from dataclasses import dataclass import flask import pystache from typing import Optional, TypeVar, Type import lc.config as c import lc.error as e import lc.model as m import lc.request as r import lc.view as v T = TypeVar("T", bound=r.Request) @dataclass class ApiOK: response: dict class Endpoint: __slots__ = ("user",) def __init__(self): self.user = None # try finding the token token = None # first check the HTTP headers if (auth := flask.request.headers.get("Authorization", None)) : token = auth.split()[1] # if that fails, check the session elif flask.session.get("auth", None): token = flask.session["auth"] if token is None: return # if that exists and we can deserialize it, then make sure # it contains a valid user password, too try: payload = c.app.load_token(token) except: # TODO: be more specific about what errors we're catching # here! return if "name" not in payload: return try: u = m.User.by_slug(payload["name"]) self.user = u except e.LCException: return @staticmethod def just_get_user() -> Optional[m.User]: try: return Endpoint().user except: # this is going to catch everything on the off chance that # there's a bug in the user-validation code: this is used # in error handlers, so we should be resilient to that! return None SHOULD_REDIRECT = set(("application/x-www-form-urlencoded", "multipart/form-data",)) def api_ok(self, redirect: str, data: Optional[dict] = None) -> ApiOK: if data is None: data = {"status": "ok"} data["redirect"] = redirect content_type = flask.request.content_type or "" content_type = content_type.split(";")[0] if content_type in Endpoint.SHOULD_REDIRECT: raise e.LCRedirect(redirect) else: return ApiOK(response=data) def request_data(self, cls: Type[T]) -> T: """Construct a Request model from either a JSON payload or a urlencoded payload""" if flask.request.content_type == "application/json": try: return cls.from_json(flask.request.data) except KeyError as exn: raise e.BadPayload(key=exn.args[0]) elif flask.request.content_type == "application/x-www-form-urlencoded": return cls.from_form(flask.request.form) else: raise e.BadContentType(flask.request.content_type or "unknown") def require_authentication(self, name: str) -> m.User: """ Check that the currently logged-in user exists and is the same as the user whose username is given. Raises an exception otherwise. """ if not self.user or name != self.user.name: raise e.BadPermissions() return self.user def route(self, *args, **kwargs): """Forward to the appropriate routing method""" try: if flask.request.method == "POST": # all POST methods are "API methods": if we want to # display information in response to a post, then we # should redirect to the page where that information # can be viewed instead of returning that # information. (I think.) api_ok = self.api_post(*args, **kwargs) # type: ignore assert isinstance(api_ok, ApiOK) return flask.jsonify(api_ok.response) elif flask.request.method == "DELETE": return flask.jsonify(self.api_delete(*args, **kwargs).response) # type: ignore elif ( flask.request.method in ["GET", "HEAD"] and flask.request.content_type == "application/json" ): # Here we're distinguishing between an API GET (i.e. a # client trying to get JSON data about an endpoint) # versus a user-level GET (i.e. a user in a browser.) # I like using the HTTP headers to distinguish these # cases, while other APIs tend to have a separate /api # endpoint to do this. return flask.jsonify(self.api_get(*args, **kwargs).response) # type: ignore # if an exception arose from an "API method", then we should # report it as JSON except e.LCException as exn: if flask.request.content_type == "application/json": return ({"status": exn.http_code(), "error": str(exn)}, exn.http_code()) else: return (self.render_error(exn), exn.http_code()) # also maybe we tried to redirect, so just do that except e.LCRedirect as exn: return flask.redirect(exn.to_path()) # if we're here, it means we're just trying to get a typical # HTML request. try: return self.html(*args, **kwargs) # type: ignore except e.LCException as exn: return (self.render_error(exn), exn.http_code()) except e.LCRedirect as exn: return flask.redirect(exn.to_path()) def render_error(self, exn: e.LCException) -> str: error = v.Error(code=exn.http_code(), message=str(exn)) page = v.Page(title="error", content=render("error", error), user=self.user) return render("main", page) # Decorators result in some weird code in Python, especially 'cause it # doesn't make higher-order functions terse. Let's break this down a # bit. This out method, `endpoint`, takes the route... def endpoint(route: str): """Route an endpoint using our semi-smart routing machinery""" # but `endpoint` returns another function which is going to be # called with the result of the definition after it. The argument # to what we're calling `do_endpoint` here is going to be the # class object defined afterwards. def do_endpoint(endpoint_class: Type[Endpoint]): # we'll just make that explicit here assert Endpoint in endpoint_class.__bases__ # finally, we need a function that we'll give to Flask in # order to actually dispatch to. This is the actual routing # function, which is why it just creates an instance of the # endpoint provided above and calls the `route` method on it def func(*args, **kwargs): return endpoint_class().route(*args, **kwargs) # use reflection over the methods defined by the endpoint # class to decide if it needs to accept POST requests or not. methods = ["GET"] if "api_post" in dir(endpoint_class): methods.append("POST") if "api_delete" in dir(endpoint_class): methods.append("DELETE") # this is just for making error messages nicer func.__name__ = endpoint_class.__name__ # finally, use the Flask routing machinery to register our callback return c.app.app.route(route, methods=methods)(func) return do_endpoint LOADER = pystache.loader.Loader(extension="mustache", search_dirs=["templates"]) def render(name: str, data: Optional[v.View] = None) -> str: """Load and use a Mustache template from the project root""" template = LOADER.load_name(name) renderer = pystache.Renderer(missing_tags="strict", search_dirs=["templates"]) return renderer.render(template, data or {}) @c.app.app.errorhandler(404) def handle_404(e): user = Endpoint.just_get_user() url = flask.request.path error = v.Error(code=404, message=f"Page {url} not found") page = v.Page(title="not found", content=render("error", error), user=None) return render("main", page) @c.app.app.errorhandler(500) def handle_500(e): user = Endpoint.just_get_user() c.log(f"Internal error: {e}") error = v.Error(code=500, message=f"An unexpected error occurred") page = v.Page(title="500", content=render("error", error), user=None) return render("main", page)