core/txpool/legacypool: add support for SetCode transactions (#31073)

The new SetCode transaction type introduces some additional complexity
when handling the transaction pool.

This complexity stems from two new account behaviors:

1. The balance and nonce of an account can change during regular
   transaction execution *when they have a deployed delegation*.
2. The nonce and code of an account can change without any EVM execution
   at all. This is the "set code" mechanism introduced by EIP-7702.

The first issue has already been considered extensively during the design
of ERC-4337, and we're relatively confident in the solution of simply
limiting the number of in-flight pending transactions an account can have
to one. This puts a reasonable bound on transaction cancellation. Normally
to cancel, you would need to spend 21,000 gas. Now it's possible to cancel
for around the cost of warming the account and sending value
(`2,600+9,000=11,600`). So 50% cheaper.

The second issue is more novel and needs further consideration.
Since authorizations are not bound to a specific transaction, we
cannot drop transactions with conflicting authorizations. Otherwise,
it might be possible to cherry-pick authorizations from txs and front
run them with different txs at much lower fee amounts, effectively DoSing
the authority. Fortunately, conflicting authorizations do not affect the
underlying validity of the transaction so we can just accept both.

---------

Co-authored-by: Marius van der Wijden <[email protected]>
Co-authored-by: Felix Lange <[email protected]>

core/txpool/blobpool/blobpool_test.go

@@ -142,6 +142,7 @@ func (bc *testBlockChain) CurrentBlock() *types.Header {
 		GasLimit:      gasLimit,
 		BaseFee:       baseFee,
 		ExcessBlobGas: &excessBlobGas,
+		Difficulty:    common.Big0,
 	}
 }
 
@@ -1565,8 +1566,9 @@ func TestAdd(t *testing.T) {
 		if tt.block != nil {
 			// Fake a header for the new set of transactions
 			header := &types.Header{
-				Number:  big.NewInt(int64(chain.CurrentBlock().Number.Uint64() + 1)),
-				BaseFee: chain.CurrentBlock().BaseFee, // invalid, but nothing checks it, yolo
+				Number:     big.NewInt(int64(chain.CurrentBlock().Number.Uint64() + 1)),
+				Difficulty: common.Big0,
+				BaseFee:    chain.CurrentBlock().BaseFee, // invalid, but nothing checks it, yolo
 			}
 			// Inject the fake block into the chain
 			txs := make([]*types.Transaction, len(tt.block))

core/txpool/errors.go

@@ -60,4 +60,13 @@ var (
 	// input transaction of non-blob type when a blob transaction from this sender
 	// remains pending (and vice-versa).
 	ErrAlreadyReserved = errors.New("address already reserved")
+
+	// ErrAuthorityReserved is returned if a transaction has an authorization
+	// signed by an address which already has in-flight transactions known to the
+	// pool.
+	ErrAuthorityReserved = errors.New("authority already reserved")
+
+	// ErrAuthorityNonce is returned if a transaction has an authorization with
+	// a nonce that is not currently valid for the authority.
+	ErrAuthorityNonceTooLow = errors.New("authority nonce too low")
 )

core/txpool/legacypool/legacypool.go

@@ -21,6 +21,7 @@ import (
 	"errors"
 	"math"
 	"math/big"
+	"slices"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -196,6 +197,20 @@ func (config *Config) sanitize() Config {
 // The pool separates processable transactions (which can be applied to the
 // current state) and future transactions. Transactions move between those
 // two states over time as they are received and processed.
+//
+// In addition to tracking transactions, the pool also tracks a set of pending SetCode
+// authorizations (EIP7702). This helps minimize number of transactions that can be
+// trivially churned in the pool. As a standard rule, any account with a deployed
+// delegation or an in-flight authorization to deploy a delegation will only be allowed a
+// single transaction slot instead of the standard number. This is due to the possibility
+// of the account being sweeped by an unrelated account.
+//
+// Because SetCode transactions can have many authorizations included, we avoid explicitly
+// checking their validity to save the state lookup. So long as the encompassing
+// transaction is valid, the authorization will be accepted and tracked by the pool. In
+// case the pool is tracking a pending / queued transaction from a specific account, it
+// will reject new transactions with delegations from that account with standard in-flight
+// transactions.
 type LegacyPool struct {
 	config      Config
 	chainconfig *params.ChainConfig
@@ -263,7 +278,7 @@ func New(config Config, chain BlockChain) *LegacyPool {
 // pool, specifically, whether it is a Legacy, AccessList or Dynamic transaction.
 func (pool *LegacyPool) Filter(tx *types.Transaction) bool {
 	switch tx.Type() {
-	case types.LegacyTxType, types.AccessListTxType, types.DynamicFeeTxType:
+	case types.LegacyTxType, types.AccessListTxType, types.DynamicFeeTxType, types.SetCodeTxType:
 		return true
 	default:
 		return false
@@ -540,7 +555,8 @@ func (pool *LegacyPool) validateTxBasics(tx *types.Transaction) error {
 		Accept: 0 |
 			1<<types.LegacyTxType |
 			1<<types.AccessListTxType |
-			1<<types.DynamicFeeTxType,
+			1<<types.DynamicFeeTxType |
+			1<<types.SetCodeTxType,
 		MaxSize: txMaxSize,
 		MinTip:  pool.gasTip.Load().ToBig(),
 	}
@@ -565,6 +581,11 @@ func (pool *LegacyPool) validateTx(tx *types.Transaction) error {
 			if list := pool.queue[addr]; list != nil {
 				have += list.Len()
 			}
+			if pool.currentState.GetCodeHash(addr) != types.EmptyCodeHash || len(pool.all.auths[addr]) != 0 {
+				// Allow at most one in-flight tx for delegated accounts or those with
+				// a pending authorization.
+				return have, max(0, 1-have)
+			}
 			return have, math.MaxInt
 		},
 		ExistingExpenditure: func(addr common.Address) *big.Int {
@@ -581,6 +602,18 @@ func (pool *LegacyPool) validateTx(tx *types.Transaction) error {
 			}
 			return nil
 		},
+		KnownConflicts: func(from common.Address, auths []common.Address) []common.Address {
+			var conflicts []common.Address
+			// Authorities cannot conflict with any pending or queued transactions.
+			for _, addr := range auths {
+				if list := pool.pending[addr]; list != nil {
+					conflicts = append(conflicts, addr)
+				} else if list := pool.queue[addr]; list != nil {
+					conflicts = append(conflicts, addr)
+				}
+			}
+			return conflicts
+		},
 	}
 	if err := txpool.ValidateTransactionWithState(tx, pool.signer, opts); err != nil {
 		return err
@@ -1334,15 +1367,13 @@ func (pool *LegacyPool) promoteExecutables(accounts []common.Address) []*types.T
 		// Drop all transactions that are deemed too old (low nonce)
 		forwards := list.Forward(pool.currentState.GetNonce(addr))
 		for _, tx := range forwards {
-			hash := tx.Hash()
-			pool.all.Remove(hash)
+			pool.all.Remove(tx.Hash())
 		}
 		log.Trace("Removed old queued transactions", "count", len(forwards))
 		// Drop all transactions that are too costly (low balance or out of gas)
 		drops, _ := list.Filter(pool.currentState.GetBalance(addr), gasLimit)
 		for _, tx := range drops {
-			hash := tx.Hash()
-			pool.all.Remove(hash)
+			pool.all.Remove(tx.Hash())
 		}
 		log.Trace("Removed unpayable queued transactions", "count", len(drops))
 		queuedNofundsMeter.Mark(int64(len(drops)))
@@ -1531,8 +1562,8 @@ func (pool *LegacyPool) demoteUnexecutables() {
 		drops, invalids := list.Filter(pool.currentState.GetBalance(addr), gasLimit)
 		for _, tx := range drops {
 			hash := tx.Hash()
-			log.Trace("Removed unpayable pending transaction", "hash", hash)
 			pool.all.Remove(hash)
+			log.Trace("Removed unpayable pending transaction", "hash", hash)
 		}
 		pendingNofundsMeter.Mark(int64(len(drops)))
 
@@ -1641,12 +1672,15 @@ type lookup struct {
 	slots int
 	lock  sync.RWMutex
 	txs   map[common.Hash]*types.Transaction
+
+	auths map[common.Address][]common.Hash // All accounts with a pooled authorization
 }
 
 // newLookup returns a new lookup structure.
 func newLookup() *lookup {
 	return &lookup{
-		txs: make(map[common.Hash]*types.Transaction),
+		txs:   make(map[common.Hash]*types.Transaction),
+		auths: make(map[common.Address][]common.Hash),
 	}
 }
 
@@ -1697,13 +1731,15 @@ func (t *lookup) Add(tx *types.Transaction) {
 	slotsGauge.Update(int64(t.slots))
 
 	t.txs[tx.Hash()] = tx
+	t.addAuthorities(tx)
 }
 
 // Remove removes a transaction from the lookup.
 func (t *lookup) Remove(hash common.Hash) {
 	t.lock.Lock()
 	defer t.lock.Unlock()
 
+	t.removeAuthorities(hash)
 	tx, ok := t.txs[hash]
 	if !ok {
 		log.Error("No transaction found to be deleted", "hash", hash)
@@ -1727,6 +1763,43 @@ func (t *lookup) TxsBelowTip(threshold *big.Int) types.Transactions {
 	return found
 }
 
+// addAuthorities tracks the supplied tx in relation to each authority it
+// specifies.
+func (t *lookup) addAuthorities(tx *types.Transaction) {
+	for _, addr := range tx.SetCodeAuthorities() {
+		list, ok := t.auths[addr]
+		if !ok {
+			list = []common.Hash{}
+		}
+		if slices.Contains(list, tx.Hash()) {
+			// Don't add duplicates.
+			continue
+		}
+		list = append(list, tx.Hash())
+		t.auths[addr] = list
+	}
+}
+
+// removeAuthorities stops tracking the supplied tx in relation to its
+// authorities.
+func (t *lookup) removeAuthorities(hash common.Hash) {
+	for addr := range t.auths {
+		list := t.auths[addr]
+		// Remove tx from tracker.
+		if i := slices.Index(list, hash); i >= 0 {
+			list = append(list[:i], list[i+1:]...)
+		} else {
+			log.Error("Authority with untracked tx", "addr", addr, "hash", hash)
+		}
+		if len(list) == 0 {
+			// If list is newly empty, delete it entirely.
+			delete(t.auths, addr)
+			continue
+		}
+		t.auths[addr] = list
+	}
+}
+
 // numSlots calculates the number of slots needed for a single transaction.
 func numSlots(tx *types.Transaction) int {
 	return int((tx.Size() + txSlotSize - 1) / txSlotSize)