merge master (doh)

2020-01-25 19:38:53 -07:00 · 2020-01-25 19:38:53 -07:00 · 42b1adf442
parent 90a96c698c 054f5383c4
commit 42b1adf442
44 changed files with 1924 additions and 538 deletions
--- a/clientapi/routing/joinroom.go
+++ b/clientapi/routing/joinroom.go
@ -320,7 +320,7 @@ func (r joinRoomReq) joinRoomUsingServer(roomID string, server gomatrixserverlib
 	}

 	if err = r.producer.SendEventWithState(
-		r.req.Context(), gomatrixserverlib.RespState(respSendJoin), event,
+		r.req.Context(), gomatrixserverlib.RespState(respSendJoin.RespState), event,
 	); err != nil {
 		res := httputil.LogThenError(r.req, err)
 		return &res, nil
--- a/clientapi/routing/login.go
+++ b/clientapi/routing/login.go
@ -40,9 +40,14 @@ type flow struct {
 	Stages []string `json:"stages"`
 }

+type loginIdentifier struct {
+	Type string `json:"type"`
+	User string `json:"user"`
+}
+
 type passwordRequest struct {
-	User     string `json:"user"`
-	Password string `json:"password"`
+	Identifier loginIdentifier `json:"identifier"`
+	Password   string          `json:"password"`
 	// Both DeviceID and InitialDisplayName can be omitted, or empty strings ("")
 	// Thus a pointer is needed to differentiate between the two
 	InitialDisplayName *string `json:"initial_device_display_name"`
@ -75,34 +80,43 @@ func Login(
 		}
 	} else if req.Method == http.MethodPost {
 		var r passwordRequest
+		var acc *authtypes.Account
 		resErr := httputil.UnmarshalJSONRequest(req, &r)
 		if resErr != nil {
 			return *resErr
 		}
-		if r.User == "" {
+		switch r.Identifier.Type {
+		case "m.id.user":
+			if r.Identifier.User == "" {
+				return util.JSONResponse{
+					Code: http.StatusBadRequest,
+					JSON: jsonerror.BadJSON("'user' must be supplied."),
+				}
+			}
+
+			util.GetLogger(req.Context()).WithField("user", r.Identifier.User).Info("Processing login request")
+
+			localpart, err := userutil.ParseUsernameParam(r.Identifier.User, &cfg.Matrix.ServerName)
+			if err != nil {
+				return util.JSONResponse{
+					Code: http.StatusBadRequest,
+					JSON: jsonerror.InvalidUsername(err.Error()),
+				}
+			}
+
+			acc, err = accountDB.GetAccountByPassword(req.Context(), localpart, r.Password)
+			if err != nil {
+				// Technically we could tell them if the user does not exist by checking if err == sql.ErrNoRows
+				// but that would leak the existence of the user.
+				return util.JSONResponse{
+					Code: http.StatusForbidden,
+					JSON: jsonerror.Forbidden("username or password was incorrect, or the account does not exist"),
+				}
+			}
+		default:
 			return util.JSONResponse{
 				Code: http.StatusBadRequest,
-				JSON: jsonerror.BadJSON("'user' must be supplied."),
-			}
-		}
-
-		util.GetLogger(req.Context()).WithField("user", r.User).Info("Processing login request")
-
-		localpart, err := userutil.ParseUsernameParam(r.User, &cfg.Matrix.ServerName)
-		if err != nil {
-			return util.JSONResponse{
-				Code: http.StatusBadRequest,
-				JSON: jsonerror.InvalidUsername(err.Error()),
-			}
-		}
-
-		acc, err := accountDB.GetAccountByPassword(req.Context(), localpart, r.Password)
-		if err != nil {
-			// Technically we could tell them if the user does not exist by checking if err == sql.ErrNoRows
-			// but that would leak the existence of the user.
-			return util.JSONResponse{
-				Code: http.StatusForbidden,
-				JSON: jsonerror.Forbidden("username or password was incorrect, or the account does not exist"),
+				JSON: jsonerror.BadJSON("login identifier '" + r.Identifier.Type + "' not supported"),
 			}
 		}

--- a/cmd/dendrite-monolith-server/main.go
+++ b/cmd/dendrite-monolith-server/main.go
@ -71,8 +71,8 @@ func main() {
 	)
 	federationapi.SetupFederationAPIComponent(base, accountDB, deviceDB, federation, &keyRing, alias, input, query, asQuery, fedSenderAPI)
 	mediaapi.SetupMediaAPIComponent(base, deviceDB)
-	publicroomsapi.SetupPublicRoomsAPIComponent(base, deviceDB)
-	syncapi.SetupSyncAPIComponent(base, deviceDB, accountDB, query)
+	publicroomsapi.SetupPublicRoomsAPIComponent(base, deviceDB, query)
+	syncapi.SetupSyncAPIComponent(base, deviceDB, accountDB, query, federation, cfg)

 	httpHandler := common.WrapHandlerInCORS(base.APIMux)

--- a/cmd/dendrite-public-rooms-api-server/main.go
+++ b/cmd/dendrite-public-rooms-api-server/main.go
@ -26,7 +26,9 @@ func main() {

 	deviceDB := base.CreateDeviceDB()

-	publicroomsapi.SetupPublicRoomsAPIComponent(base, deviceDB)
+	_, _, query := base.CreateHTTPRoomserverAPIs()
+
+	publicroomsapi.SetupPublicRoomsAPIComponent(base, deviceDB, query)

 	base.SetupAndServeHTTP(string(base.Cfg.Bind.PublicRoomsAPI), string(base.Cfg.Listen.PublicRoomsAPI))

--- a/cmd/dendrite-sync-api-server/main.go
+++ b/cmd/dendrite-sync-api-server/main.go
@ -26,10 +26,11 @@ func main() {

 	deviceDB := base.CreateDeviceDB()
 	accountDB := base.CreateAccountsDB()
+	federation := base.CreateFederationClient()

 	_, _, query := base.CreateHTTPRoomserverAPIs()

-	syncapi.SetupSyncAPIComponent(base, deviceDB, accountDB, query)
+	syncapi.SetupSyncAPIComponent(base, deviceDB, accountDB, query, federation, cfg)

 	base.SetupAndServeHTTP(string(base.Cfg.Bind.SyncAPI), string(base.Cfg.Listen.SyncAPI))

--- a/common/basecomponent/base.go
+++ b/common/basecomponent/base.go
@ -20,6 +20,8 @@ import (
 	"fmt"
 	"net/http"

+	"golang.org/x/crypto/ed25519"
+
 	"github.com/matrix-org/dendrite/common/keydb"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/naffka"
@ -151,7 +153,12 @@ func (b *BaseDendrite) CreateAccountsDB() *accounts.Database {
 // CreateKeyDB creates a new instance of the key database. Should only be called
 // once per component.
 func (b *BaseDendrite) CreateKeyDB() keydb.Database {
-	db, err := keydb.NewDatabase(string(b.Cfg.Database.ServerKey))
+	db, err := keydb.NewDatabase(
+		string(b.Cfg.Database.ServerKey),
+		b.Cfg.Matrix.ServerName,
+		b.Cfg.Matrix.PrivateKey.Public().(ed25519.PublicKey),
+		b.Cfg.Matrix.KeyID,
+	)
 	if err != nil {
 		logrus.WithError(err).Panicf("failed to connect to keys db")
 	}
--- a/common/keydb/keydb.go
+++ b/common/keydb/keydb.go
@ -16,9 +16,10 @@ package keydb

 import (
 	"context"
-	"errors"
 	"net/url"

+	"golang.org/x/crypto/ed25519"
+
 	"github.com/matrix-org/dendrite/common/keydb/postgres"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@ -30,15 +31,20 @@ type Database interface {
 }

 // NewDatabase opens a database connection.
-func NewDatabase(dataSourceName string) (Database, error) {
+func NewDatabase(
+	dataSourceName string,
+	serverName gomatrixserverlib.ServerName,
+	serverKey ed25519.PublicKey,
+	serverKeyID gomatrixserverlib.KeyID,
+) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.NewDatabase(dataSourceName, serverName, serverKey, serverKeyID)
 	}
 	switch uri.Scheme {
 	case "postgres":
-		return postgres.NewDatabase(dataSourceName)
+		return postgres.NewDatabase(dataSourceName, serverName, serverKey, serverKeyID)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.NewDatabase(dataSourceName, serverName, serverKey, serverKeyID)
 	}
 }
--- a/common/keydb/postgres/keydb.go
+++ b/common/keydb/postgres/keydb.go
@ -18,6 +18,9 @@ package postgres
 import (
 	"context"
 	"database/sql"
+	"math"
+
+	"golang.org/x/crypto/ed25519"

 	"github.com/matrix-org/gomatrixserverlib"
 )
@ -32,7 +35,12 @@ type Database struct {
 // It creates the necessary tables if they don't already exist.
 // It prepares all the SQL statements that it will use.
 // Returns an error if there was a problem talking to the database.
-func NewDatabase(dataSourceName string) (*Database, error) {
+func NewDatabase(
+	dataSourceName string,
+	serverName gomatrixserverlib.ServerName,
+	serverKey ed25519.PublicKey,
+	serverKeyID gomatrixserverlib.KeyID,
+) (*Database, error) {
 	db, err := sql.Open("postgres", dataSourceName)
 	if err != nil {
 		return nil, err
@ -42,6 +50,28 @@ func NewDatabase(dataSourceName string) (*Database, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Store our own keys so that we don't end up making HTTP requests to find our
+	// own keys
+	index := gomatrixserverlib.PublicKeyLookupRequest{
+		ServerName: serverName,
+		KeyID:      serverKeyID,
+	}
+	value := gomatrixserverlib.PublicKeyLookupResult{
+		VerifyKey: gomatrixserverlib.VerifyKey{
+			Key: gomatrixserverlib.Base64String(serverKey),
+		},
+		ValidUntilTS: math.MaxUint64 >> 1,
+		ExpiredTS:    gomatrixserverlib.PublicKeyNotExpired,
+	}
+	err = d.StoreKeys(
+		context.Background(),
+		map[gomatrixserverlib.PublicKeyLookupRequest]gomatrixserverlib.PublicKeyLookupResult{
+			index: value,
+		},
+	)
+	if err != nil {
+		return nil, err
+	}
 	return d, nil
 }

--- a/docs/sytest.md
+++ b/docs/sytest.md
@ -2,16 +2,17 @@

 Dendrite uses [SyTest](https://github.com/matrix-org/sytest) for its
 integration testing. When creating a new PR, add the test IDs (see below) that
-your PR should allow to pass to `testfile` in dendrite's root directory. Not all
-PRs need to make new tests pass. If we find your PR should be making a test pass
-we may ask you to add to that file, as generally Dendrite's progress can be
-tracked through the amount of SyTest tests it passes.
+your PR should allow to pass to `sytest-whitelist` in dendrite's root
+directory. Not all PRs need to make new tests pass. If we find your PR should
+be making a test pass we may ask you to add to that file, as generally
+Dendrite's progress can be tracked through the amount of SyTest tests it
+passes.

 ## Finding out which tests to add

 We recommend you run the tests locally by manually setting up SyTest or using a
 SyTest docker image. After running the tests, a script will print the tests you
-need to add to `testfile` for you.
+need to add to `sytest-whitelist`.

 You should proceed after you see no build problems for dendrite after running:

@ -50,16 +51,16 @@ EOF
 Run the tests:

 ```sh
-./run-tests.pl -I Dendrite::Monolith -d ../dendrite/bin -W ../dendrite/testfile -O tap --all | tee results.tap
+./run-tests.pl -I Dendrite::Monolith -d ../dendrite/bin -W ../dendrite/sytest-whitelist -O tap --all | tee results.tap
 ```

 where `tee` lets you see the results while they're being piped to the file.

 Once the tests are complete, run the helper script to see if you need to add
-any newly passing test names to `testfile` in the project's root directory:
+any newly passing test names to `sytest-whitelist` in the project's root directory:

 ```sh
-../dendrite/show-expected-fail-tests.sh results.tap ../dendrite/testfile
+../dendrite/show-expected-fail-tests.sh results.tap ../dendrite/sytest-whitelist ../dendrite/sytest-blacklist
 ```

 If the script prints nothing/exits with 0, then you're good to go.
@ -75,4 +76,4 @@ docker run --rm -v /path/to/dendrite/:/src/ matrixdotorg/sytest-dendrite

 where `/path/to/dendrite/` should be replaced with the actual path to your
 dendrite source code. The output should tell you if you need to add any tests to
-`testfile`.
+`sytest-whitelist`.
--- a/federationsender/storage/storage.go
+++ b/federationsender/storage/storage.go
@ -16,7 +16,6 @@ package storage

 import (
 	"context"
-	"errors"
 	"net/url"

 	"github.com/matrix-org/dendrite/common"
@ -34,12 +33,12 @@ type Database interface {
 func NewDatabase(dataSourceName string) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.NewDatabase(dataSourceName)
 	}
 	switch uri.Scheme {
 	case "postgres":
 		return postgres.NewDatabase(dataSourceName)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.NewDatabase(dataSourceName)
 	}
 }
--- a/go.mod
+++ b/go.mod
@ -2,68 +2,41 @@ module github.com/matrix-org/dendrite

 require (
 	github.com/Shopify/sarama v0.0.0-20170127151855-574d3147eee3
-	github.com/alecthomas/gometalinter v2.0.2+incompatible
-	github.com/alecthomas/units v0.0.0-20190717042225-c3de453c63f4
-	github.com/apache/thrift v0.0.0-20161221203622-b2a4d4ae21c7
-	github.com/beorn7/perks v1.0.1
-	github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd
-	github.com/crossdock/crossdock-go v0.0.0-20160816171116-049aabb0122b
-	github.com/davecgh/go-spew v1.1.1
-	github.com/eapache/go-resiliency v0.0.0-20160104191539-b86b1ec0dd42
-	github.com/eapache/go-xerial-snappy v0.0.0-20160609142408-bb955e01b934
-	github.com/eapache/queue v1.1.0
-	github.com/golang/protobuf v1.3.2
-	github.com/golang/snappy v0.0.0-20170119014723-7db9049039a0
-	github.com/google/shlex v0.0.0-20150127133951-6f45313302b9
-	github.com/gorilla/context v1.1.1
+	github.com/Shopify/toxiproxy v2.1.4+incompatible // indirect
+	github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd // indirect
+	github.com/eapache/go-resiliency v0.0.0-20160104191539-b86b1ec0dd42 // indirect
+	github.com/eapache/go-xerial-snappy v0.0.0-20160609142408-bb955e01b934 // indirect
+	github.com/eapache/queue v1.1.0 // indirect
+	github.com/golang/snappy v0.0.0-20180518054509-2e65f85255db // indirect
 	github.com/gorilla/mux v1.7.3
-	github.com/jaegertracing/jaeger-client-go v0.0.0-20170921145708-3ad49a1d839b
-	github.com/jaegertracing/jaeger-lib v0.0.0-20170920222118-21a3da6d66fe
-	github.com/klauspost/crc32 v0.0.0-20161016154125-cb6bfca970f6
+	github.com/klauspost/crc32 v0.0.0-20161016154125-cb6bfca970f6 // indirect
 	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
-	github.com/lib/pq v0.0.0-20170918175043-23da1db4f16d
+	github.com/lib/pq v1.2.0
 	github.com/matrix-org/dugong v0.0.0-20171220115018-ea0a4690a0d5
 	github.com/matrix-org/go-http-js-libp2p v0.0.0-20200125063821-6eb06b102bda
 	github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26
 	github.com/matrix-org/gomatrixserverlib v0.0.0-20200124100636-0c2ec91d1df5
 	github.com/matrix-org/naffka v0.0.0-20171115094957-662bfd0841d0
 	github.com/matrix-org/util v0.0.0-20171127121716-2e2df66af2f5
-	github.com/matttproud/golang_protobuf_extensions v1.0.1
 	github.com/nfnt/resize v0.0.0-20160724205520-891127d8d1b5
-	github.com/nicksnyder/go-i18n v1.8.1
-	github.com/opentracing/opentracing-go v0.0.0-20170806192116-8ebe5d4e236e
-	github.com/pelletier/go-toml v0.0.0-20170904195809-1d6b12b7cb29
-	github.com/pierrec/lz4 v0.0.0-20161206202305-5c9560bfa9ac
-	github.com/pierrec/xxHash v0.0.0-20160112165351-5a004441f897
+	github.com/opentracing/opentracing-go v1.0.2
+	github.com/pierrec/lz4 v0.0.0-20161206202305-5c9560bfa9ac // indirect
+	github.com/pierrec/xxHash v0.0.0-20160112165351-5a004441f897 // indirect
 	github.com/pkg/errors v0.8.1
-	github.com/pmezard/go-difflib v1.0.0
 	github.com/prometheus/client_golang v1.2.1
-	github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4
-	github.com/prometheus/common v0.7.0
-	github.com/prometheus/procfs v0.0.5
-	github.com/rcrowley/go-metrics v0.0.0-20161128210544-1f30fe9094a5
+	github.com/rcrowley/go-metrics v0.0.0-20161128210544-1f30fe9094a5 // indirect
 	github.com/sirupsen/logrus v1.4.2
-	github.com/stretchr/objx v0.2.0 // indirect
-	github.com/stretchr/testify v1.3.0
-	github.com/tidwall/gjson v1.1.5
-	github.com/tidwall/match v1.0.1
-	github.com/tidwall/sjson v1.0.3
-	github.com/uber-go/atomic v1.3.0
+	github.com/stretchr/testify v1.4.0 // indirect
+	github.com/uber-go/atomic v1.3.0 // indirect
 	github.com/uber/jaeger-client-go v2.15.0+incompatible
 	github.com/uber/jaeger-lib v1.5.0
-	github.com/uber/tchannel-go v0.0.0-20170927010734-b3e26487e291
-	go.uber.org/atomic v1.3.0
-	go.uber.org/multierr v0.0.0-20170829224307-fb7d312c2c04
-	go.uber.org/zap v1.7.1
-	golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2
-	golang.org/x/net v0.0.0-20190613194153-d28f0bde5980
-	golang.org/x/sys v0.0.0-20191010194322-b09406accb47
+	go.uber.org/atomic v1.3.0 // indirect
+	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550
+	golang.org/x/net v0.0.0-20190620200207-3b0461eec859 // indirect
+	golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6 // indirect
 	gopkg.in/Shopify/sarama.v1 v1.11.0
-	gopkg.in/airbrake/gobrake.v2 v2.0.9
-	gopkg.in/alecthomas/kingpin.v3-unstable v3.0.0-20170727041045-23bcc3c4eae3
-	gopkg.in/gemnasium/logrus-airbrake-hook.v2 v2.1.2
+	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 	gopkg.in/h2non/bimg.v1 v1.0.18
-	gopkg.in/macaroon.v2 v2.1.0
 	gopkg.in/yaml.v2 v2.2.2
 )

--- a/go.sum
+++ b/go.sum
@ -1,13 +1,11 @@
 github.com/Shopify/sarama v0.0.0-20170127151855-574d3147eee3 h1:j6BAEHYn1kUyW2j7kY0mOJ/R8A0qWwXpvUAEHGemm/g=
 github.com/Shopify/sarama v0.0.0-20170127151855-574d3147eee3/go.mod h1:FVkBWblsNy7DGZRfXLU0O9RCGt5g3g3yEuWXgklEdEo=
-github.com/alecthomas/gometalinter v2.0.2+incompatible/go.mod h1:qfIpQGGz3d+NmgyPBqv+LSh50emm1pt72EtcX2vKYQk=
+github.com/Shopify/toxiproxy v2.1.4+incompatible h1:TKdv8HiTLgE5wdJuEML90aBgNWsokNbMijUGhmcoBJc=
+github.com/Shopify/toxiproxy v2.1.4+incompatible/go.mod h1:OXgGpZ6Cli1/URJOF1DMxUHB2q5Ap20/P/eIdh4G0pI=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alecthomas/units v0.0.0-20190717042225-c3de453c63f4/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
-github.com/apache/thrift v0.0.0-20161221203622-b2a4d4ae21c7/go.mod h1:cp2SuWMxlEZw2r+iP2GNCdIi4C1qmUzdZFSVb+bacwQ=
-github.com/beorn7/perks v0.0.0-20160804104726-4c0e84591b9a h1:BtpsbiV638WQZwhA98cEZw2BsbnQJrbd0BI7tsy0W1c=
-github.com/beorn7/perks v0.0.0-20160804104726-4c0e84591b9a/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
@ -16,7 +14,6 @@ github.com/cespare/xxhash/v2 v2.1.0 h1:yTUvW7Vhb89inJ+8irsUqiWjh8iT6sQPZiQzI6ReG
 github.com/cespare/xxhash/v2 v2.1.0/go.mod h1:dgIUBU3pDso/gPgZ1osOZ0iQf77oPR28Tjxl5dIMyVM=
 github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd h1:qMd81Ts1T2OTKmB4acZcyKaMtRnY5Y44NuXGX2GFJ1w=
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@ -156,75 +122,67 @@ github.com/sirupsen/logrus v1.4.2 h1:SPIRibHv4MatM3XXNO2BJeFLZwZ2LvZgfQ5+UNI2im4
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--- a/mediaapi/storage/storage.go
+++ b/mediaapi/storage/storage.go
@ -16,7 +16,6 @@ package storage

 import (
 	"context"
-	"errors"
 	"net/url"

 	"github.com/matrix-org/dendrite/mediaapi/storage/postgres"
@ -36,12 +35,12 @@ type Database interface {
 func Open(dataSourceName string) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.Open(dataSourceName)
 	}
 	switch uri.Scheme {
 	case "postgres":
 		return postgres.Open(dataSourceName)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.Open(dataSourceName)
 	}
 }
--- a/publicroomsapi/publicroomsapi.go
+++ b/publicroomsapi/publicroomsapi.go
@ -17,8 +17,10 @@ package publicroomsapi
 import (
 	"github.com/matrix-org/dendrite/clientapi/auth/storage/devices"
 	"github.com/matrix-org/dendrite/common/basecomponent"
+	"github.com/matrix-org/dendrite/publicroomsapi/consumers"
 	"github.com/matrix-org/dendrite/publicroomsapi/routing"
 	"github.com/matrix-org/dendrite/publicroomsapi/storage"
+	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/sirupsen/logrus"
 )

@ -27,11 +29,19 @@ import (
 func SetupPublicRoomsAPIComponent(
 	base *basecomponent.BaseDendrite,
 	deviceDB *devices.Database,
+	rsQueryAPI roomserverAPI.RoomserverQueryAPI,
 ) {
 	publicRoomsDB, err := storage.NewPublicRoomsServerDatabase(string(base.Cfg.Database.PublicRoomsAPI))
 	if err != nil {
 		logrus.WithError(err).Panicf("failed to connect to public rooms db")
 	}

+	rsConsumer := consumers.NewOutputRoomEventConsumer(
+		base.Cfg, base.KafkaConsumer, publicRoomsDB, rsQueryAPI,
+	)
+	if err = rsConsumer.Start(); err != nil {
+		logrus.WithError(err).Panic("failed to start public rooms server consumer")
+	}
+
 	routing.Setup(base.APIMux, deviceDB, publicRoomsDB)
 }
--- a/publicroomsapi/storage/postgres/storage.go
+++ b/publicroomsapi/storage/postgres/storage.go
@ -42,15 +42,16 @@ func NewPublicRoomsServerDatabase(dataSourceName string) (*PublicRoomsServerData
 	if db, err = sql.Open("postgres", dataSourceName); err != nil {
 		return nil, err
 	}
-	partitions := common.PartitionOffsetStatements{}
-	if err = partitions.Prepare(db, "publicroomsapi"); err != nil {
+	storage := PublicRoomsServerDatabase{
+		db: db,
+	}
+	if err = storage.PartitionOffsetStatements.Prepare(db, "publicroomsapi"); err != nil {
 		return nil, err
 	}
-	statements := publicRoomsStatements{}
-	if err = statements.prepare(db); err != nil {
+	if err = storage.statements.prepare(db); err != nil {
 		return nil, err
 	}
-	return &PublicRoomsServerDatabase{db, partitions, statements}, nil
+	return &storage, nil
 }

 // GetRoomVisibility returns the room visibility as a boolean: true if the room
--- a/publicroomsapi/storage/storage.go
+++ b/publicroomsapi/storage/storage.go
@ -16,7 +16,6 @@ package storage

 import (
 	"context"
-	"errors"
 	"net/url"

 	"github.com/matrix-org/dendrite/common"
@ -39,12 +38,12 @@ type Database interface {
 func NewPublicRoomsServerDatabase(dataSourceName string) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.NewPublicRoomsServerDatabase(dataSourceName)
 	}
 	switch uri.Scheme {
 	case "postgres":
 		return postgres.NewPublicRoomsServerDatabase(dataSourceName)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.NewPublicRoomsServerDatabase(dataSourceName)
 	}
 }
--- a/roomserver/api/query.go
+++ b/roomserver/api/query.go
@ -230,6 +230,20 @@ type QueryBackfillResponse struct {
 	Events []gomatrixserverlib.Event `json:"events"`
 }

+// QueryServersInRoomAtEventRequest is a request to QueryServersInRoomAtEvent
+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"`
+}
+
 // RoomserverQueryAPI is used to query information from the room server.
 type RoomserverQueryAPI interface {
 	// Query the latest events and state for a room from the room server.
@ -303,6 +317,12 @@ type RoomserverQueryAPI interface {
 		request *QueryBackfillRequest,
 		response *QueryBackfillResponse,
 	) error
+
+	QueryServersInRoomAtEvent(
+		ctx context.Context,
+		request *QueryServersInRoomAtEventRequest,
+		response *QueryServersInRoomAtEventResponse,
+	) error
 }

 // RoomserverQueryLatestEventsAndStatePath is the HTTP path for the QueryLatestEventsAndState API.
@ -332,8 +352,11 @@ const RoomserverQueryMissingEventsPath = "/api/roomserver/queryMissingEvents"
 // RoomserverQueryStateAndAuthChainPath is the HTTP path for the QueryStateAndAuthChain API
 const RoomserverQueryStateAndAuthChainPath = "/api/roomserver/queryStateAndAuthChain"

-// RoomserverQueryBackfillPath is the HTTP path for the QueryBackfill API
-const RoomserverQueryBackfillPath = "/api/roomserver/QueryBackfill"
+// 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"

 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
 // If httpClient is nil then it uses the http.DefaultClient
@ -478,3 +501,16 @@ func (h *httpRoomserverQueryAPI) QueryBackfill(
 	apiURL := h.roomserverURL + RoomserverQueryBackfillPath
 	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)
+}
--- a/roomserver/query/query.go
+++ b/roomserver/query/query.go
@ -609,53 +609,92 @@ func (r *RoomserverQueryAPI) QueryStateAndAuthChain(
 	return err
 }

-// getAuthChain fetches the auth chain for the given auth events.
-// An auth chain is the list of all events that are referenced in the
-// auth_events section, and all their auth_events, recursively.
-// The returned set of events contain the given events.
-// Will *not* error if we don't have all auth events.
+// getAuthChain fetches the auth chain for the given auth events. An auth chain
+// is the list of all events that are referenced in the auth_events section, and
+// all their auth_events, recursively. The returned set of events contain the
+// given events. Will *not* error if we don't have all auth events.
 func getAuthChain(
 	ctx context.Context, dB RoomserverQueryAPIEventDB, authEventIDs []string,
 ) ([]gomatrixserverlib.Event, error) {
-	var authEvents []gomatrixserverlib.Event
-
-	// List of event ids to fetch. These will be added to the result and
-	// their auth events will be fetched (if they haven't been previously)
+	// List of event IDs to fetch. On each pass, these events will be requested
+	// from the database and the `eventsToFetch` will be updated with any new
+	// events that we have learned about and need to find. When `eventsToFetch`
+	// is eventually empty, we should have reached the end of the chain.
 	eventsToFetch := authEventIDs
+	authEventsMap := make(map[string]gomatrixserverlib.Event)

-	// Set of events we've already fetched.
-	fetchedEventMap := make(map[string]bool)
-
-	// Check if there's anything left to do
 	for len(eventsToFetch) > 0 {
-		// Convert eventIDs to events. First need to fetch NIDs
+		// Try to retrieve the events from the database.
 		events, err := dB.EventsFromIDs(ctx, eventsToFetch)
 		if err != nil {
 			return nil, err
 		}

-		// Work out a) which events we should add to the returned list of
-		// events and b) which of the auth events we haven't seen yet and
-		// add them to the list of events to fetch.
+		// We've now fetched these events so clear out `eventsToFetch`. Soon we may
+		// add newly discovered events to this for the next pass.
 		eventsToFetch = eventsToFetch[:0]
-		for _, event := range events {
-			fetchedEventMap[event.EventID()] = true
-			authEvents = append(authEvents, event.Event)

-			// Now we need to fetch any auth events that we haven't
-			// previously seen.
-			for _, authEventID := range event.AuthEventIDs() {
-				if !fetchedEventMap[authEventID] {
-					fetchedEventMap[authEventID] = true
-					eventsToFetch = append(eventsToFetch, authEventID)
+		for _, event := range events {
+			// Store the event in the event map - this prevents us from requesting it
+			// from the database again.
+			authEventsMap[event.EventID()] = event.Event
+
+			// Extract all of the auth events from the newly obtained event. If we
+			// don't already have a record of the event, record it in the list of
+			// events we want to request for the next pass.
+			for _, authEvent := range event.AuthEvents() {
+				if _, ok := authEventsMap[authEvent.EventID]; !ok {
+					eventsToFetch = append(eventsToFetch, authEvent.EventID)
 				}
 			}
 		}
 	}

+	// We've now retrieved all of the events we can. Flatten them down into an
+	// array and return them.
+	var authEvents []gomatrixserverlib.Event
+	for _, event := range authEventsMap {
+		authEvents = append(authEvents, event)
+	}
+
 	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
+}
+
 // SetupHTTP adds the RoomserverQueryAPI handlers to the http.ServeMux.
 // nolint: gocyclo
 func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
@ -799,4 +838,18 @@ 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}
+		}),
+	)
 }
--- a/roomserver/storage/storage.go
+++ b/roomserver/storage/storage.go
@ -16,7 +16,6 @@ package storage

 import (
 	"context"
-	"errors"
 	"net/url"

 	"github.com/matrix-org/dendrite/roomserver/api"
@ -61,12 +60,12 @@ type Database interface {
 func Open(dataSourceName string) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.Open(dataSourceName)
 	}
 	switch uri.Scheme {
 	case "postgres":
 		return postgres.Open(dataSourceName)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.Open(dataSourceName)
 	}
 }
--- a/show-expected-fail-tests.sh
+++ b/show-expected-fail-tests.sh
@ -1,45 +1,89 @@
 #! /bin/bash
+#
+# Parses a results.tap file from SyTest output and a file containing test names (a test whitelist)
+# and checks whether a test name that exists in the whitelist (that should pass), failed or not.
+#
+# An optional blacklist file can be added, also containing test names, where if a test name is
+# present, the script will not error even if the test is in the whitelist file and failed
+#
+# For each of these files, lines starting with '#' are ignored.
+#
+# Usage ./show-expected-fail-tests.sh results.tap whitelist [blacklist]

 results_file=$1
-testfile=$2
+whitelist_file=$2
+blacklist_file=$3

 fail_build=0

+if [ $# -lt 2 ]; then
+	echo "Usage: $0 results.tap whitelist [blacklist]"
+	exit 1
+fi
+
 if [ ! -f "$results_file" ]; then
-	echo "ERROR: Specified results file ${results_file} doesn't exist."
+	echo "ERROR: Specified results file '${results_file}' doesn't exist."
 	fail_build=1
 fi

-if [ ! -f "$testfile" ]; then
-	echo "ERROR: Specified testfile ${testfile} doesn't exist."
+if [ ! -f "$whitelist_file" ]; then
+	echo "ERROR: Specified test whitelist '${whitelist_file}' doesn't exist."
 	fail_build=1
 fi

+blacklisted_tests=()
+
+# Check if a blacklist file was provided
+if [ $# -eq 3 ]; then
+	# Read test blacklist file
+	if [ ! -f "$blacklist_file" ]; then
+		echo "ERROR: Specified test blacklist file '${blacklist_file}' doesn't exist."
+		fail_build=1
+	fi
+
+	# Read each line, ignoring those that start with '#'
+	blacklisted_tests=""
+	search_non_comments=$(grep -v '^#' ${blacklist_file})
+	while read -r line ; do
+		# Record the blacklisted test name
+		blacklisted_tests+=("${line}")
+	done <<< "${search_non_comments}"  # This allows us to edit blacklisted_tests in the while loop
+fi
+
 [ "$fail_build" = 0 ] || exit 1

 passed_but_expected_fail=$(grep ' # TODO passed but expected fail' ${results_file} | sed -E 's/^ok [0-9]+ (\(expected fail\) )?//' | sed -E 's/( \([0-9]+ subtests\))? # TODO passed but expected fail$//')
 tests_to_add=""
-already_in_testfile=""
+already_in_whitelist=""

-while read -r test_id; do
-	[ "${test_id}" = "" ] && continue
-	grep "${test_id}" "${testfile}" > /dev/null 2>&1
+while read -r test_name; do
+	# Ignore empty lines
+	[ "${test_name}" = "" ] && continue
+
+	grep "${test_name}" "${whitelist_file}" > /dev/null 2>&1
 	if [ "$?" != "0" ]; then
-		tests_to_add="${tests_to_add}${test_id}\n"
+		# Check if this test name is blacklisted
+		if printf '%s\n' "${blacklisted_tests[@]}" | grep -q -P "^${test_name}$"; then
+			# Don't notify about this test
+			continue
+		fi
+
+		# Append this test_name to the existing list
+		tests_to_add="${tests_to_add}${test_name}\n"
 		fail_build=1
 	else
-		already_in_testfile="${already_in_testfile}${test_id}\n"
+		already_in_whitelist="${already_in_whitelist}${test_name}\n"
 	fi
 done <<< "${passed_but_expected_fail}"

 if [ -n "${tests_to_add}" ]; then
-	echo "ERROR: The following passed tests are not present in testfile. Please append them to the file:"
+	echo "ERROR: The following passed tests are not present in $2. Please append them to the file:"
 	echo -e "${tests_to_add}"
 fi

-if [ -n "${already_in_testfile}" ]; then
-	echo "WARN: Tests in testfile still marked as expected fail:"
-	echo -e "${already_in_testfile}"
+if [ -n "${already_in_whitelist}" ]; then
+	echo "WARN: Tests in the whitelist still marked as expected fail:"
+	echo -e "${already_in_whitelist}"
 fi

 exit ${fail_build}
--- a/syncapi/consumers/clientapi.go
+++ b/syncapi/consumers/clientapi.go
@ -90,7 +90,7 @@ func (s *OutputClientDataConsumer) onMessage(msg *sarama.ConsumerMessage) error
 		}).Panicf("could not save account data")
 	}

-	s.notifier.OnNewEvent(nil, "", []string{string(msg.Key)}, types.SyncPosition{PDUPosition: pduPos})
+	s.notifier.OnNewEvent(nil, "", []string{string(msg.Key)}, types.PaginationToken{PDUPosition: pduPos})

 	return nil
 }
--- a/syncapi/consumers/roomserver.go
+++ b/syncapi/consumers/roomserver.go
@ -133,6 +133,7 @@ func (s *OutputRoomEventConsumer) onNewRoomEvent(
 		msg.AddsStateEventIDs,
 		msg.RemovesStateEventIDs,
 		msg.TransactionID,
+		false,
 	)
 	if err != nil {
 		// panic rather than continue with an inconsistent database
@ -144,7 +145,7 @@ func (s *OutputRoomEventConsumer) onNewRoomEvent(
 		}).Panicf("roomserver output log: write event failure")
 		return nil
 	}
-	s.notifier.OnNewEvent(&ev, "", nil, types.SyncPosition{PDUPosition: pduPos})
+	s.notifier.OnNewEvent(&ev, "", nil, types.PaginationToken{PDUPosition: pduPos})

 	return nil
 }
@ -161,7 +162,7 @@ func (s *OutputRoomEventConsumer) onNewInviteEvent(
 		}).Panicf("roomserver output log: write invite failure")
 		return nil
 	}
-	s.notifier.OnNewEvent(&msg.Event, "", nil, types.SyncPosition{PDUPosition: pduPos})
+	s.notifier.OnNewEvent(&msg.Event, "", nil, types.PaginationToken{PDUPosition: pduPos})
 	return nil
 }

--- a/syncapi/consumers/typingserver.go
+++ b/syncapi/consumers/typingserver.go
@ -63,7 +63,12 @@ func NewOutputTypingEventConsumer(
 // Start consuming from typing api
 func (s *OutputTypingEventConsumer) Start() error {
 	s.db.SetTypingTimeoutCallback(func(userID, roomID string, latestSyncPosition int64) {
-		s.notifier.OnNewEvent(nil, roomID, nil, types.SyncPosition{TypingPosition: latestSyncPosition})
+		s.notifier.OnNewEvent(
+			nil, roomID, nil,
+			types.PaginationToken{
+				EDUTypingPosition: types.StreamPosition(latestSyncPosition),
+			},
+		)
 	})

 	return s.typingConsumer.Start()
@ -83,7 +88,7 @@ func (s *OutputTypingEventConsumer) onMessage(msg *sarama.ConsumerMessage) error
 		"typing":  output.Event.Typing,
 	}).Debug("received data from typing server")

-	var typingPos int64
+	var typingPos types.StreamPosition
 	typingEvent := output.Event
 	if typingEvent.Typing {
 		typingPos = s.db.AddTypingUser(typingEvent.UserID, typingEvent.RoomID, output.ExpireTime)
@ -91,6 +96,6 @@ func (s *OutputTypingEventConsumer) onMessage(msg *sarama.ConsumerMessage) error
 		typingPos = s.db.RemoveTypingUser(typingEvent.UserID, typingEvent.RoomID)
 	}

-	s.notifier.OnNewEvent(nil, output.Event.RoomID, nil, types.SyncPosition{TypingPosition: typingPos})
+	s.notifier.OnNewEvent(nil, output.Event.RoomID, nil, types.PaginationToken{EDUTypingPosition: typingPos})
 	return nil
 }
--- a/syncapi/routing/messages.go
+++ b/syncapi/routing/messages.go
@ -0,0 +1,487 @@
+// Copyright 2018 New Vector Ltd
+//
+// 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 routing
+
+import (
+	"context"
+	"net/http"
+	"sort"
+	"strconv"
+
+	"github.com/matrix-org/dendrite/clientapi/httputil"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	log "github.com/sirupsen/logrus"
+)
+
+type messagesReq struct {
+	ctx              context.Context
+	db               storage.Database
+	queryAPI         api.RoomserverQueryAPI
+	federation       *gomatrixserverlib.FederationClient
+	cfg              *config.Dendrite
+	roomID           string
+	from             *types.PaginationToken
+	to               *types.PaginationToken
+	wasToProvided    bool
+	limit            int
+	backwardOrdering bool
+}
+
+type messagesResp struct {
+	Start string                          `json:"start"`
+	End   string                          `json:"end"`
+	Chunk []gomatrixserverlib.ClientEvent `json:"chunk"`
+}
+
+const defaultMessagesLimit = 10
+
+// OnIncomingMessagesRequest implements the /messages endpoint from the
+// client-server API.
+// See: https://matrix.org/docs/spec/client_server/latest.html#get-matrix-client-r0-rooms-roomid-messages
+func OnIncomingMessagesRequest(
+	req *http.Request, db storage.Database, roomID string,
+	federation *gomatrixserverlib.FederationClient,
+	queryAPI api.RoomserverQueryAPI,
+	cfg *config.Dendrite,
+) util.JSONResponse {
+	var err error
+
+	// Extract parameters from the request's URL.
+	// Pagination tokens.
+	from, err := types.NewPaginationTokenFromString(req.URL.Query().Get("from"))
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.InvalidArgumentValue("Invalid from parameter: " + err.Error()),
+		}
+	}
+
+	// Direction to return events from.
+	dir := req.URL.Query().Get("dir")
+	if dir != "b" && dir != "f" {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.MissingArgument("Bad or missing dir query parameter (should be either 'b' or 'f')"),
+		}
+	}
+	// A boolean is easier to handle in this case, especially since dir is sure
+	// to have one of the two accepted values (so dir == "f" <=> !backwardOrdering).
+	backwardOrdering := (dir == "b")
+
+	// Pagination tokens. To is optional, and its default value depends on the
+	// direction ("b" or "f").
+	var to *types.PaginationToken
+	wasToProvided := true
+	if s := req.URL.Query().Get("to"); len(s) > 0 {
+		to, err = types.NewPaginationTokenFromString(s)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidArgumentValue("Invalid to parameter: " + err.Error()),
+			}
+		}
+	} else {
+		// If "to" isn't provided, it defaults to either the earliest stream
+		// position (if we're going backward) or to the latest one (if we're
+		// going forward).
+		to, err = setToDefault(req.Context(), db, backwardOrdering, roomID)
+		if err != nil {
+			return httputil.LogThenError(req, err)
+		}
+		wasToProvided = false
+	}
+
+	// Maximum number of events to return; defaults to 10.
+	limit := defaultMessagesLimit
+	if len(req.URL.Query().Get("limit")) > 0 {
+		limit, err = strconv.Atoi(req.URL.Query().Get("limit"))
+
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidArgumentValue("limit could not be parsed into an integer: " + err.Error()),
+			}
+		}
+	}
+	// TODO: Implement filtering (#587)
+
+	// Check the room ID's format.
+	if _, _, err = gomatrixserverlib.SplitID('!', roomID); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.MissingArgument("Bad room ID: " + err.Error()),
+		}
+	}
+
+	mReq := messagesReq{
+		ctx:              req.Context(),
+		db:               db,
+		queryAPI:         queryAPI,
+		federation:       federation,
+		cfg:              cfg,
+		roomID:           roomID,
+		from:             from,
+		to:               to,
+		wasToProvided:    wasToProvided,
+		limit:            limit,
+		backwardOrdering: backwardOrdering,
+	}
+
+	clientEvents, start, end, err := mReq.retrieveEvents()
+	if err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	// Respond with the events.
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: messagesResp{
+			Chunk: clientEvents,
+			Start: start.String(),
+			End:   end.String(),
+		},
+	}
+}
+
+// retrieveEvents retrieve events from the local database for a request on
+// /messages. If there's not enough events to retrieve, it asks another
+// homeserver in the room for older events.
+// Returns an error if there was an issue talking to the database or with the
+// remote homeserver.
+func (r *messagesReq) retrieveEvents() (
+	clientEvents []gomatrixserverlib.ClientEvent, start,
+	end *types.PaginationToken, err error,
+) {
+	// Retrieve the events from the local database.
+	streamEvents, err := r.db.GetEventsInRange(
+		r.ctx, r.from, r.to, r.roomID, r.limit, r.backwardOrdering,
+	)
+	if err != nil {
+		return
+	}
+
+	var events []gomatrixserverlib.Event
+
+	// There can be two reasons for streamEvents to be empty: either we've
+	// reached the oldest event in the room (or the most recent one, depending
+	// on the ordering), or we've reached a backward extremity.
+	if len(streamEvents) == 0 {
+		if events, err = r.handleEmptyEventsSlice(); err != nil {
+			return
+		}
+	} else {
+		if events, err = r.handleNonEmptyEventsSlice(streamEvents); err != nil {
+			return
+		}
+	}
+
+	// If we didn't get any event, we don't need to proceed any further.
+	if len(events) == 0 {
+		return []gomatrixserverlib.ClientEvent{}, r.from, r.to, nil
+	}
+
+	// Sort the events to ensure we send them in the right order. We currently
+	// do that based on the event's timestamp.
+	if r.backwardOrdering {
+		sort.SliceStable(events, func(i int, j int) bool {
+			// Backward ordering is antichronological (latest event to oldest
+			// one).
+			return sortEvents(&(events[j]), &(events[i]))
+		})
+	} else {
+		sort.SliceStable(events, func(i int, j int) bool {
+			// Forward ordering is chronological (oldest event to latest one).
+			return sortEvents(&(events[i]), &(events[j]))
+		})
+	}
+
+	// Convert all of the events into client events.
+	clientEvents = gomatrixserverlib.ToClientEvents(events, gomatrixserverlib.FormatAll)
+	// Get the position of the first and the last event in the room's topology.
+	// This position is currently determined by the event's depth, so we could
+	// also use it instead of retrieving from the database. However, if we ever
+	// change the way topological positions are defined (as depth isn't the most
+	// reliable way to define it), it would be easier and less troublesome to
+	// only have to change it in one place, i.e. the database.
+	startPos, err := r.db.EventPositionInTopology(
+		r.ctx, events[0].EventID(),
+	)
+	if err != nil {
+		return
+	}
+	endPos, err := r.db.EventPositionInTopology(
+		r.ctx, events[len(events)-1].EventID(),
+	)
+	if err != nil {
+		return
+	}
+	// Generate pagination tokens to send to the client using the positions
+	// retrieved previously.
+	start = types.NewPaginationTokenFromTypeAndPosition(
+		types.PaginationTokenTypeTopology, startPos, 0,
+	)
+	end = types.NewPaginationTokenFromTypeAndPosition(
+		types.PaginationTokenTypeTopology, endPos, 0,
+	)
+
+	if r.backwardOrdering {
+		// A stream/topological position is a cursor located between two events.
+		// While they are identified in the code by the event on their right (if
+		// we consider a left to right chronological order), tokens need to refer
+		// to them by the event on their left, therefore we need to decrement the
+		// end position we send in the response if we're going backward.
+		end.PDUPosition--
+	}
+
+	// The lowest token value is 1, therefore we need to manually set it to that
+	// value if we're below it.
+	if end.PDUPosition < types.StreamPosition(1) {
+		end.PDUPosition = types.StreamPosition(1)
+	}
+
+	return clientEvents, start, end, err
+}
+
+// handleEmptyEventsSlice handles the case where the initial request to the
+// database returned an empty slice of events. It does so by checking whether
+// the set is empty because we've reached a backward extremity, and if that is
+// the case, by retrieving as much events as requested by backfilling from
+// another homeserver.
+// Returns an error if there was an issue talking with the database or
+// backfilling.
+func (r *messagesReq) handleEmptyEventsSlice() (
+	events []gomatrixserverlib.Event, err error,
+) {
+	backwardExtremities, err := r.db.BackwardExtremitiesForRoom(r.ctx, r.roomID)
+
+	// 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)
+		if err != nil {
+			return
+		}
+	} else {
+		// If not, it means the slice was empty because we reached the room's
+		// creation, so return an empty slice.
+		events = []gomatrixserverlib.Event{}
+	}
+
+	return
+}
+
+// handleNonEmptyEventsSlice handles the case where the initial request to the
+// database returned a non-empty slice of events. It does so by checking whether
+// events are missing from the expected result, and retrieve missing events
+// through backfilling if needed.
+// Returns an error if there was an issue while backfilling.
+func (r *messagesReq) handleNonEmptyEventsSlice(streamEvents []types.StreamEvent) (
+	events []gomatrixserverlib.Event, err error,
+) {
+	// Check if we have enough events.
+	isSetLargeEnough := true
+	if len(streamEvents) < r.limit {
+		if r.backwardOrdering {
+			if r.wasToProvided {
+				// The condition in the SQL query is a strict "greater than" so
+				// we need to check against to-1.
+				streamPos := types.StreamPosition(streamEvents[len(streamEvents)-1].StreamPosition)
+				isSetLargeEnough = (r.to.PDUPosition-1 == streamPos)
+			}
+		} else {
+			streamPos := types.StreamPosition(streamEvents[0].StreamPosition)
+			isSetLargeEnough = (r.from.PDUPosition-1 == streamPos)
+		}
+	}
+
+	// Check if the slice contains a backward extremity.
+	backwardExtremities, err := r.db.BackwardExtremitiesForRoom(r.ctx, r.roomID)
+	if err != nil {
+		return
+	}
+
+	// Backfill is needed if we've reached a backward extremity and need more
+	// events. It's only needed if the direction is backward.
+	if len(backwardExtremities) > 0 && !isSetLargeEnough && r.backwardOrdering {
+		var pdus []gomatrixserverlib.Event
+		// Only ask the remote server for enough events to reach the limit.
+		pdus, err = r.backfill(backwardExtremities, r.limit-len(streamEvents))
+		if err != nil {
+			return
+		}
+
+		// Append the PDUs to the list to send back to the client.
+		events = append(events, pdus...)
+	}
+
+	// Append the events ve previously retrieved locally.
+	events = append(events, r.db.StreamEventsToEvents(nil, streamEvents)...)
+
+	return
+}
+
+// containsBackwardExtremity checks if a slice of StreamEvent contains a
+// backward extremity. It does so by selecting the earliest event in the slice
+// and by checking the presence in the database of all of its parent events, and
+// considers the event itself a backward extremity if at least one of the parent
+// events doesn't exist in the database.
+// Returns an error if there was an issue with talking to the database.
+//
+// This function is unused but currently set to nolint for now until we are
+// absolutely sure that the changes in matrix-org/dendrite#847 are behaving
+// properly.
+// nolint:unused
+func (r *messagesReq) containsBackwardExtremity(events []types.StreamEvent) (bool, error) {
+	// Select the earliest retrieved event.
+	var ev *types.StreamEvent
+	if r.backwardOrdering {
+		ev = &(events[len(events)-1])
+	} else {
+		ev = &(events[0])
+	}
+	// Get the earliest retrieved event's parents.
+	prevIDs := ev.PrevEventIDs()
+	prevs, err := r.db.Events(r.ctx, prevIDs)
+	if err != nil {
+		return false, nil
+	}
+	// Check if we have all of the events we requested. If not, it means we've
+	// reached a backward extremity.
+	var eventInDB bool
+	var id string
+	// Iterate over the IDs we used in the request.
+	for _, id = range prevIDs {
+		eventInDB = false
+		// Iterate over the events we got in response.
+		for _, ev := range prevs {
+			if ev.EventID() == id {
+				eventInDB = true
+			}
+		}
+		// One occurrence of one the event's parents not being present in the
+		// database is enough to say that the event is a backward extremity.
+		if !eventInDB {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+// backfill performs a backfill request over the federation on another
+// homeserver in the room.
+// See: https://matrix.org/docs/spec/server_server/latest#get-matrix-federation-v1-backfill-roomid
+// It also stores the PDUs retrieved from the remote homeserver's response to
+// the database.
+// Returns with an empty string if the remote homeserver didn't return with any
+// 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.Event, 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 {
+		return nil, 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 {
+			srvToBackfillFrom = gomatrixserverlib.ServerName("")
+			log.Warn("Not enough servers to backfill from")
+		}
+	}
+
+	pdus := make([]gomatrixserverlib.Event, 0)
+
+	// If the roomserver responded with at least one server that isn't us,
+	// send it a request for backfill.
+	if len(srvToBackfillFrom) > 0 {
+		txn, err := r.federation.Backfill(
+			r.ctx, srvToBackfillFrom, r.roomID, limit, fromEventIDs,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		pdus = txn.PDUs
+
+		// Store the events in the database, while marking them as unfit to show
+		// up in responses to sync requests.
+		for _, pdu := range pdus {
+			if _, err = r.db.WriteEvent(
+				r.ctx, &pdu, []gomatrixserverlib.Event{}, []string{}, []string{},
+				nil, true,
+			); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return pdus, nil
+}
+
+// setToDefault returns the default value for the "to" query parameter of a
+// request to /messages if not provided. It defaults to either the earliest
+// topological position (if we're going backward) or to the latest one (if we're
+// going forward).
+// Returns an error if there was an issue with retrieving the latest position
+// from the database
+func setToDefault(
+	ctx context.Context, db storage.Database, backwardOrdering bool,
+	roomID string,
+) (to *types.PaginationToken, err error) {
+	if backwardOrdering {
+		to = types.NewPaginationTokenFromTypeAndPosition(types.PaginationTokenTypeTopology, 1, 0)
+	} else {
+		var pos types.StreamPosition
+		pos, err = db.MaxTopologicalPosition(ctx, roomID)
+		if err != nil {
+			return
+		}
+
+		to = types.NewPaginationTokenFromTypeAndPosition(types.PaginationTokenTypeTopology, pos, 0)
+	}
+
+	return
+}
+
+// sortEvents is a function to give to sort.SliceStable, and compares the
+// timestamp of two Matrix events.
+// Returns true if the first event happened before the second one, false
+// otherwise.
+func sortEvents(e1 *gomatrixserverlib.Event, e2 *gomatrixserverlib.Event) bool {
+	t := e1.OriginServerTS().Time()
+	return e2.OriginServerTS().Time().After(t)
+}
--- a/syncapi/routing/routing.go
+++ b/syncapi/routing/routing.go
@ -22,8 +22,11 @@ import (
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/clientapi/auth/storage/devices"
 	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/sync"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 )

@ -34,7 +37,12 @@ const pathPrefixR0 = "/_matrix/client/r0"
 // Due to Setup being used to call many other functions, a gocyclo nolint is
 // applied:
 // nolint: gocyclo
-func Setup(apiMux *mux.Router, srp *sync.RequestPool, syncDB storage.Database, deviceDB *devices.Database) {
+func Setup(
+	apiMux *mux.Router, srp *sync.RequestPool, syncDB storage.Database,
+	deviceDB *devices.Database, federation *gomatrixserverlib.FederationClient,
+	queryAPI api.RoomserverQueryAPI,
+	cfg *config.Dendrite,
+) {
 	r0mux := apiMux.PathPrefix(pathPrefixR0).Subrouter()

 	authData := auth.Data{
@ -71,4 +79,12 @@ func Setup(apiMux *mux.Router, srp *sync.RequestPool, syncDB storage.Database, d
 		}
 		return OnIncomingStateTypeRequest(req, syncDB, vars["roomID"], vars["type"], vars["stateKey"])
 	})).Methods(http.MethodGet, http.MethodOptions)
+
+	r0mux.Handle("/rooms/{roomID}/messages", common.MakeAuthAPI("room_messages", authData, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
+		vars, err := common.URLDecodeMapValues(mux.Vars(req))
+		if err != nil {
+			return util.ErrorResponse(err)
+		}
+		return OnIncomingMessagesRequest(req, syncDB, vars["roomID"], federation, queryAPI, cfg)
+	})).Methods(http.MethodGet, http.MethodOptions)
 }
--- a/syncapi/routing/state.go
+++ b/syncapi/routing/state.go
@ -22,6 +22,7 @@ import (
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	log "github.com/sirupsen/logrus"
@ -44,7 +45,7 @@ func OnIncomingStateRequest(req *http.Request, db storage.Database, roomID strin
 	// TODO(#287): Auth request and handle the case where the user has left (where
 	// we should return the state at the poin they left)

-	stateFilterPart := gomatrixserverlib.DefaultFilterPart()
+	stateFilterPart := gomatrix.DefaultFilterPart()
 	// TODO: stateFilterPart should not limit the number of state events (or only limits abusive number of events)

 	stateEvents, err := db.GetStateEventsForRoom(req.Context(), roomID, &stateFilterPart)
--- a/syncapi/storage/postgres/account_data_table.go
+++ b/syncapi/storage/postgres/account_data_table.go
@ -21,7 +21,8 @@ import (

 	"github.com/lib/pq"
 	"github.com/matrix-org/dendrite/common"
-	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrix"
 )

 const accountDataSchema = `
@ -89,7 +90,7 @@ func (s *accountDataStatements) prepare(db *sql.DB) (err error) {
 func (s *accountDataStatements) insertAccountData(
 	ctx context.Context,
 	userID, roomID, dataType string,
-) (pos int64, err error) {
+) (pos types.StreamPosition, err error) {
 	err = s.insertAccountDataStmt.QueryRowContext(ctx, userID, roomID, dataType).Scan(&pos)
 	return
 }
@ -97,8 +98,8 @@ func (s *accountDataStatements) insertAccountData(
 func (s *accountDataStatements) selectAccountDataInRange(
 	ctx context.Context,
 	userID string,
-	oldPos, newPos int64,
-	accountDataFilterPart *gomatrixserverlib.FilterPart,
+	oldPos, newPos types.StreamPosition,
+	accountDataFilterPart *gomatrix.FilterPart,
 ) (data map[string][]string, err error) {
 	data = make(map[string][]string)

--- a/syncapi/storage/postgres/backward_extremities_table.go
+++ b/syncapi/storage/postgres/backward_extremities_table.go
@ -0,0 +1,119 @@
+// Copyright 2018 New Vector Ltd
+//
+// 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 postgres
+
+import (
+	"context"
+	"database/sql"
+)
+
+const backwardExtremitiesSchema = `
+-- Stores output room events received from the roomserver.
+CREATE TABLE IF NOT EXISTS syncapi_backward_extremities (
+	-- The 'room_id' key for the event.
+	room_id TEXT NOT NULL,
+	-- The event ID for the event.
+	event_id TEXT NOT NULL,
+
+	PRIMARY KEY(room_id, event_id)
+);
+`
+
+const insertBackwardExtremitySQL = "" +
+	"INSERT INTO syncapi_backward_extremities (room_id, event_id)" +
+	" VALUES ($1, $2)" +
+	" ON CONFLICT DO NOTHING"
+
+const selectBackwardExtremitiesForRoomSQL = "" +
+	"SELECT event_id FROM syncapi_backward_extremities WHERE room_id = $1"
+
+const isBackwardExtremitySQL = "" +
+	"SELECT EXISTS (" +
+	" SELECT TRUE FROM syncapi_backward_extremities" +
+	" WHERE room_id = $1 AND event_id = $2" +
+	")"
+
+const deleteBackwardExtremitySQL = "" +
+	"DELETE FROM syncapi_backward_extremities WHERE room_id = $1 AND event_id = $2"
+
+type backwardExtremitiesStatements struct {
+	insertBackwardExtremityStmt          *sql.Stmt
+	selectBackwardExtremitiesForRoomStmt *sql.Stmt
+	isBackwardExtremityStmt              *sql.Stmt
+	deleteBackwardExtremityStmt          *sql.Stmt
+}
+
+func (s *backwardExtremitiesStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(backwardExtremitiesSchema)
+	if err != nil {
+		return
+	}
+	if s.insertBackwardExtremityStmt, err = db.Prepare(insertBackwardExtremitySQL); err != nil {
+		return
+	}
+	if s.selectBackwardExtremitiesForRoomStmt, err = db.Prepare(selectBackwardExtremitiesForRoomSQL); err != nil {
+		return
+	}
+	if s.isBackwardExtremityStmt, err = db.Prepare(isBackwardExtremitySQL); err != nil {
+		return
+	}
+	if s.deleteBackwardExtremityStmt, err = db.Prepare(deleteBackwardExtremitySQL); err != nil {
+		return
+	}
+	return
+}
+
+func (s *backwardExtremitiesStatements) insertsBackwardExtremity(
+	ctx context.Context, roomID, eventID string,
+) (err error) {
+	_, err = s.insertBackwardExtremityStmt.ExecContext(ctx, roomID, eventID)
+	return
+}
+
+func (s *backwardExtremitiesStatements) selectBackwardExtremitiesForRoom(
+	ctx context.Context, roomID string,
+) (eventIDs []string, err error) {
+	eventIDs = make([]string, 0)
+
+	rows, err := s.selectBackwardExtremitiesForRoomStmt.QueryContext(ctx, roomID)
+	if err != nil {
+		return
+	}
+
+	for rows.Next() {
+		var eID string
+		if err = rows.Scan(&eID); err != nil {
+			return
+		}
+
+		eventIDs = append(eventIDs, eID)
+	}
+
+	return
+}
+
+func (s *backwardExtremitiesStatements) isBackwardExtremity(
+	ctx context.Context, roomID, eventID string,
+) (isBE bool, err error) {
+	err = s.isBackwardExtremityStmt.QueryRowContext(ctx, roomID, eventID).Scan(&isBE)
+	return
+}
+
+func (s *backwardExtremitiesStatements) deleteBackwardExtremity(
+	ctx context.Context, roomID, eventID string,
+) (err error) {
+	_, err = s.insertBackwardExtremityStmt.ExecContext(ctx, roomID, eventID)
+	return
+}
--- a/syncapi/storage/postgres/current_room_state_table.go
+++ b/syncapi/storage/postgres/current_room_state_table.go
@ -22,6 +22,8 @@ import (

 	"github.com/lib/pq"
 	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
 )

@ -86,10 +88,10 @@ const selectStateEventSQL = "" +

 const selectEventsWithEventIDsSQL = "" +
 	// TODO: The session_id and transaction_id blanks are here because otherwise
-	// the rowsToStreamEvents expects there to be exactly four columns. We need to
+	// the rowsToStreamEvents expects there to be exactly five columns. We need to
 	// figure out if these really need to be in the DB, and if so, we need a
 	// better permanent fix for this. - neilalexander, 2 Jan 2020
-	"SELECT added_at, event_json, 0 AS session_id, '' AS transaction_id" +
+	"SELECT added_at, event_json, 0 AS session_id, false AS exclude_from_sync, '' AS transaction_id" +
 	" FROM syncapi_current_room_state WHERE event_id = ANY($1)"

 type currentRoomStateStatements struct {
@ -183,7 +185,7 @@ func (s *currentRoomStateStatements) selectRoomIDsWithMembership(
 // CurrentState returns all the current state events for the given room.
 func (s *currentRoomStateStatements) selectCurrentState(
 	ctx context.Context, txn *sql.Tx, roomID string,
-	stateFilterPart *gomatrixserverlib.FilterPart,
+	stateFilterPart *gomatrix.FilterPart,
 ) ([]gomatrixserverlib.Event, error) {
 	stmt := common.TxStmt(txn, s.selectCurrentStateStmt)
 	rows, err := stmt.QueryContext(ctx, roomID,
@ -212,7 +214,7 @@ func (s *currentRoomStateStatements) deleteRoomStateByEventID(

 func (s *currentRoomStateStatements) upsertRoomState(
 	ctx context.Context, txn *sql.Tx,
-	event gomatrixserverlib.Event, membership *string, addedAt int64,
+	event gomatrixserverlib.Event, membership *string, addedAt types.StreamPosition,
 ) error {
 	// Parse content as JSON and search for an "url" key
 	containsURL := false
@ -241,7 +243,7 @@ func (s *currentRoomStateStatements) upsertRoomState(

 func (s *currentRoomStateStatements) selectEventsWithEventIDs(
 	ctx context.Context, txn *sql.Tx, eventIDs []string,
-) ([]streamEvent, error) {
+) ([]types.StreamEvent, error) {
 	stmt := common.TxStmt(txn, s.selectEventsWithEventIDsStmt)
 	rows, err := stmt.QueryContext(ctx, pq.StringArray(eventIDs))
 	if err != nil {
--- a/syncapi/storage/postgres/invites_table.go
+++ b/syncapi/storage/postgres/invites_table.go
@ -20,6 +20,7 @@ import (
 	"database/sql"

 	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )

@ -86,7 +87,7 @@ func (s *inviteEventsStatements) prepare(db *sql.DB) (err error) {

 func (s *inviteEventsStatements) insertInviteEvent(
 	ctx context.Context, inviteEvent gomatrixserverlib.Event,
-) (streamPos int64, err error) {
+) (streamPos types.StreamPosition, err error) {
 	err = s.insertInviteEventStmt.QueryRowContext(
 		ctx,
 		inviteEvent.RoomID(),
@ -107,7 +108,7 @@ func (s *inviteEventsStatements) deleteInviteEvent(
 // selectInviteEventsInRange returns a map of room ID to invite event for the
 // active invites for the target user ID in the supplied range.
 func (s *inviteEventsStatements) selectInviteEventsInRange(
-	ctx context.Context, txn *sql.Tx, targetUserID string, startPos, endPos int64,
+	ctx context.Context, txn *sql.Tx, targetUserID string, startPos, endPos types.StreamPosition,
 ) (map[string]gomatrixserverlib.Event, error) {
 	stmt := common.TxStmt(txn, s.selectInviteEventsInRangeStmt)
 	rows, err := stmt.QueryContext(ctx, targetUserID, startPos, endPos)
--- a/syncapi/storage/postgres/output_room_events_table.go
+++ b/syncapi/storage/postgres/output_room_events_table.go
@ -22,6 +22,8 @@ import (
 	"sort"

 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrix"

 	"github.com/lib/pq"
 	"github.com/matrix-org/dendrite/common"
@ -35,52 +37,69 @@ CREATE SEQUENCE IF NOT EXISTS syncapi_stream_id;

 -- Stores output room events received from the roomserver.
 CREATE TABLE IF NOT EXISTS syncapi_output_room_events (
-    -- An incrementing ID which denotes the position in the log that this event resides at.
-    -- NB: 'serial' makes no guarantees to increment by 1 every time, only that it increments.
-    --     This isn't a problem for us since we just want to order by this field.
-    id BIGINT PRIMARY KEY DEFAULT nextval('syncapi_stream_id'),
-    -- The event ID for the event
-    event_id TEXT NOT NULL,
-    -- The 'room_id' key for the event.
-    room_id TEXT NOT NULL,
-    -- The JSON for the event. Stored as TEXT because this should be valid UTF-8.
-    event_json TEXT NOT NULL,
-    -- The event type e.g 'm.room.member'.
-    type TEXT NOT NULL,
-    -- The 'sender' property of the event.
-    sender TEXT NOT NULL,
-	-- true if the event content contains a url key.
-    contains_url BOOL NOT NULL,
-    -- A list of event IDs which represent a delta of added/removed room state. This can be NULL
-    -- if there is no delta.
-    add_state_ids TEXT[],
-    remove_state_ids TEXT[],
-    session_id BIGINT,  -- The client session that sent the event, if any
-    transaction_id TEXT  -- The transaction id used to send the event, if any
+  -- An incrementing ID which denotes the position in the log that this event resides at.
+  -- NB: 'serial' makes no guarantees to increment by 1 every time, only that it increments.
+  --     This isn't a problem for us since we just want to order by this field.
+  id BIGINT PRIMARY KEY DEFAULT nextval('syncapi_stream_id'),
+  -- The event ID for the event
+  event_id TEXT NOT NULL CONSTRAINT syncapi_event_id_idx UNIQUE,
+  -- The 'room_id' key for the event.
+  room_id TEXT NOT NULL,
+  -- The JSON for the event. Stored as TEXT because this should be valid UTF-8.
+  event_json TEXT NOT NULL,
+  -- The event type e.g 'm.room.member'.
+  type TEXT NOT NULL,
+  -- The 'sender' property of the event.
+  sender TEXT NOT NULL,
+  -- true if the event content contains a url key.
+  contains_url BOOL NOT NULL,
+  -- A list of event IDs which represent a delta of added/removed room state. This can be NULL
+  -- if there is no delta.
+  add_state_ids TEXT[],
+  remove_state_ids TEXT[],
+  -- The client session that sent the event, if any
+  session_id BIGINT,
+  -- The transaction id used to send the event, if any
+  transaction_id TEXT,
+  -- Should the event be excluded from responses to /sync requests. Useful for
+  -- events retrieved through backfilling that have a position in the stream
+  -- that relates to the moment these were retrieved rather than the moment these
+  -- were emitted.
+  exclude_from_sync BOOL DEFAULT FALSE
 );
-- for event selection
-CREATE UNIQUE INDEX IF NOT EXISTS syncapi_event_id_idx ON syncapi_output_room_events(event_id);
 `

 const insertEventSQL = "" +
 	"INSERT INTO syncapi_output_room_events (" +
-	"room_id, event_id, event_json, type, sender, contains_url, add_state_ids, remove_state_ids, session_id, transaction_id" +
-	") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10) RETURNING id"
+	"room_id, event_id, event_json, type, sender, contains_url, add_state_ids, remove_state_ids, session_id, transaction_id, exclude_from_sync" +
+	") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11) " +
+	"ON CONFLICT ON CONSTRAINT syncapi_event_id_idx DO UPDATE SET exclude_from_sync = $11 " +
+	"RETURNING id"

 const selectEventsSQL = "" +
-	"SELECT id, event_json, session_id, transaction_id FROM syncapi_output_room_events WHERE event_id = ANY($1)"
+	"SELECT id, event_json, session_id, exclude_from_sync, transaction_id FROM syncapi_output_room_events WHERE event_id = ANY($1)"

 const selectRecentEventsSQL = "" +
-	"SELECT id, event_json, session_id, transaction_id FROM syncapi_output_room_events" +
+	"SELECT id, event_json, session_id, exclude_from_sync, transaction_id FROM syncapi_output_room_events" +
 	" WHERE room_id = $1 AND id > $2 AND id <= $3" +
 	" ORDER BY id DESC LIMIT $4"

+const selectRecentEventsForSyncSQL = "" +
+	"SELECT id, event_json, session_id, exclude_from_sync, transaction_id FROM syncapi_output_room_events" +
+	" WHERE room_id = $1 AND id > $2 AND id <= $3 AND exclude_from_sync = FALSE" +
+	" ORDER BY id DESC LIMIT $4"
+
+const selectEarlyEventsSQL = "" +
+	"SELECT id, event_json, session_id, exclude_from_sync, transaction_id FROM syncapi_output_room_events" +
+	" WHERE room_id = $1 AND id > $2 AND id <= $3" +
+	" ORDER BY id ASC LIMIT $4"
+
 const selectMaxEventIDSQL = "" +
 	"SELECT MAX(id) FROM syncapi_output_room_events"

 // In order for us to apply the state updates correctly, rows need to be ordered in the order they were received (id).
 const selectStateInRangeSQL = "" +
-	"SELECT id, event_json, add_state_ids, remove_state_ids" +
+	"SELECT id, event_json, exclude_from_sync, add_state_ids, remove_state_ids" +
 	" FROM syncapi_output_room_events" +
 	" WHERE (id > $1 AND id <= $2) AND (add_state_ids IS NOT NULL OR remove_state_ids IS NOT NULL)" +
 	" AND ( $3::text[] IS NULL OR     sender  = ANY($3)  )" +
@ -92,11 +111,13 @@ const selectStateInRangeSQL = "" +
 	" LIMIT $8"

 type outputRoomEventsStatements struct {
-	insertEventStmt        *sql.Stmt
-	selectEventsStmt       *sql.Stmt
-	selectMaxEventIDStmt   *sql.Stmt
-	selectRecentEventsStmt *sql.Stmt
-	selectStateInRangeStmt *sql.Stmt
+	insertEventStmt               *sql.Stmt
+	selectEventsStmt              *sql.Stmt
+	selectMaxEventIDStmt          *sql.Stmt
+	selectRecentEventsStmt        *sql.Stmt
+	selectRecentEventsForSyncStmt *sql.Stmt
+	selectEarlyEventsStmt         *sql.Stmt
+	selectStateInRangeStmt        *sql.Stmt
 }

 func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
@ -116,6 +137,12 @@ func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
 	if s.selectRecentEventsStmt, err = db.Prepare(selectRecentEventsSQL); err != nil {
 		return
 	}
+	if s.selectRecentEventsForSyncStmt, err = db.Prepare(selectRecentEventsForSyncSQL); err != nil {
+		return
+	}
+	if s.selectEarlyEventsStmt, err = db.Prepare(selectEarlyEventsSQL); err != nil {
+		return
+	}
 	if s.selectStateInRangeStmt, err = db.Prepare(selectStateInRangeSQL); err != nil {
 		return
 	}
@ -126,9 +153,9 @@ func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
 // Results are bucketed based on the room ID. If the same state is overwritten multiple times between the
 // two positions, only the most recent state is returned.
 func (s *outputRoomEventsStatements) selectStateInRange(
-	ctx context.Context, txn *sql.Tx, oldPos, newPos int64,
-	stateFilterPart *gomatrixserverlib.FilterPart,
-) (map[string]map[string]bool, map[string]streamEvent, error) {
+	ctx context.Context, txn *sql.Tx, oldPos, newPos types.StreamPosition,
+	stateFilterPart *gomatrix.FilterPart,
+) (map[string]map[string]bool, map[string]types.StreamEvent, error) {
 	stmt := common.TxStmt(txn, s.selectStateInRangeStmt)

 	rows, err := stmt.QueryContext(
@ -148,19 +175,20 @@ func (s *outputRoomEventsStatements) selectStateInRange(
 	//  - For each room ID, build up an array of event IDs which represents cumulative adds/removes
 	// For each room, map cumulative event IDs to events and return. This may need to a batch SELECT based on event ID
 	// if they aren't in the event ID cache. We don't handle state deletion yet.
-	eventIDToEvent := make(map[string]streamEvent)
+	eventIDToEvent := make(map[string]types.StreamEvent)

 	// RoomID => A set (map[string]bool) of state event IDs which are between the two positions
 	stateNeeded := make(map[string]map[string]bool)

 	for rows.Next() {
 		var (
-			streamPos  int64
-			eventBytes []byte
-			addIDs     pq.StringArray
-			delIDs     pq.StringArray
+			streamPos       types.StreamPosition
+			eventBytes      []byte
+			excludeFromSync bool
+			addIDs          pq.StringArray
+			delIDs          pq.StringArray
 		)
-		if err := rows.Scan(&streamPos, &eventBytes, &addIDs, &delIDs); err != nil {
+		if err := rows.Scan(&streamPos, &eventBytes, &excludeFromSync, &addIDs, &delIDs); err != nil {
 			return nil, nil, err
 		}
 		// Sanity check for deleted state and whine if we see it. We don't need to do anything
@ -191,9 +219,10 @@ func (s *outputRoomEventsStatements) selectStateInRange(
 		}
 		stateNeeded[ev.RoomID()] = needSet

-		eventIDToEvent[ev.EventID()] = streamEvent{
-			Event:          ev,
-			streamPosition: streamPos,
+		eventIDToEvent[ev.EventID()] = types.StreamEvent{
+			Event:           ev,
+			StreamPosition:  streamPos,
+			ExcludeFromSync: excludeFromSync,
 		}
 	}

@ -220,8 +249,8 @@ func (s *outputRoomEventsStatements) selectMaxEventID(
 func (s *outputRoomEventsStatements) insertEvent(
 	ctx context.Context, txn *sql.Tx,
 	event *gomatrixserverlib.Event, addState, removeState []string,
-	transactionID *api.TransactionID,
-) (streamPos int64, err error) {
+	transactionID *api.TransactionID, excludeFromSync bool,
+) (streamPos types.StreamPosition, err error) {
 	var txnID *string
 	var sessionID *int64
 	if transactionID != nil {
@ -250,16 +279,53 @@ func (s *outputRoomEventsStatements) insertEvent(
 		pq.StringArray(removeState),
 		sessionID,
 		txnID,
+		excludeFromSync,
 	).Scan(&streamPos)
 	return
 }

-// RecentEventsInRoom returns the most recent events in the given room, up to a maximum of 'limit'.
+// selectRecentEvents returns the most recent events in the given room, up to a maximum of 'limit'.
+// If onlySyncEvents has a value of true, only returns the events that aren't marked as to exclude
+// from sync.
 func (s *outputRoomEventsStatements) selectRecentEvents(
 	ctx context.Context, txn *sql.Tx,
-	roomID string, fromPos, toPos int64, limit int,
-) ([]streamEvent, error) {
-	stmt := common.TxStmt(txn, s.selectRecentEventsStmt)
+	roomID string, fromPos, toPos types.StreamPosition, limit int,
+	chronologicalOrder bool, onlySyncEvents bool,
+) ([]types.StreamEvent, error) {
+	var stmt *sql.Stmt
+	if onlySyncEvents {
+		stmt = common.TxStmt(txn, s.selectRecentEventsForSyncStmt)
+	} else {
+		stmt = common.TxStmt(txn, s.selectRecentEventsStmt)
+	}
+
+	rows, err := stmt.QueryContext(ctx, roomID, fromPos, toPos, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close() // nolint: errcheck
+	events, err := rowsToStreamEvents(rows)
+	if err != nil {
+		return nil, err
+	}
+	if chronologicalOrder {
+		// The events need to be returned from oldest to latest, which isn't
+		// necessary the way the SQL query returns them, so a sort is necessary to
+		// ensure the events are in the right order in the slice.
+		sort.SliceStable(events, func(i int, j int) bool {
+			return events[i].StreamPosition < events[j].StreamPosition
+		})
+	}
+	return events, nil
+}
+
+// selectEarlyEvents returns the earliest events in the given room, starting
+// from a given position, up to a maximum of 'limit'.
+func (s *outputRoomEventsStatements) selectEarlyEvents(
+	ctx context.Context, txn *sql.Tx,
+	roomID string, fromPos, toPos types.StreamPosition, limit int,
+) ([]types.StreamEvent, error) {
+	stmt := common.TxStmt(txn, s.selectEarlyEventsStmt)
 	rows, err := stmt.QueryContext(ctx, roomID, fromPos, toPos, limit)
 	if err != nil {
 		return nil, err
@ -273,16 +339,16 @@ func (s *outputRoomEventsStatements) selectRecentEvents(
 	// necessarily the way the SQL query returns them, so a sort is necessary to
 	// ensure the events are in the right order in the slice.
 	sort.SliceStable(events, func(i int, j int) bool {
-		return events[i].streamPosition < events[j].streamPosition
+		return events[i].StreamPosition < events[j].StreamPosition
 	})
 	return events, nil
 }

-// Events returns the events for the given event IDs. Returns an error if any one of the event IDs given are missing
-// from the database.
+// selectEvents returns the events for the given event IDs. If an event is
+// missing from the database, it will be omitted.
 func (s *outputRoomEventsStatements) selectEvents(
 	ctx context.Context, txn *sql.Tx, eventIDs []string,
-) ([]streamEvent, error) {
+) ([]types.StreamEvent, error) {
 	stmt := common.TxStmt(txn, s.selectEventsStmt)
 	rows, err := stmt.QueryContext(ctx, pq.StringArray(eventIDs))
 	if err != nil {
@ -292,17 +358,18 @@ func (s *outputRoomEventsStatements) selectEvents(
 	return rowsToStreamEvents(rows)
 }

-func rowsToStreamEvents(rows *sql.Rows) ([]streamEvent, error) {
-	var result []streamEvent
+func rowsToStreamEvents(rows *sql.Rows) ([]types.StreamEvent, error) {
+	var result []types.StreamEvent
 	for rows.Next() {
 		var (
-			streamPos     int64
-			eventBytes    []byte
-			sessionID     *int64
-			txnID         *string
-			transactionID *api.TransactionID
+			streamPos       types.StreamPosition
+			eventBytes      []byte
+			excludeFromSync bool
+			sessionID       *int64
+			txnID           *string
+			transactionID   *api.TransactionID
 		)
-		if err := rows.Scan(&streamPos, &eventBytes, &sessionID, &txnID); err != nil {
+		if err := rows.Scan(&streamPos, &eventBytes, &sessionID, &excludeFromSync, &txnID); err != nil {
 			return nil, err
 		}
 		// TODO: Handle redacted events
@ -318,10 +385,11 @@ func rowsToStreamEvents(rows *sql.Rows) ([]streamEvent, error) {
 			}
 		}

-		result = append(result, streamEvent{
-			Event:          ev,
-			streamPosition: streamPos,
-			transactionID:  transactionID,
+		result = append(result, types.StreamEvent{
+			Event:           ev,
+			StreamPosition:  streamPos,
+			TransactionID:   transactionID,
+			ExcludeFromSync: excludeFromSync,
 		})
 	}
 	return result, nil
--- a/syncapi/storage/postgres/output_room_events_topology_table.go
+++ b/syncapi/storage/postgres/output_room_events_topology_table.go
@ -0,0 +1,188 @@
+// Copyright 2018 New Vector Ltd
+//
+// 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 postgres
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const outputRoomEventsTopologySchema = `
+-- Stores output room events received from the roomserver.
+CREATE TABLE IF NOT EXISTS syncapi_output_room_events_topology (
+	-- The event ID for the event.
+    event_id TEXT PRIMARY KEY,
+	-- The place of the event in the room's topology. This can usually be determined
+	-- from the event's depth.
+	topological_position BIGINT NOT NULL,
+    -- The 'room_id' key for the event.
+    room_id TEXT NOT NULL
+);
+-- The topological order will be used in events selection and ordering
+CREATE UNIQUE INDEX IF NOT EXISTS syncapi_event_topological_position_idx ON syncapi_output_room_events_topology(topological_position, room_id);
+`
+
+const insertEventInTopologySQL = "" +
+	"INSERT INTO syncapi_output_room_events_topology (event_id, topological_position, room_id)" +
+	" VALUES ($1, $2, $3)" +
+	" ON CONFLICT (topological_position, room_id) DO UPDATE SET event_id = $1"
+
+const selectEventIDsInRangeASCSQL = "" +
+	"SELECT event_id FROM syncapi_output_room_events_topology" +
+	" WHERE room_id = $1 AND topological_position > $2 AND topological_position <= $3" +
+	" ORDER BY topological_position ASC LIMIT $4"
+
+const selectEventIDsInRangeDESCSQL = "" +
+	"SELECT event_id FROM syncapi_output_room_events_topology" +
+	" WHERE room_id = $1 AND topological_position > $2 AND topological_position <= $3" +
+	" ORDER BY topological_position DESC LIMIT $4"
+
+const selectPositionInTopologySQL = "" +
+	"SELECT topological_position FROM syncapi_output_room_events_topology" +
+	" WHERE event_id = $1"
+
+const selectMaxPositionInTopologySQL = "" +
+	"SELECT MAX(topological_position) FROM syncapi_output_room_events_topology" +
+	" WHERE room_id = $1"
+
+const selectEventIDsFromPositionSQL = "" +
+	"SELECT event_id FROM syncapi_output_room_events_topology" +
+	" WHERE room_id = $1 AND topological_position = $2"
+
+type outputRoomEventsTopologyStatements struct {
+	insertEventInTopologyStmt       *sql.Stmt
+	selectEventIDsInRangeASCStmt    *sql.Stmt
+	selectEventIDsInRangeDESCStmt   *sql.Stmt
+	selectPositionInTopologyStmt    *sql.Stmt
+	selectMaxPositionInTopologyStmt *sql.Stmt
+	selectEventIDsFromPositionStmt  *sql.Stmt
+}
+
+func (s *outputRoomEventsTopologyStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(outputRoomEventsTopologySchema)
+	if err != nil {
+		return
+	}
+	if s.insertEventInTopologyStmt, err = db.Prepare(insertEventInTopologySQL); err != nil {
+		return
+	}
+	if s.selectEventIDsInRangeASCStmt, err = db.Prepare(selectEventIDsInRangeASCSQL); err != nil {
+		return
+	}
+	if s.selectEventIDsInRangeDESCStmt, err = db.Prepare(selectEventIDsInRangeDESCSQL); err != nil {
+		return
+	}
+	if s.selectPositionInTopologyStmt, err = db.Prepare(selectPositionInTopologySQL); err != nil {
+		return
+	}
+	if s.selectMaxPositionInTopologyStmt, err = db.Prepare(selectMaxPositionInTopologySQL); err != nil {
+		return
+	}
+	if s.selectEventIDsFromPositionStmt, err = db.Prepare(selectEventIDsFromPositionSQL); err != nil {
+		return
+	}
+	return
+}
+
+// insertEventInTopology inserts the given event in the room's topology, based
+// on the event's depth.
+func (s *outputRoomEventsTopologyStatements) insertEventInTopology(
+	ctx context.Context, event *gomatrixserverlib.Event,
+) (err error) {
+	_, err = s.insertEventInTopologyStmt.ExecContext(
+		ctx, event.EventID(), event.Depth(), event.RoomID(),
+	)
+	return
+}
+
+// selectEventIDsInRange selects the IDs of events which positions are within a
+// given range in a given room's topological order.
+// Returns an empty slice if no events match the given range.
+func (s *outputRoomEventsTopologyStatements) selectEventIDsInRange(
+	ctx context.Context, roomID string, fromPos, toPos types.StreamPosition,
+	limit int, chronologicalOrder bool,
+) (eventIDs []string, err error) {
+	// Decide on the selection's order according to whether chronological order
+	// is requested or not.
+	var stmt *sql.Stmt
+	if chronologicalOrder {
+		stmt = s.selectEventIDsInRangeASCStmt
+	} else {
+		stmt = s.selectEventIDsInRangeDESCStmt
+	}
+
+	// Query the event IDs.
+	rows, err := stmt.QueryContext(ctx, roomID, fromPos, toPos, limit)
+	if err == sql.ErrNoRows {
+		// If no event matched the request, return an empty slice.
+		return []string{}, nil
+	} else if err != nil {
+		return
+	}
+
+	// Return the IDs.
+	var eventID string
+	for rows.Next() {
+		if err = rows.Scan(&eventID); err != nil {
+			return
+		}
+		eventIDs = append(eventIDs, eventID)
+	}
+
+	return
+}
+
+// selectPositionInTopology returns the position of a given event in the
+// topology of the room it belongs to.
+func (s *outputRoomEventsTopologyStatements) selectPositionInTopology(
+	ctx context.Context, eventID string,
+) (pos types.StreamPosition, err error) {
+	err = s.selectPositionInTopologyStmt.QueryRowContext(ctx, eventID).Scan(&pos)
+	return
+}
+
+func (s *outputRoomEventsTopologyStatements) selectMaxPositionInTopology(
+	ctx context.Context, roomID string,
+) (pos types.StreamPosition, err error) {
+	err = s.selectMaxPositionInTopologyStmt.QueryRowContext(ctx, roomID).Scan(&pos)
+	return
+}
+
+// selectEventIDsFromPosition returns the IDs of all events that have a given
+// position in the topology of a given room.
+func (s *outputRoomEventsTopologyStatements) selectEventIDsFromPosition(
+	ctx context.Context, roomID string, pos types.StreamPosition,
+) (eventIDs []string, err error) {
+	// Query the event IDs.
+	rows, err := s.selectEventIDsFromPositionStmt.QueryContext(ctx, roomID, pos)
+	if err == sql.ErrNoRows {
+		// If no event matched the request, return an empty slice.
+		return []string{}, nil
+	} else if err != nil {
+		return
+	}
+	// Return the IDs.
+	var eventID string
+	for rows.Next() {
+		if err = rows.Scan(&eventID); err != nil {
+			return
+		}
+		eventIDs = append(eventIDs, eventID)
+	}
+	return
+}
--- a/syncapi/storage/postgres/syncserver.go
+++ b/syncapi/storage/postgres/syncserver.go
@ -20,13 +20,13 @@ import (
 	"database/sql"
 	"encoding/json"
 	"fmt"
-	"strconv"
 	"time"

 	"github.com/sirupsen/logrus"

 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrix"

 	// Import the postgres database driver.
 	_ "github.com/lib/pq"
@ -42,29 +42,24 @@ type stateDelta struct {
 	membership  string
 	// The PDU stream position of the latest membership event for this user, if applicable.
 	// Can be 0 if there is no membership event in this delta.
-	membershipPos int64
+	membershipPos types.StreamPosition
 }

-// Same as gomatrixserverlib.Event but also has the PDU stream position for this event.
-type streamEvent struct {
-	gomatrixserverlib.Event
-	streamPosition int64
-	transactionID  *api.TransactionID
-}
-
-// SyncServerDatabase represents a sync server datasource which manages
+// SyncServerDatasource represents a sync server datasource which manages
 // both the database for PDUs and caches for EDUs.
 type SyncServerDatasource struct {
 	db *sql.DB
 	common.PartitionOffsetStatements
-	accountData accountDataStatements
-	events      outputRoomEventsStatements
-	roomstate   currentRoomStateStatements
-	invites     inviteEventsStatements
-	typingCache *cache.TypingCache
+	accountData         accountDataStatements
+	events              outputRoomEventsStatements
+	roomstate           currentRoomStateStatements
+	invites             inviteEventsStatements
+	typingCache         *cache.TypingCache
+	topology            outputRoomEventsTopologyStatements
+	backwardExtremities backwardExtremitiesStatements
 }

-// NewSyncServerDatabase creates a new sync server database
+// NewSyncServerDatasource creates a new sync server database
 func NewSyncServerDatasource(dbDataSourceName string) (*SyncServerDatasource, error) {
 	var d SyncServerDatasource
 	var err error
@ -86,6 +81,12 @@ func NewSyncServerDatasource(dbDataSourceName string) (*SyncServerDatasource, er
 	if err := d.invites.prepare(d.db); err != nil {
 		return nil, err
 	}
+	if err := d.topology.prepare(d.db); err != nil {
+		return nil, err
+	}
+	if err := d.backwardExtremities.prepare(d.db); err != nil {
+		return nil, err
+	}
 	d.typingCache = cache.NewTypingCache()
 	return &d, nil
 }
@ -108,7 +109,46 @@ func (d *SyncServerDatasource) Events(ctx context.Context, eventIDs []string) ([

 	// We don't include a device here as we only include transaction IDs in
 	// incremental syncs.
-	return streamEventsToEvents(nil, streamEvents), nil
+	return d.StreamEventsToEvents(nil, streamEvents), nil
+}
+
+func (d *SyncServerDatasource) handleBackwardExtremities(ctx context.Context, ev *gomatrixserverlib.Event) error {
+	// If the event is already known as a backward extremity, don't consider
+	// it as such anymore now that we have it.
+	isBackwardExtremity, err := d.backwardExtremities.isBackwardExtremity(ctx, ev.RoomID(), ev.EventID())
+	if err != nil {
+		return err
+	}
+	if isBackwardExtremity {
+		if err = d.backwardExtremities.deleteBackwardExtremity(ctx, ev.RoomID(), ev.EventID()); err != nil {
+			return err
+		}
+	}
+
+	// Check if we have all of the event's previous events. If an event is
+	// missing, add it to the room's backward extremities.
+	prevEvents, err := d.events.selectEvents(ctx, nil, ev.PrevEventIDs())
+	if err != nil {
+		return err
+	}
+	var found bool
+	for _, eID := range ev.PrevEventIDs() {
+		found = false
+		for _, prevEv := range prevEvents {
+			if eID == prevEv.EventID() {
+				found = true
+			}
+		}
+
+		// If the event is missing, consider it a backward extremity.
+		if !found {
+			if err = d.backwardExtremities.insertsBackwardExtremity(ctx, ev.RoomID(), ev.EventID()); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
 }

 // WriteEvent into the database. It is not safe to call this function from multiple goroutines, as it would create races
@ -119,16 +159,26 @@ func (d *SyncServerDatasource) WriteEvent(
 	ev *gomatrixserverlib.Event,
 	addStateEvents []gomatrixserverlib.Event,
 	addStateEventIDs, removeStateEventIDs []string,
-	transactionID *api.TransactionID,
-) (pduPosition int64, returnErr error) {
+	transactionID *api.TransactionID, excludeFromSync bool,
+) (pduPosition types.StreamPosition, returnErr error) {
 	returnErr = common.WithTransaction(d.db, func(txn *sql.Tx) error {
 		var err error
-		pos, err := d.events.insertEvent(ctx, txn, ev, addStateEventIDs, removeStateEventIDs, transactionID)
+		pos, err := d.events.insertEvent(
+			ctx, txn, ev, addStateEventIDs, removeStateEventIDs, transactionID, excludeFromSync,
+		)
 		if err != nil {
 			return err
 		}
 		pduPosition = pos

+		if err = d.topology.insertEventInTopology(ctx, ev); err != nil {
+			return err
+		}
+
+		if err = d.handleBackwardExtremities(ctx, ev); err != nil {
+			return err
+		}
+
 		if len(addStateEvents) == 0 && len(removeStateEventIDs) == 0 {
 			// Nothing to do, the event may have just been a message event.
 			return nil
@ -136,14 +186,15 @@ func (d *SyncServerDatasource) WriteEvent(

 		return d.updateRoomState(ctx, txn, removeStateEventIDs, addStateEvents, pduPosition)
 	})
-	return
+
+	return pduPosition, returnErr
 }

 func (d *SyncServerDatasource) updateRoomState(
 	ctx context.Context, txn *sql.Tx,
 	removedEventIDs []string,
 	addedEvents []gomatrixserverlib.Event,
-	pduPosition int64,
+	pduPosition types.StreamPosition,
 ) error {
 	// remove first, then add, as we do not ever delete state, but do replace state which is a remove followed by an add.
 	for _, eventID := range removedEventIDs {
@ -186,7 +237,7 @@ func (d *SyncServerDatasource) GetStateEvent(
 // Returns an empty slice if no state events could be found for this room.
 // Returns an error if there was an issue with the retrieval.
 func (d *SyncServerDatasource) GetStateEventsForRoom(
-	ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.FilterPart,
+	ctx context.Context, roomID string, stateFilterPart *gomatrix.FilterPart,
 ) (stateEvents []gomatrixserverlib.Event, err error) {
 	err = common.WithTransaction(d.db, func(txn *sql.Tx) error {
 		stateEvents, err = d.roomstate.selectCurrentState(ctx, txn, roomID, stateFilterPart)
@ -195,14 +246,141 @@ func (d *SyncServerDatasource) GetStateEventsForRoom(
 	return
 }

+// GetEventsInRange retrieves all of the events on a given ordering using the
+// given extremities and limit.
+func (d *SyncServerDatasource) GetEventsInRange(
+	ctx context.Context,
+	from, to *types.PaginationToken,
+	roomID string, limit int,
+	backwardOrdering bool,
+) (events []types.StreamEvent, err error) {
+	// If the pagination token's type is types.PaginationTokenTypeTopology, the
+	// events must be retrieved from the rooms' topology table rather than the
+	// table contaning the syncapi server's whole stream of events.
+	if from.Type == types.PaginationTokenTypeTopology {
+		// Determine the backward and forward limit, i.e. the upper and lower
+		// limits to the selection in the room's topology, from the direction.
+		var backwardLimit, forwardLimit types.StreamPosition
+		if backwardOrdering {
+			// Backward ordering is antichronological (latest event to oldest
+			// one).
+			backwardLimit = to.PDUPosition
+			forwardLimit = from.PDUPosition
+		} else {
+			// Forward ordering is chronological (oldest event to latest one).
+			backwardLimit = from.PDUPosition
+			forwardLimit = to.PDUPosition
+		}
+
+		// Select the event IDs from the defined range.
+		var eIDs []string
+		eIDs, err = d.topology.selectEventIDsInRange(
+			ctx, roomID, backwardLimit, forwardLimit, limit, !backwardOrdering,
+		)
+		if err != nil {
+			return
+		}
+
+		// Retrieve the events' contents using their IDs.
+		events, err = d.events.selectEvents(ctx, nil, eIDs)
+		return
+	}
+
+	// If the pagination token's type is types.PaginationTokenTypeStream, the
+	// events must be retrieved from the table contaning the syncapi server's
+	// whole stream of events.
+
+	if backwardOrdering {
+		// When using backward ordering, we want the most recent events first.
+		if events, err = d.events.selectRecentEvents(
+			ctx, nil, roomID, to.PDUPosition, from.PDUPosition, limit, false, false,
+		); err != nil {
+			return
+		}
+	} else {
+		// When using forward ordering, we want the least recent events first.
+		if events, err = d.events.selectEarlyEvents(
+			ctx, nil, roomID, from.PDUPosition, to.PDUPosition, limit,
+		); err != nil {
+			return
+		}
+	}
+
+	return
+}
+
 // SyncPosition returns the latest positions for syncing.
-func (d *SyncServerDatasource) SyncPosition(ctx context.Context) (types.SyncPosition, error) {
+func (d *SyncServerDatasource) SyncPosition(ctx context.Context) (types.PaginationToken, error) {
 	return d.syncPositionTx(ctx, nil)
 }

+// BackwardExtremitiesForRoom returns the event IDs of all of the backward
+// extremities we know of for a given room.
+func (d *SyncServerDatasource) BackwardExtremitiesForRoom(
+	ctx context.Context, roomID string,
+) (backwardExtremities []string, err error) {
+	return d.backwardExtremities.selectBackwardExtremitiesForRoom(ctx, roomID)
+}
+
+// MaxTopologicalPosition returns the highest topological position for a given
+// room.
+func (d *SyncServerDatasource) MaxTopologicalPosition(
+	ctx context.Context, roomID string,
+) (types.StreamPosition, error) {
+	return d.topology.selectMaxPositionInTopology(ctx, roomID)
+}
+
+// EventsAtTopologicalPosition returns all of the events matching a given
+// position in the topology of a given room.
+func (d *SyncServerDatasource) EventsAtTopologicalPosition(
+	ctx context.Context, roomID string, pos types.StreamPosition,
+) ([]types.StreamEvent, error) {
+	eIDs, err := d.topology.selectEventIDsFromPosition(ctx, roomID, pos)
+	if err != nil {
+		return nil, err
+	}
+
+	return d.events.selectEvents(ctx, nil, eIDs)
+}
+
+func (d *SyncServerDatasource) EventPositionInTopology(
+	ctx context.Context, eventID string,
+) (types.StreamPosition, error) {
+	return d.topology.selectPositionInTopology(ctx, eventID)
+}
+
+// SyncStreamPosition returns the latest position in the sync stream. Returns 0 if there are no events yet.
+func (d *SyncServerDatasource) SyncStreamPosition(ctx context.Context) (types.StreamPosition, error) {
+	return d.syncStreamPositionTx(ctx, nil)
+}
+
+func (d *SyncServerDatasource) syncStreamPositionTx(
+	ctx context.Context, txn *sql.Tx,
+) (types.StreamPosition, error) {
+	maxID, err := d.events.selectMaxEventID(ctx, txn)
+	if err != nil {
+		return 0, err
+	}
+	maxAccountDataID, err := d.accountData.selectMaxAccountDataID(ctx, txn)
+	if err != nil {
+		return 0, err
+	}
+	if maxAccountDataID > maxID {
+		maxID = maxAccountDataID
+	}
+	maxInviteID, err := d.invites.selectMaxInviteID(ctx, txn)
+	if err != nil {
+		return 0, err
+	}
+	if maxInviteID > maxID {
+		maxID = maxInviteID
+	}
+	return types.StreamPosition(maxID), nil
+}
+
 func (d *SyncServerDatasource) syncPositionTx(
 	ctx context.Context, txn *sql.Tx,
-) (sp types.SyncPosition, err error) {
+) (sp types.PaginationToken, err error) {

 	maxEventID, err := d.events.selectMaxEventID(ctx, txn)
 	if err != nil {
@ -222,10 +400,8 @@ func (d *SyncServerDatasource) syncPositionTx(
 	if maxInviteID > maxEventID {
 		maxEventID = maxInviteID
 	}
-	sp.PDUPosition = maxEventID
-
-	sp.TypingPosition = d.typingCache.GetLatestSyncPosition()
-
+	sp.PDUPosition = types.StreamPosition(maxEventID)
+	sp.EDUTypingPosition = types.StreamPosition(d.typingCache.GetLatestSyncPosition())
 	return
 }

@ -234,7 +410,7 @@ func (d *SyncServerDatasource) syncPositionTx(
 func (d *SyncServerDatasource) addPDUDeltaToResponse(
 	ctx context.Context,
 	device authtypes.Device,
-	fromPos, toPos int64,
+	fromPos, toPos types.StreamPosition,
 	numRecentEventsPerRoom int,
 	wantFullState bool,
 	res *types.Response,
@ -246,7 +422,7 @@ func (d *SyncServerDatasource) addPDUDeltaToResponse(
 	var succeeded bool
 	defer common.EndTransaction(txn, &succeeded)

-	stateFilterPart := gomatrixserverlib.DefaultFilterPart() // TODO: use filter provided in request
+	stateFilterPart := gomatrix.DefaultFilterPart() // TODO: use filter provided in request

 	// Work out which rooms to return in the response. This is done by getting not only the currently
 	// joined rooms, but also which rooms have membership transitions for this user between the 2 PDU stream positions.
@ -286,7 +462,7 @@ func (d *SyncServerDatasource) addPDUDeltaToResponse(
 // addTypingDeltaToResponse adds all typing notifications to a sync response
 // since the specified position.
 func (d *SyncServerDatasource) addTypingDeltaToResponse(
-	since int64,
+	since types.PaginationToken,
 	joinedRoomIDs []string,
 	res *types.Response,
 ) error {
@ -295,7 +471,7 @@ func (d *SyncServerDatasource) addTypingDeltaToResponse(
 	var err error
 	for _, roomID := range joinedRoomIDs {
 		if typingUsers, updated := d.typingCache.GetTypingUsersIfUpdatedAfter(
-			roomID, since,
+			roomID, int64(since.EDUTypingPosition),
 		); updated {
 			ev := gomatrixserverlib.ClientEvent{
 				Type: gomatrixserverlib.MTyping,
@ -320,14 +496,14 @@ func (d *SyncServerDatasource) addTypingDeltaToResponse(
 // addEDUDeltaToResponse adds updates for EDUs of each type since fromPos if
 // the positions of that type are not equal in fromPos and toPos.
 func (d *SyncServerDatasource) addEDUDeltaToResponse(
-	fromPos, toPos types.SyncPosition,
+	fromPos, toPos types.PaginationToken,
 	joinedRoomIDs []string,
 	res *types.Response,
 ) (err error) {

-	if fromPos.TypingPosition != toPos.TypingPosition {
+	if fromPos.EDUTypingPosition != toPos.EDUTypingPosition {
 		err = d.addTypingDeltaToResponse(
-			fromPos.TypingPosition, joinedRoomIDs, res,
+			fromPos, joinedRoomIDs, res,
 		)
 	}

@ -342,7 +518,7 @@ func (d *SyncServerDatasource) addEDUDeltaToResponse(
 func (d *SyncServerDatasource) IncrementalSync(
 	ctx context.Context,
 	device authtypes.Device,
-	fromPos, toPos types.SyncPosition,
+	fromPos, toPos types.PaginationToken,
 	numRecentEventsPerRoom int,
 	wantFullState bool,
 ) (*types.Response, error) {
@ -382,7 +558,7 @@ func (d *SyncServerDatasource) getResponseWithPDUsForCompleteSync(
 	numRecentEventsPerRoom int,
 ) (
 	res *types.Response,
-	toPos types.SyncPosition,
+	toPos types.PaginationToken,
 	joinedRoomIDs []string,
 	err error,
 ) {
@ -411,7 +587,7 @@ func (d *SyncServerDatasource) getResponseWithPDUsForCompleteSync(
 		return
 	}

-	stateFilterPart := gomatrixserverlib.DefaultFilterPart() // TODO: use filter provided in request
+	stateFilterPart := gomatrix.DefaultFilterPart() // TODO: use filter provided in request

 	// Build up a /sync response. Add joined rooms.
 	for _, roomID := range joinedRoomIDs {
@ -422,27 +598,36 @@ func (d *SyncServerDatasource) getResponseWithPDUsForCompleteSync(
 		}
 		// TODO: When filters are added, we may need to call this multiple times to get enough events.
 		//       See: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L316
-		var recentStreamEvents []streamEvent
+		var recentStreamEvents []types.StreamEvent
 		recentStreamEvents, err = d.events.selectRecentEvents(
-			ctx, txn, roomID, 0, toPos.PDUPosition, numRecentEventsPerRoom,
+			ctx, txn, roomID, types.StreamPosition(0), toPos.PDUPosition,
+			numRecentEventsPerRoom, true, true,
 		)
 		if err != nil {
 			return
 		}

+		// Retrieve the backward topology position, i.e. the position of the
+		// oldest event in the room's topology.
+		var backwardTopologyPos types.StreamPosition
+		backwardTopologyPos, err = d.topology.selectPositionInTopology(ctx, recentStreamEvents[0].EventID())
+		if err != nil {
+			return nil, types.PaginationToken{}, []string{}, err
+		}
+		if backwardTopologyPos-1 <= 0 {
+			backwardTopologyPos = types.StreamPosition(1)
+		} else {
+			backwardTopologyPos--
+		}
+
 		// We don't include a device here as we don't need to send down
 		// transaction IDs for complete syncs
-		recentEvents := streamEventsToEvents(nil, recentStreamEvents)
-
+		recentEvents := d.StreamEventsToEvents(nil, recentStreamEvents)
 		stateEvents = removeDuplicates(stateEvents, recentEvents)
 		jr := types.NewJoinResponse()
-		if prevPDUPos := recentStreamEvents[0].streamPosition - 1; prevPDUPos > 0 {
-			// Use the short form of batch token for prev_batch
-			jr.Timeline.PrevBatch = strconv.FormatInt(prevPDUPos, 10)
-		} else {
-			// Use the short form of batch token for prev_batch
-			jr.Timeline.PrevBatch = "1"
-		}
+		jr.Timeline.PrevBatch = types.NewPaginationTokenFromTypeAndPosition(
+			types.PaginationTokenTypeTopology, backwardTopologyPos, 0,
+		).String()
 		jr.Timeline.Events = gomatrixserverlib.ToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
 		jr.Timeline.Limited = true
 		jr.State.Events = gomatrixserverlib.ToClientEvents(stateEvents, gomatrixserverlib.FormatSync)
@ -470,7 +655,7 @@ func (d *SyncServerDatasource) CompleteSync(

 	// Use a zero value SyncPosition for fromPos so all EDU states are added.
 	err = d.addEDUDeltaToResponse(
-		types.SyncPosition{}, toPos, joinedRoomIDs, res,
+		types.PaginationToken{}, toPos, joinedRoomIDs, res,
 	)
 	if err != nil {
 		return nil, err
@ -495,8 +680,8 @@ var txReadOnlySnapshot = sql.TxOptions{
 // If no data is retrieved, returns an empty map
 // If there was an issue with the retrieval, returns an error
 func (d *SyncServerDatasource) GetAccountDataInRange(
-	ctx context.Context, userID string, oldPos, newPos int64,
-	accountDataFilterPart *gomatrixserverlib.FilterPart,
+	ctx context.Context, userID string, oldPos, newPos types.StreamPosition,
+	accountDataFilterPart *gomatrix.FilterPart,
 ) (map[string][]string, error) {
 	return d.accountData.selectAccountDataInRange(ctx, userID, oldPos, newPos, accountDataFilterPart)
 }
@ -509,7 +694,7 @@ func (d *SyncServerDatasource) GetAccountDataInRange(
 // Returns an error if there was an issue with the upsert
 func (d *SyncServerDatasource) UpsertAccountData(
 	ctx context.Context, userID, roomID, dataType string,
-) (int64, error) {
+) (types.StreamPosition, error) {
 	return d.accountData.insertAccountData(ctx, userID, roomID, dataType)
 }

@ -518,7 +703,7 @@ func (d *SyncServerDatasource) UpsertAccountData(
 // Returns an error if there was a problem communicating with the database.
 func (d *SyncServerDatasource) AddInviteEvent(
 	ctx context.Context, inviteEvent gomatrixserverlib.Event,
-) (int64, error) {
+) (types.StreamPosition, error) {
 	return d.invites.insertInviteEvent(ctx, inviteEvent)
 }

@ -541,26 +726,26 @@ func (d *SyncServerDatasource) SetTypingTimeoutCallback(fn cache.TimeoutCallback
 // Returns the newly calculated sync position for typing notifications.
 func (d *SyncServerDatasource) AddTypingUser(
 	userID, roomID string, expireTime *time.Time,
-) int64 {
-	return d.typingCache.AddTypingUser(userID, roomID, expireTime)
+) types.StreamPosition {
+	return types.StreamPosition(d.typingCache.AddTypingUser(userID, roomID, expireTime))
 }

 // RemoveTypingUser removes a typing user from the typing cache.
 // Returns the newly calculated sync position for typing notifications.
 func (d *SyncServerDatasource) RemoveTypingUser(
 	userID, roomID string,
-) int64 {
-	return d.typingCache.RemoveUser(userID, roomID)
+) types.StreamPosition {
+	return types.StreamPosition(d.typingCache.RemoveUser(userID, roomID))
 }

 func (d *SyncServerDatasource) addInvitesToResponse(
 	ctx context.Context, txn *sql.Tx,
 	userID string,
-	fromPos, toPos int64,
+	fromPos, toPos types.StreamPosition,
 	res *types.Response,
 ) error {
 	invites, err := d.invites.selectInviteEventsInRange(
-		ctx, txn, userID, int64(fromPos), int64(toPos),
+		ctx, txn, userID, fromPos, toPos,
 	)
 	if err != nil {
 		return err
@ -576,12 +761,29 @@ func (d *SyncServerDatasource) addInvitesToResponse(
 	return nil
 }

+// Retrieve the backward topology position, i.e. the position of the
+// oldest event in the room's topology.
+func (d *SyncServerDatasource) getBackwardTopologyPos(
+	ctx context.Context,
+	events []types.StreamEvent,
+) (pos types.StreamPosition) {
+	if len(events) > 0 {
+		pos, _ = d.topology.selectPositionInTopology(ctx, events[0].EventID())
+	}
+	if pos-1 <= 0 {
+		pos = types.StreamPosition(1)
+	} else {
+		pos = pos - 1
+	}
+	return
+}
+
 // addRoomDeltaToResponse adds a room state delta to a sync response
 func (d *SyncServerDatasource) addRoomDeltaToResponse(
 	ctx context.Context,
 	device *authtypes.Device,
 	txn *sql.Tx,
-	fromPos, toPos int64,
+	fromPos, toPos types.StreamPosition,
 	delta stateDelta,
 	numRecentEventsPerRoom int,
 	res *types.Response,
@ -597,38 +799,23 @@ func (d *SyncServerDatasource) addRoomDeltaToResponse(
 		endPos = delta.membershipPos
 	}
 	recentStreamEvents, err := d.events.selectRecentEvents(
-		ctx, txn, delta.roomID, fromPos, endPos, numRecentEventsPerRoom,
+		ctx, txn, delta.roomID, types.StreamPosition(fromPos), types.StreamPosition(endPos),
+		numRecentEventsPerRoom, true, true,
 	)
 	if err != nil {
 		return err
 	}
-	recentEvents := streamEventsToEvents(device, recentStreamEvents)
+	recentEvents := d.StreamEventsToEvents(device, recentStreamEvents)
 	delta.stateEvents = removeDuplicates(delta.stateEvents, recentEvents) // roll back
-
-	var prevPDUPos int64
-
-	if len(recentEvents) == 0 {
-		if len(delta.stateEvents) == 0 {
-			// Don't bother appending empty room entries
-			return nil
-		}
-
-		// If full_state=true and since is already up to date, then we'll have
-		// state events but no recent events.
-		prevPDUPos = toPos - 1
-	} else {
-		prevPDUPos = recentStreamEvents[0].streamPosition - 1
-	}
-
-	if prevPDUPos <= 0 {
-		prevPDUPos = 1
-	}
+	backwardTopologyPos := d.getBackwardTopologyPos(ctx, recentStreamEvents)

 	switch delta.membership {
 	case gomatrixserverlib.Join:
 		jr := types.NewJoinResponse()
-		// Use the short form of batch token for prev_batch
-		jr.Timeline.PrevBatch = strconv.FormatInt(prevPDUPos, 10)
+
+		jr.Timeline.PrevBatch = types.NewPaginationTokenFromTypeAndPosition(
+			types.PaginationTokenTypeTopology, backwardTopologyPos, 0,
+		).String()
 		jr.Timeline.Events = gomatrixserverlib.ToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
 		jr.Timeline.Limited = false // TODO: if len(events) >= numRecents + 1 and then set limited:true
 		jr.State.Events = gomatrixserverlib.ToClientEvents(delta.stateEvents, gomatrixserverlib.FormatSync)
@ -639,8 +826,9 @@ func (d *SyncServerDatasource) addRoomDeltaToResponse(
 		// TODO: recentEvents may contain events that this user is not allowed to see because they are
 		//       no longer in the room.
 		lr := types.NewLeaveResponse()
-		// Use the short form of batch token for prev_batch
-		lr.Timeline.PrevBatch = strconv.FormatInt(prevPDUPos, 10)
+		lr.Timeline.PrevBatch = types.NewPaginationTokenFromTypeAndPosition(
+			types.PaginationTokenTypeTopology, backwardTopologyPos, 0,
+		).String()
 		lr.Timeline.Events = gomatrixserverlib.ToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
 		lr.Timeline.Limited = false // TODO: if len(events) >= numRecents + 1 and then set limited:true
 		lr.State.Events = gomatrixserverlib.ToClientEvents(delta.stateEvents, gomatrixserverlib.FormatSync)
@ -655,9 +843,9 @@ func (d *SyncServerDatasource) addRoomDeltaToResponse(
 func (d *SyncServerDatasource) fetchStateEvents(
 	ctx context.Context, txn *sql.Tx,
 	roomIDToEventIDSet map[string]map[string]bool,
-	eventIDToEvent map[string]streamEvent,
-) (map[string][]streamEvent, error) {
-	stateBetween := make(map[string][]streamEvent)
+	eventIDToEvent map[string]types.StreamEvent,
+) (map[string][]types.StreamEvent, error) {
+	stateBetween := make(map[string][]types.StreamEvent)
 	missingEvents := make(map[string][]string)
 	for roomID, ids := range roomIDToEventIDSet {
 		events := stateBetween[roomID]
@ -699,7 +887,7 @@ func (d *SyncServerDatasource) fetchStateEvents(

 func (d *SyncServerDatasource) fetchMissingStateEvents(
 	ctx context.Context, txn *sql.Tx, eventIDs []string,
-) ([]streamEvent, error) {
+) ([]types.StreamEvent, error) {
 	// Fetch from the events table first so we pick up the stream ID for the
 	// event.
 	events, err := d.events.selectEvents(ctx, txn, eventIDs)
@ -742,8 +930,8 @@ func (d *SyncServerDatasource) fetchMissingStateEvents(
 // A list of joined room IDs is also returned in case the caller needs it.
 func (d *SyncServerDatasource) getStateDeltas(
 	ctx context.Context, device *authtypes.Device, txn *sql.Tx,
-	fromPos, toPos int64, userID string,
-	stateFilterPart *gomatrixserverlib.FilterPart,
+	fromPos, toPos types.StreamPosition, userID string,
+	stateFilterPart *gomatrix.FilterPart,
 ) ([]stateDelta, []string, error) {
 	// Implement membership change algorithm: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L821
 	// - Get membership list changes for this user in this sync response
@ -775,7 +963,7 @@ func (d *SyncServerDatasource) getStateDeltas(
 			if membership := getMembershipFromEvent(&ev.Event, userID); membership != "" {
 				if membership == gomatrixserverlib.Join {
 					// send full room state down instead of a delta
-					var s []streamEvent
+					var s []types.StreamEvent
 					s, err = d.currentStateStreamEventsForRoom(ctx, txn, roomID, stateFilterPart)
 					if err != nil {
 						return nil, nil, err
@ -786,8 +974,8 @@ func (d *SyncServerDatasource) getStateDeltas(

 				deltas = append(deltas, stateDelta{
 					membership:    membership,
-					membershipPos: ev.streamPosition,
-					stateEvents:   streamEventsToEvents(device, stateStreamEvents),
+					membershipPos: ev.StreamPosition,
+					stateEvents:   d.StreamEventsToEvents(device, stateStreamEvents),
 					roomID:        roomID,
 				})
 				break
@ -803,7 +991,7 @@ func (d *SyncServerDatasource) getStateDeltas(
 	for _, joinedRoomID := range joinedRoomIDs {
 		deltas = append(deltas, stateDelta{
 			membership:  gomatrixserverlib.Join,
-			stateEvents: streamEventsToEvents(device, state[joinedRoomID]),
+			stateEvents: d.StreamEventsToEvents(device, state[joinedRoomID]),
 			roomID:      joinedRoomID,
 		})
 	}
@ -817,8 +1005,8 @@ func (d *SyncServerDatasource) getStateDeltas(
 // updates for other rooms.
 func (d *SyncServerDatasource) getStateDeltasForFullStateSync(
 	ctx context.Context, device *authtypes.Device, txn *sql.Tx,
-	fromPos, toPos int64, userID string,
-	stateFilterPart *gomatrixserverlib.FilterPart,
+	fromPos, toPos types.StreamPosition, userID string,
+	stateFilterPart *gomatrix.FilterPart,
 ) ([]stateDelta, []string, error) {
 	joinedRoomIDs, err := d.roomstate.selectRoomIDsWithMembership(ctx, txn, userID, gomatrixserverlib.Join)
 	if err != nil {
@ -836,7 +1024,7 @@ func (d *SyncServerDatasource) getStateDeltasForFullStateSync(
 		}
 		deltas = append(deltas, stateDelta{
 			membership:  gomatrixserverlib.Join,
-			stateEvents: streamEventsToEvents(device, s),
+			stateEvents: d.StreamEventsToEvents(device, s),
 			roomID:      joinedRoomID,
 		})
 	}
@ -857,8 +1045,8 @@ func (d *SyncServerDatasource) getStateDeltasForFullStateSync(
 				if membership != gomatrixserverlib.Join { // We've already added full state for all joined rooms above.
 					deltas = append(deltas, stateDelta{
 						membership:    membership,
-						membershipPos: ev.streamPosition,
-						stateEvents:   streamEventsToEvents(device, stateStreamEvents),
+						membershipPos: ev.StreamPosition,
+						stateEvents:   d.StreamEventsToEvents(device, stateStreamEvents),
 						roomID:        roomID,
 					})
 				}
@ -873,30 +1061,30 @@ func (d *SyncServerDatasource) getStateDeltasForFullStateSync(

 func (d *SyncServerDatasource) currentStateStreamEventsForRoom(
 	ctx context.Context, txn *sql.Tx, roomID string,
-	stateFilterPart *gomatrixserverlib.FilterPart,
-) ([]streamEvent, error) {
+	stateFilterPart *gomatrix.FilterPart,
+) ([]types.StreamEvent, error) {
 	allState, err := d.roomstate.selectCurrentState(ctx, txn, roomID, stateFilterPart)
 	if err != nil {
 		return nil, err
 	}
-	s := make([]streamEvent, len(allState))
+	s := make([]types.StreamEvent, len(allState))
 	for i := 0; i < len(s); i++ {
-		s[i] = streamEvent{Event: allState[i], streamPosition: 0}
+		s[i] = types.StreamEvent{Event: allState[i], StreamPosition: 0}
 	}
 	return s, nil
 }

-// streamEventsToEvents converts streamEvent to Event. If device is non-nil and
+// StreamEventsToEvents converts streamEvent to Event. If device is non-nil and
 // matches the streamevent.transactionID device then the transaction ID gets
 // added to the unsigned section of the output event.
-func streamEventsToEvents(device *authtypes.Device, in []streamEvent) []gomatrixserverlib.Event {
+func (d *SyncServerDatasource) StreamEventsToEvents(device *authtypes.Device, in []types.StreamEvent) []gomatrixserverlib.Event {
 	out := make([]gomatrixserverlib.Event, len(in))
 	for i := 0; i < len(in); i++ {
 		out[i] = in[i].Event
-		if device != nil && in[i].transactionID != nil {
-			if device.UserID == in[i].Sender() && device.SessionID == in[i].transactionID.SessionID {
+		if device != nil && in[i].TransactionID != nil {
+			if device.UserID == in[i].Sender() && device.SessionID == in[i].TransactionID.SessionID {
 				err := out[i].SetUnsignedField(
-					"transaction_id", in[i].transactionID.TransactionID,
+					"transaction_id", in[i].TransactionID.TransactionID,
 				)
 				if err != nil {
 					logrus.WithFields(logrus.Fields{
--- a/syncapi/storage/storage.go
+++ b/syncapi/storage/storage.go
@ -16,7 +16,6 @@ package storage

 import (
 	"context"
-	"errors"
 	"net/url"
 	"time"

@ -26,6 +25,7 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/storage/postgres"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/dendrite/typingserver/cache"
+	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
 )

@ -33,31 +33,38 @@ type Database interface {
 	common.PartitionStorer
 	AllJoinedUsersInRooms(ctx context.Context) (map[string][]string, error)
 	Events(ctx context.Context, eventIDs []string) ([]gomatrixserverlib.Event, error)
-	WriteEvent(ctx context.Context, ev *gomatrixserverlib.Event, addStateEvents []gomatrixserverlib.Event, addStateEventIDs, removeStateEventIDs []string, transactionID *api.TransactionID) (pduPosition int64, returnErr error)
+	WriteEvent(context.Context, *gomatrixserverlib.Event, []gomatrixserverlib.Event, []string, []string, *api.TransactionID, bool) (types.StreamPosition, error)
 	GetStateEvent(ctx context.Context, roomID, evType, stateKey string) (*gomatrixserverlib.Event, error)
-	GetStateEventsForRoom(ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.FilterPart) (stateEvents []gomatrixserverlib.Event, err error)
-	SyncPosition(ctx context.Context) (types.SyncPosition, error)
-	IncrementalSync(ctx context.Context, device authtypes.Device, fromPos, toPos types.SyncPosition, numRecentEventsPerRoom int, wantFullState bool) (*types.Response, error)
+	GetStateEventsForRoom(ctx context.Context, roomID string, stateFilterPart *gomatrix.FilterPart) (stateEvents []gomatrixserverlib.Event, err error)
+	SyncPosition(ctx context.Context) (types.PaginationToken, error)
+	IncrementalSync(ctx context.Context, device authtypes.Device, fromPos, toPos types.PaginationToken, numRecentEventsPerRoom int, wantFullState bool) (*types.Response, error)
 	CompleteSync(ctx context.Context, userID string, numRecentEventsPerRoom int) (*types.Response, error)
-	GetAccountDataInRange(ctx context.Context, userID string, oldPos, newPos int64, accountDataFilterPart *gomatrixserverlib.FilterPart) (map[string][]string, error)
-	UpsertAccountData(ctx context.Context, userID, roomID, dataType string) (int64, error)
-	AddInviteEvent(ctx context.Context, inviteEvent gomatrixserverlib.Event) (int64, error)
+	GetAccountDataInRange(ctx context.Context, userID string, oldPos, newPos types.StreamPosition, accountDataFilterPart *gomatrix.FilterPart) (map[string][]string, error)
+	UpsertAccountData(ctx context.Context, userID, roomID, dataType string) (types.StreamPosition, error)
+	AddInviteEvent(ctx context.Context, inviteEvent gomatrixserverlib.Event) (types.StreamPosition, error)
 	RetireInviteEvent(ctx context.Context, inviteEventID string) error
 	SetTypingTimeoutCallback(fn cache.TimeoutCallbackFn)
-	AddTypingUser(userID, roomID string, expireTime *time.Time) int64
-	RemoveTypingUser(userID, roomID string) int64
+	AddTypingUser(userID, roomID string, expireTime *time.Time) types.StreamPosition
+	RemoveTypingUser(userID, roomID string) types.StreamPosition
+	GetEventsInRange(ctx context.Context, from, to *types.PaginationToken, roomID string, limit int, backwardOrdering bool) (events []types.StreamEvent, err error)
+	EventPositionInTopology(ctx context.Context, eventID string) (types.StreamPosition, error)
+	EventsAtTopologicalPosition(ctx context.Context, roomID string, pos types.StreamPosition) ([]types.StreamEvent, error)
+	BackwardExtremitiesForRoom(ctx context.Context, roomID string) (backwardExtremities []string, err error)
+	MaxTopologicalPosition(ctx context.Context, roomID string) (types.StreamPosition, error)
+	StreamEventsToEvents(device *authtypes.Device, in []types.StreamEvent) []gomatrixserverlib.Event
+	SyncStreamPosition(ctx context.Context) (types.StreamPosition, error)
 }

 // NewPublicRoomsServerDatabase opens a database connection.
 func NewSyncServerDatasource(dataSourceName string) (Database, error) {
 	uri, err := url.Parse(dataSourceName)
 	if err != nil {
-		return nil, err
+		return postgres.NewSyncServerDatasource(dataSourceName)
 	}
 	switch uri.Scheme {
 	case "postgres":
 		return postgres.NewSyncServerDatasource(dataSourceName)
 	default:
-		return nil, errors.New("unknown schema")
+		return postgres.NewSyncServerDatasource(dataSourceName)
 	}
 }
--- a/syncapi/sync/notifier.go
+++ b/syncapi/sync/notifier.go
@ -36,7 +36,7 @@ type Notifier struct {
 	// Protects currPos and userStreams.
 	streamLock *sync.Mutex
 	// The latest sync position
-	currPos types.SyncPosition
+	currPos types.PaginationToken
 	// A map of user_id => UserStream which can be used to wake a given user's /sync request.
 	userStreams map[string]*UserStream
 	// The last time we cleaned out stale entries from the userStreams map
@ -46,7 +46,7 @@ type Notifier struct {
 // NewNotifier creates a new notifier set to the given sync position.
 // In order for this to be of any use, the Notifier needs to be told all rooms and
 // the joined users within each of them by calling Notifier.Load(*storage.SyncServerDatabase).
-func NewNotifier(pos types.SyncPosition) *Notifier {
+func NewNotifier(pos types.PaginationToken) *Notifier {
 	return &Notifier{
 		currPos:             pos,
 		roomIDToJoinedUsers: make(map[string]userIDSet),
@ -68,7 +68,7 @@ func NewNotifier(pos types.SyncPosition) *Notifier {
 // event type it handles, leaving other fields as 0.
 func (n *Notifier) OnNewEvent(
 	ev *gomatrixserverlib.Event, roomID string, userIDs []string,
-	posUpdate types.SyncPosition,
+	posUpdate types.PaginationToken,
 ) {
 	// update the current position then notify relevant /sync streams.
 	// This needs to be done PRIOR to waking up users as they will read this value.
@ -151,7 +151,7 @@ func (n *Notifier) Load(ctx context.Context, db storage.Database) error {
 }

 // CurrentPosition returns the current sync position
-func (n *Notifier) CurrentPosition() types.SyncPosition {
+func (n *Notifier) CurrentPosition() types.PaginationToken {
 	n.streamLock.Lock()
 	defer n.streamLock.Unlock()

@ -173,7 +173,7 @@ func (n *Notifier) setUsersJoinedToRooms(roomIDToUserIDs map[string][]string) {
 	}
 }

-func (n *Notifier) wakeupUsers(userIDs []string, newPos types.SyncPosition) {
+func (n *Notifier) wakeupUsers(userIDs []string, newPos types.PaginationToken) {
 	for _, userID := range userIDs {
 		stream := n.fetchUserStream(userID, false)
 		if stream != nil {
--- a/syncapi/sync/notifier_test.go
+++ b/syncapi/sync/notifier_test.go
@ -32,11 +32,11 @@ var (
 	randomMessageEvent  gomatrixserverlib.Event
 	aliceInviteBobEvent gomatrixserverlib.Event
 	bobLeaveEvent       gomatrixserverlib.Event
-	syncPositionVeryOld types.SyncPosition
-	syncPositionBefore  types.SyncPosition
-	syncPositionAfter   types.SyncPosition
-	syncPositionNewEDU  types.SyncPosition
-	syncPositionAfter2  types.SyncPosition
+	syncPositionVeryOld types.PaginationToken
+	syncPositionBefore  types.PaginationToken
+	syncPositionAfter   types.PaginationToken
+	syncPositionNewEDU  types.PaginationToken
+	syncPositionAfter2  types.PaginationToken
 )

 var (
@ -46,9 +46,9 @@ var (
 )

 func init() {
-	baseSyncPos := types.SyncPosition{
-		PDUPosition:    0,
-		TypingPosition: 0,
+	baseSyncPos := types.PaginationToken{
+		PDUPosition:       0,
+		EDUTypingPosition: 0,
 	}

 	syncPositionVeryOld = baseSyncPos
@ -61,7 +61,7 @@ func init() {
 	syncPositionAfter.PDUPosition = 12

 	syncPositionNewEDU = syncPositionAfter
-	syncPositionNewEDU.TypingPosition = 1
+	syncPositionNewEDU.EDUTypingPosition = 1

 	syncPositionAfter2 = baseSyncPos
 	syncPositionAfter2.PDUPosition = 13
@ -119,7 +119,7 @@ func TestImmediateNotification(t *testing.T) {
 		t.Fatalf("TestImmediateNotification error: %s", err)
 	}
 	if pos != syncPositionBefore {
-		t.Fatalf("TestImmediateNotification want %d, got %d", syncPositionBefore, pos)
+		t.Fatalf("TestImmediateNotification want %v, got %v", syncPositionBefore, pos)
 	}
 }

@ -138,7 +138,7 @@ func TestNewEventAndJoinedToRoom(t *testing.T) {
 			t.Errorf("TestNewEventAndJoinedToRoom error: %s", err)
 		}
 		if pos != syncPositionAfter {
-			t.Errorf("TestNewEventAndJoinedToRoom want %d, got %d", syncPositionAfter, pos)
+			t.Errorf("TestNewEventAndJoinedToRoom want %v, got %v", syncPositionAfter, pos)
 		}
 		wg.Done()
 	}()
@ -166,7 +166,7 @@ func TestNewInviteEventForUser(t *testing.T) {
 			t.Errorf("TestNewInviteEventForUser error: %s", err)
 		}
 		if pos != syncPositionAfter {
-			t.Errorf("TestNewInviteEventForUser want %d, got %d", syncPositionAfter, pos)
+			t.Errorf("TestNewInviteEventForUser want %v, got %v", syncPositionAfter, pos)
 		}
 		wg.Done()
 	}()
@ -194,7 +194,7 @@ func TestEDUWakeup(t *testing.T) {
 			t.Errorf("TestNewInviteEventForUser error: %s", err)
 		}
 		if pos != syncPositionNewEDU {
-			t.Errorf("TestNewInviteEventForUser want %d, got %d", syncPositionNewEDU, pos)
+			t.Errorf("TestNewInviteEventForUser want %v, got %v", syncPositionNewEDU, pos)
 		}
 		wg.Done()
 	}()
@ -222,7 +222,7 @@ func TestMultipleRequestWakeup(t *testing.T) {
 			t.Errorf("TestMultipleRequestWakeup error: %s", err)
 		}
 		if pos != syncPositionAfter {
-			t.Errorf("TestMultipleRequestWakeup want %d, got %d", syncPositionAfter, pos)
+			t.Errorf("TestMultipleRequestWakeup want %v, got %v", syncPositionAfter, pos)
 		}
 		wg.Done()
 	}
@ -262,7 +262,7 @@ func TestNewEventAndWasPreviouslyJoinedToRoom(t *testing.T) {
 			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom error: %s", err)
 		}
 		if pos != syncPositionAfter {
-			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom want %d, got %d", syncPositionAfter, pos)
+			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom want %v, got %v", syncPositionAfter, pos)
 		}
 		leaveWG.Done()
 	}()
@ -281,7 +281,7 @@ func TestNewEventAndWasPreviouslyJoinedToRoom(t *testing.T) {
 			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom error: %s", err)
 		}
 		if pos != syncPositionAfter2 {
-			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom want %d, got %d", syncPositionAfter2, pos)
+			t.Errorf("TestNewEventAndWasPreviouslyJoinedToRoom want %v, got %v", syncPositionAfter2, pos)
 		}
 		aliceWG.Done()
 	}()
@ -305,14 +305,14 @@ func TestNewEventAndWasPreviouslyJoinedToRoom(t *testing.T) {
 	time.Sleep(1 * time.Millisecond)
 }

-func waitForEvents(n *Notifier, req syncRequest) (types.SyncPosition, error) {
+func waitForEvents(n *Notifier, req syncRequest) (types.PaginationToken, error) {
 	listener := n.GetListener(req)
 	defer listener.Close()

 	select {
 	case <-time.After(5 * time.Second):
-		return types.SyncPosition{}, fmt.Errorf(
-			"waitForEvents timed out waiting for %s (pos=%d)", req.device.UserID, req.since,
+		return types.PaginationToken{}, fmt.Errorf(
+			"waitForEvents timed out waiting for %s (pos=%v)", req.device.UserID, req.since,
 		)
 	case <-listener.GetNotifyChannel(*req.since):
 		p := listener.GetSyncPosition()
@ -337,7 +337,7 @@ func lockedFetchUserStream(n *Notifier, userID string) *UserStream {
 	return n.fetchUserStream(userID, true)
 }

-func newTestSyncRequest(userID string, since types.SyncPosition) syncRequest {
+func newTestSyncRequest(userID string, since types.PaginationToken) syncRequest {
 	return syncRequest{
 		device:        authtypes.Device{UserID: userID},
 		timeout:       1 * time.Minute,
--- a/syncapi/sync/request.go
+++ b/syncapi/sync/request.go
@ -16,10 +16,8 @@ package sync

 import (
 	"context"
-	"errors"
 	"net/http"
 	"strconv"
-	"strings"
 	"time"

 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
@ -38,7 +36,7 @@ type syncRequest struct {
 	device        authtypes.Device
 	limit         int
 	timeout       time.Duration
-	since         *types.SyncPosition // nil means that no since token was supplied
+	since         *types.PaginationToken // nil means that no since token was supplied
 	wantFullState bool
 	log           *log.Entry
 }
@ -47,7 +45,7 @@ func newSyncRequest(req *http.Request, device authtypes.Device) (*syncRequest, e
 	timeout := getTimeout(req.URL.Query().Get("timeout"))
 	fullState := req.URL.Query().Get("full_state")
 	wantFullState := fullState != "" && fullState != "false"
-	since, err := getSyncStreamPosition(req.URL.Query().Get("since"))
+	since, err := getPaginationToken(req.URL.Query().Get("since"))
 	if err != nil {
 		return nil, err
 	}
@ -75,41 +73,14 @@ func getTimeout(timeoutMS string) time.Duration {
 }

 // getSyncStreamPosition tries to parse a 'since' token taken from the API to a
-// types.SyncPosition. If the string is empty then (nil, nil) is returned.
+// types.PaginationToken. If the string is empty then (nil, nil) is returned.
 // There are two forms of tokens: The full length form containing all PDU and EDU
 // positions separated by "_", and the short form containing only the PDU
 // position. Short form can be used for, e.g., `prev_batch` tokens.
-func getSyncStreamPosition(since string) (*types.SyncPosition, error) {
+func getPaginationToken(since string) (*types.PaginationToken, error) {
 	if since == "" {
 		return nil, nil
 	}

-	posStrings := strings.Split(since, "_")
-	if len(posStrings) != 2 && len(posStrings) != 1 {
-		// A token can either be full length or short (PDU-only).
-		return nil, errors.New("malformed batch token")
-	}
-
-	positions := make([]int64, len(posStrings))
-	for i, posString := range posStrings {
-		pos, err := strconv.ParseInt(posString, 10, 64)
-		if err != nil {
-			return nil, err
-		}
-		positions[i] = pos
-	}
-
-	if len(positions) == 2 {
-		// Full length token; construct SyncPosition with every entry in
-		// `positions`. These entries must have the same order with the fields
-		// in struct SyncPosition, so we disable the govet check below.
-		return &types.SyncPosition{ //nolint:govet
-			positions[0], positions[1],
-		}, nil
-	} else {
-		// Token with PDU position only
-		return &types.SyncPosition{
-			PDUPosition: positions[0],
-		}, nil
-	}
+	return types.NewPaginationTokenFromString(since)
 }
--- a/syncapi/sync/requestpool.go
+++ b/syncapi/sync/requestpool.go
@ -24,6 +24,7 @@ import (
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	log "github.com/sirupsen/logrus"
@ -129,7 +130,7 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *authtype
 	}
 }

-func (rp *RequestPool) currentSyncForUser(req syncRequest, latestPos types.SyncPosition) (res *types.Response, err error) {
+func (rp *RequestPool) currentSyncForUser(req syncRequest, latestPos types.PaginationToken) (res *types.Response, err error) {
 	// TODO: handle ignored users
 	if req.since == nil {
 		res, err = rp.db.CompleteSync(req.ctx, req.device.UserID, req.limit)
@ -141,14 +142,14 @@ func (rp *RequestPool) currentSyncForUser(req syncRequest, latestPos types.SyncP
 		return
 	}

-	accountDataFilter := gomatrixserverlib.DefaultFilterPart() // TODO: use filter provided in req instead
-	res, err = rp.appendAccountData(res, req.device.UserID, req, latestPos.PDUPosition, &accountDataFilter)
+	accountDataFilter := gomatrix.DefaultFilterPart() // TODO: use filter provided in req instead
+	res, err = rp.appendAccountData(res, req.device.UserID, req, int64(latestPos.PDUPosition), &accountDataFilter)
 	return
 }

 func (rp *RequestPool) appendAccountData(
 	data *types.Response, userID string, req syncRequest, currentPos int64,
-	accountDataFilter *gomatrixserverlib.FilterPart,
+	accountDataFilter *gomatrix.FilterPart,
 ) (*types.Response, error) {
 	// TODO: Account data doesn't have a sync position of its own, meaning that
 	// account data might be sent multiple time to the client if multiple account
@ -182,7 +183,11 @@ func (rp *RequestPool) appendAccountData(
 	}

 	// Sync is not initial, get all account data since the latest sync
-	dataTypes, err := rp.db.GetAccountDataInRange(req.ctx, userID, req.since.PDUPosition, currentPos, accountDataFilter)
+	dataTypes, err := rp.db.GetAccountDataInRange(
+		req.ctx, userID,
+		types.StreamPosition(req.since.PDUPosition), types.StreamPosition(currentPos),
+		accountDataFilter,
+	)
 	if err != nil {
 		return nil, err
 	}
--- a/syncapi/sync/userstream.go
+++ b/syncapi/sync/userstream.go
@ -35,7 +35,7 @@ type UserStream struct {
 	// Closed when there is an update.
 	signalChannel chan struct{}
 	// The last sync position that there may have been an update for the user
-	pos types.SyncPosition
+	pos types.PaginationToken
 	// The last time when we had some listeners waiting
 	timeOfLastChannel time.Time
 	// The number of listeners waiting
@ -51,7 +51,7 @@ type UserStreamListener struct {
 }

 // NewUserStream creates a new user stream
-func NewUserStream(userID string, currPos types.SyncPosition) *UserStream {
+func NewUserStream(userID string, currPos types.PaginationToken) *UserStream {
 	return &UserStream{
 		UserID:            userID,
 		timeOfLastChannel: time.Now(),
@ -85,7 +85,7 @@ func (s *UserStream) GetListener(ctx context.Context) UserStreamListener {
 }

 // Broadcast a new sync position for this user.
-func (s *UserStream) Broadcast(pos types.SyncPosition) {
+func (s *UserStream) Broadcast(pos types.PaginationToken) {
 	s.lock.Lock()
 	defer s.lock.Unlock()

@ -120,7 +120,7 @@ func (s *UserStream) TimeOfLastNonEmpty() time.Time {

 // GetStreamPosition returns last sync position which the UserStream was
 // notified about
-func (s *UserStreamListener) GetSyncPosition() types.SyncPosition {
+func (s *UserStreamListener) GetSyncPosition() types.PaginationToken {
 	s.userStream.lock.Lock()
 	defer s.userStream.lock.Unlock()

@ -132,7 +132,7 @@ func (s *UserStreamListener) GetSyncPosition() types.SyncPosition {
 // sincePos specifies from which point we want to be notified about. If there
 // has already been an update after sincePos we'll return a closed channel
 // immediately.
-func (s *UserStreamListener) GetNotifyChannel(sincePos types.SyncPosition) <-chan struct{} {
+func (s *UserStreamListener) GetNotifyChannel(sincePos types.PaginationToken) <-chan struct{} {
 	s.userStream.lock.Lock()
 	defer s.userStream.lock.Unlock()

--- a/syncapi/syncapi.go
+++ b/syncapi/syncapi.go
@ -21,7 +21,9 @@ import (

 	"github.com/matrix-org/dendrite/clientapi/auth/storage/accounts"
 	"github.com/matrix-org/dendrite/common/basecomponent"
+	"github.com/matrix-org/dendrite/common/config"
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrixserverlib"

 	"github.com/matrix-org/dendrite/clientapi/auth/storage/devices"
 	"github.com/matrix-org/dendrite/syncapi/consumers"
@ -37,6 +39,8 @@ func SetupSyncAPIComponent(
 	deviceDB *devices.Database,
 	accountsDB *accounts.Database,
 	queryAPI api.RoomserverQueryAPI,
+	federation *gomatrixserverlib.FederationClient,
+	cfg *config.Dendrite,
 ) {
 	syncDB, err := storage.NewSyncServerDatasource(string(base.Cfg.Database.SyncAPI))
 	if err != nil {
@ -77,5 +81,5 @@ func SetupSyncAPIComponent(
 		logrus.WithError(err).Panicf("failed to start typing server consumer")
 	}

-	routing.Setup(base.APIMux, requestPool, syncDB, deviceDB)
+	routing.Setup(base.APIMux, requestPool, syncDB, deviceDB, federation, queryAPI, cfg)
 }
--- a/syncapi/types/types.go
+++ b/syncapi/types/types.go
@ -16,45 +16,144 @@ package types

 import (
 	"encoding/json"
+	"errors"
+	"fmt"
 	"strconv"
+	"strings"

+	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
 )

-// SyncPosition contains the PDU and EDU stream sync positions for a client.
-type SyncPosition struct {
-	// PDUPosition is the stream position for PDUs the client is at.
-	PDUPosition int64
-	// TypingPosition is the client's position for typing notifications.
-	TypingPosition int64
+var (
+	// ErrInvalidPaginationTokenType is returned when an attempt at creating a
+	// new instance of PaginationToken with an invalid type (i.e. neither "s"
+	// nor "t").
+	ErrInvalidPaginationTokenType = fmt.Errorf("Pagination token has an unknown prefix (should be either s or t)")
+	// ErrInvalidPaginationTokenLen is returned when the pagination token is an
+	// invalid length
+	ErrInvalidPaginationTokenLen = fmt.Errorf("Pagination token has an invalid length")
+)
+
+// StreamPosition represents the offset in the sync stream a client is at.
+type StreamPosition int64
+
+// Same as gomatrixserverlib.Event but also has the PDU stream position for this event.
+type StreamEvent struct {
+	gomatrixserverlib.Event
+	StreamPosition  StreamPosition
+	TransactionID   *api.TransactionID
+	ExcludeFromSync bool
 }

-// String implements the Stringer interface.
-func (sp SyncPosition) String() string {
-	return strconv.FormatInt(sp.PDUPosition, 10) + "_" +
-		strconv.FormatInt(sp.TypingPosition, 10)
+// PaginationTokenType represents the type of a pagination token.
+// It can be either "s" (representing a position in the whole stream of events)
+// or "t" (representing a position in a room's topology/depth).
+type PaginationTokenType string
+
+const (
+	// PaginationTokenTypeStream represents a position in the server's whole
+	// stream of events
+	PaginationTokenTypeStream PaginationTokenType = "s"
+	// PaginationTokenTypeTopology represents a position in a room's topology.
+	PaginationTokenTypeTopology PaginationTokenType = "t"
+)
+
+// PaginationToken represents a pagination token, used for interactions with
+// /sync or /messages, for example.
+type PaginationToken struct {
+	//Position StreamPosition
+	Type              PaginationTokenType
+	PDUPosition       StreamPosition
+	EDUTypingPosition StreamPosition
 }

-// IsAfter returns whether one SyncPosition refers to states newer than another SyncPosition.
-func (sp SyncPosition) IsAfter(other SyncPosition) bool {
-	return sp.PDUPosition > other.PDUPosition ||
-		sp.TypingPosition > other.TypingPosition
+// NewPaginationTokenFromString takes a string of the form "xyyyy..." where "x"
+// represents the type of a pagination token and "yyyy..." the token itself, and
+// parses it in order to create a new instance of PaginationToken. Returns an
+// error if the token couldn't be parsed into an int64, or if the token type
+// isn't a known type (returns ErrInvalidPaginationTokenType in the latter
+// case).
+func NewPaginationTokenFromString(s string) (token *PaginationToken, err error) {
+	if len(s) == 0 {
+		return nil, ErrInvalidPaginationTokenLen
+	}
+
+	token = new(PaginationToken)
+	var positions []string
+
+	switch t := PaginationTokenType(s[:1]); t {
+	case PaginationTokenTypeStream, PaginationTokenTypeTopology:
+		token.Type = t
+		positions = strings.Split(s[1:], "_")
+	default:
+		token.Type = PaginationTokenTypeStream
+		positions = strings.Split(s, "_")
+	}
+
+	// Try to get the PDU position.
+	if len(positions) >= 1 {
+		if pduPos, err := strconv.ParseInt(positions[0], 10, 64); err != nil {
+			return nil, err
+		} else if pduPos < 0 {
+			return nil, errors.New("negative PDU position not allowed")
+		} else {
+			token.PDUPosition = StreamPosition(pduPos)
+		}
+	}
+
+	// Try to get the typing position.
+	if len(positions) >= 2 {
+		if typPos, err := strconv.ParseInt(positions[1], 10, 64); err != nil {
+			return nil, err
+		} else if typPos < 0 {
+			return nil, errors.New("negative EDU typing position not allowed")
+		} else {
+			token.EDUTypingPosition = StreamPosition(typPos)
+		}
+	}
+
+	return
 }

-// WithUpdates returns a copy of the SyncPosition with updates applied from another SyncPosition.
-// If the latter SyncPosition contains a field that is not 0, it is considered an update,
-// and its value will replace the corresponding value in the SyncPosition on which WithUpdates is called.
-func (sp SyncPosition) WithUpdates(other SyncPosition) SyncPosition {
-	ret := sp
+// NewPaginationTokenFromTypeAndPosition takes a PaginationTokenType and a
+// StreamPosition and returns an instance of PaginationToken.
+func NewPaginationTokenFromTypeAndPosition(
+	t PaginationTokenType, pdupos StreamPosition, typpos StreamPosition,
+) (p *PaginationToken) {
+	return &PaginationToken{
+		Type:              t,
+		PDUPosition:       pdupos,
+		EDUTypingPosition: typpos,
+	}
+}
+
+// String translates a PaginationToken to a string of the "xyyyy..." (see
+// NewPaginationToken to know what it represents).
+func (p *PaginationToken) String() string {
+	return fmt.Sprintf("%s%d_%d", p.Type, p.PDUPosition, p.EDUTypingPosition)
+}
+
+// WithUpdates returns a copy of the PaginationToken with updates applied from another PaginationToken.
+// If the latter PaginationToken contains a field that is not 0, it is considered an update,
+// and its value will replace the corresponding value in the PaginationToken on which WithUpdates is called.
+func (pt *PaginationToken) WithUpdates(other PaginationToken) PaginationToken {
+	ret := *pt
 	if other.PDUPosition != 0 {
 		ret.PDUPosition = other.PDUPosition
 	}
-	if other.TypingPosition != 0 {
-		ret.TypingPosition = other.TypingPosition
+	if other.EDUTypingPosition != 0 {
+		ret.EDUTypingPosition = other.EDUTypingPosition
 	}
 	return ret
 }

+// IsAfter returns whether one PaginationToken refers to states newer than another PaginationToken.
+func (sp *PaginationToken) IsAfter(other PaginationToken) bool {
+	return sp.PDUPosition > other.PDUPosition ||
+		sp.EDUTypingPosition > other.EDUTypingPosition
+}
+
 // PrevEventRef represents a reference to a previous event in a state event upgrade
 type PrevEventRef struct {
 	PrevContent   json.RawMessage `json:"prev_content"`
@ -79,9 +178,9 @@ type Response struct {
 }

 // NewResponse creates an empty response with initialised maps.
-func NewResponse(pos SyncPosition) *Response {
+func NewResponse(token PaginationToken) *Response {
 	res := Response{
-		NextBatch: pos.String(),
+		NextBatch: token.String(),
 	}
 	// Pre-initialise the maps. Synapse will return {} even if there are no rooms under a specific section,
 	// so let's do the same thing. Bonus: this means we can't get dreaded 'assignment to entry in nil map' errors.
@ -96,6 +195,14 @@ func NewResponse(pos SyncPosition) *Response {
 	res.AccountData.Events = make([]gomatrixserverlib.ClientEvent, 0)
 	res.Presence.Events = make([]gomatrixserverlib.ClientEvent, 0)

+	// Fill next_batch with a pagination token. Since this is a response to a sync request, we can assume
+	// we'll always return a stream token.
+	res.NextBatch = NewPaginationTokenFromTypeAndPosition(
+		PaginationTokenTypeStream,
+		StreamPosition(token.PDUPosition),
+		StreamPosition(token.EDUTypingPosition),
+	).String()
+
 	return &res
 }

--- a/syncapi/types/types_test.go
+++ b/syncapi/types/types_test.go
@ -0,0 +1,52 @@
+package types
+
+import "testing"
+
+func TestNewPaginationTokenFromString(t *testing.T) {
+	shouldPass := map[string]PaginationToken{
+		"2": PaginationToken{
+			Type:        PaginationTokenTypeStream,
+			PDUPosition: 2,
+		},
+		"s4": PaginationToken{
+			Type:        PaginationTokenTypeStream,
+			PDUPosition: 4,
+		},
+		"s3_1": PaginationToken{
+			Type:              PaginationTokenTypeStream,
+			PDUPosition:       3,
+			EDUTypingPosition: 1,
+		},
+		"t3_1_4": PaginationToken{
+			Type:              PaginationTokenTypeTopology,
+			PDUPosition:       3,
+			EDUTypingPosition: 1,
+		},
+	}
+
+	shouldFail := []string{
+		"",
+		"s_1",
+		"s_",
+		"a3_4",
+		"b",
+		"b-1",
+		"-4",
+	}
+
+	for test, expected := range shouldPass {
+		result, err := NewPaginationTokenFromString(test)
+		if err != nil {
+			t.Error(err)
+		}
+		if *result != expected {
+			t.Errorf("expected %v but got %v", expected.String(), result.String())
+		}
+	}
+
+	for _, test := range shouldFail {
+		if _, err := NewPaginationTokenFromString(test); err == nil {
+			t.Errorf("input '%v' should have errored but didn't", test)
+		}
+	}
+}
--- a/18
+++ b/18
@ -0,0 +1,18 @@
+# Blacklisted due to flakiness
+Remote users can join room by alias
+
+# Blacklisted due to flakiness
+POST /login can log in as a user with just the local part of the id
+
+# Blacklisted due to flakiness
+avatar_url updates affect room member events
+
+# Blacklisted due to flakiness
+Room members can override their displayname on a room-specific basis
+
+# Blacklisted due to flakiness
+Alias creators can delete alias with no ops
+
+# Blacklisted because matrix-org/dendrite#847 might have broken it but we're not
+# really sure and we need it pretty badly anyway
+Real non-joined users can get individual state for world_readable rooms after leaving
--- a/33
+++ b/33
@ -17,10 +17,6 @@ POST /register rejects registration of usernames with 'é'
 POST /register rejects registration of usernames with '\n'
 POST /register rejects registration of usernames with '''
 GET /login yields a set of flows
-POST /login can log in as a user
-POST /login can log in as a user with just the local part of the id
-POST /login as non-existing user is rejected
-POST /login wrong password is rejected
 GET /events initially
 GET /initialSync initially
 Version responds 200 OK with valid structure
@ -55,7 +51,6 @@ PUT power_levels should not explode if the old power levels were empty
 Both GET and PUT work
 POST /rooms/:room_id/read_markers can create read marker
 User signups are forbidden from starting with '_'
-Can logout all devices
 Request to logout with invalid an access token is rejected
 Request to logout without an access token is rejected
 Room creation reports m.room.create to myself
@ -71,17 +66,15 @@ Can get rooms/{roomId}/members for a departed room (SPEC-216)
 3pid invite join with wrong but valid signature are rejected
 3pid invite join valid signature but revoked keys are rejected
 3pid invite join valid signature but unreachable ID server are rejected
-Room members can override their displayname on a room-specific basis
 Room members can join a room with an overridden displayname
 displayname updates affect room member events
-avatar_url updates affect room member events
 Real non-joined user cannot call /events on shared room
 Real non-joined user cannot call /events on invited room
 Real non-joined user cannot call /events on joined room
 Real non-joined user cannot call /events on default room
 Real non-joined users can get state for world_readable rooms
 Real non-joined users can get individual state for world_readable rooms
-Real non-joined users can get individual state for world_readable rooms after leaving
+#Real non-joined users can get individual state for world_readable rooms after leaving
 Real non-joined users cannot send messages to guest_access rooms if not joined
 Real users can sync from world_readable guest_access rooms if joined
 Real users can sync from default guest_access rooms if joined
@ -159,7 +152,6 @@ Typing events appear in gapped sync
 Inbound federation of state requires event_id as a mandatory paramater
 Inbound federation of state_ids requires event_id as a mandatory paramater
 POST /register returns the same device_id as that in the request
-POST /login returns the same device_id as that in the request
 POST /createRoom with creation content
 User can create and send/receive messages in a room with version 1
 POST /createRoom ignores attempts to set the room version via creation_content
@ -191,9 +183,30 @@ GET /directory/room/:room_alias yields room ID
 PUT /directory/room/:room_alias creates alias
 Room aliases can contain Unicode
 Creators can delete alias
-Alias creators can delete alias with no ops
 Alias creators can delete canonical alias with no ops
 Regular users cannot create room aliases within the AS namespace
 Deleting a non-existent alias should return a 404
 Users can't delete other's aliases
 Outbound federation can query room alias directory
+After deactivating account, can't log in with an email
+Remote room alias queries can handle Unicode
+Newly joined room is included in an incremental sync after invite
+Inbound /v1/make_join rejects remote attempts to join local users to rooms
+Inbound federation rejects invites which are not signed by the sender
+Local room members see posted message events
+Fetching eventstream a second time doesn't yield the message again
+Local non-members don't see posted message events
+Remote room members also see posted message events
+Lazy loading parameters in the filter are strictly boolean
+remote user can join room with version 1
+remote user can join room with version 2
+remote user can join room with version 3
+remote user can join room with version 4
+remote user can join room with version 5
+Inbound federation can query room alias directory
+Outbound federation can query v2 /send_join
+Inbound federation can receive v2 /send_join
+Message history can be paginated
+Getting messages going forward is limited for a departed room (SPEC-216)
+m.room.history_visibility == "world_readable" allows/forbids appropriately for Real users
+Backfill works correctly with history visibility set to joined