Refactor common relay sync struct to remove duplication

5 files changed, 366 insertions, 369 deletions

diff --git a/build/gobind-pinecone/monolith.go b/build/gobind-pinecone/monolith.go
index a219621b..f44eed89 100644
--- a/build/gobind-pinecone/monolith.go
+++ b/build/gobind-pinecone/monolith.go
@@ -36,6 +36,7 @@ import (
 	"github.com/matrix-org/dendrite/appservice"
 	"github.com/matrix-org/dendrite/clientapi/userutil"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/conn"
+	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/relay"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/rooms"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/users"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-yggdrasil/signing"
@@ -70,11 +71,10 @@ import (
 )
 
 const (
-	PeerTypeRemote           = pineconeRouter.PeerTypeRemote
-	PeerTypeMulticast        = pineconeRouter.PeerTypeMulticast
-	PeerTypeBluetooth        = pineconeRouter.PeerTypeBluetooth
-	PeerTypeBonjour          = pineconeRouter.PeerTypeBonjour
-	relayServerRetryInterval = time.Second * 30
+	PeerTypeRemote    = pineconeRouter.PeerTypeRemote
+	PeerTypeMulticast = pineconeRouter.PeerTypeMulticast
+	PeerTypeBluetooth = pineconeRouter.PeerTypeBluetooth
+	PeerTypeBonjour   = pineconeRouter.PeerTypeBonjour
 )
 
 type DendriteMonolith struct {
@@ -91,7 +91,7 @@ type DendriteMonolith struct {
 	userAPI           userapiAPI.UserInternalAPI
 	federationAPI     api.FederationInternalAPI
 	relayAPI          relayServerAPI.RelayInternalAPI
-	relayRetriever    RelayServerRetriever
+	relayRetriever    relay.RelayServerRetriever
 }
 
 func (m *DendriteMonolith) PublicKey() string {
@@ -189,57 +189,6 @@ func getServerKeyFromString(nodeID string) (gomatrixserverlib.ServerName, error)
 	return nodeKey, nil
 }
 
-func updateNodeRelayServers(
-	node gomatrixserverlib.ServerName,
-	relays []gomatrixserverlib.ServerName,
-	ctx context.Context,
-	fedAPI api.FederationInternalAPI,
-) {
-	// Get the current relay list
-	request := api.P2PQueryRelayServersRequest{Server: node}
-	response := api.P2PQueryRelayServersResponse{}
-	err := fedAPI.P2PQueryRelayServers(ctx, &request, &response)
-	if err != nil {
-		logrus.Warnf("Failed obtaining list of relay servers for %s: %s", node, err.Error())
-	}
-
-	// Remove old, non-matching relays
-	var serversToRemove []gomatrixserverlib.ServerName
-	for _, existingServer := range response.RelayServers {
-		shouldRemove := true
-		for _, newServer := range relays {
-			if newServer == existingServer {
-				shouldRemove = false
-				break
-			}
-		}
-
-		if shouldRemove {
-			serversToRemove = append(serversToRemove, existingServer)
-		}
-	}
-	removeRequest := api.P2PRemoveRelayServersRequest{
-		Server:       node,
-		RelayServers: serversToRemove,
-	}
-	removeResponse := api.P2PRemoveRelayServersResponse{}
-	err = fedAPI.P2PRemoveRelayServers(ctx, &removeRequest, &removeResponse)
-	if err != nil {
-		logrus.Warnf("Failed removing old relay servers for %s: %s", node, err.Error())
-	}
-
-	// Add new relays
-	addRequest := api.P2PAddRelayServersRequest{
-		Server:       node,
-		RelayServers: relays,
-	}
-	addResponse := api.P2PAddRelayServersResponse{}
-	err = fedAPI.P2PAddRelayServers(ctx, &addRequest, &addResponse)
-	if err != nil {
-		logrus.Warnf("Failed adding relay servers for %s: %s", node, err.Error())
-	}
-}
-
 func (m *DendriteMonolith) SetRelayServers(nodeID string, uris string) {
 	relays := []gomatrixserverlib.ServerName{}
 	for _, uri := range strings.Split(uris, ",") {
@@ -266,7 +215,7 @@ func (m *DendriteMonolith) SetRelayServers(nodeID string, uris string) {
 		logrus.Infof("Setting own relay servers to: %v", relays)
 		m.relayRetriever.SetRelayServers(relays)
 	} else {
-		updateNodeRelayServers(
+		relay.UpdateNodeRelayServers(
 			gomatrixserverlib.ServerName(nodeKey),
 			relays,
 			m.baseDendrite.Context(),
@@ -610,27 +559,23 @@ func (m *DendriteMonolith) Start() {
 	}()
 
 	stopRelayServerSync := make(chan bool)
-
 	eLog := logrus.WithField("pinecone", "events")
-	m.relayRetriever = RelayServerRetriever{
-		Context:             context.Background(),
-		ServerName:          gomatrixserverlib.ServerName(m.PineconeRouter.PublicKey().String()),
-		FederationAPI:       m.federationAPI,
-		relayServersQueried: make(map[gomatrixserverlib.ServerName]bool),
-		RelayAPI:            monolith.RelayAPI,
-		running:             *atomic.NewBool(false),
-		quit:                stopRelayServerSync,
-	}
+	m.relayRetriever = relay.NewRelayServerRetriever(
+		context.Background(),
+		gomatrixserverlib.ServerName(m.PineconeRouter.PublicKey().String()),
+		m.federationAPI,
+		monolith.RelayAPI,
+		stopRelayServerSync,
+	)
 	m.relayRetriever.InitializeRelayServers(eLog)
 
 	go func(ch <-chan pineconeEvents.Event) {
-
 		for event := range ch {
 			switch e := event.(type) {
 			case pineconeEvents.PeerAdded:
 				m.relayRetriever.StartSync()
 			case pineconeEvents.PeerRemoved:
-				if m.relayRetriever.running.Load() && m.PineconeRouter.TotalPeerCount() == 0 {
+				if m.relayRetriever.IsRunning() && m.PineconeRouter.TotalPeerCount() == 0 {
 					stopRelayServerSync <- true
 				}
 			case pineconeEvents.BroadcastReceived:
@@ -658,139 +603,6 @@ func (m *DendriteMonolith) Stop() {
 	_ = m.PineconeRouter.Close()
 }
 
-type RelayServerRetriever struct {
-	Context             context.Context
-	ServerName          gomatrixserverlib.ServerName
-	FederationAPI       api.FederationInternalAPI
-	RelayAPI            relayServerAPI.RelayInternalAPI
-	relayServersQueried map[gomatrixserverlib.ServerName]bool
-	queriedServersMutex sync.Mutex
-	running             atomic.Bool
-	quit                <-chan bool
-}
-
-func (r *RelayServerRetriever) InitializeRelayServers(eLog *logrus.Entry) {
-	request := api.P2PQueryRelayServersRequest{Server: gomatrixserverlib.ServerName(r.ServerName)}
-	response := api.P2PQueryRelayServersResponse{}
-	err := r.FederationAPI.P2PQueryRelayServers(r.Context, &request, &response)
-	if err != nil {
-		eLog.Warnf("Failed obtaining list of this node's relay servers: %s", err.Error())
-	}
-
-	r.queriedServersMutex.Lock()
-	defer r.queriedServersMutex.Unlock()
-	for _, server := range response.RelayServers {
-		r.relayServersQueried[server] = false
-	}
-
-	eLog.Infof("Registered relay servers: %v", response.RelayServers)
-}
-
-func (r *RelayServerRetriever) SetRelayServers(servers []gomatrixserverlib.ServerName) {
-	updateNodeRelayServers(r.ServerName, servers, r.Context, r.FederationAPI)
-
-	// Replace list of servers to sync with and mark them all as unsynced.
-	r.queriedServersMutex.Lock()
-	defer r.queriedServersMutex.Unlock()
-	r.relayServersQueried = make(map[gomatrixserverlib.ServerName]bool)
-	for _, server := range servers {
-		r.relayServersQueried[server] = false
-	}
-
-	r.StartSync()
-}
-
-func (r *RelayServerRetriever) GetRelayServers() []gomatrixserverlib.ServerName {
-	r.queriedServersMutex.Lock()
-	defer r.queriedServersMutex.Unlock()
-	relayServers := []gomatrixserverlib.ServerName{}
-	for server := range r.relayServersQueried {
-		relayServers = append(relayServers, server)
-	}
-
-	return relayServers
-}
-
-func (r *RelayServerRetriever) StartSync() {
-	if !r.running.Load() {
-		logrus.Info("Starting relay server sync")
-		go r.SyncRelayServers(r.quit)
-	}
-}
-
-func (r *RelayServerRetriever) SyncRelayServers(stop <-chan bool) {
-	defer r.running.Store(false)
-
-	t := time.NewTimer(relayServerRetryInterval)
-	for {
-		relayServersToQuery := []gomatrixserverlib.ServerName{}
-		func() {
-			r.queriedServersMutex.Lock()
-			defer r.queriedServersMutex.Unlock()
-			for server, complete := range r.relayServersQueried {
-				if !complete {
-					relayServersToQuery = append(relayServersToQuery, server)
-				}
-			}
-		}()
-		if len(relayServersToQuery) == 0 {
-			// All relay servers have been synced.
-			logrus.Info("Finished syncing with all known relays")
-			return
-		}
-		r.queryRelayServers(relayServersToQuery)
-		t.Reset(relayServerRetryInterval)
-
-		select {
-		case <-stop:
-			if !t.Stop() {
-				<-t.C
-			}
-			return
-		case <-t.C:
-		}
-	}
-}
-
-func (r *RelayServerRetriever) GetQueriedServerStatus() map[gomatrixserverlib.ServerName]bool {
-	r.queriedServersMutex.Lock()
-	defer r.queriedServersMutex.Unlock()
-
-	result := map[gomatrixserverlib.ServerName]bool{}
-	for server, queried := range r.relayServersQueried {
-		result[server] = queried
-	}
-	return result
-}
-
-func (r *RelayServerRetriever) queryRelayServers(relayServers []gomatrixserverlib.ServerName) {
-	logrus.Info("Querying relay servers for any available transactions")
-	for _, server := range relayServers {
-		userID, err := gomatrixserverlib.NewUserID("@user:"+string(r.ServerName), false)
-		if err != nil {
-			return
-		}
-
-		logrus.Infof("Syncing with relay: %s", string(server))
-		err = r.RelayAPI.PerformRelayServerSync(context.Background(), *userID, server)
-		if err == nil {
-			func() {
-				r.queriedServersMutex.Lock()
-				defer r.queriedServersMutex.Unlock()
-				r.relayServersQueried[server] = true
-			}()
-			// TODO : What happens if your relay receives new messages after this point?
-			// Should you continue to check with them, or should they try and contact you?
-			// They could send a "new_async_events" message your way maybe?
-			// Then you could mark them as needing to be queried again.
-			// What if you miss this message?
-			// Maybe you should try querying them again after a certain period of time as a backup?
-		} else {
-			logrus.Errorf("Failed querying relay server: %s", err.Error())
-		}
-	}
-}
-
 const MaxFrameSize = types.MaxFrameSize
 
 type Conduit struct {
diff --git a/build/gobind-pinecone/monolith_test.go b/build/gobind-pinecone/monolith_test.go
index 3c8873e0..f6bf2ef0 100644
--- a/build/gobind-pinecone/monolith_test.go
+++ b/build/gobind-pinecone/monolith_test.go
@@ -15,19 +15,13 @@
 package gobind
 
 import (
-	"context"
 	"fmt"
 	"net"
 	"strings"
 	"testing"
-	"time"
 
-	"github.com/matrix-org/dendrite/federationapi/api"
-	relayServerAPI "github.com/matrix-org/dendrite/relayapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
-	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
-	"gotest.tools/v3/poll"
 )
 
 var TestBuf = []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
@@ -128,69 +122,6 @@ func TestConduitReadCopyFails(t *testing.T) {
 	assert.Error(t, err)
 }
 
-var testRelayServers = []gomatrixserverlib.ServerName{"relay1", "relay2"}
-
-type FakeFedAPI struct {
-	api.FederationInternalAPI
-}
-
-func (f *FakeFedAPI) P2PQueryRelayServers(ctx context.Context, req *api.P2PQueryRelayServersRequest, res *api.P2PQueryRelayServersResponse) error {
-	res.RelayServers = testRelayServers
-	return nil
-}
-
-type FakeRelayAPI struct {
-	relayServerAPI.RelayInternalAPI
-}
-
-func (r *FakeRelayAPI) PerformRelayServerSync(ctx context.Context, userID gomatrixserverlib.UserID, relayServer gomatrixserverlib.ServerName) error {
-	return nil
-}
-
-func TestRelayRetrieverInitialization(t *testing.T) {
-	retriever := RelayServerRetriever{
-		Context:             context.Background(),
-		ServerName:          "server",
-		relayServersQueried: make(map[gomatrixserverlib.ServerName]bool),
-		FederationAPI:       &FakeFedAPI{},
-		RelayAPI:            &FakeRelayAPI{},
-	}
-
-	retriever.InitializeRelayServers(logrus.WithField("test", "relay"))
-	relayServers := retriever.GetQueriedServerStatus()
-	assert.Equal(t, 2, len(relayServers))
-}
-
-func TestRelayRetrieverSync(t *testing.T) {
-	retriever := RelayServerRetriever{
-		Context:             context.Background(),
-		ServerName:          "server",
-		relayServersQueried: make(map[gomatrixserverlib.ServerName]bool),
-		FederationAPI:       &FakeFedAPI{},
-		RelayAPI:            &FakeRelayAPI{},
-	}
-
-	retriever.InitializeRelayServers(logrus.WithField("test", "relay"))
-	relayServers := retriever.GetQueriedServerStatus()
-	assert.Equal(t, 2, len(relayServers))
-
-	stopRelayServerSync := make(chan bool)
-	go retriever.SyncRelayServers(stopRelayServerSync)
-
-	check := func(log poll.LogT) poll.Result {
-		relayServers := retriever.GetQueriedServerStatus()
-		for _, queried := range relayServers {
-			if !queried {
-				return poll.Continue("waiting for all servers to be queried")
-			}
-		}
-
-		stopRelayServerSync <- true
-		return poll.Success()
-	}
-	poll.WaitOn(t, check, poll.WithTimeout(5*time.Second), poll.WithDelay(100*time.Millisecond))
-}
-
 func TestMonolithStarts(t *testing.T) {
 	monolith := DendriteMonolith{}
 	monolith.Start()
diff --git a/cmd/dendrite-demo-pinecone/main.go b/cmd/dendrite-demo-pinecone/main.go
index 3f63ab65..abffbb67 100644
--- a/cmd/dendrite-demo-pinecone/main.go
+++ b/cmd/dendrite-demo-pinecone/main.go
@@ -33,6 +33,7 @@ import (
 	"github.com/matrix-org/dendrite/appservice"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/conn"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/embed"
+	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/relay"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/rooms"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-pinecone/users"
 	"github.com/matrix-org/dendrite/cmd/dendrite-demo-yggdrasil/signing"
@@ -43,7 +44,6 @@ import (
 	"github.com/matrix-org/dendrite/internal/httputil"
 	"github.com/matrix-org/dendrite/keyserver"
 	"github.com/matrix-org/dendrite/relayapi"
-	relayServerAPI "github.com/matrix-org/dendrite/relayapi/api"
 	"github.com/matrix-org/dendrite/roomserver"
 	"github.com/matrix-org/dendrite/setup"
 	"github.com/matrix-org/dendrite/setup/base"
@@ -52,7 +52,6 @@ import (
 	"github.com/matrix-org/dendrite/test"
 	"github.com/matrix-org/dendrite/userapi"
 	"github.com/matrix-org/gomatrixserverlib"
-	"go.uber.org/atomic"
 
 	pineconeConnections "github.com/matrix-org/pinecone/connections"
 	pineconeMulticast "github.com/matrix-org/pinecone/multicast"
@@ -72,8 +71,6 @@ var (
 	instanceRelayingEnabled = flag.Bool("relay", false, "whether to enable store & forward relaying for other nodes")
 )
 
-const relayServerRetryInterval = time.Second * 30
-
 // nolint:gocyclo
 func main() {
 	flag.Parse()
@@ -328,28 +325,24 @@ func main() {
 		logrus.Fatal(http.ListenAndServe(httpBindAddr, httpRouter))
 	}()
 
-	go func(ch <-chan pineconeEvents.Event) {
-		eLog := logrus.WithField("pinecone", "events")
-		relayServerSyncRunning := atomic.NewBool(false)
-		stopRelayServerSync := make(chan bool)
-
-		m := RelayServerRetriever{
-			Context:             context.Background(),
-			ServerName:          gomatrixserverlib.ServerName(pRouter.PublicKey().String()),
-			FederationAPI:       fsAPI,
-			RelayServersQueried: make(map[gomatrixserverlib.ServerName]bool),
-			RelayAPI:            monolith.RelayAPI,
-		}
-		m.InitializeRelayServers(eLog)
+	stopRelayServerSync := make(chan bool)
+	eLog := logrus.WithField("pinecone", "events")
+	relayRetriever := relay.NewRelayServerRetriever(
+		context.Background(),
+		gomatrixserverlib.ServerName(pRouter.PublicKey().String()),
+		monolith.FederationAPI,
+		monolith.RelayAPI,
+		stopRelayServerSync,
+	)
+	relayRetriever.InitializeRelayServers(eLog)
 
+	go func(ch <-chan pineconeEvents.Event) {
 		for event := range ch {
 			switch e := event.(type) {
 			case pineconeEvents.PeerAdded:
-				if !relayServerSyncRunning.Load() {
-					go m.syncRelayServers(stopRelayServerSync, *relayServerSyncRunning)
-				}
+				relayRetriever.StartSync()
 			case pineconeEvents.PeerRemoved:
-				if relayServerSyncRunning.Load() && pRouter.TotalPeerCount() == 0 {
+				if relayRetriever.IsRunning() && pRouter.TotalPeerCount() == 0 {
 					stopRelayServerSync <- true
 				}
 			case pineconeEvents.BroadcastReceived:
@@ -359,7 +352,7 @@ func main() {
 					ServerNames: []gomatrixserverlib.ServerName{gomatrixserverlib.ServerName(e.PeerID)},
 				}
 				res := &api.PerformWakeupServersResponse{}
-				if err := fsAPI.PerformWakeupServers(base.Context(), req, res); err != nil {
+				if err := monolith.FederationAPI.PerformWakeupServers(base.Context(), req, res); err != nil {
 					eLog.WithError(err).Error("Failed to wakeup destination", e.PeerID)
 				}
 			default:
@@ -369,78 +362,3 @@ func main() {
 
 	base.WaitForShutdown()
 }
-
-type RelayServerRetriever struct {
-	Context             context.Context
-	ServerName          gomatrixserverlib.ServerName
-	FederationAPI       api.FederationInternalAPI
-	RelayServersQueried map[gomatrixserverlib.ServerName]bool
-	RelayAPI            relayServerAPI.RelayInternalAPI
-}
-
-func (m *RelayServerRetriever) InitializeRelayServers(eLog *logrus.Entry) {
-	request := api.P2PQueryRelayServersRequest{Server: gomatrixserverlib.ServerName(m.ServerName)}
-	response := api.P2PQueryRelayServersResponse{}
-	err := m.FederationAPI.P2PQueryRelayServers(m.Context, &request, &response)
-	if err != nil {
-		eLog.Warnf("Failed obtaining list of this node's relay servers: %s", err.Error())
-	}
-	for _, server := range response.RelayServers {
-		m.RelayServersQueried[server] = false
-	}
-
-	eLog.Infof("Registered relay servers: %v", response.RelayServers)
-}
-
-func (m *RelayServerRetriever) syncRelayServers(stop <-chan bool, running atomic.Bool) {
-	defer running.Store(false)
-
-	t := time.NewTimer(relayServerRetryInterval)
-	for {
-		relayServersToQuery := []gomatrixserverlib.ServerName{}
-		for server, complete := range m.RelayServersQueried {
-			if !complete {
-				relayServersToQuery = append(relayServersToQuery, server)
-			}
-		}
-		if len(relayServersToQuery) == 0 {
-			// All relay servers have been synced.
-			return
-		}
-		m.queryRelayServers(relayServersToQuery)
-		t.Reset(relayServerRetryInterval)
-
-		select {
-		case <-stop:
-			// We have been asked to stop syncing, drain the timer and return.
-			if !t.Stop() {
-				<-t.C
-			}
-			return
-		case <-t.C:
-			// The timer has expired. Continue to the next loop iteration.
-		}
-	}
-}
-
-func (m *RelayServerRetriever) queryRelayServers(relayServers []gomatrixserverlib.ServerName) {
-	logrus.Info("querying relay servers for any available transactions")
-	for _, server := range relayServers {
-		userID, err := gomatrixserverlib.NewUserID("@user:"+string(m.ServerName), false)
-		if err != nil {
-			return
-		}
-		err = m.RelayAPI.PerformRelayServerSync(context.Background(), *userID, server)
-		if err == nil {
-			m.RelayServersQueried[server] = true
-			// TODO : What happens if your relay receives new messages after this point?
-			// Should you continue to check with them, or should they try and contact you?
-			// They could send a "new_async_events" message your way maybe?
-			// Then you could mark them as needing to be queried again.
-			// What if you miss this message?
-			// Maybe you should try querying them again after a certain period of time as a backup?
-		} else {
-			logrus.Errorf("Failed querying relay server: %s", err.Error())
-		}
-	}
-}
diff --git a/cmd/dendrite-demo-pinecone/relay/retriever.go b/cmd/dendrite-demo-pinecone/relay/retriever.go
new file mode 100644
index 00000000..1b5c617e
--- /dev/null
+++ b/cmd/dendrite-demo-pinecone/relay/retriever.go
@@ -0,0 +1,237 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package relay
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	federationAPI "github.com/matrix-org/dendrite/federationapi/api"
+	relayServerAPI "github.com/matrix-org/dendrite/relayapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+	"go.uber.org/atomic"
+)
+
+const (
+	relayServerRetryInterval = time.Second * 30
+)
+
+type RelayServerRetriever struct {
+	ctx                 context.Context
+	serverName          gomatrixserverlib.ServerName
+	federationAPI       federationAPI.FederationInternalAPI
+	relayAPI            relayServerAPI.RelayInternalAPI
+	relayServersQueried map[gomatrixserverlib.ServerName]bool
+	queriedServersMutex sync.Mutex
+	running             atomic.Bool
+	quit                <-chan bool
+}
+
+func NewRelayServerRetriever(
+	ctx context.Context,
+	serverName gomatrixserverlib.ServerName,
+	federationAPI federationAPI.FederationInternalAPI,
+	relayAPI relayServerAPI.RelayInternalAPI,
+	quit <-chan bool,
+) RelayServerRetriever {
+	return RelayServerRetriever{
+		ctx:                 ctx,
+		serverName:          serverName,
+		federationAPI:       federationAPI,
+		relayAPI:            relayAPI,
+		relayServersQueried: make(map[gomatrixserverlib.ServerName]bool),
+		running:             *atomic.NewBool(false),
+		quit:                quit,
+	}
+}
+
+func (r *RelayServerRetriever) InitializeRelayServers(eLog *logrus.Entry) {
+	request := federationAPI.P2PQueryRelayServersRequest{Server: gomatrixserverlib.ServerName(r.serverName)}
+	response := federationAPI.P2PQueryRelayServersResponse{}
+	err := r.federationAPI.P2PQueryRelayServers(r.ctx, &request, &response)
+	if err != nil {
+		eLog.Warnf("Failed obtaining list of this node's relay servers: %s", err.Error())
+	}
+
+	r.queriedServersMutex.Lock()
+	defer r.queriedServersMutex.Unlock()
+	for _, server := range response.RelayServers {
+		r.relayServersQueried[server] = false
+	}
+
+	eLog.Infof("Registered relay servers: %v", response.RelayServers)
+}
+
+func (r *RelayServerRetriever) SetRelayServers(servers []gomatrixserverlib.ServerName) {
+	UpdateNodeRelayServers(r.serverName, servers, r.ctx, r.federationAPI)
+
+	// Replace list of servers to sync with and mark them all as unsynced.
+	r.queriedServersMutex.Lock()
+	defer r.queriedServersMutex.Unlock()
+	r.relayServersQueried = make(map[gomatrixserverlib.ServerName]bool)
+	for _, server := range servers {
+		r.relayServersQueried[server] = false
+	}
+
+	r.StartSync()
+}
+
+func (r *RelayServerRetriever) GetRelayServers() []gomatrixserverlib.ServerName {
+	r.queriedServersMutex.Lock()
+	defer r.queriedServersMutex.Unlock()
+	relayServers := []gomatrixserverlib.ServerName{}
+	for server := range r.relayServersQueried {
+		relayServers = append(relayServers, server)
+	}
+
+	return relayServers
+}
+
+func (r *RelayServerRetriever) GetQueriedServerStatus() map[gomatrixserverlib.ServerName]bool {
+	r.queriedServersMutex.Lock()
+	defer r.queriedServersMutex.Unlock()
+
+	result := map[gomatrixserverlib.ServerName]bool{}
+	for server, queried := range r.relayServersQueried {
+		result[server] = queried
+	}
+	return result
+}
+
+func (r *RelayServerRetriever) StartSync() {
+	if !r.running.Load() {
+		logrus.Info("Starting relay server sync")
+		go r.SyncRelayServers(r.quit)
+	}
+}
+
+func (r *RelayServerRetriever) IsRunning() bool {
+	return r.running.Load()
+}
+
+func (r *RelayServerRetriever) SyncRelayServers(stop <-chan bool) {
+	defer r.running.Store(false)
+
+	t := time.NewTimer(relayServerRetryInterval)
+	for {
+		relayServersToQuery := []gomatrixserverlib.ServerName{}
+		func() {
+			r.queriedServersMutex.Lock()
+			defer r.queriedServersMutex.Unlock()
+			for server, complete := range r.relayServersQueried {
+				if !complete {
+					relayServersToQuery = append(relayServersToQuery, server)
+				}
+			}
+		}()
+		if len(relayServersToQuery) == 0 {
+			// All relay servers have been synced.
+			logrus.Info("Finished syncing with all known relays")
+			return
+		}
+		r.queryRelayServers(relayServersToQuery)
+		t.Reset(relayServerRetryInterval)
+
+		select {
+		case <-stop:
+			if !t.Stop() {
+				<-t.C
+			}
+			return
+		case <-t.C:
+		}
+	}
+}
+
+func (r *RelayServerRetriever) queryRelayServers(relayServers []gomatrixserverlib.ServerName) {
+	logrus.Info("Querying relay servers for any available transactions")
+	for _, server := range relayServers {
+		userID, err := gomatrixserverlib.NewUserID("@user:"+string(r.serverName), false)
+		if err != nil {
+			return
+		}
+
+		logrus.Infof("Syncing with relay: %s", string(server))
+		err = r.relayAPI.PerformRelayServerSync(context.Background(), *userID, server)
+		if err == nil {
+			func() {
+				r.queriedServersMutex.Lock()
+				defer r.queriedServersMutex.Unlock()
+				r.relayServersQueried[server] = true
+			}()
+			// TODO : What happens if your relay receives new messages after this point?
+			// Should you continue to check with them, or should they try and contact you?
+			// They could send a "new_async_events" message your way maybe?
+			// Then you could mark them as needing to be queried again.
+			// What if you miss this message?
+			// Maybe you should try querying them again after a certain period of time as a backup?
+		} else {
+			logrus.Errorf("Failed querying relay server: %s", err.Error())
+		}
+	}
+}
+
+func UpdateNodeRelayServers(
+	node gomatrixserverlib.ServerName,
+	relays []gomatrixserverlib.ServerName,
+	ctx context.Context,
+	fedAPI federationAPI.FederationInternalAPI,
+) {
+	// Get the current relay list
+	request := federationAPI.P2PQueryRelayServersRequest{Server: node}
+	response := federationAPI.P2PQueryRelayServersResponse{}
+	err := fedAPI.P2PQueryRelayServers(ctx, &request, &response)
+	if err != nil {
+		logrus.Warnf("Failed obtaining list of relay servers for %s: %s", node, err.Error())
+	}
+
+	// Remove old, non-matching relays
+	var serversToRemove []gomatrixserverlib.ServerName
+	for _, existingServer := range response.RelayServers {
+		shouldRemove := true
+		for _, newServer := range relays {
+			if newServer == existingServer {
+				shouldRemove = false
+				break
+			}
+		}
+
+		if shouldRemove {
+			serversToRemove = append(serversToRemove, existingServer)
+		}
+	}
+	removeRequest := federationAPI.P2PRemoveRelayServersRequest{
+		Server:       node,
+		RelayServers: serversToRemove,
+	}
+	removeResponse := federationAPI.P2PRemoveRelayServersResponse{}
+	err = fedAPI.P2PRemoveRelayServers(ctx, &removeRequest, &removeResponse)
+	if err != nil {
+		logrus.Warnf("Failed removing old relay servers for %s: %s", node, err.Error())
+	}
+
+	// Add new relays
+	addRequest := federationAPI.P2PAddRelayServersRequest{
+		Server:       node,
+		RelayServers: relays,
+	}
+	addResponse := federationAPI.P2PAddRelayServersResponse{}
+	err = fedAPI.P2PAddRelayServers(ctx, &addRequest, &addResponse)
+	if err != nil {
+		logrus.Warnf("Failed adding relay servers for %s: %s", node, err.Error())
+	}
+}
diff --git a/cmd/dendrite-demo-pinecone/relay/retriever_test.go b/cmd/dendrite-demo-pinecone/relay/retriever_test.go
new file mode 100644
index 00000000..8f86a377
--- /dev/null
+++ b/cmd/dendrite-demo-pinecone/relay/retriever_test.go
@@ -0,0 +1,99 @@
+// Copyright 2023 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package relay
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	federationAPI "github.com/matrix-org/dendrite/federationapi/api"
+	relayServerAPI "github.com/matrix-org/dendrite/relayapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"gotest.tools/v3/poll"
+)
+
+var testRelayServers = []gomatrixserverlib.ServerName{"relay1", "relay2"}
+
+type FakeFedAPI struct {
+	federationAPI.FederationInternalAPI
+}
+
+func (f *FakeFedAPI) P2PQueryRelayServers(
+	ctx context.Context,
+	req *federationAPI.P2PQueryRelayServersRequest,
+	res *federationAPI.P2PQueryRelayServersResponse,
+) error {
+	res.RelayServers = testRelayServers
+	return nil
+}
+
+type FakeRelayAPI struct {
+	relayServerAPI.RelayInternalAPI
+}
+
+func (r *FakeRelayAPI) PerformRelayServerSync(
+	ctx context.Context,
+	userID gomatrixserverlib.UserID,
+	relayServer gomatrixserverlib.ServerName,
+) error {
+	return nil
+}
+
+func TestRelayRetrieverInitialization(t *testing.T) {
+	retriever := NewRelayServerRetriever(
+		context.Background(),
+		"server",
+		&FakeFedAPI{},
+		&FakeRelayAPI{},
+		make(<-chan bool),
+	)
+
+	retriever.InitializeRelayServers(logrus.WithField("test", "relay"))
+	relayServers := retriever.GetQueriedServerStatus()
+	assert.Equal(t, 2, len(relayServers))
+}
+
+func TestRelayRetrieverSync(t *testing.T) {
+	retriever := NewRelayServerRetriever(
+		context.Background(),
+		"server",
+		&FakeFedAPI{},
+		&FakeRelayAPI{},
+		make(<-chan bool),
+	)
+
+	retriever.InitializeRelayServers(logrus.WithField("test", "relay"))
+	relayServers := retriever.GetQueriedServerStatus()
+	assert.Equal(t, 2, len(relayServers))
+
+	stopRelayServerSync := make(chan bool)
+	go retriever.SyncRelayServers(stopRelayServerSync)
+
+	check := func(log poll.LogT) poll.Result {
+		relayServers := retriever.GetQueriedServerStatus()
+		for _, queried := range relayServers {
+			if !queried {
+				return poll.Continue("waiting for all servers to be queried")
+			}
+		}
+
+		stopRelayServerSync <- true
+		return poll.Success()
+	}
+	poll.WaitOn(t, check, poll.WithTimeout(5*time.Second), poll.WithDelay(100*time.Millisecond))
+}