[pseudoIDs] More pseudo ID fixes - Part 2 (#3181)

Fixes include:
- Translating state keys that contain user IDs to their respective room
keys for both querying and sending state events
- **NOTE**: there may be design discussion needed on what should happen
when sender keys cannot be found for users
- A simple fix for kicking guests from rooms properly
- Logic for boundary history visibilities was slightly off (I'm
surprised this only manifested in pseudo ID room versions)

Signed-off-by: `Sam Wedgwood <sam@wedgwood.dev>`

clientapi/routing/sendevent.go

@@ -29,6 +29,7 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/syncapi/synctypes"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
@@ -92,6 +93,30 @@ func SendEvent(
 		}
 	}
 
+	// Translate user ID state keys to room keys in pseudo ID rooms
+	if roomVersion == gomatrixserverlib.RoomVersionPseudoIDs && stateKey != nil {
+		parsedRoomID, innerErr := spec.NewRoomID(roomID)
+		if innerErr != nil {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.InvalidParam("invalid room ID"),
+			}
+		}
+
+		newStateKey, innerErr := synctypes.FromClientStateKey(*parsedRoomID, *stateKey, func(roomID spec.RoomID, userID spec.UserID) (*spec.SenderID, error) {
+			return rsAPI.QuerySenderIDForUser(req.Context(), roomID, userID)
+		})
+		if innerErr != nil {
+			// TODO: work out better logic for failure cases (e.g. sender ID not found)
+			util.GetLogger(req.Context()).WithError(innerErr).Error("synctypes.FromClientStateKey failed")
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.Unknown("internal server error"),
+			}
+		}
+		stateKey = newStateKey
+	}
+
 	// create a mutex for the specific user in the specific room
 	// this avoids a situation where events that are received in quick succession are sent to the roomserver in a jumbled order
 	userID := device.UserID

clientapi/routing/sendevent_test.go

@@ -0,0 +1,275 @@
+package routing
+
+import (
+	"context"
+	"crypto/ed25519"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	rsapi "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/dendrite/setup/config"
+	uapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/gomatrixserverlib/fclient"
+	"github.com/matrix-org/gomatrixserverlib/spec"
+	"gotest.tools/v3/assert"
+)
+
+// Mock roomserver API for testing
+//
+// Currently pretty specialised for the pseudo ID test, so will need
+// editing if future (other) sendevent tests are using this.
+type sendEventTestRoomserverAPI struct {
+	rsapi.ClientRoomserverAPI
+	t           *testing.T
+	roomIDStr   string
+	roomVersion gomatrixserverlib.RoomVersion
+	roomState   []*types.HeaderedEvent
+
+	// userID -> room key
+	senderMapping map[string]ed25519.PrivateKey
+
+	savedInputRoomEvents []rsapi.InputRoomEvent
+}
+
+func (s *sendEventTestRoomserverAPI) QueryRoomVersionForRoom(ctx context.Context, roomID string) (gomatrixserverlib.RoomVersion, error) {
+	if roomID == s.roomIDStr {
+		return s.roomVersion, nil
+	} else {
+		s.t.Logf("room version queried for %s", roomID)
+		return "", fmt.Errorf("unknown room")
+	}
+}
+
+func (s *sendEventTestRoomserverAPI) QueryCurrentState(ctx context.Context, req *rsapi.QueryCurrentStateRequest, res *rsapi.QueryCurrentStateResponse) error {
+	res.StateEvents = map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent{}
+	for _, stateKeyTuple := range req.StateTuples {
+		for _, stateEv := range s.roomState {
+			if stateEv.Type() == stateKeyTuple.EventType && stateEv.StateKey() != nil && *stateEv.StateKey() == stateKeyTuple.StateKey {
+				res.StateEvents[stateKeyTuple] = stateEv
+			}
+		}
+	}
+	return nil
+}
+
+func (s *sendEventTestRoomserverAPI) QueryLatestEventsAndState(ctx context.Context, req *rsapi.QueryLatestEventsAndStateRequest, res *rsapi.QueryLatestEventsAndStateResponse) error {
+	if req.RoomID == s.roomIDStr {
+		res.RoomExists = true
+		res.RoomVersion = s.roomVersion
+
+		res.StateEvents = make([]*types.HeaderedEvent, len(s.roomState))
+		copy(res.StateEvents, s.roomState)
+
+		res.LatestEvents = []string{}
+		res.Depth = 1
+		return nil
+	} else {
+		s.t.Logf("room event/state queried for %s", req.RoomID)
+		return fmt.Errorf("unknown room")
+	}
+
+}
+
+func (s *sendEventTestRoomserverAPI) QuerySenderIDForUser(
+	ctx context.Context,
+	roomID spec.RoomID,
+	userID spec.UserID,
+) (*spec.SenderID, error) {
+	if roomID.String() == s.roomIDStr {
+		if s.roomVersion == gomatrixserverlib.RoomVersionPseudoIDs {
+			roomKey, ok := s.senderMapping[userID.String()]
+			if ok {
+				sender := spec.SenderIDFromPseudoIDKey(roomKey)
+				return &sender, nil
+			} else {
+				return nil, nil
+			}
+		} else {
+			senderID := spec.SenderIDFromUserID(userID)
+			return &senderID, nil
+		}
+	}
+
+	return nil, fmt.Errorf("room not found")
+}
+
+func (s *sendEventTestRoomserverAPI) QueryUserIDForSender(
+	ctx context.Context,
+	roomID spec.RoomID,
+	senderID spec.SenderID,
+) (*spec.UserID, error) {
+	if roomID.String() == s.roomIDStr {
+		if s.roomVersion == gomatrixserverlib.RoomVersionPseudoIDs {
+			for uID, roomKey := range s.senderMapping {
+				if string(spec.SenderIDFromPseudoIDKey(roomKey)) == string(senderID) {
+					parsedUserID, err := spec.NewUserID(uID, true)
+					if err != nil {
+						s.t.Fatalf("Mock QueryUserIDForSender failed: %s", err)
+					}
+					return parsedUserID, nil
+				}
+			}
+		} else {
+			userID := senderID.ToUserID()
+			if userID == nil {
+				return nil, fmt.Errorf("bad sender ID")
+			}
+			return userID, nil
+		}
+	}
+
+	return nil, fmt.Errorf("room not found")
+}
+
+func (s *sendEventTestRoomserverAPI) SigningIdentityFor(ctx context.Context, roomID spec.RoomID, sender spec.UserID) (fclient.SigningIdentity, error) {
+	if s.roomIDStr == roomID.String() {
+		if s.roomVersion == gomatrixserverlib.RoomVersionPseudoIDs {
+			roomKey, ok := s.senderMapping[sender.String()]
+			if !ok {
+				s.t.Logf("SigningIdentityFor used with unknown user ID: %v", sender.String())
+				return fclient.SigningIdentity{}, fmt.Errorf("could not get signing identity for %v", sender.String())
+			}
+			return fclient.SigningIdentity{PrivateKey: roomKey}, nil
+		} else {
+			return fclient.SigningIdentity{PrivateKey: ed25519.NewKeyFromSeed(make([]byte, 32))}, nil
+		}
+	}
+
+	return fclient.SigningIdentity{}, fmt.Errorf("room not found")
+}
+
+func (s *sendEventTestRoomserverAPI) InputRoomEvents(ctx context.Context, req *rsapi.InputRoomEventsRequest, res *rsapi.InputRoomEventsResponse) {
+	s.savedInputRoomEvents = req.InputRoomEvents
+}
+
+// Test that user ID state keys are translated correctly
+func Test_SendEvent_PseudoIDStateKeys(t *testing.T) {
+	nonpseudoIDRoomVersion := gomatrixserverlib.RoomVersionV10
+	pseudoIDRoomVersion := gomatrixserverlib.RoomVersionPseudoIDs
+
+	senderKeySeed := make([]byte, 32)
+	senderUserID := "@testuser:domain"
+	senderPrivKey := ed25519.NewKeyFromSeed(senderKeySeed)
+	senderPseudoID := string(spec.SenderIDFromPseudoIDKey(senderPrivKey))
+
+	eventType := "com.example.test"
+	roomIDStr := "!id:domain"
+
+	device := &uapi.Device{
+		UserID: senderUserID,
+	}
+
+	t.Run("user ID state key are not translated to room key in non-pseudo ID room", func(t *testing.T) {
+		eventsJSON := []string{
+			fmt.Sprintf(`{"type":"m.room.create","state_key":"","room_id":"%v","sender":"%v","content":{"creator":"%v","room_version":"%v"}}`, roomIDStr, senderUserID, senderUserID, nonpseudoIDRoomVersion),
+			fmt.Sprintf(`{"type":"m.room.member","state_key":"%v","room_id":"%v","sender":"%v","content":{"membership":"join"}}`, senderUserID, roomIDStr, senderUserID),
+		}
+
+		roomState, err := createEvents(eventsJSON, nonpseudoIDRoomVersion)
+		if err != nil {
+			t.Fatalf("failed to prepare state events: %s", err.Error())
+		}
+
+		rsAPI := &sendEventTestRoomserverAPI{
+			t:           t,
+			roomIDStr:   roomIDStr,
+			roomVersion: nonpseudoIDRoomVersion,
+			roomState:   roomState,
+		}
+
+		req, err := http.NewRequest("POST", "https://domain", io.NopCloser(strings.NewReader("{}")))
+		if err != nil {
+			t.Fatalf("failed to make new request: %s", err.Error())
+		}
+
+		cfg := &config.ClientAPI{}
+
+		resp := SendEvent(req, device, roomIDStr, eventType, nil, &senderUserID, cfg, rsAPI, nil)
+
+		if resp.Code != http.StatusOK {
+			t.Fatalf("non-200 HTTP code returned: %v\nfull response: %v", resp.Code, resp)
+		}
+
+		assert.Equal(t, len(rsAPI.savedInputRoomEvents), 1)
+
+		ev := rsAPI.savedInputRoomEvents[0]
+		stateKey := ev.Event.StateKey()
+		if stateKey == nil {
+			t.Fatalf("submitted InputRoomEvent has nil state key, when it should be %v", senderUserID)
+		}
+		if *stateKey != senderUserID {
+			t.Fatalf("expected submitted InputRoomEvent to have user ID state key\nfound: %v\nexpected: %v", *stateKey, senderUserID)
+		}
+	})
+
+	t.Run("user ID state key are translated to room key in pseudo ID room", func(t *testing.T) {
+		eventsJSON := []string{
+			fmt.Sprintf(`{"type":"m.room.create","state_key":"","room_id":"%v","sender":"%v","content":{"creator":"%v","room_version":"%v"}}`, roomIDStr, senderPseudoID, senderPseudoID, pseudoIDRoomVersion),
+			fmt.Sprintf(`{"type":"m.room.member","state_key":"%v","room_id":"%v","sender":"%v","content":{"membership":"join"}}`, senderPseudoID, roomIDStr, senderPseudoID),
+		}
+
+		roomState, err := createEvents(eventsJSON, pseudoIDRoomVersion)
+		if err != nil {
+			t.Fatalf("failed to prepare state events: %s", err.Error())
+		}
+
+		rsAPI := &sendEventTestRoomserverAPI{
+			t:           t,
+			roomIDStr:   roomIDStr,
+			roomVersion: pseudoIDRoomVersion,
+			senderMapping: map[string]ed25519.PrivateKey{
+				senderUserID: senderPrivKey,
+			},
+			roomState: roomState,
+		}
+
+		req, err := http.NewRequest("POST", "https://domain", io.NopCloser(strings.NewReader("{}")))
+		if err != nil {
+			t.Fatalf("failed to make new request: %s", err.Error())
+		}
+
+		cfg := &config.ClientAPI{}
+
+		resp := SendEvent(req, device, roomIDStr, eventType, nil, &senderUserID, cfg, rsAPI, nil)
+
+		if resp.Code != http.StatusOK {
+			t.Fatalf("non-200 HTTP code returned: %v\nfull response: %v", resp.Code, resp)
+		}
+
+		assert.Equal(t, len(rsAPI.savedInputRoomEvents), 1)
+
+		ev := rsAPI.savedInputRoomEvents[0]
+		stateKey := ev.Event.StateKey()
+		if stateKey == nil {
+			t.Fatalf("submitted InputRoomEvent has nil state key, when it should be %v", senderPseudoID)
+		}
+		if *stateKey != senderPseudoID {
+			t.Fatalf("expected submitted InputRoomEvent to have pseudo ID state key\nfound: %v\nexpected: %v", *stateKey, senderPseudoID)
+		}
+	})
+}
+
+func createEvents(eventsJSON []string, roomVer gomatrixserverlib.RoomVersion) ([]*types.HeaderedEvent, error) {
+	events := make([]*types.HeaderedEvent, len(eventsJSON))
+
+	roomVerImpl, err := gomatrixserverlib.GetRoomVersion(roomVer)
+	if err != nil {
+		return nil, fmt.Errorf("no roomver impl: %s", err.Error())
+	}
+
+	for i, eventJSON := range eventsJSON {
+		pdu, evErr := roomVerImpl.NewEventFromTrustedJSON([]byte(eventJSON), false)
+		if evErr != nil {
+			return nil, fmt.Errorf("failed to make event: %s", err.Error())
+		}
+		ev := types.HeaderedEvent{PDU: pdu}
+		events[i] = &ev
+	}
+
+	return events, nil
+}

clientapi/routing/state.go

@@ -217,6 +217,37 @@ func OnIncomingStateTypeRequest(
 	var worldReadable bool
 	var wantLatestState bool
 
+	roomVer, err := rsAPI.QueryRoomVersionForRoom(ctx, roomID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden(fmt.Sprintf("Unknown room %q or user %q has never joined this room", roomID, device.UserID)),
+		}
+	}
+
+	// Translate user ID state keys to room keys in pseudo ID rooms
+	if roomVer == gomatrixserverlib.RoomVersionPseudoIDs {
+		parsedRoomID, err := spec.NewRoomID(roomID)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusNotFound,
+				JSON: spec.InvalidParam("invalid room ID"),
+			}
+		}
+		newStateKey, err := synctypes.FromClientStateKey(*parsedRoomID, stateKey, func(roomID spec.RoomID, userID spec.UserID) (*spec.SenderID, error) {
+			return rsAPI.QuerySenderIDForUser(ctx, roomID, userID)
+		})
+		if err != nil {
+			// TODO: work out better logic for failure cases (e.g. sender ID not found)
+			util.GetLogger(ctx).WithError(err).Error("synctypes.FromClientStateKey failed")
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.Unknown("internal server error"),
+			}
+		}
+		stateKey = *newStateKey
+	}
+
 	// 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

clientapi/routing/state_test.go

@@ -0,0 +1,253 @@
+package routing
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"testing"
+
+	rsapi "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/dendrite/setup/config"
+	uapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/gomatrixserverlib/spec"
+	"github.com/matrix-org/util"
+	"gotest.tools/v3/assert"
+)
+
+var ()
+
+type stateTestRoomserverAPI struct {
+	rsapi.RoomserverInternalAPI
+	t           *testing.T
+	roomState   map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent
+	roomIDStr   string
+	roomVersion gomatrixserverlib.RoomVersion
+	userIDStr   string
+	// userID -> senderID
+	senderMapping map[string]string
+}
+
+func (s stateTestRoomserverAPI) QueryRoomVersionForRoom(ctx context.Context, roomID string) (gomatrixserverlib.RoomVersion, error) {
+	if roomID == s.roomIDStr {
+		return s.roomVersion, nil
+	} else {
+		s.t.Logf("room version queried for %s", roomID)
+		return "", fmt.Errorf("unknown room")
+	}
+}
+
+func (s stateTestRoomserverAPI) QueryLatestEventsAndState(
+	ctx context.Context,
+	req *rsapi.QueryLatestEventsAndStateRequest,
+	res *rsapi.QueryLatestEventsAndStateResponse,
+) error {
+	res.RoomExists = req.RoomID == s.roomIDStr
+	if !res.RoomExists {
+		return nil
+	}
+
+	res.StateEvents = []*types.HeaderedEvent{}
+	for _, stateKeyTuple := range req.StateToFetch {
+		val, ok := s.roomState[stateKeyTuple]
+		if ok && val != nil {
+			res.StateEvents = append(res.StateEvents, val)
+		}
+	}
+
+	return nil
+}
+
+func (s stateTestRoomserverAPI) QueryMembershipForUser(
+	ctx context.Context,
+	req *rsapi.QueryMembershipForUserRequest,
+	res *rsapi.QueryMembershipForUserResponse,
+) error {
+	if req.UserID.String() == s.userIDStr {
+		res.HasBeenInRoom = true
+		res.IsInRoom = true
+		res.RoomExists = true
+		res.Membership = spec.Join
+	}
+
+	return nil
+}
+
+func (s stateTestRoomserverAPI) QuerySenderIDForUser(
+	ctx context.Context,
+	roomID spec.RoomID,
+	userID spec.UserID,
+) (*spec.SenderID, error) {
+	sID, ok := s.senderMapping[userID.String()]
+	if ok {
+		sender := spec.SenderID(sID)
+		return &sender, nil
+	} else {
+		return nil, nil
+	}
+}
+
+func (s stateTestRoomserverAPI) QueryUserIDForSender(
+	ctx context.Context,
+	roomID spec.RoomID,
+	senderID spec.SenderID,
+) (*spec.UserID, error) {
+	for uID, sID := range s.senderMapping {
+		if sID == string(senderID) {
+			parsedUserID, err := spec.NewUserID(uID, true)
+			if err != nil {
+				s.t.Fatalf("Mock QueryUserIDForSender failed: %s", err)
+			}
+			return parsedUserID, nil
+		}
+	}
+	return nil, nil
+}
+
+func (s stateTestRoomserverAPI) QueryStateAfterEvents(
+	ctx context.Context,
+	req *rsapi.QueryStateAfterEventsRequest,
+	res *rsapi.QueryStateAfterEventsResponse,
+) error {
+	return nil
+}
+
+func Test_OnIncomingStateTypeRequest(t *testing.T) {
+	var tempRoomServerCfg config.RoomServer
+	tempRoomServerCfg.Defaults(config.DefaultOpts{})
+	defaultRoomVersion := tempRoomServerCfg.DefaultRoomVersion
+	pseudoIDRoomVersion := gomatrixserverlib.RoomVersionPseudoIDs
+	nonPseudoIDRoomVersion := gomatrixserverlib.RoomVersionV10
+
+	userIDStr := "@testuser:domain"
+	eventType := "com.example.test"
+	stateKey := "testStateKey"
+	roomIDStr := "!id:domain"
+
+	device := &uapi.Device{
+		UserID: userIDStr,
+	}
+
+	t.Run("request simple state key", func(t *testing.T) {
+		ctx := context.Background()
+
+		rsAPI := stateTestRoomserverAPI{
+			roomVersion: defaultRoomVersion,
+			roomIDStr:   roomIDStr,
+			roomState: map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent{
+				{
+					EventType: eventType,
+					StateKey:  stateKey,
+				}: mustCreateStatePDU(t, defaultRoomVersion, roomIDStr, eventType, stateKey, map[string]interface{}{
+					"foo": "bar",
+				}),
+			},
+			userIDStr: userIDStr,
+		}
+
+		jsonResp := OnIncomingStateTypeRequest(ctx, device, rsAPI, roomIDStr, eventType, stateKey, false)
+
+		assert.DeepEqual(t, jsonResp, util.JSONResponse{
+			Code: http.StatusOK,
+			JSON: spec.RawJSON(`{"foo":"bar"}`),
+		})
+	})
+
+	t.Run("user ID key translated to room key in pseudo ID rooms", func(t *testing.T) {
+		ctx := context.Background()
+
+		stateSenderUserID := "@sender:domain"
+		stateSenderRoomKey := "testsenderkey"
+
+		rsAPI := stateTestRoomserverAPI{
+			roomVersion: pseudoIDRoomVersion,
+			roomIDStr:   roomIDStr,
+			roomState: map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent{
+				{
+					EventType: eventType,
+					StateKey:  stateSenderRoomKey,
+				}: mustCreateStatePDU(t, pseudoIDRoomVersion, roomIDStr, eventType, stateSenderRoomKey, map[string]interface{}{
+					"foo": "bar",
+				}),
+				{
+					EventType: eventType,
+					StateKey:  stateSenderUserID,
+				}: mustCreateStatePDU(t, pseudoIDRoomVersion, roomIDStr, eventType, stateSenderUserID, map[string]interface{}{
+					"not": "thisone",
+				}),
+			},
+			userIDStr: userIDStr,
+			senderMapping: map[string]string{
+				stateSenderUserID: stateSenderRoomKey,
+			},
+		}
+
+		jsonResp := OnIncomingStateTypeRequest(ctx, device, rsAPI, roomIDStr, eventType, stateSenderUserID, false)
+
+		assert.DeepEqual(t, jsonResp, util.JSONResponse{
+			Code: http.StatusOK,
+			JSON: spec.RawJSON(`{"foo":"bar"}`),
+		})
+	})
+
+	t.Run("user ID key not translated to room key in non-pseudo ID rooms", func(t *testing.T) {
+		ctx := context.Background()
+
+		stateSenderUserID := "@sender:domain"
+		stateSenderRoomKey := "testsenderkey"
+
+		rsAPI := stateTestRoomserverAPI{
+			roomVersion: nonPseudoIDRoomVersion,
+			roomIDStr:   roomIDStr,
+			roomState: map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent{
+				{
+					EventType: eventType,
+					StateKey:  stateSenderRoomKey,
+				}: mustCreateStatePDU(t, nonPseudoIDRoomVersion, roomIDStr, eventType, stateSenderRoomKey, map[string]interface{}{
+					"not": "thisone",
+				}),
+				{
+					EventType: eventType,
+					StateKey:  stateSenderUserID,
+				}: mustCreateStatePDU(t, nonPseudoIDRoomVersion, roomIDStr, eventType, stateSenderUserID, map[string]interface{}{
+					"foo": "bar",
+				}),
+			},
+			userIDStr: userIDStr,
+			senderMapping: map[string]string{
+				stateSenderUserID: stateSenderUserID,
+			},
+		}
+
+		jsonResp := OnIncomingStateTypeRequest(ctx, device, rsAPI, roomIDStr, eventType, stateSenderUserID, false)
+
+		assert.DeepEqual(t, jsonResp, util.JSONResponse{
+			Code: http.StatusOK,
+			JSON: spec.RawJSON(`{"foo":"bar"}`),
+		})
+	})
+}
+
+func mustCreateStatePDU(t *testing.T, roomVer gomatrixserverlib.RoomVersion, roomID string, stateType string, stateKey string, stateContent map[string]interface{}) *types.HeaderedEvent {
+	t.Helper()
+	roomVerImpl := gomatrixserverlib.MustGetRoomVersion(roomVer)
+
+	evBytes, err := json.Marshal(map[string]interface{}{
+		"room_id":   roomID,
+		"type":      stateType,
+		"state_key": stateKey,
+		"content":   stateContent,
+	})
+	if err != nil {
+		t.Fatalf("failed to create event: %v", err)
+	}
+
+	ev, err := roomVerImpl.NewEventFromTrustedJSON(evBytes, false)
+	if err != nil {
+		t.Fatalf("failed to create event: %v", err)
+	}
+
+	return &types.HeaderedEvent{PDU: ev}
+}

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/matrix-org/dugong v0.0.0-20210921133753-66e6b1c67e2e
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91
 	github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20230807152937-c48e302e15ac
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230823153616-484e7693bb8d
 	github.com/matrix-org/pinecone v0.11.1-0.20230810010612-ea4c33717fd7
 	github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
 	github.com/mattn/go-sqlite3 v1.14.17
@@ -36,7 +36,7 @@ require (
 	github.com/prometheus/client_golang v1.16.0
 	github.com/sirupsen/logrus v1.9.3
 	github.com/stretchr/testify v1.8.2
-	github.com/tidwall/gjson v1.15.0
+	github.com/tidwall/gjson v1.16.0
 	github.com/tidwall/sjson v1.2.5
 	github.com/uber/jaeger-client-go v2.30.0+incompatible
 	github.com/uber/jaeger-lib v2.4.1+incompatible

go.sum

@@ -208,8 +208,8 @@ github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91 h1:s7fexw
 github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91/go.mod h1:e+cg2q7C7yE5QnAXgzo512tgFh1RbQLC0+jozuegKgo=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530 h1:kHKxCOLcHH8r4Fzarl4+Y3K5hjothkVW5z7T1dUM11U=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230807152937-c48e302e15ac h1:s4EZRNT6/TtGAzcO6yzL+UTv96vEeeaH6y2RrIOfsWw=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230823153616-484e7693bb8d h1:yFoT2nyjD4TFrgYMJGgrotFbTLjaYKfZbRmnsj7lvZE=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230807152937-c48e302e15ac/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230823153616-484e7693bb8d/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
 github.com/matrix-org/pinecone v0.11.1-0.20230810010612-ea4c33717fd7 h1:6t8kJr8i1/1I5nNttw6nn1ryQJgzVlBmSGgPiiaTdw4=
 github.com/matrix-org/pinecone v0.11.1-0.20230810010612-ea4c33717fd7/go.mod h1:ReWMS/LoVnOiRAdq9sNUC2NZnd1mZkMNB52QhpTRWjg=
 github.com/matrix-org/util v0.0.0-20221111132719-399730281e66 h1:6z4KxomXSIGWqhHcfzExgkH3Z3UkIXry4ibJS4Aqz2Y=
@@ -318,8 +318,8 @@ github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO
 github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
 github.com/stretchr/testify v1.8.2/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 github.com/tidwall/gjson v1.14.2/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
-github.com/tidwall/gjson v1.15.0 h1:5n/pM+v3r5ujuNl4YLZLsQ+UE5jlkLVm7jMzT5Mpolw=
+github.com/tidwall/gjson v1.16.0 h1:SyXa+dsSPpUlcwEDuKuEBJEz5vzTvOea+9rjyYodQFg=
-github.com/tidwall/gjson v1.15.0/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
+github.com/tidwall/gjson v1.16.0/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
 github.com/tidwall/match v1.1.1 h1:+Ho715JplO36QYgwN9PGYNhgZvoUSc9X2c80KVTi+GA=
 github.com/tidwall/match v1.1.1/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
 github.com/tidwall/pretty v1.2.0/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=

roomserver/internal/input/input_events.go

@@ -933,12 +933,7 @@ func (r *Inputer) kickGuests(ctx context.Context, event gomatrixserverlib.PDU, r
 			return err
 		}
 
-		userID, err := spec.NewUserID(stateKey, true)
+		signingIdentity, err := r.SigningIdentity(ctx, *validRoomID, *memberUserID)
-		if err != nil {
-			return err
-		}
-
-		signingIdentity, err := r.SigningIdentity(ctx, *validRoomID, *userID)
 		if err != nil {
 			return err
 		}

syncapi/internal/history_visibility.go

@@ -163,7 +163,10 @@ func ApplyHistoryVisibilityFilter(
 		// by setting the effective evVis to the least restrictive
 		// of the old vs new.
 		// https://spec.matrix.org/v1.3/client-server-api/#server-behaviour-5
-		if hisVis, err := ev.HistoryVisibility(); err == nil {
+		if ev.Type() == spec.MRoomHistoryVisibility {
+			hisVis, err := ev.HistoryVisibility()
+
+			if err == nil && hisVis != "" {
 				prevHisVis := gjson.GetBytes(ev.Unsigned(), "prev_content.history_visibility").String()
 				oldPrio, ok := historyVisibilityPriority[gomatrixserverlib.HistoryVisibility(prevHisVis)]
 				// if we can't get the previous history visibility, default to shared.
@@ -174,6 +177,9 @@ func ApplyHistoryVisibilityFilter(
 				newPrio := historyVisibilityPriority[hisVis]
 				if oldPrio < newPrio {
 					evVis.visibility = gomatrixserverlib.HistoryVisibility(prevHisVis)
+				} else {
+					evVis.visibility = hisVis
+				}
 			}
 		}
 		// do the actual check

syncapi/internal/history_visibility_test.go

@@ -0,0 +1,214 @@
+package internal
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"testing"
+
+	rsapi "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/gomatrixserverlib/spec"
+	"gotest.tools/v3/assert"
+)
+
+type mockHisVisRoomserverAPI struct {
+	rsapi.RoomserverInternalAPI
+	events []*types.HeaderedEvent
+	roomID string
+}
+
+func (s *mockHisVisRoomserverAPI) QueryMembershipAtEvent(ctx context.Context, roomID spec.RoomID, eventIDs []string, senderID spec.SenderID) (map[string]*types.HeaderedEvent, error) {
+	if roomID.String() == s.roomID {
+		membershipMap := map[string]*types.HeaderedEvent{}
+
+		for _, queriedEventID := range eventIDs {
+			for _, event := range s.events {
+				if event.EventID() == queriedEventID {
+					membershipMap[queriedEventID] = event
+				}
+			}
+		}
+
+		return membershipMap, nil
+	} else {
+		return nil, fmt.Errorf("room not found: \"%v\"", roomID)
+	}
+}
+
+func (s *mockHisVisRoomserverAPI) QuerySenderIDForUser(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (*spec.SenderID, error) {
+	senderID := spec.SenderIDFromUserID(userID)
+	return &senderID, nil
+}
+
+func (s *mockHisVisRoomserverAPI) QueryUserIDForSender(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+	userID := senderID.ToUserID()
+	if userID == nil {
+		return nil, fmt.Errorf("sender ID not user ID")
+	}
+	return userID, nil
+}
+
+type mockDB struct {
+	storage.DatabaseTransaction
+	// user ID -> membership (i.e. 'join', 'leave', etc.)
+	currentMembership map[string]string
+	roomID            string
+}
+
+func (s *mockDB) SelectMembershipForUser(ctx context.Context, roomID string, userID string, pos int64) (string, int, error) {
+	if roomID == s.roomID {
+		membership, ok := s.currentMembership[userID]
+		if !ok {
+			return spec.Leave, math.MaxInt64, nil
+		}
+		return membership, math.MaxInt64, nil
+	}
+
+	return "", 0, fmt.Errorf("room not found: \"%v\"", roomID)
+}
+
+// Tests logic around history visibility boundaries
+//
+// Specifically that if a room's history visibility before or after a particular history visibility event
+// allows them to see events (a boundary), then the history visibility event itself should be shown
+// ( spec: https://spec.matrix.org/v1.8/client-server-api/#server-behaviour-5 )
+//
+// This also aims to emulate "Only see history_visibility changes on bounadries" in sytest/tests/30rooms/30history-visibility.pl
+func Test_ApplyHistoryVisbility_Boundaries(t *testing.T) {
+	ctx := context.Background()
+
+	roomID := "!roomid:domain"
+
+	creatorUserID := spec.NewUserIDOrPanic("@creator:domain", false)
+	otherUserID := spec.NewUserIDOrPanic("@other:domain", false)
+	roomVersion := gomatrixserverlib.RoomVersionV10
+	roomVerImpl := gomatrixserverlib.MustGetRoomVersion(roomVersion)
+
+	eventsJSON := []struct {
+		id   string
+		json string
+	}{
+		{id: "$create-event", json: fmt.Sprintf(`{
+			"type": "m.room.create", "state_key": "",
+			"room_id": "%v", "sender": "%v",
+			"content": {"creator": "%v", "room_version": "%v"}
+		}`, roomID, creatorUserID.String(), creatorUserID.String(), roomVersion)},
+		{id: "$creator-joined", json: fmt.Sprintf(`{
+			"type": "m.room.member", "state_key": "%v",
+			"room_id": "%v", "sender": "%v",
+			"content": {"membership": "join"}
+		}`, creatorUserID.String(), roomID, creatorUserID.String())},
+		{id: "$hisvis-1", json: fmt.Sprintf(`{
+			"type": "m.room.history_visibility", "state_key": "",
+			"room_id": "%v", "sender": "%v",
+			"content": {"history_visibility": "shared"}
+		}`, roomID, creatorUserID.String())},
+		{id: "$msg-1", json: fmt.Sprintf(`{
+			"type": "m.room.message",
+			"room_id": "%v", "sender": "%v",
+			"content": {"body": "1"}
+		}`, roomID, creatorUserID.String())},
+		{id: "$hisvis-2", json: fmt.Sprintf(`{
+			"type": "m.room.history_visibility", "state_key": "",
+			"room_id": "%v", "sender": "%v",
+			"content": {"history_visibility": "joined"},
+			"unsigned": {"prev_content": {"history_visibility": "shared"}}
+		}`, roomID, creatorUserID.String())},
+		{id: "$msg-2", json: fmt.Sprintf(`{
+			"type": "m.room.message",
+			"room_id": "%v", "sender": "%v",
+			"content": {"body": "1"}
+		}`, roomID, creatorUserID.String())},
+		{id: "$hisvis-3", json: fmt.Sprintf(`{
+			"type": "m.room.history_visibility", "state_key": "",
+			"room_id": "%v", "sender": "%v",
+			"content": {"history_visibility": "invited"},
+			"unsigned": {"prev_content": {"history_visibility": "joined"}}
+		}`, roomID, creatorUserID.String())},
+		{id: "$msg-3", json: fmt.Sprintf(`{
+			"type": "m.room.message",
+			"room_id": "%v", "sender": "%v",
+			"content": {"body": "2"}
+		}`, roomID, creatorUserID.String())},
+		{id: "$hisvis-4", json: fmt.Sprintf(`{
+			"type": "m.room.history_visibility", "state_key": "",
+			"room_id": "%v", "sender": "%v",
+			"content": {"history_visibility": "shared"},
+			"unsigned": {"prev_content": {"history_visibility": "invited"}}
+		}`, roomID, creatorUserID.String())},
+		{id: "$msg-4", json: fmt.Sprintf(`{
+			"type": "m.room.message",
+			"room_id": "%v", "sender": "%v",
+			"content": {"body": "3"}
+		}`, roomID, creatorUserID.String())},
+		{id: "$other-joined", json: fmt.Sprintf(`{
+			"type": "m.room.member", "state_key": "%v",
+			"room_id": "%v", "sender": "%v",
+			"content": {"membership": "join"}
+		}`, otherUserID.String(), roomID, otherUserID.String())},
+	}
+
+	events := make([]*types.HeaderedEvent, len(eventsJSON))
+
+	hisVis := gomatrixserverlib.HistoryVisibilityShared
+
+	for i, eventJSON := range eventsJSON {
+		pdu, err := roomVerImpl.NewEventFromTrustedJSONWithEventID(eventJSON.id, []byte(eventJSON.json), false)
+		if err != nil {
+			t.Fatalf("failed to prepare event %s for test: %s", eventJSON.id, err.Error())
+		}
+		events[i] = &types.HeaderedEvent{PDU: pdu}
+
+		// 'Visibility' should be the visibility of the room just before this event was sent
+		// (according to processRoomEvent in roomserver/internal/input/input_events.go)
+		events[i].Visibility = hisVis
+		if pdu.Type() == spec.MRoomHistoryVisibility {
+			newHisVis, err := pdu.HistoryVisibility()
+			if err != nil {
+				t.Fatalf("failed to prepare history visibility event: %s", err.Error())
+			}
+			hisVis = newHisVis
+		}
+	}
+
+	rsAPI := &mockHisVisRoomserverAPI{
+		events: events,
+		roomID: roomID,
+	}
+	syncDB := &mockDB{
+		roomID: roomID,
+		currentMembership: map[string]string{
+			creatorUserID.String(): spec.Join,
+			otherUserID.String():   spec.Join,
+		},
+	}
+
+	filteredEvents, err := ApplyHistoryVisibilityFilter(ctx, syncDB, rsAPI, events, nil, otherUserID, "hisVisTest")
+	if err != nil {
+		t.Fatalf("ApplyHistoryVisibility returned non-nil error: %s", err.Error())
+	}
+
+	filteredEventIDs := make([]string, len(filteredEvents))
+	for i, event := range filteredEvents {
+		filteredEventIDs[i] = event.EventID()
+	}
+
+	assert.DeepEqual(t,
+		[]string{
+			"$create-event",   // Always see m.room.create
+			"$creator-joined", // Always see membership
+			"$hisvis-1",       // Sets room to shared (technically the room is already shared since shared is default)
+			"$msg-1",          // Room currently 'shared'
+			"$hisvis-2",       // Room changed from 'shared' to 'joined', so boundary event and should be shared
+			// Other events hidden, as other is not joined yet
+			// hisvis-3 is also hidden, as it changes from joined to invited, neither of which is visible to other
+			"$hisvis-4",     // Changes from 'invited' to 'shared', so is a boundary event and visible
+			"$msg-4",        // Room is 'shared', so visible
+			"$other-joined", // other's membership
+		},
+		filteredEventIDs,
+	)
+}

syncapi/internal/keychange_test.go

@@ -59,22 +59,22 @@ func (k *mockKeyAPI) QueryDeviceMessages(ctx context.Context, req *userapi.Query
 func (k *mockKeyAPI) QuerySignatures(ctx context.Context, req *userapi.QuerySignaturesRequest, res *userapi.QuerySignaturesResponse) {
 }
 
-type mockRoomserverAPI struct {
+type keyChangeMockRoomserverAPI struct {
 	api.RoomserverInternalAPI
 	roomIDToJoinedMembers map[string][]string
 }
 
-func (s *mockRoomserverAPI) QueryUserIDForSender(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+func (s *keyChangeMockRoomserverAPI) QueryUserIDForSender(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
 	return spec.NewUserID(string(senderID), true)
 }
 
 // QueryRoomsForUser retrieves a list of room IDs matching the given query.
-func (s *mockRoomserverAPI) QueryRoomsForUser(ctx context.Context, userID spec.UserID, desiredMembership string) ([]spec.RoomID, error) {
+func (s *keyChangeMockRoomserverAPI) QueryRoomsForUser(ctx context.Context, userID spec.UserID, desiredMembership string) ([]spec.RoomID, error) {
 	return nil, nil
 }
 
 // QueryBulkStateContent does a bulk query for state event content in the given rooms.
-func (s *mockRoomserverAPI) QueryBulkStateContent(ctx context.Context, req *api.QueryBulkStateContentRequest, res *api.QueryBulkStateContentResponse) error {
+func (s *keyChangeMockRoomserverAPI) QueryBulkStateContent(ctx context.Context, req *api.QueryBulkStateContentRequest, res *api.QueryBulkStateContentResponse) error {
 	res.Rooms = make(map[string]map[gomatrixserverlib.StateKeyTuple]string)
 	if req.AllowWildcards && len(req.StateTuples) == 1 && req.StateTuples[0].EventType == spec.MRoomMember && req.StateTuples[0].StateKey == "*" {
 		for _, roomID := range req.RoomIDs {
@@ -91,7 +91,7 @@ func (s *mockRoomserverAPI) QueryBulkStateContent(ctx context.Context, req *api.
 }
 
 // QuerySharedUsers returns a list of users who share at least 1 room in common with the given user.
-func (s *mockRoomserverAPI) QuerySharedUsers(ctx context.Context, req *api.QuerySharedUsersRequest, res *api.QuerySharedUsersResponse) error {
+func (s *keyChangeMockRoomserverAPI) QuerySharedUsers(ctx context.Context, req *api.QuerySharedUsersRequest, res *api.QuerySharedUsersResponse) error {
 	roomsToQuery := req.IncludeRoomIDs
 	for roomID, members := range s.roomIDToJoinedMembers {
 		exclude := false
@@ -123,7 +123,7 @@ func (s *mockRoomserverAPI) QuerySharedUsers(ctx context.Context, req *api.Query
 
 // This is actually a database function, but seeing as we track the state inside the
 // *mockRoomserverAPI, we'll just comply with the interface here instead.
-func (s *mockRoomserverAPI) SharedUsers(ctx context.Context, userID string, otherUserIDs []string) ([]string, error) {
+func (s *keyChangeMockRoomserverAPI) SharedUsers(ctx context.Context, userID string, otherUserIDs []string) ([]string, error) {
 	commonUsers := []string{}
 	for _, members := range s.roomIDToJoinedMembers {
 		for _, member := range members {
@@ -211,7 +211,7 @@ func TestKeyChangeCatchupOnJoinShareNewUser(t *testing.T) {
 	syncResponse := types.NewResponse()
 	syncResponse = joinResponseWithRooms(syncResponse, syncingUser, []string{newlyJoinedRoom})
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			newlyJoinedRoom: {syncingUser, newShareUser},
 			"!another:room": {syncingUser},
@@ -234,7 +234,7 @@ func TestKeyChangeCatchupOnLeaveShareLeftUser(t *testing.T) {
 	syncResponse := types.NewResponse()
 	syncResponse = leaveResponseWithRooms(syncResponse, syncingUser, []string{newlyLeftRoom})
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			newlyLeftRoom:   {removeUser},
 			"!another:room": {syncingUser},
@@ -257,7 +257,7 @@ func TestKeyChangeCatchupOnJoinShareNoNewUsers(t *testing.T) {
 	syncResponse := types.NewResponse()
 	syncResponse = joinResponseWithRooms(syncResponse, syncingUser, []string{newlyJoinedRoom})
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			newlyJoinedRoom: {syncingUser, existingUser},
 			"!another:room": {syncingUser, existingUser},
@@ -279,7 +279,7 @@ func TestKeyChangeCatchupOnLeaveShareNoUsers(t *testing.T) {
 	syncResponse := types.NewResponse()
 	syncResponse = leaveResponseWithRooms(syncResponse, syncingUser, []string{newlyLeftRoom})
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			newlyLeftRoom:   {existingUser},
 			"!another:room": {syncingUser, existingUser},
@@ -343,7 +343,7 @@ func TestKeyChangeCatchupNoNewJoinsButMessages(t *testing.T) {
 	jr.Timeline = &types.Timeline{Events: roomTimelineEvents}
 	syncResponse.Rooms.Join[roomID] = jr
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			roomID: {syncingUser, existingUser},
 		},
@@ -369,7 +369,7 @@ func TestKeyChangeCatchupChangeAndLeft(t *testing.T) {
 	syncResponse = joinResponseWithRooms(syncResponse, syncingUser, []string{newlyJoinedRoom})
 	syncResponse = leaveResponseWithRooms(syncResponse, syncingUser, []string{newlyLeftRoom})
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			newlyJoinedRoom: {syncingUser, newShareUser, newShareUser2},
 			newlyLeftRoom:   {newlyLeftUser, newlyLeftUser2},
@@ -459,7 +459,7 @@ func TestKeyChangeCatchupChangeAndLeftSameRoom(t *testing.T) {
 	lr.Timeline = &types.Timeline{Events: roomEvents}
 	syncResponse.Rooms.Leave[roomID] = lr
 
-	rsAPI := &mockRoomserverAPI{
+	rsAPI := &keyChangeMockRoomserverAPI{
 		roomIDToJoinedMembers: map[string][]string{
 			roomID:          {newShareUser, newShareUser2},
 			"!another:room": {syncingUser},

syncapi/synctypes/clientevent.go

@@ -16,6 +16,8 @@
 package synctypes
 
 import (
+	"fmt"
+
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
@@ -118,3 +120,31 @@ func ToClientEventDefault(userIDQuery spec.UserIDForSender, event gomatrixserver
 	}
 	return ToClientEvent(event, FormatAll, sender, sk)
 }
+
+// If provided state key is a user ID (state keys beginning with @ are reserved for this purpose)
+// fetch it's associated sender ID and use that instead. Otherwise returns the same state key back.
+//
+// # This function either returns the state key that should be used, or an error
+//
+// TODO: handle failure cases better (e.g. no sender ID)
+func FromClientStateKey(roomID spec.RoomID, stateKey string, senderIDQuery spec.SenderIDForUser) (*string, error) {
+	if len(stateKey) >= 1 && stateKey[0] == '@' {
+		parsedStateKey, err := spec.NewUserID(stateKey, true)
+		if err != nil {
+			// If invalid user ID, then there is no associated state event.
+			return nil, fmt.Errorf("Provided state key begins with @ but is not a valid user ID: %s", err.Error())
+		}
+		senderID, err := senderIDQuery(roomID, *parsedStateKey)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to query sender ID: %s", err.Error())
+		}
+		if senderID == nil {
+			// If no sender ID, then there is no associated state event.
+			return nil, fmt.Errorf("No associated sender ID found.")
+		}
+		newStateKey := string(*senderID)
+		return &newStateKey, nil
+	} else {
+		return &stateKey, nil
+	}
+}