以太坊源码学习-交易体创建

这篇文章学习以太坊转账中交易生成流程。

// internal/ethapi/api.go

// SendTransaction will create a transaction from the given arguments and
// tries to sign it with the key associated with args.To. If the given passwd isn't
// able to decrypt the key it fails.
func (s *PrivateAccountAPI) SendTransaction(ctx context.Context, args SendTxArgs, passwd string) (common.Hash, error) {
    if args.Nonce == nil {
        // Hold the addresse's mutex around signing to prevent concurrent assignment of
        // the same nonce to multiple accounts.
        s.nonceLock.LockAddr(args.From)
        defer s.nonceLock.UnlockAddr(args.From)
    }
    signed, err := s.signTransaction(ctx, &args, passwd)
    if err != nil {
        log.Warn("Failed transaction send attempt", "from", args.From, "to", args.To, "value", args.Value.ToInt(), "err", err)
        return common.Hash{}, err
    }
    return submitTransaction(ctx, s.b, signed)
}

如果 args.Nonce == nil，那么后面会通过 GetPoolNonce() 来获取一个 Nonce，这里需要上锁，也可以指定 Nonce。

signTransaction 是构造交易和签名的流程。

// signTransaction sets defaults and signs the given transaction
// NOTE: the caller needs to ensure that the nonceLock is held, if applicable,
// and release it after the transaction has been submitted to the tx pool
func (s *PrivateAccountAPI) signTransaction(ctx context.Context, args *SendTxArgs, passwd string) (*types.Transaction, error) {
    // Look up the wallet containing the requested signer
    account := accounts.Account{Address: args.From}
    wallet, err := s.am.Find(account)
    if err != nil {
        return nil, err
    }
    // Set some sanity defaults and terminate on failure
    if err := args.setDefaults(ctx, s.b); err != nil {
        return nil, err
    }
    // Assemble the transaction and sign with the wallet
    tx := args.toTransaction()

    var chainID *big.Int
    if config := s.b.ChainConfig(); config.IsEIP155(s.b.CurrentBlock().Number()) {
        chainID = config.ChainID
    }
    return wallet.SignTxWithPassphrase(account, passwd, tx, chainID)
}

setDefaults 是对交易体做一些默认配置。 toTransaction 是构造交易体。 SignTxWithPassphrase 是签名流程。 先看下 setDefaults ：

// setDefaults is a helper function that fills in default values for unspecified tx fields.
func (args *SendTxArgs) setDefaults(ctx context.Context, b Backend) error {
    if args.Gas == nil {
        args.Gas = new(hexutil.Uint64)
        *(*uint64)(args.Gas) = 90000
    }
    if args.GasPrice == nil {
        price, err := b.SuggestPrice(ctx)
        if err != nil {
            return err
        }
        args.GasPrice = (*hexutil.Big)(price)
    }
    if args.Value == nil {
        args.Value = new(hexutil.Big)
    }
    if args.Nonce == nil {
        nonce, err := b.GetPoolNonce(ctx, args.From)
        if err != nil {
            return err
        }
        args.Nonce = (*hexutil.Uint64)(&nonce)
    }
    if args.Data != nil && args.Input != nil && !bytes.Equal(*args.Data, *args.Input) {
        return errors.New(`Both "data" and "input" are set and not equal. Please use "input" to pass transaction call data.`)
    }
    if args.To == nil {
        // Contract creation
        var input []byte
        if args.Data != nil {
            input = *args.Data
        } else if args.Input != nil {
            input = *args.Input
        }
        if len(input) == 0 {
            return errors.New(`contract creation without any data provided`)
        }
    }
    return nil
}

如果不提供 gas 限制值，那么默认是 90000.

如果不提供 GasPrice，那么会通过 SuggestPrice() 获得一个推荐值。

如果没有 nonce， 那么会通过 GetPoolNonce() 来得到一个。

在 to == nil 的时候，是创建智能合约，那么会对 data 和 input 进行一系列检查。

下面是构造交易体流程：

func (args *SendTxArgs) toTransaction() *types.Transaction {
    var input []byte
    if args.Data != nil {
        input = *args.Data
    } else if args.Input != nil {
        input = *args.Input
    }
    if args.To == nil {
        return types.NewContractCreation(uint64(*args.Nonce), (*big.Int)(args.Value), uint64(*args.Gas), (*big.Int)(args.GasPrice), input)
    }
    return types.NewTransaction(uint64(*args.Nonce), *args.To, (*big.Int)(args.Value), uint64(*args.Gas), (*big.Int)(args.GasPrice), input)
}

func NewTransaction(nonce uint64, to common.Address, amount *big.Int, gasLimit uint64, gasPrice *big.Int, data []byte) *Transaction {
    return newTransaction(nonce, &to, amount, gasLimit, gasPrice, data)
}

func newTransaction(nonce uint64, to *common.Address, amount *big.Int, gasLimit uint64, gasPrice *big.Int, data []byte) *Transaction {
    if len(data) > 0 {
        data = common.CopyBytes(data)
    }
    d := txdata{
        AccountNonce: nonce,
        Recipient:    to,
        Payload:      data,
        Amount:       new(big.Int),
        GasLimit:     gasLimit,
        Price:        new(big.Int),
        V:            new(big.Int),
        R:            new(big.Int),
        S:            new(big.Int),
    }
    if amount != nil {
        d.Amount.Set(amount)
    }
    if gasPrice != nil {
        d.Price.Set(gasPrice)
    }

    return &Transaction{data: d}
}

下面是签名的流程：

// SignTxWithPassphrase signs the transaction if the private key matching the
// given address can be decrypted with the given passphrase.
func (ks *KeyStore) SignTxWithPassphrase(a accounts.Account, passphrase string, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
    _, key, err := ks.getDecryptedKey(a, passphrase)
    if err != nil {
        return nil, err
    }
    defer zeroKey(key.PrivateKey)

    // Depending on the presence of the chain ID, sign with EIP155 or homestead
    if chainID != nil {
        return types.SignTx(tx, types.NewEIP155Signer(chainID), key.PrivateKey)
    }
    return types.SignTx(tx, types.HomesteadSigner{}, key.PrivateKey)
}

先通过密码得到解密的密钥，然后调用 SignTx 来签名，注意的是 defer zeroKey，这里保证在函数结束的时候，会清空内存中的私钥。

// SignTx signs the transaction using the given signer and private key
func SignTx(tx *Transaction, s Signer, prv *ecdsa.PrivateKey) (*Transaction, error) {
    h := s.Hash(tx)
    sig, err := crypto.Sign(h[:], prv)
    if err != nil {
        return nil, err
    }
    return tx.WithSignature(s, sig)
}

先求 hash 然后做 sign。

看下 hash 的过程：

// Hash returns the hash to be signed by the sender.
// It does not uniquely identify the transaction.
func (fs FrontierSigner) Hash(tx *Transaction) common.Hash {
    return rlpHash([]interface{}{
        tx.data.AccountNonce,
        tx.data.Price,
        tx.data.GasLimit,
        tx.data.Recipient,
        tx.data.Amount,
        tx.data.Payload,
    })
}

这里是 rlpHash，即先做 RLP 转换，然后做 Keccak256 hash。这里 hash 的数据，包括：账户 nonce，gas price，gas limint，目标地址，金额，额外数据。

// submitTransaction is a helper function that submits tx to txPool and logs a message.
func submitTransaction(ctx context.Context, b Backend, tx *types.Transaction) (common.Hash, error) {
    if err := b.SendTx(ctx, tx); err != nil {
        return common.Hash{}, err
    }
    if tx.To() == nil {
        signer := types.MakeSigner(b.ChainConfig(), b.CurrentBlock().Number())
        from, err := types.Sender(signer, tx)
        if err != nil {
            return common.Hash{}, err
        }
        addr := crypto.CreateAddress(from, tx.Nonce())
        log.Info("Submitted contract creation", "fullhash", tx.Hash().Hex(), "contract", addr.Hex())
    } else {
        log.Info("Submitted transaction", "fullhash", tx.Hash().Hex(), "recipient", tx.To())
    }
    return tx.Hash(), nil
}

这里提交交易体到网络上，并且如果是创建智能合约的交易，那么会将智能合约地址计算出来，并记录到 log，最后返回交易体的 hash。

// CreateAddress creates an ethereum address given the bytes and the nonce
func CreateAddress(b common.Address, nonce uint64) common.Address {
    data, _ := rlp.EncodeToBytes([]interface{}{b, nonce})
    return common.BytesToAddress(Keccak256(data)[12:])
}

智能合约的地址是通过 创建者地址 和 nonce 计算出来的，可以保证唯一。

再看下 SendTx 的流程：

func (b *EthAPIBackend) SendTx(ctx context.Context, signedTx *types.Transaction) error {
    return b.eth.txPool.AddLocal(signedTx)
}

// AddLocal enqueues a single transaction into the pool if it is valid, marking
// the sender as a local one in the mean time, ensuring it goes around the local
// pricing constraints.
func (pool *TxPool) AddLocal(tx *types.Transaction) error {
    return pool.addTx(tx, !pool.config.NoLocals)
}

// addTx enqueues a single transaction into the pool if it is valid.
func (pool *TxPool) addTx(tx *types.Transaction, local bool) error {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    // Try to inject the transaction and update any state
    replace, err := pool.add(tx, local)
    if err != nil {
        return err
    }
    // If we added a new transaction, run promotion checks and return
    if !replace {
        from, _ := types.Sender(pool.signer, tx) // already validated
        pool.promoteExecutables([]common.Address{from})
    }
    return nil
}

主要的验证流程在 add 内：

// add validates a transaction and inserts it into the non-executable queue for
// later pending promotion and execution. If the transaction is a replacement for
// an already pending or queued one, it overwrites the previous and returns this
// so outer code doesn't uselessly call promote.
//
// If a newly added transaction is marked as local, its sending account will be
// whitelisted, preventing any associated transaction from being dropped out of
// the pool due to pricing constraints.
func (pool *TxPool) add(tx *types.Transaction, local bool) (bool, error) {
    // If the transaction is already known, discard it
    hash := tx.Hash()
    if pool.all.Get(hash) != nil {
        log.Trace("Discarding already known transaction", "hash", hash)
        return false, fmt.Errorf("known transaction: %x", hash)
    }
    // If the transaction fails basic validation, discard it
    if err := pool.validateTx(tx, local); err != nil {
        log.Trace("Discarding invalid transaction", "hash", hash, "err", err)
        invalidTxCounter.Inc(1)
        return false, err
    }
    // If the transaction pool is full, discard underpriced transactions
    if uint64(pool.all.Count()) >= pool.config.GlobalSlots+pool.config.GlobalQueue {
        // If the new transaction is underpriced, don't accept it
        if !local && pool.priced.Underpriced(tx, pool.locals) {
            log.Trace("Discarding underpriced transaction", "hash", hash, "price", tx.GasPrice())
            underpricedTxCounter.Inc(1)
            return false, ErrUnderpriced
        }
        // New transaction is better than our worse ones, make room for it
        drop := pool.priced.Discard(pool.all.Count()-int(pool.config.GlobalSlots+pool.config.GlobalQueue-1), pool.locals)
        for _, tx := range drop {
            log.Trace("Discarding freshly underpriced transaction", "hash", tx.Hash(), "price", tx.GasPrice())
            underpricedTxCounter.Inc(1)
            pool.removeTx(tx.Hash(), false)
        }
    }
    // If the transaction is replacing an already pending one, do directly
    from, _ := types.Sender(pool.signer, tx) // already validated
    if list := pool.pending[from]; list != nil && list.Overlaps(tx) {
        // Nonce already pending, check if required price bump is met
        inserted, old := list.Add(tx, pool.config.PriceBump)
        if !inserted {
            pendingDiscardCounter.Inc(1)
            return false, ErrReplaceUnderpriced
        }
        // New transaction is better, replace old one
        if old != nil {
            pool.all.Remove(old.Hash())
            pool.priced.Removed()
            pendingReplaceCounter.Inc(1)
        }
        pool.all.Add(tx)
        pool.priced.Put(tx)
        pool.journalTx(from, tx)

        log.Trace("Pooled new executable transaction", "hash", hash, "from", from, "to", tx.To())

        // We've directly injected a replacement transaction, notify subsystems
        go pool.txFeed.Send(NewTxsEvent{types.Transactions{tx}})

        return old != nil, nil
    }
    // New transaction isn't replacing a pending one, push into queue
    replace, err := pool.enqueueTx(hash, tx)
    if err != nil {
        return false, err
    }
    // Mark local addresses and journal local transactions
    if local {
        if !pool.locals.contains(from) {
            log.Info("Setting new local account", "address", from)
            pool.locals.add(from)
        }
    }
    pool.journalTx(from, tx)

    log.Trace("Pooled new future transaction", "hash", hash, "from", from, "to", tx.To())
    return replace, nil
}

1. 如果 hash 在池内已经存在，那么忽略
2. 验证 tx 的有效性
3. 如果池子已经满了，tx 不是 local，而且tx的价格最低，那么忽略，否则的话，清除目前最低价格的腾出一个位置。
4. 如果 from 和 nonce 都相同，那么就替换掉之前的交易，否则就插入队列。
5. 更新下 pool 的 locals 列表。

// validateTx checks whether a transaction is valid according to the consensus
// rules and adheres to some heuristic limits of the local node (price and size).
func (pool *TxPool) validateTx(tx *types.Transaction, local bool) error {
    // Heuristic limit, reject transactions over 32KB to prevent DOS attacks
    if tx.Size() > 32*1024 {
        return ErrOversizedData
    }
    // Transactions can't be negative. This may never happen using RLP decoded
    // transactions but may occur if you create a transaction using the RPC.
    if tx.Value().Sign() < 0 {
        return ErrNegativeValue
    }
    // Ensure the transaction doesn't exceed the current block limit gas.
    if pool.currentMaxGas < tx.Gas() {
        return ErrGasLimit
    }
    // Make sure the transaction is signed properly
    from, err := types.Sender(pool.signer, tx)
    if err != nil {
        return ErrInvalidSender
    }
    // Drop non-local transactions under our own minimal accepted gas price
    local = local || pool.locals.contains(from) // account may be local even if the transaction arrived from the network
    if !local && pool.gasPrice.Cmp(tx.GasPrice()) > 0 {
        return ErrUnderpriced
    }
    // Ensure the transaction adheres to nonce ordering
    if pool.currentState.GetNonce(from) > tx.Nonce() {
        return ErrNonceTooLow
    }
    // Transactor should have enough funds to cover the costs
    // cost == V + GP * GL
    if pool.currentState.GetBalance(from).Cmp(tx.Cost()) < 0 {
        return ErrInsufficientFunds
    }
    intrGas, err := IntrinsicGas(tx.Data(), tx.To() == nil, pool.homestead)
    if err != nil {
        return err
    }
    if tx.Gas() < intrGas {
        return ErrIntrinsicGas
    }
    return nil
}

1. 交易的大小不能超过 32K
2. 签名不能小于0
3. 交易gas limit 不能小于现在 pool 的 limits
4. 什么是 signer? signer 可以用来从 tx 得到 from
5. 如果不是 local，那么 price 不能小于现在池子的 price
6. nonce 不能小于 池子的 nonce
7. 余额要足够
8. 计算实际的 gas 消耗，不能大于交易的 gas limit
9. 都没问题的话，就返回成功