How to use the synapse.api.errors.SynapseError function in synapse

if ratelimit:
            yield self.base_handler.ratelimit(requester)

        yield self.base_handler.maybe_kick_guest_users(event, context)

        if event.type == EventTypes.CanonicalAlias:
            # Check the alias is acually valid (at this time at least)
            room_alias_str = event.content.get("alias", None)
            if room_alias_str:
                room_alias = RoomAlias.from_string(room_alias_str)
                directory_handler = self.hs.get_handlers().directory_handler
                mapping = yield directory_handler.get_association(room_alias)

                if mapping["room_id"] != event.room_id:
                    raise SynapseError(
                        400,
                        "Room alias %s does not point to the room" % (
                            room_alias_str,
                        )
                    )

        federation_handler = self.hs.get_handlers().federation_handler

        if event.type == EventTypes.Member:
            if event.content["membership"] == Membership.INVITE:
                def is_inviter_member_event(e):
                    return (
                        e.type == EventTypes.Member and
                        e.sender == event.sender
                    )

def _join_user_to_room(self, requester, room_identifier):
        room_id = None
        room_member_handler = self.hs.get_room_member_handler()
        if RoomID.is_valid(room_identifier):
            room_id = room_identifier
        elif RoomAlias.is_valid(room_identifier):
            room_alias = RoomAlias.from_string(room_identifier)
            room_id, remote_room_hosts = (
                yield room_member_handler.lookup_room_alias(room_alias)
            )
            room_id = room_id.to_string()
        else:
            raise SynapseError(400, "%s was not legal room ID or room alias" % (
                room_identifier,
            ))

        yield room_member_handler.update_membership(
            requester=requester,
            target=requester.user,
            room_id=room_id,
            remote_room_hosts=remote_room_hosts,
            action="join",
            ratelimit=False,
        )

local_query = []

        result_dict = {}
        for user_id, device_ids in query.items():
            # we use UserID.from_string to catch invalid user ids
            if not self.is_mine(UserID.from_string(user_id)):
                logger.warning("Request for keys for non-local user %s", user_id)
                log_kv(
                    {
                        "message": "Requested a local key for a user which"
                        " was not local to the homeserver",
                        "user_id": user_id,
                    }
                )
                set_tag("error", True)
                raise SynapseError(400, "Not a user here")

            if not device_ids:
                local_query.append((user_id, None))
            else:
                for device_id in device_ids:
                    local_query.append((user_id, device_id))

            # make sure that each queried user appears in the result dict
            result_dict[user_id] = {}

        results = yield self.store.get_e2e_device_keys(local_query)

        # Build the result structure
        for user_id, device_keys in results.items():
            for device_id, device_info in device_keys.items():
                result_dict[user_id][device_id] = device_info

if not is_requester_admin:
                if self.config.block_non_admin_invites:
                    logger.info(
                        "Blocking invite: user is not admin and non-admin "
                        "invites disabled"
                    )
                    block_invite = True

                if not self.spam_checker.user_may_invite(
                    requester.user.to_string(), target.to_string(), room_id,
                ):
                    logger.info("Blocking invite due to spam checker")
                    block_invite = True

            if block_invite:
                raise SynapseError(
                    403, "Invites have been disabled on this server",
                )

        prev_events_and_hashes = yield self.store.get_prev_events_for_room(
            room_id,
        )
        latest_event_ids = (
            event_id for (event_id, _, _) in prev_events_and_hashes
        )

        current_state_ids = yield self.state_handler.get_current_state_ids(
            room_id, latest_event_ids=latest_event_ids,
        )

        # TODO: Refactor into dictionary of explicitly allowed transitions
        # between old and new state, with specific error messages for some

def request(self, method, uri, headers=None, bodyProducer=None):
        h = urllib.parse.urlparse(uri.decode("ascii"))

        try:
            ip_address = IPAddress(h.hostname)

            if check_against_blacklist(
                ip_address, self._ip_whitelist, self._ip_blacklist
            ):
                logger.info("Blocking access to %s due to blacklist" % (ip_address,))
                e = SynapseError(403, "IP address blocked by IP blacklist entry")
                return defer.fail(Failure(e))
        except Exception:
            # Not an IP
            pass

        return self._agent.request(
            method, uri, headers=headers, bodyProducer=bodyProducer
        )

def _create_association(self, room_alias, room_id, servers=None, creator=None):
        # general association creation for both human users and app services

        for wchar in string.whitespace:
            if wchar in room_alias.localpart:
                raise SynapseError(400, "Invalid characters in room alias")

        if not self.hs.is_mine(room_alias):
            raise SynapseError(400, "Room alias must be local")
            # TODO(erikj): Change this.

        # TODO(erikj): Add transactions.
        # TODO(erikj): Check if there is a current association.
        if not servers:
            users = yield self.state.get_current_users_in_room(room_id)
            servers = set(get_domain_from_id(u) for u in users)

        if not servers:
            raise SynapseError(400, "Failed to get server list")

        yield self.store.create_room_alias_association(
            room_alias,

def from_string(cls, s):
        group_id = super(GroupID, cls).from_string(s)
        if not group_id.localpart:
            raise SynapseError(400, "Group ID cannot be empty")

        if contains_invalid_mxid_characters(group_id.localpart):
            raise SynapseError(
                400, "Group ID can only contain characters a-z, 0-9, or '=_-./'"
            )

        return group_id

logger.debug("%s : session info %s   request info %s",
                         login_type, session_info, register_json)
            response = yield stages[login_type](
                request,
                register_json,
                session_info
            )

            if "access_token" not in response:
                # isn't a final response
                response["session"] = session_info["id"]

            defer.returnValue((200, response))
        except KeyError as e:
            logger.exception(e)
            raise SynapseError(400, "Missing JSON keys for login type %s." % (
                login_type,
            ))

"""

        actual_headers = {b"User-Agent": [self.user_agent]}
        if headers:
            actual_headers.update(headers)

        response = yield self.request("GET", url, headers=Headers(actual_headers))

        resp_headers = dict(response.headers.getAllRawHeaders())

        if (
            b"Content-Length" in resp_headers
            and int(resp_headers[b"Content-Length"][0]) > max_size
        ):
            logger.warning("Requested URL is too large > %r bytes" % (self.max_size,))
            raise SynapseError(
                502,
                "Requested file is too large > %r bytes" % (self.max_size,),
                Codes.TOO_LARGE,
            )

        if response.code > 299:
            logger.warning("Got %d when downloading %s" % (response.code, url))
            raise SynapseError(502, "Got error %d" % (response.code,), Codes.UNKNOWN)

        # TODO: if our Content-Type is HTML or something, just read the first
        # N bytes into RAM rather than saving it all to disk only to read it
        # straight back in again

        try:
            length = yield make_deferred_yieldable(
                _readBodyToFile(response, output_stream, max_size)