simulated.go

//<developer>
//    <name>linapex 曹一峰</name>
//    <email>linapex@163.com</email>
//    <wx>superexc</wx>
//    <qqgroup>128148617</qqgroup>
//    <url>https://jsq.ink</url>
//    <role>pku engineer</role>
//    <date>2019-03-16 19:16:30</date>
//</624450059852845056>


package backends

import (
	"context"
	"errors"
	"fmt"
	"math/big"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum"
	"github.com/ethereum/go-ethereum/accounts/abi/bind"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/math"
	"github.com/ethereum/go-ethereum/consensus/ethash"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/bloombits"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/eth/filters"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rpc"
)

//这个nil分配确保了模拟后端实现bind.contractbackend的编译时间。
var _ bind.ContractBackend = (*SimulatedBackend)(nil)

var errBlockNumberUnsupported = errors.New("SimulatedBackend cannot access blocks other than the latest block")
var errGasEstimationFailed = errors.New("gas required exceeds allowance or always failing transaction")

//Simulatedbackend实现bind.contractbackend，在
//背景。其主要目的是允许轻松测试合同绑定。
type SimulatedBackend struct {
database   ethdb.Database   //存储测试数据的内存数据库
blockchain *core.BlockChain //以太坊区块链处理共识

	mu           sync.Mutex
pendingBlock *types.Block   //将根据请求导入的当前挂起块
pendingState *state.StateDB //当前处于挂起状态，根据请求将处于活动状态

events *filters.EventSystem //用于实时筛选日志事件的事件系统

	config *params.ChainConfig
}

//NewSimulatedBackend使用模拟区块链创建新的绑定后端
//用于测试。
func NewSimulatedBackend(alloc core.GenesisAlloc, gasLimit uint64) *SimulatedBackend {
	database := ethdb.NewMemDatabase()
	genesis := core.Genesis{Config: params.AllEthashProtocolChanges, GasLimit: gasLimit, Alloc: alloc}
	genesis.MustCommit(database)
	blockchain, _ := core.NewBlockChain(database, nil, genesis.Config, ethash.NewFaker(), vm.Config{}, nil)

	backend := &SimulatedBackend{
		database:   database,
		blockchain: blockchain,
		config:     genesis.Config,
		events:     filters.NewEventSystem(new(event.TypeMux), &filterBackend{database, blockchain}, false),
	}
	backend.rollback()
	return backend
}

//commit将所有挂起的事务作为单个块导入并启动
//新的状态。
func (b *SimulatedBackend) Commit() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if _, err := b.blockchain.InsertChain([]*types.Block{b.pendingBlock}); err != nil {
panic(err) //除非模拟器出错，否则不会发生这种情况，在这种情况下会失败。
	}
	b.rollback()
}

//回滚将中止所有挂起的事务，恢复到上一次提交的状态。
func (b *SimulatedBackend) Rollback() {
	b.mu.Lock()
	defer b.mu.Unlock()

	b.rollback()
}

func (b *SimulatedBackend) rollback() {
	blocks, _ := core.GenerateChain(b.config, b.blockchain.CurrentBlock(), ethash.NewFaker(), b.database, 1, func(int, *core.BlockGen) {})
	statedb, _ := b.blockchain.State()

	b.pendingBlock = blocks[0]
	b.pendingState, _ = state.New(b.pendingBlock.Root(), statedb.Database())
}

//codeat返回与区块链中某个帐户关联的代码。
func (b *SimulatedBackend) CodeAt(ctx context.Context, contract common.Address, blockNumber *big.Int) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
		return nil, errBlockNumberUnsupported
	}
	statedb, _ := b.blockchain.State()
	return statedb.GetCode(contract), nil
}

//balanceat返回区块链中某个账户的wei余额。
func (b *SimulatedBackend) BalanceAt(ctx context.Context, contract common.Address, blockNumber *big.Int) (*big.Int, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
		return nil, errBlockNumberUnsupported
	}
	statedb, _ := b.blockchain.State()
	return statedb.GetBalance(contract), nil
}

//nonceat返回区块链中某个帐户的nonce。
func (b *SimulatedBackend) NonceAt(ctx context.Context, contract common.Address, blockNumber *big.Int) (uint64, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
		return 0, errBlockNumberUnsupported
	}
	statedb, _ := b.blockchain.State()
	return statedb.GetNonce(contract), nil
}

//storageat返回在区块链中存储帐户的密钥的值。
func (b *SimulatedBackend) StorageAt(ctx context.Context, contract common.Address, key common.Hash, blockNumber *big.Int) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
		return nil, errBlockNumberUnsupported
	}
	statedb, _ := b.blockchain.State()
	val := statedb.GetState(contract, key)
	return val[:], nil
}

//TransactionReceipt返回交易的收据。
func (b *SimulatedBackend) TransactionReceipt(ctx context.Context, txHash common.Hash) (*types.Receipt, error) {
	receipt, _, _, _ := rawdb.ReadReceipt(b.database, txHash)
	return receipt, nil
}

//PendingCodeAt返回与处于挂起状态的帐户关联的代码。
func (b *SimulatedBackend) PendingCodeAt(ctx context.Context, contract common.Address) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	return b.pendingState.GetCode(contract), nil
}

//CallContract执行合同调用。
func (b *SimulatedBackend) CallContract(ctx context.Context, call ethereum.CallMsg, blockNumber *big.Int) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if blockNumber != nil && blockNumber.Cmp(b.blockchain.CurrentBlock().Number()) != 0 {
		return nil, errBlockNumberUnsupported
	}
	state, err := b.blockchain.State()
	if err != nil {
		return nil, err
	}
	rval, _, _, err := b.callContract(ctx, call, b.blockchain.CurrentBlock(), state)
	return rval, err
}

//PendingCallContract对挂起状态执行合同调用。
func (b *SimulatedBackend) PendingCallContract(ctx context.Context, call ethereum.CallMsg) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	defer b.pendingState.RevertToSnapshot(b.pendingState.Snapshot())

	rval, _, _, err := b.callContract(ctx, call, b.pendingBlock, b.pendingState)
	return rval, err
}

//PendingOnCate实现PendingStateReader.PendingOnCate，检索
//当前为帐户挂起的非现金。
func (b *SimulatedBackend) PendingNonceAt(ctx context.Context, account common.Address) (uint64, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	return b.pendingState.GetOrNewStateObject(account).Nonce(), nil
}

//Suggestgasprice执行ContractTransactor.Suggestgasprice。自从模拟
//这家连锁店没有矿工，我们只要回电1美元就可以了。
func (b *SimulatedBackend) SuggestGasPrice(ctx context.Context) (*big.Int, error) {
	return big.NewInt(1), nil
}

//EstimateGas针对当前挂起的块/状态执行请求的代码，并且
//返回使用的气体量。
func (b *SimulatedBackend) EstimateGas(ctx context.Context, call ethereum.CallMsg) (uint64, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

//确定二元搜索的最低和最高气体限制
	var (
		lo  uint64 = params.TxGas - 1
		hi  uint64
		cap uint64
	)
	if call.Gas >= params.TxGas {
		hi = call.Gas
	} else {
		hi = b.pendingBlock.GasLimit()
	}
	cap = hi

//创建一个助手以检查气体限额是否导致可执行事务
	executable := func(gas uint64) bool {
		call.Gas = gas

		snapshot := b.pendingState.Snapshot()
		_, _, failed, err := b.callContract(ctx, call, b.pendingBlock, b.pendingState)
		b.pendingState.RevertToSnapshot(snapshot)

		if err != nil || failed {
			return false
		}
		return true
	}
//执行二进制搜索并按可执行的气体限值接通。
	for lo+1 < hi {
		mid := (hi + lo) / 2
		if !executable(mid) {
			lo = mid
		} else {
			hi = mid
		}
	}
//如果交易仍以最高限额失败，则将其视为无效拒绝交易
	if hi == cap {
		if !executable(hi) {
			return 0, errGasEstimationFailed
		}
	}
	return hi, nil
}

//CallContract实现正常和挂起的合同调用之间的公共代码。
//状态在执行期间被修改，请确保在必要时复制它。
func (b *SimulatedBackend) callContract(ctx context.Context, call ethereum.CallMsg, block *types.Block, statedb *state.StateDB) ([]byte, uint64, bool, error) {
//确保消息已正确初始化。
	if call.GasPrice == nil {
		call.GasPrice = big.NewInt(1)
	}
	if call.Gas == 0 {
		call.Gas = 50000000
	}
	if call.Value == nil {
		call.Value = new(big.Int)
	}
//将无限余额设置为假呼叫者帐户。
	from := statedb.GetOrNewStateObject(call.From)
	from.SetBalance(math.MaxBig256)
//执行呼叫。
	msg := callmsg{call}

	evmContext := core.NewEVMContext(msg, block.Header(), b.blockchain, nil)
//创建一个保存所有相关信息的新环境
//关于事务和调用机制。
	vmenv := vm.NewEVM(evmContext, statedb, b.config, vm.Config{})
	gaspool := new(core.GasPool).AddGas(math.MaxUint64)

	return core.NewStateTransition(vmenv, msg, gaspool).TransitionDb()
}

//sendTransaction更新挂起块以包括给定的事务。
//如果事务无效，它会恐慌。
func (b *SimulatedBackend) SendTransaction(ctx context.Context, tx *types.Transaction) error {
	b.mu.Lock()
	defer b.mu.Unlock()

	sender, err := types.Sender(types.HomesteadSigner{}, tx)
	if err != nil {
		panic(fmt.Errorf("invalid transaction: %v", err))
	}
	nonce := b.pendingState.GetNonce(sender)
	if tx.Nonce() != nonce {
		panic(fmt.Errorf("invalid transaction nonce: got %d, want %d", tx.Nonce(), nonce))
	}

	blocks, _ := core.GenerateChain(b.config, b.blockchain.CurrentBlock(), ethash.NewFaker(), b.database, 1, func(number int, block *core.BlockGen) {
		for _, tx := range b.pendingBlock.Transactions() {
			block.AddTxWithChain(b.blockchain, tx)
		}
		block.AddTxWithChain(b.blockchain, tx)
	})
	statedb, _ := b.blockchain.State()

	b.pendingBlock = blocks[0]
	b.pendingState, _ = state.New(b.pendingBlock.Root(), statedb.Database())
	return nil
}

//filterlogs执行日志筛选操作，在执行期间阻塞，以及
//一批返回所有结果。
//
//TODO（karalabe）：当订阅可以返回过去的数据时，取消预测。
func (b *SimulatedBackend) FilterLogs(ctx context.Context, query ethereum.FilterQuery) ([]types.Log, error) {
	var filter *filters.Filter
	if query.BlockHash != nil {
//请求块筛选器，构造一个单镜头筛选器
		filter = filters.NewBlockFilter(&filterBackend{b.database, b.blockchain}, *query.BlockHash, query.Addresses, query.Topics)
	} else {
//初始化从Genesis运行到链头的未设置过滤器
		from := int64(0)
		if query.FromBlock != nil {
			from = query.FromBlock.Int64()
		}
		to := int64(-1)
		if query.ToBlock != nil {
			to = query.ToBlock.Int64()
		}
//构造范围过滤器
		filter = filters.NewRangeFilter(&filterBackend{b.database, b.blockchain}, from, to, query.Addresses, query.Topics)
	}
//运行过滤器并返回所有日志
	logs, err := filter.Logs(ctx)
	if err != nil {
		return nil, err
	}
	res := make([]types.Log, len(logs))
	for i, log := range logs {
		res[i] = *log
	}
	return res, nil
}

//subscribeBilterLogs创建后台日志筛选操作，返回
//立即订阅，可用于流式处理找到的事件。
func (b *SimulatedBackend) SubscribeFilterLogs(ctx context.Context, query ethereum.FilterQuery, ch chan<- types.Log) (ethereum.Subscription, error) {
//订阅合同事件
	sink := make(chan []*types.Log)

	sub, err := b.events.SubscribeLogs(query, sink)
	if err != nil {
		return nil, err
	}
//因为我们要批量获取日志，所以我们需要将它们展平成一条普通的流。
	return event.NewSubscription(func(quit <-chan struct{}) error {
		defer sub.Unsubscribe()
		for {
			select {
			case logs := <-sink:
				for _, log := range logs {
					select {
					case ch <- *log:
					case err := <-sub.Err():
						return err
					case <-quit:
						return nil
					}
				}
			case err := <-sub.Err():
				return err
			case <-quit:
				return nil
			}
		}
	}), nil
}

//AdjustTime为模拟时钟增加了一个时间偏移。
func (b *SimulatedBackend) AdjustTime(adjustment time.Duration) error {
	b.mu.Lock()
	defer b.mu.Unlock()
	blocks, _ := core.GenerateChain(b.config, b.blockchain.CurrentBlock(), ethash.NewFaker(), b.database, 1, func(number int, block *core.BlockGen) {
		for _, tx := range b.pendingBlock.Transactions() {
			block.AddTx(tx)
		}
		block.OffsetTime(int64(adjustment.Seconds()))
	})
	statedb, _ := b.blockchain.State()

	b.pendingBlock = blocks[0]
	b.pendingState, _ = state.New(b.pendingBlock.Root(), statedb.Database())

	return nil
}

//callmsg实现core.message以允许将其作为事务模拟器传递。
type callmsg struct {
	ethereum.CallMsg
}

func (m callmsg) From() common.Address { return m.CallMsg.From }
func (m callmsg) Nonce() uint64        { return 0 }
func (m callmsg) CheckNonce() bool     { return false }
func (m callmsg) To() *common.Address  { return m.CallMsg.To }
func (m callmsg) GasPrice() *big.Int   { return m.CallMsg.GasPrice }
func (m callmsg) Gas() uint64          { return m.CallMsg.Gas }
func (m callmsg) Value() *big.Int      { return m.CallMsg.Value }
func (m callmsg) Data() []byte         { return m.CallMsg.Data }

//filterbackend实现筛选器。backend支持筛选不包含
//考虑到布卢姆钻头的加速结构。
type filterBackend struct {
	db ethdb.Database
	bc *core.BlockChain
}

func (fb *filterBackend) ChainDb() ethdb.Database  { return fb.db }
func (fb *filterBackend) EventMux() *event.TypeMux { panic("not supported") }

func (fb *filterBackend) HeaderByNumber(ctx context.Context, block rpc.BlockNumber) (*types.Header, error) {
	if block == rpc.LatestBlockNumber {
		return fb.bc.CurrentHeader(), nil
	}
	return fb.bc.GetHeaderByNumber(uint64(block.Int64())), nil
}

func (fb *filterBackend) HeaderByHash(ctx context.Context, hash common.Hash) (*types.Header, error) {
	return fb.bc.GetHeaderByHash(hash), nil
}

func (fb *filterBackend) GetReceipts(ctx context.Context, hash common.Hash) (types.Receipts, error) {
	number := rawdb.ReadHeaderNumber(fb.db, hash)
	if number == nil {
		return nil, nil
	}
	return rawdb.ReadReceipts(fb.db, hash, *number), nil
}

func (fb *filterBackend) GetLogs(ctx context.Context, hash common.Hash) ([][]*types.Log, error) {
	number := rawdb.ReadHeaderNumber(fb.db, hash)
	if number == nil {
		return nil, nil
	}
	receipts := rawdb.ReadReceipts(fb.db, hash, *number)
	if receipts == nil {
		return nil, nil
	}
	logs := make([][]*types.Log, len(receipts))
	for i, receipt := range receipts {
		logs[i] = receipt.Logs
	}
	return logs, nil
}

func (fb *filterBackend) SubscribeNewTxsEvent(ch chan<- core.NewTxsEvent) event.Subscription {
	return event.NewSubscription(func(quit <-chan struct{}) error {
		<-quit
		return nil
	})
}
func (fb *filterBackend) SubscribeChainEvent(ch chan<- core.ChainEvent) event.Subscription {
	return fb.bc.SubscribeChainEvent(ch)
}
func (fb *filterBackend) SubscribeRemovedLogsEvent(ch chan<- core.RemovedLogsEvent) event.Subscription {
	return fb.bc.SubscribeRemovedLogsEvent(ch)
}
func (fb *filterBackend) SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscription {
	return fb.bc.SubscribeLogsEvent(ch)
}

func (fb *filterBackend) BloomStatus() (uint64, uint64) { return 4096, 0 }
func (fb *filterBackend) ServiceFilter(ctx context.Context, ms *bloombits.MatcherSession) {
	panic("not supported")
}