[EVM-697]: Implement eth_maxPriorityFeePerGas (#1629)

* Initial change

* UTs

* Small fix

* Small fix

* Comments fix

* Comments fix

* Comments fix

* Comments fix

gasprice/gasprice.go

@@ -0,0 +1,254 @@
+package gasprice
+
+import (
+	"fmt"
+	"math/big"
+	"sort"
+	"sync"
+
+	"github.com/0xPolygon/polygon-edge/chain"
+	"github.com/0xPolygon/polygon-edge/crypto"
+	"github.com/0xPolygon/polygon-edge/types"
+	"github.com/umbracle/ethgo"
+)
+
+const couldNotFoundBlockFormat = "could not find block. Number: %d, Hash: %s"
+
+// DefaultGasHelperConfig is the default config for gas helper (as per ethereum)
+var DefaultGasHelperConfig = &Config{
+	NumOfBlocksToCheck: 20,
+	PricePercentile:    60,
+	SampleNumber:       3,
+	MaxPrice:           ethgo.Gwei(500),
+	LastPrice:          ethgo.Gwei(1),
+	IgnorePrice:        big.NewInt(2), // 2 wei
+}
+
+// Config is a struct that holds configuration of GasHelper
+type Config struct {
+	// NumOfBlocksToCheck is the number of blocks to sample
+	NumOfBlocksToCheck uint64
+	// PricePercentile is the sample percentile of transactions in a block
+	PricePercentile uint64
+	// SampleNumber is number of transactions sampled in a block
+	SampleNumber uint64
+	// MaxPrice is the tip max price
+	MaxPrice *big.Int
+	// LastPrice is the last price returned for maxPriorityFeePerGas
+	// when starting node it will be some default value
+	LastPrice *big.Int
+	// IgnorePrice is the lowest price to take into consideration
+	// when collecting transactions
+	IgnorePrice *big.Int
+}
+
+// Blockchain is the interface representing blockchain
+type Blockchain interface {
+	GetBlockByHash(hash types.Hash, full bool) (*types.Block, bool)
+	Header() *types.Header
+	Config() *chain.Params
+}
+
+// GasStore interface is providing functions regarding gas and fees
+type GasStore interface {
+	// MaxPriorityFeePerGas calculates the priority fee needed for transaction to be included in a block
+	MaxPriorityFeePerGas() (*big.Int, error)
+}
+
+var _ GasStore = (*GasHelper)(nil)
+
+// GasHelper struct implements functions from the GasStore interface
+type GasHelper struct {
+	// numOfBlocksToCheck is the number of blocks to sample
+	numOfBlocksToCheck uint64
+	// pricePercentile is the sample percentile of transactions in a block
+	pricePercentile uint64
+	// sampleNumber is number of transactions sampled in a block
+	sampleNumber uint64
+	// maxPrice is the tip max price
+	maxPrice *big.Int
+	// lastPrice is the last price returned for maxPriorityFeePerGas
+	lastPrice *big.Int
+	// ignorePrice is the lowest price to take into consideration
+	// when collecting transactions
+	ignorePrice *big.Int
+	// backend is an abstraction of blockchain
+	backend Blockchain
+	// lastHeaderHash is the last header for which maxPriorityFeePerGas was returned
+	lastHeaderHash types.Hash
+
+	lock sync.Mutex
+}
+
+// NewGasHelper is the constructor function for GasHelper struct
+func NewGasHelper(config *Config, backend Blockchain) *GasHelper {
+	pricePercentile := config.PricePercentile
+	if pricePercentile > 100 {
+		pricePercentile = 100
+	}
+
+	return &GasHelper{
+		numOfBlocksToCheck: config.NumOfBlocksToCheck,
+		pricePercentile:    pricePercentile,
+		sampleNumber:       config.SampleNumber,
+		ignorePrice:        config.IgnorePrice,
+		lastPrice:          config.LastPrice,
+		maxPrice:           config.MaxPrice,
+		backend:            backend,
+	}
+}
+
+// MaxPriorityFeePerGas calculates the priority fee needed for transaction to be included in a block
+// The function does following:
+//   - takes chain header
+//   - iterates for numOfBlocksToCheck from chain header to previous blocks
+//   - collects at most the sample number of sorted transactions in block
+//   - if not enough transactions were collected and their tips, go through some more blocks to get
+//     more accurate calculation
+//   - when enough transactions and their tips are collected, take the one that is in pricePercentile
+//   - if given price is larger then maxPrice then return the maxPrice
+func (g *GasHelper) MaxPriorityFeePerGas() (*big.Int, error) {
+	currentHeader := g.backend.Header()
+
+	currentBlock, found := g.backend.GetBlockByHash(currentHeader.Hash, true)
+	if !found {
+		return nil, fmt.Errorf(couldNotFoundBlockFormat, currentHeader.Number, currentHeader.Hash)
+	}
+
+	g.lock.Lock()
+	lastPrice := g.lastPrice
+	lastHeader := g.lastHeaderHash
+	g.lock.Unlock()
+
+	if currentHeader.Hash == lastHeader {
+		// small optimization, if we calculated already the price for given block
+		return new(big.Int).Set(lastPrice), nil
+	}
+
+	var allPrices []*big.Int
+
+	collectPrices := func(block *types.Block) error {
+		baseFee := block.Header.BaseFee
+		txSorter := newTxByEffectiveTipSorter(block.Transactions, baseFee)
+		sort.Sort(txSorter)
+
+		blockMiner := types.BytesToAddress(block.Header.Miner)
+		signer := crypto.NewSigner(g.backend.Config().Forks.At(block.Number()),
+			uint64(g.backend.Config().ChainID))
+		blockTxPrices := make([]*big.Int, 0)
+
+		for _, tx := range txSorter.txs {
+			tip := tx.EffectiveTip(baseFee)
+
+			if tip.Cmp(g.ignorePrice) == -1 {
+				// ignore transactions with tip lower than ignore price
+				continue
+			}
+
+			sender, err := signer.Sender(tx)
+			if err != nil {
+				return fmt.Errorf("could not get sender of transaction: %s. Error: %w", tx.Hash, err)
+			}
+
+			if sender != blockMiner {
+				blockTxPrices = append(blockTxPrices, tip)
+
+				// if sample number of txs from block is reached,
+				// don't process any more txs
+				if len(blockTxPrices) >= int(g.sampleNumber) {
+					break
+				}
+			}
+		}
+
+		if len(blockTxPrices) == 0 {
+			// either block is empty or all transactions in block are sent by the miner.
+			// in this case add the latests calculated price for sampling
+			blockTxPrices = append(blockTxPrices, lastPrice)
+		}
+
+		// add the block prices to the slice of all prices
+		allPrices = append(allPrices, blockTxPrices...)
+
+		return nil
+	}
+
+	// iterate from current block to previous blocks determined by numOfBlocksToCheck
+	// if chain doesn't have that many blocks, we need to stop the loop (currentBlock.Number() > 0)
+	for i := uint64(0); i < g.numOfBlocksToCheck && currentBlock.Number() > 0; i++ {
+		if err := collectPrices(currentBlock); err != nil {
+			return nil, err
+		}
+
+		currentBlock, found = g.backend.GetBlockByHash(currentBlock.ParentHash(), true)
+		if !found {
+			return nil, fmt.Errorf(couldNotFoundBlockFormat, currentHeader.Number, currentHeader.Hash)
+		}
+	}
+
+	// at least amount of transactions to get
+	minNumOfTx := int(g.numOfBlocksToCheck) * 2
+	// collect some more blocks and transactions if not enough transactions were collected
+	for len(allPrices) < minNumOfTx && currentBlock.Number() > 0 {
+		if err := collectPrices(currentBlock); err != nil {
+			return nil, err
+		}
+	}
+
+	price := lastPrice
+
+	if len(allPrices) > 0 {
+		// sort prices from lowest to highest
+		sort.Slice(allPrices, func(i, j int) bool {
+			return allPrices[i].Cmp(allPrices[j]) < 0
+		})
+		// take the biggest price that is in the configured percentage
+		// by default it's 60, so it will take the price on that percentage
+		// of all prices in the array
+		price = allPrices[(len(allPrices)-1)*int(g.pricePercentile)/100]
+	}
+
+	if price.Cmp(g.maxPrice) > 0 {
+		// if price is larger than the configured max price
+		// return max price
+		price = new(big.Int).Set(g.maxPrice)
+	}
+
+	// cache the calculated price and header hash
+	g.lock.Lock()
+	g.lastPrice = price
+	g.lastHeaderHash = currentHeader.Hash
+	g.lock.Unlock()
+
+	return price, nil
+}
+
+// txSortedByEffectiveTip sorts transactions by effective tip from smallest to largest
+type txSortedByEffectiveTip struct {
+	txs     []*types.Transaction
+	baseFee uint64
+}
+
+// newTxByEffectiveTipSorter is constructor function for txSortedByEffectiveTip
+func newTxByEffectiveTipSorter(txs []*types.Transaction, baseFee uint64) *txSortedByEffectiveTip {
+	return &txSortedByEffectiveTip{
+		txs:     txs,
+		baseFee: baseFee,
+	}
+}
+
+// Len is implementation of sort.Interface
+func (t *txSortedByEffectiveTip) Len() int { return len(t.txs) }
+
+// Swap is implementation of sort.Interface
+func (t *txSortedByEffectiveTip) Swap(i, j int) {
+	t.txs[i], t.txs[j] = t.txs[j], t.txs[i]
+}
+
+// Less is implementation of sort.Interface
+func (t *txSortedByEffectiveTip) Less(i, j int) bool {
+	tip1 := t.txs[i].EffectiveTip(t.baseFee)
+	tip2 := t.txs[j].EffectiveTip(t.baseFee)
+
+	return tip1.Cmp(tip2) < 0
+}