routing.py

import asyncio
import inspect
import re
import traceback
import typing
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


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


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


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

    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

        param_convertors[param_name] = convertor

        idx = match.end()

    path_regex += re.escape(path[idx:]) + "$"
    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: str) -> 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

        if inspect.isfunction(endpoint) or inspect.ismethod(endpoint):
            # 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 = set(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: str) -> 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()

        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:
            if "app" in scope:
                raise HTTPException(status_code=405)
            else:
                response = PlainTextResponse("Method Not Allowed", status_code=405)
            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

        if inspect.isfunction(endpoint) or inspect.ismethod(endpoint):
            # 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: str) -> 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()

        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 = app  # type: ASGIApp
        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", None)

    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: str) -> 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()

    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", None)

    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: str) -> 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()

    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
        )


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.AsyncGenerator] = 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)

        async def default_lifespan(app: typing.Any) -> typing.AsyncGenerator:
            await self.startup()
            yield
            await self.shutdown()

        self.lifespan_context = default_lifespan if lifespan is None else 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: str) -> URLPath:
        for route in self.routes:
            try:
                return route.url_path_for(name, **path_params)
            except NoMatchFound:
                pass
        raise NoMatchFound()

    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.
        """
        first = True
        app = scope.get("app")
        await receive()
        try:
            if inspect.isasyncgenfunction(self.lifespan_context):
                async for item in self.lifespan_context(app):
                    assert first, "Lifespan context yielded multiple times."
                    first = False
                    await send({"type": "lifespan.startup.complete"})
                    await receive()
            else:
                for item in self.lifespan_context(app):  # type: ignore
                    assert first, "Lifespan context yielded multiple times."
                    first = False
                    await send({"type": "lifespan.startup.complete"})
                    await receive()
        except BaseException:
            if first:
                exc_text = traceback.format_exc()
                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:
        route = Mount(path, app=app, name=name)
        self.routes.append(route)

    def host(self, host: str, app: ASGIApp, name: str = None) -> None:
        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:
        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:
        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:
        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:
        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:
        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:
        def decorator(func: typing.Callable) -> typing.Callable:
            self.add_event_handler(event_type, func)
            return func

        return decorator