Implement read receipts (#1528)

* fix conversion from int to string yields a string of one rune, not a string of digits

* Add receipts table to syncapi

* Use StreamingToken as the since value

* Add required method to testEDUProducer

* Make receipt json creation "easier" to read

* Add receipts api to the eduserver

* Add receipts endpoint

* Add eduserver kafka consumer

* Add missing kafka config

* Add passing tests to whitelist

Signed-off-by: Till Faelligen <tfaelligen@gmail.com>

* Fix copy & paste error

* Fix column count error

* Make outbound federation receipts pass

* Make "Inbound federation rejects receipts from wrong remote" pass

* Don't use errors package

* - Add TODO for batching requests
- Rename variable

* Return a better error message

* - Use OutputReceiptEvent instead of InputReceiptEvent as result
- Don't use the errors package for errors
- Defer CloseAndLogIfError to close rows
- Fix Copyright

* Better creation/usage of JoinResponse

* Query all joined rooms instead of just one

* Update gomatrixserverlib

* Add sqlite3 migration

* Add postgres migration

* Ensure required sequence exists before running migrations

* Clarification on comment

* - Fix a bug when creating client receipts
- Use concrete types instead of interface{}

* Remove dead code
Use key for timestamp

* Fix postgres query...

* Remove single purpose struct

* Use key/value directly

* Only apply receipts on initial sync or if edu positions differ,
otherwise we'll be sending the same receipts over and over again.

* Actually update the id, so it is correctly send in syncs

* Set receipt on request to /read_markers

* Fix issue with receipts getting overwritten

* Use fmt.Errorf instead of pkg/errors

* Revert "Add postgres migration"

This reverts commit 722fe5a04628882b787d096942459961db159b06.

* Revert "Add sqlite3 migration"

This reverts commit d113b03f6495a4b8f8bcf158a3d00b510b4240cc.

* Fix selectRoomReceipts query

* Make golangci-lint happy

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

10 files changed, 442 insertions, 7 deletions

diff --git a/syncapi/consumers/eduserver_receipts.go b/syncapi/consumers/eduserver_receipts.go
new file mode 100644
index 00000000..c5d17414
--- /dev/null
+++ b/syncapi/consumers/eduserver_receipts.go
@@ -0,0 +1,94 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package consumers
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/syncapi/types"
+
+	"github.com/Shopify/sarama"
+	"github.com/matrix-org/dendrite/eduserver/api"
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/config"
+	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/sync"
+	log "github.com/sirupsen/logrus"
+)
+
+// OutputReceiptEventConsumer consumes events that originated in the EDU server.
+type OutputReceiptEventConsumer struct {
+	receiptConsumer *internal.ContinualConsumer
+	db              storage.Database
+	notifier        *sync.Notifier
+}
+
+// NewOutputReceiptEventConsumer creates a new OutputReceiptEventConsumer.
+// Call Start() to begin consuming from the EDU server.
+func NewOutputReceiptEventConsumer(
+	cfg *config.SyncAPI,
+	kafkaConsumer sarama.Consumer,
+	n *sync.Notifier,
+	store storage.Database,
+) *OutputReceiptEventConsumer {
+
+	consumer := internal.ContinualConsumer{
+		ComponentName:  "syncapi/eduserver/receipt",
+		Topic:          cfg.Matrix.Kafka.TopicFor(config.TopicOutputReceiptEvent),
+		Consumer:       kafkaConsumer,
+		PartitionStore: store,
+	}
+
+	s := &OutputReceiptEventConsumer{
+		receiptConsumer: &consumer,
+		db:              store,
+		notifier:        n,
+	}
+
+	consumer.ProcessMessage = s.onMessage
+
+	return s
+}
+
+// Start consuming from EDU api
+func (s *OutputReceiptEventConsumer) Start() error {
+	return s.receiptConsumer.Start()
+}
+
+func (s *OutputReceiptEventConsumer) onMessage(msg *sarama.ConsumerMessage) error {
+	var output api.OutputReceiptEvent
+	if err := json.Unmarshal(msg.Value, &output); err != nil {
+		// If the message was invalid, log it and move on to the next message in the stream
+		log.WithError(err).Errorf("EDU server output log: message parse failure")
+		return nil
+	}
+
+	streamPos, err := s.db.StoreReceipt(
+		context.TODO(),
+		output.RoomID,
+		output.Type,
+		output.UserID,
+		output.EventID,
+		output.Timestamp,
+	)
+	if err != nil {
+		return err
+	}
+	// update stream position
+	s.notifier.OnNewReceipt(types.NewStreamToken(0, streamPos, nil))
+
+	return nil
+}
diff --git a/syncapi/storage/interface.go b/syncapi/storage/interface.go
index e12a1166..727cc048 100644
--- a/syncapi/storage/interface.go
+++ b/syncapi/storage/interface.go
@@ -18,6 +18,8 @@ import (
 	"context"
 	"time"
 
+	eduAPI "github.com/matrix-org/dendrite/eduserver/api"
+
 	"github.com/matrix-org/dendrite/eduserver/cache"
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/roomserver/api"
@@ -147,4 +149,8 @@ type Database interface {
 	PutFilter(ctx context.Context, localpart string, filter *gomatrixserverlib.Filter) (string, error)
 	// RedactEvent wipes an event in the database and sets the unsigned.redacted_because key to the redaction event
 	RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *gomatrixserverlib.HeaderedEvent) error
+	// StoreReceipt stores new receipt events
+	StoreReceipt(ctx context.Context, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error)
+	// GetRoomReceipts gets all receipts for a given roomID
+	GetRoomReceipts(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]eduAPI.OutputReceiptEvent, error)
 }
diff --git a/syncapi/storage/postgres/receipt_table.go b/syncapi/storage/postgres/receipt_table.go
new file mode 100644
index 00000000..c5ec6cbc
--- /dev/null
+++ b/syncapi/storage/postgres/receipt_table.go
@@ -0,0 +1,106 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/lib/pq"
+
+	"github.com/matrix-org/dendrite/eduserver/api"
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const receiptsSchema = `
+CREATE SEQUENCE IF NOT EXISTS syncapi_stream_id;
+-- Stores data about receipts
+CREATE TABLE IF NOT EXISTS syncapi_receipts (
+	-- The ID
+	id BIGINT PRIMARY KEY DEFAULT nextval('syncapi_stream_id'),
+	room_id TEXT NOT NULL,
+	receipt_type TEXT NOT NULL,
+	user_id TEXT NOT NULL,
+	event_id TEXT NOT NULL,
+	receipt_ts BIGINT NOT NULL,
+	CONSTRAINT syncapi_receipts_unique UNIQUE (room_id, receipt_type, user_id)
+);
+CREATE INDEX IF NOT EXISTS syncapi_receipts_room_id ON syncapi_receipts(room_id);
+`
+
+const upsertReceipt = "" +
+	"INSERT INTO syncapi_receipts" +
+	" (room_id, receipt_type, user_id, event_id, receipt_ts)" +
+	" VALUES ($1, $2, $3, $4, $5)" +
+	" ON CONFLICT (room_id, receipt_type, user_id)" +
+	" DO UPDATE SET id = nextval('syncapi_stream_id'), event_id = $4, receipt_ts = $5" +
+	" RETURNING id"
+
+const selectRoomReceipts = "" +
+	"SELECT room_id, receipt_type, user_id, event_id, receipt_ts" +
+	" FROM syncapi_receipts" +
+	" WHERE room_id = ANY($1) AND id > $2"
+
+type receiptStatements struct {
+	db                 *sql.DB
+	upsertReceipt      *sql.Stmt
+	selectRoomReceipts *sql.Stmt
+}
+
+func NewPostgresReceiptsTable(db *sql.DB) (tables.Receipts, error) {
+	_, err := db.Exec(receiptsSchema)
+	if err != nil {
+		return nil, err
+	}
+	r := &receiptStatements{
+		db: db,
+	}
+	if r.upsertReceipt, err = db.Prepare(upsertReceipt); err != nil {
+		return nil, fmt.Errorf("unable to prepare upsertReceipt statement: %w", err)
+	}
+	if r.selectRoomReceipts, err = db.Prepare(selectRoomReceipts); err != nil {
+		return nil, fmt.Errorf("unable to prepare selectRoomReceipts statement: %w", err)
+	}
+	return r, nil
+}
+
+func (r *receiptStatements) UpsertReceipt(ctx context.Context, txn *sql.Tx, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error) {
+	stmt := sqlutil.TxStmt(txn, r.upsertReceipt)
+	err = stmt.QueryRowContext(ctx, roomId, receiptType, userId, eventId, timestamp).Scan(&pos)
+	return
+}
+
+func (r *receiptStatements) SelectRoomReceiptsAfter(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]api.OutputReceiptEvent, error) {
+	rows, err := r.selectRoomReceipts.QueryContext(ctx, pq.Array(roomIDs), streamPos)
+	if err != nil {
+		return nil, fmt.Errorf("unable to query room receipts: %w", err)
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "SelectRoomReceiptsAfter: rows.close() failed")
+	var res []api.OutputReceiptEvent
+	for rows.Next() {
+		r := api.OutputReceiptEvent{}
+		err = rows.Scan(&r.RoomID, &r.Type, &r.UserID, &r.EventID, &r.Timestamp)
+		if err != nil {
+			return res, fmt.Errorf("unable to scan row to api.Receipts: %w", err)
+		}
+		res = append(res, r)
+	}
+	return res, rows.Err()
+}
diff --git a/syncapi/storage/postgres/syncserver.go b/syncapi/storage/postgres/syncserver.go
index 7f19722a..979e19a0 100644
--- a/syncapi/storage/postgres/syncserver.go
+++ b/syncapi/storage/postgres/syncserver.go
@@ -82,6 +82,10 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 	if err != nil {
 		return nil, err
 	}
+	receipts, err := NewPostgresReceiptsTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	d.Database = shared.Database{
 		DB:                  d.db,
 		Writer:              d.writer,
@@ -94,6 +98,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 		BackwardExtremities: backwardExtremities,
 		Filter:              filter,
 		SendToDevice:        sendToDevice,
+		Receipts:            receipts,
 		EDUCache:            cache.New(),
 	}
 	return &d, nil
diff --git a/syncapi/storage/shared/syncserver.go b/syncapi/storage/shared/syncserver.go
index a7c07f94..2b82ee33 100644
--- a/syncapi/storage/shared/syncserver.go
+++ b/syncapi/storage/shared/syncserver.go
@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"time"
 
+	eduAPI "github.com/matrix-org/dendrite/eduserver/api"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 
 	"github.com/matrix-org/dendrite/eduserver/cache"
@@ -47,6 +48,7 @@ type Database struct {
 	BackwardExtremities tables.BackwardsExtremities
 	SendToDevice        tables.SendToDevice
 	Filter              tables.Filter
+	Receipts            tables.Receipts
 	EDUCache            *cache.EDUCache
 }
 
@@ -527,10 +529,10 @@ func (d *Database) addTypingDeltaToResponse(
 	joinedRoomIDs []string,
 	res *types.Response,
 ) error {
-	var jr types.JoinResponse
 	var ok bool
 	var err error
 	for _, roomID := range joinedRoomIDs {
+		var jr types.JoinResponse
 		if typingUsers, updated := d.EDUCache.GetTypingUsersIfUpdatedAfter(
 			roomID, int64(since.EDUPosition()),
 		); updated {
@@ -554,21 +556,84 @@ func (d *Database) addTypingDeltaToResponse(
 	return nil
 }
 
+// addReceiptDeltaToResponse adds all receipt information to a sync response
+// since the specified position
+func (d *Database) addReceiptDeltaToResponse(
+	since types.StreamingToken,
+	joinedRoomIDs []string,
+	res *types.Response,
+) error {
+	receipts, err := d.Receipts.SelectRoomReceiptsAfter(context.TODO(), joinedRoomIDs, since.EDUPosition())
+	if err != nil {
+		return fmt.Errorf("unable to select receipts for rooms: %w", err)
+	}
+
+	// Group receipts by room, so we can create one ClientEvent for every room
+	receiptsByRoom := make(map[string][]eduAPI.OutputReceiptEvent)
+	for _, receipt := range receipts {
+		receiptsByRoom[receipt.RoomID] = append(receiptsByRoom[receipt.RoomID], receipt)
+	}
+
+	for roomID, receipts := range receiptsByRoom {
+		var jr types.JoinResponse
+		var ok bool
+
+		// Make sure we use an existing JoinResponse if there is one.
+		// If not, we'll create a new one
+		if jr, ok = res.Rooms.Join[roomID]; !ok {
+			jr = types.JoinResponse{}
+		}
+
+		ev := gomatrixserverlib.ClientEvent{
+			Type:   gomatrixserverlib.MReceipt,
+			RoomID: roomID,
+		}
+		content := make(map[string]eduAPI.ReceiptMRead)
+		for _, receipt := range receipts {
+			var read eduAPI.ReceiptMRead
+			if read, ok = content[receipt.EventID]; !ok {
+				read = eduAPI.ReceiptMRead{
+					User: make(map[string]eduAPI.ReceiptTS),
+				}
+			}
+			read.User[receipt.UserID] = eduAPI.ReceiptTS{TS: receipt.Timestamp}
+			content[receipt.EventID] = read
+		}
+		ev.Content, err = json.Marshal(content)
+		if err != nil {
+			return err
+		}
+
+		jr.Ephemeral.Events = append(jr.Ephemeral.Events, ev)
+		res.Rooms.Join[roomID] = jr
+	}
+
+	return nil
+}
+
 // 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 *Database) addEDUDeltaToResponse(
 	fromPos, toPos types.StreamingToken,
 	joinedRoomIDs []string,
 	res *types.Response,
-) (err error) {
-
+) error {
 	if fromPos.EDUPosition() != toPos.EDUPosition() {
-		err = d.addTypingDeltaToResponse(
-			fromPos, joinedRoomIDs, res,
-		)
+		// add typing deltas
+		if err := d.addTypingDeltaToResponse(fromPos, joinedRoomIDs, res); err != nil {
+			return fmt.Errorf("unable to apply typing delta to response: %w", err)
+		}
 	}
 
-	return
+	// Check on initial sync and if EDUPositions differ
+	if (fromPos.EDUPosition() == 0 && toPos.EDUPosition() == 0) ||
+		fromPos.EDUPosition() != toPos.EDUPosition() {
+		if err := d.addReceiptDeltaToResponse(fromPos, joinedRoomIDs, res); err != nil {
+			return fmt.Errorf("unable to apply receipts to response: %w", err)
+		}
+	}
+
+	return nil
 }
 
 func (d *Database) GetFilter(
@@ -1404,3 +1469,16 @@ type stateDelta struct {
 	// Can be 0 if there is no membership event in this delta.
 	membershipPos types.StreamPosition
 }
+
+// StoreReceipt stores user receipts
+func (d *Database) StoreReceipt(ctx context.Context, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		pos, err = d.Receipts.UpsertReceipt(ctx, txn, roomId, receiptType, userId, eventId, timestamp)
+		return err
+	})
+	return
+}
+
+func (d *Database) GetRoomReceipts(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]eduAPI.OutputReceiptEvent, error) {
+	return d.Receipts.SelectRoomReceiptsAfter(ctx, roomIDs, streamPos)
+}
diff --git a/syncapi/storage/sqlite3/receipt_table.go b/syncapi/storage/sqlite3/receipt_table.go
new file mode 100644
index 00000000..b1770e80
--- /dev/null
+++ b/syncapi/storage/sqlite3/receipt_table.go
@@ -0,0 +1,118 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+
+	"github.com/matrix-org/dendrite/eduserver/api"
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const receiptsSchema = `
+-- Stores data about receipts
+CREATE TABLE IF NOT EXISTS syncapi_receipts (
+	-- The ID
+	id BIGINT,
+	room_id TEXT NOT NULL,
+	receipt_type TEXT NOT NULL,
+	user_id TEXT NOT NULL,
+	event_id TEXT NOT NULL,
+	receipt_ts BIGINT NOT NULL,
+	CONSTRAINT syncapi_receipts_unique UNIQUE (room_id, receipt_type, user_id)
+);
+CREATE INDEX IF NOT EXISTS syncapi_receipts_room_id_idx ON syncapi_receipts(room_id);
+`
+
+const upsertReceipt = "" +
+	"INSERT INTO syncapi_receipts" +
+	" (id, room_id, receipt_type, user_id, event_id, receipt_ts)" +
+	" VALUES ($1, $2, $3, $4, $5, $6)" +
+	" ON CONFLICT (room_id, receipt_type, user_id)" +
+	" DO UPDATE SET id = $7, event_id = $8, receipt_ts = $9"
+
+const selectRoomReceipts = "" +
+	"SELECT room_id, receipt_type, user_id, event_id, receipt_ts" +
+	" FROM syncapi_receipts" +
+	" WHERE id > $1 and room_id in ($2)"
+
+type receiptStatements struct {
+	db                 *sql.DB
+	streamIDStatements *streamIDStatements
+	upsertReceipt      *sql.Stmt
+	selectRoomReceipts *sql.Stmt
+}
+
+func NewSqliteReceiptsTable(db *sql.DB, streamID *streamIDStatements) (tables.Receipts, error) {
+	_, err := db.Exec(receiptsSchema)
+	if err != nil {
+		return nil, err
+	}
+	r := &receiptStatements{
+		db:                 db,
+		streamIDStatements: streamID,
+	}
+	if r.upsertReceipt, err = db.Prepare(upsertReceipt); err != nil {
+		return nil, fmt.Errorf("unable to prepare upsertReceipt statement: %w", err)
+	}
+	if r.selectRoomReceipts, err = db.Prepare(selectRoomReceipts); err != nil {
+		return nil, fmt.Errorf("unable to prepare selectRoomReceipts statement: %w", err)
+	}
+	return r, nil
+}
+
+// UpsertReceipt creates new user receipts
+func (r *receiptStatements) UpsertReceipt(ctx context.Context, txn *sql.Tx, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error) {
+	pos, err = r.streamIDStatements.nextStreamID(ctx, txn)
+	if err != nil {
+		return
+	}
+	stmt := sqlutil.TxStmt(txn, r.upsertReceipt)
+	_, err = stmt.ExecContext(ctx, pos, roomId, receiptType, userId, eventId, timestamp, pos, eventId, timestamp)
+	return
+}
+
+// SelectRoomReceiptsAfter select all receipts for a given room after a specific timestamp
+func (r *receiptStatements) SelectRoomReceiptsAfter(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]api.OutputReceiptEvent, error) {
+	selectSQL := strings.Replace(selectRoomReceipts, "($2)", sqlutil.QueryVariadicOffset(len(roomIDs), 1), 1)
+
+	params := make([]interface{}, len(roomIDs)+1)
+	params[0] = streamPos
+	for k, v := range roomIDs {
+		params[k+1] = v
+	}
+	rows, err := r.db.QueryContext(ctx, selectSQL, params...)
+	if err != nil {
+		return nil, fmt.Errorf("unable to query room receipts: %w", err)
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "SelectRoomReceiptsAfter: rows.close() failed")
+	var res []api.OutputReceiptEvent
+	for rows.Next() {
+		r := api.OutputReceiptEvent{}
+		err = rows.Scan(&r.RoomID, &r.Type, &r.UserID, &r.EventID, &r.Timestamp)
+		if err != nil {
+			return res, fmt.Errorf("unable to scan row to api.Receipts: %w", err)
+		}
+		res = append(res, r)
+	}
+	return res, rows.Err()
+}
diff --git a/syncapi/storage/sqlite3/syncserver.go b/syncapi/storage/sqlite3/syncserver.go
index 86d83ec9..036e2b2e 100644
--- a/syncapi/storage/sqlite3/syncserver.go
+++ b/syncapi/storage/sqlite3/syncserver.go
@@ -95,6 +95,10 @@ func (d *SyncServerDatasource) prepare() (err error) {
 	if err != nil {
 		return err
 	}
+	receipts, err := NewSqliteReceiptsTable(d.db, &d.streamID)
+	if err != nil {
+		return err
+	}
 	d.Database = shared.Database{
 		DB:                  d.db,
 		Writer:              d.writer,
@@ -107,6 +111,7 @@ func (d *SyncServerDatasource) prepare() (err error) {
 		Topology:            topology,
 		Filter:              filter,
 		SendToDevice:        sendToDevice,
+		Receipts:            receipts,
 		EDUCache:            cache.New(),
 	}
 	return nil
diff --git a/syncapi/storage/tables/interface.go b/syncapi/storage/tables/interface.go
index da095be5..f8e7a224 100644
--- a/syncapi/storage/tables/interface.go
+++ b/syncapi/storage/tables/interface.go
@@ -18,6 +18,7 @@ import (
 	"context"
 	"database/sql"
 
+	eduAPI "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -156,3 +157,8 @@ type Filter interface {
 	SelectFilter(ctx context.Context, localpart string, filterID string) (*gomatrixserverlib.Filter, error)
 	InsertFilter(ctx context.Context, filter *gomatrixserverlib.Filter, localpart string) (filterID string, err error)
 }
+
+type Receipts interface {
+	UpsertReceipt(ctx context.Context, txn *sql.Tx, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error)
+	SelectRoomReceiptsAfter(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]eduAPI.OutputReceiptEvent, error)
+}
diff --git a/syncapi/sync/notifier.go b/syncapi/sync/notifier.go
index fcac3f16..daa3a1d8 100644
--- a/syncapi/sync/notifier.go
+++ b/syncapi/sync/notifier.go
@@ -149,6 +149,16 @@ func (n *Notifier) OnNewSendToDevice(
 	n.wakeupUserDevice(userID, deviceIDs, latestPos)
 }
 
+// OnNewReceipt updates the current position
+func (n *Notifier) OnNewReceipt(
+	posUpdate types.StreamingToken,
+) {
+	n.streamLock.Lock()
+	defer n.streamLock.Unlock()
+	latestPos := n.currPos.WithUpdates(posUpdate)
+	n.currPos = latestPos
+}
+
 func (n *Notifier) OnNewKeyChange(
 	posUpdate types.StreamingToken, wakeUserID, keyChangeUserID string,
 ) {
diff --git a/syncapi/syncapi.go b/syncapi/syncapi.go
index de0bb434..393a7aa5 100644
--- a/syncapi/syncapi.go
+++ b/syncapi/syncapi.go
@@ -99,5 +99,12 @@ func AddPublicRoutes(
 		logrus.WithError(err).Panicf("failed to start send-to-device consumer")
 	}
 
+	receiptConsumer := consumers.NewOutputReceiptEventConsumer(
+		cfg, consumer, notifier, syncDB,
+	)
+	if err = receiptConsumer.Start(); err != nil {
+		logrus.WithError(err).Panicf("failed to start receipts consumer")
+	}
+
 	routing.Setup(router, requestPool, syncDB, userAPI, federation, rsAPI, cfg)
 }