Persistent federation sender blacklist (#1214)

* Initial persistence of blacklists

* Move statistics folder

* Make MaxFederationRetries configurable

* Set lower failure thresholds for Yggdrasil demos

* Still write events into database for blacklisted hosts (they can be tidied up later)

* Review comments

12 files changed, 330 insertions, 51 deletions

diff --git a/federationsender/federationsender.go b/federationsender/federationsender.go
index 79a2c084..9e14f6ec 100644
--- a/federationsender/federationsender.go
+++ b/federationsender/federationsender.go
@@ -21,8 +21,8 @@ import (
 	"github.com/matrix-org/dendrite/federationsender/internal"
 	"github.com/matrix-org/dendrite/federationsender/inthttp"
 	"github.com/matrix-org/dendrite/federationsender/queue"
+	"github.com/matrix-org/dendrite/federationsender/statistics"
 	"github.com/matrix-org/dendrite/federationsender/storage"
-	"github.com/matrix-org/dendrite/federationsender/types"
 	"github.com/matrix-org/dendrite/internal/setup"
 	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -48,9 +48,13 @@ func NewInternalAPI(
 		logrus.WithError(err).Panic("failed to connect to federation sender db")
 	}
 
-	statistics := &types.Statistics{}
+	stats := &statistics.Statistics{
+		DB:                     federationSenderDB,
+		FailuresUntilBlacklist: base.Cfg.Matrix.FederationMaxRetries,
+	}
+
 	queues := queue.NewOutgoingQueues(
-		federationSenderDB, base.Cfg.Matrix.ServerName, federation, rsAPI, statistics,
+		federationSenderDB, base.Cfg.Matrix.ServerName, federation, rsAPI, stats,
 		&queue.SigningInfo{
 			KeyID:      base.Cfg.Matrix.KeyID,
 			PrivateKey: base.Cfg.Matrix.PrivateKey,
@@ -73,5 +77,5 @@ func NewInternalAPI(
 		logrus.WithError(err).Panic("failed to start typing server consumer")
 	}
 
-	return internal.NewFederationSenderInternalAPI(federationSenderDB, base.Cfg, rsAPI, federation, keyRing, statistics, queues)
+	return internal.NewFederationSenderInternalAPI(federationSenderDB, base.Cfg, rsAPI, federation, keyRing, stats, queues)
 }
diff --git a/federationsender/internal/api.go b/federationsender/internal/api.go
index 0dca32fc..9a9880ce 100644
--- a/federationsender/internal/api.go
+++ b/federationsender/internal/api.go
@@ -2,8 +2,8 @@ package internal
 
 import (
 	"github.com/matrix-org/dendrite/federationsender/queue"
+	"github.com/matrix-org/dendrite/federationsender/statistics"
 	"github.com/matrix-org/dendrite/federationsender/storage"
-	"github.com/matrix-org/dendrite/federationsender/types"
 	"github.com/matrix-org/dendrite/internal/config"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -13,7 +13,7 @@ import (
 type FederationSenderInternalAPI struct {
 	db         storage.Database
 	cfg        *config.Dendrite
-	statistics *types.Statistics
+	statistics *statistics.Statistics
 	rsAPI      api.RoomserverInternalAPI
 	federation *gomatrixserverlib.FederationClient
 	keyRing    *gomatrixserverlib.KeyRing
@@ -25,7 +25,7 @@ func NewFederationSenderInternalAPI(
 	rsAPI api.RoomserverInternalAPI,
 	federation *gomatrixserverlib.FederationClient,
 	keyRing *gomatrixserverlib.KeyRing,
-	statistics *types.Statistics,
+	statistics *statistics.Statistics,
 	queues *queue.OutgoingQueues,
 ) *FederationSenderInternalAPI {
 	return &FederationSenderInternalAPI{
diff --git a/federationsender/queue/destinationqueue.go b/federationsender/queue/destinationqueue.go
index b7582bf9..dc2d4091 100644
--- a/federationsender/queue/destinationqueue.go
+++ b/federationsender/queue/destinationqueue.go
@@ -21,9 +21,9 @@ import (
 	"sync"
 	"time"
 
+	"github.com/matrix-org/dendrite/federationsender/statistics"
 	"github.com/matrix-org/dendrite/federationsender/storage"
 	"github.com/matrix-org/dendrite/federationsender/storage/shared"
-	"github.com/matrix-org/dendrite/federationsender/types"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -51,7 +51,7 @@ type destinationQueue struct {
 	destination        gomatrixserverlib.ServerName            // destination of requests
 	running            atomic.Bool                             // is the queue worker running?
 	backingOff         atomic.Bool                             // true if we're backing off
-	statistics         *types.ServerStatistics                 // statistics about this remote server
+	statistics         *statistics.ServerStatistics            // statistics about this remote server
 	incomingInvites    chan *gomatrixserverlib.InviteV2Request // invites to send
 	transactionIDMutex sync.Mutex                              // protects transactionID
 	transactionID      gomatrixserverlib.TransactionID         // last transaction ID
@@ -66,11 +66,6 @@ type destinationQueue struct {
 // If the queue is empty then it starts a background goroutine to
 // start sending events to that destination.
 func (oq *destinationQueue) sendEvent(receipt *shared.Receipt) {
-	if oq.statistics.Blacklisted() {
-		// If the destination is blacklisted then drop the event.
-		log.Infof("%s is blacklisted; dropping event", oq.destination)
-		return
-	}
 	// Create a transaction ID. We'll either do this if we don't have
 	// one made up yet, or if we've exceeded the number of maximum
 	// events allowed in a single tranaction. We'll reset the counter
@@ -97,13 +92,17 @@ func (oq *destinationQueue) sendEvent(receipt *shared.Receipt) {
 	// We've successfully added a PDU to the transaction so increase
 	// the counter.
 	oq.transactionCount.Add(1)
-	// Wake up the queue if it's asleep.
-	oq.wakeQueueIfNeeded()
-	// If we're blocking on waiting PDUs then tell the queue that we
-	// have work to do.
-	select {
-	case oq.notifyPDUs <- true:
-	default:
+	// Check if the destination is blacklisted. If it isn't then wake
+	// up the queue.
+	if !oq.statistics.Blacklisted() {
+		// Wake up the queue if it's asleep.
+		oq.wakeQueueIfNeeded()
+		// If we're blocking on waiting PDUs then tell the queue that we
+		// have work to do.
+		select {
+		case oq.notifyPDUs <- true:
+		default:
+		}
 	}
 }
 
@@ -111,11 +110,6 @@ func (oq *destinationQueue) sendEvent(receipt *shared.Receipt) {
 // If the queue is empty then it starts a background goroutine to
 // start sending events to that destination.
 func (oq *destinationQueue) sendEDU(receipt *shared.Receipt) {
-	if oq.statistics.Blacklisted() {
-		// If the destination is blacklisted then drop the event.
-		log.Infof("%s is blacklisted; dropping ephemeral event", oq.destination)
-		return
-	}
 	// Create a database entry that associates the given PDU NID with
 	// this destination queue. We'll then be able to retrieve the PDU
 	// later.
@@ -130,13 +124,17 @@ func (oq *destinationQueue) sendEDU(receipt *shared.Receipt) {
 	// We've successfully added an EDU to the transaction so increase
 	// the counter.
 	oq.transactionCount.Add(1)
-	// Wake up the queue if it's asleep.
-	oq.wakeQueueIfNeeded()
-	// If we're blocking on waiting PDUs then tell the queue that we
-	// have work to do.
-	select {
-	case oq.notifyEDUs <- true:
-	default:
+	// Check if the destination is blacklisted. If it isn't then wake
+	// up the queue.
+	if !oq.statistics.Blacklisted() {
+		// Wake up the queue if it's asleep.
+		oq.wakeQueueIfNeeded()
+		// If we're blocking on waiting EDUs then tell the queue that we
+		// have work to do.
+		select {
+		case oq.notifyEDUs <- true:
+		default:
+		}
 	}
 }
 
diff --git a/federationsender/queue/queue.go b/federationsender/queue/queue.go
index e488a34a..5651fba2 100644
--- a/federationsender/queue/queue.go
+++ b/federationsender/queue/queue.go
@@ -21,8 +21,8 @@ import (
 	"fmt"
 	"sync"
 
+	"github.com/matrix-org/dendrite/federationsender/statistics"
 	"github.com/matrix-org/dendrite/federationsender/storage"
-	"github.com/matrix-org/dendrite/federationsender/types"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
@@ -36,7 +36,7 @@ type OutgoingQueues struct {
 	rsAPI       api.RoomserverInternalAPI
 	origin      gomatrixserverlib.ServerName
 	client      *gomatrixserverlib.FederationClient
-	statistics  *types.Statistics
+	statistics  *statistics.Statistics
 	signing     *SigningInfo
 	queuesMutex sync.Mutex // protects the below
 	queues      map[gomatrixserverlib.ServerName]*destinationQueue
@@ -48,7 +48,7 @@ func NewOutgoingQueues(
 	origin gomatrixserverlib.ServerName,
 	client *gomatrixserverlib.FederationClient,
 	rsAPI api.RoomserverInternalAPI,
-	statistics *types.Statistics,
+	statistics *statistics.Statistics,
 	signing *SigningInfo,
 ) *OutgoingQueues {
 	queues := &OutgoingQueues{
@@ -77,7 +77,9 @@ func NewOutgoingQueues(
 		log.WithError(err).Error("Failed to get EDU server names for destination queue hydration")
 	}
 	for serverName := range serverNames {
-		queues.getQueue(serverName).wakeQueueIfNeeded()
+		if !queues.getQueue(serverName).statistics.Blacklisted() {
+			queues.getQueue(serverName).wakeQueueIfNeeded()
+		}
 	}
 	return queues
 }
diff --git a/federationsender/types/statistics.go b/federationsender/statistics/statistics.go
index 63f82756..17dd896d 100644
--- a/federationsender/types/statistics.go
+++ b/federationsender/statistics/statistics.go
@@ -1,27 +1,28 @@
-package types
+package statistics
 
 import (
 	"math"
 	"sync"
 	"time"
 
+	"github.com/matrix-org/dendrite/federationsender/storage"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	"go.uber.org/atomic"
 )
 
-const (
-	// How many times should we tolerate consecutive failures before we
-	// just blacklist the host altogether? Bear in mind that the backoff
-	// is exponential, so the max time here to attempt is 2**failures.
-	FailuresUntilBlacklist = 16 // 16 equates to roughly 18 hours.
-)
-
 // Statistics contains information about all of the remote federated
 // hosts that we have interacted with. It is basically a threadsafe
 // wrapper.
 type Statistics struct {
+	DB      storage.Database
 	servers map[gomatrixserverlib.ServerName]*ServerStatistics
 	mutex   sync.RWMutex
+
+	// How many times should we tolerate consecutive failures before we
+	// just blacklist the host altogether? The backoff is exponential,
+	// so the max time here to attempt is 2**failures seconds.
+	FailuresUntilBlacklist uint32
 }
 
 // ForServer returns server statistics for the given server name. If it
@@ -40,9 +41,18 @@ func (s *Statistics) ForServer(serverName gomatrixserverlib.ServerName) *ServerS
 	// If we don't, then make one.
 	if !found {
 		s.mutex.Lock()
-		server = &ServerStatistics{}
+		server = &ServerStatistics{
+			statistics: s,
+			serverName: serverName,
+		}
 		s.servers[serverName] = server
 		s.mutex.Unlock()
+		blacklisted, err := s.DB.IsServerBlacklisted(serverName)
+		if err != nil {
+			logrus.WithError(err).Errorf("Failed to get blacklist entry %q", serverName)
+		} else {
+			server.blacklisted.Store(blacklisted)
+		}
 	}
 	return server
 }
@@ -52,10 +62,12 @@ func (s *Statistics) ForServer(serverName gomatrixserverlib.ServerName) *ServerS
 // many times we failed etc. It also manages the backoff time and black-
 // listing a remote host if it remains uncooperative.
 type ServerStatistics struct {
-	blacklisted    atomic.Bool   // is the remote side dead?
-	backoffUntil   atomic.Value  // time.Time to wait until before sending requests
-	failCounter    atomic.Uint32 // how many times have we failed?
-	successCounter atomic.Uint32 // how many times have we succeeded?
+	statistics     *Statistics                  //
+	serverName     gomatrixserverlib.ServerName //
+	blacklisted    atomic.Bool                  // is the node blacklisted
+	backoffUntil   atomic.Value                 // time.Time to wait until before sending requests
+	failCounter    atomic.Uint32                // how many times have we failed?
+	successCounter atomic.Uint32                // how many times have we succeeded?
 }
 
 // Success updates the server statistics with a new successful
@@ -66,6 +78,9 @@ func (s *ServerStatistics) Success() {
 	s.successCounter.Add(1)
 	s.failCounter.Store(0)
 	s.blacklisted.Store(false)
+	if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil {
+		logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName)
+	}
 }
 
 // Failure marks a failure and works out when to backoff until. It
@@ -77,12 +92,15 @@ func (s *ServerStatistics) Failure() bool {
 	failCounter := s.failCounter.Add(1)
 
 	// Check that we haven't failed more times than is acceptable.
-	if failCounter >= FailuresUntilBlacklist {
+	if failCounter >= s.statistics.FailuresUntilBlacklist {
 		// We've exceeded the maximum amount of times we're willing
 		// to back off, which is probably in the region of hours by
 		// now. Mark the host as blacklisted and tell the caller to
 		// give up.
 		s.blacklisted.Store(true)
+		if err := s.statistics.DB.AddServerToBlacklist(s.serverName); err != nil {
+			logrus.WithError(err).Errorf("Failed to add %q to blacklist", s.serverName)
+		}
 		return true
 	}
 
diff --git a/federationsender/storage/interface.go b/federationsender/storage/interface.go
index 1bea83e2..b79499d3 100644
--- a/federationsender/storage/interface.go
+++ b/federationsender/storage/interface.go
@@ -47,4 +47,8 @@ type Database interface {
 
 	GetPendingPDUServerNames(ctx context.Context) ([]gomatrixserverlib.ServerName, error)
 	GetPendingEDUServerNames(ctx context.Context) ([]gomatrixserverlib.ServerName, error)
+
+	AddServerToBlacklist(serverName gomatrixserverlib.ServerName) error
+	RemoveServerFromBlacklist(serverName gomatrixserverlib.ServerName) error
+	IsServerBlacklisted(serverName gomatrixserverlib.ServerName) (bool, error)
 }
diff --git a/federationsender/storage/postgres/blacklist_table.go b/federationsender/storage/postgres/blacklist_table.go
new file mode 100644
index 00000000..f1db9fae
--- /dev/null
+++ b/federationsender/storage/postgres/blacklist_table.go
@@ -0,0 +1,112 @@
+// 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"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const blacklistSchema = `
+CREATE TABLE IF NOT EXISTS federationsender_blacklist (
+    -- The blacklisted server name
+    server_name TEXT NOT NULL
+);
+`
+
+const insertBlacklistSQL = "" +
+	"INSERT INTO federationsender_blacklist (server_name) VALUES ($1)" +
+	" ON CONFLICT DO NOTHING"
+
+const selectBlacklistSQL = "" +
+	"SELECT server_name FROM federationsender_blacklist WHERE server_name = $1"
+
+const deleteBlacklistSQL = "" +
+	"DELETE FROM federationsender_blacklist WHERE server_name = $1"
+
+type blacklistStatements struct {
+	db                  *sql.DB
+	writer              *sqlutil.TransactionWriter
+	insertBlacklistStmt *sql.Stmt
+	selectBlacklistStmt *sql.Stmt
+	deleteBlacklistStmt *sql.Stmt
+}
+
+func NewPostgresBlacklistTable(db *sql.DB) (s *blacklistStatements, err error) {
+	s = &blacklistStatements{
+		db:     db,
+		writer: sqlutil.NewTransactionWriter(),
+	}
+	_, err = db.Exec(blacklistSchema)
+	if err != nil {
+		return
+	}
+
+	if s.insertBlacklistStmt, err = db.Prepare(insertBlacklistSQL); err != nil {
+		return
+	}
+	if s.selectBlacklistStmt, err = db.Prepare(selectBlacklistSQL); err != nil {
+		return
+	}
+	if s.deleteBlacklistStmt, err = db.Prepare(deleteBlacklistSQL); err != nil {
+		return
+	}
+	return
+}
+
+// insertRoom inserts the room if it didn't already exist.
+// If the room didn't exist then last_event_id is set to the empty string.
+func (s *blacklistStatements) InsertBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) error {
+	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.insertBlacklistStmt)
+		_, err := stmt.ExecContext(ctx, serverName)
+		return err
+	})
+}
+
+// selectRoomForUpdate locks the row for the room and returns the last_event_id.
+// The row must already exist in the table. Callers can ensure that the row
+// exists by calling insertRoom first.
+func (s *blacklistStatements) SelectBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) (bool, error) {
+	stmt := sqlutil.TxStmt(txn, s.selectBlacklistStmt)
+	res, err := stmt.QueryContext(ctx, serverName)
+	if err != nil {
+		return false, err
+	}
+	defer res.Close() // nolint:errcheck
+	// The query will return the server name if the server is blacklisted, and
+	// will return no rows if not. By calling Next, we find out if a row was
+	// returned or not - we don't care about the value itself.
+	return res.Next(), nil
+}
+
+// updateRoom updates the last_event_id for the room. selectRoomForUpdate should
+// have already been called earlier within the transaction.
+func (s *blacklistStatements) DeleteBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) error {
+	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.deleteBlacklistStmt)
+		_, err := stmt.ExecContext(ctx, serverName)
+		return err
+	})
+}
diff --git a/federationsender/storage/postgres/storage.go b/federationsender/storage/postgres/storage.go
index 66388bfe..a3094bda 100644
--- a/federationsender/storage/postgres/storage.go
+++ b/federationsender/storage/postgres/storage.go
@@ -56,6 +56,10 @@ func NewDatabase(dataSourceName string, dbProperties sqlutil.DbProperties) (*Dat
 	if err != nil {
 		return nil, err
 	}
+	blacklist, err := NewPostgresBlacklistTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	d.Database = shared.Database{
 		DB:                          d.db,
 		FederationSenderJoinedHosts: joinedHosts,
@@ -63,6 +67,7 @@ func NewDatabase(dataSourceName string, dbProperties sqlutil.DbProperties) (*Dat
 		FederationSenderQueueEDUs:   queueEDUs,
 		FederationSenderQueueJSON:   queueJSON,
 		FederationSenderRooms:       rooms,
+		FederationSenderBlacklist:   blacklist,
 	}
 	if err = d.PartitionOffsetStatements.Prepare(d.db, "federationsender"); err != nil {
 		return nil, err
diff --git a/federationsender/storage/shared/storage.go b/federationsender/storage/shared/storage.go
index 75681ea3..52f02a28 100644
--- a/federationsender/storage/shared/storage.go
+++ b/federationsender/storage/shared/storage.go
@@ -33,6 +33,7 @@ type Database struct {
 	FederationSenderQueueJSON   tables.FederationSenderQueueJSON
 	FederationSenderJoinedHosts tables.FederationSenderJoinedHosts
 	FederationSenderRooms       tables.FederationSenderRooms
+	FederationSenderBlacklist   tables.FederationSenderBlacklist
 }
 
 // An Receipt contains the NIDs of a call to GetNextTransactionPDUs/EDUs.
@@ -136,3 +137,15 @@ func (d *Database) StoreJSON(
 		nids: []int64{nid},
 	}, nil
 }
+
+func (d *Database) AddServerToBlacklist(serverName gomatrixserverlib.ServerName) error {
+	return d.FederationSenderBlacklist.InsertBlacklist(context.TODO(), nil, serverName)
+}
+
+func (d *Database) RemoveServerFromBlacklist(serverName gomatrixserverlib.ServerName) error {
+	return d.FederationSenderBlacklist.DeleteBlacklist(context.TODO(), nil, serverName)
+}
+
+func (d *Database) IsServerBlacklisted(serverName gomatrixserverlib.ServerName) (bool, error) {
+	return d.FederationSenderBlacklist.SelectBlacklist(context.TODO(), nil, serverName)
+}
diff --git a/federationsender/storage/sqlite3/blacklist_table.go b/federationsender/storage/sqlite3/blacklist_table.go
new file mode 100644
index 00000000..3e302906
--- /dev/null
+++ b/federationsender/storage/sqlite3/blacklist_table.go
@@ -0,0 +1,112 @@
+// 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"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const blacklistSchema = `
+CREATE TABLE IF NOT EXISTS federationsender_blacklist (
+    -- The blacklisted server name
+    server_name TEXT NOT NULL
+);
+`
+
+const insertBlacklistSQL = "" +
+	"INSERT INTO federationsender_blacklist (server_name) VALUES ($1)" +
+	" ON CONFLICT DO NOTHING"
+
+const selectBlacklistSQL = "" +
+	"SELECT server_name FROM federationsender_blacklist WHERE server_name = $1"
+
+const deleteBlacklistSQL = "" +
+	"DELETE FROM federationsender_blacklist WHERE server_name = $1"
+
+type blacklistStatements struct {
+	db                  *sql.DB
+	writer              *sqlutil.TransactionWriter
+	insertBlacklistStmt *sql.Stmt
+	selectBlacklistStmt *sql.Stmt
+	deleteBlacklistStmt *sql.Stmt
+}
+
+func NewSQLiteBlacklistTable(db *sql.DB) (s *blacklistStatements, err error) {
+	s = &blacklistStatements{
+		db:     db,
+		writer: sqlutil.NewTransactionWriter(),
+	}
+	_, err = db.Exec(blacklistSchema)
+	if err != nil {
+		return
+	}
+
+	if s.insertBlacklistStmt, err = db.Prepare(insertBlacklistSQL); err != nil {
+		return
+	}
+	if s.selectBlacklistStmt, err = db.Prepare(selectBlacklistSQL); err != nil {
+		return
+	}
+	if s.deleteBlacklistStmt, err = db.Prepare(deleteBlacklistSQL); err != nil {
+		return
+	}
+	return
+}
+
+// insertRoom inserts the room if it didn't already exist.
+// If the room didn't exist then last_event_id is set to the empty string.
+func (s *blacklistStatements) InsertBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) error {
+	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.insertBlacklistStmt)
+		_, err := stmt.ExecContext(ctx, serverName)
+		return err
+	})
+}
+
+// selectRoomForUpdate locks the row for the room and returns the last_event_id.
+// The row must already exist in the table. Callers can ensure that the row
+// exists by calling insertRoom first.
+func (s *blacklistStatements) SelectBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) (bool, error) {
+	stmt := sqlutil.TxStmt(txn, s.selectBlacklistStmt)
+	res, err := stmt.QueryContext(ctx, serverName)
+	if err != nil {
+		return false, err
+	}
+	defer res.Close() // nolint:errcheck
+	// The query will return the server name if the server is blacklisted, and
+	// will return no rows if not. By calling Next, we find out if a row was
+	// returned or not - we don't care about the value itself.
+	return res.Next(), nil
+}
+
+// updateRoom updates the last_event_id for the room. selectRoomForUpdate should
+// have already been called earlier within the transaction.
+func (s *blacklistStatements) DeleteBlacklist(
+	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
+) error {
+	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.deleteBlacklistStmt)
+		_, err := stmt.ExecContext(ctx, serverName)
+		return err
+	})
+}
diff --git a/federationsender/storage/sqlite3/storage.go b/federationsender/storage/sqlite3/storage.go
index 545a229c..c303d094 100644
--- a/federationsender/storage/sqlite3/storage.go
+++ b/federationsender/storage/sqlite3/storage.go
@@ -62,6 +62,10 @@ func NewDatabase(dataSourceName string) (*Database, error) {
 	if err != nil {
 		return nil, err
 	}
+	blacklist, err := NewSQLiteBlacklistTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	d.Database = shared.Database{
 		DB:                          d.db,
 		FederationSenderJoinedHosts: joinedHosts,
@@ -69,6 +73,7 @@ func NewDatabase(dataSourceName string) (*Database, error) {
 		FederationSenderQueueEDUs:   queueEDUs,
 		FederationSenderQueueJSON:   queueJSON,
 		FederationSenderRooms:       rooms,
+		FederationSenderBlacklist:   blacklist,
 	}
 	if err = d.PartitionOffsetStatements.Prepare(d.db, "federationsender"); err != nil {
 		return nil, err
diff --git a/federationsender/storage/tables/interface.go b/federationsender/storage/tables/interface.go
index 55d9119f..2def48d0 100644
--- a/federationsender/storage/tables/interface.go
+++ b/federationsender/storage/tables/interface.go
@@ -60,3 +60,9 @@ type FederationSenderRooms interface {
 	SelectRoomForUpdate(ctx context.Context, txn *sql.Tx, roomID string) (string, error)
 	UpdateRoom(ctx context.Context, txn *sql.Tx, roomID, lastEventID string) error
 }
+
+type FederationSenderBlacklist interface {
+	InsertBlacklist(ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName) error
+	SelectBlacklist(ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName) (bool, error)
+	DeleteBlacklist(ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName) error
+}