core/types: fix transaction pool price-heap comparison

core/txpool/legacypool/list_test.go

@@ -68,6 +68,43 @@ func TestListAddVeryExpensive(t *testing.T) {
 	}
 }
 
+// TestPriceHeapCmp tests that the price heap comparison function works as intended.
+// It also tests combinations where the basefee is higher than the gas fee cap, which
+// are useful to sort in the mempool to support basefee changes.
+func TestPriceHeapCmp(t *testing.T) {
+	key, _ := crypto.GenerateKey()
+	txs := []*types.Transaction{
+		// nonce, gaslimit, gasfee, gastip
+		dynamicFeeTx(0, 1000, big.NewInt(2), big.NewInt(1), key),
+		dynamicFeeTx(0, 1000, big.NewInt(1), big.NewInt(2), key),
+		dynamicFeeTx(0, 1000, big.NewInt(1), big.NewInt(1), key),
+		dynamicFeeTx(0, 1000, big.NewInt(1), big.NewInt(0), key),
+	}
+
+	// create priceHeap
+	ph := &priceHeap{}
+
+	// now set the basefee on the heap
+	for _, basefee := range []uint64{0, 1, 2, 3} {
+		ph.baseFee = uint256.NewInt(basefee)
+
+		for i := 0; i < len(txs); i++ {
+			for j := 0; j < len(txs); j++ {
+				switch {
+				case i == j:
+					if c := ph.cmp(txs[i], txs[j]); c != 0 {
+						t.Errorf("tx %d should be equal priority to tx %d with basefee %d (cmp=%d)", i, j, basefee, c)
+					}
+				case i < j:
+					if c := ph.cmp(txs[i], txs[j]); c != 1 {
+						t.Errorf("tx %d vs tx %d comparison inconsistent with basefee %d (cmp=%d)", i, j, basefee, c)
+					}
+				}
+			}
+		}
+	}
+}
+
 func BenchmarkListAdd(b *testing.B) {
 	// Generate a list of transactions to insert
 	key, _ := crypto.GenerateKey()

core/types/transaction.go

@@ -396,14 +396,37 @@ func (tx *Transaction) calcEffectiveGasTip(dst *uint256.Int, baseFee *uint256.In
 	return err
 }
 
+// EffectiveGasTipValue returns the effective gasTip value for the given base fee,
+// even if it would be negative. This can be used for sorting purposes.
+func (tx *Transaction) EffectiveGasTipValue(baseFee *big.Int) *big.Int {
+	// min(gasTipCap, gasFeeCap - baseFee)
+	dst := new(big.Int)
+	if baseFee == nil {
+		dst.Set(tx.inner.gasTipCap())
+		return dst
+	}
+
+	dst.Sub(tx.inner.gasFeeCap(), baseFee) // gasFeeCap - baseFee
+	gasTipCap := tx.inner.gasTipCap()
+	if gasTipCap.Cmp(dst) < 0 { // gasTipCap < (gasFeeCap - baseFee)
+		dst.Set(gasTipCap)
+	}
+	return dst
+}
+
 func (tx *Transaction) EffectiveGasTipCmp(other *Transaction, baseFee *uint256.Int) int {
 	if baseFee == nil {
 		return tx.GasTipCapCmp(other)
 	}
 	// Use more efficient internal method.
 	txTip, otherTip := new(uint256.Int), new(uint256.Int)
-	tx.calcEffectiveGasTip(txTip, baseFee)
-	other.calcEffectiveGasTip(otherTip, baseFee)
+	err1 := tx.calcEffectiveGasTip(txTip, baseFee)
+	err2 := other.calcEffectiveGasTip(otherTip, baseFee)
+	if err1 != nil || err2 != nil {
+		// fall back to big int comparison in case of error
+		base := baseFee.ToBig()
+		return tx.EffectiveGasTipValue(base).Cmp(other.EffectiveGasTipValue(base))
+	}
 	return txTip.Cmp(otherTip)
 }