Process inbound device list updates from federation (#1240)

* Add InputDeviceListUpdate

* Unbreak unit tests

* Process inbound device list updates from federation

- Persist the keys in the keyserver and produce key changes
- Does not currently fetch keys from the remote server if the prev IDs are missing

* Linting

keyserver/storage/postgres/device_keys_table.go

@@ -19,6 +19,7 @@ import (
 	"database/sql"
 	"time"
 
+	"github.com/lib/pq"
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/keyserver/storage/tables"
@@ -56,12 +57,16 @@ const selectBatchDeviceKeysSQL = "" +
 const selectMaxStreamForUserSQL = "" +
 	"SELECT MAX(stream_id) FROM keyserver_device_keys WHERE user_id=$1"
 
+const countStreamIDsForUserSQL = "" +
+	"SELECT COUNT(*) FROM keyserver_device_keys WHERE user_id=$1 AND stream_id = ANY($2)"
+
 type deviceKeysStatements struct {
 	db                         *sql.DB
 	upsertDeviceKeysStmt       *sql.Stmt
 	selectDeviceKeysStmt       *sql.Stmt
 	selectBatchDeviceKeysStmt  *sql.Stmt
 	selectMaxStreamForUserStmt *sql.Stmt
+	countStreamIDsForUserStmt  *sql.Stmt
 }
 
 func NewPostgresDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
@@ -84,6 +89,9 @@ func NewPostgresDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
 	if s.selectMaxStreamForUserStmt, err = db.Prepare(selectMaxStreamForUserSQL); err != nil {
 		return nil, err
 	}
+	if s.countStreamIDsForUserStmt, err = db.Prepare(countStreamIDsForUserSQL); err != nil {
+		return nil, err
+	}
 	return s, nil
 }
 
@@ -115,6 +123,19 @@ func (s *deviceKeysStatements) SelectMaxStreamIDForUser(ctx context.Context, txn
 	return
 }
 
+func (s *deviceKeysStatements) CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error) {
+	// nullable if there are no results
+	var count sql.NullInt32
+	err := s.countStreamIDsForUserStmt.QueryRowContext(ctx, userID, pq.Int64Array(streamIDs)).Scan(&count)
+	if err != nil {
+		return 0, err
+	}
+	if count.Valid {
+		return int(count.Int32), nil
+	}
+	return 0, nil
+}
+
 func (s *deviceKeysStatements) InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error {
 	for _, key := range keys {
 		now := time.Now().Unix()