Membership viewing API (#174)

* Basic memberships retrieval

* Change the way the memberships are saved in the client API database

* Retrieve single membership

* Get memberships only if the user is or has been in the room

* Check server name on room ID instead of user ID

* Save the join membership event and updates it when necessary

* Membership events retrieval + update on leave

* Implement the API on the roomserver and client API server

* Fix comments

* Remove the functions and attributes used before the new query API

* Explicitely state what we return in query

* Remove tab

src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/membership_table.go

@@ -44,9 +44,6 @@ const insertMembershipSQL = `
 	ON CONFLICT (localpart, room_id) DO UPDATE SET event_id = EXCLUDED.event_id
 `
 
-const selectMembershipSQL = "" +
-	"SELECT * from account_memberships WHERE localpart = $1 AND room_id = $2"
-
 const selectMembershipsByLocalpartSQL = "" +
 	"SELECT room_id, event_id FROM account_memberships WHERE localpart = $1"
 

src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/storage.go

@@ -121,7 +121,8 @@ func (d *Database) SetPartitionOffset(topic string, partition int32, offset int6
 }
 
 // SaveMembership saves the user matching a given localpart as a member of a given
-// room. It also stores the ID of the `join` membership event.
+// room. It also stores the ID of the membership event and a flag on whether the user
+// is still in the room.
 // If a membership already exists between the user and the room, or of the
 // insert fails, returns the SQL error
 func (d *Database) SaveMembership(localpart string, roomID string, eventID string, txn *sql.Tx) error {
@@ -156,23 +157,19 @@ func (d *Database) UpdateMemberships(eventsToAdd []gomatrixserverlib.Event, idsT
 	})
 }
 
-// GetMembershipsByLocalpart returns an array containing the IDs of all the rooms
-// a user matching a given localpart is a member of
+// GetMembershipsByLocalpart returns an array containing the memberships for all
+// the rooms a user matching a given localpart is a member of
 // If no membership match the given localpart, returns an empty array
 // If there was an issue during the retrieval, returns the SQL error
 func (d *Database) GetMembershipsByLocalpart(localpart string) (memberships []authtypes.Membership, err error) {
 	return d.memberships.selectMembershipsByLocalpart(localpart)
 }
 
-// UpdateMembership update the "join" membership event ID of a membership.
-// This is useful in case of membership upgrade (e.g. profile update)
-// If there was an issue during the update, returns the SQL error
-func (d *Database) UpdateMembership(oldEventID string, newEventID string) error {
-	return d.memberships.updateMembershipByEventID(oldEventID, newEventID)
-}
-
-// newMembership will save a new membership in the database if the given state
-// event is a "join" membership event
+// newMembership will save a new membership in the database, with a flag on whether
+// the user is still in the room. This flag is set to true if the given state
+// event is a "join" membership event and false if the event is a "leave" or "ban"
+// membership. If the event isn't a m.room.member event with one of these three
+// values, does nothing.
 // If the event isn't a "join" membership event, does nothing
 // If an error occurred, returns it
 func (d *Database) newMembership(ev gomatrixserverlib.Event, txn *sql.Tx) error {

src/github.com/matrix-org/dendrite/clientapi/readers/memberships.go

@@ -0,0 +1,55 @@
+// Copyright 2017 Vector Creations 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 readers
+
+import (
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
+	"github.com/matrix-org/dendrite/clientapi/auth/storage/accounts"
+	"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/util"
+)
+
+// GetMemberships implements GET /rooms/{roomId}/members
+func GetMemberships(
+	req *http.Request, device *authtypes.Device, roomID string,
+	accountDB *accounts.Database, cfg config.Dendrite,
+	queryAPI api.RoomserverQueryAPI,
+) util.JSONResponse {
+	queryReq := api.QueryMembershipsForRoomRequest{
+		RoomID: roomID,
+		Sender: device.UserID,
+	}
+	var queryRes api.QueryMembershipsForRoomResponse
+	if err := queryAPI.QueryMembershipsForRoom(&queryReq, &queryRes); err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	if !queryRes.HasBeenInRoom {
+		return util.JSONResponse{
+			Code: 403,
+			JSON: jsonerror.Forbidden("You aren't a member of the room and weren't previously a member of the room."),
+		}
+	}
+
+	return util.JSONResponse{
+		Code: 200,
+		JSON: queryRes.JoinEvents,
+	}
+}

src/github.com/matrix-org/dendrite/clientapi/routing/routing.go

@@ -313,6 +313,13 @@ func Setup(
 		}),
 	)
 
+	r0mux.Handle("/rooms/{roomID}/members",
+		common.MakeAuthAPI("rooms_members", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
+			vars := mux.Vars(req)
+			return readers.GetMemberships(req, device, vars["roomID"], accountDB, cfg, queryAPI)
+		}),
+	)
+
 	r0mux.Handle("/rooms/{roomID}/read_markers",
 		common.MakeAPI("rooms_read_markers", func(req *http.Request) util.JSONResponse {
 			// TODO: return the read_markers.

src/github.com/matrix-org/dendrite/roomserver/api/query.go

@@ -100,6 +100,23 @@ type QueryEventsByIDResponse struct {
 	Events []gomatrixserverlib.Event `json:"events"`
 }
 
+// QueryMembershipsForRoomRequest is a request to QueryMembershipsForRoom
+type QueryMembershipsForRoomRequest struct {
+	// ID of the room to fetch memberships from
+	RoomID string `json:"room_id"`
+	// ID of the user sending the request
+	Sender string `json:"sender"`
+}
+
+// QueryMembershipsForRoomResponse is a response to QueryMembershipsForRoom
+type QueryMembershipsForRoomResponse struct {
+	// The "m.room.member" events (of "join" membership) in the client format
+	JoinEvents []gomatrixserverlib.ClientEvent `json:"join_events"`
+	// True if the user has been in room before and has either stayed in it or
+	// left it.
+	HasBeenInRoom bool `json:"has_been_in_room"`
+}
+
 // 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.
@@ -119,6 +136,12 @@ type RoomserverQueryAPI interface {
 		request *QueryEventsByIDRequest,
 		response *QueryEventsByIDResponse,
 	) error
+
+	// Query a list of membership events for a room
+	QueryMembershipsForRoom(
+		request *QueryMembershipsForRoomRequest,
+		response *QueryMembershipsForRoomResponse,
+	) error
 }
 
 // RoomserverQueryLatestEventsAndStatePath is the HTTP path for the QueryLatestEventsAndState API.
@@ -130,6 +153,9 @@ const RoomserverQueryStateAfterEventsPath = "/api/roomserver/queryStateAfterEven
 // RoomserverQueryEventsByIDPath is the HTTP path for the QueryEventsByID API.
 const RoomserverQueryEventsByIDPath = "/api/roomserver/queryEventsByID"
 
+// RoomserverQueryMembershipsForRoomPath is the HTTP path for the QueryMembershipsForRoom API
+const RoomserverQueryMembershipsForRoomPath = "/api/roomserver/queryMembershipsForRoom"
+
 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
 // If httpClient is nil then it uses the http.DefaultClient
 func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverQueryAPI {
@@ -171,6 +197,15 @@ func (h *httpRoomserverQueryAPI) QueryEventsByID(
 	return postJSON(h.httpClient, apiURL, request, response)
 }
 
+// QueryMembershipsForRoom implements RoomserverQueryAPI
+func (h *httpRoomserverQueryAPI) QueryMembershipsForRoom(
+	request *QueryMembershipsForRoomRequest,
+	response *QueryMembershipsForRoomResponse,
+) error {
+	apiURL := h.roomserverURL + RoomserverQueryMembershipsForRoomPath
+	return postJSON(h.httpClient, apiURL, request, response)
+}
+
 func postJSON(httpClient *http.Client, apiURL string, request, response interface{}) error {
 	jsonBytes, err := json.Marshal(request)
 	if err != nil {

src/github.com/matrix-org/dendrite/roomserver/input/membership.go

@@ -95,10 +95,9 @@ func updateMembership(
 			return nil, err
 		}
 	}
-	if old == new {
+	if old == new && new != "join" {
 		// If the membership is the same then nothing changed and we can return
-		// immediately. This should help speed up processing for display name
-		// changes where the membership is "join" both before and after.
+		// immediately, unless it's a "join" update (e.g. profile update).
 		return updates, nil
 	}
 
@@ -152,16 +151,21 @@ func updateToInviteMembership(
 func updateToJoinMembership(
 	mu types.MembershipUpdater, add *gomatrixserverlib.Event, updates []api.OutputEvent,
 ) ([]api.OutputEvent, error) {
-	// If the user is already marked as being joined then we can return immediately.
-	// TODO: Is this code reachable given the "old != new" guard in updateMembership?
+	// If the user is already marked as being joined, we call SetToJoin to update
+	// the event ID then we can return immediately. Retired is ignored as there
+	// is no invite event to retire.
 	if mu.IsJoin() {
+		_, err := mu.SetToJoin(add.Sender(), add.EventID(), true)
+		if err != nil {
+			return nil, err
+		}
 		return updates, nil
 	}
 	// When we mark a user as being joined we will invalidate any invites that
 	// are active for that user. We notify the consumers that the invites have
 	// been retired using a special event, even though they could infer this
 	// by studying the state changes in the room event stream.
-	retired, err := mu.SetToJoin(add.Sender())
+	retired, err := mu.SetToJoin(add.Sender(), add.EventID(), false)
 	if err != nil {
 		return nil, err
 	}
@@ -194,7 +198,7 @@ func updateToLeaveMembership(
 	// are active for that user. We notify the consumers that the invites have
 	// been retired using a special event, even though they could infer this
 	// by studying the state changes in the room event stream.
-	retired, err := mu.SetToLeave(add.Sender())
+	retired, err := mu.SetToLeave(add.Sender(), add.EventID())
 	if err != nil {
 		return nil, err
 	}

src/github.com/matrix-org/dendrite/roomserver/query/query.go

@@ -52,6 +52,13 @@ type RoomserverQueryAPIDatabase interface {
 	// Remove a given room alias.
 	// Returns an error if there was a problem talking to the database.
 	RemoveRoomAlias(alias string) error
+	// Lookup the join events for all members in a room as requested by a given
+	// user. If the user is currently in the room, returns the room's current
+	// members, if not returns an empty array (TODO: Fix it)
+	// If the user requesting the list of members has never been in the room,
+	// returns nil.
+	// If there was an issue retrieving the events, returns an error.
+	GetMembershipEvents(roomNID types.RoomNID, requestSenderUserID string) (events []types.Event, err error)
 }
 
 // RoomserverQueryAPI is an implementation of api.RoomserverQueryAPI
@@ -182,6 +189,37 @@ func (r *RoomserverQueryAPI) loadEvents(eventNIDs []types.EventNID) ([]gomatrixs
 	return result, nil
 }
 
+// QueryMembershipsForRoom implements api.RoomserverQueryAPI
+func (r *RoomserverQueryAPI) QueryMembershipsForRoom(
+	request *api.QueryMembershipsForRoomRequest,
+	response *api.QueryMembershipsForRoomResponse,
+) error {
+	roomNID, err := r.DB.RoomNID(request.RoomID)
+	if err != nil {
+		return err
+	}
+
+	events, err := r.DB.GetMembershipEvents(roomNID, request.Sender)
+	if err != nil {
+		return nil
+	}
+
+	if events == nil {
+		response.HasBeenInRoom = false
+		response.JoinEvents = nil
+		return nil
+	}
+
+	response.HasBeenInRoom = true
+	response.JoinEvents = []gomatrixserverlib.ClientEvent{}
+	for _, event := range events {
+		clientEvent := gomatrixserverlib.ToClientEvent(event.Event, gomatrixserverlib.FormatAll)
+		response.JoinEvents = append(response.JoinEvents, clientEvent)
+	}
+
+	return nil
+}
+
 // SetupHTTP adds the RoomserverQueryAPI handlers to the http.ServeMux.
 func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
 	servMux.Handle(
@@ -226,4 +264,18 @@ func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
 			return util.JSONResponse{Code: 200, JSON: &response}
 		}),
 	)
+	servMux.Handle(
+		api.RoomserverQueryMembershipsForRoomPath,
+		common.MakeAPI("queryMembershipsForRoom", func(req *http.Request) util.JSONResponse {
+			var request api.QueryMembershipsForRoomRequest
+			var response api.QueryMembershipsForRoomResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.QueryMembershipsForRoom(&request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
 }

src/github.com/matrix-org/dendrite/roomserver/storage/event_state_keys_table.go

@@ -58,10 +58,22 @@ const bulkSelectEventStateKeyNIDSQL = "" +
 	"SELECT event_state_key, event_state_key_nid FROM roomserver_event_state_keys" +
 	" WHERE event_state_key = ANY($1)"
 
+const selectEventStateKeySQL = "" +
+	"SELECT event_state_key FROM roomserver_event_state_keys" +
+	" WHERE event_state_key_nid = $1"
+
+// Bulk lookup from numeric ID to string state key for that state key.
+// Takes an array of strings as the query parameter.
+const bulkSelectEventStateKeySQL = "" +
+	"SELECT event_state_key, event_state_key_nid FROM roomserver_event_state_keys" +
+	" WHERE event_state_key_nid = ANY($1)"
+
 type eventStateKeyStatements struct {
 	insertEventStateKeyNIDStmt     *sql.Stmt
 	selectEventStateKeyNIDStmt     *sql.Stmt
+	selectEventStateKeyStmt        *sql.Stmt
 	bulkSelectEventStateKeyNIDStmt *sql.Stmt
+	bulkSelectEventStateKeyStmt    *sql.Stmt
 }
 
 func (s *eventStateKeyStatements) prepare(db *sql.DB) (err error) {
@@ -72,7 +84,9 @@ func (s *eventStateKeyStatements) prepare(db *sql.DB) (err error) {
 	return statementList{
 		{&s.insertEventStateKeyNIDStmt, insertEventStateKeyNIDSQL},
 		{&s.selectEventStateKeyNIDStmt, selectEventStateKeyNIDSQL},
+		{&s.selectEventStateKeyStmt, selectEventStateKeySQL},
 		{&s.bulkSelectEventStateKeyNIDStmt, bulkSelectEventStateKeyNIDSQL},
+		{&s.bulkSelectEventStateKeyStmt, bulkSelectEventStateKeySQL},
 	}.prepare(db)
 }
 
@@ -114,3 +128,36 @@ func (s *eventStateKeyStatements) bulkSelectEventStateKeyNID(eventStateKeys []st
 	}
 	return result, nil
 }
+
+func (s *eventStateKeyStatements) selectEventStateKey(txn *sql.Tx, eventStateKeyNID types.EventStateKeyNID) (string, error) {
+	var eventStateKey string
+	stmt := s.selectEventStateKeyStmt
+	if txn != nil {
+		stmt = txn.Stmt(stmt)
+	}
+	err := stmt.QueryRow(eventStateKeyNID).Scan(&eventStateKey)
+	return eventStateKey, err
+}
+
+func (s *eventStateKeyStatements) bulkSelectEventStateKey(eventStateKeyNIDs []types.EventStateKeyNID) (map[types.EventStateKeyNID]string, error) {
+	var nIDs pq.Int64Array
+	for i := range eventStateKeyNIDs {
+		nIDs[i] = int64(eventStateKeyNIDs[i])
+	}
+	rows, err := s.bulkSelectEventStateKeyStmt.Query(nIDs)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	result := make(map[types.EventStateKeyNID]string, len(eventStateKeyNIDs))
+	for rows.Next() {
+		var stateKey string
+		var stateKeyNID int64
+		if err := rows.Scan(&stateKey, &stateKeyNID); err != nil {
+			return nil, err
+		}
+		result[types.EventStateKeyNID(stateKeyNID)] = stateKey
+	}
+	return result, nil
+}

src/github.com/matrix-org/dendrite/roomserver/storage/membership_table.go

@@ -33,7 +33,7 @@ const membershipSchema = `
 -- and the room state tables.
 -- This table is updated in one of 3 ways:
 --   1) The membership of a user changes within the current state of the room.
---   2) An invite is received outside of a room over federation. 
+--   2) An invite is received outside of a room over federation.
 --   3) An invite is rejected outside of a room over federation.
 CREATE TABLE IF NOT EXISTS roomserver_membership (
 	room_nid BIGINT NOT NULL,
@@ -46,6 +46,16 @@ CREATE TABLE IF NOT EXISTS roomserver_membership (
 	-- The state the user is in within this room.
 	-- Default value is "membershipStateLeaveOrBan"
 	membership_nid BIGINT NOT NULL DEFAULT 1,
+	-- The numeric ID of the membership event.
+	-- It refers to the join membership event if the membership_nid is join (3),
+	-- and to the leave/ban membership event if the membership_nid is leave or
+	-- ban (1).
+	-- If the membership_nid is invite (2) and the user has been in the room
+	-- before, it will refer to the previous leave/ban membership event, and will
+	-- be equals to 0 (its default) if the user never joined the room before.
+	-- This NID is updated if the join event gets updated (e.g. profile update),
+	-- or if the user leaves/joins the room.
+	event_nid BIGINT NOT NULL DEFAULT 0,
 	UNIQUE (room_nid, target_nid)
 );
 `
@@ -57,18 +67,33 @@ const insertMembershipSQL = "" +
 	" VALUES ($1, $2)" +
 	" ON CONFLICT DO NOTHING"
 
+const selectMembershipFromRoomAndTargetSQL = "" +
+	"SELECT membership_nid, event_nid FROM roomserver_membership" +
+	" WHERE room_nid = $1 AND target_nid = $2"
+
+const selectMembershipsFromRoomAndMembershipSQL = "" +
+	"SELECT event_nid FROM roomserver_membership" +
+	" WHERE room_nid = $1 AND membership_nid = $2"
+
+const selectMembershipsFromRoomSQL = "" +
+	"SELECT membership_nid, event_nid FROM roomserver_membership" +
+	" WHERE room_nid = $1"
+
 const selectMembershipForUpdateSQL = "" +
 	"SELECT membership_nid FROM roomserver_membership" +
 	" WHERE room_nid = $1 AND target_nid = $2 FOR UPDATE"
 
 const updateMembershipSQL = "" +
-	"UPDATE roomserver_membership SET sender_nid = $3, membership_nid = $4" +
+	"UPDATE roomserver_membership SET sender_nid = $3, membership_nid = $4, event_nid = $5" +
 	" WHERE room_nid = $1 AND target_nid = $2"
 
 type membershipStatements struct {
-	insertMembershipStmt          *sql.Stmt
-	selectMembershipForUpdateStmt *sql.Stmt
-	updateMembershipStmt          *sql.Stmt
+	insertMembershipStmt                       *sql.Stmt
+	selectMembershipForUpdateStmt              *sql.Stmt
+	selectMembershipFromRoomAndTargetStmt      *sql.Stmt
+	selectMembershipsFromRoomAndMembershipStmt *sql.Stmt
+	selectMembershipsFromRoomStmt              *sql.Stmt
+	updateMembershipStmt                       *sql.Stmt
 }
 
 func (s *membershipStatements) prepare(db *sql.DB) (err error) {
@@ -80,6 +105,9 @@ func (s *membershipStatements) prepare(db *sql.DB) (err error) {
 	return statementList{
 		{&s.insertMembershipStmt, insertMembershipSQL},
 		{&s.selectMembershipForUpdateStmt, selectMembershipForUpdateSQL},
+		{&s.selectMembershipFromRoomAndTargetStmt, selectMembershipFromRoomAndTargetSQL},
+		{&s.selectMembershipsFromRoomAndMembershipStmt, selectMembershipsFromRoomAndMembershipSQL},
+		{&s.selectMembershipsFromRoomStmt, selectMembershipsFromRoomSQL},
 		{&s.updateMembershipStmt, updateMembershipSQL},
 	}.prepare(db)
 }
@@ -100,12 +128,59 @@ func (s *membershipStatements) selectMembershipForUpdate(
 	return
 }
 
+func (s *membershipStatements) selectMembershipFromRoomAndTarget(
+	roomNID types.RoomNID, targetUserNID types.EventStateKeyNID,
+) (eventNID types.EventNID, membership membershipState, err error) {
+	err = s.selectMembershipFromRoomAndTargetStmt.QueryRow(
+		roomNID, targetUserNID,
+	).Scan(&membership, &eventNID)
+	return
+}
+
+func (s *membershipStatements) selectMembershipsFromRoom(
+	roomNID types.RoomNID,
+) (eventNIDs map[types.EventNID]membershipState, err error) {
+	rows, err := s.selectMembershipsFromRoomStmt.Query(roomNID)
+	if err != nil {
+		return
+	}
+
+	eventNIDs = make(map[types.EventNID]membershipState)
+	for rows.Next() {
+		var eNID types.EventNID
+		var membership membershipState
+		if err = rows.Scan(&membership, &eNID); err != nil {
+			return
+		}
+		eventNIDs[eNID] = membership
+	}
+	return
+}
+func (s *membershipStatements) selectMembershipsFromRoomAndMembership(
+	roomNID types.RoomNID, membership membershipState,
+) (eventNIDs []types.EventNID, err error) {
+	rows, err := s.selectMembershipsFromRoomAndMembershipStmt.Query(roomNID, membership)
+	if err != nil {
+		return
+	}
+
+	for rows.Next() {
+		var eNID types.EventNID
+		if err = rows.Scan(&eNID); err != nil {
+			return
+		}
+		eventNIDs = append(eventNIDs, eNID)
+	}
+	return
+}
+
 func (s *membershipStatements) updateMembership(
 	txn *sql.Tx, roomNID types.RoomNID, targetUserNID types.EventStateKeyNID,
 	senderUserNID types.EventStateKeyNID, membership membershipState,
+	eventNID types.EventNID,
 ) error {
 	_, err := txn.Stmt(s.updateMembershipStmt).Exec(
-		roomNID, targetUserNID, senderUserNID, membership,
+		roomNID, targetUserNID, senderUserNID, membership, eventNID,
 	)
 	return err
 }

src/github.com/matrix-org/dendrite/roomserver/storage/storage.go

@@ -435,7 +435,7 @@ func (u *membershipUpdater) SetToInvite(event gomatrixserverlib.Event) (bool, er
 	}
 	if u.membership != membershipStateInvite {
 		if err = u.d.statements.updateMembership(
-			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateInvite,
+			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateInvite, 0,
 		); err != nil {
 			return false, err
 		}
@@ -444,7 +444,43 @@ func (u *membershipUpdater) SetToInvite(event gomatrixserverlib.Event) (bool, er
 }
 
 // SetToJoin implements types.MembershipUpdater
-func (u *membershipUpdater) SetToJoin(senderUserID string) ([]string, error) {
+func (u *membershipUpdater) SetToJoin(senderUserID string, eventID string, isUpdate bool) ([]string, error) {
+	var inviteEventIDs []string
+
+	senderUserNID, err := u.d.assignStateKeyNID(u.txn, senderUserID)
+	if err != nil {
+		return nil, err
+	}
+
+	// If this is a join event update, there is no invite to update
+	if !isUpdate {
+		inviteEventIDs, err = u.d.statements.updateInviteRetired(
+			u.txn, u.roomNID, u.targetUserNID,
+		)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Lookup the NID of the new join event
+	nIDs, err := u.d.EventNIDs([]string{eventID})
+	if err != nil {
+		return nil, err
+	}
+
+	if u.membership != membershipStateJoin || isUpdate {
+		if err = u.d.statements.updateMembership(
+			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateJoin, nIDs[eventID],
+		); err != nil {
+			return nil, err
+		}
+	}
+
+	return inviteEventIDs, nil
+}
+
+// SetToLeave implements types.MembershipUpdater
+func (u *membershipUpdater) SetToLeave(senderUserID string, eventID string) ([]string, error) {
 	senderUserNID, err := u.d.assignStateKeyNID(u.txn, senderUserID)
 	if err != nil {
 		return nil, err
@@ -455,9 +491,16 @@ func (u *membershipUpdater) SetToJoin(senderUserID string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
-	if u.membership != membershipStateJoin {
+
+	// Lookup the NID of the new leave event
+	nIDs, err := u.d.EventNIDs([]string{eventID})
+	if err != nil {
+		return nil, err
+	}
+
+	if u.membership != membershipStateLeaveOrBan {
 		if err = u.d.statements.updateMembership(
-			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateJoin,
+			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateLeaveOrBan, nIDs[eventID],
 		); err != nil {
 			return nil, err
 		}
@@ -465,26 +508,49 @@ func (u *membershipUpdater) SetToJoin(senderUserID string) ([]string, error) {
 	return inviteEventIDs, nil
 }
 
-// SetToLeave implements types.MembershipUpdater
-func (u *membershipUpdater) SetToLeave(senderUserID string) ([]string, error) {
-	senderUserNID, err := u.d.assignStateKeyNID(u.txn, senderUserID)
+// GetMembershipEvents implements query.RoomserverQueryAPIDB
+func (d *Database) GetMembershipEvents(roomNID types.RoomNID, requestSenderUserID string) (events []types.Event, err error) {
+	txn, err := d.db.Begin()
 	if err != nil {
-		return nil, err
+		return
 	}
-	inviteEventIDs, err := u.d.statements.updateInviteRetired(
-		u.txn, u.roomNID, u.targetUserNID,
-	)
+	defer txn.Commit()
+
+	requestSenderUserNID, err := d.assignStateKeyNID(txn, requestSenderUserID)
 	if err != nil {
-		return nil, err
+		return
 	}
-	if u.membership != membershipStateLeaveOrBan {
-		if err = u.d.statements.updateMembership(
-			u.txn, u.roomNID, u.targetUserNID, senderUserNID, membershipStateLeaveOrBan,
-		); err != nil {
+
+	_, senderMembership, err := d.statements.selectMembershipFromRoomAndTarget(roomNID, requestSenderUserNID)
+	if err == sql.ErrNoRows {
+		// The user has never been a member of that room
+		return nil, nil
+	} else if err != nil {
+		return
+	}
+
+	if senderMembership == membershipStateJoin {
+		// The user is still in the room: Send the current list of joined members
+		var joinEventNIDs []types.EventNID
+		joinEventNIDs, err = d.statements.selectMembershipsFromRoomAndMembership(roomNID, membershipStateJoin)
+		if err != nil {
 			return nil, err
 		}
+
+		events, err = d.Events(joinEventNIDs)
+	} else {
+		// The user isn't in the room anymore
+		// TODO: Send the list of joined member as it was when the user left
+		//       We cannot do this using only the memberships database, as it
+		//       only stores the latest join event NID for a given target user.
+		//       The solution would be to build the state of a room after before
+		//       the leave event and extract a members list from it.
+		//       For now, we return an empty slice so we know the user has been
+		//       in the room before.
+		events = []types.Event{}
 	}
-	return inviteEventIDs, nil
+
+	return
 }
 
 type transaction struct {

src/github.com/matrix-org/dendrite/roomserver/types/types.go

@@ -193,12 +193,12 @@ type MembershipUpdater interface {
 	// Set the state to invite.
 	// Returns whether this invite needs to be sent
 	SetToInvite(event gomatrixserverlib.Event) (needsSending bool, err error)
-	// Set the state to join.
+	// Set the state to join or updates the event ID in the database.
 	// Returns a list of invite event IDs that this state change retired.
-	SetToJoin(senderUserID string) (inviteEventIDs []string, err error)
+	SetToJoin(senderUserID string, eventID string, isUpdate bool) (inviteEventIDs []string, err error)
 	// Set the state to leave.
 	// Returns a list of invite event IDs that this state change retired.
-	SetToLeave(senderUserID string) (inviteEventIDs []string, err error)
+	SetToLeave(senderUserID string, eventID string) (inviteEventIDs []string, err error)
 	// Implements Transaction so it can be committed or rolledback.
 	Transaction
 }