les, les/lespay/client: add service value statistics and API (#20837)

This PR adds service value measurement statistics to the light client. It
also adds a private API that makes these statistics accessible. A follow-up
PR will add the new server pool which uses these statistics to select
servers with good performance.

This document describes the function of the new components:
https://gist.github.com/zsfelfoldi/3c7ace895234b7b345ab4f71dab102d4

Co-authored-by: rjl493456442 <garyrong0905@gmail.com>
Co-authored-by: rjl493456442 <garyrong0905@gmail.com>

internal/web3ext/web3ext.go

@@ -33,6 +33,7 @@ var Modules = map[string]string{
 	"swarmfs":    SwarmfsJs,
 	"txpool":     TxpoolJs,
 	"les":        LESJs,
+	"lespay":     LESPayJs,
 }
 
 const ChequebookJs = `
@@ -856,3 +857,34 @@ web3._extend({
 	]
 });
 `
+
+const LESPayJs = `
+web3._extend({
+	property: 'lespay',
+	methods:
+	[
+		new web3._extend.Method({
+			name: 'distribution',
+			call: 'lespay_distribution',
+			params: 2
+		}),
+		new web3._extend.Method({
+			name: 'timeout',
+			call: 'lespay_timeout',
+			params: 2
+		}),
+		new web3._extend.Method({
+			name: 'value',
+			call: 'lespay_value',
+			params: 2
+		}),
+	],
+	properties:
+	[
+		new web3._extend.Property({
+			name: 'requestStats',
+			getter: 'lespay_requestStats'
+		}),
+	]
+});
+`

les/benchmark.go

@@ -191,7 +191,7 @@ func (b *benchmarkTxSend) init(h *serverHandler, count int) error {
 
 func (b *benchmarkTxSend) request(peer *serverPeer, index int) error {
 	enc, _ := rlp.EncodeToBytes(types.Transactions{b.txs[index]})
-	return peer.sendTxs(0, enc)
+	return peer.sendTxs(0, 1, enc)
 }
 
 // benchmarkTxStatus implements requestBenchmark

les/client.go

@@ -19,6 +19,7 @@ package les
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/accounts/abi/bind"
@@ -37,6 +38,7 @@ import (
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/internal/ethapi"
 	"github.com/ethereum/go-ethereum/les/checkpointoracle"
+	lpc "github.com/ethereum/go-ethereum/les/lespay/client"
 	"github.com/ethereum/go-ethereum/light"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
@@ -58,6 +60,7 @@ type LightEthereum struct {
 	txPool       *light.TxPool
 	blockchain   *light.LightChain
 	serverPool   *serverPool
+	valueTracker *lpc.ValueTracker
 
 	bloomRequests chan chan *bloombits.Retrieval // Channel receiving bloom data retrieval requests
 	bloomIndexer  *core.ChainIndexer             // Bloom indexer operating during block imports
@@ -74,6 +77,10 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 	if err != nil {
 		return nil, err
 	}
+	lespayDb, err := ctx.OpenDatabase("lespay", 0, 0, "eth/db/lespay")
+	if err != nil {
+		return nil, err
+	}
 	chainConfig, genesisHash, genesisErr := core.SetupGenesisBlockWithOverride(chainDb, config.Genesis,
 		config.OverrideIstanbul, config.OverrideMuirGlacier)
 	if _, isCompat := genesisErr.(*params.ConfigCompatError); genesisErr != nil && !isCompat {
@@ -99,7 +106,9 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 		bloomRequests:  make(chan chan *bloombits.Retrieval),
 		bloomIndexer:   eth.NewBloomIndexer(chainDb, params.BloomBitsBlocksClient, params.HelperTrieConfirmations),
 		serverPool:     newServerPool(chainDb, config.UltraLightServers),
+		valueTracker:   lpc.NewValueTracker(lespayDb, &mclock.System{}, requestList, time.Minute, 1/float64(time.Hour), 1/float64(time.Hour*100), 1/float64(time.Hour*1000)),
 	}
+	peers.subscribe((*vtSubscription)(leth.valueTracker))
 	leth.retriever = newRetrieveManager(peers, leth.reqDist, leth.serverPool)
 	leth.relay = newLesTxRelay(peers, leth.retriever)
 
@@ -154,6 +163,23 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 	return leth, nil
 }
 
+// vtSubscription implements serverPeerSubscriber
+type vtSubscription lpc.ValueTracker
+
+// registerPeer implements serverPeerSubscriber
+func (v *vtSubscription) registerPeer(p *serverPeer) {
+	vt := (*lpc.ValueTracker)(v)
+	p.setValueTracker(vt, vt.Register(p.ID()))
+	p.updateVtParams()
+}
+
+// unregisterPeer implements serverPeerSubscriber
+func (v *vtSubscription) unregisterPeer(p *serverPeer) {
+	vt := (*lpc.ValueTracker)(v)
+	vt.Unregister(p.ID())
+	p.setValueTracker(nil, nil)
+}
+
 type LightDummyAPI struct{}
 
 // Etherbase is the address that mining rewards will be send to
@@ -207,6 +233,11 @@ func (s *LightEthereum) APIs() []rpc.API {
 			Version:   "1.0",
 			Service:   NewPrivateLightAPI(&s.lesCommons),
 			Public:    false,
+		}, {
+			Namespace: "lespay",
+			Version:   "1.0",
+			Service:   lpc.NewPrivateClientAPI(s.valueTracker),
+			Public:    false,
 		},
 	}...)
 }
@@ -266,6 +297,7 @@ func (s *LightEthereum) Stop() error {
 	s.engine.Close()
 	s.eventMux.Stop()
 	s.serverPool.stop()
+	s.valueTracker.Stop()
 	s.chainDb.Close()
 	s.wg.Wait()
 	log.Info("Light ethereum stopped")

les/client_handler.go

@@ -180,6 +180,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrRequestRejected, "")
 		}
 		p.updateFlowControl(update)
+		p.updateVtParams()
 
 		if req.Hash != (common.Hash{}) {
 			if p.announceType == announceTypeNone {
@@ -205,6 +206,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		if h.fetcher.requestedID(resp.ReqID) {
 			h.fetcher.deliverHeaders(p, resp.ReqID, resp.Headers)
 		} else {
@@ -222,6 +224,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgBlockBodies,
 			ReqID:   resp.ReqID,
@@ -237,6 +240,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgCode,
 			ReqID:   resp.ReqID,
@@ -252,6 +256,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgReceipts,
 			ReqID:   resp.ReqID,
@@ -267,6 +272,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgProofsV2,
 			ReqID:   resp.ReqID,
@@ -282,6 +288,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgHelperTrieProofs,
 			ReqID:   resp.ReqID,
@@ -297,6 +304,7 @@ func (h *clientHandler) handleMsg(p *serverPeer) error {
 			return errResp(ErrDecode, "msg %v: %v", msg, err)
 		}
 		p.fcServer.ReceivedReply(resp.ReqID, resp.BV)
+		p.answeredRequest(resp.ReqID)
 		deliverMsg = &Msg{
 			MsgType: MsgTxStatus,
 			ReqID:   resp.ReqID,

les/lespay/client/api.go

@@ -0,0 +1,107 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+	"github.com/ethereum/go-ethereum/les/utils"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+// PrivateClientAPI implements the lespay client side API
+type PrivateClientAPI struct {
+	vt *ValueTracker
+}
+
+// NewPrivateClientAPI creates a PrivateClientAPI
+func NewPrivateClientAPI(vt *ValueTracker) *PrivateClientAPI {
+	return &PrivateClientAPI{vt}
+}
+
+// parseNodeStr converts either an enode address or a plain hex node id to enode.ID
+func parseNodeStr(nodeStr string) (enode.ID, error) {
+	if id, err := enode.ParseID(nodeStr); err == nil {
+		return id, nil
+	}
+	if node, err := enode.Parse(enode.ValidSchemes, nodeStr); err == nil {
+		return node.ID(), nil
+	} else {
+		return enode.ID{}, err
+	}
+}
+
+// RequestStats returns the current contents of the reference request basket, with
+// request values meaning average per request rather than total.
+func (api *PrivateClientAPI) RequestStats() []RequestStatsItem {
+	return api.vt.RequestStats()
+}
+
+// Distribution returns a distribution as a series of (X, Y) chart coordinates,
+// where the X axis is the response time in seconds while the Y axis is the amount of
+// service value received with a response time close to the X coordinate.
+// The distribution is optionally normalized to a sum of 1.
+// If nodeStr == "" then the global distribution is returned, otherwise the individual
+// distribution of the specified server node.
+func (api *PrivateClientAPI) Distribution(nodeStr string, normalized bool) (RtDistribution, error) {
+	var expFactor utils.ExpirationFactor
+	if !normalized {
+		expFactor = utils.ExpFactor(api.vt.StatsExpirer().LogOffset(mclock.Now()))
+	}
+	if nodeStr == "" {
+		return api.vt.RtStats().Distribution(normalized, expFactor), nil
+	}
+	if id, err := parseNodeStr(nodeStr); err == nil {
+		return api.vt.GetNode(id).RtStats().Distribution(normalized, expFactor), nil
+	} else {
+		return RtDistribution{}, err
+	}
+}
+
+// Timeout suggests a timeout value based on either the global distribution or the
+// distribution of the specified node. The parameter is the desired rate of timeouts
+// assuming a similar distribution in the future.
+// Note that the actual timeout should have a sensible minimum bound so that operating
+// under ideal working conditions for a long time (for example, using a local server
+// with very low response times) will not make it very hard for the system to accommodate
+// longer response times in the future.
+func (api *PrivateClientAPI) Timeout(nodeStr string, failRate float64) (float64, error) {
+	if nodeStr == "" {
+		return float64(api.vt.RtStats().Timeout(failRate)) / float64(time.Second), nil
+	}
+	if id, err := parseNodeStr(nodeStr); err == nil {
+		return float64(api.vt.GetNode(id).RtStats().Timeout(failRate)) / float64(time.Second), nil
+	} else {
+		return 0, err
+	}
+}
+
+// Value calculates the total service value provided either globally or by the specified
+// server node, using a weight function based on the given timeout.
+func (api *PrivateClientAPI) Value(nodeStr string, timeout float64) (float64, error) {
+	wt := TimeoutWeights(time.Duration(timeout * float64(time.Second)))
+	expFactor := utils.ExpFactor(api.vt.StatsExpirer().LogOffset(mclock.Now()))
+	if nodeStr == "" {
+		return api.vt.RtStats().Value(wt, expFactor), nil
+	}
+	if id, err := parseNodeStr(nodeStr); err == nil {
+		return api.vt.GetNode(id).RtStats().Value(wt, expFactor), nil
+	} else {
+		return 0, err
+	}
+}

les/lespay/client/requestbasket.go

@@ -0,0 +1,285 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"io"
+
+	"github.com/ethereum/go-ethereum/les/utils"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+const basketFactor = 1000000 // reference basket amount and value scale factor
+
+// referenceBasket keeps track of global request usage statistics and the usual prices
+// of each used request type relative to each other. The amounts in the basket are scaled
+// up by basketFactor because of the exponential expiration of long-term statistical data.
+// Values are scaled so that the sum of all amounts and the sum of all values are equal.
+//
+// reqValues represent the internal relative value estimates for each request type and are
+// calculated as value / amount. The average reqValue of all used requests is 1.
+// In other words: SUM(refBasket[type].amount * reqValue[type]) = SUM(refBasket[type].amount)
+type referenceBasket struct {
+	basket    requestBasket
+	reqValues []float64 // contents are read only, new slice is created for each update
+}
+
+// serverBasket collects served request amount and value statistics for a single server.
+//
+// Values are gradually transferred to the global reference basket with a long time
+// constant so that each server basket represents long term usage and price statistics.
+// When the transferred part is added to the reference basket the values are scaled so
+// that their sum equals the total value calculated according to the previous reqValues.
+// The ratio of request values coming from the server basket represent the pricing of
+// the specific server and modify the global estimates with a weight proportional to
+// the amount of service provided by the server.
+type serverBasket struct {
+	basket   requestBasket
+	rvFactor float64
+}
+
+type (
+	// requestBasket holds amounts and values for each request type.
+	// These values are exponentially expired (see utils.ExpiredValue). The power of 2
+	// exponent is applicable to all values within.
+	requestBasket struct {
+		items []basketItem
+		exp   uint64
+	}
+	// basketItem holds amount and value for a single request type. Value is the total
+	// relative request value accumulated for served requests while amount is the counter
+	// for each request type.
+	// Note that these values are both scaled up by basketFactor because of the exponential
+	// expiration.
+	basketItem struct {
+		amount, value uint64
+	}
+)
+
+// setExp sets the power of 2 exponent of the structure, scaling base values (the amounts
+// and request values) up or down if necessary.
+func (b *requestBasket) setExp(exp uint64) {
+	if exp > b.exp {
+		shift := exp - b.exp
+		for i, item := range b.items {
+			item.amount >>= shift
+			item.value >>= shift
+			b.items[i] = item
+		}
+		b.exp = exp
+	}
+	if exp < b.exp {
+		shift := b.exp - exp
+		for i, item := range b.items {
+			item.amount <<= shift
+			item.value <<= shift
+			b.items[i] = item
+		}
+		b.exp = exp
+	}
+}
+
+// init initializes a new server basket with the given service vector size (number of
+// different request types)
+func (s *serverBasket) init(size int) {
+	if s.basket.items == nil {
+		s.basket.items = make([]basketItem, size)
+	}
+}
+
+// add adds the give type and amount of requests to the basket. Cost is calculated
+// according to the server's own cost table.
+func (s *serverBasket) add(reqType, reqAmount uint32, reqCost uint64, expFactor utils.ExpirationFactor) {
+	s.basket.setExp(expFactor.Exp)
+	i := &s.basket.items[reqType]
+	i.amount += uint64(float64(uint64(reqAmount)*basketFactor) * expFactor.Factor)
+	i.value += uint64(float64(reqCost) * s.rvFactor * expFactor.Factor)
+}
+
+// updateRvFactor updates the request value factor that scales server costs into the
+// local value dimensions.
+func (s *serverBasket) updateRvFactor(rvFactor float64) {
+	s.rvFactor = rvFactor
+}
+
+// transfer decreases amounts and values in the basket with the given ratio and
+// moves the removed amounts into a new basket which is returned and can be added
+// to the global reference basket.
+func (s *serverBasket) transfer(ratio float64) requestBasket {
+	res := requestBasket{
+		items: make([]basketItem, len(s.basket.items)),
+		exp:   s.basket.exp,
+	}
+	for i, v := range s.basket.items {
+		ta := uint64(float64(v.amount) * ratio)
+		tv := uint64(float64(v.value) * ratio)
+		if ta > v.amount {
+			ta = v.amount
+		}
+		if tv > v.value {
+			tv = v.value
+		}
+		s.basket.items[i] = basketItem{v.amount - ta, v.value - tv}
+		res.items[i] = basketItem{ta, tv}
+	}
+	return res
+}
+
+// init initializes the reference basket with the given service vector size (number of
+// different request types)
+func (r *referenceBasket) init(size int) {
+	r.reqValues = make([]float64, size)
+	r.normalize()
+	r.updateReqValues()
+}
+
+// add adds the transferred part of a server basket to the reference basket while scaling
+// value amounts so that their sum equals the total value calculated according to the
+// previous reqValues.
+func (r *referenceBasket) add(newBasket requestBasket) {
+	r.basket.setExp(newBasket.exp)
+	// scale newBasket to match service unit value
+	var (
+		totalCost  uint64
+		totalValue float64
+	)
+	for i, v := range newBasket.items {
+		totalCost += v.value
+		totalValue += float64(v.amount) * r.reqValues[i]
+	}
+	if totalCost > 0 {
+		// add to reference with scaled values
+		scaleValues := totalValue / float64(totalCost)
+		for i, v := range newBasket.items {
+			r.basket.items[i].amount += v.amount
+			r.basket.items[i].value += uint64(float64(v.value) * scaleValues)
+		}
+	}
+	r.updateReqValues()
+}
+
+// updateReqValues recalculates reqValues after adding transferred baskets. Note that
+// values should be normalized first.
+func (r *referenceBasket) updateReqValues() {
+	r.reqValues = make([]float64, len(r.reqValues))
+	for i, b := range r.basket.items {
+		if b.amount > 0 {
+			r.reqValues[i] = float64(b.value) / float64(b.amount)
+		} else {
+			r.reqValues[i] = 0
+		}
+	}
+}
+
+// normalize ensures that the sum of values equal the sum of amounts in the basket.
+func (r *referenceBasket) normalize() {
+	var sumAmount, sumValue uint64
+	for _, b := range r.basket.items {
+		sumAmount += b.amount
+		sumValue += b.value
+	}
+	add := float64(int64(sumAmount-sumValue)) / float64(sumValue)
+	for i, b := range r.basket.items {
+		b.value += uint64(int64(float64(b.value) * add))
+		r.basket.items[i] = b
+	}
+}
+
+// reqValueFactor calculates the request value factor applicable to the server with
+// the given announced request cost list
+func (r *referenceBasket) reqValueFactor(costList []uint64) float64 {
+	var (
+		totalCost  float64
+		totalValue uint64
+	)
+	for i, b := range r.basket.items {
+		totalCost += float64(costList[i]) * float64(b.amount) // use floats to avoid overflow
+		totalValue += b.value
+	}
+	if totalCost < 1 {
+		return 0
+	}
+	return float64(totalValue) * basketFactor / totalCost
+}
+
+// EncodeRLP implements rlp.Encoder
+func (b *basketItem) EncodeRLP(w io.Writer) error {
+	return rlp.Encode(w, []interface{}{b.amount, b.value})
+}
+
+// DecodeRLP implements rlp.Decoder
+func (b *basketItem) DecodeRLP(s *rlp.Stream) error {
+	var item struct {
+		Amount, Value uint64
+	}
+	if err := s.Decode(&item); err != nil {
+		return err
+	}
+	b.amount, b.value = item.Amount, item.Value
+	return nil
+}
+
+// EncodeRLP implements rlp.Encoder
+func (r *requestBasket) EncodeRLP(w io.Writer) error {
+	return rlp.Encode(w, []interface{}{r.items, r.exp})
+}
+
+// DecodeRLP implements rlp.Decoder
+func (r *requestBasket) DecodeRLP(s *rlp.Stream) error {
+	var enc struct {
+		Items []basketItem
+		Exp   uint64
+	}
+	if err := s.Decode(&enc); err != nil {
+		return err
+	}
+	r.items, r.exp = enc.Items, enc.Exp
+	return nil
+}
+
+// convertMapping converts a basket loaded from the database into the current format.
+// If the available request types and their mapping into the service vector differ from
+// the one used when saving the basket then this function reorders old fields and fills
+// in previously unknown fields by scaling up amounts and values taken from the
+// initialization basket.
+func (r requestBasket) convertMapping(oldMapping, newMapping []string, initBasket requestBasket) requestBasket {
+	nameMap := make(map[string]int)
+	for i, name := range oldMapping {
+		nameMap[name] = i
+	}
+	rc := requestBasket{items: make([]basketItem, len(newMapping))}
+	var scale, oldScale, newScale float64
+	for i, name := range newMapping {
+		if ii, ok := nameMap[name]; ok {
+			rc.items[i] = r.items[ii]
+			oldScale += float64(initBasket.items[i].amount) * float64(initBasket.items[i].amount)
+			newScale += float64(rc.items[i].amount) * float64(initBasket.items[i].amount)
+		}
+	}
+	if oldScale > 1e-10 {
+		scale = newScale / oldScale
+	} else {
+		scale = 1
+	}
+	for i, name := range newMapping {
+		if _, ok := nameMap[name]; !ok {
+			rc.items[i].amount = uint64(float64(initBasket.items[i].amount) * scale)
+			rc.items[i].value = uint64(float64(initBasket.items[i].value) * scale)
+		}
+	}
+	return rc
+}

les/lespay/client/requestbasket_test.go

@@ -0,0 +1,161 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/les/utils"
+)
+
+func checkU64(t *testing.T, name string, value, exp uint64) {
+	if value != exp {
+		t.Errorf("Incorrect value for %s: got %d, expected %d", name, value, exp)
+	}
+}
+
+func checkF64(t *testing.T, name string, value, exp, tol float64) {
+	if value < exp-tol || value > exp+tol {
+		t.Errorf("Incorrect value for %s: got %f, expected %f", name, value, exp)
+	}
+}
+
+func TestServerBasket(t *testing.T) {
+	var s serverBasket
+	s.init(2)
+	// add some requests with different request value factors
+	s.updateRvFactor(1)
+	noexp := utils.ExpirationFactor{Factor: 1}
+	s.add(0, 1000, 10000, noexp)
+	s.add(1, 3000, 60000, noexp)
+	s.updateRvFactor(10)
+	s.add(0, 4000, 4000, noexp)
+	s.add(1, 2000, 4000, noexp)
+	s.updateRvFactor(10)
+	// check basket contents directly
+	checkU64(t, "s.basket[0].amount", s.basket.items[0].amount, 5000*basketFactor)
+	checkU64(t, "s.basket[0].value", s.basket.items[0].value, 50000)
+	checkU64(t, "s.basket[1].amount", s.basket.items[1].amount, 5000*basketFactor)
+	checkU64(t, "s.basket[1].value", s.basket.items[1].value, 100000)
+	// transfer 50% of the contents of the basket
+	transfer1 := s.transfer(0.5)
+	checkU64(t, "transfer1[0].amount", transfer1.items[0].amount, 2500*basketFactor)
+	checkU64(t, "transfer1[0].value", transfer1.items[0].value, 25000)
+	checkU64(t, "transfer1[1].amount", transfer1.items[1].amount, 2500*basketFactor)
+	checkU64(t, "transfer1[1].value", transfer1.items[1].value, 50000)
+	// add more requests
+	s.updateRvFactor(100)
+	s.add(0, 1000, 100, noexp)
+	// transfer 25% of the contents of the basket
+	transfer2 := s.transfer(0.25)
+	checkU64(t, "transfer2[0].amount", transfer2.items[0].amount, (2500+1000)/4*basketFactor)
+	checkU64(t, "transfer2[0].value", transfer2.items[0].value, (25000+10000)/4)
+	checkU64(t, "transfer2[1].amount", transfer2.items[1].amount, 2500/4*basketFactor)
+	checkU64(t, "transfer2[1].value", transfer2.items[1].value, 50000/4)
+}
+
+func TestConvertMapping(t *testing.T) {
+	b := requestBasket{items: []basketItem{{3, 3}, {1, 1}, {2, 2}}}
+	oldMap := []string{"req3", "req1", "req2"}
+	newMap := []string{"req1", "req2", "req3", "req4"}
+	init := requestBasket{items: []basketItem{{2, 2}, {4, 4}, {6, 6}, {8, 8}}}
+	bc := b.convertMapping(oldMap, newMap, init)
+	checkU64(t, "bc[0].amount", bc.items[0].amount, 1)
+	checkU64(t, "bc[1].amount", bc.items[1].amount, 2)
+	checkU64(t, "bc[2].amount", bc.items[2].amount, 3)
+	checkU64(t, "bc[3].amount", bc.items[3].amount, 4) // 8 should be scaled down to 4
+}
+
+func TestReqValueFactor(t *testing.T) {
+	var ref referenceBasket
+	ref.basket = requestBasket{items: make([]basketItem, 4)}
+	for i := range ref.basket.items {
+		ref.basket.items[i].amount = uint64(i+1) * basketFactor
+		ref.basket.items[i].value = uint64(i+1) * basketFactor
+	}
+	ref.init(4)
+	rvf := ref.reqValueFactor([]uint64{1000, 2000, 3000, 4000})
+	// expected value is (1000000+2000000+3000000+4000000) / (1*1000+2*2000+3*3000+4*4000) = 10000000/30000 = 333.333
+	checkF64(t, "reqValueFactor", rvf, 333.333, 1)
+}
+
+func TestNormalize(t *testing.T) {
+	for cycle := 0; cycle < 100; cycle += 1 {
+		// Initialize data for testing
+		valueRange, lower := 1000000, 1000000
+		ref := referenceBasket{basket: requestBasket{items: make([]basketItem, 10)}}
+		for i := 0; i < 10; i++ {
+			ref.basket.items[i].amount = uint64(rand.Intn(valueRange) + lower)
+			ref.basket.items[i].value = uint64(rand.Intn(valueRange) + lower)
+		}
+		ref.normalize()
+
+		// Check whether SUM(amount) ~= SUM(value)
+		var sumAmount, sumValue uint64
+		for i := 0; i < 10; i++ {
+			sumAmount += ref.basket.items[i].amount
+			sumValue += ref.basket.items[i].value
+		}
+		var epsilon = 0.01
+		if float64(sumAmount)*(1+epsilon) < float64(sumValue) || float64(sumAmount)*(1-epsilon) > float64(sumValue) {
+			t.Fatalf("Failed to normalize sumAmount: %d sumValue: %d", sumAmount, sumValue)
+		}
+	}
+}
+
+func TestReqValueAdjustment(t *testing.T) {
+	var s1, s2 serverBasket
+	s1.init(3)
+	s2.init(3)
+	cost1 := []uint64{30000, 60000, 90000}
+	cost2 := []uint64{100000, 200000, 300000}
+	var ref referenceBasket
+	ref.basket = requestBasket{items: make([]basketItem, 3)}
+	for i := range ref.basket.items {
+		ref.basket.items[i].amount = 123 * basketFactor
+		ref.basket.items[i].value = 123 * basketFactor
+	}
+	ref.init(3)
+	// initial reqValues are expected to be {1, 1, 1}
+	checkF64(t, "reqValues[0]", ref.reqValues[0], 1, 0.01)
+	checkF64(t, "reqValues[1]", ref.reqValues[1], 1, 0.01)
+	checkF64(t, "reqValues[2]", ref.reqValues[2], 1, 0.01)
+	var logOffset utils.Fixed64
+	for period := 0; period < 1000; period++ {
+		exp := utils.ExpFactor(logOffset)
+		s1.updateRvFactor(ref.reqValueFactor(cost1))
+		s2.updateRvFactor(ref.reqValueFactor(cost2))
+		// throw in random requests into each basket using their internal pricing
+		for i := 0; i < 1000; i++ {
+			reqType, reqAmount := uint32(rand.Intn(3)), uint32(rand.Intn(10)+1)
+			reqCost := uint64(reqAmount) * cost1[reqType]
+			s1.add(reqType, reqAmount, reqCost, exp)
+			reqType, reqAmount = uint32(rand.Intn(3)), uint32(rand.Intn(10)+1)
+			reqCost = uint64(reqAmount) * cost2[reqType]
+			s2.add(reqType, reqAmount, reqCost, exp)
+		}
+		ref.add(s1.transfer(0.1))
+		ref.add(s2.transfer(0.1))
+		ref.normalize()
+		ref.updateReqValues()
+		logOffset += utils.Float64ToFixed64(0.1)
+	}
+	checkF64(t, "reqValues[0]", ref.reqValues[0], 0.5, 0.01)
+	checkF64(t, "reqValues[1]", ref.reqValues[1], 1, 0.01)
+	checkF64(t, "reqValues[2]", ref.reqValues[2], 1.5, 0.01)
+}

les/lespay/client/timestats.go

@@ -0,0 +1,237 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"io"
+	"math"
+	"time"
+
+	"github.com/ethereum/go-ethereum/les/utils"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+const (
+	minResponseTime   = time.Millisecond * 50
+	maxResponseTime   = time.Second * 10
+	timeStatLength    = 32
+	weightScaleFactor = 1000000
+)
+
+// ResponseTimeStats is the response time distribution of a set of answered requests,
+// weighted with request value, either served by a single server or aggregated for
+// multiple servers.
+// It it a fixed length (timeStatLength) distribution vector with linear interpolation.
+// The X axis (the time values) are not linear, they should be transformed with
+// TimeToStatScale and StatScaleToTime.
+type (
+	ResponseTimeStats struct {
+		stats [timeStatLength]uint64
+		exp   uint64
+	}
+	ResponseTimeWeights [timeStatLength]float64
+)
+
+var timeStatsLogFactor = (timeStatLength - 1) / (math.Log(float64(maxResponseTime)/float64(minResponseTime)) + 1)
+
+// TimeToStatScale converts a response time to a distribution vector index. The index
+// is represented by a float64 so that linear interpolation can be applied.
+func TimeToStatScale(d time.Duration) float64 {
+	if d < 0 {
+		return 0
+	}
+	r := float64(d) / float64(minResponseTime)
+	if r > 1 {
+		r = math.Log(r) + 1
+	}
+	r *= timeStatsLogFactor
+	if r > timeStatLength-1 {
+		return timeStatLength - 1
+	}
+	return r
+}
+
+// StatScaleToTime converts a distribution vector index to a response time. The index
+// is represented by a float64 so that linear interpolation can be applied.
+func StatScaleToTime(r float64) time.Duration {
+	r /= timeStatsLogFactor
+	if r > 1 {
+		r = math.Exp(r - 1)
+	}
+	return time.Duration(r * float64(minResponseTime))
+}
+
+// TimeoutWeights calculates the weight function used for calculating service value
+// based on the response time distribution of the received service.
+// It is based on the request timeout value of the system. It consists of a half cosine
+// function starting with 1, crossing zero at timeout and reaching -1 at 2*timeout.
+// After 2*timeout the weight is constant -1.
+func TimeoutWeights(timeout time.Duration) (res ResponseTimeWeights) {
+	for i := range res {
+		t := StatScaleToTime(float64(i))
+		if t < 2*timeout {
+			res[i] = math.Cos(math.Pi / 2 * float64(t) / float64(timeout))
+		} else {
+			res[i] = -1
+		}
+	}
+	return
+}
+
+// EncodeRLP implements rlp.Encoder
+func (rt *ResponseTimeStats) EncodeRLP(w io.Writer) error {
+	enc := struct {
+		Stats [timeStatLength]uint64
+		Exp   uint64
+	}{rt.stats, rt.exp}
+	return rlp.Encode(w, &enc)
+}
+
+// DecodeRLP implements rlp.Decoder
+func (rt *ResponseTimeStats) DecodeRLP(s *rlp.Stream) error {
+	var enc struct {
+		Stats [timeStatLength]uint64
+		Exp   uint64
+	}
+	if err := s.Decode(&enc); err != nil {
+		return err
+	}
+	rt.stats, rt.exp = enc.Stats, enc.Exp
+	return nil
+}
+
+// Add adds a new response time with the given weight to the distribution.
+func (rt *ResponseTimeStats) Add(respTime time.Duration, weight float64, expFactor utils.ExpirationFactor) {
+	rt.setExp(expFactor.Exp)
+	weight *= expFactor.Factor * weightScaleFactor
+	r := TimeToStatScale(respTime)
+	i := int(r)
+	r -= float64(i)
+	rt.stats[i] += uint64(weight * (1 - r))
+	if i < timeStatLength-1 {
+		rt.stats[i+1] += uint64(weight * r)
+	}
+}
+
+// setExp sets the power of 2 exponent of the structure, scaling base values (the vector
+// itself) up or down if necessary.
+func (rt *ResponseTimeStats) setExp(exp uint64) {
+	if exp > rt.exp {
+		shift := exp - rt.exp
+		for i, v := range rt.stats {
+			rt.stats[i] = v >> shift
+		}
+		rt.exp = exp
+	}
+	if exp < rt.exp {
+		shift := rt.exp - exp
+		for i, v := range rt.stats {
+			rt.stats[i] = v << shift
+		}
+		rt.exp = exp
+	}
+}
+
+// Value calculates the total service value based on the given distribution, using the
+// specified weight function.
+func (rt ResponseTimeStats) Value(weights ResponseTimeWeights, expFactor utils.ExpirationFactor) float64 {
+	var v float64
+	for i, s := range rt.stats {
+		v += float64(s) * weights[i]
+	}
+	if v < 0 {
+		return 0
+	}
+	return expFactor.Value(v, rt.exp) / weightScaleFactor
+}
+
+// AddStats adds the given ResponseTimeStats to the current one.
+func (rt *ResponseTimeStats) AddStats(s *ResponseTimeStats) {
+	rt.setExp(s.exp)
+	for i, v := range s.stats {
+		rt.stats[i] += v
+	}
+}
+
+// SubStats subtracts the given ResponseTimeStats from the current one.
+func (rt *ResponseTimeStats) SubStats(s *ResponseTimeStats) {
+	rt.setExp(s.exp)
+	for i, v := range s.stats {
+		if v < rt.stats[i] {
+			rt.stats[i] -= v
+		} else {
+			rt.stats[i] = 0
+		}
+	}
+}
+
+// Timeout suggests a timeout value based on the previous distribution. The parameter
+// is the desired rate of timeouts assuming a similar distribution in the future.
+// Note that the actual timeout should have a sensible minimum bound so that operating
+// under ideal working conditions for a long time (for example, using a local server
+// with very low response times) will not make it very hard for the system to accommodate
+// longer response times in the future.
+func (rt ResponseTimeStats) Timeout(failRatio float64) time.Duration {
+	var sum uint64
+	for _, v := range rt.stats {
+		sum += v
+	}
+	s := uint64(float64(sum) * failRatio)
+	i := timeStatLength - 1
+	for i > 0 && s >= rt.stats[i] {
+		s -= rt.stats[i]
+		i--
+	}
+	r := float64(i) + 0.5
+	if rt.stats[i] > 0 {
+		r -= float64(s) / float64(rt.stats[i])
+	}
+	if r < 0 {
+		r = 0
+	}
+	th := StatScaleToTime(r)
+	if th > maxResponseTime {
+		th = maxResponseTime
+	}
+	return th
+}
+
+// RtDistribution represents a distribution as a series of (X, Y) chart coordinates,
+// where the X axis is the response time in seconds while the Y axis is the amount of
+// service value received with a response time close to the X coordinate.
+type RtDistribution [timeStatLength][2]float64
+
+// Distribution returns a RtDistribution, optionally normalized to a sum of 1.
+func (rt ResponseTimeStats) Distribution(normalized bool, expFactor utils.ExpirationFactor) (res RtDistribution) {
+	var mul float64
+	if normalized {
+		var sum uint64
+		for _, v := range rt.stats {
+			sum += v
+		}
+		if sum > 0 {
+			mul = 1 / float64(sum)
+		}
+	} else {
+		mul = expFactor.Value(float64(1)/weightScaleFactor, rt.exp)
+	}
+	for i, v := range rt.stats {
+		res[i][0] = float64(StatScaleToTime(float64(i))) / float64(time.Second)
+		res[i][1] = float64(v) * mul
+	}
+	return
+}

les/lespay/client/timestats_test.go

@@ -0,0 +1,137 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"math"
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/les/utils"
+)
+
+func TestTransition(t *testing.T) {
+	var epsilon = 0.01
+	var cases = []time.Duration{
+		time.Millisecond, minResponseTime,
+		time.Second, time.Second * 5, maxResponseTime,
+	}
+	for _, c := range cases {
+		got := StatScaleToTime(TimeToStatScale(c))
+		if float64(got)*(1+epsilon) < float64(c) || float64(got)*(1-epsilon) > float64(c) {
+			t.Fatalf("Failed to transition back")
+		}
+	}
+	// If the time is too large(exceeds the max response time.
+	got := StatScaleToTime(TimeToStatScale(2 * maxResponseTime))
+	if float64(got)*(1+epsilon) < float64(maxResponseTime) || float64(got)*(1-epsilon) > float64(maxResponseTime) {
+		t.Fatalf("Failed to transition back")
+	}
+}
+
+var maxResponseWeights = TimeoutWeights(maxResponseTime)
+
+func TestValue(t *testing.T) {
+	noexp := utils.ExpirationFactor{Factor: 1}
+	for i := 0; i < 1000; i++ {
+		max := minResponseTime + time.Duration(rand.Int63n(int64(maxResponseTime-minResponseTime)))
+		min := minResponseTime + time.Duration(rand.Int63n(int64(max-minResponseTime)))
+		timeout := max/2 + time.Duration(rand.Int63n(int64(maxResponseTime-max/2)))
+		s := makeRangeStats(min, max, 1000, noexp)
+		value := s.Value(TimeoutWeights(timeout), noexp)
+		// calculate the average weight (the average of the given range of the half cosine
+		// weight function).
+		minx := math.Pi / 2 * float64(min) / float64(timeout)
+		maxx := math.Pi / 2 * float64(max) / float64(timeout)
+		avgWeight := (math.Sin(maxx) - math.Sin(minx)) / (maxx - minx)
+		expv := 1000 * avgWeight
+		if expv < 0 {
+			expv = 0
+		}
+		if value < expv-10 || value > expv+10 {
+			t.Errorf("Value failed (expected %v, got %v)", expv, value)
+		}
+	}
+}
+
+func TestAddSubExpire(t *testing.T) {
+	var (
+		sum1, sum2                 ResponseTimeStats
+		sum1ValueExp, sum2ValueExp float64
+		logOffset                  utils.Fixed64
+	)
+	for i := 0; i < 1000; i++ {
+		exp := utils.ExpFactor(logOffset)
+		max := minResponseTime + time.Duration(rand.Int63n(int64(maxResponseTime-minResponseTime)))
+		min := minResponseTime + time.Duration(rand.Int63n(int64(max-minResponseTime)))
+		s := makeRangeStats(min, max, 1000, exp)
+		value := s.Value(maxResponseWeights, exp)
+		sum1.AddStats(&s)
+		sum1ValueExp += value
+		if rand.Intn(2) == 1 {
+			sum2.AddStats(&s)
+			sum2ValueExp += value
+		}
+		logOffset += utils.Float64ToFixed64(0.001 / math.Log(2))
+		sum1ValueExp -= sum1ValueExp * 0.001
+		sum2ValueExp -= sum2ValueExp * 0.001
+	}
+	exp := utils.ExpFactor(logOffset)
+	sum1Value := sum1.Value(maxResponseWeights, exp)
+	if sum1Value < sum1ValueExp*0.99 || sum1Value > sum1ValueExp*1.01 {
+		t.Errorf("sum1Value failed (expected %v, got %v)", sum1ValueExp, sum1Value)
+	}
+	sum2Value := sum2.Value(maxResponseWeights, exp)
+	if sum2Value < sum2ValueExp*0.99 || sum2Value > sum2ValueExp*1.01 {
+		t.Errorf("sum2Value failed (expected %v, got %v)", sum2ValueExp, sum2Value)
+	}
+	diff := sum1
+	diff.SubStats(&sum2)
+	diffValue := diff.Value(maxResponseWeights, exp)
+	diffValueExp := sum1ValueExp - sum2ValueExp
+	if diffValue < diffValueExp*0.99 || diffValue > diffValueExp*1.01 {
+		t.Errorf("diffValue failed (expected %v, got %v)", diffValueExp, diffValue)
+	}
+}
+
+func TestTimeout(t *testing.T) {
+	testTimeoutRange(t, 0, time.Second)
+	testTimeoutRange(t, time.Second, time.Second*2)
+	testTimeoutRange(t, time.Second, maxResponseTime)
+}
+
+func testTimeoutRange(t *testing.T, min, max time.Duration) {
+	s := makeRangeStats(min, max, 1000, utils.ExpirationFactor{Factor: 1})
+	for i := 2; i < 9; i++ {
+		to := s.Timeout(float64(i) / 10)
+		exp := max - (max-min)*time.Duration(i)/10
+		tol := (max - min) / 50
+		if to < exp-tol || to > exp+tol {
+			t.Errorf("Timeout failed (expected %v, got %v)", exp, to)
+		}
+	}
+}
+
+func makeRangeStats(min, max time.Duration, amount float64, exp utils.ExpirationFactor) ResponseTimeStats {
+	var s ResponseTimeStats
+	amount /= 1000
+	for i := 0; i < 1000; i++ {
+		s.Add(min+(max-min)*time.Duration(i)/999, amount, exp)
+	}
+	return s
+}

les/lespay/client/valuetracker.go

@@ -0,0 +1,515 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"bytes"
+	"fmt"
+	"math"
+	"sync"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/les/utils"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+const (
+	vtVersion  = 1 // database encoding format for ValueTracker
+	nvtVersion = 1 // database encoding format for NodeValueTracker
+)
+
+var (
+	vtKey     = []byte("vt:")
+	vtNodeKey = []byte("vtNode:")
+)
+
+// NodeValueTracker collects service value statistics for a specific server node
+type NodeValueTracker struct {
+	lock sync.Mutex
+
+	rtStats, lastRtStats ResponseTimeStats
+	lastTransfer         mclock.AbsTime
+	basket               serverBasket
+	reqCosts             []uint64
+	reqValues            *[]float64
+}
+
+// init initializes a NodeValueTracker.
+// Note that the contents of the referenced reqValues slice will not change; a new
+// reference is passed if the values are updated by ValueTracker.
+func (nv *NodeValueTracker) init(now mclock.AbsTime, reqValues *[]float64) {
+	reqTypeCount := len(*reqValues)
+	nv.reqCosts = make([]uint64, reqTypeCount)
+	nv.lastTransfer = now
+	nv.reqValues = reqValues
+	nv.basket.init(reqTypeCount)
+}
+
+// updateCosts updates the request cost table of the server. The request value factor
+// is also updated based on the given cost table and the current reference basket.
+// Note that the contents of the referenced reqValues slice will not change; a new
+// reference is passed if the values are updated by ValueTracker.
+func (nv *NodeValueTracker) updateCosts(reqCosts []uint64, reqValues *[]float64, rvFactor float64) {
+	nv.lock.Lock()
+	defer nv.lock.Unlock()
+
+	nv.reqCosts = reqCosts
+	nv.reqValues = reqValues
+	nv.basket.updateRvFactor(rvFactor)
+}
+
+// transferStats returns request basket and response time statistics that should be
+// added to the global statistics. The contents of the server's own request basket are
+// gradually transferred to the main reference basket and removed from the server basket
+// with the specified transfer rate.
+// The response time statistics are retained at both places and therefore the global
+// distribution is always the sum of the individual server distributions.
+func (nv *NodeValueTracker) transferStats(now mclock.AbsTime, transferRate float64) (requestBasket, ResponseTimeStats) {
+	nv.lock.Lock()
+	defer nv.lock.Unlock()
+
+	dt := now - nv.lastTransfer
+	nv.lastTransfer = now
+	if dt < 0 {
+		dt = 0
+	}
+	recentRtStats := nv.rtStats
+	recentRtStats.SubStats(&nv.lastRtStats)
+	nv.lastRtStats = nv.rtStats
+	return nv.basket.transfer(-math.Expm1(-transferRate * float64(dt))), recentRtStats
+}
+
+// RtStats returns the node's own response time distribution statistics
+func (nv *NodeValueTracker) RtStats() ResponseTimeStats {
+	nv.lock.Lock()
+	defer nv.lock.Unlock()
+
+	return nv.rtStats
+}
+
+// ValueTracker coordinates service value calculation for individual servers and updates
+// global statistics
+type ValueTracker struct {
+	clock        mclock.Clock
+	lock         sync.Mutex
+	quit         chan chan struct{}
+	db           ethdb.KeyValueStore
+	connected    map[enode.ID]*NodeValueTracker
+	reqTypeCount int
+
+	refBasket      referenceBasket
+	mappings       [][]string
+	currentMapping int
+	initRefBasket  requestBasket
+	rtStats        ResponseTimeStats
+
+	transferRate                 float64
+	statsExpLock                 sync.RWMutex
+	statsExpRate, offlineExpRate float64
+	statsExpirer                 utils.Expirer
+	statsExpFactor               utils.ExpirationFactor
+}
+
+type valueTrackerEncV1 struct {
+	Mappings           [][]string
+	RefBasketMapping   uint
+	RefBasket          requestBasket
+	RtStats            ResponseTimeStats
+	ExpOffset, SavedAt uint64
+}
+
+type nodeValueTrackerEncV1 struct {
+	RtStats             ResponseTimeStats
+	ServerBasketMapping uint
+	ServerBasket        requestBasket
+}
+
+// RequestInfo is an initializer structure for the service vector.
+type RequestInfo struct {
+	// Name identifies the request type and is used for re-mapping the service vector if necessary
+	Name string
+	// InitAmount and InitValue are used to initialize the reference basket
+	InitAmount, InitValue float64
+}
+
+// NewValueTracker creates a new ValueTracker and loads its previously saved state from
+// the database if possible.
+func NewValueTracker(db ethdb.KeyValueStore, clock mclock.Clock, reqInfo []RequestInfo, updatePeriod time.Duration, transferRate, statsExpRate, offlineExpRate float64) *ValueTracker {
+	now := clock.Now()
+
+	initRefBasket := requestBasket{items: make([]basketItem, len(reqInfo))}
+	mapping := make([]string, len(reqInfo))
+
+	var sumAmount, sumValue float64
+	for _, req := range reqInfo {
+		sumAmount += req.InitAmount
+		sumValue += req.InitAmount * req.InitValue
+	}
+	scaleValues := sumAmount * basketFactor / sumValue
+	for i, req := range reqInfo {
+		mapping[i] = req.Name
+		initRefBasket.items[i].amount = uint64(req.InitAmount * basketFactor)
+		initRefBasket.items[i].value = uint64(req.InitAmount * req.InitValue * scaleValues)
+	}
+
+	vt := &ValueTracker{
+		clock:          clock,
+		connected:      make(map[enode.ID]*NodeValueTracker),
+		quit:           make(chan chan struct{}),
+		db:             db,
+		reqTypeCount:   len(initRefBasket.items),
+		initRefBasket:  initRefBasket,
+		transferRate:   transferRate,
+		statsExpRate:   statsExpRate,
+		offlineExpRate: offlineExpRate,
+	}
+	if vt.loadFromDb(mapping) != nil {
+		// previous state not saved or invalid, init with default values
+		vt.refBasket.basket = initRefBasket
+		vt.mappings = [][]string{mapping}
+		vt.currentMapping = 0
+	}
+	vt.statsExpirer.SetRate(now, statsExpRate)
+	vt.refBasket.init(vt.reqTypeCount)
+	vt.periodicUpdate()
+
+	go func() {
+		for {
+			select {
+			case <-clock.After(updatePeriod):
+				vt.lock.Lock()
+				vt.periodicUpdate()
+				vt.lock.Unlock()
+			case quit := <-vt.quit:
+				close(quit)
+				return
+			}
+		}
+	}()
+	return vt
+}
+
+// StatsExpirer returns the statistics expirer so that other values can be expired
+// with the same rate as the service value statistics.
+func (vt *ValueTracker) StatsExpirer() *utils.Expirer {
+	return &vt.statsExpirer
+}
+
+// loadFromDb loads the value tracker's state from the database and converts saved
+// request basket index mapping if it does not match the specified index to name mapping.
+func (vt *ValueTracker) loadFromDb(mapping []string) error {
+	enc, err := vt.db.Get(vtKey)
+	if err != nil {
+		return err
+	}
+	r := bytes.NewReader(enc)
+	var version uint
+	if err := rlp.Decode(r, &version); err != nil {
+		log.Error("Decoding value tracker state failed", "err", err)
+		return err
+	}
+	if version != vtVersion {
+		log.Error("Unknown ValueTracker version", "stored", version, "current", nvtVersion)
+		return fmt.Errorf("Unknown ValueTracker version %d (current version is %d)", version, vtVersion)
+	}
+	var vte valueTrackerEncV1
+	if err := rlp.Decode(r, &vte); err != nil {
+		log.Error("Decoding value tracker state failed", "err", err)
+		return err
+	}
+	logOffset := utils.Fixed64(vte.ExpOffset)
+	dt := time.Now().UnixNano() - int64(vte.SavedAt)
+	if dt > 0 {
+		logOffset += utils.Float64ToFixed64(float64(dt) * vt.offlineExpRate / math.Log(2))
+	}
+	vt.statsExpirer.SetLogOffset(vt.clock.Now(), logOffset)
+	vt.rtStats = vte.RtStats
+	vt.mappings = vte.Mappings
+	vt.currentMapping = -1
+loop:
+	for i, m := range vt.mappings {
+		if len(m) != len(mapping) {
+			continue loop
+		}
+		for j, s := range mapping {
+			if m[j] != s {
+				continue loop
+			}
+		}
+		vt.currentMapping = i
+		break
+	}
+	if vt.currentMapping == -1 {
+		vt.currentMapping = len(vt.mappings)
+		vt.mappings = append(vt.mappings, mapping)
+	}
+	if int(vte.RefBasketMapping) == vt.currentMapping {
+		vt.refBasket.basket = vte.RefBasket
+	} else {
+		if vte.RefBasketMapping >= uint(len(vt.mappings)) {
+			log.Error("Unknown request basket mapping", "stored", vte.RefBasketMapping, "current", vt.currentMapping)
+			return fmt.Errorf("Unknown request basket mapping %d (current version is %d)", vte.RefBasketMapping, vt.currentMapping)
+		}
+		vt.refBasket.basket = vte.RefBasket.convertMapping(vt.mappings[vte.RefBasketMapping], mapping, vt.initRefBasket)
+	}
+	return nil
+}
+
+// saveToDb saves the value tracker's state to the database
+func (vt *ValueTracker) saveToDb() {
+	vte := valueTrackerEncV1{
+		Mappings:         vt.mappings,
+		RefBasketMapping: uint(vt.currentMapping),
+		RefBasket:        vt.refBasket.basket,
+		RtStats:          vt.rtStats,
+		ExpOffset:        uint64(vt.statsExpirer.LogOffset(vt.clock.Now())),
+		SavedAt:          uint64(time.Now().UnixNano()),
+	}
+	enc1, err := rlp.EncodeToBytes(uint(vtVersion))
+	if err != nil {
+		log.Error("Encoding value tracker state failed", "err", err)
+		return
+	}
+	enc2, err := rlp.EncodeToBytes(&vte)
+	if err != nil {
+		log.Error("Encoding value tracker state failed", "err", err)
+		return
+	}
+	if err := vt.db.Put(vtKey, append(enc1, enc2...)); err != nil {
+		log.Error("Saving value tracker state failed", "err", err)
+	}
+}
+
+// Stop saves the value tracker's state and each loaded node's individual state and
+// returns after shutting the internal goroutines down.
+func (vt *ValueTracker) Stop() {
+	quit := make(chan struct{})
+	vt.quit <- quit
+	<-quit
+	vt.lock.Lock()
+	vt.periodicUpdate()
+	for id, nv := range vt.connected {
+		vt.saveNode(id, nv)
+	}
+	vt.connected = nil
+	vt.saveToDb()
+	vt.lock.Unlock()
+}
+
+// Register adds a server node to the value tracker
+func (vt *ValueTracker) Register(id enode.ID) *NodeValueTracker {
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	if vt.connected == nil {
+		// ValueTracker has already been stopped
+		return nil
+	}
+	nv := vt.loadOrNewNode(id)
+	nv.init(vt.clock.Now(), &vt.refBasket.reqValues)
+	vt.connected[id] = nv
+	return nv
+}
+
+// Unregister removes a server node from the value tracker
+func (vt *ValueTracker) Unregister(id enode.ID) {
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	if nv := vt.connected[id]; nv != nil {
+		vt.saveNode(id, nv)
+		delete(vt.connected, id)
+	}
+}
+
+// GetNode returns an individual server node's value tracker. If it did not exist before
+// then a new node is created.
+func (vt *ValueTracker) GetNode(id enode.ID) *NodeValueTracker {
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	return vt.loadOrNewNode(id)
+}
+
+// loadOrNewNode returns an individual server node's value tracker. If it did not exist before
+// then a new node is created.
+func (vt *ValueTracker) loadOrNewNode(id enode.ID) *NodeValueTracker {
+	if nv, ok := vt.connected[id]; ok {
+		return nv
+	}
+	nv := &NodeValueTracker{lastTransfer: vt.clock.Now()}
+	enc, err := vt.db.Get(append(vtNodeKey, id[:]...))
+	if err != nil {
+		return nv
+	}
+	r := bytes.NewReader(enc)
+	var version uint
+	if err := rlp.Decode(r, &version); err != nil {
+		log.Error("Failed to decode node value tracker", "id", id, "err", err)
+		return nv
+	}
+	if version != nvtVersion {
+		log.Error("Unknown NodeValueTracker version", "stored", version, "current", nvtVersion)
+		return nv
+	}
+	var nve nodeValueTrackerEncV1
+	if err := rlp.Decode(r, &nve); err != nil {
+		log.Error("Failed to decode node value tracker", "id", id, "err", err)
+		return nv
+	}
+	nv.rtStats = nve.RtStats
+	nv.lastRtStats = nve.RtStats
+	if int(nve.ServerBasketMapping) == vt.currentMapping {
+		nv.basket.basket = nve.ServerBasket
+	} else {
+		if nve.ServerBasketMapping >= uint(len(vt.mappings)) {
+			log.Error("Unknown request basket mapping", "stored", nve.ServerBasketMapping, "current", vt.currentMapping)
+			return nv
+		}
+		nv.basket.basket = nve.ServerBasket.convertMapping(vt.mappings[nve.ServerBasketMapping], vt.mappings[vt.currentMapping], vt.initRefBasket)
+	}
+	return nv
+}
+
+// saveNode saves a server node's value tracker to the database
+func (vt *ValueTracker) saveNode(id enode.ID, nv *NodeValueTracker) {
+	recentRtStats := nv.rtStats
+	recentRtStats.SubStats(&nv.lastRtStats)
+	vt.rtStats.AddStats(&recentRtStats)
+	nv.lastRtStats = nv.rtStats
+
+	nve := nodeValueTrackerEncV1{
+		RtStats:             nv.rtStats,
+		ServerBasketMapping: uint(vt.currentMapping),
+		ServerBasket:        nv.basket.basket,
+	}
+	enc1, err := rlp.EncodeToBytes(uint(nvtVersion))
+	if err != nil {
+		log.Error("Failed to encode service value information", "id", id, "err", err)
+		return
+	}
+	enc2, err := rlp.EncodeToBytes(&nve)
+	if err != nil {
+		log.Error("Failed to encode service value information", "id", id, "err", err)
+		return
+	}
+	if err := vt.db.Put(append(vtNodeKey, id[:]...), append(enc1, enc2...)); err != nil {
+		log.Error("Failed to save service value information", "id", id, "err", err)
+	}
+}
+
+// UpdateCosts updates the node value tracker's request cost table
+func (vt *ValueTracker) UpdateCosts(nv *NodeValueTracker, reqCosts []uint64) {
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	nv.updateCosts(reqCosts, &vt.refBasket.reqValues, vt.refBasket.reqValueFactor(reqCosts))
+}
+
+// RtStats returns the global response time distribution statistics
+func (vt *ValueTracker) RtStats() ResponseTimeStats {
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	vt.periodicUpdate()
+	return vt.rtStats
+}
+
+// periodicUpdate transfers individual node data to the global statistics, normalizes
+// the reference basket and updates request values. The global state is also saved to
+// the database with each update.
+func (vt *ValueTracker) periodicUpdate() {
+	now := vt.clock.Now()
+	vt.statsExpLock.Lock()
+	vt.statsExpFactor = utils.ExpFactor(vt.statsExpirer.LogOffset(now))
+	vt.statsExpLock.Unlock()
+
+	for _, nv := range vt.connected {
+		basket, rtStats := nv.transferStats(now, vt.transferRate)
+		vt.refBasket.add(basket)
+		vt.rtStats.AddStats(&rtStats)
+	}
+	vt.refBasket.normalize()
+	vt.refBasket.updateReqValues()
+	for _, nv := range vt.connected {
+		nv.updateCosts(nv.reqCosts, &vt.refBasket.reqValues, vt.refBasket.reqValueFactor(nv.reqCosts))
+	}
+	vt.saveToDb()
+}
+
+type ServedRequest struct {
+	ReqType, Amount uint32
+}
+
+// Served adds a served request to the node's statistics. An actual request may be composed
+// of one or more request types (service vector indices).
+func (vt *ValueTracker) Served(nv *NodeValueTracker, reqs []ServedRequest, respTime time.Duration) {
+	vt.statsExpLock.RLock()
+	expFactor := vt.statsExpFactor
+	vt.statsExpLock.RUnlock()
+
+	nv.lock.Lock()
+	defer nv.lock.Unlock()
+
+	var value float64
+	for _, r := range reqs {
+		nv.basket.add(r.ReqType, r.Amount, nv.reqCosts[r.ReqType]*uint64(r.Amount), expFactor)
+		value += (*nv.reqValues)[r.ReqType] * float64(r.Amount)
+	}
+	nv.rtStats.Add(respTime, value, vt.statsExpFactor)
+}
+
+type RequestStatsItem struct {
+	Name                string
+	ReqAmount, ReqValue float64
+}
+
+// RequestStats returns the current contents of the reference request basket, with
+// request values meaning average per request rather than total.
+func (vt *ValueTracker) RequestStats() []RequestStatsItem {
+	vt.statsExpLock.RLock()
+	expFactor := vt.statsExpFactor
+	vt.statsExpLock.RUnlock()
+	vt.lock.Lock()
+	defer vt.lock.Unlock()
+
+	vt.periodicUpdate()
+	res := make([]RequestStatsItem, len(vt.refBasket.basket.items))
+	for i, item := range vt.refBasket.basket.items {
+		res[i].Name = vt.mappings[vt.currentMapping][i]
+		res[i].ReqAmount = expFactor.Value(float64(item.amount)/basketFactor, vt.refBasket.basket.exp)
+		res[i].ReqValue = vt.refBasket.reqValues[i]
+	}
+	return res
+}
+
+// TotalServiceValue returns the total service value provided by the given node (as
+// a function of the weights which are calculated from the request timeout value).
+func (vt *ValueTracker) TotalServiceValue(nv *NodeValueTracker, weights ResponseTimeWeights) float64 {
+	vt.statsExpLock.RLock()
+	expFactor := vt.statsExpFactor
+	vt.statsExpLock.RUnlock()
+
+	nv.lock.Lock()
+	defer nv.lock.Unlock()
+
+	return nv.rtStats.Value(weights, expFactor)
+}

les/lespay/client/valuetracker_test.go

@@ -0,0 +1,135 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package client
+
+import (
+	"math"
+	"math/rand"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+	"github.com/ethereum/go-ethereum/ethdb/memorydb"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+
+	"github.com/ethereum/go-ethereum/les/utils"
+)
+
+const (
+	testReqTypes  = 3
+	testNodeCount = 5
+	testReqCount  = 10000
+	testRounds    = 10
+)
+
+func TestValueTracker(t *testing.T) {
+	db := memorydb.New()
+	clock := &mclock.Simulated{}
+	requestList := make([]RequestInfo, testReqTypes)
+	relPrices := make([]float64, testReqTypes)
+	totalAmount := make([]uint64, testReqTypes)
+	for i := range requestList {
+		requestList[i] = RequestInfo{Name: "testreq" + strconv.Itoa(i), InitAmount: 1, InitValue: 1}
+		totalAmount[i] = 1
+		relPrices[i] = rand.Float64() + 0.1
+	}
+	nodes := make([]*NodeValueTracker, testNodeCount)
+	for round := 0; round < testRounds; round++ {
+		makeRequests := round < testRounds-2
+		useExpiration := round == testRounds-1
+		var expRate float64
+		if useExpiration {
+			expRate = math.Log(2) / float64(time.Hour*100)
+		}
+
+		vt := NewValueTracker(db, clock, requestList, time.Minute, 1/float64(time.Hour), expRate, expRate)
+		updateCosts := func(i int) {
+			costList := make([]uint64, testReqTypes)
+			baseCost := rand.Float64()*10000000 + 100000
+			for j := range costList {
+				costList[j] = uint64(baseCost * relPrices[j])
+			}
+			vt.UpdateCosts(nodes[i], costList)
+		}
+		for i := range nodes {
+			nodes[i] = vt.Register(enode.ID{byte(i)})
+			updateCosts(i)
+		}
+		if makeRequests {
+			for i := 0; i < testReqCount; i++ {
+				reqType := rand.Intn(testReqTypes)
+				reqAmount := rand.Intn(10) + 1
+				node := rand.Intn(testNodeCount)
+				respTime := time.Duration((rand.Float64() + 1) * float64(time.Second) * float64(node+1) / testNodeCount)
+				totalAmount[reqType] += uint64(reqAmount)
+				vt.Served(nodes[node], []ServedRequest{{uint32(reqType), uint32(reqAmount)}}, respTime)
+				clock.Run(time.Second)
+			}
+		} else {
+			clock.Run(time.Hour * 100)
+			if useExpiration {
+				for i, a := range totalAmount {
+					totalAmount[i] = a / 2
+				}
+			}
+		}
+		vt.Stop()
+		var sumrp, sumrv float64
+		for i, rp := range relPrices {
+			sumrp += rp
+			sumrv += vt.refBasket.reqValues[i]
+		}
+		for i, rp := range relPrices {
+			ratio := vt.refBasket.reqValues[i] * sumrp / (rp * sumrv)
+			if ratio < 0.99 || ratio > 1.01 {
+				t.Errorf("reqValues (%v) does not match relPrices (%v)", vt.refBasket.reqValues, relPrices)
+				break
+			}
+		}
+		exp := utils.ExpFactor(vt.StatsExpirer().LogOffset(clock.Now()))
+		basketAmount := make([]uint64, testReqTypes)
+		for i, bi := range vt.refBasket.basket.items {
+			basketAmount[i] += uint64(exp.Value(float64(bi.amount), vt.refBasket.basket.exp))
+		}
+		if makeRequests {
+			// if we did not make requests in this round then we expect all amounts to be
+			// in the reference basket
+			for _, node := range nodes {
+				for i, bi := range node.basket.basket.items {
+					basketAmount[i] += uint64(exp.Value(float64(bi.amount), node.basket.basket.exp))
+				}
+			}
+		}
+		for i, a := range basketAmount {
+			amount := a / basketFactor
+			if amount+10 < totalAmount[i] || amount > totalAmount[i]+10 {
+				t.Errorf("totalAmount[%d] mismatch in round %d (expected %d, got %d)", i, round, totalAmount[i], amount)
+			}
+		}
+		var sumValue float64
+		for _, node := range nodes {
+			s := node.RtStats()
+			sumValue += s.Value(maxResponseWeights, exp)
+		}
+		s := vt.RtStats()
+		mainValue := s.Value(maxResponseWeights, exp)
+		if sumValue < mainValue-10 || sumValue > mainValue+10 {
+			t.Errorf("Main rtStats value does not match sum of node rtStats values in round %d (main %v, sum %v)", round, mainValue, sumValue)
+		}
+	}
+}

les/peer.go

@@ -32,6 +32,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/eth"
 	"github.com/ethereum/go-ethereum/les/flowcontrol"
+	lpc "github.com/ethereum/go-ethereum/les/lespay/client"
 	"github.com/ethereum/go-ethereum/les/utils"
 	"github.com/ethereum/go-ethereum/light"
 	"github.com/ethereum/go-ethereum/p2p"
@@ -358,6 +359,10 @@ type serverPeer struct {
 
 	poolEntry        *poolEntry              // Statistic for server peer.
 	fcServer         *flowcontrol.ServerNode // Client side mirror token bucket.
+	vtLock           sync.Mutex
+	valueTracker     *lpc.ValueTracker
+	nodeValueTracker *lpc.NodeValueTracker
+	sentReqs         map[uint64]sentReqEntry
 
 	// Statistics
 	errCount    int // Counter the invalid responses server has replied
@@ -428,62 +433,71 @@ func sendRequest(w p2p.MsgWriter, msgcode, reqID uint64, data interface{}) error
 	return p2p.Send(w, msgcode, req{reqID, data})
 }
 
+func (p *serverPeer) sendRequest(msgcode, reqID uint64, data interface{}, amount int) error {
+	p.sentRequest(reqID, uint32(msgcode), uint32(amount))
+	return sendRequest(p.rw, msgcode, reqID, data)
+}
+
 // requestHeadersByHash fetches a batch of blocks' headers corresponding to the
 // specified header query, based on the hash of an origin block.
 func (p *serverPeer) requestHeadersByHash(reqID uint64, origin common.Hash, amount int, skip int, reverse bool) error {
 	p.Log().Debug("Fetching batch of headers", "count", amount, "fromhash", origin, "skip", skip, "reverse", reverse)
-	return sendRequest(p.rw, GetBlockHeadersMsg, reqID, &getBlockHeadersData{Origin: hashOrNumber{Hash: origin}, Amount: uint64(amount), Skip: uint64(skip), Reverse: reverse})
+	return p.sendRequest(GetBlockHeadersMsg, reqID, &getBlockHeadersData{Origin: hashOrNumber{Hash: origin}, Amount: uint64(amount), Skip: uint64(skip), Reverse: reverse}, amount)
 }
 
 // requestHeadersByNumber fetches a batch of blocks' headers corresponding to the
 // specified header query, based on the number of an origin block.
 func (p *serverPeer) requestHeadersByNumber(reqID, origin uint64, amount int, skip int, reverse bool) error {
 	p.Log().Debug("Fetching batch of headers", "count", amount, "fromnum", origin, "skip", skip, "reverse", reverse)
-	return sendRequest(p.rw, GetBlockHeadersMsg, reqID, &getBlockHeadersData{Origin: hashOrNumber{Number: origin}, Amount: uint64(amount), Skip: uint64(skip), Reverse: reverse})
+	return p.sendRequest(GetBlockHeadersMsg, reqID, &getBlockHeadersData{Origin: hashOrNumber{Number: origin}, Amount: uint64(amount), Skip: uint64(skip), Reverse: reverse}, amount)
 }
 
 // requestBodies fetches a batch of blocks' bodies corresponding to the hashes
 // specified.
 func (p *serverPeer) requestBodies(reqID uint64, hashes []common.Hash) error {
 	p.Log().Debug("Fetching batch of block bodies", "count", len(hashes))
-	return sendRequest(p.rw, GetBlockBodiesMsg, reqID, hashes)
+	return p.sendRequest(GetBlockBodiesMsg, reqID, hashes, len(hashes))
 }
 
 // requestCode fetches a batch of arbitrary data from a node's known state
 // data, corresponding to the specified hashes.
 func (p *serverPeer) requestCode(reqID uint64, reqs []CodeReq) error {
 	p.Log().Debug("Fetching batch of codes", "count", len(reqs))
-	return sendRequest(p.rw, GetCodeMsg, reqID, reqs)
+	return p.sendRequest(GetCodeMsg, reqID, reqs, len(reqs))
 }
 
 // requestReceipts fetches a batch of transaction receipts from a remote node.
 func (p *serverPeer) requestReceipts(reqID uint64, hashes []common.Hash) error {
 	p.Log().Debug("Fetching batch of receipts", "count", len(hashes))
-	return sendRequest(p.rw, GetReceiptsMsg, reqID, hashes)
+	return p.sendRequest(GetReceiptsMsg, reqID, hashes, len(hashes))
 }
 
 // requestProofs fetches a batch of merkle proofs from a remote node.
 func (p *serverPeer) requestProofs(reqID uint64, reqs []ProofReq) error {
 	p.Log().Debug("Fetching batch of proofs", "count", len(reqs))
-	return sendRequest(p.rw, GetProofsV2Msg, reqID, reqs)
+	return p.sendRequest(GetProofsV2Msg, reqID, reqs, len(reqs))
 }
 
 // requestHelperTrieProofs fetches a batch of HelperTrie merkle proofs from a remote node.
 func (p *serverPeer) requestHelperTrieProofs(reqID uint64, reqs []HelperTrieReq) error {
 	p.Log().Debug("Fetching batch of HelperTrie proofs", "count", len(reqs))
-	return sendRequest(p.rw, GetHelperTrieProofsMsg, reqID, reqs)
+	return p.sendRequest(GetHelperTrieProofsMsg, reqID, reqs, len(reqs))
 }
 
 // requestTxStatus fetches a batch of transaction status records from a remote node.
 func (p *serverPeer) requestTxStatus(reqID uint64, txHashes []common.Hash) error {
 	p.Log().Debug("Requesting transaction status", "count", len(txHashes))
-	return sendRequest(p.rw, GetTxStatusMsg, reqID, txHashes)
+	return p.sendRequest(GetTxStatusMsg, reqID, txHashes, len(txHashes))
 }
 
 // SendTxStatus creates a reply with a batch of transactions to be added to the remote transaction pool.
-func (p *serverPeer) sendTxs(reqID uint64, txs rlp.RawValue) error {
-	p.Log().Debug("Sending batch of transactions", "size", len(txs))
-	return sendRequest(p.rw, SendTxV2Msg, reqID, txs)
+func (p *serverPeer) sendTxs(reqID uint64, amount int, txs rlp.RawValue) error {
+	p.Log().Debug("Sending batch of transactions", "amount", amount, "size", len(txs))
+	sizeFactor := (len(txs) + txSizeCostLimit/2) / txSizeCostLimit
+	if sizeFactor > amount {
+		amount = sizeFactor
+	}
+	return p.sendRequest(SendTxV2Msg, reqID, txs, amount)
 }
 
 // waitBefore implements distPeer interface
@@ -532,6 +546,7 @@ func (p *serverPeer) getTxRelayCost(amount, size int) uint64 {
 // HasBlock checks if the peer has a given block
 func (p *serverPeer) HasBlock(hash common.Hash, number uint64, hasState bool) bool {
 	p.lock.RLock()
+
 	head := p.headInfo.Number
 	var since, recent uint64
 	if hasState {
@@ -630,6 +645,87 @@ func (p *serverPeer) Handshake(td *big.Int, head common.Hash, headNum uint64, ge
 	})
 }
 
+// setValueTracker sets the value tracker references for connected servers. Note that the
+// references should be removed upon disconnection by setValueTracker(nil, nil).
+func (p *serverPeer) setValueTracker(vt *lpc.ValueTracker, nvt *lpc.NodeValueTracker) {
+	p.vtLock.Lock()
+	p.valueTracker = vt
+	p.nodeValueTracker = nvt
+	if nvt != nil {
+		p.sentReqs = make(map[uint64]sentReqEntry)
+	} else {
+		p.sentReqs = nil
+	}
+	p.vtLock.Unlock()
+}
+
+// updateVtParams updates the server's price table in the value tracker.
+func (p *serverPeer) updateVtParams() {
+	p.vtLock.Lock()
+	defer p.vtLock.Unlock()
+
+	if p.nodeValueTracker == nil {
+		return
+	}
+	reqCosts := make([]uint64, len(requestList))
+	for code, costs := range p.fcCosts {
+		if m, ok := requestMapping[uint32(code)]; ok {
+			reqCosts[m.first] = costs.baseCost + costs.reqCost
+			if m.rest != -1 {
+				reqCosts[m.rest] = costs.reqCost
+			}
+		}
+	}
+	p.valueTracker.UpdateCosts(p.nodeValueTracker, reqCosts)
+}
+
+// sentReqEntry remembers sent requests and their sending times
+type sentReqEntry struct {
+	reqType, amount uint32
+	at              mclock.AbsTime
+}
+
+// sentRequest marks a request sent at the current moment to this server.
+func (p *serverPeer) sentRequest(id uint64, reqType, amount uint32) {
+	p.vtLock.Lock()
+	if p.sentReqs != nil {
+		p.sentReqs[id] = sentReqEntry{reqType, amount, mclock.Now()}
+	}
+	p.vtLock.Unlock()
+}
+
+// answeredRequest marks a request answered at the current moment by this server.
+func (p *serverPeer) answeredRequest(id uint64) {
+	p.vtLock.Lock()
+	if p.sentReqs == nil {
+		p.vtLock.Unlock()
+		return
+	}
+	e, ok := p.sentReqs[id]
+	delete(p.sentReqs, id)
+	vt := p.valueTracker
+	nvt := p.nodeValueTracker
+	p.vtLock.Unlock()
+	if !ok {
+		return
+	}
+	var (
+		vtReqs   [2]lpc.ServedRequest
+		reqCount int
+	)
+	m := requestMapping[e.reqType]
+	if m.rest == -1 || e.amount <= 1 {
+		reqCount = 1
+		vtReqs[0] = lpc.ServedRequest{ReqType: uint32(m.first), Amount: e.amount}
+	} else {
+		reqCount = 2
+		vtReqs[0] = lpc.ServedRequest{ReqType: uint32(m.first), Amount: 1}
+		vtReqs[1] = lpc.ServedRequest{ReqType: uint32(m.rest), Amount: e.amount - 1}
+	}
+	dt := time.Duration(mclock.Now() - e.at)
+	vt.Served(nvt, vtReqs[:reqCount], dt)
+}
+
 // clientPeer represents each node to which the les server is connected.
 // The node here refers to the light client.
 type clientPeer struct {

les/protocol.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
+	lpc "github.com/ethereum/go-ethereum/les/lespay/client"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/rlp"
 )
@@ -79,17 +80,57 @@ const (
 type requestInfo struct {
 	name                          string
 	maxCount                      uint64
+	refBasketFirst, refBasketRest float64
+}
+
+// reqMapping maps an LES request to one or two lespay service vector entries.
+// If rest != -1 and the request type is used with amounts larger than one then the
+// first one of the multi-request is mapped to first while the rest is mapped to rest.
+type reqMapping struct {
+	first, rest int
+}
+
+var (
+	// requests describes the available LES request types and their initializing amounts
+	// in the lespay/client.ValueTracker reference basket. Initial values are estimates
+	// based on the same values as the server's default cost estimates (reqAvgTimeCost).
+	requests = map[uint64]requestInfo{
+		GetBlockHeadersMsg:     {"GetBlockHeaders", MaxHeaderFetch, 10, 1000},
+		GetBlockBodiesMsg:      {"GetBlockBodies", MaxBodyFetch, 1, 0},
+		GetReceiptsMsg:         {"GetReceipts", MaxReceiptFetch, 1, 0},
+		GetCodeMsg:             {"GetCode", MaxCodeFetch, 1, 0},
+		GetProofsV2Msg:         {"GetProofsV2", MaxProofsFetch, 10, 0},
+		GetHelperTrieProofsMsg: {"GetHelperTrieProofs", MaxHelperTrieProofsFetch, 10, 100},
+		SendTxV2Msg:            {"SendTxV2", MaxTxSend, 1, 0},
+		GetTxStatusMsg:         {"GetTxStatus", MaxTxStatus, 10, 0},
+	}
+	requestList    []lpc.RequestInfo
+	requestMapping map[uint32]reqMapping
+)
+
+// init creates a request list and mapping between protocol message codes and lespay
+// service vector indices.
+func init() {
+	requestMapping = make(map[uint32]reqMapping)
+	for code, req := range requests {
+		cost := reqAvgTimeCost[code]
+		rm := reqMapping{len(requestList), -1}
+		requestList = append(requestList, lpc.RequestInfo{
+			Name:       req.name + ".first",
+			InitAmount: req.refBasketFirst,
+			InitValue:  float64(cost.baseCost + cost.reqCost),
+		})
+		if req.refBasketRest != 0 {
+			rm.rest = len(requestList)
+			requestList = append(requestList, lpc.RequestInfo{
+				Name:       req.name + ".rest",
+				InitAmount: req.refBasketRest,
+				InitValue:  float64(cost.reqCost),
+			})
+		}
+		requestMapping[uint32(code)] = rm
 	}
 
-var requests = map[uint64]requestInfo{
-	GetBlockHeadersMsg:     {"GetBlockHeaders", MaxHeaderFetch},
-	GetBlockBodiesMsg:      {"GetBlockBodies", MaxBodyFetch},
-	GetReceiptsMsg:         {"GetReceipts", MaxReceiptFetch},
-	GetCodeMsg:             {"GetCode", MaxCodeFetch},
-	GetProofsV2Msg:         {"GetProofsV2", MaxProofsFetch},
-	GetHelperTrieProofsMsg: {"GetHelperTrieProofs", MaxHelperTrieProofsFetch},
-	SendTxV2Msg:            {"SendTxV2", MaxTxSend},
-	GetTxStatusMsg:         {"GetTxStatus", MaxTxStatus},
 }
 
 type errCode int

les/txrelay.go

@@ -144,7 +144,7 @@ func (ltrx *lesTxRelay) send(txs types.Transactions, count int) {
 				peer := dp.(*serverPeer)
 				cost := peer.getTxRelayCost(len(ll), len(enc))
 				peer.fcServer.QueuedRequest(reqID, cost)
-				return func() { peer.sendTxs(reqID, enc) }
+				return func() { peer.sendTxs(reqID, len(ll), enc) }
 			},
 		}
 		go ltrx.retriever.retrieve(context.Background(), reqID, rq, func(p distPeer, msg *Msg) error { return nil }, ltrx.stop)

les/utils/expiredvalue.go

@@ -0,0 +1,202 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package utils
+
+import (
+	"math"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+)
+
+// ExpiredValue is a scalar value that is continuously expired (decreased
+// exponentially) based on the provided logarithmic expiration offset value.
+//
+// The formula for value calculation is: base*2^(exp-logOffset). In order to
+// simplify the calculation of ExpiredValue, its value is expressed in the form
+// of an exponent with a base of 2.
+//
+// Also here is a trick to reduce a lot of calculations. In theory, when a value X
+// decays over time and then a new value Y is added, the final result should be
+// X*2^(exp-logOffset)+Y. However it's very hard to represent in memory.
+// So the trick is using the idea of inflation instead of exponential decay. At this
+// moment the temporary value becomes: X*2^exp+Y*2^logOffset_1, apply the exponential
+// decay when we actually want to calculate the value.
+//
+// e.g.
+// t0: V = 100
+// t1: add 30, inflationary value is: 100 + 30/0.3, 0.3 is the decay coefficient
+// t2: get value, decay coefficient is 0.2 now, final result is: 200*0.2 = 40
+type ExpiredValue struct {
+	Base, Exp uint64 // rlp encoding works by default
+}
+
+// ExpirationFactor is calculated from logOffset. 1 <= Factor < 2 and Factor*2^Exp
+// describes the multiplier applicable for additions and the divider for readouts.
+// If logOffset changes slowly then it saves some expensive operations to not calculate
+// them for each addition and readout but cache this intermediate form for some time.
+// It is also useful for structures where multiple values are expired with the same
+// Expirer.
+type ExpirationFactor struct {
+	Exp    uint64
+	Factor float64
+}
+
+// ExpFactor calculates ExpirationFactor based on logOffset
+func ExpFactor(logOffset Fixed64) ExpirationFactor {
+	return ExpirationFactor{Exp: logOffset.ToUint64(), Factor: logOffset.Fraction().Pow2()}
+}
+
+// Value calculates the expired value based on a floating point base and integer
+// power-of-2 exponent. This function should be used by multi-value expired structures.
+func (e ExpirationFactor) Value(base float64, exp uint64) float64 {
+	res := base / e.Factor
+	if exp > e.Exp {
+		res *= float64(uint64(1) << (exp - e.Exp))
+	}
+	if exp < e.Exp {
+		res /= float64(uint64(1) << (e.Exp - exp))
+	}
+	return res
+}
+
+// value calculates the value at the given moment.
+func (e ExpiredValue) Value(logOffset Fixed64) uint64 {
+	offset := Uint64ToFixed64(e.Exp) - logOffset
+	return uint64(float64(e.Base) * offset.Pow2())
+}
+
+// add adds a signed value at the given moment
+func (e *ExpiredValue) Add(amount int64, logOffset Fixed64) int64 {
+	integer, frac := logOffset.ToUint64(), logOffset.Fraction()
+	factor := frac.Pow2()
+	base := factor * float64(amount)
+	if integer < e.Exp {
+		base /= math.Pow(2, float64(e.Exp-integer))
+	}
+	if integer > e.Exp {
+		e.Base >>= (integer - e.Exp)
+		e.Exp = integer
+	}
+	if base >= 0 || uint64(-base) <= e.Base {
+		e.Base += uint64(base)
+		return amount
+	}
+	net := int64(-float64(e.Base) / factor)
+	e.Base = 0
+	return net
+}
+
+// addExp adds another ExpiredValue
+func (e *ExpiredValue) AddExp(a ExpiredValue) {
+	if e.Exp > a.Exp {
+		a.Base >>= (e.Exp - a.Exp)
+	}
+	if e.Exp < a.Exp {
+		e.Base >>= (a.Exp - e.Exp)
+		e.Exp = a.Exp
+	}
+	e.Base += a.Base
+}
+
+// subExp subtracts another ExpiredValue
+func (e *ExpiredValue) SubExp(a ExpiredValue) {
+	if e.Exp > a.Exp {
+		a.Base >>= (e.Exp - a.Exp)
+	}
+	if e.Exp < a.Exp {
+		e.Base >>= (a.Exp - e.Exp)
+		e.Exp = a.Exp
+	}
+	if e.Base > a.Base {
+		e.Base -= a.Base
+	} else {
+		e.Base = 0
+	}
+}
+
+// Expirer changes logOffset with a linear rate which can be changed during operation.
+// It is not thread safe, if access by multiple goroutines is needed then it should be
+// encapsulated into a locked structure.
+// Note that if neither SetRate nor SetLogOffset are used during operation then LogOffset
+// is thread safe.
+type Expirer struct {
+	logOffset  Fixed64
+	rate       float64
+	lastUpdate mclock.AbsTime
+}
+
+// SetRate changes the expiration rate which is the inverse of the time constant in
+// nanoseconds.
+func (e *Expirer) SetRate(now mclock.AbsTime, rate float64) {
+	dt := now - e.lastUpdate
+	if dt > 0 {
+		e.logOffset += Fixed64(logToFixedFactor * float64(dt) * e.rate)
+	}
+	e.lastUpdate = now
+	e.rate = rate
+}
+
+// SetLogOffset sets logOffset instantly.
+func (e *Expirer) SetLogOffset(now mclock.AbsTime, logOffset Fixed64) {
+	e.lastUpdate = now
+	e.logOffset = logOffset
+}
+
+// LogOffset returns the current logarithmic offset.
+func (e *Expirer) LogOffset(now mclock.AbsTime) Fixed64 {
+	dt := now - e.lastUpdate
+	if dt <= 0 {
+		return e.logOffset
+	}
+	return e.logOffset + Fixed64(logToFixedFactor*float64(dt)*e.rate)
+}
+
+// fixedFactor is the fixed point multiplier factor used by Fixed64.
+const fixedFactor = 0x1000000
+
+// Fixed64 implements 64-bit fixed point arithmetic functions.
+type Fixed64 int64
+
+// Uint64ToFixed64 converts uint64 integer to Fixed64 format.
+func Uint64ToFixed64(f uint64) Fixed64 {
+	return Fixed64(f * fixedFactor)
+}
+
+// float64ToFixed64 converts float64 to Fixed64 format.
+func Float64ToFixed64(f float64) Fixed64 {
+	return Fixed64(f * fixedFactor)
+}
+
+// toUint64 converts Fixed64 format to uint64.
+func (f64 Fixed64) ToUint64() uint64 {
+	return uint64(f64) / fixedFactor
+}
+
+// fraction returns the fractional part of a Fixed64 value.
+func (f64 Fixed64) Fraction() Fixed64 {
+	return f64 % fixedFactor
+}
+
+var (
+	logToFixedFactor = float64(fixedFactor) / math.Log(2)
+	fixedToLogFactor = math.Log(2) / float64(fixedFactor)
+)
+
+// pow2Fixed returns the base 2 power of the fixed point value.
+func (f64 Fixed64) Pow2() float64 {
+	return math.Exp(float64(f64) * fixedToLogFactor)
+}

les/utils/expiredvalue_test.go

@@ -0,0 +1,116 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package utils
+
+import "testing"
+
+func TestValueExpiration(t *testing.T) {
+	var cases = []struct {
+		input      ExpiredValue
+		timeOffset Fixed64
+		expect     uint64
+	}{
+		{ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(0), 128},
+		{ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(1), 64},
+		{ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(2), 32},
+		{ExpiredValue{Base: 128, Exp: 2}, Uint64ToFixed64(2), 128},
+		{ExpiredValue{Base: 128, Exp: 2}, Uint64ToFixed64(3), 64},
+	}
+	for _, c := range cases {
+		if got := c.input.Value(c.timeOffset); got != c.expect {
+			t.Fatalf("Value mismatch, want=%d, got=%d", c.expect, got)
+		}
+	}
+}
+
+func TestValueAddition(t *testing.T) {
+	var cases = []struct {
+		input      ExpiredValue
+		addend     int64
+		timeOffset Fixed64
+		expect     uint64
+		expectNet  int64
+	}{
+		// Addition
+		{ExpiredValue{Base: 128, Exp: 0}, 128, Uint64ToFixed64(0), 256, 128},
+		{ExpiredValue{Base: 128, Exp: 2}, 128, Uint64ToFixed64(0), 640, 128},
+
+		// Addition with offset
+		{ExpiredValue{Base: 128, Exp: 0}, 128, Uint64ToFixed64(1), 192, 128},
+		{ExpiredValue{Base: 128, Exp: 2}, 128, Uint64ToFixed64(1), 384, 128},
+		{ExpiredValue{Base: 128, Exp: 2}, 128, Uint64ToFixed64(3), 192, 128},
+
+		// Subtraction
+		{ExpiredValue{Base: 128, Exp: 0}, -64, Uint64ToFixed64(0), 64, -64},
+		{ExpiredValue{Base: 128, Exp: 0}, -128, Uint64ToFixed64(0), 0, -128},
+		{ExpiredValue{Base: 128, Exp: 0}, -192, Uint64ToFixed64(0), 0, -128},
+
+		// Subtraction with offset
+		{ExpiredValue{Base: 128, Exp: 0}, -64, Uint64ToFixed64(1), 0, -64},
+		{ExpiredValue{Base: 128, Exp: 0}, -128, Uint64ToFixed64(1), 0, -64},
+		{ExpiredValue{Base: 128, Exp: 2}, -128, Uint64ToFixed64(1), 128, -128},
+		{ExpiredValue{Base: 128, Exp: 2}, -128, Uint64ToFixed64(2), 0, -128},
+	}
+	for _, c := range cases {
+		if net := c.input.Add(c.addend, c.timeOffset); net != c.expectNet {
+			t.Fatalf("Net amount mismatch, want=%d, got=%d", c.expectNet, net)
+		}
+		if got := c.input.Value(c.timeOffset); got != c.expect {
+			t.Fatalf("Value mismatch, want=%d, got=%d", c.expect, got)
+		}
+	}
+}
+
+func TestExpiredValueAddition(t *testing.T) {
+	var cases = []struct {
+		input      ExpiredValue
+		another    ExpiredValue
+		timeOffset Fixed64
+		expect     uint64
+	}{
+		{ExpiredValue{Base: 128, Exp: 0}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(0), 256},
+		{ExpiredValue{Base: 128, Exp: 1}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(0), 384},
+		{ExpiredValue{Base: 128, Exp: 0}, ExpiredValue{Base: 128, Exp: 1}, Uint64ToFixed64(0), 384},
+		{ExpiredValue{Base: 128, Exp: 0}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(1), 128},
+	}
+	for _, c := range cases {
+		c.input.AddExp(c.another)
+		if got := c.input.Value(c.timeOffset); got != c.expect {
+			t.Fatalf("Value mismatch, want=%d, got=%d", c.expect, got)
+		}
+	}
+}
+
+func TestExpiredValueSubtraction(t *testing.T) {
+	var cases = []struct {
+		input      ExpiredValue
+		another    ExpiredValue
+		timeOffset Fixed64
+		expect     uint64
+	}{
+		{ExpiredValue{Base: 128, Exp: 0}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(0), 0},
+		{ExpiredValue{Base: 128, Exp: 0}, ExpiredValue{Base: 128, Exp: 1}, Uint64ToFixed64(0), 0},
+		{ExpiredValue{Base: 128, Exp: 1}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(0), 128},
+		{ExpiredValue{Base: 128, Exp: 1}, ExpiredValue{Base: 128, Exp: 0}, Uint64ToFixed64(1), 64},
+	}
+	for _, c := range cases {
+		c.input.SubExp(c.another)
+		if got := c.input.Value(c.timeOffset); got != c.expect {
+			t.Fatalf("Value mismatch, want=%d, got=%d", c.expect, got)
+		}
+	}
+}

p2p/enode/node.go

@@ -217,7 +217,7 @@ func (n ID) MarshalText() ([]byte, error) {
 
 // UnmarshalText implements the encoding.TextUnmarshaler interface.
 func (n *ID) UnmarshalText(text []byte) error {
-	id, err := parseID(string(text))
+	id, err := ParseID(string(text))
 	if err != nil {
 		return err
 	}
@@ -229,14 +229,14 @@ func (n *ID) UnmarshalText(text []byte) error {
 // The string may be prefixed with 0x.
 // It panics if the string is not a valid ID.
 func HexID(in string) ID {
-	id, err := parseID(in)
+	id, err := ParseID(in)
 	if err != nil {
 		panic(err)
 	}
 	return id
 }
 
-func parseID(in string) (ID, error) {
+func ParseID(in string) (ID, error) {
 	var id ID
 	b, err := hex.DecodeString(strings.TrimPrefix(in, "0x"))
 	if err != nil {