Move MakeJoin logic to GMSL (#3081)

80 files changed, 1161 insertions, 497 deletions

diff --git a/clientapi/auth/auth.go b/clientapi/auth/auth.go
index 479b9ac7..8fae45b8 100644
--- a/clientapi/auth/auth.go
+++ b/clientapi/auth/auth.go
@@ -68,8 +68,10 @@ func VerifyUserFromRequest(
 	}, &res)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("userAPI.QueryAccessToken failed")
-		jsonErr := spec.InternalServerError()
-		return nil, &jsonErr
+		return nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if res.Err != "" {
 		if strings.HasPrefix(strings.ToLower(res.Err), "forbidden:") { // TODO: use actual error and no string comparison
diff --git a/clientapi/auth/login_test.go b/clientapi/auth/login_test.go
index eb87d5e8..93d3e271 100644
--- a/clientapi/auth/login_test.go
+++ b/clientapi/auth/login_test.go
@@ -107,13 +107,13 @@ func TestBadLoginFromJSONReader(t *testing.T) {
 		Name string
 		Body string
 
-		WantErrCode string
+		WantErrCode spec.MatrixErrorCode
 	}{
-		{Name: "empty", WantErrCode: "M_BAD_JSON"},
+		{Name: "empty", WantErrCode: spec.ErrorBadJSON},
 		{
 			Name:        "badUnmarshal",
 			Body:        `badsyntaxJSON`,
-			WantErrCode: "M_BAD_JSON",
+			WantErrCode: spec.ErrorBadJSON,
 		},
 		{
 			Name: "badPassword",
@@ -123,7 +123,7 @@ func TestBadLoginFromJSONReader(t *testing.T) {
 				"password": "invalidpassword",
 				"device_id": "adevice"
             }`,
-			WantErrCode: "M_FORBIDDEN",
+			WantErrCode: spec.ErrorForbidden,
 		},
 		{
 			Name: "badToken",
@@ -132,7 +132,7 @@ func TestBadLoginFromJSONReader(t *testing.T) {
 				"token": "invalidtoken",
 				"device_id": "adevice"
             }`,
-			WantErrCode: "M_FORBIDDEN",
+			WantErrCode: spec.ErrorForbidden,
 		},
 		{
 			Name: "badType",
@@ -140,7 +140,7 @@ func TestBadLoginFromJSONReader(t *testing.T) {
 				"type": "m.login.invalid",
 				"device_id": "adevice"
             }`,
-			WantErrCode: "M_INVALID_PARAM",
+			WantErrCode: spec.ErrorInvalidParam,
 		},
 	}
 	for _, tst := range tsts {
@@ -157,7 +157,7 @@ func TestBadLoginFromJSONReader(t *testing.T) {
 			if errRes == nil {
 				cleanup(ctx, nil)
 				t.Fatalf("LoginFromJSONReader err: got %+v, want code %q", errRes, tst.WantErrCode)
-			} else if merr, ok := errRes.JSON.(*spec.MatrixError); ok && merr.ErrCode != tst.WantErrCode {
+			} else if merr, ok := errRes.JSON.(spec.MatrixError); ok && merr.ErrCode != tst.WantErrCode {
 				t.Fatalf("LoginFromJSONReader err: got %+v, want code %q", errRes, tst.WantErrCode)
 			}
 		})
diff --git a/clientapi/auth/login_token.go b/clientapi/auth/login_token.go
index 073f728d..eb631481 100644
--- a/clientapi/auth/login_token.go
+++ b/clientapi/auth/login_token.go
@@ -48,8 +48,10 @@ func (t *LoginTypeToken) LoginFromJSON(ctx context.Context, reqBytes []byte) (*L
 	var res uapi.QueryLoginTokenResponse
 	if err := t.UserAPI.QueryLoginToken(ctx, &uapi.QueryLoginTokenRequest{Token: r.Token}, &res); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("UserAPI.QueryLoginToken failed")
-		jsonErr := spec.InternalServerError()
-		return nil, nil, &jsonErr
+		return nil, nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if res.Data == nil {
 		return nil, nil, &util.JSONResponse{
diff --git a/clientapi/auth/user_interactive.go b/clientapi/auth/user_interactive.go
index 58d34865..92d83ad2 100644
--- a/clientapi/auth/user_interactive.go
+++ b/clientapi/auth/user_interactive.go
@@ -178,8 +178,10 @@ func (u *UserInteractive) NewSession() *util.JSONResponse {
 	sessionID, err := GenerateAccessToken()
 	if err != nil {
 		logrus.WithError(err).Error("failed to generate session ID")
-		res := spec.InternalServerError()
-		return &res
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	u.Lock()
 	u.Sessions[sessionID] = []string{}
@@ -193,15 +195,19 @@ func (u *UserInteractive) ResponseWithChallenge(sessionID string, response inter
 	mixedObjects := make(map[string]interface{})
 	b, err := json.Marshal(response)
 	if err != nil {
-		ise := spec.InternalServerError()
-		return &ise
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	_ = json.Unmarshal(b, &mixedObjects)
 	challenge := u.challenge(sessionID)
 	b, err = json.Marshal(challenge.JSON)
 	if err != nil {
-		ise := spec.InternalServerError()
-		return &ise
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	_ = json.Unmarshal(b, &mixedObjects)
 
diff --git a/clientapi/clientapi_test.go b/clientapi/clientapi_test.go
index 2c34c109..b339818a 100644
--- a/clientapi/clientapi_test.go
+++ b/clientapi/clientapi_test.go
@@ -33,6 +33,7 @@ import (
 	uapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrix"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/gomatrixserverlib/spec"
 	"github.com/matrix-org/util"
 	"github.com/stretchr/testify/assert"
 	"github.com/tidwall/gjson"
@@ -1105,7 +1106,7 @@ func Test3PID(t *testing.T) {
 				resp := threepid.GetValidatedResponse{}
 				switch r.URL.Query().Get("client_secret") {
 				case "fail":
-					resp.ErrCode = "M_SESSION_NOT_VALIDATED"
+					resp.ErrCode = string(spec.ErrorSessionNotValidated)
 				case "fail2":
 					resp.ErrCode = "some other error"
 				case "fail3":
diff --git a/clientapi/httputil/httputil.go b/clientapi/httputil/httputil.go
index aea0c3db..d9f44232 100644
--- a/clientapi/httputil/httputil.go
+++ b/clientapi/httputil/httputil.go
@@ -32,8 +32,10 @@ func UnmarshalJSONRequest(req *http.Request, iface interface{}) *util.JSONRespon
 	body, err := io.ReadAll(req.Body)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("io.ReadAll failed")
-		resp := spec.InternalServerError()
-		return &resp
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return UnmarshalJSON(body, iface)
diff --git a/clientapi/routing/account_data.go b/clientapi/routing/account_data.go
index 572b28ef..7eacf9cc 100644
--- a/clientapi/routing/account_data.go
+++ b/clientapi/routing/account_data.go
@@ -104,7 +104,10 @@ func SaveAccountData(
 	body, err := io.ReadAll(req.Body)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("io.ReadAll failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !json.Valid(body) {
@@ -157,7 +160,10 @@ func SaveReadMarker(
 	if r.FullyRead != "" {
 		data, err := json.Marshal(fullyReadEvent{EventID: r.FullyRead})
 		if err != nil {
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		dataReq := api.InputAccountDataRequest{
diff --git a/clientapi/routing/admin.go b/clientapi/routing/admin.go
index 4d2cea68..8dd662a1 100644
--- a/clientapi/routing/admin.go
+++ b/clientapi/routing/admin.go
@@ -31,7 +31,7 @@ func AdminEvacuateRoom(req *http.Request, rsAPI roomserverAPI.ClientRoomserverAP
 	}
 
 	affected, err := rsAPI.PerformAdminEvacuateRoom(req.Context(), vars["roomID"])
-	switch err {
+	switch err.(type) {
 	case nil:
 	case eventutil.ErrRoomNoExists:
 		return util.JSONResponse{
@@ -113,7 +113,7 @@ func AdminResetPassword(req *http.Request, cfg *config.ClientAPI, device *api.De
 	}, accAvailableResp); err != nil {
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 	if accAvailableResp.Available {
@@ -169,7 +169,10 @@ func AdminReindex(req *http.Request, cfg *config.ClientAPI, device *api.Device,
 	_, err := natsClient.RequestMsg(nats.NewMsg(cfg.Matrix.JetStream.Prefixed(jetstream.InputFulltextReindex)), time.Second*10)
 	if err != nil {
 		logrus.WithError(err).Error("failed to publish nats message")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: http.StatusOK,
@@ -231,10 +234,10 @@ func AdminDownloadState(req *http.Request, device *api.Device, rsAPI roomserverA
 		}
 	}
 	if err = rsAPI.PerformAdminDownloadState(req.Context(), roomID, device.UserID, spec.ServerName(serverName)); err != nil {
-		if errors.Is(err, eventutil.ErrRoomNoExists) {
+		if errors.Is(err, eventutil.ErrRoomNoExists{}) {
 			return util.JSONResponse{
 				Code: 200,
-				JSON: spec.NotFound(eventutil.ErrRoomNoExists.Error()),
+				JSON: spec.NotFound(err.Error()),
 			}
 		}
 		logrus.WithError(err).WithFields(logrus.Fields{
diff --git a/clientapi/routing/admin_whois.go b/clientapi/routing/admin_whois.go
index cb2b8a26..7d753656 100644
--- a/clientapi/routing/admin_whois.go
+++ b/clientapi/routing/admin_whois.go
@@ -61,7 +61,10 @@ func GetAdminWhois(
 	}, &queryRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("GetAdminWhois failed to query user devices")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	devices := make(map[string]deviceInfo)
diff --git a/clientapi/routing/aliases.go b/clientapi/routing/aliases.go
index 87c1f9ff..f6603be8 100644
--- a/clientapi/routing/aliases.go
+++ b/clientapi/routing/aliases.go
@@ -62,7 +62,10 @@ func GetAliases(
 		var queryRes api.QueryMembershipForUserResponse
 		if err := rsAPI.QueryMembershipForUser(req.Context(), &queryReq, &queryRes); err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("rsAPI.QueryMembershipsForRoom failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if !queryRes.IsInRoom {
 			return util.JSONResponse{
diff --git a/clientapi/routing/createroom.go b/clientapi/routing/createroom.go
index f0cdd6f5..bc960006 100644
--- a/clientapi/routing/createroom.go
+++ b/clientapi/routing/createroom.go
@@ -174,7 +174,10 @@ func createRoom(
 	_, userDomain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !cfg.Matrix.IsLocalServerName(userDomain) {
 		return util.JSONResponse{
@@ -218,7 +221,10 @@ func createRoom(
 	profile, err := appserviceAPI.RetrieveUserProfile(ctx, userID, asAPI, profileAPI)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("appserviceAPI.RetrieveUserProfile failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	createContent := map[string]interface{}{}
@@ -342,7 +348,10 @@ func createRoom(
 		err = rsAPI.GetRoomIDForAlias(ctx, &hasAliasReq, &aliasResp)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("aliasAPI.GetRoomIDForAlias failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if aliasResp.RoomID != "" {
 			return util.JSONResponse{
@@ -455,7 +464,10 @@ func createRoom(
 		err = builder.SetContent(e.Content)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("builder.SetContent failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if i > 0 {
 			builder.PrevEvents = []gomatrixserverlib.EventReference{builtEvents[i-1].EventReference()}
@@ -463,17 +475,26 @@ func createRoom(
 		var ev gomatrixserverlib.PDU
 		if err = builder.AddAuthEvents(&authEvents); err != nil {
 			util.GetLogger(ctx).WithError(err).Error("AddAuthEvents failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		ev, err = builder.Build(evTime, userDomain, cfg.Matrix.KeyID, cfg.Matrix.PrivateKey)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("buildEvent failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		if err = gomatrixserverlib.Allowed(ev, &authEvents); err != nil {
 			util.GetLogger(ctx).WithError(err).Error("gomatrixserverlib.Allowed failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		// Add the event to the list of auth events
@@ -481,7 +502,10 @@ func createRoom(
 		err = authEvents.AddEvent(ev)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("authEvents.AddEvent failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
@@ -496,7 +520,10 @@ func createRoom(
 	}
 	if err = roomserverAPI.SendInputRoomEvents(ctx, rsAPI, device.UserDomain(), inputs, false); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("roomserverAPI.SendInputRoomEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// TODO(#269): Reserve room alias while we create the room. This stops us
@@ -513,7 +540,10 @@ func createRoom(
 		err = rsAPI.SetRoomAlias(ctx, &aliasReq, &aliasResp)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("aliasAPI.SetRoomAlias failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		if aliasResp.AliasExists {
@@ -596,7 +626,7 @@ func createRoom(
 				sentry.CaptureException(err)
 				return util.JSONResponse{
 					Code: http.StatusInternalServerError,
-					JSON: spec.InternalServerError(),
+					JSON: spec.InternalServerError{},
 				}
 			}
 		}
@@ -609,7 +639,10 @@ func createRoom(
 			Visibility: spec.Public,
 		}); err != nil {
 			util.GetLogger(ctx).WithError(err).Error("failed to publish room")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
diff --git a/clientapi/routing/deactivate.go b/clientapi/routing/deactivate.go
index 78cf9fe3..c151c130 100644
--- a/clientapi/routing/deactivate.go
+++ b/clientapi/routing/deactivate.go
@@ -36,7 +36,10 @@ func Deactivate(
 	localpart, serverName, err := gomatrixserverlib.SplitID('@', login.Username())
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var res api.PerformAccountDeactivationResponse
@@ -46,7 +49,10 @@ func Deactivate(
 	}, &res)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("userAPI.PerformAccountDeactivation failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/device.go b/clientapi/routing/device.go
index 6209d8e9..6f2de353 100644
--- a/clientapi/routing/device.go
+++ b/clientapi/routing/device.go
@@ -60,7 +60,10 @@ func GetDeviceByID(
 	}, &queryRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryDevices failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var targetDevice *api.Device
 	for _, device := range queryRes.Devices {
@@ -97,7 +100,10 @@ func GetDevicesByLocalpart(
 	}, &queryRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryDevices failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	res := devicesJSON{}
@@ -139,7 +145,10 @@ func UpdateDeviceByID(
 	}, &performRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("PerformDeviceUpdate failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !performRes.DeviceExists {
 		return util.JSONResponse{
@@ -206,7 +215,10 @@ func DeleteDeviceById(
 	localpart, _, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// make sure that the access token being used matches the login creds used for user interactive auth, else
@@ -224,7 +236,10 @@ func DeleteDeviceById(
 		DeviceIDs: []string{deviceID},
 	}, &res); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("userAPI.PerformDeviceDeletion failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	deleteOK = true
@@ -266,7 +281,10 @@ func DeleteDevices(
 	payload := devicesDeleteJSON{}
 	if err = json.Unmarshal(bodyBytes, &payload); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("unable to unmarshal device deletion request")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var res api.PerformDeviceDeletionResponse
@@ -275,7 +293,10 @@ func DeleteDevices(
 		DeviceIDs: payload.Devices,
 	}, &res); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("userAPI.PerformDeviceDeletion failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/directory.go b/clientapi/routing/directory.go
index 0ca9475d..c786f8cc 100644
--- a/clientapi/routing/directory.go
+++ b/clientapi/routing/directory.go
@@ -69,7 +69,10 @@ func DirectoryRoom(
 	queryRes := &roomserverAPI.GetRoomIDForAliasResponse{}
 	if err = rsAPI.GetRoomIDForAlias(req.Context(), queryReq, queryRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("rsAPI.GetRoomIDForAlias failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	res.RoomID = queryRes.RoomID
@@ -83,7 +86,10 @@ func DirectoryRoom(
 				// TODO: Return 502 if the remote server errored.
 				// TODO: Return 504 if the remote server timed out.
 				util.GetLogger(req.Context()).WithError(fedErr).Error("federation.LookupRoomAlias failed")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			res.RoomID = fedRes.RoomID
 			res.fillServers(fedRes.Servers)
@@ -102,7 +108,10 @@ func DirectoryRoom(
 		var joinedHostsRes federationAPI.QueryJoinedHostServerNamesInRoomResponse
 		if err = fedSenderAPI.QueryJoinedHostServerNamesInRoom(req.Context(), &joinedHostsReq, &joinedHostsRes); err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("fedSenderAPI.QueryJoinedHostServerNamesInRoom failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		res.fillServers(joinedHostsRes.ServerNames)
 	}
@@ -180,7 +189,10 @@ func SetLocalAlias(
 	var queryRes roomserverAPI.SetRoomAliasResponse
 	if err := rsAPI.SetRoomAlias(req.Context(), &queryReq, &queryRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("aliasAPI.SetRoomAlias failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if queryRes.AliasExists {
@@ -210,7 +222,10 @@ func RemoveLocalAlias(
 	var queryRes roomserverAPI.RemoveRoomAliasResponse
 	if err := rsAPI.RemoveRoomAlias(req.Context(), &queryReq, &queryRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("aliasAPI.RemoveRoomAlias failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !queryRes.Found {
@@ -248,7 +263,10 @@ func GetVisibility(
 	}, &res)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryPublishedRooms failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var v roomVisibility
@@ -286,7 +304,10 @@ func SetVisibility(
 	err := rsAPI.QueryLatestEventsAndState(req.Context(), &queryEventsReq, &queryEventsRes)
 	if err != nil || len(queryEventsRes.StateEvents) == 0 {
 		util.GetLogger(req.Context()).WithError(err).Error("could not query events from room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// NOTSPEC: Check if the user's power is greater than power required to change m.room.canonical_alias event
@@ -308,7 +329,10 @@ func SetVisibility(
 		Visibility: v.Visibility,
 	}); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("failed to publish room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -344,7 +368,10 @@ func SetVisibilityAS(
 		AppserviceID: dev.AppserviceID,
 	}); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("failed to publish room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/directory_public.go b/clientapi/routing/directory_public.go
index 9718ccab..67146630 100644
--- a/clientapi/routing/directory_public.go
+++ b/clientapi/routing/directory_public.go
@@ -81,7 +81,10 @@ func GetPostPublicRooms(
 		)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("failed to get public rooms")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		return util.JSONResponse{
 			Code: http.StatusOK,
@@ -92,7 +95,10 @@ func GetPostPublicRooms(
 	response, err := publicRooms(req.Context(), request, rsAPI, extRoomsProvider)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Errorf("failed to work out public rooms")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: http.StatusOK,
diff --git a/clientapi/routing/joined_rooms.go b/clientapi/routing/joined_rooms.go
index 51a96e4d..f664183f 100644
--- a/clientapi/routing/joined_rooms.go
+++ b/clientapi/routing/joined_rooms.go
@@ -40,7 +40,10 @@ func GetJoinedRooms(
 	}, &res)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryRoomsForUser failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if res.RoomIDs == nil {
 		res.RoomIDs = []string{}
diff --git a/clientapi/routing/joinroom.go b/clientapi/routing/joinroom.go
index a67d5132..43331b42 100644
--- a/clientapi/routing/joinroom.go
+++ b/clientapi/routing/joinroom.go
@@ -16,7 +16,6 @@ package routing
 
 import (
 	"encoding/json"
-	"errors"
 	"net/http"
 	"time"
 
@@ -114,16 +113,15 @@ func JoinRoomByIDOrAlias(
 				Code: e.Code,
 				JSON: json.RawMessage(e.Message),
 			}
+		case eventutil.ErrRoomNoExists:
+			response = util.JSONResponse{
+				Code: http.StatusNotFound,
+				JSON: spec.NotFound(e.Error()),
+			}
 		default:
 			response = util.JSONResponse{
 				Code: http.StatusInternalServerError,
-				JSON: spec.InternalServerError(),
-			}
-			if errors.Is(err, eventutil.ErrRoomNoExists) {
-				response = util.JSONResponse{
-					Code: http.StatusNotFound,
-					JSON: spec.NotFound(e.Error()),
-				}
+				JSON: spec.InternalServerError{},
 			}
 		}
 		done <- response
diff --git a/clientapi/routing/key_backup.go b/clientapi/routing/key_backup.go
index b7b1cadd..7f8bd9f4 100644
--- a/clientapi/routing/key_backup.go
+++ b/clientapi/routing/key_backup.go
@@ -128,7 +128,7 @@ func ModifyKeyBackupVersionAuthData(req *http.Request, userAPI userapi.ClientUse
 		Algorithm: kb.Algorithm,
 	})
 	switch e := err.(type) {
-	case *spec.ErrRoomKeysVersion:
+	case spec.ErrRoomKeysVersion:
 		return util.JSONResponse{
 			Code: http.StatusForbidden,
 			JSON: e,
@@ -182,7 +182,7 @@ func UploadBackupKeys(
 	})
 
 	switch e := err.(type) {
-	case *spec.ErrRoomKeysVersion:
+	case spec.ErrRoomKeysVersion:
 		return util.JSONResponse{
 			Code: http.StatusForbidden,
 			JSON: e,
diff --git a/clientapi/routing/keys.go b/clientapi/routing/keys.go
index 363ae3dc..72785cda 100644
--- a/clientapi/routing/keys.go
+++ b/clientapi/routing/keys.go
@@ -67,7 +67,10 @@ func UploadKeys(req *http.Request, keyAPI api.ClientKeyAPI, device *api.Device)
 	}
 	if uploadRes.Error != nil {
 		util.GetLogger(req.Context()).WithError(uploadRes.Error).Error("Failed to PerformUploadKeys")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if len(uploadRes.KeyErrors) > 0 {
 		util.GetLogger(req.Context()).WithField("key_errors", uploadRes.KeyErrors).Error("Failed to upload one or more keys")
@@ -156,7 +159,10 @@ func ClaimKeys(req *http.Request, keyAPI api.ClientKeyAPI) util.JSONResponse {
 	}, &claimRes)
 	if claimRes.Error != nil {
 		util.GetLogger(req.Context()).WithError(claimRes.Error).Error("failed to PerformClaimKeys")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: 200,
diff --git a/clientapi/routing/login.go b/clientapi/routing/login.go
index d326bff7..bc38b834 100644
--- a/clientapi/routing/login.go
+++ b/clientapi/routing/login.go
@@ -83,13 +83,19 @@ func completeAuth(
 	token, err := auth.GenerateAccessToken()
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("auth.GenerateAccessToken failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	localpart, serverName, err := userutil.ParseUsernameParam(login.Username(), cfg)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("auth.ParseUsernameParam failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var performRes userapi.PerformDeviceCreationResponse
diff --git a/clientapi/routing/logout.go b/clientapi/routing/logout.go
index 049c88d5..d06bac78 100644
--- a/clientapi/routing/logout.go
+++ b/clientapi/routing/logout.go
@@ -33,7 +33,10 @@ func Logout(
 	}, &performRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("PerformDeviceDeletion failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -53,7 +56,10 @@ func LogoutAll(
 	}, &performRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("PerformDeviceDeletion failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/membership.go b/clientapi/routing/membership.go
index 9b95ba5d..4f2a0e39 100644
--- a/clientapi/routing/membership.go
+++ b/clientapi/routing/membership.go
@@ -85,7 +85,10 @@ func sendMembership(ctx context.Context, profileAPI userapi.ClientUserAPI, devic
 	)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("buildMembershipEvent failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	serverName := device.UserDomain()
@@ -100,7 +103,10 @@ func sendMembership(ctx context.Context, profileAPI userapi.ClientUserAPI, devic
 		false,
 	); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -262,7 +268,10 @@ func sendInvite(
 	)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("buildMembershipEvent failed")
-		return spec.InternalServerError(), err
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}, err
 	}
 
 	err = rsAPI.PerformInvite(ctx, &api.PerformInviteRequest{
@@ -289,7 +298,7 @@ func sendInvite(
 		sentry.CaptureException(err)
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}, err
 	}
 
@@ -398,31 +407,38 @@ func checkAndProcessThreepid(
 		req.Context(), device, body, cfg, rsAPI, profileAPI,
 		roomID, evTime,
 	)
-	if err == threepid.ErrMissingParameter {
+	switch e := err.(type) {
+	case nil:
+	case threepid.ErrMissingParameter:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAndProcessInvite failed")
 		return inviteStored, &util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.BadJSON(err.Error()),
 		}
-	} else if err == threepid.ErrNotTrusted {
+	case threepid.ErrNotTrusted:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAndProcessInvite failed")
 		return inviteStored, &util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.NotTrusted(body.IDServer),
 		}
-	} else if err == eventutil.ErrRoomNoExists {
+	case eventutil.ErrRoomNoExists:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAndProcessInvite failed")
 		return inviteStored, &util.JSONResponse{
 			Code: http.StatusNotFound,
 			JSON: spec.NotFound(err.Error()),
 		}
-	} else if e, ok := err.(gomatrixserverlib.BadJSONError); ok {
+	case gomatrixserverlib.BadJSONError:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAndProcessInvite failed")
 		return inviteStored, &util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.BadJSON(e.Error()),
 		}
-	}
-	if err != nil {
+	default:
 		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAndProcessInvite failed")
-		er := spec.InternalServerError()
-		return inviteStored, &er
+		return inviteStored, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return
 }
@@ -435,8 +451,10 @@ func checkMemberInRoom(ctx context.Context, rsAPI roomserverAPI.ClientRoomserver
 	}, &membershipRes)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("QueryMembershipForUser: could not query membership for user")
-		e := spec.InternalServerError()
-		return &e
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !membershipRes.IsInRoom {
 		return &util.JSONResponse{
@@ -461,7 +479,10 @@ func SendForget(
 	err := rsAPI.QueryMembershipForUser(ctx, &membershipReq, &membershipRes)
 	if err != nil {
 		logger.WithError(err).Error("QueryMembershipForUser: could not query membership for user")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !membershipRes.RoomExists {
 		return util.JSONResponse{
@@ -483,7 +504,10 @@ func SendForget(
 	response := roomserverAPI.PerformForgetResponse{}
 	if err := rsAPI.PerformForget(ctx, &request, &response); err != nil {
 		logger.WithError(err).Error("PerformForget: unable to forget room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: http.StatusOK,
diff --git a/clientapi/routing/notification.go b/clientapi/routing/notification.go
index 8ac12ce5..4b9043fa 100644
--- a/clientapi/routing/notification.go
+++ b/clientapi/routing/notification.go
@@ -35,7 +35,10 @@ func GetNotifications(
 		limit, err = strconv.ParseInt(limitStr, 10, 64)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("ParseInt(limit) failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
@@ -43,7 +46,10 @@ func GetNotifications(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	err = userAPI.QueryNotifications(req.Context(), &userapi.QueryNotificationsRequest{
 		Localpart:  localpart,
@@ -54,7 +60,10 @@ func GetNotifications(
 	}, &queryRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryNotifications failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	util.GetLogger(req.Context()).WithField("from", req.URL.Query().Get("from")).WithField("limit", limit).WithField("only", req.URL.Query().Get("only")).WithField("next", queryRes.NextToken).Infof("QueryNotifications: len %d", len(queryRes.Notifications))
 	return util.JSONResponse{
diff --git a/clientapi/routing/openid.go b/clientapi/routing/openid.go
index 1ead00eb..8dfba8af 100644
--- a/clientapi/routing/openid.go
+++ b/clientapi/routing/openid.go
@@ -55,7 +55,10 @@ func CreateOpenIDToken(
 	err := userAPI.PerformOpenIDTokenCreation(req.Context(), &request, &response)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("userAPI.CreateOpenIDToken failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/password.go b/clientapi/routing/password.go
index 68466a77..24c52b06 100644
--- a/clientapi/routing/password.go
+++ b/clientapi/routing/password.go
@@ -90,7 +90,10 @@ func Password(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Ask the user API to perform the password change.
@@ -102,11 +105,17 @@ func Password(
 	passwordRes := &api.PerformPasswordUpdateResponse{}
 	if err := userAPI.PerformPasswordUpdate(req.Context(), passwordReq, passwordRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("PerformPasswordUpdate failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !passwordRes.PasswordUpdated {
 		util.GetLogger(req.Context()).Error("Expected password to have been updated but wasn't")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// If the request asks us to log out all other devices then
@@ -120,7 +129,10 @@ func Password(
 		logoutRes := &api.PerformDeviceDeletionResponse{}
 		if err := userAPI.PerformDeviceDeletion(req.Context(), logoutReq, logoutRes); err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("PerformDeviceDeletion failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		pushersReq := &api.PerformPusherDeletionRequest{
@@ -130,7 +142,10 @@ func Password(
 		}
 		if err := userAPI.PerformPusherDeletion(req.Context(), pushersReq, &struct{}{}); err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("PerformPusherDeletion failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
diff --git a/clientapi/routing/peekroom.go b/clientapi/routing/peekroom.go
index af486f6d..772dc847 100644
--- a/clientapi/routing/peekroom.go
+++ b/clientapi/routing/peekroom.go
@@ -75,7 +75,10 @@ func PeekRoomByIDOrAlias(
 	case nil:
 	default:
 		logrus.WithError(err).WithField("roomID", roomIDOrAlias).Errorf("Failed to peek room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// if this user is already joined to the room, we let them peek anyway
@@ -111,7 +114,10 @@ func UnpeekRoomByID(
 	case nil:
 	default:
 		logrus.WithError(err).WithField("roomID", roomID).Errorf("Failed to un-peek room")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/presence.go b/clientapi/routing/presence.go
index d915f060..5aa6d8dd 100644
--- a/clientapi/routing/presence.go
+++ b/clientapi/routing/presence.go
@@ -74,7 +74,7 @@ func SetPresence(
 		log.WithError(err).Errorf("failed to update presence")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
@@ -99,7 +99,7 @@ func GetPresence(
 		log.WithError(err).Errorf("unable to get presence")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
@@ -118,7 +118,7 @@ func GetPresence(
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
diff --git a/clientapi/routing/profile.go b/clientapi/routing/profile.go
index 8e88e7c8..76129f0a 100644
--- a/clientapi/routing/profile.go
+++ b/clientapi/routing/profile.go
@@ -52,7 +52,10 @@ func GetProfile(
 		}
 
 		util.GetLogger(req.Context()).WithError(err).Error("getProfile failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -111,7 +114,10 @@ func SetAvatarURL(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !cfg.Matrix.IsLocalServerName(domain) {
@@ -132,7 +138,10 @@ func SetAvatarURL(
 	profile, changed, err := profileAPI.SetAvatarURL(req.Context(), localpart, domain, r.AvatarURL)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("profileAPI.SetAvatarURL failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	// No need to build new membership events, since nothing changed
 	if !changed {
@@ -200,7 +209,10 @@ func SetDisplayName(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !cfg.Matrix.IsLocalServerName(domain) {
@@ -221,7 +233,10 @@ func SetDisplayName(
 	profile, changed, err := profileAPI.SetDisplayName(req.Context(), localpart, domain, r.DisplayName)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("profileAPI.SetDisplayName failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	// No need to build new membership events, since nothing changed
 	if !changed {
@@ -254,13 +269,19 @@ func updateProfile(
 	}, &res)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("QueryRoomsForUser failed")
-		return spec.InternalServerError(), err
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}, err
 	}
 
 	_, domain, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError(), err
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}, err
 	}
 
 	events, err := buildMembershipEvents(
@@ -275,12 +296,18 @@ func updateProfile(
 		}, e
 	default:
 		util.GetLogger(ctx).WithError(err).Error("buildMembershipEvents failed")
-		return spec.InternalServerError(), e
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}, e
 	}
 
 	if err := api.SendEvents(ctx, rsAPI, api.KindNew, events, device.UserDomain(), domain, domain, nil, true); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError(), err
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}, err
 	}
 	return util.JSONResponse{}, nil
 }
diff --git a/clientapi/routing/pusher.go b/clientapi/routing/pusher.go
index 2f51583f..ed59129c 100644
--- a/clientapi/routing/pusher.go
+++ b/clientapi/routing/pusher.go
@@ -34,7 +34,10 @@ func GetPushers(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	err = userAPI.QueryPushers(req.Context(), &userapi.QueryPushersRequest{
 		Localpart:  localpart,
@@ -42,7 +45,10 @@ func GetPushers(
 	}, &queryRes)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("QueryPushers failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	for i := range queryRes.Pushers {
 		queryRes.Pushers[i].SessionID = 0
@@ -63,7 +69,10 @@ func SetPusher(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	body := userapi.PerformPusherSetRequest{}
 	if resErr := httputil.UnmarshalJSONRequest(req, &body); resErr != nil {
@@ -99,7 +108,10 @@ func SetPusher(
 	err = userAPI.PerformPusherSet(req.Context(), &body, &struct{}{})
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("PerformPusherSet failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/pushrules.go b/clientapi/routing/pushrules.go
index 7be6d2a7..74873d5c 100644
--- a/clientapi/routing/pushrules.go
+++ b/clientapi/routing/pushrules.go
@@ -14,20 +14,23 @@ import (
 )
 
 func errorResponse(ctx context.Context, err error, msg string, args ...interface{}) util.JSONResponse {
-	if eerr, ok := err.(*spec.MatrixError); ok {
+	if eerr, ok := err.(spec.MatrixError); ok {
 		var status int
 		switch eerr.ErrCode {
-		case "M_INVALID_PARAM":
+		case spec.ErrorInvalidParam:
 			status = http.StatusBadRequest
-		case "M_NOT_FOUND":
+		case spec.ErrorNotFound:
 			status = http.StatusNotFound
 		default:
 			status = http.StatusInternalServerError
 		}
-		return util.MatrixErrorResponse(status, eerr.ErrCode, eerr.Err)
+		return util.MatrixErrorResponse(status, string(eerr.ErrCode), eerr.Err)
 	}
 	util.GetLogger(ctx).WithError(err).Errorf(msg, args...)
-	return spec.InternalServerError()
+	return util.JSONResponse{
+		Code: http.StatusInternalServerError,
+		JSON: spec.InternalServerError{},
+	}
 }
 
 func GetAllPushRules(ctx context.Context, device *userapi.Device, userAPI userapi.ClientUserAPI) util.JSONResponse {
diff --git a/clientapi/routing/receipt.go b/clientapi/routing/receipt.go
index 0bbb20b9..be654297 100644
--- a/clientapi/routing/receipt.go
+++ b/clientapi/routing/receipt.go
@@ -48,7 +48,10 @@ func SetReceipt(req *http.Request, userAPI api.ClientUserAPI, syncProducer *prod
 	case "m.fully_read":
 		data, err := json.Marshal(fullyReadEvent{EventID: eventID})
 		if err != nil {
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		dataReq := api.InputAccountDataRequest{
diff --git a/clientapi/routing/redaction.go b/clientapi/routing/redaction.go
index 12391d26..ed70e5c5 100644
--- a/clientapi/routing/redaction.go
+++ b/clientapi/routing/redaction.go
@@ -16,6 +16,7 @@ package routing
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"time"
 
@@ -121,17 +122,23 @@ func SendRedaction(
 	err := proto.SetContent(r)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("proto.SetContent failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	identity, err := cfg.Matrix.SigningIdentityFor(device.UserDomain())
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var queryRes roomserverAPI.QueryLatestEventsAndStateResponse
 	e, err := eventutil.QueryAndBuildEvent(req.Context(), &proto, cfg.Matrix, identity, time.Now(), rsAPI, &queryRes)
-	if err == eventutil.ErrRoomNoExists {
+	if errors.Is(err, eventutil.ErrRoomNoExists{}) {
 		return util.JSONResponse{
 			Code: http.StatusNotFound,
 			JSON: spec.NotFound("Room does not exist"),
@@ -140,7 +147,10 @@ func SendRedaction(
 	domain := device.UserDomain()
 	if err = roomserverAPI.SendEvents(context.Background(), rsAPI, roomserverAPI.KindNew, []*types.HeaderedEvent{e}, device.UserDomain(), domain, domain, nil, false); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Errorf("failed to SendEvents")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	res := util.JSONResponse{
diff --git a/clientapi/routing/register.go b/clientapi/routing/register.go
index 615ff201..565c4153 100644
--- a/clientapi/routing/register.go
+++ b/clientapi/routing/register.go
@@ -528,7 +528,10 @@ func Register(
 		nres := &userapi.QueryNumericLocalpartResponse{}
 		if err = userAPI.QueryNumericLocalpart(req.Context(), nreq, nres); err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("userAPI.QueryNumericLocalpart failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		r.Username = strconv.FormatInt(nres.ID, 10)
 	}
@@ -713,7 +716,7 @@ func handleRegistrationFlow(
 		case nil:
 		default:
 			util.GetLogger(req.Context()).WithError(err).Error("failed to validate recaptcha")
-			return util.JSONResponse{Code: http.StatusInternalServerError, JSON: spec.InternalServerError()}
+			return util.JSONResponse{Code: http.StatusInternalServerError, JSON: spec.InternalServerError{}}
 		}
 
 		// Add Recaptcha to the list of completed registration stages
diff --git a/clientapi/routing/register_test.go b/clientapi/routing/register_test.go
index 9a60f531..2a88ec38 100644
--- a/clientapi/routing/register_test.go
+++ b/clientapi/routing/register_test.go
@@ -402,7 +402,7 @@ func Test_register(t *testing.T) {
 			enableRecaptcha: true,
 			loginType:       authtypes.LoginTypeRecaptcha,
 			captchaBody:     `i should fail for other reasons`,
-			wantResponse:    util.JSONResponse{Code: http.StatusInternalServerError, JSON: spec.InternalServerError()},
+			wantResponse:    util.JSONResponse{Code: http.StatusInternalServerError, JSON: spec.InternalServerError{}},
 		},
 	}
 
@@ -484,7 +484,7 @@ func Test_register(t *testing.T) {
 					if !reflect.DeepEqual(r.Flows, cfg.Derived.Registration.Flows) {
 						t.Fatalf("unexpected registration flows: %+v, want %+v", r.Flows, cfg.Derived.Registration.Flows)
 					}
-				case *spec.MatrixError:
+				case spec.MatrixError:
 					if !reflect.DeepEqual(tc.wantResponse, resp) {
 						t.Fatalf("(%s), unexpected response: %+v, want: %+v", tc.name, resp, tc.wantResponse)
 					}
@@ -541,7 +541,12 @@ func Test_register(t *testing.T) {
 				resp = Register(req, userAPI, &cfg.ClientAPI)
 
 				switch resp.JSON.(type) {
-				case *spec.MatrixError:
+				case spec.InternalServerError:
+					if !reflect.DeepEqual(tc.wantResponse, resp) {
+						t.Fatalf("unexpected response: %+v, want: %+v", resp, tc.wantResponse)
+					}
+					return
+				case spec.MatrixError:
 					if !reflect.DeepEqual(tc.wantResponse, resp) {
 						t.Fatalf("unexpected response: %+v, want: %+v", resp, tc.wantResponse)
 					}
diff --git a/clientapi/routing/room_tagging.go b/clientapi/routing/room_tagging.go
index 8802d22a..5a5296bf 100644
--- a/clientapi/routing/room_tagging.go
+++ b/clientapi/routing/room_tagging.go
@@ -46,7 +46,10 @@ func GetTags(
 	tagContent, err := obtainSavedTags(req, userID, roomID, userAPI)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("obtainSavedTags failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -83,7 +86,10 @@ func PutTag(
 	tagContent, err := obtainSavedTags(req, userID, roomID, userAPI)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("obtainSavedTags failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if tagContent.Tags == nil {
@@ -93,7 +99,10 @@ func PutTag(
 
 	if err = saveTagData(req, userID, roomID, userAPI, tagContent); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("saveTagData failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -125,7 +134,10 @@ func DeleteTag(
 	tagContent, err := obtainSavedTags(req, userID, roomID, userAPI)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("obtainSavedTags failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Check whether the tag to be deleted exists
@@ -141,7 +153,10 @@ func DeleteTag(
 
 	if err = saveTagData(req, userID, roomID, userAPI, tagContent); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("saveTagData failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/sendevent.go b/clientapi/routing/sendevent.go
index 2e3cd411..bc14642f 100644
--- a/clientapi/routing/sendevent.go
+++ b/clientapi/routing/sendevent.go
@@ -149,7 +149,10 @@ func SendEvent(
 		}
 		aliasRes := &api.GetAliasesForRoomIDResponse{}
 		if err = rsAPI.GetAliasesForRoomID(req.Context(), &api.GetAliasesForRoomIDRequest{RoomID: roomID}, aliasRes); err != nil {
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		var found int
 		requestAliases := append(aliasReq.AltAliases, aliasReq.Alias)
@@ -193,7 +196,10 @@ func SendEvent(
 		false,
 	); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	timeToSubmitEvent := time.Since(startedSubmittingEvent)
 	util.GetLogger(req.Context()).WithFields(logrus.Fields{
@@ -272,43 +278,51 @@ func generateSendEvent(
 	err := proto.SetContent(r)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("proto.SetContent failed")
-		resErr := spec.InternalServerError()
-		return nil, &resErr
+		return nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	identity, err := cfg.Matrix.SigningIdentityFor(device.UserDomain())
 	if err != nil {
-		resErr := spec.InternalServerError()
-		return nil, &resErr
+		return nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var queryRes api.QueryLatestEventsAndStateResponse
 	e, err := eventutil.QueryAndBuildEvent(ctx, &proto, cfg.Matrix, identity, evTime, rsAPI, &queryRes)
-	if err == eventutil.ErrRoomNoExists {
+	switch specificErr := err.(type) {
+	case nil:
+	case eventutil.ErrRoomNoExists:
 		return nil, &util.JSONResponse{
 			Code: http.StatusNotFound,
 			JSON: spec.NotFound("Room does not exist"),
 		}
-	} else if e, ok := err.(gomatrixserverlib.BadJSONError); ok {
+	case gomatrixserverlib.BadJSONError:
 		return nil, &util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON(e.Error()),
+			JSON: spec.BadJSON(specificErr.Error()),
 		}
-	} else if e, ok := err.(gomatrixserverlib.EventValidationError); ok {
-		if e.Code == gomatrixserverlib.EventValidationTooLarge {
+	case gomatrixserverlib.EventValidationError:
+		if specificErr.Code == gomatrixserverlib.EventValidationTooLarge {
 			return nil, &util.JSONResponse{
 				Code: http.StatusRequestEntityTooLarge,
-				JSON: spec.BadJSON(e.Error()),
+				JSON: spec.BadJSON(specificErr.Error()),
 			}
 		}
 		return nil, &util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON(e.Error()),
+			JSON: spec.BadJSON(specificErr.Error()),
 		}
-	} else if err != nil {
+	default:
 		util.GetLogger(ctx).WithError(err).Error("eventutil.BuildEvent failed")
-		resErr := spec.InternalServerError()
-		return nil, &resErr
+		return nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// check to see if this user can perform this operation
diff --git a/clientapi/routing/sendtodevice.go b/clientapi/routing/sendtodevice.go
index 6d4af072..58d3053e 100644
--- a/clientapi/routing/sendtodevice.go
+++ b/clientapi/routing/sendtodevice.go
@@ -53,7 +53,10 @@ func SendToDevice(
 				req.Context(), device.UserID, userID, deviceID, eventType, message,
 			); err != nil {
 				util.GetLogger(req.Context()).WithError(err).Error("eduProducer.SendToDevice failed")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 		}
 	}
diff --git a/clientapi/routing/sendtyping.go b/clientapi/routing/sendtyping.go
index 17532a2d..c5b29297 100644
--- a/clientapi/routing/sendtyping.go
+++ b/clientapi/routing/sendtyping.go
@@ -58,7 +58,10 @@ func SendTyping(
 
 	if err := syncProducer.SendTyping(req.Context(), userID, roomID, r.Typing, r.Timeout); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("eduProducer.Send failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/server_notices.go b/clientapi/routing/server_notices.go
index a418677e..ad50cc80 100644
--- a/clientapi/routing/server_notices.go
+++ b/clientapi/routing/server_notices.go
@@ -175,7 +175,10 @@ func SendServerNotice(
 			}}
 			if err = saveTagData(req, r.UserID, roomID, userAPI, serverAlertTag); err != nil {
 				util.GetLogger(ctx).WithError(err).Error("saveTagData failed")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 
 		default:
@@ -189,7 +192,10 @@ func SendServerNotice(
 		err := rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{UserID: r.UserID, RoomID: roomID}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("unable to query membership for user")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if !membershipRes.IsInRoom {
 			// re-invite the user
@@ -237,7 +243,10 @@ func SendServerNotice(
 		false,
 	); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	util.GetLogger(ctx).WithFields(logrus.Fields{
 		"event_id":     e.EventID(),
diff --git a/clientapi/routing/state.go b/clientapi/routing/state.go
index 75abbda9..319f4eba 100644
--- a/clientapi/routing/state.go
+++ b/clientapi/routing/state.go
@@ -56,7 +56,10 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 		StateToFetch: []gomatrixserverlib.StateKeyTuple{},
 	}, &stateRes); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("queryAPI.QueryLatestEventsAndState failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !stateRes.RoomExists {
 		return util.JSONResponse{
@@ -73,7 +76,10 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 			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 spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			if visibility, ok := content["history_visibility"]; ok {
 				worldReadable = visibility == "world_readable"
@@ -99,7 +105,10 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 		}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.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.
@@ -147,7 +156,10 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 		}, &stateAfterRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		for _, ev := range stateAfterRes.StateEvents {
 			stateEvents = append(
@@ -202,7 +214,10 @@ func OnIncomingStateTypeRequest(
 		StateToFetch: stateToFetch,
 	}, &stateRes); err != nil {
 		util.GetLogger(ctx).WithError(err).Error("queryAPI.QueryLatestEventsAndState failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Look at the room state and see if we have a history visibility event
@@ -213,7 +228,10 @@ func OnIncomingStateTypeRequest(
 			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 spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			if visibility, ok := content["history_visibility"]; ok {
 				worldReadable = visibility == "world_readable"
@@ -239,7 +257,10 @@ func OnIncomingStateTypeRequest(
 		}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.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.
@@ -294,7 +315,10 @@ func OnIncomingStateTypeRequest(
 		}, &stateAfterRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if len(stateAfterRes.StateEvents) > 0 {
 			event = stateAfterRes.StateEvents[0]
diff --git a/clientapi/routing/thirdparty.go b/clientapi/routing/thirdparty.go
index 0ee21855..b805d4b5 100644
--- a/clientapi/routing/thirdparty.go
+++ b/clientapi/routing/thirdparty.go
@@ -33,7 +33,10 @@ func Protocols(req *http.Request, asAPI appserviceAPI.AppServiceInternalAPI, dev
 	resp := &appserviceAPI.ProtocolResponse{}
 
 	if err := asAPI.Protocols(req.Context(), &appserviceAPI.ProtocolRequest{Protocol: protocol}, resp); err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !resp.Exists {
 		if protocol != "" {
@@ -71,7 +74,10 @@ func User(req *http.Request, asAPI appserviceAPI.AppServiceInternalAPI, device *
 		Protocol: protocol,
 		Params:   params.Encode(),
 	}, resp); err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !resp.Exists {
 		return util.JSONResponse{
@@ -97,7 +103,10 @@ func Location(req *http.Request, asAPI appserviceAPI.AppServiceInternalAPI, devi
 		Protocol: protocol,
 		Params:   params.Encode(),
 	}, resp); err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !resp.Exists {
 		return util.JSONResponse{
diff --git a/clientapi/routing/threepid.go b/clientapi/routing/threepid.go
index 64fa59e4..5261a140 100644
--- a/clientapi/routing/threepid.go
+++ b/clientapi/routing/threepid.go
@@ -60,28 +60,37 @@ func RequestEmailToken(req *http.Request, threePIDAPI api.ClientUserAPI, cfg *co
 
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("threePIDAPI.QueryLocalpartForThreePID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if len(res.Localpart) > 0 {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.MatrixError{
-				ErrCode: "M_THREEPID_IN_USE",
+				ErrCode: spec.ErrorThreePIDInUse,
 				Err:     userdb.Err3PIDInUse.Error(),
 			},
 		}
 	}
 
 	resp.SID, err = threepid.CreateSession(req.Context(), body, cfg, client)
-	if err == threepid.ErrNotTrusted {
+	switch err.(type) {
+	case nil:
+	case threepid.ErrNotTrusted:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CreateSession failed")
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.NotTrusted(body.IDServer),
 		}
-	} else if err != nil {
+	default:
 		util.GetLogger(req.Context()).WithError(err).Error("threepid.CreateSession failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -102,21 +111,27 @@ func CheckAndSave3PIDAssociation(
 
 	// Check if the association has been validated
 	verified, address, medium, err := threepid.CheckAssociation(req.Context(), body.Creds, cfg, client)
-	if err == threepid.ErrNotTrusted {
+	switch err.(type) {
+	case nil:
+	case threepid.ErrNotTrusted:
+		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAssociation failed")
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.NotTrusted(body.Creds.IDServer),
 		}
-	} else if err != nil {
+	default:
 		util.GetLogger(req.Context()).WithError(err).Error("threepid.CheckAssociation failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !verified {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.MatrixError{
-				ErrCode: "M_THREEPID_AUTH_FAILED",
+				ErrCode: spec.ErrorThreePIDAuthFailed,
 				Err:     "Failed to auth 3pid",
 			},
 		}
@@ -127,7 +142,10 @@ func CheckAndSave3PIDAssociation(
 		err = threepid.PublishAssociation(req.Context(), body.Creds, device.UserID, cfg, client)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("threepid.PublishAssociation failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
@@ -135,7 +153,10 @@ func CheckAndSave3PIDAssociation(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if err = threePIDAPI.PerformSaveThreePIDAssociation(req.Context(), &api.PerformSaveThreePIDAssociationRequest{
@@ -145,7 +166,10 @@ func CheckAndSave3PIDAssociation(
 		Medium:     medium,
 	}, &struct{}{}); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("threePIDAPI.PerformSaveThreePIDAssociation failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -161,7 +185,10 @@ func GetAssociated3PIDs(
 	localpart, domain, err := gomatrixserverlib.SplitID('@', device.UserID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	res := &api.QueryThreePIDsForLocalpartResponse{}
@@ -171,7 +198,10 @@ func GetAssociated3PIDs(
 	}, res)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("threepidAPI.QueryThreePIDsForLocalpart failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -192,7 +222,10 @@ func Forget3PID(req *http.Request, threepidAPI api.ClientUserAPI) util.JSONRespo
 		Medium:   body.Medium,
 	}, &struct{}{}); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("threepidAPI.PerformForgetThreePID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/upgrade_room.go b/clientapi/routing/upgrade_room.go
index 43f8d3e2..a0b28078 100644
--- a/clientapi/routing/upgrade_room.go
+++ b/clientapi/routing/upgrade_room.go
@@ -68,13 +68,16 @@ func UpgradeRoom(
 			JSON: spec.Forbidden(e.Error()),
 		}
 	default:
-		if errors.Is(err, eventutil.ErrRoomNoExists) {
+		if errors.Is(err, eventutil.ErrRoomNoExists{}) {
 			return util.JSONResponse{
 				Code: http.StatusNotFound,
 				JSON: spec.NotFound("Room does not exist"),
 			}
 		}
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/clientapi/routing/voip.go b/clientapi/routing/voip.go
index f3db0cbe..14a08b79 100644
--- a/clientapi/routing/voip.go
+++ b/clientapi/routing/voip.go
@@ -60,7 +60,10 @@ func RequestTurnServer(req *http.Request, device *api.Device, cfg *config.Client
 
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("mac.Write failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		resp.Password = base64.StdEncoding.EncodeToString(mac.Sum(nil))
diff --git a/clientapi/threepid/invites.go b/clientapi/threepid/invites.go
index 2e9c1261..c296939d 100644
--- a/clientapi/threepid/invites.go
+++ b/clientapi/threepid/invites.go
@@ -64,14 +64,34 @@ type idServerStoreInviteResponse struct {
 }
 
 var (
-	// ErrMissingParameter is the error raised if a request for 3PID invite has
-	// an incomplete body
-	ErrMissingParameter = errors.New("'address', 'id_server' and 'medium' must all be supplied")
-	// ErrNotTrusted is the error raised if an identity server isn't in the list
-	// of trusted servers in the configuration file.
-	ErrNotTrusted = errors.New("untrusted server")
+	errMissingParameter = fmt.Errorf("'address', 'id_server' and 'medium' must all be supplied")
+	errNotTrusted       = fmt.Errorf("untrusted server")
 )
 
+// ErrMissingParameter is the error raised if a request for 3PID invite has
+// an incomplete body
+type ErrMissingParameter struct{}
+
+func (e ErrMissingParameter) Error() string {
+	return errMissingParameter.Error()
+}
+
+func (e ErrMissingParameter) Unwrap() error {
+	return errMissingParameter
+}
+
+// ErrNotTrusted is the error raised if an identity server isn't in the list
+// of trusted servers in the configuration file.
+type ErrNotTrusted struct{}
+
+func (e ErrNotTrusted) Error() string {
+	return errNotTrusted.Error()
+}
+
+func (e ErrNotTrusted) Unwrap() error {
+	return errNotTrusted
+}
+
 // CheckAndProcessInvite analyses the body of an incoming membership request.
 // If the fields relative to a third-party-invite are all supplied, lookups the
 // matching Matrix ID from the given identity server. If no Matrix ID is
@@ -99,7 +119,7 @@ func CheckAndProcessInvite(
 	} else if body.Address == "" || body.IDServer == "" || body.Medium == "" {
 		// If at least one of the 3PID-specific fields is supplied but not all
 		// of them, return an error
-		err = ErrMissingParameter
+		err = ErrMissingParameter{}
 		return
 	}
 
diff --git a/clientapi/threepid/threepid.go b/clientapi/threepid/threepid.go
index 1fe573b1..d61052cc 100644
--- a/clientapi/threepid/threepid.go
+++ b/clientapi/threepid/threepid.go
@@ -26,6 +26,7 @@ import (
 
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/gomatrixserverlib/fclient"
+	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
 // EmailAssociationRequest represents the request defined at https://matrix.org/docs/spec/client_server/r0.2.0.html#post-matrix-client-r0-register-email-requesttoken
@@ -133,7 +134,7 @@ func CheckAssociation(
 		return false, "", "", err
 	}
 
-	if respBody.ErrCode == "M_SESSION_NOT_VALIDATED" {
+	if respBody.ErrCode == string(spec.ErrorSessionNotValidated) {
 		return false, "", "", nil
 	} else if len(respBody.ErrCode) > 0 {
 		return false, "", "", errors.New(respBody.Error)
@@ -186,5 +187,5 @@ func isTrusted(idServer string, cfg *config.ClientAPI) error {
 			return nil
 		}
 	}
-	return ErrNotTrusted
+	return ErrNotTrusted{}
 }
diff --git a/federationapi/routing/backfill.go b/federationapi/routing/backfill.go
index 81b61322..9e159505 100644
--- a/federationapi/routing/backfill.go
+++ b/federationapi/routing/backfill.go
@@ -98,7 +98,10 @@ func Backfill(
 	// Query the roomserver.
 	if err = rsAPI.PerformBackfill(httpReq.Context(), &req, &res); err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("query.PerformBackfill failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Filter any event that's not from the requested room out.
diff --git a/federationapi/routing/devices.go b/federationapi/routing/devices.go
index 318c0a34..a54ff0d9 100644
--- a/federationapi/routing/devices.go
+++ b/federationapi/routing/devices.go
@@ -38,7 +38,10 @@ func GetUserDevices(
 	}
 	if res.Error != nil {
 		util.GetLogger(req.Context()).WithError(res.Error).Error("keyAPI.QueryDeviceMessages failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	sigReq := &api.QuerySignaturesRequest{
diff --git a/federationapi/routing/invite.go b/federationapi/routing/invite.go
index bdfe2c82..993d4046 100644
--- a/federationapi/routing/invite.go
+++ b/federationapi/routing/invite.go
@@ -183,7 +183,10 @@ func processInvite(
 	verifyResults, err := keys.VerifyJSONs(ctx, verifyRequests)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("keys.VerifyJSONs failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if verifyResults[0].Error != nil {
 		return util.JSONResponse{
@@ -211,7 +214,7 @@ func processInvite(
 		util.GetLogger(ctx).WithError(err).Error("PerformInvite failed")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
@@ -232,7 +235,7 @@ func processInvite(
 		sentry.CaptureException(err)
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
diff --git a/federationapi/routing/join.go b/federationapi/routing/join.go
index c301785c..cc22690a 100644
--- a/federationapi/routing/join.go
+++ b/federationapi/routing/join.go
@@ -15,6 +15,7 @@
 package routing
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -33,153 +34,187 @@ import (
 	"github.com/matrix-org/dendrite/setup/config"
 )
 
+type JoinRoomQuerier struct {
+	roomserver api.FederationRoomserverAPI
+}
+
+func (rq *JoinRoomQuerier) CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eventType string, stateKey string) (gomatrixserverlib.PDU, error) {
+	return rq.roomserver.CurrentStateEvent(ctx, roomID, eventType, stateKey)
+}
+
+func (rq *JoinRoomQuerier) InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error) {
+	return rq.roomserver.InvitePending(ctx, roomID, userID)
+}
+
+func (rq *JoinRoomQuerier) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, userID spec.UserID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error) {
+	roomInfo, err := rq.roomserver.QueryRoomInfo(ctx, roomID)
+	if err != nil || roomInfo == nil || roomInfo.IsStub() {
+		return nil, err
+	}
+
+	req := api.QueryServerJoinedToRoomRequest{
+		ServerName: localServerName,
+		RoomID:     roomID.String(),
+	}
+	res := api.QueryServerJoinedToRoomResponse{}
+	if err = rq.roomserver.QueryServerJoinedToRoom(ctx, &req, &res); err != nil {
+		util.GetLogger(ctx).WithError(err).Error("rsAPI.QueryServerJoinedToRoom failed")
+		return nil, fmt.Errorf("InternalServerError: Failed to query room: %w", err)
+	}
+
+	userJoinedToRoom, err := rq.roomserver.UserJoinedToRoom(ctx, types.RoomNID(roomInfo.RoomNID), userID)
+	if err != nil {
+		util.GetLogger(ctx).WithError(err).Error("rsAPI.UserJoinedToRoom failed")
+		return nil, fmt.Errorf("InternalServerError: %w", err)
+	}
+
+	locallyJoinedUsers, err := rq.roomserver.LocallyJoinedUsers(ctx, roomInfo.RoomVersion, types.RoomNID(roomInfo.RoomNID))
+	if err != nil {
+		util.GetLogger(ctx).WithError(err).Error("rsAPI.GetLocallyJoinedUsers failed")
+		return nil, fmt.Errorf("InternalServerError: %w", err)
+	}
+
+	return &gomatrixserverlib.RestrictedRoomJoinInfo{
+		LocalServerInRoom: res.RoomExists && res.IsInRoom,
+		UserJoinedToRoom:  userJoinedToRoom,
+		JoinedUsers:       locallyJoinedUsers,
+	}, nil
+}
+
 // MakeJoin implements the /make_join API
 func MakeJoin(
 	httpReq *http.Request,
 	request *fclient.FederationRequest,
 	cfg *config.FederationAPI,
 	rsAPI api.FederationRoomserverAPI,
-	roomID, userID string,
+	roomID spec.RoomID, userID spec.UserID,
 	remoteVersions []gomatrixserverlib.RoomVersion,
 ) util.JSONResponse {
-	roomVersion, err := rsAPI.QueryRoomVersionForRoom(httpReq.Context(), roomID)
+	roomVersion, err := rsAPI.QueryRoomVersionForRoom(httpReq.Context(), roomID.String())
 	if err != nil {
+		util.GetLogger(httpReq.Context()).WithError(err).Error("failed obtaining room version")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
-		}
-	}
-
-	// Check that the room that the remote side is trying to join is actually
-	// one of the room versions that they listed in their supported ?ver= in
-	// the make_join URL.
-	// https://matrix.org/docs/spec/server_server/r0.1.3#get-matrix-federation-v1-make-join-roomid-userid
-	remoteSupportsVersion := false
-	for _, v := range remoteVersions {
-		if v == roomVersion {
-			remoteSupportsVersion = true
-			break
-		}
-	}
-	// If it isn't, stop trying to join the room.
-	if !remoteSupportsVersion {
-		return util.JSONResponse{
-			Code: http.StatusBadRequest,
-			JSON: spec.IncompatibleRoomVersion(string(roomVersion)),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
-	_, domain, err := gomatrixserverlib.SplitID('@', userID)
-	if err != nil {
-		return util.JSONResponse{
-			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON("Invalid UserID"),
-		}
-	}
-	if domain != request.Origin() {
-		return util.JSONResponse{
-			Code: http.StatusForbidden,
-			JSON: spec.Forbidden("The join must be sent by the server of the user"),
-		}
-	}
-
-	// Check if we think we are still joined to the room
-	inRoomReq := &api.QueryServerJoinedToRoomRequest{
+	req := api.QueryServerJoinedToRoomRequest{
 		ServerName: cfg.Matrix.ServerName,
-		RoomID:     roomID,
+		RoomID:     roomID.String(),
 	}
-	inRoomRes := &api.QueryServerJoinedToRoomResponse{}
-	if err = rsAPI.QueryServerJoinedToRoom(httpReq.Context(), inRoomReq, inRoomRes); err != nil {
+	res := api.QueryServerJoinedToRoomResponse{}
+	if err := rsAPI.QueryServerJoinedToRoom(httpReq.Context(), &req, &res); err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("rsAPI.QueryServerJoinedToRoom failed")
-		return spec.InternalServerError()
-	}
-	if !inRoomRes.RoomExists {
 		return util.JSONResponse{
-			Code: http.StatusNotFound,
-			JSON: spec.NotFound(fmt.Sprintf("Room ID %q was not found on this server", roomID)),
-		}
-	}
-	if !inRoomRes.IsInRoom {
-		return util.JSONResponse{
-			Code: http.StatusNotFound,
-			JSON: spec.NotFound(fmt.Sprintf("Room ID %q has no remaining users on this server", roomID)),
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
 		}
 	}
 
-	// Check if the restricted join is allowed. If the room doesn't
-	// support restricted joins then this is effectively a no-op.
-	res, authorisedVia, err := checkRestrictedJoin(httpReq, rsAPI, roomVersion, roomID, userID)
-	if err != nil {
-		util.GetLogger(httpReq.Context()).WithError(err).Error("checkRestrictedJoin failed")
-		return spec.InternalServerError()
-	} else if res != nil {
-		return *res
-	}
-
-	// Try building an event for the server
-	proto := gomatrixserverlib.ProtoEvent{
-		Sender:   userID,
-		RoomID:   roomID,
-		Type:     "m.room.member",
-		StateKey: &userID,
-	}
-	content := gomatrixserverlib.MemberContent{
-		Membership:    spec.Join,
-		AuthorisedVia: authorisedVia,
-	}
-	if err = proto.SetContent(content); err != nil {
-		util.GetLogger(httpReq.Context()).WithError(err).Error("builder.SetContent failed")
-		return spec.InternalServerError()
-	}
-
-	identity, err := cfg.Matrix.SigningIdentityFor(request.Destination())
-	if err != nil {
-		return util.JSONResponse{
-			Code: http.StatusNotFound,
-			JSON: spec.NotFound(
-				fmt.Sprintf("Server name %q does not exist", request.Destination()),
-			),
-		}
-	}
+	createJoinTemplate := func(proto *gomatrixserverlib.ProtoEvent) (gomatrixserverlib.PDU, []gomatrixserverlib.PDU, error) {
+		identity, err := cfg.Matrix.SigningIdentityFor(request.Destination())
+		if err != nil {
+			util.GetLogger(httpReq.Context()).WithError(err).Errorf("obtaining signing identity for %s failed", request.Destination())
+			return nil, nil, spec.NotFound(fmt.Sprintf("Server name %q does not exist", request.Destination()))
+		}
+
+		queryRes := api.QueryLatestEventsAndStateResponse{
+			RoomVersion: roomVersion,
+		}
+		event, err := eventutil.QueryAndBuildEvent(httpReq.Context(), proto, cfg.Matrix, identity, time.Now(), rsAPI, &queryRes)
+		switch e := err.(type) {
+		case nil:
+		case eventutil.ErrRoomNoExists:
+			util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
+			return nil, nil, spec.NotFound("Room does not exist")
+		case gomatrixserverlib.BadJSONError:
+			util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
+			return nil, nil, spec.BadJSON(e.Error())
+		default:
+			util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
+			return nil, nil, spec.InternalServerError{}
+		}
+
+		stateEvents := make([]gomatrixserverlib.PDU, len(queryRes.StateEvents))
+		for i, stateEvent := range queryRes.StateEvents {
+			stateEvents[i] = stateEvent.PDU
+		}
+		return event, stateEvents, nil
+	}
+
+	roomQuerier := JoinRoomQuerier{
+		roomserver: rsAPI,
+	}
+
+	input := gomatrixserverlib.HandleMakeJoinInput{
+		Context:            httpReq.Context(),
+		UserID:             userID,
+		RoomID:             roomID,
+		RoomVersion:        roomVersion,
+		RemoteVersions:     remoteVersions,
+		RequestOrigin:      request.Origin(),
+		LocalServerName:    cfg.Matrix.ServerName,
+		LocalServerInRoom:  res.RoomExists && res.IsInRoom,
+		RoomQuerier:        &roomQuerier,
+		BuildEventTemplate: createJoinTemplate,
+	}
+	response, internalErr := gomatrixserverlib.HandleMakeJoin(input)
+	if internalErr != nil {
+		switch e := internalErr.(type) {
+		case nil:
+		case spec.InternalServerError:
+			util.GetLogger(httpReq.Context()).WithError(internalErr)
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
+		case spec.MatrixError:
+			util.GetLogger(httpReq.Context()).WithError(internalErr)
+			code := http.StatusInternalServerError
+			switch e.ErrCode {
+			case spec.ErrorForbidden:
+				code = http.StatusForbidden
+			case spec.ErrorNotFound:
+				code = http.StatusNotFound
+			case spec.ErrorUnableToAuthoriseJoin:
+				code = http.StatusBadRequest
+			case spec.ErrorBadJSON:
+				code = http.StatusBadRequest
+			}
 
-	queryRes := api.QueryLatestEventsAndStateResponse{
-		RoomVersion: roomVersion,
-	}
-	event, err := eventutil.QueryAndBuildEvent(httpReq.Context(), &proto, cfg.Matrix, identity, time.Now(), rsAPI, &queryRes)
-	if err == eventutil.ErrRoomNoExists {
-		return util.JSONResponse{
-			Code: http.StatusNotFound,
-			JSON: spec.NotFound("Room does not exist"),
-		}
-	} else if e, ok := err.(gomatrixserverlib.BadJSONError); ok {
-		return util.JSONResponse{
-			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON(e.Error()),
+			return util.JSONResponse{
+				Code: code,
+				JSON: e,
+			}
+		case spec.IncompatibleRoomVersionError:
+			util.GetLogger(httpReq.Context()).WithError(internalErr)
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: e,
+			}
+		default:
+			util.GetLogger(httpReq.Context()).WithError(internalErr)
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.Unknown("unknown error"),
+			}
 		}
-	} else if err != nil {
-		util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
-		return spec.InternalServerError()
-	}
-
-	// Check that the join is allowed or not
-	stateEvents := make([]gomatrixserverlib.PDU, len(queryRes.StateEvents))
-	for i := range queryRes.StateEvents {
-		stateEvents[i] = queryRes.StateEvents[i].PDU
 	}
 
-	provider := gomatrixserverlib.NewAuthEvents(stateEvents)
-	if err = gomatrixserverlib.Allowed(event.PDU, &provider); err != nil {
+	if response == nil {
+		util.GetLogger(httpReq.Context()).Error("gmsl.HandleMakeJoin returned invalid response")
 		return util.JSONResponse{
-			Code: http.StatusForbidden,
-			JSON: spec.Forbidden(err.Error()),
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
 		}
 	}
 
 	return util.JSONResponse{
 		Code: http.StatusOK,
 		JSON: map[string]interface{}{
-			"event":        proto,
-			"room_version": roomVersion,
+			"event":        response.JoinTemplateEvent,
+			"room_version": response.RoomVersion,
 		},
 	}
 }
@@ -201,7 +236,7 @@ func SendJoin(
 		util.GetLogger(httpReq.Context()).WithError(err).Error("rsAPI.QueryRoomVersionForRoom failed")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 	verImpl, err := gomatrixserverlib.GetRoomVersion(roomVersion)
@@ -311,7 +346,10 @@ func SendJoin(
 	verifyResults, err := keys.VerifyJSONs(httpReq.Context(), verifyRequests)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("keys.VerifyJSONs failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if verifyResults[0].Error != nil {
 		return util.JSONResponse{
@@ -331,7 +369,10 @@ func SendJoin(
 	}, &stateAndAuthChainResponse)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("rsAPI.QueryStateAndAuthChain failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !stateAndAuthChainResponse.RoomExists {
@@ -427,7 +468,10 @@ func SendJoin(
 					JSON: spec.Forbidden(response.ErrMsg),
 				}
 			}
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
@@ -449,74 +493,6 @@ func SendJoin(
 	}
 }
 
-// checkRestrictedJoin finds out whether or not we can assist in processing
-// a restricted room join. If the room version does not support restricted
-// joins then this function returns with no side effects. This returns three
-// values:
-//   - an optional JSON response body (i.e. M_UNABLE_TO_AUTHORISE_JOIN) which
-//     should always be sent back to the client if one is specified
-//   - a user ID of an authorising user, typically a user that has power to
-//     issue invites in the room, if one has been found
-//   - an error if there was a problem finding out if this was allowable,
-//     like if the room version isn't known or a problem happened talking to
-//     the roomserver
-func checkRestrictedJoin(
-	httpReq *http.Request,
-	rsAPI api.FederationRoomserverAPI,
-	roomVersion gomatrixserverlib.RoomVersion,
-	roomID, userID string,
-) (*util.JSONResponse, string, error) {
-	verImpl, err := gomatrixserverlib.GetRoomVersion(roomVersion)
-	if err != nil {
-		return nil, "", err
-	}
-	if !verImpl.MayAllowRestrictedJoinsInEventAuth() {
-		return nil, "", nil
-	}
-	req := &api.QueryRestrictedJoinAllowedRequest{
-		RoomID: roomID,
-		UserID: userID,
-	}
-	res := &api.QueryRestrictedJoinAllowedResponse{}
-	if err := rsAPI.QueryRestrictedJoinAllowed(httpReq.Context(), req, res); err != nil {
-		return nil, "", err
-	}
-
-	switch {
-	case !res.Restricted:
-		// The join rules for the room don't restrict membership.
-		return nil, "", nil
-
-	case !res.Resident:
-		// The join rules restrict membership but our server isn't currently
-		// joined to all of the allowed rooms, so we can't actually decide
-		// whether or not to allow the user to join. This error code should
-		// tell the joining server to try joining via another resident server
-		// instead.
-		return &util.JSONResponse{
-			Code: http.StatusBadRequest,
-			JSON: spec.UnableToAuthoriseJoin("This server cannot authorise the join."),
-		}, "", nil
-
-	case !res.Allowed:
-		// The join rules restrict membership, our server is in the relevant
-		// rooms and the user wasn't joined to join any of the allowed rooms
-		// and therefore can't join this room.
-		return &util.JSONResponse{
-			Code: http.StatusForbidden,
-			JSON: spec.Forbidden("You are not joined to any matching rooms."),
-		}, "", nil
-
-	default:
-		// The join rules restrict membership, our server is in the relevant
-		// rooms and the user was allowed to join because they belong to one
-		// of the allowed rooms. We now need to pick one of our own local users
-		// from within the room to use as the authorising user ID, so that it
-		// can be referred to from within the membership content.
-		return nil, res.AuthorisedVia, nil
-	}
-}
-
 type eventsByDepth []*types.HeaderedEvent
 
 func (e eventsByDepth) Len() int {
diff --git a/federationapi/routing/keys.go b/federationapi/routing/keys.go
index d85de73d..3d8ff2de 100644
--- a/federationapi/routing/keys.go
+++ b/federationapi/routing/keys.go
@@ -67,7 +67,10 @@ func QueryDeviceKeys(
 	}, &queryRes)
 	if queryRes.Error != nil {
 		util.GetLogger(httpReq.Context()).WithError(queryRes.Error).Error("Failed to QueryKeys")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: 200,
@@ -119,7 +122,10 @@ func ClaimOneTimeKeys(
 	}, &claimRes)
 	if claimRes.Error != nil {
 		util.GetLogger(httpReq.Context()).WithError(claimRes.Error).Error("Failed to PerformClaimKeys")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: 200,
@@ -243,7 +249,10 @@ func NotaryKeys(
 			j, err := json.Marshal(keys)
 			if err != nil {
 				logrus.WithError(err).Errorf("Failed to marshal %q response", serverName)
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 
 			js, err := gomatrixserverlib.SignJSON(
@@ -251,7 +260,10 @@ func NotaryKeys(
 			)
 			if err != nil {
 				logrus.WithError(err).Errorf("Failed to sign %q response", serverName)
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 
 			response.ServerKeys = append(response.ServerKeys, js)
diff --git a/federationapi/routing/leave.go b/federationapi/routing/leave.go
index fdfbf15d..e6540340 100644
--- a/federationapi/routing/leave.go
+++ b/federationapi/routing/leave.go
@@ -60,7 +60,10 @@ func MakeLeave(
 	err = proto.SetContent(map[string]interface{}{"membership": spec.Leave})
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("proto.SetContent failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	identity, err := cfg.Matrix.SigningIdentityFor(request.Destination())
@@ -75,19 +78,26 @@ func MakeLeave(
 
 	var queryRes api.QueryLatestEventsAndStateResponse
 	event, err := eventutil.QueryAndBuildEvent(httpReq.Context(), &proto, cfg.Matrix, identity, time.Now(), rsAPI, &queryRes)
-	if err == eventutil.ErrRoomNoExists {
+	switch e := err.(type) {
+	case nil:
+	case eventutil.ErrRoomNoExists:
+		util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
 		return util.JSONResponse{
 			Code: http.StatusNotFound,
 			JSON: spec.NotFound("Room does not exist"),
 		}
-	} else if e, ok := err.(gomatrixserverlib.BadJSONError); ok {
+	case gomatrixserverlib.BadJSONError:
+		util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.BadJSON(e.Error()),
 		}
-	} else if err != nil {
+	default:
 		util.GetLogger(httpReq.Context()).WithError(err).Error("eventutil.BuildEvent failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// If the user has already left then just return their last leave
@@ -233,7 +243,10 @@ func SendLeave(
 	err = rsAPI.QueryLatestEventsAndState(httpReq.Context(), queryReq, queryRes)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("rsAPI.QueryLatestEventsAndState failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	// The room doesn't exist or we weren't ever joined to it. Might as well
 	// no-op here.
@@ -279,7 +292,10 @@ func SendLeave(
 	verifyResults, err := keys.VerifyJSONs(httpReq.Context(), verifyRequests)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("keys.VerifyJSONs failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if verifyResults[0].Error != nil {
 		return util.JSONResponse{
@@ -327,7 +343,10 @@ func SendLeave(
 				JSON: spec.Forbidden(response.ErrMsg),
 			}
 		}
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/federationapi/routing/missingevents.go b/federationapi/routing/missingevents.go
index f8dd9e4f..f57d3020 100644
--- a/federationapi/routing/missingevents.go
+++ b/federationapi/routing/missingevents.go
@@ -63,7 +63,10 @@ func GetMissingEvents(
 		&eventsResponse,
 	); err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("query.QueryMissingEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	eventsResponse.Events = filterEvents(eventsResponse.Events, roomID)
diff --git a/federationapi/routing/peek.go b/federationapi/routing/peek.go
index 9e924556..f5003b14 100644
--- a/federationapi/routing/peek.go
+++ b/federationapi/routing/peek.go
@@ -40,7 +40,7 @@ func Peek(
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
diff --git a/federationapi/routing/profile.go b/federationapi/routing/profile.go
index 7d6cfcaa..e6a488ba 100644
--- a/federationapi/routing/profile.go
+++ b/federationapi/routing/profile.go
@@ -53,7 +53,10 @@ func GetProfile(
 	profile, err := userAPI.QueryProfile(httpReq.Context(), userID)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("userAPI.QueryProfile failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var res interface{}
diff --git a/federationapi/routing/publicrooms.go b/federationapi/routing/publicrooms.go
index 59ff4eb2..213d1631 100644
--- a/federationapi/routing/publicrooms.go
+++ b/federationapi/routing/publicrooms.go
@@ -39,7 +39,10 @@ func GetPostPublicRooms(req *http.Request, rsAPI roomserverAPI.FederationRoomser
 	}
 	response, err := publicRooms(req.Context(), request, rsAPI)
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	return util.JSONResponse{
 		Code: http.StatusOK,
@@ -106,8 +109,10 @@ func fillPublicRoomsReq(httpReq *http.Request, request *PublicRoomReq) *util.JSO
 		// In that case, we want to assign 0 so we ignore the error
 		if err != nil && len(httpReq.FormValue("limit")) > 0 {
 			util.GetLogger(httpReq.Context()).WithError(err).Error("strconv.Atoi failed")
-			reqErr := spec.InternalServerError()
-			return &reqErr
+			return &util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		request.Limit = int16(limit)
 		request.Since = httpReq.FormValue("since")
diff --git a/federationapi/routing/query.go b/federationapi/routing/query.go
index 233290e2..2e845f32 100644
--- a/federationapi/routing/query.go
+++ b/federationapi/routing/query.go
@@ -61,7 +61,10 @@ func RoomAliasToID(
 		queryRes := &roomserverAPI.GetRoomIDForAliasResponse{}
 		if err = rsAPI.GetRoomIDForAlias(httpReq.Context(), queryReq, queryRes); err != nil {
 			util.GetLogger(httpReq.Context()).WithError(err).Error("aliasAPI.GetRoomIDForAlias failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		if queryRes.RoomID != "" {
@@ -69,7 +72,10 @@ func RoomAliasToID(
 			var serverQueryRes federationAPI.QueryJoinedHostServerNamesInRoomResponse
 			if err = senderAPI.QueryJoinedHostServerNamesInRoom(httpReq.Context(), &serverQueryReq, &serverQueryRes); err != nil {
 				util.GetLogger(httpReq.Context()).WithError(err).Error("senderAPI.QueryJoinedHostServerNamesInRoom failed")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 
 			resp = fclient.RespDirectory{
@@ -98,7 +104,10 @@ func RoomAliasToID(
 			// TODO: Return 502 if the remote server errored.
 			// TODO: Return 504 if the remote server timed out.
 			util.GetLogger(httpReq.Context()).WithError(err).Error("federation.LookupRoomAlias failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
diff --git a/federationapi/routing/routing.go b/federationapi/routing/routing.go
index f62a8f46..44faad91 100644
--- a/federationapi/routing/routing.go
+++ b/federationapi/routing/routing.go
@@ -312,8 +312,6 @@ func Setup(
 					JSON: spec.Forbidden("Forbidden by server ACLs"),
 				}
 			}
-			roomID := vars["roomID"]
-			userID := vars["userID"]
 			queryVars := httpReq.URL.Query()
 			remoteVersions := []gomatrixserverlib.RoomVersion{}
 			if vers, ok := queryVars["ver"]; ok {
@@ -328,8 +326,25 @@ func Setup(
 				// https://matrix.org/docs/spec/server_server/r0.1.3#get-matrix-federation-v1-make-join-roomid-userid
 				remoteVersions = append(remoteVersions, gomatrixserverlib.RoomVersionV1)
 			}
+
+			userID, err := spec.NewUserID(vars["userID"], true)
+			if err != nil {
+				return util.JSONResponse{
+					Code: http.StatusBadRequest,
+					JSON: spec.BadJSON("Invalid UserID"),
+				}
+			}
+			roomID, err := spec.NewRoomID(vars["roomID"])
+			if err != nil {
+				return util.JSONResponse{
+					Code: http.StatusBadRequest,
+					JSON: spec.BadJSON("Invalid RoomID"),
+				}
+			}
+
+			logrus.Debugf("Processing make_join for user %s, room %s", userID.String(), roomID.String())
 			return MakeJoin(
-				httpReq, request, cfg, rsAPI, roomID, userID, remoteVersions,
+				httpReq, request, cfg, rsAPI, *roomID, *userID, remoteVersions,
 			)
 		},
 	)).Methods(http.MethodGet)
@@ -353,7 +368,7 @@ func Setup(
 			body = []interface{}{
 				res.Code, res.JSON,
 			}
-			jerr, ok := res.JSON.(*spec.MatrixError)
+			jerr, ok := res.JSON.(spec.MatrixError)
 			if ok {
 				body = jerr
 			}
@@ -419,7 +434,7 @@ func Setup(
 			body = []interface{}{
 				res.Code, res.JSON,
 			}
-			jerr, ok := res.JSON.(*spec.MatrixError)
+			jerr, ok := res.JSON.(spec.MatrixError)
 			if ok {
 				body = jerr
 			}
@@ -566,7 +581,7 @@ func MakeFedAPI(
 		go wakeup.Wakeup(req.Context(), fedReq.Origin())
 		vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
 		if err != nil {
-			return util.MatrixErrorResponse(400, "M_UNRECOGNISED", "badly encoded query params")
+			return util.MatrixErrorResponse(400, string(spec.ErrorUnrecognized), "badly encoded query params")
 		}
 
 		jsonRes := f(req, fedReq, vars)
diff --git a/federationapi/routing/threepid.go b/federationapi/routing/threepid.go
index adfafe74..beeb5249 100644
--- a/federationapi/routing/threepid.go
+++ b/federationapi/routing/threepid.go
@@ -80,7 +80,10 @@ func CreateInvitesFrom3PIDInvites(
 		)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("createInviteFrom3PIDInvite failed")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		if event != nil {
 			evs = append(evs, &types.HeaderedEvent{PDU: event})
@@ -100,7 +103,10 @@ func CreateInvitesFrom3PIDInvites(
 		false,
 	); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
@@ -176,7 +182,10 @@ func ExchangeThirdPartyInvite(
 		}
 	} else if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("buildMembershipEvent failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Ask the requesting server to sign the newly created event so we know it
@@ -184,22 +193,34 @@ func ExchangeThirdPartyInvite(
 	inviteReq, err := fclient.NewInviteV2Request(event, nil)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("failed to make invite v2 request")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	signedEvent, err := federation.SendInviteV2(httpReq.Context(), senderDomain, request.Origin(), inviteReq)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("federation.SendInvite failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	verImpl, err := gomatrixserverlib.GetRoomVersion(roomVersion)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Errorf("unknown room version: %s", roomVersion)
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	inviteEvent, err := verImpl.NewEventFromUntrustedJSON(signedEvent.Event)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("federation.SendInvite failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// Send the event to the roomserver
@@ -216,7 +237,10 @@ func ExchangeThirdPartyInvite(
 		false,
 	); err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("SendEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/go.mod b/go.mod
index bd1d43fc..eff9e50f 100644
--- a/go.mod
+++ b/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 v0.0.0-20230509222610-6fd532036ab6
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230517000105-1ff06fc8a6a2
 	github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a
 	github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
 	github.com/mattn/go-sqlite3 v1.14.16
@@ -34,7 +34,7 @@ require (
 	github.com/patrickmn/go-cache v2.1.0+incompatible
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.13.0
-	github.com/sirupsen/logrus v1.9.0
+	github.com/sirupsen/logrus v1.9.1
 	github.com/stretchr/testify v1.8.2
 	github.com/tidwall/gjson v1.14.4
 	github.com/tidwall/sjson v1.2.5
diff --git a/go.sum b/go.sum
index 733d6e24..faf70c6d 100644
--- a/go.sum
+++ b/go.sum
@@ -323,8 +323,8 @@ 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 v0.0.0-20230509222610-6fd532036ab6 h1:cF6fNfxC73fU9zT3pgzDXI9NDihAdnilqqGcpDWgNP4=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230509222610-6fd532036ab6/go.mod h1:7HTbSZe+CIdmeqVyFMekwD5dFU8khWQyngKATvd12FU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230517000105-1ff06fc8a6a2 h1:V36yCWt2CoSfI1xr6WYJ9Mb3eyl95SknMRLGFvEuYak=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230517000105-1ff06fc8a6a2/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a h1:awrPDf9LEFySxTLKYBMCiObelNx/cBuv/wzllvCCH3A=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a/go.mod h1:HchJX9oKMXaT2xYFs0Ha/6Zs06mxLU8k6F1ODnrGkeQ=
 github.com/matrix-org/util v0.0.0-20221111132719-399730281e66 h1:6z4KxomXSIGWqhHcfzExgkH3Z3UkIXry4ibJS4Aqz2Y=
@@ -444,8 +444,8 @@ github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPx
 github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
 github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
-github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
-github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/sirupsen/logrus v1.9.1 h1:Ou41VVR3nMWWmTiEUnj0OlsgOSCUFgsPAOl6jRIcVtQ=
+github.com/sirupsen/logrus v1.9.1/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
 github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d/go.mod h1:OnSkiWE9lh6wB0YB77sQom3nweQdgAjqCqsofrRNTgc=
 github.com/smartystreets/goconvey v0.0.0-20181108003508-044398e4856c/go.mod h1:XDJAKZRPZ1CvBcN2aX5YOUTYGHki24fSF0Iv48Ibg0s=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
diff --git a/internal/eventutil/events.go b/internal/eventutil/events.go
index dff45968..79882d8d 100644
--- a/internal/eventutil/events.go
+++ b/internal/eventutil/events.go
@@ -31,7 +31,17 @@ import (
 
 // ErrRoomNoExists is returned when trying to lookup the state of a room that
 // doesn't exist
-var ErrRoomNoExists = errors.New("room does not exist")
+var errRoomNoExists = fmt.Errorf("room does not exist")
+
+type ErrRoomNoExists struct{}
+
+func (e ErrRoomNoExists) Error() string {
+	return errRoomNoExists.Error()
+}
+
+func (e ErrRoomNoExists) Unwrap() error {
+	return errRoomNoExists
+}
 
 // QueryAndBuildEvent builds a Matrix event using the event builder and roomserver query
 // API client provided. If also fills roomserver query API response (if provided)
@@ -116,7 +126,7 @@ func addPrevEventsToEvent(
 	queryRes *api.QueryLatestEventsAndStateResponse,
 ) error {
 	if !queryRes.RoomExists {
-		return ErrRoomNoExists
+		return ErrRoomNoExists{}
 	}
 
 	verImpl, err := gomatrixserverlib.GetRoomVersion(queryRes.RoomVersion)
diff --git a/internal/httputil/routing.go b/internal/httputil/routing.go
index c733c8ce..2052c798 100644
--- a/internal/httputil/routing.go
+++ b/internal/httputil/routing.go
@@ -15,10 +15,12 @@
 package httputil
 
 import (
+	"encoding/json"
 	"net/http"
 	"net/url"
 
 	"github.com/gorilla/mux"
+	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
 // URLDecodeMapValues is a function that iterates through each of the items in a
@@ -66,13 +68,15 @@ func NewRouters() Routers {
 var NotAllowedHandler = WrapHandlerInCORS(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusMethodNotAllowed)
 	w.Header().Set("Content-Type", "application/json")
-	_, _ = w.Write([]byte(`{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}`)) // nolint:misspell
+	unrecognizedErr, _ := json.Marshal(spec.Unrecognized("Unrecognized request")) // nolint:misspell
+	_, _ = w.Write(unrecognizedErr)                                               // nolint:misspell
 }))
 
 var NotFoundCORSHandler = WrapHandlerInCORS(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusNotFound)
 	w.Header().Set("Content-Type", "application/json")
-	_, _ = w.Write([]byte(`{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}`)) // nolint:misspell
+	unrecognizedErr, _ := json.Marshal(spec.Unrecognized("Unrecognized request")) // nolint:misspell
+	_, _ = w.Write(unrecognizedErr)                                               // nolint:misspell
 }))
 
 func (r *Routers) configureHTTPErrors() {
diff --git a/mediaapi/routing/upload.go b/mediaapi/routing/upload.go
index 5061d476..5ac1d076 100644
--- a/mediaapi/routing/upload.go
+++ b/mediaapi/routing/upload.go
@@ -184,8 +184,10 @@ func (r *uploadRequest) doUpload(
 	if err != nil {
 		fileutils.RemoveDir(tmpDir, r.Logger)
 		r.Logger.WithError(err).Error("Error querying the database by hash.")
-		resErr := spec.InternalServerError()
-		return &resErr
+		return &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if existingMetadata != nil {
 		// The file already exists, delete the uploaded temporary file.
@@ -194,8 +196,10 @@ func (r *uploadRequest) doUpload(
 		mediaID, merr := r.generateMediaID(ctx, db)
 		if merr != nil {
 			r.Logger.WithError(merr).Error("Failed to generate media ID for existing file")
-			resErr := spec.InternalServerError()
-			return &resErr
+			return &util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		// Then amend the upload metadata.
@@ -217,8 +221,10 @@ func (r *uploadRequest) doUpload(
 		if err != nil {
 			fileutils.RemoveDir(tmpDir, r.Logger)
 			r.Logger.WithError(err).Error("Failed to generate media ID for new upload")
-			resErr := spec.InternalServerError()
-			return &resErr
+			return &util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
diff --git a/relayapi/routing/routing.go b/relayapi/routing/routing.go
index f6e55611..f11b0a7c 100644
--- a/relayapi/routing/routing.go
+++ b/relayapi/routing/routing.go
@@ -122,7 +122,7 @@ func MakeRelayAPI(
 		}()
 		vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
 		if err != nil {
-			return util.MatrixErrorResponse(400, "M_UNRECOGNISED", "badly encoded query params")
+			return util.MatrixErrorResponse(400, string(spec.ErrorUnrecognized), "badly encoded query params")
 		}
 
 		jsonRes := f(req, fedReq, vars)
diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index ab1ec28f..f2e2bf84 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -8,6 +8,7 @@ import (
 
 	asAPI "github.com/matrix-org/dendrite/appservice/api"
 	fsAPI "github.com/matrix-org/dendrite/federationapi/api"
+	"github.com/matrix-org/dendrite/roomserver/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 )
 
@@ -224,6 +225,12 @@ type FederationRoomserverAPI interface {
 	PerformInvite(ctx context.Context, req *PerformInviteRequest) error
 	// Query a given amount (or less) of events prior to a given set of events.
 	PerformBackfill(ctx context.Context, req *PerformBackfillRequest, res *PerformBackfillResponse) error
+
+	CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eventType string, stateKey string) (gomatrixserverlib.PDU, error)
+	InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error)
+	QueryRoomInfo(ctx context.Context, roomID spec.RoomID) (*types.RoomInfo, error)
+	UserJoinedToRoom(ctx context.Context, roomID types.RoomNID, userID spec.UserID) (bool, error)
+	LocallyJoinedUsers(ctx context.Context, roomVersion gomatrixserverlib.RoomVersion, roomNID types.RoomNID) ([]gomatrixserverlib.PDU, error)
 }
 
 type KeyserverRoomserverAPI interface {
diff --git a/roomserver/internal/perform/perform_admin.go b/roomserver/internal/perform/perform_admin.go
index a539efd1..fadc8bcf 100644
--- a/roomserver/internal/perform/perform_admin.go
+++ b/roomserver/internal/perform/perform_admin.go
@@ -52,7 +52,7 @@ func (r *Admin) PerformAdminEvacuateRoom(
 		return nil, err
 	}
 	if roomInfo == nil || roomInfo.IsStub() {
-		return nil, eventutil.ErrRoomNoExists
+		return nil, eventutil.ErrRoomNoExists{}
 	}
 
 	memberNIDs, err := r.DB.GetMembershipEventNIDsForRoom(ctx, roomInfo.RoomNID, true, true)
@@ -240,7 +240,7 @@ func (r *Admin) PerformAdminDownloadState(
 	}
 
 	if roomInfo == nil || roomInfo.IsStub() {
-		return eventutil.ErrRoomNoExists
+		return eventutil.ErrRoomNoExists{}
 	}
 
 	fwdExtremities, _, depth, err := r.DB.LatestEventIDs(ctx, roomInfo.RoomNID)
diff --git a/roomserver/internal/perform/perform_join.go b/roomserver/internal/perform/perform_join.go
index a836eb1a..5f4ad186 100644
--- a/roomserver/internal/perform/perform_join.go
+++ b/roomserver/internal/perform/perform_join.go
@@ -145,7 +145,7 @@ func (r *Joiner) performJoinRoomByAlias(
 	return r.performJoinRoomByID(ctx, req)
 }
 
-// TODO: Break this function up a bit
+// TODO: Break this function up a bit & move to GMSL
 // nolint:gocyclo
 func (r *Joiner) performJoinRoomByID(
 	ctx context.Context,
@@ -286,7 +286,7 @@ func (r *Joiner) performJoinRoomByID(
 	}
 	event, err := eventutil.QueryAndBuildEvent(ctx, &proto, r.Cfg.Matrix, identity, time.Now(), r.RSAPI, &buildRes)
 
-	switch err {
+	switch err.(type) {
 	case nil:
 		// The room join is local. Send the new join event into the
 		// roomserver. First of all check that the user isn't already
@@ -328,7 +328,7 @@ func (r *Joiner) performJoinRoomByID(
 			// Otherwise we'll try a federated join as normal, since it's quite
 			// possible that the room still exists on other servers.
 			if len(req.ServerNames) == 0 {
-				return "", "", eventutil.ErrRoomNoExists
+				return "", "", eventutil.ErrRoomNoExists{}
 			}
 		}
 
diff --git a/roomserver/internal/perform/perform_upgrade.go b/roomserver/internal/perform/perform_upgrade.go
index e88cb1dc..abe63145 100644
--- a/roomserver/internal/perform/perform_upgrade.go
+++ b/roomserver/internal/perform/perform_upgrade.go
@@ -274,7 +274,7 @@ func publishNewRoomAndUnpublishOldRoom(
 
 func (r *Upgrader) validateRoomExists(ctx context.Context, roomID string) error {
 	if _, err := r.URSAPI.QueryRoomVersionForRoom(ctx, roomID); err != nil {
-		return eventutil.ErrRoomNoExists
+		return eventutil.ErrRoomNoExists{}
 	}
 	return nil
 }
@@ -556,15 +556,18 @@ func (r *Upgrader) makeHeaderedEvent(ctx context.Context, evTime time.Time, user
 	}
 	var queryRes api.QueryLatestEventsAndStateResponse
 	headeredEvent, err := eventutil.QueryAndBuildEvent(ctx, &proto, r.Cfg.Matrix, identity, evTime, r.URSAPI, &queryRes)
-	if err == eventutil.ErrRoomNoExists {
-		return nil, err
-	} else if e, ok := err.(gomatrixserverlib.BadJSONError); ok {
+	switch e := err.(type) {
+	case nil:
+	case eventutil.ErrRoomNoExists:
+		return nil, e
+	case gomatrixserverlib.BadJSONError:
 		return nil, e
-	} else if e, ok := err.(gomatrixserverlib.EventValidationError); ok {
+	case gomatrixserverlib.EventValidationError:
 		return nil, e
-	} else if err != nil {
+	default:
 		return nil, fmt.Errorf("failed to build new %q event: %w", proto.Type, err)
 	}
+
 	// check to see if this user can perform this operation
 	stateEvents := make([]gomatrixserverlib.PDU, len(queryRes.StateEvents))
 	for i := range queryRes.StateEvents {
diff --git a/roomserver/internal/query/query.go b/roomserver/internal/query/query.go
index 27c0dd0c..e4dac45e 100644
--- a/roomserver/internal/query/query.go
+++ b/roomserver/internal/query/query.go
@@ -858,6 +858,49 @@ func (r *Queryer) QueryAuthChain(ctx context.Context, req *api.QueryAuthChainReq
 	return nil
 }
 
+func (r *Queryer) InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error) {
+	pending, _, _, _, err := helpers.IsInvitePending(ctx, r.DB, roomID.String(), userID.String())
+	return pending, err
+}
+
+func (r *Queryer) QueryRoomInfo(ctx context.Context, roomID spec.RoomID) (*types.RoomInfo, error) {
+	return r.DB.RoomInfo(ctx, roomID.String())
+}
+
+func (r *Queryer) CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eventType string, stateKey string) (gomatrixserverlib.PDU, error) {
+	return r.DB.GetStateEvent(ctx, roomID.String(), string(eventType), "")
+}
+
+func (r *Queryer) UserJoinedToRoom(ctx context.Context, roomNID types.RoomNID, userID spec.UserID) (bool, error) {
+	_, isIn, _, err := r.DB.GetMembership(ctx, roomNID, userID.String())
+	return isIn, err
+}
+
+func (r *Queryer) LocallyJoinedUsers(ctx context.Context, roomVersion gomatrixserverlib.RoomVersion, roomNID types.RoomNID) ([]gomatrixserverlib.PDU, error) {
+	joinNIDs, err := r.DB.GetMembershipEventNIDsForRoom(ctx, roomNID, true, true)
+	if err != nil {
+		return nil, err
+	}
+
+	events, err := r.DB.Events(ctx, roomVersion, joinNIDs)
+	if err != nil {
+		return nil, err
+	}
+
+	// For each of the joined users, let's see if we can get a valid
+	// membership event.
+	joinedUsers := []gomatrixserverlib.PDU{}
+	for _, event := range events {
+		if event.Type() != spec.MRoomMember || event.StateKey() == nil {
+			continue // shouldn't happen
+		}
+
+		joinedUsers = append(joinedUsers, event)
+	}
+
+	return joinedUsers, nil
+}
+
 // nolint:gocyclo
 func (r *Queryer) QueryRestrictedJoinAllowed(ctx context.Context, req *api.QueryRestrictedJoinAllowedRequest, res *api.QueryRestrictedJoinAllowedResponse) error {
 	// Look up if we know anything about the room. If it doesn't exist
diff --git a/setup/mscs/msc2836/msc2836.go b/setup/mscs/msc2836/msc2836.go
index e9d61fed..f468b048 100644
--- a/setup/mscs/msc2836/msc2836.go
+++ b/setup/mscs/msc2836/msc2836.go
@@ -427,8 +427,10 @@ func (rc *reqCtx) includeChildren(db Database, parentID string, limit int, recen
 	children, err := db.ChildrenForParent(rc.ctx, parentID, constRelType, recentFirst)
 	if err != nil {
 		util.GetLogger(rc.ctx).WithError(err).Error("failed to get ChildrenForParent")
-		resErr := spec.InternalServerError()
-		return nil, &resErr
+		return nil, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var childEvents []*types.HeaderedEvent
 	for _, child := range children {
diff --git a/syncapi/routing/context.go b/syncapi/routing/context.go
index 8ff656e7..ac17d39d 100644
--- a/syncapi/routing/context.go
+++ b/syncapi/routing/context.go
@@ -56,7 +56,10 @@ func Context(
 ) util.JSONResponse {
 	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var succeeded bool
 	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
@@ -87,7 +90,10 @@ func Context(
 	membershipReq := roomserver.QueryMembershipForUserRequest{UserID: device.UserID, RoomID: roomID}
 	if err = rsAPI.QueryMembershipForUser(ctx, &membershipReq, &membershipRes); err != nil {
 		logrus.WithError(err).Error("unable to query membership")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !membershipRes.RoomExists {
 		return util.JSONResponse{
@@ -117,7 +123,10 @@ func Context(
 			}
 		}
 		logrus.WithError(err).WithField("eventID", eventID).Error("unable to find requested event")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// verify the user is allowed to see the context for this room/event
@@ -125,7 +134,10 @@ func Context(
 	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(ctx, snapshot, rsAPI, []*rstypes.HeaderedEvent{&requestedEvent}, nil, device.UserID, "context")
 	if err != nil {
 		logrus.WithError(err).Error("unable to apply history visibility filter")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	logrus.WithFields(logrus.Fields{
 		"duration": time.Since(startTime),
@@ -141,20 +153,29 @@ func Context(
 	eventsBefore, err := snapshot.SelectContextBeforeEvent(ctx, id, roomID, filter)
 	if err != nil && err != sql.ErrNoRows {
 		logrus.WithError(err).Error("unable to fetch before events")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	_, eventsAfter, err := snapshot.SelectContextAfterEvent(ctx, id, roomID, filter)
 	if err != nil && err != sql.ErrNoRows {
 		logrus.WithError(err).Error("unable to fetch after events")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	startTime = time.Now()
 	eventsBeforeFiltered, eventsAfterFiltered, err := applyHistoryVisibilityOnContextEvents(ctx, snapshot, rsAPI, eventsBefore, eventsAfter, device.UserID)
 	if err != nil {
 		logrus.WithError(err).Error("unable to apply history visibility filter")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	logrus.WithFields(logrus.Fields{
@@ -166,7 +187,10 @@ func Context(
 	state, err := snapshot.CurrentState(ctx, roomID, &stateFilter, nil)
 	if err != nil {
 		logrus.WithError(err).Error("unable to fetch current room state")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	eventsBeforeClient := synctypes.ToClientEvents(gomatrixserverlib.ToPDUs(eventsBeforeFiltered), synctypes.FormatAll)
@@ -180,7 +204,10 @@ func Context(
 		newState, err = applyLazyLoadMembers(ctx, device, snapshot, roomID, evs, lazyLoadCache)
 		if err != nil {
 			logrus.WithError(err).Error("unable to load membership events")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
diff --git a/syncapi/routing/filter.go b/syncapi/routing/filter.go
index 5152e1f8..c4eecbdb 100644
--- a/syncapi/routing/filter.go
+++ b/syncapi/routing/filter.go
@@ -43,7 +43,10 @@ func GetFilter(
 	localpart, _, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	filter := synctypes.DefaultFilter()
@@ -83,7 +86,10 @@ func PutFilter(
 	localpart, _, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	var filter synctypes.Filter
@@ -122,7 +128,10 @@ func PutFilter(
 	filterID, err := syncDB.PutFilter(req.Context(), localpart, &filter)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("syncDB.PutFilter failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	return util.JSONResponse{
diff --git a/syncapi/routing/getevent.go b/syncapi/routing/getevent.go
index e3d77cc3..0d3d412f 100644
--- a/syncapi/routing/getevent.go
+++ b/syncapi/routing/getevent.go
@@ -51,13 +51,19 @@ func GetEvent(
 	})
 	if err != nil {
 		logger.WithError(err).Error("GetEvent: syncDB.NewDatabaseTransaction failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	events, err := db.Events(ctx, []string{eventID})
 	if err != nil {
 		logger.WithError(err).Error("GetEvent: syncDB.Events failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	// The requested event does not exist in our database
@@ -81,7 +87,7 @@ func GetEvent(
 		logger.WithError(err).Error("GetEvent: internal.ApplyHistoryVisibilityFilter failed")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError(),
+			JSON: spec.InternalServerError{},
 		}
 	}
 
diff --git a/syncapi/routing/memberships.go b/syncapi/routing/memberships.go
index 5a66009c..7d2e137d 100644
--- a/syncapi/routing/memberships.go
+++ b/syncapi/routing/memberships.go
@@ -67,7 +67,10 @@ func GetMemberships(
 	var queryRes api.QueryMembershipForUserResponse
 	if err := rsAPI.QueryMembershipForUser(req.Context(), &queryReq, &queryRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("rsAPI.QueryMembershipsForRoom failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	if !queryRes.HasBeenInRoom {
@@ -86,7 +89,10 @@ func GetMemberships(
 
 	db, err := syncDB.NewDatabaseSnapshot(req.Context())
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	defer db.Rollback() // nolint: errcheck
 
@@ -98,7 +104,10 @@ func GetMemberships(
 			atToken, err = db.EventPositionInTopology(req.Context(), queryRes.EventID)
 			if err != nil {
 				util.GetLogger(req.Context()).WithError(err).Error("unable to get 'atToken'")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 		}
 	}
@@ -106,13 +115,19 @@ func GetMemberships(
 	eventIDs, err := db.SelectMemberships(req.Context(), roomID, atToken, membership, notMembership)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("db.SelectMemberships failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	qryRes := &api.QueryEventsByIDResponse{}
 	if err := rsAPI.QueryEventsByID(req.Context(), &api.QueryEventsByIDRequest{EventIDs: eventIDs, RoomID: roomID}, qryRes); err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("rsAPI.QueryEventsByID failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	result := qryRes.Events
@@ -124,7 +139,10 @@ func GetMemberships(
 			var content databaseJoinedMember
 			if err := json.Unmarshal(ev.Content(), &content); err != nil {
 				util.GetLogger(req.Context()).WithError(err).Error("failed to unmarshal event content")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			res.Joined[ev.Sender()] = joinedMember(content)
 		}
diff --git a/syncapi/routing/messages.go b/syncapi/routing/messages.go
index 4d3c9e2e..58f663d0 100644
--- a/syncapi/routing/messages.go
+++ b/syncapi/routing/messages.go
@@ -81,7 +81,10 @@ func OnIncomingMessagesRequest(
 	// request that requires backfilling from the roomserver or federation.
 	snapshot, err := db.NewDatabaseTransaction(req.Context())
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var succeeded bool
 	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
@@ -89,7 +92,10 @@ func OnIncomingMessagesRequest(
 	// check if the user has already forgotten about this room
 	membershipResp, err := getMembershipForUser(req.Context(), roomID, device.UserID, rsAPI)
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if !membershipResp.RoomExists {
 		return util.JSONResponse{
@@ -151,7 +157,10 @@ func OnIncomingMessagesRequest(
 			from, err = snapshot.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, backwardOrdering)
 			if err != nil {
 				logrus.WithError(err).Errorf("Failed to get topological position for streaming token %v", streamToken)
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 		}
 	}
@@ -173,7 +182,10 @@ func OnIncomingMessagesRequest(
 				to, err = snapshot.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, !backwardOrdering)
 				if err != nil {
 					logrus.WithError(err).Errorf("Failed to get topological position for streaming token %v", streamToken)
-					return spec.InternalServerError()
+					return util.JSONResponse{
+						Code: http.StatusInternalServerError,
+						JSON: spec.InternalServerError{},
+					}
 				}
 			}
 		}
@@ -232,7 +244,10 @@ func OnIncomingMessagesRequest(
 	clientEvents, start, end, err := mReq.retrieveEvents()
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("mreq.retrieveEvents failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	util.GetLogger(req.Context()).WithFields(logrus.Fields{
@@ -253,7 +268,10 @@ func OnIncomingMessagesRequest(
 		membershipEvents, err := applyLazyLoadMembers(req.Context(), device, snapshot, roomID, clientEvents, lazyLoadCache)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("failed to apply lazy loading")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		res.State = append(res.State, synctypes.ToClientEvents(gomatrixserverlib.ToPDUs(membershipEvents), synctypes.FormatAll)...)
 	}
diff --git a/syncapi/routing/relations.go b/syncapi/routing/relations.go
index 2bf11a56..8374bf5b 100644
--- a/syncapi/routing/relations.go
+++ b/syncapi/routing/relations.go
@@ -80,7 +80,10 @@ func Relations(
 	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
 	if err != nil {
 		logrus.WithError(err).Error("Failed to get snapshot for relations")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var succeeded bool
 	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
diff --git a/syncapi/routing/routing.go b/syncapi/routing/routing.go
index 88c5c504..9ad0c047 100644
--- a/syncapi/routing/routing.go
+++ b/syncapi/routing/routing.go
@@ -162,7 +162,10 @@ func Setup(
 			}
 			var nextBatch *string
 			if err := req.ParseForm(); err != nil {
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			if req.Form.Has("next_batch") {
 				nb := req.FormValue("next_batch")
diff --git a/syncapi/routing/search.go b/syncapi/routing/search.go
index 986284d0..b7191873 100644
--- a/syncapi/routing/search.go
+++ b/syncapi/routing/search.go
@@ -55,7 +55,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 	if from != nil && *from != "" {
 		nextBatch, err = strconv.Atoi(*from)
 		if err != nil {
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 	}
 
@@ -65,7 +68,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 
 	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var succeeded bool
 	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
@@ -73,7 +79,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 	// only search rooms the user is actually joined to
 	joinedRooms, err := snapshot.RoomIDsWithMembership(ctx, device.UserID, "join")
 	if err != nil {
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	if len(joinedRooms) == 0 {
 		return util.JSONResponse{
@@ -115,7 +124,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 	)
 	if err != nil {
 		logrus.WithError(err).Error("failed to search fulltext")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	logrus.Debugf("Search took %s", result.Took)
 
@@ -155,7 +167,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 	evs, err := syncDB.Events(ctx, wantEvents)
 	if err != nil {
 		logrus.WithError(err).Error("failed to get events from database")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 
 	groups := make(map[string]RoomResult)
@@ -173,12 +188,18 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 		eventsBefore, eventsAfter, err := contextEvents(ctx, snapshot, event, roomFilter, searchReq)
 		if err != nil {
 			logrus.WithError(err).Error("failed to get context events")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 		startToken, endToken, err := getStartEnd(ctx, snapshot, eventsBefore, eventsAfter)
 		if err != nil {
 			logrus.WithError(err).Error("failed to get start/end")
-			return spec.InternalServerError()
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.InternalServerError{},
+			}
 		}
 
 		profileInfos := make(map[string]ProfileInfoResponse)
@@ -221,7 +242,10 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 			state, err := snapshot.CurrentState(ctx, event.RoomID(), &stateFilter, nil)
 			if err != nil {
 				logrus.WithError(err).Error("unable to get current state")
-				return spec.InternalServerError()
+				return util.JSONResponse{
+					Code: http.StatusInternalServerError,
+					JSON: spec.InternalServerError{},
+				}
 			}
 			stateForRooms[event.RoomID()] = synctypes.ToClientEvents(gomatrixserverlib.ToPDUs(state), synctypes.FormatSync)
 		}
diff --git a/syncapi/sync/requestpool.go b/syncapi/sync/requestpool.go
index 09e5dee1..5a92c70e 100644
--- a/syncapi/sync/requestpool.go
+++ b/syncapi/sync/requestpool.go
@@ -536,12 +536,18 @@ func (rp *RequestPool) OnIncomingKeyChangeRequest(req *http.Request, device *use
 	syncReq, err := newSyncRequest(req, *device, rp.db)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("newSyncRequest failed")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	snapshot, err := rp.db.NewDatabaseSnapshot(req.Context())
 	if err != nil {
 		logrus.WithError(err).Error("Failed to acquire database snapshot for key change")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	var succeeded bool
 	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
@@ -552,7 +558,10 @@ func (rp *RequestPool) OnIncomingKeyChangeRequest(req *http.Request, device *use
 	)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("Failed to DeviceListCatchup info")
-		return spec.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
 	}
 	succeeded = true
 	return util.JSONResponse{