.getStateObject(addr)  //4.2.1
    if stateObject != nil {
        return stateObject.Balance()  //4.2.2
    }
    return common.Big0
}

4.2.1. getStateObject

• 一级缓存：StateDB.stateObjects获取stateObject
• 缓存未命中，从StateDB.trie获取
  go-ethereum/core/state/statedb.go

// 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 { //StateDB.stateObjects获取stateObject
        if obj.deleted {
            return nil
        }
        return obj
    }

    // Load the object from the database.
    enc, err := self.trie.TryGet(addr[:])  //从StateDB.trie获取
    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)  //new
    self.setStateObject(obj)  //add to map 放入缓存
    return obj
}

4.2.2. Balance

• 从stateObject的data获取Balance
  go-ethereum/core/state/state_object.go

func (self *stateObject) Balance() *big.Int {
    return self.data.Balance  //data：Acount
}