Initial cut for backfilling

The syncserver now asks the roomserver via QueryBackfill (which already
existed to *handle* backfill requests) which then makes federation requests
via gomatrixserverlib.RequestBackfill.

Currently, tests fail on subsequent /messages requests because we don't know
which servers are in the room, because we are unable to get state snapshots
from a backfilled event because that code doesn't exist yet.

cmd/dendrite-demo-libp2p/main.go

@@ -148,7 +148,7 @@ func main() {
 	federation := createFederationClient(base)
 	keyRing := keydb.CreateKeyRing(federation.Client, keyDB, cfg.Matrix.KeyPerspectives)
 
-	alias, input, query := roomserver.SetupRoomServerComponent(&base.Base)
+	alias, input, query := roomserver.SetupRoomServerComponent(&base.Base, keyRing)
 	eduInputAPI := eduserver.SetupEDUServerComponent(&base.Base, cache.New())
 	asQuery := appservice.SetupAppServiceAPIComponent(
 		&base.Base, accountDB, deviceDB, federation, alias, query, transactions.New(),

cmd/dendrite-monolith-server/main.go

@@ -57,7 +57,7 @@ func main() {
 	federation := base.CreateFederationClient()
 	keyRing := keydb.CreateKeyRing(federation.Client, keyDB, cfg.Matrix.KeyPerspectives)
 
-	alias, input, query := roomserver.SetupRoomServerComponent(base)
+	alias, input, query := roomserver.SetupRoomServerComponent(base, keyRing)
 	eduInputAPI := eduserver.SetupEDUServerComponent(base, cache.New())
 	asQuery := appservice.SetupAppServiceAPIComponent(
 		base, accountDB, deviceDB, federation, alias, query, transactions.New(),

cmd/dendrite-room-server/main.go

@@ -18,6 +18,7 @@ import (
 	_ "net/http/pprof"
 
 	"github.com/matrix-org/dendrite/common/basecomponent"
+	"github.com/matrix-org/dendrite/common/keydb"
 	"github.com/matrix-org/dendrite/roomserver"
 )
 
@@ -25,8 +26,11 @@ func main() {
 	cfg := basecomponent.ParseFlags()
 	base := basecomponent.NewBaseDendrite(cfg, "RoomServerAPI")
 	defer base.Close() // nolint: errcheck
+	keyDB := base.CreateKeyDB()
+	federation := base.CreateFederationClient()
+	keyRing := keydb.CreateKeyRing(federation.Client, keyDB, cfg.Matrix.KeyPerspectives)
 
-	roomserver.SetupRoomServerComponent(base)
+	roomserver.SetupRoomServerComponent(base, keyRing)
 
 	base.SetupAndServeHTTP(string(base.Cfg.Bind.RoomServer), string(base.Cfg.Listen.RoomServer))
 

federationapi/routing/backfill.go

@@ -69,6 +69,7 @@ func Backfill(
 
 	// Populate the request.
 	req := api.QueryBackfillRequest{
+		RoomID:            roomID,
 		EarliestEventsIDs: eIDs,
 		ServerName:        request.Origin(),
 	}

go.mod

@@ -17,7 +17,7 @@ require (
 	github.com/matrix-org/go-http-js-libp2p v0.0.0-20200318135427-31631a9ef51f
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20200325174927-327088cdef10
 	github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20200422082552-d7b4202c47f3
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20200423090438-562549dbe799
 	github.com/matrix-org/naffka v0.0.0-20200422140631-181f1ee7401f
 	github.com/matrix-org/util v0.0.0-20190711121626-527ce5ddefc7
 	github.com/mattn/go-sqlite3 v2.0.2+incompatible

go.sum

@@ -369,6 +369,8 @@ github.com/matrix-org/gomatrixserverlib v0.0.0-20200124100636-0c2ec91d1df5 h1:km
 github.com/matrix-org/gomatrixserverlib v0.0.0-20200124100636-0c2ec91d1df5/go.mod h1:FsKa2pWE/bpQql9H7U4boOPXFoJX/QcqaZZ6ijLkaZI=
 github.com/matrix-org/gomatrixserverlib v0.0.0-20200422082552-d7b4202c47f3 h1:xis1ojN99vjygwqudzB9VQq3cM2SJ7aCAMlXj/YN+88=
 github.com/matrix-org/gomatrixserverlib v0.0.0-20200422082552-d7b4202c47f3/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20200423090438-562549dbe799 h1:OsoUMTirIpeuZJdYkKKiYe6jm0E5viZR7aOS9K465QI=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20200423090438-562549dbe799/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
 github.com/matrix-org/naffka v0.0.0-20200127221512-0716baaabaf1 h1:osLoFdOy+ChQqVUn2PeTDETFftVkl4w9t/OW18g3lnk=
 github.com/matrix-org/naffka v0.0.0-20200127221512-0716baaabaf1/go.mod h1:cXoYQIENbdWIQHt1SyCo6Bl3C3raHwJ0wgVrXHSqf+A=
 github.com/matrix-org/naffka v0.0.0-20200422140631-181f1ee7401f h1:pRz4VTiRCO4zPlEMc3ESdUOcW4PXHH4Kj+YDz1XyE+Y=

roomserver/api/query.go

@@ -229,6 +229,8 @@ type QueryStateAndAuthChainResponse struct {
 
 // QueryBackfillRequest is a request to QueryBackfill.
 type QueryBackfillRequest struct {
+	// The room to backfill
+	RoomID string `json:"room_id"`
 	// Events to start paginating from.
 	EarliestEventsIDs []string `json:"earliest_event_ids"`
 	// The maximum number of events to retrieve.
@@ -243,21 +245,7 @@ type QueryBackfillResponse struct {
 	Events []gomatrixserverlib.HeaderedEvent `json:"events"`
 }
 
-// QueryServersInRoomAtEventRequest is a request to QueryServersInRoomAtEvent
+// QueryRoomVersionCapabilitiesRequest asks for the default room version
-type QueryServersInRoomAtEventRequest struct {
-	// ID of the room to retrieve member servers for.
-	RoomID string `json:"room_id"`
-	// ID of the event for which to retrieve member servers.
-	EventID string `json:"event_id"`
-}
-
-// QueryServersInRoomAtEventResponse is a response to QueryServersInRoomAtEvent
-type QueryServersInRoomAtEventResponse struct {
-	// Servers present in the room for these events.
-	Servers []gomatrixserverlib.ServerName `json:"servers"`
-}
-
-// QueryRoomVersionCapabilities asks for the default room version
 type QueryRoomVersionCapabilitiesRequest struct{}
 
 // QueryRoomVersionCapabilitiesResponse is a response to QueryRoomVersionCapabilitiesRequest
@@ -266,12 +254,12 @@ type QueryRoomVersionCapabilitiesResponse struct {
 	AvailableRoomVersions map[gomatrixserverlib.RoomVersion]string `json:"available"`
 }
 
-// QueryRoomVersionForRoom asks for the room version for a given room.
+// QueryRoomVersionForRoomRequest asks for the room version for a given room.
 type QueryRoomVersionForRoomRequest struct {
 	RoomID string `json:"room_id"`
 }
 
-// QueryRoomVersionCapabilitiesResponse is a response to QueryServersInRoomAtEventResponse
+// QueryRoomVersionForRoomResponse is a response to QueryRoomVersionForRoomRequest
 type QueryRoomVersionForRoomResponse struct {
 	RoomVersion gomatrixserverlib.RoomVersion `json:"room_version"`
 }
@@ -350,12 +338,6 @@ type RoomserverQueryAPI interface {
 		response *QueryBackfillResponse,
 	) error
 
-	QueryServersInRoomAtEvent(
-		ctx context.Context,
-		request *QueryServersInRoomAtEventRequest,
-		response *QueryServersInRoomAtEventResponse,
-	) error
-
 	// Asks for the default room version as preferred by the server.
 	QueryRoomVersionCapabilities(
 		ctx context.Context,
@@ -401,13 +383,10 @@ const RoomserverQueryStateAndAuthChainPath = "/api/roomserver/queryStateAndAuthC
 // RoomserverQueryBackfillPath is the HTTP path for the QueryBackfillPath API
 const RoomserverQueryBackfillPath = "/api/roomserver/queryBackfill"
 
-// RoomserverQueryServersInRoomAtEventPath is the HTTP path for the QueryServersInRoomAtEvent API
-const RoomserverQueryServersInRoomAtEventPath = "/api/roomserver/queryServersInRoomAtEvents"
-
 // RoomserverQueryRoomVersionCapabilitiesPath is the HTTP path for the QueryRoomVersionCapabilities API
 const RoomserverQueryRoomVersionCapabilitiesPath = "/api/roomserver/queryRoomVersionCapabilities"
 
-// RoomserverQueryRoomVersionCapabilitiesPath is the HTTP path for the QueryRoomVersionCapabilities API
+// RoomserverQueryRoomVersionForRoomPath is the HTTP path for the QueryRoomVersionForRoom API
 const RoomserverQueryRoomVersionForRoomPath = "/api/roomserver/queryRoomVersionForRoom"
 
 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
@@ -555,19 +534,6 @@ func (h *httpRoomserverQueryAPI) QueryBackfill(
 	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
 }
 
-// QueryServersInRoomAtEvent implements RoomServerQueryAPI
-func (h *httpRoomserverQueryAPI) QueryServersInRoomAtEvent(
-	ctx context.Context,
-	request *QueryServersInRoomAtEventRequest,
-	response *QueryServersInRoomAtEventResponse,
-) error {
-	span, ctx := opentracing.StartSpanFromContext(ctx, "QueryServersInRoomAtEvent")
-	defer span.Finish()
-
-	apiURL := h.roomserverURL + RoomserverQueryServersInRoomAtEventPath
-	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
-}
-
 // QueryRoomVersionCapabilities implements RoomServerQueryAPI
 func (h *httpRoomserverQueryAPI) QueryRoomVersionCapabilities(
 	ctx context.Context,

roomserver/input/events.go

@@ -26,6 +26,7 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/state/database"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -104,6 +105,7 @@ func processRoomEvent(
 	// Check that the event passes authentication checks and work out the numeric IDs for the auth events.
 	authEventNIDs, err := checkAuthEvents(ctx, db, headered, input.AuthEventIDs)
 	if err != nil {
+		logrus.WithError(err).WithField("event_id", event.EventID()).Error("processRoomEvent.checkAuthEvents failed for event")
 		return
 	}
 
@@ -128,6 +130,7 @@ func processRoomEvent(
 		// For outliers we can stop after we've stored the event itself as it
 		// doesn't have any associated state to store and we don't need to
 		// notify anyone about it.
+		logrus.WithField("event_id", event.EventID()).WithField("type", event.Type()).WithField("room", event.RoomID()).Info("Stored outlier")
 		return event.EventID(), nil
 	}
 

roomserver/query/backfill.go

@@ -0,0 +1,86 @@
+package query
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+)
+
+// backfillRequester implements gomatrixserverlib.BackfillRequester
+type backfillRequester struct {
+	db         RoomserverQueryAPIDatabase
+	fedClient  *gomatrixserverlib.FederationClient
+	thisServer gomatrixserverlib.ServerName
+}
+
+// ServersAtEvent is called when trying to determine which server to request from.
+// It returns a list of servers which can be queried for backfill requests. These servers
+// will be servers that are in the room already. The entries at the beginning are preferred servers
+// and will be tried first. An empty list will fail the request.
+func (b *backfillRequester) ServersAtEvent(ctx context.Context, roomID, eventID string) (servers []gomatrixserverlib.ServerName) {
+	// getMembershipsBeforeEventNID requires a NID, so retrieving the NID for
+	// the event is necessary.
+	NIDs, err := b.db.EventNIDs(ctx, []string{eventID})
+	if err != nil {
+		logrus.WithField("event_id", eventID).WithError(err).Error("ServersAtEvent: failed to get event NID for event")
+		return
+	}
+
+	// Retrieve all "m.room.member" state events of "join" membership, which
+	// contains the list of users in the room before the event, therefore all
+	// the servers in it at that moment.
+	events, err := getMembershipsBeforeEventNID(ctx, b.db, NIDs[eventID], true)
+	if err != nil {
+		logrus.WithField("event_id", eventID).WithError(err).Error("ServersAtEvent: failed to get memberships before event")
+		return
+	}
+
+	// Store the server names in a temporary map to avoid duplicates.
+	serverSet := make(map[gomatrixserverlib.ServerName]bool)
+	for _, event := range events {
+		serverSet[event.Origin()] = true
+	}
+	for server := range serverSet {
+		if server == b.thisServer {
+			continue
+		}
+		servers = append(servers, server)
+	}
+	return
+}
+
+// Backfill performs a backfill request to the given server.
+// https://matrix.org/docs/spec/server_server/latest#get-matrix-federation-v1-backfill-roomid
+func (b *backfillRequester) Backfill(ctx context.Context, server gomatrixserverlib.ServerName, roomID string, fromEventIDs []string, limit int) (*gomatrixserverlib.Transaction, error) {
+	tx, err := b.fedClient.Backfill(ctx, server, roomID, limit, fromEventIDs)
+	return &tx, err
+}
+
+func (b *backfillRequester) ProvideEvents(roomVer gomatrixserverlib.RoomVersion, eventIDs []string) ([]gomatrixserverlib.Event, error) {
+	logrus.Info("backfillRequester.ProvideEvents ", eventIDs)
+	ctx := context.Background()
+	nidMap, err := b.db.EventNIDs(ctx, eventIDs)
+	if err != nil {
+		logrus.WithError(err).WithField("event_ids", eventIDs).Error("Failed to find events")
+		return nil, err
+	}
+	eventNIDs := make([]types.EventNID, len(nidMap))
+	i := 0
+	for _, nid := range nidMap {
+		eventNIDs[i] = nid
+		i++
+	}
+	eventsWithNids, err := b.db.Events(ctx, eventNIDs)
+	if err != nil {
+		logrus.WithError(err).WithField("event_nids", eventNIDs).Error("Failed to load events")
+		return nil, err
+	}
+	events := make([]gomatrixserverlib.Event, len(eventsWithNids))
+	for i := range eventsWithNids {
+		events[i] = eventsWithNids[i].Event
+	}
+	logrus.Infof("backfillRequester.ProvideEvents Returning %+v", events)
+	return events, nil
+}

roomserver/query/query.go

@@ -19,6 +19,7 @@ package query
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 
 	"github.com/matrix-org/dendrite/common"
@@ -31,6 +32,7 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/version"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
 )
 
 // RoomserverQueryAPIEventDB has a convenience API to fetch events directly by
@@ -100,6 +102,9 @@ type RoomserverQueryAPIDatabase interface {
 type RoomserverQueryAPI struct {
 	DB             RoomserverQueryAPIDatabase
 	ImmutableCache caching.ImmutableCache
+	ServerName     gomatrixserverlib.ServerName
+	KeyRing        gomatrixserverlib.JSONVerifier
+	FedClient      *gomatrixserverlib.FederationClient
 }
 
 // QueryLatestEventsAndState implements api.RoomserverQueryAPI
@@ -344,7 +349,7 @@ func (r *RoomserverQueryAPI) QueryMembershipsForRoom(
 
 		events, err = r.DB.Events(ctx, eventNIDs)
 	} else {
-		events, err = r.getMembershipsBeforeEventNID(ctx, membershipEventNID, request.JoinedOnly)
+		events, err = getMembershipsBeforeEventNID(ctx, r.DB, membershipEventNID, request.JoinedOnly)
 	}
 
 	if err != nil {
@@ -363,19 +368,19 @@ func (r *RoomserverQueryAPI) QueryMembershipsForRoom(
 // of the event's room as it was when this event was fired, then filters the state events to
 // only keep the "m.room.member" events with a "join" membership. These events are returned.
 // Returns an error if there was an issue fetching the events.
-func (r *RoomserverQueryAPI) getMembershipsBeforeEventNID(
+func getMembershipsBeforeEventNID(
-	ctx context.Context, eventNID types.EventNID, joinedOnly bool,
+	ctx context.Context, db RoomserverQueryAPIDatabase, eventNID types.EventNID, joinedOnly bool,
 ) ([]types.Event, error) {
-	roomState := state.NewStateResolution(r.DB)
+	roomState := state.NewStateResolution(db)
 	events := []types.Event{}
 	// Lookup the event NID
-	eIDs, err := r.DB.EventIDs(ctx, []types.EventNID{eventNID})
+	eIDs, err := db.EventIDs(ctx, []types.EventNID{eventNID})
 	if err != nil {
 		return nil, err
 	}
 	eventIDs := []string{eIDs[eventNID]}
 
-	prevState, err := r.DB.StateAtEventIDs(ctx, eventIDs)
+	prevState, err := db.StateAtEventIDs(ctx, eventIDs)
 	if err != nil {
 		return nil, err
 	}
@@ -395,7 +400,7 @@ func (r *RoomserverQueryAPI) getMembershipsBeforeEventNID(
 	}
 
 	// Get all of the events in this state
-	stateEvents, err := r.DB.Events(ctx, eventNIDs)
+	stateEvents, err := db.Events(ctx, eventNIDs)
 	if err != nil {
 		return nil, err
 	}
@@ -547,6 +552,13 @@ func (r *RoomserverQueryAPI) QueryBackfill(
 	request *api.QueryBackfillRequest,
 	response *api.QueryBackfillResponse,
 ) error {
+	logrus.WithField("req", request).Info("QueryBackfill - I am " + r.ServerName)
+	// if we are requesting the backfill then we need to do a federation hit
+	// TODO: we could be more sensible and fetch as many events we already have then request the rest
+	//       which is what the syncapi does already.
+	if request.ServerName == r.ServerName {
+		return r.backfillViaFederation(ctx, request, response)
+	}
 	var err error
 	var front []string
 
@@ -588,6 +600,26 @@ func (r *RoomserverQueryAPI) QueryBackfill(
 	return err
 }
 
+func (r *RoomserverQueryAPI) backfillViaFederation(ctx context.Context, req *api.QueryBackfillRequest, res *api.QueryBackfillResponse) error {
+	roomVer, err := r.DB.GetRoomVersionForRoom(ctx, req.RoomID)
+	if err != nil {
+		return fmt.Errorf("backfillViaFederation: unknown room version for room %s : %w", req.RoomID, err)
+	}
+	events, err := gomatrixserverlib.RequestBackfill(ctx, &backfillRequester{
+		db:         r.DB,
+		fedClient:  r.FedClient,
+		thisServer: r.ServerName,
+	}, r.KeyRing, req.RoomID, roomVer, req.EarliestEventsIDs, req.Limit)
+	if err != nil {
+		return err
+	}
+	// TODO: persist these new events and update the state db so we can get state snapshots at these new backfilled events
+	// this will be important if we want to backfill multiple times as we get the join memberships from state snapshots.
+
+	res.Events = events
+	return nil
+}
+
 func (r *RoomserverQueryAPI) isServerCurrentlyInRoom(ctx context.Context, serverName gomatrixserverlib.ServerName, roomID string) (bool, error) {
 	roomNID, err := r.DB.RoomNID(ctx, roomID)
 	if err != nil {
@@ -839,41 +871,6 @@ func getAuthChain(
 	return authEvents, nil
 }
 
-// QueryServersInRoomAtEvent implements api.RoomserverQueryAPI
-func (r *RoomserverQueryAPI) QueryServersInRoomAtEvent(
-	ctx context.Context,
-	request *api.QueryServersInRoomAtEventRequest,
-	response *api.QueryServersInRoomAtEventResponse,
-) error {
-	// getMembershipsBeforeEventNID requires a NID, so retrieving the NID for
-	// the event is necessary.
-	NIDs, err := r.DB.EventNIDs(ctx, []string{request.EventID})
-	if err != nil {
-		return err
-	}
-
-	// Retrieve all "m.room.member" state events of "join" membership, which
-	// contains the list of users in the room before the event, therefore all
-	// the servers in it at that moment.
-	events, err := r.getMembershipsBeforeEventNID(ctx, NIDs[request.EventID], true)
-	if err != nil {
-		return err
-	}
-
-	// Store the server names in a temporary map to avoid duplicates.
-	servers := make(map[gomatrixserverlib.ServerName]bool)
-	for _, event := range events {
-		servers[event.Origin()] = true
-	}
-
-	// Populate the response.
-	for server := range servers {
-		response.Servers = append(response.Servers, server)
-	}
-
-	return nil
-}
-
 // QueryRoomVersionCapabilities implements api.RoomserverQueryAPI
 func (r *RoomserverQueryAPI) QueryRoomVersionCapabilities(
 	ctx context.Context,
@@ -1055,20 +1052,6 @@ func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
-	servMux.Handle(
-		api.RoomserverQueryServersInRoomAtEventPath,
-		common.MakeInternalAPI("QueryServersInRoomAtEvent", func(req *http.Request) util.JSONResponse {
-			var request api.QueryServersInRoomAtEventRequest
-			var response api.QueryServersInRoomAtEventResponse
-			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
-				return util.ErrorResponse(err)
-			}
-			if err := r.QueryServersInRoomAtEvent(req.Context(), &request, &response); err != nil {
-				return util.ErrorResponse(err)
-			}
-			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
-		}),
-	)
 	servMux.Handle(
 		api.RoomserverQueryRoomVersionCapabilitiesPath,
 		common.MakeInternalAPI("QueryRoomVersionCapabilities", func(req *http.Request) util.JSONResponse {

roomserver/roomserver.go

@@ -18,6 +18,7 @@ import (
 	"net/http"
 
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrixserverlib"
 
 	asQuery "github.com/matrix-org/dendrite/appservice/query"
 	"github.com/matrix-org/dendrite/common/basecomponent"
@@ -33,7 +34,7 @@ import (
 // allowing other components running in the same process to hit the query the
 // APIs directly instead of having to use HTTP.
 func SetupRoomServerComponent(
-	base *basecomponent.BaseDendrite,
+	base *basecomponent.BaseDendrite, keyRing gomatrixserverlib.JSONVerifier,
 ) (api.RoomserverAliasAPI, api.RoomserverInputAPI, api.RoomserverQueryAPI) {
 	roomserverDB, err := storage.Open(string(base.Cfg.Database.RoomServer))
 	if err != nil {
@@ -51,6 +52,11 @@ func SetupRoomServerComponent(
 	queryAPI := query.RoomserverQueryAPI{
 		DB:             roomserverDB,
 		ImmutableCache: base.ImmutableCache,
+		ServerName:     base.Cfg.Matrix.ServerName,
+		FedClient:      base.CreateFederationClient(),
+		// TODO: We should have a key server so we don't keep adding components
+		// which talk to the same DB.
+		KeyRing: keyRing,
 	}
 
 	queryAPI.SetupHTTP(http.DefaultServeMux)

syncapi/routing/messages.go

@@ -282,7 +282,7 @@ func (r *messagesReq) handleEmptyEventsSlice() (
 	// Check if we have backward extremities for this room.
 	if len(backwardExtremities) > 0 {
 		// If so, retrieve as much events as needed through backfilling.
-		events, err = r.backfill(backwardExtremities, r.limit)
+		events, err = r.backfill(r.roomID, backwardExtremities, r.limit)
 		if err != nil {
 			return
 		}
@@ -331,7 +331,7 @@ func (r *messagesReq) handleNonEmptyEventsSlice(streamEvents []types.StreamEvent
 	if len(backwardExtremities) > 0 && !isSetLargeEnough && r.backwardOrdering {
 		var pdus []gomatrixserverlib.HeaderedEvent
 		// Only ask the remote server for enough events to reach the limit.
-		pdus, err = r.backfill(backwardExtremities, r.limit-len(streamEvents))
+		pdus, err = r.backfill(r.roomID, backwardExtremities, r.limit-len(streamEvents))
 		if err != nil {
 			return
 		}
@@ -355,45 +355,29 @@ func (r *messagesReq) handleNonEmptyEventsSlice(streamEvents []types.StreamEvent
 // event, or if there is no remote homeserver to contact.
 // Returns an error if there was an issue with retrieving the list of servers in
 // the room or sending the request.
-func (r *messagesReq) backfill(fromEventIDs []string, limit int) ([]gomatrixserverlib.HeaderedEvent, error) {
+func (r *messagesReq) backfill(roomID string, fromEventIDs []string, limit int) ([]gomatrixserverlib.HeaderedEvent, error) {
-	verReq := api.QueryRoomVersionForRoomRequest{RoomID: r.roomID}
+	var res api.QueryBackfillResponse
-	verRes := api.QueryRoomVersionForRoomResponse{}
+	err := r.queryAPI.QueryBackfill(context.Background(), &api.QueryBackfillRequest{
-	if err := r.queryAPI.QueryRoomVersionForRoom(r.ctx, &verReq, &verRes); err != nil {
+		RoomID:            roomID,
-		return nil, err
+		EarliestEventsIDs: fromEventIDs,
-	}
+		Limit:             limit,
-
+		ServerName:        r.cfg.Matrix.ServerName,
-	srvToBackfillFrom, err := r.serverToBackfillFrom(fromEventIDs)
+	}, &res)
 	if err != nil {
-		return nil, fmt.Errorf("Cannot find server to backfill from: %w", err)
+		return nil, fmt.Errorf("QueryBackfill failed: %w", err)
 	}
+	util.GetLogger(r.ctx).WithField("new_events", len(res.Events)).Info("Storing new events from backfill")
 
-	headered := make([]gomatrixserverlib.HeaderedEvent, 0)
+	// TODO: we should only be inserting events into the database from the roomserver's kafka output stream.
-
+	// Currently, this can race with live events for the room and cause problems. It's also just a bit unclear
-	// If the roomserver responded with at least one server that isn't us,
+	// when you have multiple entry points to write events.
-	// send it a request for backfill.
-	util.GetLogger(r.ctx).WithField("server", srvToBackfillFrom).WithField("limit", limit).Info("Backfilling from server")
-	txn, err := r.federation.Backfill(
-		r.ctx, srvToBackfillFrom, r.roomID, limit, fromEventIDs,
-	)
-	if err != nil {
-		return nil, err
-	}
-
-	for _, p := range txn.PDUs {
-		event, e := gomatrixserverlib.NewEventFromUntrustedJSON(p, verRes.RoomVersion)
-		if e != nil {
-			continue
-		}
-		headered = append(headered, event.Headered(verRes.RoomVersion))
-	}
-	util.GetLogger(r.ctx).WithField("server", srvToBackfillFrom).WithField("new_events", len(headered)).Info("Storing new events from backfill")
 
 	// Store the events in the database, while marking them as unfit to show
 	// up in responses to sync requests.
-	for i := range headered {
+	for i := range res.Events {
 		if _, err = r.db.WriteEvent(
 			r.ctx,
-			&headered[i],
+			&res.Events[i],
 			[]gomatrixserverlib.HeaderedEvent{},
 			[]string{},
 			[]string{},
@@ -403,63 +387,7 @@ func (r *messagesReq) backfill(fromEventIDs []string, limit int) ([]gomatrixserv
 		}
 	}
 
-	return headered, nil
+	return res.Events, nil
-}
-
-func (r *messagesReq) serverToBackfillFrom(fromEventIDs []string) (gomatrixserverlib.ServerName, error) {
-	// Query the list of servers in the room when one of the backward extremities
-	// was sent.
-	var serversResponse api.QueryServersInRoomAtEventResponse
-	serversRequest := api.QueryServersInRoomAtEventRequest{
-		RoomID:  r.roomID,
-		EventID: fromEventIDs[0],
-	}
-	if err := r.queryAPI.QueryServersInRoomAtEvent(r.ctx, &serversRequest, &serversResponse); err != nil {
-		util.GetLogger(r.ctx).WithError(err).Warn("Failed to query servers in room at event, falling back to event sender")
-		// FIXME: We shouldn't be doing this but in situations where we have already backfilled once
-		// the query API doesn't work as backfilled events do not make it to the room server.
-		// This means QueryServersInRoomAtEvent returns an error as it doesn't have the event ID in question.
-		// We need to inject backfilled events into the room server and store them appropriately.
-		events, err := r.db.Events(r.ctx, fromEventIDs)
-		if err != nil {
-			return "", err
-		}
-		if len(events) == 0 {
-			// should be impossible as these event IDs are backwards extremities
-			return "", fmt.Errorf("backfill: missing backwards extremities, event IDs: %s", fromEventIDs)
-		}
-		// The rationale here is that the last event was unlikely to be sent by us, so poke the server who sent it.
-		// We shouldn't be doing this really, but as a heuristic it should work pretty well for now.
-		for _, e := range events {
-			_, srv, srverr := gomatrixserverlib.SplitID('@', e.Sender())
-			if srverr != nil {
-				util.GetLogger(r.ctx).WithError(srverr).Warn("Failed to extract domain from event sender")
-				continue
-			}
-			if srv != r.cfg.Matrix.ServerName {
-				return srv, nil
-			}
-		}
-		// no valid events which have a remote server, fail.
-		return "", err
-	}
-
-	// Use the first server from the response, except if that server is us.
-	// In that case, use the second one if the roomserver responded with
-	// enough servers. If not, use an empty string to prevent the backfill
-	// from happening as there's no server to direct the request towards.
-	// TODO: Be smarter at selecting the server to direct the request
-	// towards.
-	srvToBackfillFrom := serversResponse.Servers[0]
-	if srvToBackfillFrom == r.cfg.Matrix.ServerName {
-		if len(serversResponse.Servers) > 1 {
-			srvToBackfillFrom = serversResponse.Servers[1]
-		} else {
-			util.GetLogger(r.ctx).Info("Not enough servers to backfill from")
-			return "", nil
-		}
-	}
-	return srvToBackfillFrom, nil
 }
 
 // setToDefault returns the default value for the "to" query parameter of a