beacon/light: new Module and Requester interfaces

beacon/light/request/scheduler.go

@@ -17,7 +17,6 @@
 package request
 
 import (
-	"math"
 	"sync"
 
 	"github.com/ethereum/go-ethereum/log"
@@ -45,19 +44,13 @@ type Module interface {
 	// Note: Process functions of different modules are never called concurrently;
 	// they are called by Scheduler in the same order of priority as they were
 	// registered in.
-	Process([]Event)
+	Process(Requester, []Event)
-	// MakeRequest generates a request candidate based on the state of the target
+}
-	// structure(s) and the internal state of the module. This candidate is
+
-	// typically the next obtainable item (or range of items) of the target
+type Requester interface {
-	// structure that is assumed to be available at the given server and has not
+	CanSendTo() []Server
-	// been requested yet (or has been requested but already timed out and should
+	Send(Server, Request) ID
-	// be resent).
+	Fail(Server, string)
-	// MakeRequest is always called after Process. Note that it is the Scheduler's
-	// job to select the best possible requests and actually send them. If a
-	// request has been sent, the module is notified through an EvRequest event
-	// which also immediately triggers a next processing round, allowing modules
-	// to send more requests if possible and necessary.
-	MakeRequest(Server) (Request, float32)
 }
 
 // Scheduler is a modular network data retrieval framework that coordinates multiple
@@ -72,7 +65,10 @@ type Scheduler struct {
 	servers map[server]struct{}
 	targets map[targetData]uint64
 
-	pending map[ServerAndID]pendingRequest
+	requesterLock sync.RWMutex
+	serverOrder   []server
+	pending       map[ServerAndID]pendingRequest
+
 	// eventLock guards access to the events list. Note that eventLock can be
 	// locked either while lock is locked or unlocked but lock cannot be locked
 	// while eventLock is locked.
@@ -87,15 +83,12 @@ type Scheduler struct {
 }
 
 type (
-	// Server identifies a server without allowing any direct interaction except
+	// Server identifies a server without allowing any direct interaction.
-	// for reporting a server side failure.
 	// Note: server interface is used by Scheduler and Tracker but not used by
 	// the modules that do not interact with them directly.
 	// In order to make module testing easier, Server interface is used in
 	// events and modules.
-	Server interface {
+	Server      any
-		Fail(desc string)
-	}
 	Request     any
 	Response    any
 	ID          uint64
@@ -238,91 +231,16 @@ func (s *Scheduler) targetChanged() (changed bool) {
 // requests are generated and sent if necessary and possible.
 func (s *Scheduler) processRound() {
 	for {
-		filteredEvents := s.filterEvents()
 		log.Debug("Processing modules")
+		filteredEvents := s.filterEvents()
 		for _, module := range s.modules {
 			log.Debug("Processing module", "name", s.names[module], "events", len(filteredEvents[module]))
-			module.Process(filteredEvents[module])
+			module.Process(requester{s, module}, filteredEvents[module])
 		}
 		if !s.targetChanged() {
 			break
 		}
 	}
-	s.sendRequests()
-}
-
-// sendRequests lets each module generate a request if necessary and sends it to
-// a suitable server if possible.
-// Note that if a request is sent, an EvRequest event will immediately trigger a
-// next processing round, thereby allowing modules to create any number of requests
-// in any suitable moment as long as there is a server that can accept them.
-func (s *Scheduler) sendRequests() {
-	servers := make(map[server]struct{})
-	for server := range s.servers {
-		if ok, _ := server.canRequestNow(); ok {
-			servers[server] = struct{}{}
-		}
-	}
-	log.Debug("Generating request candidates", "servers", len(servers))
-
-	for _, module := range s.modules {
-		if len(servers) == 0 {
-			return
-		}
-		if s.tryRequest(module, servers) {
-			log.Debug("Sent request", "module", s.names[module])
-		}
-	}
-}
-
-// tryRequest tries to generate request candidates for a given module and a given
-// set of servers, then selects the best candidate if there is one and sends the
-// request to the server it was generated for.
-// The candidates are primarily ranked based on "request priority", a number that
-// Module.MakeRequest has returned along with the request candidate. This ranking
-// may or may not be used depending on the type of the request, identical requests
-// typically have the same priority while multiple item requests may have a
-// priority based on the number of items requested.
-// If there are multiple candidates with identical request priority then they are
-// ranked based on "server priority" which is determined by the server. This value
-// is typically higher is the server is expected to respond quicker or with a
-// higher chance (typically a lower number of pending requests).
-// Note that tryRequest can also remove items from the set of available servers
-// if they are no longer able to accept requests in the current processing round.
-func (s *Scheduler) tryRequest(module Module, servers map[server]struct{}) bool {
-	var (
-		maxServerPriority, maxRequestPriority float32
-		bestServer                            server
-		bestRequest                           Request
-	)
-	maxServerPriority, maxRequestPriority = -math.MaxFloat32, -math.MaxFloat32
-	serverCount := len(servers)
-	var removed, candidates int
-	for server := range servers {
-		canRequest, serverPriority := server.canRequestNow()
-		if !canRequest {
-			delete(servers, server)
-			removed++
-			continue
-		}
-		request, requestPriority := module.MakeRequest(server)
-		if request != nil {
-			candidates++
-		}
-		if request == nil || requestPriority < maxRequestPriority ||
-			(requestPriority == maxRequestPriority && serverPriority <= maxServerPriority) {
-			continue
-		}
-		maxServerPriority, maxRequestPriority = serverPriority, requestPriority
-		bestServer, bestRequest = server, request
-	}
-	log.Debug("Request attempt", "serverCount", serverCount, "removedServers", removed, "requestCandidates", candidates)
-	if bestServer == nil {
-		return false
-	}
-	sid := ServerAndID{Server: bestServer, ID: bestServer.sendRequest(bestRequest)}
-	s.pending[sid] = pendingRequest{request: bestRequest, module: module}
-	return true
 }
 
 // Trigger starts a new processing round. If fired during processing, it ensures
@@ -358,6 +276,9 @@ func (s *Scheduler) filterEvents() map[Module][]Event {
 	s.events = nil
 	s.eventLock.Unlock()
 
+	s.requesterLock.Lock()
+	defer s.requesterLock.Unlock()
+
 	filteredEvents := make(map[Module][]Event)
 	for _, event := range events {
 		server := event.Server.(server)
@@ -379,9 +300,19 @@ func (s *Scheduler) filterEvents() map[Module][]Event {
 			switch event.Type {
 			case EvRegistered:
 				s.servers[server] = struct{}{}
+				s.serverOrder = append(s.serverOrder, nil)
+				copy(s.serverOrder[1:], s.serverOrder[:len(s.serverOrder)-1])
+				s.serverOrder[0] = server
 			case EvUnregistered:
 				s.closePending(event.Server, filteredEvents)
 				delete(s.servers, server)
+				for i, srv := range s.serverOrder {
+					if srv == server {
+						copy(s.serverOrder[i:len(s.serverOrder)-1], s.serverOrder[i+1:])
+						s.serverOrder = s.serverOrder[:len(s.serverOrder)-1]
+						break
+					}
+				}
 			}
 			for _, module := range s.modules {
 				filteredEvents[module] = append(filteredEvents[module], event)
@@ -408,3 +339,44 @@ func (s *Scheduler) closePending(server Server, filteredEvents map[Module][]Even
 		}
 	}
 }
+
+type requester struct {
+	*Scheduler
+	module Module
+}
+
+func (s requester) CanSendTo() []Server {
+	s.requesterLock.RLock()
+	defer s.requesterLock.RUnlock()
+
+	list := make([]Server, 0, len(s.serverOrder))
+	for _, server := range s.serverOrder {
+		if server.canRequestNow() {
+			list = append(list, server)
+		}
+	}
+	return list
+}
+
+func (s requester) Send(srv Server, req Request) ID {
+	s.requesterLock.Lock()
+	defer s.requesterLock.Unlock()
+
+	server := srv.(server)
+	id := server.sendRequest(req)
+	sid := ServerAndID{Server: srv, ID: id}
+	s.pending[sid] = pendingRequest{request: req, module: s.module}
+	for i, ss := range s.serverOrder {
+		if ss == server {
+			copy(s.serverOrder[i:len(s.serverOrder)-1], s.serverOrder[i+1:])
+			s.serverOrder[len(s.serverOrder)-1] = server
+			return id
+		}
+	}
+	log.Error("Target server not found in ordered list of registered servers")
+	return id
+}
+
+func (s requester) Fail(srv Server, desc string) {
+	srv.(server).fail(desc)
+}

beacon/light/request/server.go

@@ -18,7 +18,6 @@ package request
 
 import (
 	"math"
-	"math/rand"
 	"sync"
 	"time"
 
@@ -28,7 +27,6 @@ import (
 
 var (
 	// request events
-	EvRequest  = &EventType{Name: "request", requestEvent: true}  // data: RequestResponse; sent by Scheduler
 	EvResponse = &EventType{Name: "response", requestEvent: true} // data: RequestResponse; sent by requestServer
 	EvFail     = &EventType{Name: "fail", requestEvent: true}     // data: RequestResponse; sent by requestServer
 	EvTimeout  = &EventType{Name: "timeout", requestEvent: true}  // data: RequestResponse; sent by serverWithTimeout
@@ -70,9 +68,9 @@ type requestServer interface {
 // new requests based on timeouts and response failures.
 type server interface {
 	subscribe(eventCallback func(Event))
-	canRequestNow() (bool, float32)
+	canRequestNow() bool
 	sendRequest(Request) ID
-	Fail(string)
+	fail(string)
 	unsubscribe()
 }
 
@@ -121,7 +119,7 @@ type RequestResponse struct {
 	Response Response
 }
 
-// serverWithTimeout wraps a requestServer and introduces two new request event
+//TODO serverWithTimeout wraps a requestServer and introduces two new request event
 // types: EvRequest and EvTimeout. Whenever a request is successfully sent, an
 // EvRequest event is emitted first. The request's lifecycle is concluded if
 // EvResponse or EvFail emitted by the parent requestServer. If this does not
@@ -161,9 +159,7 @@ func (s *serverWithTimeout) sendRequest(request Request) (reqId ID) {
 	s.lock.Lock()
 	s.lastID++
 	id := s.lastID
-	reqData := RequestResponse{ID: id, Request: request}
+	s.startTimeout(RequestResponse{ID: id, Request: request})
-	s.childEventCb(Event{Type: EvRequest, Data: reqData})
-	s.startTimeout(reqData)
 	s.lock.Unlock()
 	s.parent.SendRequest(id, request)
 	return id
@@ -293,12 +289,12 @@ func (s *serverWithLimits) eventCallback(event Event) {
 			s.parallelLimit += parallelAdjustUp
 		}
 		s.pendingCount--
-		if canRequest, _ := s.canRequest(); canRequest {
+		if s.canRequest() {
 			sendCanRequestAgain = s.sendEvent
 			s.sendEvent = false
 		}
 		if event.Type == EvFail {
-			s.fail("failed request")
+			s.failLocked("failed request")
 		}
 	}
 	childEventCb := s.childEventCb
@@ -331,14 +327,14 @@ func (s *serverWithLimits) unsubscribe() {
 }
 
 // canRequest checks whether a new request can be started.
-func (s *serverWithLimits) canRequest() (bool, float32) {
+func (s *serverWithLimits) canRequest() bool {
 	if s.delayTimer != nil || s.pendingCount >= int(s.parallelLimit) || s.timeoutCount > 0 {
-		return false, 0
+		return false
 	}
 	if s.parallelLimit < minParallelLimit {
 		s.parallelLimit = minParallelLimit
 	}
-	return true, -(float32(s.pendingCount) + rand.Float32()) / s.parallelLimit
+	return true
 }
 
 // canRequestNow checks whether a new request can be started, according to the
@@ -349,10 +345,10 @@ func (s *serverWithLimits) canRequest() (bool, float32) {
 // set of servers.
 // If it returns false then it is guaranteed that an EvCanRequestAgain will be
 // sent whenever the server becomes available for requesting again.
-func (s *serverWithLimits) canRequestNow() (bool, float32) {
+func (s *serverWithLimits) canRequestNow() bool {
 	var sendCanRequestAgain bool
 	s.lock.Lock()
-	canRequest, priority := s.canRequest()
+	canRequest := s.canRequest()
 	if canRequest {
 		sendCanRequestAgain = s.sendEvent
 		s.sendEvent = false
@@ -362,7 +358,7 @@ func (s *serverWithLimits) canRequestNow() (bool, float32) {
 	if sendCanRequestAgain {
 		childEventCb(Event{Type: EvCanRequestAgain})
 	}
-	return canRequest, priority
+	return canRequest
 }
 
 // delay sets the delay timer to the given duration, disabling new requests for
@@ -384,7 +380,7 @@ func (s *serverWithLimits) delay(delay time.Duration) {
 		s.lock.Lock()
 		if s.delayTimer != nil && s.delayCounter == delayCounter { // do nothing if there is a new timer now
 			s.delayTimer = nil
-			if canRequest, _ := s.canRequest(); canRequest {
+			if s.canRequest() {
 				sendCanRequestAgain = s.sendEvent
 				s.sendEvent = false
 			}
@@ -399,15 +395,15 @@ func (s *serverWithLimits) delay(delay time.Duration) {
 
 // fail reports that a response from the server was found invalid by the processing
 // Module, disabling new requests for a dynamically adjused time period.
-func (s *serverWithLimits) Fail(desc string) {
+func (s *serverWithLimits) fail(desc string) {
 	s.lock.Lock()
 	defer s.lock.Unlock()
 
-	s.fail(desc)
+	s.failLocked(desc)
 }
 
-// fail calculates the dynamic failure delay and applies it.
+// failLocked calculates the dynamic failure delay and applies it.
-func (s *serverWithLimits) fail(desc string) {
+func (s *serverWithLimits) failLocked(desc string) {
 	log.Debug("Server error", "description", desc)
 	s.failureDelay *= 2
 	now := s.clock.Now()

beacon/light/sync/head_sync.go

@@ -67,7 +67,7 @@ func NewHeadSync(headTracker headTracker, chain committeeChain) *HeadSync {
 	return s
 }
 
-func (s *HeadSync) Process(events []request.Event) {
+func (s *HeadSync) Process(requester request.Requester, events []request.Event) {
 	for _, event := range events {
 		switch event.Type {
 		case EvNewHead:
@@ -90,10 +90,6 @@ func (s *HeadSync) Process(events []request.Event) {
 	}
 }
 
-func (s *HeadSync) MakeRequest(server request.Server) (request.Request, float32) {
-	return nil, 0
-}
-
 // newSignedHead handles received signed head; either validates it if the chain
 // is properly synced or stores it for further validation.
 func (s *HeadSync) newSignedHead(server request.Server, signedHead types.SignedHeader) {

beacon/light/sync/head_sync_test.go

@@ -24,10 +24,10 @@ import (
 )
 
 var (
-	testServer1 = &TestServer{ID: 1}
+	testServer1 = "testServer1"
-	testServer2 = &TestServer{ID: 2}
+	testServer2 = "testServer2"
-	testServer3 = &TestServer{ID: 3}
+	testServer3 = "testServer3"
-	testServer4 = &TestServer{ID: 4}
+	testServer4 = "testServer4"
 
 	testHead0 = types.HeadInfo{}
 	testHead1 = types.HeadInfo{Slot: 123, BlockRoot: common.Hash{1}}
@@ -52,12 +52,12 @@ func TestValidatedHead(t *testing.T) {
 
 	ts.AddServer(testServer1, 1)
 	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead1)
-	ts.Run(1, nil, nil)
+	ts.Run(1)
 	// announced head should be queued because of uninitialized chain
 	ht.ExpValidated(t, 1, nil)
 
 	chain.SetNextSyncPeriod(0) // initialize chain
-	ts.Run(2, nil, nil)
+	ts.Run(2)
 	// expect previously queued head to be validated
 	ht.ExpValidated(t, 2, []types.SignedHeader{testSHead1})
 
@@ -65,34 +65,34 @@ func TestValidatedHead(t *testing.T) {
 	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead2)
 	ts.AddServer(testServer2, 1)
 	ts.ServerEvent(EvNewSignedHead, testServer2, testSHead2)
-	ts.Run(3, nil, nil)
+	ts.Run(3)
 	// expect both head announcements to be validated instantly
 	ht.ExpValidated(t, 3, []types.SignedHeader{testSHead2, testSHead2})
 
 	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead3)
 	ts.AddServer(testServer3, 1)
 	ts.ServerEvent(EvNewSignedHead, testServer3, testSHead4)
-	ts.Run(4, nil, nil)
+	ts.Run(4)
 	// future period annonced heads should be queued
 	ht.ExpValidated(t, 4, nil)
 
 	chain.SetNextSyncPeriod(2)
-	ts.Run(5, nil, nil)
+	ts.Run(5)
 	// testSHead3 can be validated now but not testSHead4
 	ht.ExpValidated(t, 5, []types.SignedHeader{testSHead3})
 
 	// server 3 disconnected without proving period 3, its announced head should be dropped
 	ts.RemoveServer(testServer3)
-	ts.Run(6, nil, nil)
+	ts.Run(6)
 	ht.ExpValidated(t, 6, nil)
 
 	chain.SetNextSyncPeriod(3)
-	ts.Run(7, nil, nil)
+	ts.Run(7)
 	// testSHead4 could be validated now but it's not queued by any registered server
 	ht.ExpValidated(t, 7, nil)
 
 	ts.ServerEvent(EvNewSignedHead, testServer2, testSHead4)
-	ts.Run(8, nil, nil)
+	ts.Run(8)
 	// now testSHead4 should be validated
 	ht.ExpValidated(t, 8, []types.SignedHeader{testSHead4})
 }
@@ -107,45 +107,45 @@ func TestPrefetchHead(t *testing.T) {
 
 	ts.AddServer(testServer1, 1)
 	ts.ServerEvent(EvNewHead, testServer1, testHead1)
-	ts.Run(1, nil, nil)
+	ts.Run(1)
 	ht.ExpPrefetch(t, 1, testHead1) // s1: h1
 
 	ts.AddServer(testServer2, 1)
 	ts.ServerEvent(EvNewHead, testServer2, testHead2)
-	ts.Run(2, nil, nil)
+	ts.Run(2)
 	ht.ExpPrefetch(t, 2, testHead2) // s1: h1, s2: h2
 
 	ts.ServerEvent(EvNewHead, testServer1, testHead2)
-	ts.Run(3, nil, nil)
+	ts.Run(3)
 	ht.ExpPrefetch(t, 3, testHead2) // s1: h2, s2: h2
 
 	ts.AddServer(testServer3, 1)
 	ts.ServerEvent(EvNewHead, testServer3, testHead3)
-	ts.Run(4, nil, nil)
+	ts.Run(4)
 	ht.ExpPrefetch(t, 4, testHead2) // s1: h2, s2: h2, s3: h3
 
 	ts.AddServer(testServer4, 1)
 	ts.ServerEvent(EvNewHead, testServer4, testHead4)
-	ts.Run(5, nil, nil)
+	ts.Run(5)
 	ht.ExpPrefetch(t, 5, testHead2) // s1: h2, s2: h2, s3: h3, s4: h4
 
 	ts.ServerEvent(EvNewHead, testServer2, testHead3)
-	ts.Run(6, nil, nil)
+	ts.Run(6)
 	ht.ExpPrefetch(t, 6, testHead3) // s1: h2, s2: h3, s3: h3, s4: h4
 
 	ts.RemoveServer(testServer3)
-	ts.Run(7, nil, nil)
+	ts.Run(7)
 	ht.ExpPrefetch(t, 7, testHead4) // s1: h2, s2: h3, s4: h4
 
 	ts.RemoveServer(testServer1)
-	ts.Run(8, nil, nil)
+	ts.Run(8)
 	ht.ExpPrefetch(t, 8, testHead4) // s2: h3, s4: h4
 
 	ts.RemoveServer(testServer4)
-	ts.Run(9, nil, nil)
+	ts.Run(9)
 	ht.ExpPrefetch(t, 9, testHead3) // s2: h3
 
 	ts.RemoveServer(testServer2)
-	ts.Run(10, nil, nil)
+	ts.Run(10)
 	ht.ExpPrefetch(t, 10, testHead0) // no servers registered
 }

beacon/light/sync/test_helpers.go

@@ -17,6 +17,7 @@
 package sync
 
 import (
+	"reflect"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/beacon/light"
@@ -24,15 +25,6 @@ import (
 	"github.com/ethereum/go-ethereum/beacon/types"
 )
 
-type TestServer struct {
-	ts *TestScheduler
-	ID int
-}
-
-func (s *TestServer) Fail(desc string) {
-	s.ts.serverFail(s)
-}
-
 type requestWithID struct {
 	sid     request.ServerAndID
 	request request.Request
@@ -44,7 +36,7 @@ type TestScheduler struct {
 	events    []request.Event
 	servers   []request.Server
 	allowance map[request.Server]int
-	sent      map[int]requestWithID
+	sent      map[int][]requestWithID
 	testIndex int
 	expFail   map[request.Server]int // expected Server.Fail calls during next Run
 	lastId    request.ID
@@ -56,13 +48,26 @@ func NewTestScheduler(t *testing.T, module request.Module) *TestScheduler {
 		module:    module,
 		allowance: make(map[request.Server]int),
 		expFail:   make(map[request.Server]int),
-		sent:      make(map[int]requestWithID),
+		sent:      make(map[int][]requestWithID),
 	}
 }
 
-func (ts *TestScheduler) Run(testIndex int, expServer request.Server, expReq request.Request) {
+func (ts *TestScheduler) Run(testIndex int, exp ...any) {
+	expReqs := make([]requestWithID, len(exp)/2)
+	id := ts.lastId
+	for i := range expReqs {
+		id++
+		expReqs[i] = requestWithID{
+			sid:     request.ServerAndID{Server: exp[i*2].(request.Server), ID: id},
+			request: exp[i*2+1].(request.Request),
+		}
+	}
+	if len(expReqs) == 0 {
+		expReqs = nil
+	}
+
 	ts.testIndex = testIndex
-	ts.module.Process(ts.events)
+	ts.module.Process(ts, ts.events)
 	ts.events = nil
 
 	for server, count := range ts.expFail {
@@ -70,31 +75,47 @@ func (ts *TestScheduler) Run(testIndex int, expServer request.Server, expReq req
 		if count == 0 {
 			continue
 		}
-		ts.t.Errorf("Missing %d Server.Fail(s) from server %d in test case #%d", count, server.(*TestServer).ID, testIndex)
+		ts.t.Errorf("Missing %d Server.Fail(s) from server %s in test case #%d", count, server.(string), testIndex)
 	}
 
-	expReqWithID := requestWithID{
+	if !reflect.DeepEqual(ts.sent[testIndex], expReqs) {
-		sid:     request.ServerAndID{Server: expServer, ID: ts.lastId + 1},
+		ts.t.Errorf("Wrong sent requests in test case #%d (expected %v, got %v)", testIndex, expReqs, ts.sent[testIndex])
-		request: expReq,
-	}
-	req, ok := ts.tryRequest(testIndex, ts.module.MakeRequest)
-	if expReq == nil {
-		if ok {
-			ts.t.Errorf("Unexpected request in test case #%d (expected none, got %v)", testIndex, req)
-		}
-		return
-	}
-	if !ok {
-		ts.t.Errorf("Missing request in test case #%d (expected %v, got none)", testIndex, expReqWithID)
-		return
-	}
-	if req != expReqWithID {
-		ts.t.Errorf("Wrong request in test case #%d (expected %v, got %v)", testIndex, expReqWithID, req)
 	}
 }
 
-func (ts *TestScheduler) Request(testIndex int) request.Request {
+func (ts *TestScheduler) CanSendTo() (cs []request.Server) {
-	return ts.sent[testIndex].request
+	for _, server := range ts.servers {
+		if ts.allowance[server] > 0 {
+			cs = append(cs, server)
+		}
+	}
+	return
+}
+
+func (ts *TestScheduler) Send(server request.Server, req request.Request) request.ID {
+	ts.lastId++
+	ts.sent[ts.testIndex] = append(ts.sent[ts.testIndex], requestWithID{
+		sid:     request.ServerAndID{Server: server, ID: ts.lastId},
+		request: req,
+	})
+	ts.allowance[server]--
+	return ts.lastId
+}
+
+func (ts *TestScheduler) Fail(server request.Server, desc string) {
+	if ts.expFail[server] == 0 {
+		ts.t.Errorf("Unexpected Fail from server %s in test case #%d: %s", server.(string), ts.testIndex, desc)
+		return
+	}
+	ts.expFail[server]--
+}
+
+func (ts *TestScheduler) Request(testIndex, reqIndex int) requestWithID {
+	if len(ts.sent[testIndex]) < reqIndex {
+		ts.t.Errorf("Missing request from test case %d index %d", testIndex, reqIndex)
+		return requestWithID{}
+	}
+	return ts.sent[testIndex][reqIndex-1]
 }
 
 func (ts *TestScheduler) ServerEvent(evType *request.EventType, server request.Server, data any) {
@@ -105,10 +126,8 @@ func (ts *TestScheduler) ServerEvent(evType *request.EventType, server request.S
 	})
 }
 
-func (ts *TestScheduler) RequestEvent(evType *request.EventType, testIndex int, resp request.Response) {
+func (ts *TestScheduler) RequestEvent(evType *request.EventType, req requestWithID, resp request.Response) {
-	req, ok := ts.sent[testIndex]
+	if req.request == nil {
-	if !ok {
-		ts.t.Errorf("Missing request from test case %v", testIndex)
 		return
 	}
 	ts.events = append(ts.events, request.Event{
@@ -123,7 +142,6 @@ func (ts *TestScheduler) RequestEvent(evType *request.EventType, testIndex int,
 }
 
 func (ts *TestScheduler) AddServer(server request.Server, allowance int) {
-	server.(*TestServer).ts = ts
 	ts.servers = append(ts.servers, server)
 	ts.allowance[server] = allowance
 	ts.ServerEvent(request.EvRegistered, server, nil)
@@ -150,43 +168,6 @@ func (ts *TestScheduler) ExpFail(server request.Server) {
 	ts.expFail[server]++
 }
 
-func (ts *TestScheduler) serverFail(server request.Server) {
-	if ts.expFail[server] == 0 {
-		ts.t.Errorf("Unexpected Server.Fail from server %d in test case #%d", server.(*TestServer).ID, ts.testIndex)
-		return
-	}
-	ts.expFail[server]--
-}
-
-func (ts *TestScheduler) tryRequest(testIndex int, requestFn func(server request.Server) (request.Request, float32)) (requestWithID, bool) {
-	var (
-		bestServer request.Server
-		bestReq    request.Request
-		bestPri    float32
-	)
-	for _, server := range ts.servers {
-		if ts.allowance[server] == 0 {
-			continue
-		}
-		req, pri := requestFn(server)
-		if req != nil && (bestReq == nil || pri > bestPri) {
-			bestServer, bestReq, bestPri = server, req, pri
-		}
-	}
-	if bestServer == nil {
-		return requestWithID{}, false
-	}
-	ts.allowance[bestServer]--
-	ts.lastId++
-	req := requestWithID{
-		sid:     request.ServerAndID{Server: bestServer, ID: ts.lastId},
-		request: bestReq,
-	}
-	ts.sent[testIndex] = req
-	ts.RequestEvent(request.EvRequest, testIndex, nil)
-	return req, true
-}
-
 type TestCommitteeChain struct {
 	fsp, nsp uint64
 	init     bool

beacon/light/sync/update_sync.go

@@ -52,16 +52,12 @@ func NewCheckpointInit(chain committeeChain, checkpointHash common.Hash) *Checkp
 	}
 }
 
-func (s *CheckpointInit) Process(events []request.Event) {
+func (s *CheckpointInit) Process(requester request.Requester, events []request.Event) {
 	for _, event := range events {
 		if !event.IsRequestEvent() {
 			continue
 		}
 		sid, req, resp := event.RequestInfo()
-		if event.Type == request.EvRequest {
-			s.locked = sid
-			continue
-		}
 		if s.locked == sid {
 			s.locked = request.ServerAndID{}
 		}
@@ -71,16 +67,21 @@ func (s *CheckpointInit) Process(events []request.Event) {
 				s.initialized = true
 				return
 			}
-			event.Server.Fail("invalid checkpoint data")
+
+			requester.Fail(event.Server, "invalid checkpoint data")
 		}
 	}
-}
+	// start a request if possible
-
-func (s *CheckpointInit) MakeRequest(server request.Server) (request.Request, float32) {
 	if s.initialized || s.locked != (request.ServerAndID{}) {
-		return nil, 0
+		return
 	}
-	return ReqCheckpointData(s.checkpointHash), 0
+	cs := requester.CanSendTo()
+	if len(cs) == 0 {
+		return
+	}
+	server := cs[0]
+	id := requester.Send(server, ReqCheckpointData(s.checkpointHash))
+	s.locked = request.ServerAndID{Server: server, ID: id}
 }
 
 // ForwardUpdateSync implements request.Module; it fetches updates between the
@@ -194,12 +195,9 @@ func (u updateResponseList) Less(i, j int) bool {
 	return u[i].request.FirstPeriod < u[j].request.FirstPeriod
 }
 
-func (s *ForwardUpdateSync) Process(events []request.Event) {
+func (s *ForwardUpdateSync) Process(requester request.Requester, events []request.Event) {
 	for _, event := range events {
 		switch event.Type {
-		case request.EvRequest:
-			sid, req, _ := event.RequestInfo()
-			s.lockRange(sid, req.(ReqUpdates))
 		case request.EvResponse, request.EvFail, request.EvTimeout:
 			sid, rq, rs := event.RequestInfo()
 			req := rq.(ReqUpdates)
@@ -212,7 +210,7 @@ func (s *ForwardUpdateSync) Process(events []request.Event) {
 					s.lockRange(sid, req)
 					queued = true
 				} else {
-					event.Server.Fail("invalid update range")
+					requester.Fail(event.Server, "invalid update range")
 				}
 			}
 			if !queued {
@@ -230,8 +228,8 @@ func (s *ForwardUpdateSync) Process(events []request.Event) {
 	sort.Sort(updateResponseList(s.processQueue))
 	for s.processQueue != nil {
 		u := s.processQueue[0]
-		if !s.processResponse(u) {
+		if !s.processResponse(requester, u) {
-			return
+			break
 		}
 		s.unlockRange(u.sid, u.request)
 		s.processQueue = s.processQueue[1:]
@@ -239,11 +237,43 @@ func (s *ForwardUpdateSync) Process(events []request.Event) {
 			s.processQueue = nil
 		}
 	}
+
+	// start new requests if possible
+	startPeriod, chainInit := s.chain.NextSyncPeriod()
+	if !chainInit {
+		return
+	}
+	for {
+		firstPeriod, maxCount := s.rangeLock.firstUnlocked(startPeriod, maxUpdateRequest)
+		var (
+			sendTo    request.Server
+			bestCount uint64
+		)
+		for _, server := range requester.CanSendTo() {
+			nextPeriod := s.nextSyncPeriod[server]
+			if nextPeriod <= firstPeriod {
+				continue
+			}
+			count := maxCount
+			if nextPeriod < firstPeriod+maxCount {
+				count = nextPeriod - firstPeriod
+			}
+			if count > bestCount {
+				sendTo, bestCount = server, count
+			}
+		}
+		if sendTo == nil {
+			return
+		}
+		req := ReqUpdates{FirstPeriod: firstPeriod, Count: bestCount}
+		id := requester.Send(sendTo, req)
+		s.lockRange(request.ServerAndID{Server: sendTo, ID: id}, req)
+	}
 }
 
 // processResponse adds the fetched updates and committees to the committee chain.
 // Returns true in case of full or partial success.
-func (s *ForwardUpdateSync) processResponse(u updateResponse) (success bool) {
+func (s *ForwardUpdateSync) processResponse(requester request.Requester, u updateResponse) (success bool) {
 	for i, update := range u.response.Updates {
 		if err := s.chain.InsertUpdate(update, u.response.Committees[i]); err != nil {
 			if err == light.ErrInvalidPeriod {
@@ -252,7 +282,7 @@ func (s *ForwardUpdateSync) processResponse(u updateResponse) (success bool) {
 				return
 			}
 			if err == light.ErrInvalidUpdate || err == light.ErrWrongCommitteeRoot || err == light.ErrCannotReorg {
-				u.sid.Server.Fail("invalid update received")
+				requester.Fail(u.sid.Server, "invalid update received")
 			} else {
 				log.Error("Unexpected InsertUpdate error", "error", err)
 			}
@@ -262,20 +292,3 @@ func (s *ForwardUpdateSync) processResponse(u updateResponse) (success bool) {
 	}
 	return
 }
-
-func (s *ForwardUpdateSync) MakeRequest(server request.Server) (request.Request, float32) {
-	startPeriod, chainInit := s.chain.NextSyncPeriod()
-	if !chainInit {
-		return nil, 0
-	}
-	firstPeriod, maxCount := s.rangeLock.firstUnlocked(startPeriod, maxUpdateRequest)
-	nextPeriod := s.nextSyncPeriod[server]
-	if nextPeriod <= firstPeriod {
-		return nil, 0
-	}
-	count := maxCount
-	if nextPeriod < firstPeriod+maxCount {
-		count = nextPeriod - firstPeriod
-	}
-	return ReqUpdates{FirstPeriod: firstPeriod, Count: count}, float32(count)
-}

beacon/light/sync/update_sync_test.go

@@ -37,18 +37,18 @@ func TestCheckpointInit(t *testing.T) {
 	ts.Run(1, testServer1, ReqCheckpointData(checkpointHash))
 
 	// server 1 times out; expect request to server 2
-	ts.RequestEvent(request.EvTimeout, 1, nil)
+	ts.RequestEvent(request.EvTimeout, ts.Request(1, 1), nil)
 	ts.Run(2, testServer2, ReqCheckpointData(checkpointHash))
 
 	// invalid response from server 2; expect init state to still be false
-	ts.RequestEvent(request.EvResponse, 2, &types.BootstrapData{Header: types.Header{Slot: 123456}})
+	ts.RequestEvent(request.EvResponse, ts.Request(2, 1), &types.BootstrapData{Header: types.Header{Slot: 123456}})
 	ts.ExpFail(testServer2)
-	ts.Run(3, nil, nil)
+	ts.Run(3)
 	chain.ExpInit(t, false)
 
 	// server 1 fails (hard timeout)
-	ts.RequestEvent(request.EvFail, 1, nil)
+	ts.RequestEvent(request.EvFail, ts.Request(1, 1), nil)
-	ts.Run(4, nil, nil)
+	ts.Run(4)
 	chain.ExpInit(t, false)
 
 	// server 3 is registered; expect bootstrap request to server 3
@@ -56,8 +56,8 @@ func TestCheckpointInit(t *testing.T) {
 	ts.Run(5, testServer3, ReqCheckpointData(checkpointHash))
 
 	// valid response from server 3; expect chain to be initialized
-	ts.RequestEvent(request.EvResponse, 5, checkpoint)
+	ts.RequestEvent(request.EvResponse, ts.Request(5, 1), checkpoint)
-	ts.Run(6, nil, nil)
+	ts.Run(6)
 	chain.ExpInit(t, true)
 }
 
@@ -73,68 +73,72 @@ func TestUpdateSyncParallel(t *testing.T) {
 	ts.ServerEvent(EvNewSignedHead, testServer2, types.SignedHeader{SignatureSlot: 0x2000*100 + 0x1000})
 
 	// expect 6 requests to be sent
-	ts.Run(1, testServer1, ReqUpdates{FirstPeriod: 0, Count: 8})
+	ts.Run(1,
-	ts.Run(2, testServer1, ReqUpdates{FirstPeriod: 8, Count: 8})
+		testServer1, ReqUpdates{FirstPeriod: 0, Count: 8},
-	ts.Run(3, testServer1, ReqUpdates{FirstPeriod: 16, Count: 8})
+		testServer1, ReqUpdates{FirstPeriod: 8, Count: 8},
-	ts.Run(4, testServer2, ReqUpdates{FirstPeriod: 24, Count: 8})
+		testServer1, ReqUpdates{FirstPeriod: 16, Count: 8},
-	ts.Run(5, testServer2, ReqUpdates{FirstPeriod: 32, Count: 8})
+		testServer2, ReqUpdates{FirstPeriod: 24, Count: 8},
-	ts.Run(6, testServer2, ReqUpdates{FirstPeriod: 40, Count: 8})
+		testServer2, ReqUpdates{FirstPeriod: 32, Count: 8},
+		testServer2, ReqUpdates{FirstPeriod: 40, Count: 8})
 
 	// valid response to request 1; expect 8 periods synced and a new request started
-	ts.RequestEvent(request.EvResponse, 1, testRespUpdate(ts.Request(1)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 1), testRespUpdate(ts.Request(1, 1)))
 	ts.AddAllowance(testServer1, 1)
 	ts.Run(7, testServer1, ReqUpdates{FirstPeriod: 48, Count: 8})
 	chain.ExpNextSyncPeriod(t, 8)
 
 	// valid response to requests 4 and 5
-	ts.RequestEvent(request.EvResponse, 4, testRespUpdate(ts.Request(4)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 4), testRespUpdate(ts.Request(1, 4)))
-	ts.RequestEvent(request.EvResponse, 5, testRespUpdate(ts.Request(5)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 5), testRespUpdate(ts.Request(1, 5)))
 	ts.AddAllowance(testServer2, 2)
 	// expect 2 more requests but no sync progress (responses 4 and 5 cannot be added before 2 and 3)
-	ts.Run(8, testServer2, ReqUpdates{FirstPeriod: 56, Count: 8})
+	ts.Run(8,
-	ts.Run(9, testServer2, ReqUpdates{FirstPeriod: 64, Count: 8})
+		testServer2, ReqUpdates{FirstPeriod: 56, Count: 8},
+		testServer2, ReqUpdates{FirstPeriod: 64, Count: 8})
 	chain.ExpNextSyncPeriod(t, 8)
 
 	// soft timeout for requests 2 and 3 (server 1 is overloaded)
-	ts.RequestEvent(request.EvTimeout, 2, nil)
+	ts.RequestEvent(request.EvTimeout, ts.Request(1, 2), nil)
-	ts.RequestEvent(request.EvTimeout, 3, nil)
+	ts.RequestEvent(request.EvTimeout, ts.Request(1, 3), nil)
 	// no allowance, no more requests
-	ts.Run(10, nil, nil)
+	ts.Run(10)
 
 	// valid response to requests 6 and 8 and 9
-	ts.RequestEvent(request.EvResponse, 6, testRespUpdate(ts.Request(6)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 6), testRespUpdate(ts.Request(1, 6)))
-	ts.RequestEvent(request.EvResponse, 8, testRespUpdate(ts.Request(8)))
+	ts.RequestEvent(request.EvResponse, ts.Request(8, 1), testRespUpdate(ts.Request(8, 1)))
-	ts.RequestEvent(request.EvResponse, 9, testRespUpdate(ts.Request(9)))
+	ts.RequestEvent(request.EvResponse, ts.Request(8, 2), testRespUpdate(ts.Request(8, 2)))
 	ts.AddAllowance(testServer2, 3)
 	// server 2 can now resend requests 2 and 3 (timed out by server 1) and also send a new one
-	ts.Run(11, testServer2, ReqUpdates{FirstPeriod: 8, Count: 8})
+	ts.Run(11,
-	ts.Run(12, testServer2, ReqUpdates{FirstPeriod: 16, Count: 8})
+		testServer2, ReqUpdates{FirstPeriod: 8, Count: 8},
-	ts.Run(13, testServer2, ReqUpdates{FirstPeriod: 72, Count: 8})
+		testServer2, ReqUpdates{FirstPeriod: 16, Count: 8},
+		testServer2, ReqUpdates{FirstPeriod: 72, Count: 8})
 
 	// server 1 finally answers timed out request 2
-	ts.RequestEvent(request.EvResponse, 2, testRespUpdate(ts.Request(2)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 2), testRespUpdate(ts.Request(1, 2)))
 	ts.AddAllowance(testServer1, 1)
 	// expect sync progress and one new request
 	ts.Run(14, testServer1, ReqUpdates{FirstPeriod: 80, Count: 8})
 	chain.ExpNextSyncPeriod(t, 16)
 
 	// server 2 answers requests 11 and 12 (resends of requests 2 and 3)
-	ts.RequestEvent(request.EvResponse, 11, testRespUpdate(ts.Request(11)))
+	ts.RequestEvent(request.EvResponse, ts.Request(11, 1), testRespUpdate(ts.Request(11, 1)))
-	ts.RequestEvent(request.EvResponse, 12, testRespUpdate(ts.Request(12)))
+	ts.RequestEvent(request.EvResponse, ts.Request(11, 2), testRespUpdate(ts.Request(11, 2)))
 	ts.AddAllowance(testServer2, 2)
-	ts.Run(15, testServer2, ReqUpdates{FirstPeriod: 88, Count: 8})
+	ts.Run(15,
-	ts.Run(16, testServer2, ReqUpdates{FirstPeriod: 96, Count: 4})
+		testServer2, ReqUpdates{FirstPeriod: 88, Count: 8},
+		testServer2, ReqUpdates{FirstPeriod: 96, Count: 4})
 	// finally the gap is filled, update can process responses up to req6
 	chain.ExpNextSyncPeriod(t, 48)
 
 	// all remaining requests are answered
-	ts.RequestEvent(request.EvResponse, 3, testRespUpdate(ts.Request(3)))
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 3), testRespUpdate(ts.Request(1, 3)))
-	ts.RequestEvent(request.EvResponse, 7, testRespUpdate(ts.Request(7)))
+	ts.RequestEvent(request.EvResponse, ts.Request(7, 1), testRespUpdate(ts.Request(7, 1)))
-	ts.RequestEvent(request.EvResponse, 13, testRespUpdate(ts.Request(13)))
+	ts.RequestEvent(request.EvResponse, ts.Request(11, 3), testRespUpdate(ts.Request(11, 3)))
-	ts.RequestEvent(request.EvResponse, 14, testRespUpdate(ts.Request(14)))
+	ts.RequestEvent(request.EvResponse, ts.Request(14, 1), testRespUpdate(ts.Request(14, 1)))
-	ts.RequestEvent(request.EvResponse, 15, testRespUpdate(ts.Request(15)))
+	ts.RequestEvent(request.EvResponse, ts.Request(15, 1), testRespUpdate(ts.Request(15, 1)))
-	ts.RequestEvent(request.EvResponse, 16, testRespUpdate(ts.Request(16)))
+	ts.RequestEvent(request.EvResponse, ts.Request(15, 2), testRespUpdate(ts.Request(15, 2)))
-	ts.Run(17, nil, nil)
+	ts.Run(17)
 	// expect chain to be fully synced
 	chain.ExpNextSyncPeriod(t, 100)
 }
@@ -156,30 +160,32 @@ func TestUpdateSyncDifferentHeads(t *testing.T) {
 	ts.Run(1, testServer3, ReqUpdates{FirstPeriod: 10, Count: 7})
 
 	// request times out, expect request to the next best head
-	ts.RequestEvent(request.EvTimeout, 1, nil)
+	ts.RequestEvent(request.EvTimeout, ts.Request(1, 1), nil)
 	ts.Run(2, testServer2, ReqUpdates{FirstPeriod: 10, Count: 6})
 
 	// request times out, expect request to the last available server
-	ts.RequestEvent(request.EvTimeout, 2, nil)
+	ts.RequestEvent(request.EvTimeout, ts.Request(2, 1), nil)
 	ts.Run(3, testServer1, ReqUpdates{FirstPeriod: 10, Count: 5})
 
 	// valid response to request 3, expect chain synced to period 15
-	ts.RequestEvent(request.EvResponse, 3, testRespUpdate(ts.Request(3)))
+	ts.RequestEvent(request.EvResponse, ts.Request(3, 1), testRespUpdate(ts.Request(3, 1)))
 	ts.AddAllowance(testServer1, 1)
-	ts.Run(4, nil, nil)
+	ts.Run(4)
 	chain.ExpNextSyncPeriod(t, 15)
 
 	// invalid response to request 1, server can only deliver updates up to period 15 despite announced head
-	ts.RequestEvent(request.EvResponse, 1, testRespUpdate(ReqUpdates{FirstPeriod: 10, Count: 5}))
+	truncated := ts.Request(1, 1)
+	truncated.request = ReqUpdates{FirstPeriod: 10, Count: 5}
+	ts.RequestEvent(request.EvResponse, ts.Request(1, 1), testRespUpdate(truncated))
 	ts.ExpFail(testServer3)
-	ts.Run(5, nil, nil)
+	ts.Run(5)
 	// expect no progress of chain head
 	chain.ExpNextSyncPeriod(t, 15)
 
 	// valid response to request 2, expect chain synced to period 16
-	ts.RequestEvent(request.EvResponse, 2, testRespUpdate(ts.Request(2)))
+	ts.RequestEvent(request.EvResponse, ts.Request(2, 1), testRespUpdate(ts.Request(2, 1)))
 	ts.AddAllowance(testServer2, 1)
-	ts.Run(6, nil, nil)
+	ts.Run(6)
 	chain.ExpNextSyncPeriod(t, 16)
 
 	// a new server is registered with announced head period 17
@@ -189,15 +195,18 @@ func TestUpdateSyncDifferentHeads(t *testing.T) {
 	ts.Run(7, testServer4, ReqUpdates{FirstPeriod: 16, Count: 1})
 
 	// valid response, expect chain synced to period 17
-	ts.RequestEvent(request.EvResponse, 7, testRespUpdate(ts.Request(7)))
+	ts.RequestEvent(request.EvResponse, ts.Request(7, 1), testRespUpdate(ts.Request(7, 1)))
 	ts.AddAllowance(testServer4, 1)
-	ts.Run(8, nil, nil)
+	ts.Run(8)
 	chain.ExpNextSyncPeriod(t, 17)
 }
 
-func testRespUpdate(request request.Request) request.Response {
+func testRespUpdate(request requestWithID) request.Response {
 	var resp RespUpdates
-	req := request.(ReqUpdates)
+	if request.request == nil {
+		return resp
+	}
+	req := request.request.(ReqUpdates)
 	resp.Updates = make([]*types.LightClientUpdate, int(req.Count))
 	resp.Committees = make([]*types.SerializedSyncCommittee, int(req.Count))
 	period := req.FirstPeriod

cmd/blsync/block_sync.go

@@ -29,7 +29,7 @@ import (
 // to the validated and prefetch heads.
 type beaconBlockSync struct {
 	recentBlocks *lru.Cache[common.Hash, *capella.BeaconBlock]
-	locked       map[common.Hash]struct{}
+	locked       map[common.Hash]request.ServerAndID
 	serverHeads  map[request.Server]common.Hash
 	headTracker  headTracker
 
@@ -53,34 +53,42 @@ func newBeaconBlockSync(headTracker headTracker) *beaconBlockSync {
 	return &beaconBlockSync{
 		headTracker:  headTracker,
 		recentBlocks: lru.NewCache[common.Hash, *capella.BeaconBlock](10),
-		locked:       make(map[common.Hash]struct{}),
+		locked:       make(map[common.Hash]request.ServerAndID),
 		serverHeads:  make(map[request.Server]common.Hash),
 		headCh:       make(chan headData, 1),
 	}
 }
 
-func (s *beaconBlockSync) Process(events []request.Event) {
+func (s *beaconBlockSync) Process(requester request.Requester, events []request.Event) {
 	for _, event := range events {
 		switch event.Type {
-		case request.EvRequest:
-			_, req, _ := event.RequestInfo()
-			blockRoot := common.Hash(req.(sync.ReqBeaconBlock))
-			s.locked[blockRoot] = struct{}{}
 		case request.EvResponse, request.EvFail, request.EvTimeout:
-			_, req, resp := event.RequestInfo()
+			sid, req, resp := event.RequestInfo()
 			blockRoot := common.Hash(req.(sync.ReqBeaconBlock))
 			if resp != nil {
 				s.recentBlocks.Add(blockRoot, resp.(*capella.BeaconBlock))
 			}
-			delete(s.locked, blockRoot)
+			if s.locked[blockRoot] == sid {
+				delete(s.locked, blockRoot)
+			}
 		case sync.EvNewHead:
 			s.serverHeads[event.Server] = event.Data.(types.HeadInfo).BlockRoot
 		case request.EvUnregistered:
 			delete(s.serverHeads, event.Server)
 		}
 	}
+	s.updateValidatedHead()
+	// request validated head block if unavailable and not yet requested
+	if vh, ok := s.headTracker.ValidatedHead(); ok {
+		s.tryRequestBlock(requester, vh.Header.Hash(), false)
+	}
+	// request prefetch head if the given server has announced it
+	if prefetchHead := s.headTracker.PrefetchHead().BlockRoot; prefetchHead != (common.Hash{}) {
+		s.tryRequestBlock(requester, prefetchHead, true)
+	}
+}
 
-	// send validated head block
+func (s *beaconBlockSync) updateValidatedHead() {
 	head, ok := s.headTracker.ValidatedHead()
 	if !ok {
 		return
@@ -105,27 +113,22 @@ func (s *beaconBlockSync) Process(events []request.Event) {
 	}
 }
 
-func (s *beaconBlockSync) MakeRequest(server request.Server) (request.Request, float32) {
+func (s *beaconBlockSync) tryRequestBlock(requester request.Requester, blockRoot common.Hash, needSameHead bool) {
-	// request validated head block if unavailable and not yet requested
+	if _, ok := s.recentBlocks.Get(blockRoot); ok {
-	if vh, ok := s.headTracker.ValidatedHead(); ok {
+		return
-		validatedHead := vh.Header.Hash()
-		if _, ok := s.recentBlocks.Get(validatedHead); !ok {
-			if _, ok := s.locked[validatedHead]; !ok {
-				return sync.ReqBeaconBlock(validatedHead), 1
-			}
-		}
 	}
-	// request prefetch head if the given server has announced it
+	if _, ok := s.locked[blockRoot]; ok {
-	if prefetchHead := s.headTracker.PrefetchHead().BlockRoot; prefetchHead != (common.Hash{}) && prefetchHead == s.serverHeads[server] {
+		return
-		if _, ok := s.recentBlocks.Get(prefetchHead); !ok {
+	}
-			if _, ok := s.locked[prefetchHead]; !ok {
+	for _, server := range requester.CanSendTo() {
-				return sync.ReqBeaconBlock(prefetchHead), 0
+		if needSameHead && (s.serverHeads[server] != blockRoot) {
-			}
+			continue
-		}
+		}
+		id := requester.Send(server, sync.ReqBeaconBlock(blockRoot))
+		s.locked[blockRoot] = request.ServerAndID{Server: server, ID: id}
+		return
 	}
-	return nil, 0
 }
-
 func blockHeadInfo(block *capella.BeaconBlock) types.HeadInfo {
 	if block == nil {
 		return types.HeadInfo{}

cmd/blsync/block_sync_test.go

@@ -29,8 +29,8 @@ import (
 )
 
 var (
-	testServer1 = &sync.TestServer{ID: 1}
+	testServer1 = "testServer1"
-	testServer2 = &sync.TestServer{ID: 2}
+	testServer2 = "testServer2"
 
 	testBlock1 = &capella.BeaconBlock{Slot: 123}
 	testBlock2 = &capella.BeaconBlock{Slot: 124}
@@ -57,7 +57,7 @@ func TestBlockSync(t *testing.T) {
 	}
 
 	// no block requests expected until head tracker knows about a head
-	ts.Run(1, nil, nil)
+	ts.Run(1)
 	expHeadBlock(1, nil)
 
 	// set block 1 as prefetch head, announced by server 2
@@ -68,15 +68,15 @@ func TestBlockSync(t *testing.T) {
 	ts.Run(2, testServer2, sync.ReqBeaconBlock(head1.BlockRoot))
 
 	// valid response
-	ts.RequestEvent(request.EvResponse, 2, testBlock1)
+	ts.RequestEvent(request.EvResponse, ts.Request(2, 1), testBlock1)
 	ts.AddAllowance(testServer2, 1)
-	ts.Run(3, nil, nil)
+	ts.Run(3)
 	// head block still not expected as the fetched block is not the validated head yet
 	expHeadBlock(3, nil)
 
 	// set as validated head, expect no further requests but block 1 set as head block
 	ht.validated.Header = blockHeader(testBlock1)
-	ts.Run(4, nil, nil)
+	ts.Run(4)
 	expHeadBlock(4, testBlock1)
 
 	// set block 2 as prefetch head, announced by server 1
@@ -87,8 +87,8 @@ func TestBlockSync(t *testing.T) {
 	ts.Run(5, testServer1, sync.ReqBeaconBlock(head2.BlockRoot))
 
 	// req2 fails, no further requests expected because server 2 has not announced it
-	ts.RequestEvent(request.EvFail, 5, nil)
+	ts.RequestEvent(request.EvFail, ts.Request(5, 1), nil)
-	ts.Run(6, nil, nil)
+	ts.Run(6)
 
 	// set as validated head before retrieving block; now it's assumed to be available from server 2 too
 	ht.validated.Header = blockHeader(testBlock2)
@@ -98,8 +98,8 @@ func TestBlockSync(t *testing.T) {
 	expHeadBlock(4, nil)
 
 	// valid response, now head block should be block 2 immediately as it is already validated
-	ts.RequestEvent(request.EvResponse, 7, testBlock2)
+	ts.RequestEvent(request.EvResponse, ts.Request(7, 1), testBlock2)
-	ts.Run(8, nil, nil)
+	ts.Run(8)
 	expHeadBlock(5, testBlock2)
 }