Pass join errors through internal API boundaries (#1157)

* Pass join errors through internal API boundaries

Required for certain invite sytests. We will need to think of a
better way of handling this going forwards.

* Include m.room.avatar in stripped state; handle trailing slashes when GETing state events

* Update whitelist

* Update whitelist

4 files changed, 30 insertions, 1 deletions

diff --git a/roomserver/api/perform.go b/roomserver/api/perform.go
index 3e5cae1b..0f5394c9 100644
--- a/roomserver/api/perform.go
+++ b/roomserver/api/perform.go
@@ -5,6 +5,17 @@ import (
 	"github.com/matrix-org/util"
 )
 
+type JoinError int
+
+const (
+	// JoinErrorNotAllowed means the user is not allowed to join this room (e.g join_rule:invite or banned)
+	JoinErrorNotAllowed JoinError = 1
+	// JoinErrorBadRequest means the request was wrong in some way (invalid user ID, wrong server, etc)
+	JoinErrorBadRequest JoinError = 2
+	// JoinErrorNoRoom means that the room being joined doesn't exist.
+	JoinErrorNoRoom JoinError = 3
+)
+
 type PerformJoinRequest struct {
 	RoomIDOrAlias string                         `json:"room_id_or_alias"`
 	UserID        string                         `json:"user_id"`
@@ -13,7 +24,12 @@ type PerformJoinRequest struct {
 }
 
 type PerformJoinResponse struct {
+	// The room ID, populated on success.
 	RoomID string `json:"room_id"`
+	// The reason why the join failed. Can be blank.
+	Error JoinError `json:"error"`
+	// Debugging description of the error. Always present on failure.
+	ErrMsg string `json:"err_msg"`
 }
 
 type PerformLeaveRequest struct {
diff --git a/roomserver/internal/input_events.go b/roomserver/internal/input_events.go
index 4487aea0..fe3bdf4b 100644
--- a/roomserver/internal/input_events.go
+++ b/roomserver/internal/input_events.go
@@ -298,9 +298,12 @@ func buildInviteStrippedState(
 		return nil, fmt.Errorf("room %q unknown", input.Event.RoomID())
 	}
 	stateWanted := []gomatrixserverlib.StateKeyTuple{}
+	// "If they are set on the room, at least the state for m.room.avatar, m.room.canonical_alias, m.room.join_rules, and m.room.name SHOULD be included."
+	// https://matrix.org/docs/spec/client_server/r0.6.0#m-room-member
 	for _, t := range []string{
 		gomatrixserverlib.MRoomName, gomatrixserverlib.MRoomCanonicalAlias,
 		gomatrixserverlib.MRoomAliases, gomatrixserverlib.MRoomJoinRules,
+		"m.room.avatar",
 	} {
 		stateWanted = append(stateWanted, gomatrixserverlib.StateKeyTuple{
 			EventType: t,
diff --git a/roomserver/internal/perform_join.go b/roomserver/internal/perform_join.go
index 1c951bb1..44f84240 100644
--- a/roomserver/internal/perform_join.go
+++ b/roomserver/internal/perform_join.go
@@ -2,6 +2,7 @@ package internal
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -21,9 +22,11 @@ func (r *RoomserverInternalAPI) PerformJoin(
 ) error {
 	_, domain, err := gomatrixserverlib.SplitID('@', req.UserID)
 	if err != nil {
+		res.Error = api.JoinErrorBadRequest
 		return fmt.Errorf("Supplied user ID %q in incorrect format", req.UserID)
 	}
 	if domain != r.Cfg.Matrix.ServerName {
+		res.Error = api.JoinErrorBadRequest
 		return fmt.Errorf("User %q does not belong to this homeserver", req.UserID)
 	}
 	if strings.HasPrefix(req.RoomIDOrAlias, "!") {
@@ -32,6 +35,7 @@ func (r *RoomserverInternalAPI) PerformJoin(
 	if strings.HasPrefix(req.RoomIDOrAlias, "#") {
 		return r.performJoinRoomByAlias(ctx, req, res)
 	}
+	res.Error = api.JoinErrorBadRequest
 	return fmt.Errorf("Room ID or alias %q is invalid", req.RoomIDOrAlias)
 }
 
@@ -99,6 +103,7 @@ func (r *RoomserverInternalAPI) performJoinRoomByID(
 	// Get the domain part of the room ID.
 	_, domain, err := gomatrixserverlib.SplitID('!', req.RoomIDOrAlias)
 	if err != nil {
+		res.Error = api.JoinErrorBadRequest
 		return fmt.Errorf("Room ID %q is invalid", req.RoomIDOrAlias)
 	}
 	req.ServerNames = append(req.ServerNames, domain)
@@ -198,6 +203,10 @@ func (r *RoomserverInternalAPI) performJoinRoomByID(
 			}
 			inputRes := api.InputRoomEventsResponse{}
 			if err = r.InputRoomEvents(ctx, &inputReq, &inputRes); err != nil {
+				var notAllowed *gomatrixserverlib.NotAllowed
+				if errors.As(err, &notAllowed) {
+					res.Error = api.JoinErrorNotAllowed
+				}
 				return fmt.Errorf("r.InputRoomEvents: %w", err)
 			}
 		}
@@ -207,6 +216,7 @@ func (r *RoomserverInternalAPI) performJoinRoomByID(
 		// room. If it is then there's nothing more to do - the room just
 		// hasn't been created yet.
 		if domain == r.Cfg.Matrix.ServerName {
+			res.Error = api.JoinErrorNoRoom
 			return fmt.Errorf("Room ID %q does not exist", req.RoomIDOrAlias)
 		}
 
diff --git a/roomserver/inthttp/server.go b/roomserver/inthttp/server.go
index 822acd15..e3b81daa 100644
--- a/roomserver/inthttp/server.go
+++ b/roomserver/inthttp/server.go
@@ -34,7 +34,7 @@ func AddRoutes(r api.RoomserverInternalAPI, internalAPIMux *mux.Router) {
 				return util.MessageResponse(http.StatusBadRequest, err.Error())
 			}
 			if err := r.PerformJoin(req.Context(), &request, &response); err != nil {
-				return util.ErrorResponse(err)
+				response.ErrMsg = err.Error()
 			}
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),