以太坊交易基本流程：
完整流程分为以下几个步骤：
- 发起交易：指定目标地址和交易金额，以及需要的gas/gaslimit
- 交易签名：使用账户私钥对交易进行签名
- 提交交易：把交易加入到交易缓冲池txpool中（会先对交易签名进行验证）
- 广播交易：通知EVM执行，同时把交易信息广播给其他结点
用户通过JSON RPC发起 eth_sendTransaction 请求，最终会调用 PublicTransactionPoolAPI 的 SendTransaction 实现，
首先根据from地址查找到对应的wallet，检查一下参数值，
* 通过SendTxArgs.toTransaction()创建交易
* 通过Wallet.SignTx()对交易进行签名
* 通过submitTransaction()提交交易
//代码位于 `internal/ethapi/api.go` 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 { return common.Hash{}, err } return submitTransaction(ctx, s.b, signed) }交易签名主要实现在 signTransaction，主要功能：
toTransaction() ：创建交易 wallet.SignTxWithPassphrase(account, passwd, tx, chainID)：对交易进行签名
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) }tx := args.toTransaction() 创建交易
先看一下SendTxArgs类型的定义：
// 代码 internal/ethapi/api.go // SendTxArgs represents the arguments to sumbit a new transaction into the transaction pool. type SendTxArgs struct { From common.Address `json:"from"` To *common.Address `json:"to"` Gas *hexutil.Uint64 `json:"gas"` GasPrice *hexutil.Big `json:"gasPrice"` Value *hexutil.Big `json:"value"` Nonce *hexutil.Uint64 `json:"nonce"` // We accept "data" and "input" for backwards-compatibility reasons. "input" is the // newer name and should be preferred by clients. Data *hexutil.Bytes `json:"data"` Input *hexutil.Bytes `json:"input"` }可以看到是和JSON字段相应的，包括了地址、gas、金额这些交易信息，nonce是一个随账户交易次数自增的数字，一般会自动填充。交易还可以携带一些额外数据，存放在data或者input字段中，推荐用input，data是为了向后兼容。
toTransaction()函数：
// 代码 internal/ethapi/api.go 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) }可以看到，如果目标地址为空的话，表示这是一个创建智能合约的交易，调用NewContractCreation()。否则说明这是一个普通交易，调用NewTransaction()。不管调用哪个，最终都会生成一个Transaction实例，我们看一下Transaction类型的定义：
// 代码位于core/types/transaction.go type Transaction struct { data txdata // caches hash atomic.Value size atomic.Value from atomic.Value } type txdata struct { AccountNonce uint64 `json:"nonce" gencodec:"required"` Price *big.Int `json:"gasPrice" gencodec:"required"` GasLimit uint64 `json:"gas" gencodec:"required"` Recipient *common.Address `json:"to" rlp:"nil"` // nil means contract creation Amount *big.Int `json:"value" gencodec:"required"` Payload []byte `json:"input" gencodec:"required"` // Signature values V *big.Int `json:"v" gencodec:"required"` R *big.Int `json:"r" gencodec:"required"` S *big.Int `json:"s" gencodec:"required"` // This is only used when marshaling to JSON. Hash *common.Hash `json:"hash" rlp:"-"` }wallet.SignTxWithPassphrase 代码
// accounts/keystore/keystore_wallet.go // SignTxWithPassphrase implements accounts.Wallet, attempting to sign the given // transaction with the given account using passphrase as extra authentication. func (w *keystoreWallet) SignTxWithPassphrase(account accounts.Account, passphrase string, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) { // Make sure the requested account is contained within if account.Address != w.account.Address { return nil, accounts.ErrUnknownAccount } if account.URL != (accounts.URL{}) && account.URL != w.account.URL { return nil, accounts.ErrUnknownAccount } // Account seems valid, request the keystore to sign return w.keystore.SignTxWithPassphrase(account, passphrase, tx, chainID) }w.keystore.SignTxWithPassphrase(account, passphrase, tx, chainID) 代码：
主要就是通过 SignTx 进行签名。
// 代码 accounts/keystore/keystore.go 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) }这里会首先判断账户是否已经解锁，如果已经解锁的话就可以获取它的私钥。
最后调用一个全局函数SignTx()完成签名：
代码位于core/types/transaction_signing.go： // 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) }主要分为3个步骤：
- 生成交易的hash值
- 根据hash值和私钥生成签名
- 把签名数据填充到Transaction实例中
生成交易的hash值
以EIP155Signer为例，代码如下：
func (s EIP155Signer) 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, s.chainId, uint(0), uint(0), }) } func rlpHash(x interface{}) (h common.Hash) { hw := sha3.NewKeccak256() rlp.Encode(hw, x) hw.Sum(h[:0]) return h } 可以看到，先用SHA3-256生成hash值，然后再进行RLP编码。RLP是一种数据序列化方法。
根据hash值和私钥生成签名-crypto.Sign()
// 代码位于crypto/signature_cgo.go： func Sign(hash []byte, prv *ecdsa.PrivateKey) (sig []byte, err error) { if len(hash) != 32 { return nil, fmt.Errorf("hash is required to be exactly 32 bytes (%d)", len(hash)) } seckey := math.PaddedBigBytes(prv.D, prv.Params().BitSize/8) defer zeroBytes(seckey) return secp256k1.Sign(hash, seckey) } 这里是通过ECDSA算法生成签名数据。最终会返回的签名是一个字节数组，按R / S / V的顺序排列。
填充签名数据 - WithSignature
//代码位于 core/types/transaction.go func (tx *Transaction) WithSignature(signer Signer, sig []byte) (*Transaction, error) { r, s, v, err := signer.SignatureValues(tx, sig) if err != nil { return nil, err } cpy := &Transaction{data: tx.data} cpy.data.R, cpy.data.S, cpy.data.V = r, s, v return cpy, nil }生成的签名数据是字节数组类型，需要通过signer.SignatureValues()函数转换成3个big.Int类型的数据，然后填充到Transaction结构的R / S / V字段上
签名完成以后，就需要调用 submitTransaction() 函数提交到交易缓冲池txpool中。
先看下TxPool中的几个重要字段：
// 代码 core/tx_pool.go type TxPool struct { config TxPoolConfig chainconfig *params.ChainConfig chain blockChain gasPrice *big.Int txFeed event.Feed scope event.SubscriptionScope chainHeadCh chan ChainHeadEvent chainHeadSub event.Subscription signer types.Signer mu sync.RWMutex currentState *state.StateDB // Current state in the blockchain head pendingState *state.ManagedState // Pending state tracking virtual nonces currentMaxGas uint64 // Current gas limit for transaction caps locals *accountSet // Set of local transaction to exempt from eviction rules journal *txJournal // Journal of local transaction to back up to disk pending map[common.Address]*txList // All currently processable transactions queue map[common.Address]*txList // Queued but non-processable transactions beats map[common.Address]time.Time // Last heartbeat from each known account all *txLookup // All transactions to allow lookups priced *txPricedList // All transactions sorted by price wg sync.WaitGroup // for shutdown sync homestead bool }pending字段中包含了当前所有可被处理的交易列表，而queue字段中包含了所有不可被处理、也就是新加入进来的交易。下面查看一下pending字段 的txList的结构：
type txList struct { strict bool // Whether nonces are strictly continuous or not txs *txSortedMap // Heap indexed sorted hash map of the transactions costcap *big.Int // Price of the highest costing transaction (reset only if exceeds balance) gascap uint64 // Gas limit of the highest spending transaction (reset only if exceeds block limit) } txList内部包含一个txSortedMap结构，实现按nonce排序，其内部维护了两张表：
- 一张是包含了所有Transaction的map，key是Transaction的nonce值。之前提到过，这个nonce是随着账户的交易次数自增的一个数字，所以越新的交易，nonce值越高。
- 还有一张表是一个数组，包含了所有nonce值，其内部是进行过堆排序的（小顶堆），nonce值按照从大到小排列。每次调用heap.Pop()时会取出最小的nonce值，也就是最老的交易。
all字段 中包含了所有的交易列表，以交易的hash作为key。
priced字段 则是把all中的交易列表按照gas price从大到小排列，如果gas price一样，则按照交易的nonce值从小到大排列。最终的目标是每次取出gas price最大、nonce最小的交易。
我们提交交易的目标是：先把交易放入queue中记录在案，然后再从queue中选一部分放入pending中进行处理。如果发现txpool满了，则依据priced中的排序，剔除低油价的交易。
txpool的默认配置：
var DefaultTxPoolConfig = TxPoolConfig{ Journal: "transactions.rlp", Rejournal: time.Hour, PriceLimit: 1, PriceBump: 10, AccountSlots: 16, GlobalSlots: 4096, AccountQueue: 64, GlobalQueue: 1024, Lifetime: 3 * time.Hour, }- GlobalSlots：pending列表的最大长度，默认4096笔
- AccountSlots：pending中每个账户存储的交易数的阈值，超过这个数量可能会被认为是垃圾交易或者是攻击者，多余交易可能被丢弃
- GlobalQueue：queue列表的最大长度，默认1024笔
- AccountQueue：queue中每个账户允许存储的最大交易数，超过会被丢弃，默认64笔
- PriceLimit：允许进入txpool的最低gas price，默认1 Gwei
- PriceBump：如果出现两个nonce相同的交易，gas price的差值超过该阈值则用新交易替换老交易
现在我们分析submitTransaction()函数：
//代码位于 `internal/ethapi/api.go` 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 }这里有一个Backend参数，是在eth Service初始化时创建的，具体实现在EthApiBackend中，代码位于eth/api_backend.go。可以看到，这里先调用了SendTx()函数提交交易，然后如果发现目标地址为空，表明这是一个创建智能合约的交易，会创建合约地址。
//代码 eth/api_backend.go func (b *EthAPIBackend) SendTx(ctx context.Context, signedTx *types.Transaction) error { return b.eth.txPool.AddLocal(signedTx) }继续跟踪TxPool的AddLocal()函数：
// 代码位于 core/tx_pool.go 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 }这里有两个主要函数：add()和promoteExecuteables()。
add()会判断是否应该把当前交易加入到queue列表中，promoteExecuteables()则会从queue中选取一些交易放入pending列表中等待执行。下面分别讨论这两个函数。
TxPool.add()
// 代码位于 core/tx_pool.go 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 { pool.locals.add(from) } pool.journalTx(from, tx) log.Trace("Pooled new future transaction", "hash", hash, "from", from, "to", tx.To()) return replace, nil }我们分成一段一段的来分析：
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) }这一段是先计算交易的hash值，然后判断是不是已经在txpool 中，在的话就直接退出。
// 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 }查看 pool.validateTx(tx, local) 代码
// 代码位于 core/tx_pool.go 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 }这一段是验证交易的有效性，主要进行以下几个方面的检查：
- 数据量必须<32KB
- 交易金额必须非负（>=0）
- 交易的gas limit必须低于block的gas limit
- 签名数据必须有效，能够解析出发送者地址
- 交易的gas price必须高于pool设定的最低gas price（除非是本地交易）
- 交易的nonce值必须高于当前链上该账户的nonce值（低于则说明这笔交易已经被打包过了）
- 当前账户余额必须大于
“交易金额 + gasprice * gaslimit” - 交易的gas limit必须大于对应数据量所需的最低gas水平
if uint64(len(pool.all)) >= 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(len(pool.all)-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) } } 这一段是在当前txpool已满的情况下，剔除掉低油价的交易。还记得之前有个priced字段存储了按gas price以及nonce排序的交易列表吗？这里会先把当前交易的gas price和当前池中的最低价进行比较：
- 如果低于最低价，直接丢弃该交易返回
- 如果高于最低价，则从txpool中剔除一些低价的交易
// New transaction isn't replacing a pending one, push into queue replace, err := pool.enqueueTx(hash, tx) if err != nil { return false, err } 如果之前的那些检查都没有问题，就真正调用enqueueTx()函数把交易加入到queue列表中了。
// Mark local addresses and journal local transactions if local { pool.locals.add(from) } pool.journalTx(from, tx)最后，如果发现这个账户是本地的，就把它加到一个白名单里，默认会保证本地交易优先被加到txpool中。
TxPool.promoteExecuteables()
主要目的是把交易从queue列表“提拔”到pending列表，代码逻辑比较清楚，具体可以参见下面这张图：
根据不同的目的可以分为3块，分别以粉色、紫色、绿色标识。
粉色部分主要是为了把queue中的交易“提拔”到pending中。当然在这之前需要先要进行一番检查：
- 丢弃nonce < 账户当前nonce的交易，也就是已经被打包过的交易
- 丢弃转账金额 + gas消耗 > 账户余额的交易，也就是会out-of-gas的交易
- 丢弃gas limit > block gas limit的交易，这部分交易可能会导致区块生成失败
紫色部分主要是为了清理pending列表，使其满足GlobalSlots和AccountSlots的限制条件：
- 如果有些账户的交易数超过了AccountSlots，则先按交易数最少的账户进行均衡。举例来说，如果有10个账户交易数超过了AccountSlots（默认16），其中交易数最少的账户包含20笔交易，那么先把其他9个账户的交易数量削减到20。
- 如果经过上面的步骤，pending的长度还是超过了GlobalSlots，那就严格按照AccountSlots进行均衡，也就是把上面的10个账户的交易数进一步削减到16。
绿色部分主要是为了清理queue列表，使其满足GlobalQueue和AccountQueue的限制条件：
- 如果每个账户的交易数超过了AccountQueue，丢弃多余交易
- 如果queue的长度超过了GlobalQueue，则把账户按最后一次心跳时间排序，然后依次去除账户中的交易，直到满足限制条件位置。
// 代码位于 core/tx_pool.go func (pool *TxPool) promoteExecutables(accounts []common.Address) { // Track the promoted transactions to broadcast them at once var promoted []*types.Transaction // Gather all the accounts potentially needing updates if accounts == nil { accounts = make([]common.Address, 0, len(pool.queue)) for addr := range pool.queue { accounts = append(accounts, addr) } } // Iterate over all accounts and promote any executable transactions for _, addr := range accounts { list := pool.queue[addr] if list == nil { continue // Just in case someone calls with a non existing account } // Drop all transactions that are deemed too old (low nonce) for _, tx := range list.Forward(pool.currentState.GetNonce(addr)) { hash := tx.Hash() log.Trace("Removed old queued transaction", "hash", hash) pool.all.Remove(hash) pool.priced.Removed() } // Drop all transactions that are too costly (low balance or out of gas) drops, _ := list.Filter(pool.currentState.GetBalance(addr), pool.currentMaxGas) for _, tx := range drops { hash := tx.Hash() log.Trace("Removed unpayable queued transaction", "hash", hash) pool.all.Remove(hash) pool.priced.Removed() queuedNofundsCounter.Inc(1) } // Gather all executable transactions and promote them for _, tx := range list.Ready(pool.pendingState.GetNonce(addr)) { hash := tx.Hash() if pool.promoteTx(addr, hash, tx) { log.Trace("Promoting queued transaction", "hash", hash) promoted = append(promoted, tx) } } // Drop all transactions over the allowed limit if !pool.locals.contains(addr) { for _, tx := range list.Cap(int(pool.config.AccountQueue)) { hash := tx.Hash() pool.all.Remove(hash) pool.priced.Removed() queuedRateLimitCounter.Inc(1) log.Trace("Removed cap-exceeding queued transaction", "hash", hash) } } // Delete the entire queue entry if it became empty. if list.Empty() { delete(pool.queue, addr) } } // Notify subsystem for new promoted transactions. if len(promoted) > 0 { pool.txFeed.Send(NewTxsEvent{promoted}) } // If the pending limit is overflown, start equalizing allowances pending := uint64(0) for _, list := range pool.pending { pending += uint64(list.Len()) } if pending > pool.config.GlobalSlots { pendingBeforeCap := pending // Assemble a spam order to penalize large transactors first spammers := prque.New() for addr, list := range pool.pending { // Only evict transactions from high rollers if !pool.locals.contains(addr) && uint64(list.Len()) > pool.config.AccountSlots { spammers.Push(addr, float32(list.Len())) } } // Gradually drop transactions from offenders offenders := []common.Address{} for pending > pool.config.GlobalSlots && !spammers.Empty() { // Retrieve the next offender if not local address offender, _ := spammers.Pop() offenders = append(offenders, offender.(common.Address)) // Equalize balances until all the same or below threshold if len(offenders) > 1 { // Calculate the equalization threshold for all current offenders threshold := pool.pending[offender.(common.Address)].Len() // Iteratively reduce all offenders until below limit or threshold reached for pending > pool.config.GlobalSlots && pool.pending[offenders[len(offenders)-2]].Len() > threshold { for i := 0; i < len(offenders)-1; i++ { list := pool.pending[offenders[i]] for _, tx := range list.Cap(list.Len() - 1) { // Drop the transaction from the global pools too hash := tx.Hash() pool.all.Remove(hash) pool.priced.Removed() // Update the account nonce to the dropped transaction if nonce := tx.Nonce(); pool.pendingState.GetNonce(offenders[i]) > nonce { pool.pendingState.SetNonce(offenders[i], nonce) } log.Trace("Removed fairness-exceeding pending transaction", "hash", hash) } pending-- } } } } // If still above threshold, reduce to limit or min allowance if pending > pool.config.GlobalSlots && len(offenders) > 0 { for pending > pool.config.GlobalSlots && uint64(pool.pending[offenders[len(offenders)-1]].Len()) > pool.config.AccountSlots { for _, addr := range offenders { list := pool.pending[addr] for _, tx := range list.Cap(list.Len() - 1) { // Drop the transaction from the global pools too hash := tx.Hash() pool.all.Remove(hash) pool.priced.Removed() // Update the account nonce to the dropped transaction if nonce := tx.Nonce(); pool.pendingState.GetNonce(addr) > nonce { pool.pendingState.SetNonce(addr, nonce) } log.Trace("Removed fairness-exceeding pending transaction", "hash", hash) } pending-- } } } pendingRateLimitCounter.Inc(int64(pendingBeforeCap - pending)) } // If we've queued more transactions than the hard limit, drop oldest ones queued := uint64(0) for _, list := range pool.queue { queued += uint64(list.Len()) } if queued > pool.config.GlobalQueue { // Sort all accounts with queued transactions by heartbeat addresses := make(addresssByHeartbeat, 0, len(pool.queue)) for addr := range pool.queue { if !pool.locals.contains(addr) { // don't drop locals addresses = append(addresses, addressByHeartbeat{addr, pool.beats[addr]}) } } sort.Sort(addresses) // Drop transactions until the total is below the limit or only locals remain for drop := queued - pool.config.GlobalQueue; drop > 0 && len(addresses) > 0; { addr := addresses[len(addresses)-1] list := pool.queue[addr.address] addresses = addresses[:len(addresses)-1] // Drop all transactions if they are less than the overflow if size := uint64(list.Len()); size <= drop { for _, tx := range list.Flatten() { pool.removeTx(tx.Hash(), true) } drop -= size queuedRateLimitCounter.Inc(int64(size)) continue } // Otherwise drop only last few transactions txs := list.Flatten() for i := len(txs) - 1; i >= 0 && drop > 0; i-- { pool.removeTx(txs[i].Hash(), true) drop-- queuedRateLimitCounter.Inc(1) } } } }交易提交到txpool中后，还需要广播出去，一方面通知EVM执行该交易，另一方面要把交易信息广播给其他结点。具体调用在 promoteExecutables 提到的promoteTx()函数中：
// 代码位于 core/tx_pool.go func (pool *TxPool) promoteExecutables(accounts []common.Address) { ... // Gather all executable transactions and promote them for _, tx := range list.Ready(pool.pendingState.GetNonce(addr)) { hash := tx.Hash() if pool.promoteTx(addr, hash, tx) { log.Trace("Promoting queued transaction", "hash", hash) promoted = append(promoted, tx) } } } ... // Notify subsystem for new promoted transactions. if len(promoted) > 0 { pool.txFeed.Send(NewTxsEvent{promoted}) }promoteTx 详细代码：
// 代码 crypto/tx_pool.go func (pool *TxPool) promoteTx(addr common.Address, hash common.Hash, tx *types.Transaction) bool { // Try to insert the transaction into the pending queue if pool.pending[addr] == nil { pool.pending[addr] = newTxList(true) } list := pool.pending[addr] inserted, old := list.Add(tx, pool.config.PriceBump) if !inserted { // An older transaction was better, discard this pool.all.Remove(hash) pool.priced.Removed() pendingDiscardCounter.Inc(1) return false } // Otherwise discard any previous transaction and mark this if old != nil { pool.all.Remove(old.Hash()) pool.priced.Removed() pendingReplaceCounter.Inc(1) } // Failsafe to work around direct pending inserts (tests) if pool.all.Get(hash) == nil { pool.all.Add(tx) pool.priced.Put(tx) } // Set the potentially new pending nonce and notify any subsystems of the new tx pool.beats[addr] = time.Now() pool.pendingState.SetNonce(addr, tx.Nonce()+1) return true }先更新了最后一次心跳时间，然后更新账户的nonce值。
pool.txFeed.Send 发送一个TxPreEvent事件，外部可以通过SubscribeNewTxsEvent()函数订阅该事件：
func (pool *TxPool) SubscribeNewTxsEvent(ch chan<- core.NewTxsEvent) event.Subscription { return pool.scope.Track(pool.txFeed.Subscribe(ch)) }我们只要搜索一下这个函数，就可以知道哪些组件订阅了该事件了。
第一个订阅的地方位于miner/worker.go：
func newWorker(config *params.ChainConfig, engine consensus.Engine, coinbase common.Address, eth Backend, mux *event.TypeMux) *worker { .... // Subscribe NewTxsEvent for tx pool worker.txsSub = eth.TxPool().SubscribeNewTxsEvent(worker.txsCh) .... } 开启了一个goroutine来接收TxPreEvent，看一下update()函数：
func (self *worker) update() { defer self.txsSub.Unsubscribe() defer self.chainHeadSub.Unsubscribe() defer self.chainSideSub.Unsubscribe() for { ... // Handle NewTxsEvent case ev := <-self.txsCh: // Apply transactions to the pending state if we're not mining. // // Note all transactions received may not be continuous with transactions // already included in the current mining block. These transactions will // be automatically eliminated. if atomic.LoadInt32(&self.mining) == 0 { self.currentMu.Lock() txs := make(map[common.Address]types.Transactions) for _, tx := range ev.Txs { acc, _ := types.Sender(self.current.signer, tx) txs[acc] = append(txs[acc], tx) } txset := types.NewTransactionsByPriceAndNonce(self.current.signer, txs) self.current.commitTransactions(self.mux, txset, self.chain, self.coinbase) self.updateSnapshot() self.currentMu.Unlock() } else { // If we're mining, but nothing is being processed, wake on new transactions if self.config.Clique != nil && self.config.Clique.Period == 0 { self.commitNewWork() } } ... } } }可以看到，如果结点不挖矿的话，这里会立即调用commitTransactions()提交给EVM执行，获得本地回执。
如果结点挖矿的话，miner会调用commitNewWork()，内部也会调用commitTransactions()执行交易。
另一个订阅的地方位于eth/handler.go：
func (pm *ProtocolManager) Start(maxPeers int) { ... // broadcast transactions pm.txsCh = make(chan core.NewTxsEvent, txChanSize) pm.txsSub = pm.txpool.SubscribeNewTxsEvent(pm.txsCh) go pm.txBroadcastLoop() ... }同样也是启动了一个goroutine来接收TxPreEvent事件，看一下txBroadcastLoop()函数：
func (pm *ProtocolManager) txBroadcastLoop() { for { select { case event := <-pm.txCh: pm.BroadcastTx(event.Tx.Hash(), event.Tx) // Err() channel will be closed when unsubscribing. case <-pm.txSub.Err(): return } } }继续跟踪BroadcastTx()函数：
func (pm *ProtocolManager) BroadcastTxs(txs types.Transactions) { var txset = make(map[*peer]types.Transactions) // Broadcast transactions to a batch of peers not knowing about it for _, tx := range txs { peers := pm.peers.PeersWithoutTx(tx.Hash()) for _, peer := range peers { txset[peer] = append(txset[peer], tx) } log.Trace("Broadcast transaction", "hash", tx.Hash(), "recipients", len(peers)) } // FIXME include this again: peers = peers[:int(math.Sqrt(float64(len(peers))))] for peer, txs := range txset { peer.AsyncSendTransactions(txs) } }可以看到，这里会通过P2P向所有没有该交易的结点发送该交易。
文章来源: 以太坊源码解析 - 交易源码分析