Modify /state/{eventType}/{stateKey} to return the event at the time the user left (#1222)

* Modify /state/{eventType}/{stateKey} to return the event at the time the user left

Or live, depending on their current state. Hopefully fixes some sytests!

* Linting

* Set HasBeenInRoom

* Fix cases for world-readable history visibility

* Fix bug in finding the requested state event

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

4 files changed, 136 insertions, 22 deletions

diff --git a/clientapi/routing/routing.go b/clientapi/routing/routing.go
index 311f64d1..5724a20c 100644
--- a/clientapi/routing/routing.go
+++ b/clientapi/routing/routing.go
@@ -216,7 +216,7 @@ func Setup(
 			eventType = eventType[:len(eventType)-1]
 		}
 		eventFormat := req.URL.Query().Get("format") == "event"
-		return OnIncomingStateTypeRequest(req.Context(), rsAPI, vars["roomID"], eventType, "", eventFormat)
+		return OnIncomingStateTypeRequest(req.Context(), device, rsAPI, vars["roomID"], eventType, "", eventFormat)
 	})).Methods(http.MethodGet, http.MethodOptions)
 
 	r0mux.Handle("/rooms/{roomID}/state/{type}/{stateKey}", httputil.MakeAuthAPI("room_state", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
@@ -225,7 +225,7 @@ func Setup(
 			return util.ErrorResponse(err)
 		}
 		eventFormat := req.URL.Query().Get("format") == "event"
-		return OnIncomingStateTypeRequest(req.Context(), rsAPI, vars["roomID"], vars["type"], vars["stateKey"], eventFormat)
+		return OnIncomingStateTypeRequest(req.Context(), device, rsAPI, vars["roomID"], vars["type"], vars["stateKey"], eventFormat)
 	})).Methods(http.MethodGet, http.MethodOptions)
 
 	r0mux.Handle("/rooms/{roomID}/state/{eventType:[^/]+/?}",
diff --git a/clientapi/routing/state.go b/clientapi/routing/state.go
index 2ec7a33f..c4f7c4f2 100644
--- a/clientapi/routing/state.go
+++ b/clientapi/routing/state.go
@@ -17,11 +17,13 @@ package routing
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/syncapi/types"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	log "github.com/sirupsen/logrus"
@@ -99,40 +101,150 @@ func OnIncomingStateRequest(ctx context.Context, rsAPI api.RoomserverInternalAPI
 // state to see if there is an event with that type and state key, if there
 // is then (by default) we return the content, otherwise a 404.
 // If eventFormat=true, sends the whole event else just the content.
-func OnIncomingStateTypeRequest(ctx context.Context, rsAPI api.RoomserverInternalAPI, roomID, evType, stateKey string, eventFormat bool) util.JSONResponse {
-	// TODO(#287): Auth request and handle the case where the user has left (where
-	// we should return the state at the poin they left)
-	util.GetLogger(ctx).WithFields(log.Fields{
-		"roomID":   roomID,
-		"evType":   evType,
-		"stateKey": stateKey,
-	}).Info("Fetching state")
+// nolint:gocyclo
+func OnIncomingStateTypeRequest(
+	ctx context.Context, device *userapi.Device, rsAPI api.RoomserverInternalAPI,
+	roomID, evType, stateKey string, eventFormat bool,
+) util.JSONResponse {
+	var worldReadable bool
+	var wantLatestState bool
 
-	stateReq := api.QueryLatestEventsAndStateRequest{
-		RoomID: roomID,
-		StateToFetch: []gomatrixserverlib.StateKeyTuple{
-			gomatrixserverlib.StateKeyTuple{
-				EventType: evType,
-				StateKey:  stateKey,
-			},
+	// Always fetch visibility so that we can work out whether to show
+	// the latest events or the last event from when the user was joined.
+	// Then include the requested event type and state key, assuming it
+	// isn't for the same.
+	stateToFetch := []gomatrixserverlib.StateKeyTuple{
+		{
+			EventType: evType,
+			StateKey:  stateKey,
 		},
 	}
-	stateRes := api.QueryLatestEventsAndStateResponse{}
+	if evType != gomatrixserverlib.MRoomHistoryVisibility && stateKey != "" {
+		stateToFetch = append(stateToFetch, gomatrixserverlib.StateKeyTuple{
+			EventType: gomatrixserverlib.MRoomHistoryVisibility,
+			StateKey:  "",
+		})
+	}
 
-	if err := rsAPI.QueryLatestEventsAndState(ctx, &stateReq, &stateRes); err != nil {
+	// First of all, get the latest state of the room. We need to do this
+	// so that we can look at the history visibility of the room. If the
+	// room is world-readable then we will always return the latest state.
+	stateRes := api.QueryLatestEventsAndStateResponse{}
+	if err := rsAPI.QueryLatestEventsAndState(ctx, &api.QueryLatestEventsAndStateRequest{
+		RoomID:       roomID,
+		StateToFetch: stateToFetch,
+	}, &stateRes); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("queryAPI.QueryLatestEventsAndState failed")
 		return jsonerror.InternalServerError()
 	}
 
-	if len(stateRes.StateEvents) == 0 {
+	// Look at the room state and see if we have a history visibility event
+	// that marks the room as world-readable. If we don't then we assume that
+	// the room is not world-readable.
+	for _, ev := range stateRes.StateEvents {
+		if ev.Type() == gomatrixserverlib.MRoomHistoryVisibility {
+			content := map[string]string{}
+			if err := json.Unmarshal(ev.Content(), &content); err != nil {
+				util.GetLogger(ctx).WithError(err).Error("json.Unmarshal for history visibility failed")
+				return jsonerror.InternalServerError()
+			}
+			if visibility, ok := content["history_visibility"]; ok {
+				worldReadable = visibility == "world_readable"
+				break
+			}
+		}
+	}
+
+	// If the room isn't world-readable then we will instead try to find out
+	// the state of the room based on the user's membership. If the user is
+	// in the room then we'll want the latest state. If the user has never
+	// been in the room and the room isn't world-readable, then we won't
+	// return any state. If the user was in the room previously but is no
+	// longer then we will return the state at the time that the user left.
+	// membershipRes will only be populated if the room is not world-readable.
+	var membershipRes api.QueryMembershipForUserResponse
+	if !worldReadable {
+		// The room isn't world-readable so try to work out based on the
+		// user's membership if we want the latest state or not.
+		err := rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{
+			RoomID: roomID,
+			UserID: device.UserID,
+		}, &membershipRes)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
+			return jsonerror.InternalServerError()
+		}
+		// If the user has never been in the room then stop at this point.
+		// We won't tell the user about a room they have never joined.
+		if !membershipRes.HasBeenInRoom {
+			return util.JSONResponse{
+				Code: http.StatusForbidden,
+				JSON: jsonerror.Forbidden(fmt.Sprintf("Unknown room %q or user %q has never joined this room", roomID, device.UserID)),
+			}
+		}
+		// Otherwise, if the user has been in the room, whether or not we
+		// give them the latest state will depend on if they are *still* in
+		// the room.
+		wantLatestState = membershipRes.IsInRoom
+	} else {
+		// The room is world-readable so the user join state is irrelevant,
+		// just get the latest room state instead.
+		wantLatestState = true
+	}
+
+	util.GetLogger(ctx).WithFields(log.Fields{
+		"roomID":         roomID,
+		"evType":         evType,
+		"stateKey":       stateKey,
+		"state_at_event": !wantLatestState,
+	}).Info("Fetching state")
+
+	var event *gomatrixserverlib.HeaderedEvent
+	if wantLatestState {
+		// If we are happy to use the latest state, either because the user is
+		// still in the room, or because the room is world-readable, then just
+		// use the result of the previous QueryLatestEventsAndState response
+		// to find the state event, if provided.
+		for _, ev := range stateRes.StateEvents {
+			if ev.Type() == evType && ev.StateKeyEquals(stateKey) {
+				event = &ev
+				break
+			}
+		}
+	} else {
+		// Otherwise, take the event ID of their leave event and work out what
+		// the state of the room was before that event.
+		var stateAfterRes api.QueryStateAfterEventsResponse
+		err := rsAPI.QueryStateAfterEvents(ctx, &api.QueryStateAfterEventsRequest{
+			RoomID:       roomID,
+			PrevEventIDs: []string{membershipRes.EventID},
+			StateToFetch: []gomatrixserverlib.StateKeyTuple{
+				{
+					EventType: evType,
+					StateKey:  stateKey,
+				},
+			},
+		}, &stateAfterRes)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
+			return jsonerror.InternalServerError()
+		}
+		if len(stateAfterRes.StateEvents) > 0 {
+			event = &stateAfterRes.StateEvents[0]
+		}
+	}
+
+	// If there was no event found that matches all of the above criteria then
+	// return an error.
+	if event == nil {
 		return util.JSONResponse{
 			Code: http.StatusNotFound,
-			JSON: jsonerror.NotFound("cannot find state"),
+			JSON: jsonerror.NotFound(fmt.Sprintf("Cannot find state event for %q", evType)),
 		}
 	}
 
 	stateEvent := stateEventInStateResp{
-		ClientEvent: gomatrixserverlib.HeaderedToClientEvent(stateRes.StateEvents[0], gomatrixserverlib.FormatAll),
+		ClientEvent: gomatrixserverlib.HeaderedToClientEvent(*event, gomatrixserverlib.FormatAll),
 	}
 
 	var res interface{}
diff --git a/roomserver/internal/query.go b/roomserver/internal/query.go
index bede6c88..828e5fd3 100644
--- a/roomserver/internal/query.go
+++ b/roomserver/internal/query.go
@@ -226,6 +226,7 @@ func (r *RoomserverInternalAPI) QueryMembershipForUser(
 	}
 
 	response.IsInRoom = stillInRoom
+	response.HasBeenInRoom = true
 
 	evs, err := r.DB.Events(ctx, []types.EventNID{membershipEventNID})
 	if err != nil {
diff --git a/sytest-whitelist b/sytest-whitelist
index 234eae39..5087186b 100644
--- a/sytest-whitelist
+++ b/sytest-whitelist
@@ -415,3 +415,4 @@ We don't send redundant membership state across incremental syncs by default
 Typing notifications don't leak
 Users cannot kick users from a room they are not in
 Users cannot kick users who have already left a room
+Can get 'm.room.name' state for a departed room (SPEC-216)