Function checkRestrictedJoin

federationapi/routing/join.go:446–499

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

(
	httpReq *http.Request,
	rsAPI api.FederationRoomserverAPI,
	roomVersion gomatrixserverlib.RoomVersion,
	roomID, userID string,
)

//     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) {
	if allowRestricted, err := roomVersion.MayAllowRestrictedJoinsInEventAuth(); err != nil {
		return nil, "", err
	} else if !allowRestricted {
		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: jsonerror.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: jsonerror.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 []*gomatrixserverlib.HeaderedEvent