routing.py

import asyncio
import contextlib
import functools
import inspect
import re
import sys
import traceback
import types
import typing
import warnings
from enum import Enum

from starlette.concurrency import run_in_threadpool
from starlette.convertors import CONVERTOR_TYPES, Convertor
from starlette.datastructures import URL, Headers, URLPath
from starlette.exceptions import HTTPException
from starlette.requests import Request
from starlette.responses import PlainTextResponse, RedirectResponse
from starlette.types import ASGIApp, Receive, Scope, Send
from starlette.websockets import WebSocket, WebSocketClose

if sys.version_info >= (3, 7):
    from contextlib import asynccontextmanager  # pragma: no cover
else:
    from contextlib2 import asynccontextmanager  # pragma: no cover


class NoMatchFound(Exception):
    """
    Raised by `.url_for(name, **path_params)` and `.url_path_for(name, **path_params)`
    if no matching route exists.
    """

    def __init__(self, name: str, path_params: typing.Dict[str, typing.Any]) -> None:
        params = ", ".join(list(path_params.keys()))
        super().__init__(f'No route exists for name "{name}" and params "{params}".')


class Match(Enum):
    NONE = 0
    PARTIAL = 1
    FULL = 2


def iscoroutinefunction_or_partial(obj: typing.Any) -> bool:
    """
    Correctly determines if an object is a coroutine function,
    including those wrapped in functools.partial objects.
    """
    while isinstance(obj, functools.partial):
        obj = obj.func
    return inspect.iscoroutinefunction(obj)


def request_response(func: typing.Callable) -> ASGIApp:
    """
    Takes a function or coroutine `func(request) -> response`,
    and returns an ASGI application.
    """
    is_coroutine = iscoroutinefunction_or_partial(func)

    async def app(scope: Scope, receive: Receive, send: Send) -> None:
        request = Request(scope, receive=receive, send=send)
        if is_coroutine:
            response = await func(request)
        else:
            response = await run_in_threadpool(func, request)
        await response(scope, receive, send)

    return app


def websocket_session(func: typing.Callable) -> ASGIApp:
    """
    Takes a coroutine `func(session)`, and returns an ASGI application.
    """
    # assert asyncio.iscoroutinefunction(func), "WebSocket endpoints must be async"

    async def app(scope: Scope, receive: Receive, send: Send) -> None:
        session = WebSocket(scope, receive=receive, send=send)
        await func(session)

    return app


def get_name(endpoint: typing.Callable) -> str:
    if inspect.isroutine(endpoint) or inspect.isclass(endpoint):
        return endpoint.__name__
    return endpoint.__class__.__name__


def replace_params(
    path: str,
    param_convertors: typing.Dict[str, Convertor],
    path_params: typing.Dict[str, str],
) -> typing.Tuple[str, dict]:
    for key, value in list(path_params.items()):
        if "{" + key + "}" in path:
            convertor = param_convertors[key]
            value = convertor.to_string(value)
            path = path.replace("{" + key + "}", value)
            path_params.pop(key)
    return path, path_params


# Match parameters in URL paths, eg. '{param}', and '{param:int}'
PARAM_REGEX = re.compile("{([a-zA-Z_][a-zA-Z0-9_]*)(:[a-zA-Z_][a-zA-Z0-9_]*)?}")


def compile_path(
    path: str,
) -> typing.Tuple[typing.Pattern, str, typing.Dict[str, Convertor]]:
    """
    Given a path string, like: "/{username:str}", return a three-tuple
    of (regex, format, {param_name:convertor}).

    regex:      "/(?P<username>[^/]+)"
    format:     "/{username}"
    convertors: {"username": StringConvertor()}
    """
    path_regex = "^"
    path_format = ""
    duplicated_params = set()

    idx = 0
    param_convertors = {}
    for match in PARAM_REGEX.finditer(path):
        param_name, convertor_type = match.groups("str")
        convertor_type = convertor_type.lstrip(":")
        assert (
            convertor_type in CONVERTOR_TYPES
        ), f"Unknown path convertor '{convertor_type}'"
        convertor = CONVERTOR_TYPES[convertor_type]

        path_regex += re.escape(path[idx : match.start()])
        path_regex += f"(?P<{param_name}>{convertor.regex})"

        path_format += path[idx : match.start()]
        path_format += "{%s}" % param_name

        if param_name in param_convertors:
            duplicated_params.add(param_name)

        param_convertors[param_name] = convertor

        idx = match.end()

    if duplicated_params:
        names = ", ".join(sorted(duplicated_params))
        ending = "s" if len(duplicated_params) > 1 else ""
        raise ValueError(f"Duplicated param name{ending} {names} at path {path}")

    path_regex += re.escape(path[idx:].split(":")[0]) + "$"
    path_format += path[idx:]

    return re.compile(path_regex), path_format, param_convertors


class BaseRoute:
    def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
        raise NotImplementedError()  # pragma: no cover

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        raise NotImplementedError()  # pragma: no cover

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        raise NotImplementedError()  # pragma: no cover

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        """
        A route may be used in isolation as a stand-alone ASGI app.
        This is a somewhat contrived case, as they'll almost always be used
        within a Router, but could be useful for some tooling and minimal apps.
        """
        match, child_scope = self.matches(scope)
        if match == Match.NONE:
            if scope["type"] == "http":
                response = PlainTextResponse("Not Found", status_code=404)
                await response(scope, receive, send)
            elif scope["type"] == "websocket":
                websocket_close = WebSocketClose()
                await websocket_close(scope, receive, send)
            return

        scope.update(child_scope)
        await self.handle(scope, receive, send)


class Route(BaseRoute):
    def __init__(
        self,
        path: str,
        endpoint: typing.Callable,
        *,
        methods: typing.List[str] = None,
        name: str = None,
        include_in_schema: bool = True,
    ) -> None:
        assert path.startswith("/"), "Routed paths must start with '/'"
        self.path = path
        self.endpoint = endpoint
        self.name = get_name(endpoint) if name is None else name
        self.include_in_schema = include_in_schema

        endpoint_handler = endpoint
        while isinstance(endpoint_handler, functools.partial):
            endpoint_handler = endpoint_handler.func
        if inspect.isfunction(endpoint_handler) or inspect.ismethod(endpoint_handler):
            # Endpoint is function or method. Treat it as `func(request) -> response`.
            self.app = request_response(endpoint)
            if methods is None:
                methods = ["GET"]
        else:
            # Endpoint is a class. Treat it as ASGI.
            self.app = endpoint

        if methods is None:
            self.methods = None
        else:
            self.methods = {method.upper() for method in methods}
            if "GET" in self.methods:
                self.methods.add("HEAD")

        self.path_regex, self.path_format, self.param_convertors = compile_path(path)

    def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
        if scope["type"] == "http":
            match = self.path_regex.match(scope["path"])
            if match:
                matched_params = match.groupdict()
                for key, value in matched_params.items():
                    matched_params[key] = self.param_convertors[key].convert(value)
                path_params = dict(scope.get("path_params", {}))
                path_params.update(matched_params)
                child_scope = {"endpoint": self.endpoint, "path_params": path_params}
                if self.methods and scope["method"] not in self.methods:
                    return Match.PARTIAL, child_scope
                else:
                    return Match.FULL, child_scope
        return Match.NONE, {}

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        seen_params = set(path_params.keys())
        expected_params = set(self.param_convertors.keys())

        if name != self.name or seen_params != expected_params:
            raise NoMatchFound(name, path_params)

        path, remaining_params = replace_params(
            self.path_format, self.param_convertors, path_params
        )
        assert not remaining_params
        return URLPath(path=path, protocol="http")

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        if self.methods and scope["method"] not in self.methods:
            headers = {"Allow": ", ".join(self.methods)}
            if "app" in scope:
                raise HTTPException(status_code=405, headers=headers)
            else:
                response = PlainTextResponse(
                    "Method Not Allowed", status_code=405, headers=headers
                )
            await response(scope, receive, send)
        else:
            await self.app(scope, receive, send)

    def __eq__(self, other: typing.Any) -> bool:
        return (
            isinstance(other, Route)
            and self.path == other.path
            and self.endpoint == other.endpoint
            and self.methods == other.methods
        )


class WebSocketRoute(BaseRoute):
    def __init__(
        self, path: str, endpoint: typing.Callable, *, name: str = None
    ) -> None:
        assert path.startswith("/"), "Routed paths must start with '/'"
        self.path = path
        self.endpoint = endpoint
        self.name = get_name(endpoint) if name is None else name

        endpoint_handler = endpoint
        while isinstance(endpoint_handler, functools.partial):
            endpoint_handler = endpoint_handler.func
        if inspect.isfunction(endpoint_handler) or inspect.ismethod(endpoint_handler):
            # Endpoint is function or method. Treat it as `func(websocket)`.
            self.app = websocket_session(endpoint)
        else:
            # Endpoint is a class. Treat it as ASGI.
            self.app = endpoint

        self.path_regex, self.path_format, self.param_convertors = compile_path(path)

    def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
        if scope["type"] == "websocket":
            match = self.path_regex.match(scope["path"])
            if match:
                matched_params = match.groupdict()
                for key, value in matched_params.items():
                    matched_params[key] = self.param_convertors[key].convert(value)
                path_params = dict(scope.get("path_params", {}))
                path_params.update(matched_params)
                child_scope = {"endpoint": self.endpoint, "path_params": path_params}
                return Match.FULL, child_scope
        return Match.NONE, {}

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        seen_params = set(path_params.keys())
        expected_params = set(self.param_convertors.keys())

        if name != self.name or seen_params != expected_params:
            raise NoMatchFound(name, path_params)

        path, remaining_params = replace_params(
            self.path_format, self.param_convertors, path_params
        )
        assert not remaining_params
        return URLPath(path=path, protocol="websocket")

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        await self.app(scope, receive, send)

    def __eq__(self, other: typing.Any) -> bool:
        return (
            isinstance(other, WebSocketRoute)
            and self.path == other.path
            and self.endpoint == other.endpoint
        )


class Mount(BaseRoute):
    def __init__(
        self,
        path: str,
        app: ASGIApp = None,
        routes: typing.Sequence[BaseRoute] = None,
        name: str = None,
    ) -> None:
        assert path == "" or path.startswith("/"), "Routed paths must start with '/'"
        assert (
            app is not None or routes is not None
        ), "Either 'app=...', or 'routes=' must be specified"
        self.path = path.rstrip("/")
        if app is not None:
            self.app: ASGIApp = app
        else:
            self.app = Router(routes=routes)
        self.name = name
        self.path_regex, self.path_format, self.param_convertors = compile_path(
            self.path + "/{path:path}"
        )

    @property
    def routes(self) -> typing.List[BaseRoute]:
        return getattr(self.app, "routes", [])

    def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
        if scope["type"] in ("http", "websocket"):
            path = scope["path"]
            match = self.path_regex.match(path)
            if match:
                matched_params = match.groupdict()
                for key, value in matched_params.items():
                    matched_params[key] = self.param_convertors[key].convert(value)
                remaining_path = "/" + matched_params.pop("path")
                matched_path = path[: -len(remaining_path)]
                path_params = dict(scope.get("path_params", {}))
                path_params.update(matched_params)
                root_path = scope.get("root_path", "")
                child_scope = {
                    "path_params": path_params,
                    "app_root_path": scope.get("app_root_path", root_path),
                    "root_path": root_path + matched_path,
                    "path": remaining_path,
                    "endpoint": self.app,
                }
                return Match.FULL, child_scope
        return Match.NONE, {}

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        if self.name is not None and name == self.name and "path" in path_params:
            # 'name' matches "<mount_name>".
            path_params["path"] = path_params["path"].lstrip("/")
            path, remaining_params = replace_params(
                self.path_format, self.param_convertors, path_params
            )
            if not remaining_params:
                return URLPath(path=path)
        elif self.name is None or name.startswith(self.name + ":"):
            if self.name is None:
                # No mount name.
                remaining_name = name
            else:
                # 'name' matches "<mount_name>:<child_name>".
                remaining_name = name[len(self.name) + 1 :]
            path_kwarg = path_params.get("path")
            path_params["path"] = ""
            path_prefix, remaining_params = replace_params(
                self.path_format, self.param_convertors, path_params
            )
            if path_kwarg is not None:
                remaining_params["path"] = path_kwarg
            for route in self.routes or []:
                try:
                    url = route.url_path_for(remaining_name, **remaining_params)
                    return URLPath(
                        path=path_prefix.rstrip("/") + str(url), protocol=url.protocol
                    )
                except NoMatchFound:
                    pass
        raise NoMatchFound(name, path_params)

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        await self.app(scope, receive, send)

    def __eq__(self, other: typing.Any) -> bool:
        return (
            isinstance(other, Mount)
            and self.path == other.path
            and self.app == other.app
        )


class Host(BaseRoute):
    def __init__(self, host: str, app: ASGIApp, name: str = None) -> None:
        self.host = host
        self.app = app
        self.name = name
        self.host_regex, self.host_format, self.param_convertors = compile_path(host)

    @property
    def routes(self) -> typing.List[BaseRoute]:
        return getattr(self.app, "routes", [])

    def matches(self, scope: Scope) -> typing.Tuple[Match, Scope]:
        if scope["type"] in ("http", "websocket"):
            headers = Headers(scope=scope)
            host = headers.get("host", "").split(":")[0]
            match = self.host_regex.match(host)
            if match:
                matched_params = match.groupdict()
                for key, value in matched_params.items():
                    matched_params[key] = self.param_convertors[key].convert(value)
                path_params = dict(scope.get("path_params", {}))
                path_params.update(matched_params)
                child_scope = {"path_params": path_params, "endpoint": self.app}
                return Match.FULL, child_scope
        return Match.NONE, {}

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        if self.name is not None and name == self.name and "path" in path_params:
            # 'name' matches "<mount_name>".
            path = path_params.pop("path")
            host, remaining_params = replace_params(
                self.host_format, self.param_convertors, path_params
            )
            if not remaining_params:
                return URLPath(path=path, host=host)
        elif self.name is None or name.startswith(self.name + ":"):
            if self.name is None:
                # No mount name.
                remaining_name = name
            else:
                # 'name' matches "<mount_name>:<child_name>".
                remaining_name = name[len(self.name) + 1 :]
            host, remaining_params = replace_params(
                self.host_format, self.param_convertors, path_params
            )
            for route in self.routes or []:
                try:
                    url = route.url_path_for(remaining_name, **remaining_params)
                    return URLPath(path=str(url), protocol=url.protocol, host=host)
                except NoMatchFound:
                    pass
        raise NoMatchFound(name, path_params)

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        await self.app(scope, receive, send)

    def __eq__(self, other: typing.Any) -> bool:
        return (
            isinstance(other, Host)
            and self.host == other.host
            and self.app == other.app
        )


_T = typing.TypeVar("_T")


class _AsyncLiftContextManager(typing.AsyncContextManager[_T]):
    def __init__(self, cm: typing.ContextManager[_T]):
        self._cm = cm

    async def __aenter__(self) -> _T:
        return self._cm.__enter__()

    async def __aexit__(
        self,
        exc_type: typing.Optional[typing.Type[BaseException]],
        exc_value: typing.Optional[BaseException],
        traceback: typing.Optional[types.TracebackType],
    ) -> typing.Optional[bool]:
        return self._cm.__exit__(exc_type, exc_value, traceback)


def _wrap_gen_lifespan_context(
    lifespan_context: typing.Callable[[typing.Any], typing.Generator]
) -> typing.Callable[[typing.Any], typing.AsyncContextManager]:
    cmgr = contextlib.contextmanager(lifespan_context)

    @functools.wraps(cmgr)
    def wrapper(app: typing.Any) -> _AsyncLiftContextManager:
        return _AsyncLiftContextManager(cmgr(app))

    return wrapper


class _DefaultLifespan:
    def __init__(self, router: "Router"):
        self._router = router

    async def __aenter__(self) -> None:
        await self._router.startup()

    async def __aexit__(self, *exc_info: object) -> None:
        await self._router.shutdown()

    def __call__(self: _T, app: object) -> _T:
        return self


class Router:
    def __init__(
        self,
        routes: typing.Sequence[BaseRoute] = None,
        redirect_slashes: bool = True,
        default: ASGIApp = None,
        on_startup: typing.Sequence[typing.Callable] = None,
        on_shutdown: typing.Sequence[typing.Callable] = None,
        lifespan: typing.Callable[[typing.Any], typing.AsyncContextManager] = None,
    ) -> None:
        self.routes = [] if routes is None else list(routes)
        self.redirect_slashes = redirect_slashes
        self.default = self.not_found if default is None else default
        self.on_startup = [] if on_startup is None else list(on_startup)
        self.on_shutdown = [] if on_shutdown is None else list(on_shutdown)

        if lifespan is None:
            self.lifespan_context: typing.Callable[
                [typing.Any], typing.AsyncContextManager
            ] = _DefaultLifespan(self)

        elif inspect.isasyncgenfunction(lifespan):
            warnings.warn(
                "async generator function lifespans are deprecated, "
                "use an @contextlib.asynccontextmanager function instead",
                DeprecationWarning,
            )
            self.lifespan_context = asynccontextmanager(
                lifespan,  # type: ignore[arg-type]
            )
        elif inspect.isgeneratorfunction(lifespan):
            warnings.warn(
                "generator function lifespans are deprecated, "
                "use an @contextlib.asynccontextmanager function instead",
                DeprecationWarning,
            )
            self.lifespan_context = _wrap_gen_lifespan_context(
                lifespan,  # type: ignore[arg-type]
            )
        else:
            self.lifespan_context = lifespan

    async def not_found(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "websocket":
            websocket_close = WebSocketClose()
            await websocket_close(scope, receive, send)
            return

        # If we're running inside a starlette application then raise an
        # exception, so that the configurable exception handler can deal with
        # returning the response. For plain ASGI apps, just return the response.
        if "app" in scope:
            raise HTTPException(status_code=404)
        else:
            response = PlainTextResponse("Not Found", status_code=404)
        await response(scope, receive, send)

    def url_path_for(self, name: str, **path_params: typing.Any) -> URLPath:
        for route in self.routes:
            try:
                return route.url_path_for(name, **path_params)
            except NoMatchFound:
                pass
        raise NoMatchFound(name, path_params)

    async def startup(self) -> None:
        """
        Run any `.on_startup` event handlers.
        """
        for handler in self.on_startup:
            if asyncio.iscoroutinefunction(handler):
                await handler()
            else:
                handler()

    async def shutdown(self) -> None:
        """
        Run any `.on_shutdown` event handlers.
        """
        for handler in self.on_shutdown:
            if asyncio.iscoroutinefunction(handler):
                await handler()
            else:
                handler()

    async def lifespan(self, scope: Scope, receive: Receive, send: Send) -> None:
        """
        Handle ASGI lifespan messages, which allows us to manage application
        startup and shutdown events.
        """
        started = False
        app = scope.get("app")
        await receive()
        try:
            async with self.lifespan_context(app):
                await send({"type": "lifespan.startup.complete"})
                started = True
                await receive()
        except BaseException:
            exc_text = traceback.format_exc()
            if started:
                await send({"type": "lifespan.shutdown.failed", "message": exc_text})
            else:
                await send({"type": "lifespan.startup.failed", "message": exc_text})
            raise
        else:
            await send({"type": "lifespan.shutdown.complete"})

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        """
        The main entry point to the Router class.
        """
        assert scope["type"] in ("http", "websocket", "lifespan")

        if "router" not in scope:
            scope["router"] = self

        if scope["type"] == "lifespan":
            await self.lifespan(scope, receive, send)
            return

        partial = None

        for route in self.routes:
            # Determine if any route matches the incoming scope,
            # and hand over to the matching route if found.
            match, child_scope = route.matches(scope)
            if match == Match.FULL:
                scope.update(child_scope)
                await route.handle(scope, receive, send)
                return
            elif match == Match.PARTIAL and partial is None:
                partial = route
                partial_scope = child_scope

        if partial is not None:
            #  Handle partial matches. These are cases where an endpoint is
            # able to handle the request, but is not a preferred option.
            # We use this in particular to deal with "405 Method Not Allowed".
            scope.update(partial_scope)
            await partial.handle(scope, receive, send)
            return

        if scope["type"] == "http" and self.redirect_slashes and scope["path"] != "/":
            redirect_scope = dict(scope)
            if scope["path"].endswith("/"):
                redirect_scope["path"] = redirect_scope["path"].rstrip("/")
            else:
                redirect_scope["path"] = redirect_scope["path"] + "/"

            for route in self.routes:
                match, child_scope = route.matches(redirect_scope)
                if match != Match.NONE:
                    redirect_url = URL(scope=redirect_scope)
                    response = RedirectResponse(url=str(redirect_url))
                    await response(scope, receive, send)
                    return

        await self.default(scope, receive, send)

    def __eq__(self, other: typing.Any) -> bool:
        return isinstance(other, Router) and self.routes == other.routes

    # The following usages are now discouraged in favour of configuration
    #  during Router.__init__(...)
    def mount(
        self, path: str, app: ASGIApp, name: str = None
    ) -> None:  # pragma: nocover
        """
        We no longer document this API, and its usage is discouraged.
        Instead you should use the following approach:

        routes = [
            Mount(path, ...),
            ...
        ]

        app = Starlette(routes=routes)
        """

        route = Mount(path, app=app, name=name)
        self.routes.append(route)

    def host(
        self, host: str, app: ASGIApp, name: str = None
    ) -> None:  # pragma: no cover
        """
        We no longer document this API, and its usage is discouraged.
        Instead you should use the following approach:

        routes = [
            Host(path, ...),
            ...
        ]

        app = Starlette(routes=routes)
        """

        route = Host(host, app=app, name=name)
        self.routes.append(route)

    def add_route(
        self,
        path: str,
        endpoint: typing.Callable,
        methods: typing.List[str] = None,
        name: str = None,
        include_in_schema: bool = True,
    ) -> None:  # pragma: nocover
        route = Route(
            path,
            endpoint=endpoint,
            methods=methods,
            name=name,
            include_in_schema=include_in_schema,
        )
        self.routes.append(route)

    def add_websocket_route(
        self, path: str, endpoint: typing.Callable, name: str = None
    ) -> None:  # pragma: no cover
        route = WebSocketRoute(path, endpoint=endpoint, name=name)
        self.routes.append(route)

    def route(
        self,
        path: str,
        methods: typing.List[str] = None,
        name: str = None,
        include_in_schema: bool = True,
    ) -> typing.Callable:  # pragma: nocover
        """
        We no longer document this decorator style API, and its usage is discouraged.
        Instead you should use the following approach:

        routes = [
            Route(path, endpoint=..., ...),
            ...
        ]

        app = Starlette(routes=routes)
        """

        def decorator(func: typing.Callable) -> typing.Callable:
            self.add_route(
                path,
                func,
                methods=methods,
                name=name,
                include_in_schema=include_in_schema,
            )
            return func

        return decorator

    def websocket_route(
        self, path: str, name: str = None
    ) -> typing.Callable:  # pragma: nocover
        """
        We no longer document this decorator style API, and its usage is discouraged.
        Instead you should use the following approach:

        routes = [
            WebSocketRoute(path, endpoint=..., ...),
            ...
        ]

        app = Starlette(routes=routes)
        """

        def decorator(func: typing.Callable) -> typing.Callable:
            self.add_websocket_route(path, func, name=name)
            return func

        return decorator

    def add_event_handler(
        self, event_type: str, func: typing.Callable
    ) -> None:  # pragma: no cover
        assert event_type in ("startup", "shutdown")

        if event_type == "startup":
            self.on_startup.append(func)
        else:
            self.on_shutdown.append(func)

    def on_event(self, event_type: str) -> typing.Callable:  # pragma: nocover
        def decorator(func: typing.Callable) -> typing.Callable:
            self.add_event_handler(event_type, func)
            return func

        return decorator