✨ CORS middleware!

example.py

@@ -15,6 +15,7 @@ from spiderweb.response import (
 app = SpiderwebRouter(
     templates_dirs=["templates"],
     middleware=[
+        "spiderweb.middleware.cors.CorsMiddleware",
         "spiderweb.middleware.sessions.SessionMiddleware",
         "spiderweb.middleware.csrf.CSRFMiddleware",
         "example_middleware.TestMiddleware",

spiderweb/constants.py

@@ -8,3 +8,20 @@ __version__ = "0.12.0"
 REGEX_COOKIE_NAME = r"^[a-zA-Z0-9\s\(\)<>@,;:\/\\\[\]\?=\{\}\"\t]*$"
 
 DATABASE_PROXY = DatabaseProxy()
+
+DEFAULT_CORS_ALLOW_METHODS = (
+    "DELETE",
+    "GET",
+    "OPTIONS",
+    "PATCH",
+    "POST",
+    "PUT",
+)
+DEFAULT_CORS_ALLOW_HEADERS = (
+    "accept",
+    "authorization",
+    "content-type",
+    "user-agent",
+    "x-csrftoken",
+    "x-requested-with",
+)

spiderweb/exceptions.py

@@ -86,3 +86,7 @@ class UnusedMiddleware(SpiderwebException):
 
 class NoResponseError(SpiderwebException):
     pass
+
+
+class StartupErrors(ExceptionGroup):
+    pass

spiderweb/main.py

@@ -1,16 +1,22 @@
 import inspect
 import logging
 import pathlib
+import re
 import traceback
 import urllib.parse as urlparse
+from logging import Logger
 from threading import Thread
-from typing import Optional, Callable
+from typing import Optional, Callable, Sequence, LiteralString, Literal
 from wsgiref.simple_server import WSGIServer
 
 from jinja2 import BaseLoader, Environment, FileSystemLoader
 from peewee import Database, SqliteDatabase
 
 from spiderweb.middleware import MiddlewareMixin
+from spiderweb.constants import (
+    DEFAULT_CORS_ALLOW_METHODS,
+    DEFAULT_CORS_ALLOW_HEADERS,
+)
 from spiderweb.constants import (
     DATABASE_PROXY,
     DEFAULT_ENCODING,
@@ -30,7 +36,7 @@ from spiderweb.request import Request
 from spiderweb.response import HttpResponse, TemplateResponse, JsonResponse
 from spiderweb.routes import RoutesMixin
 from spiderweb.secrets import FernetMixin
-from spiderweb.utils import get_http_status_by_code
+from spiderweb.utils import get_http_status_by_code, convert_url_to_regex
 
 console_logger = logging.getLogger(__name__)
 logging.basicConfig(level=logging.INFO)
@@ -42,25 +48,32 @@ class SpiderwebRouter(LocalServerMixin, MiddlewareMixin, RoutesMixin, FernetMixi
         *,
         addr: str = None,
         port: int = None,
-        allowed_hosts=None,
+        allowed_hosts: Sequence[str | re.Pattern] = None,
-        cors_allowed_origins=None,
+        cors_allowed_origins: Sequence[str] = None,
-        cors_allow_all_origins=False,
+        cors_allowed_origins_regexes: Sequence[str] = None,
+        cors_allow_all_origins: bool = False,
+        cors_urls_regex: str | re.Pattern[str] = r"^.*$",
+        cors_allow_methods: Sequence[str] = None,
+        cors_allow_headers: Sequence[str] = None,
+        cors_expose_headers: Sequence[str] = None,
+        cors_preflight_max_age: int = 86400,
+        cors_allow_credentials: bool = False,
         csrf_trusted_origins: Sequence[str] = None,
         db: Optional[Database] = None,
-        templates_dirs: list[str] = None,
+        templates_dirs: Sequence[str] = None,
-        middleware: list[str] = None,
+        middleware: Sequence[str] = None,
         append_slash: bool = False,
-        staticfiles_dirs: list[str] = None,
+        staticfiles_dirs: Sequence[str] = None,
-        routes: list[tuple[str, Callable] | tuple[str, Callable, dict]] = None,
+        routes: Sequence[tuple[str, Callable] | tuple[str, Callable, dict]] = None,
         error_routes: dict[int, Callable] = None,
         secret_key: str = None,
-        session_max_age=60 * 60 * 24 * 14,  # 2 weeks
+        session_max_age: int = 60 * 60 * 24 * 14,  # 2 weeks
-        session_cookie_name="swsession",
+        session_cookie_name: str = "swsession",
-        session_cookie_secure=False,  # should be true if serving over HTTPS
+        session_cookie_secure: bool = False,  # should be true if serving over HTTPS
-        session_cookie_http_only=True,
+        session_cookie_http_only: bool = True,
-        session_cookie_same_site="lax",
+        session_cookie_same_site: Literal["strict", "lax", "none"] = "lax",
-        session_cookie_path="/",
+        session_cookie_path: str = "/",
-        log=None,
+        log: Logger = None,
         **kwargs,
     ):
         self._routes = {}
@@ -80,7 +93,15 @@ class SpiderwebRouter(LocalServerMixin, MiddlewareMixin, RoutesMixin, FernetMixi
         self.allowed_hosts = [convert_url_to_regex(i) for i in self._allowed_hosts]
 
         self.cors_allowed_origins = cors_allowed_origins or []
+        self.cors_allowed_origins_regexes = cors_allowed_origins_regexes or []
         self.cors_allow_all_origins = cors_allow_all_origins
+        self.cors_urls_regex = cors_urls_regex
+        self.cors_allow_methods = cors_allow_methods or DEFAULT_CORS_ALLOW_METHODS
+        self.cors_allow_headers = cors_allow_headers or DEFAULT_CORS_ALLOW_HEADERS
+        self.cors_expose_headers = cors_expose_headers or []
+        self.cors_preflight_max_age = cors_preflight_max_age
+        self.cors_allow_credentials = cors_allow_credentials
+
         self._csrf_trusted_origins = csrf_trusted_origins or []
         self.csrf_trusted_origins = [
             convert_url_to_regex(i) for i in self._csrf_trusted_origins

spiderweb/middleware/__init__.py

@@ -1,9 +1,11 @@
 from typing import Callable, ClassVar
+import sys
 
 from .base import SpiderwebMiddleware as SpiderwebMiddleware
+from .cors import CorsMiddleware as CorsMiddleware
 from .csrf import CSRFMiddleware as CSRFMiddleware
 from .sessions import SessionMiddleware as SessionMiddleware
-from ..exceptions import ConfigError, UnusedMiddleware
+from ..exceptions import ConfigError, UnusedMiddleware, StartupErrors
 from ..request import Request
 from ..response import HttpResponse
 from ..utils import import_by_string
@@ -27,10 +29,19 @@ class MiddlewareMixin:
             self.middleware = middleware_by_reference
 
     def run_middleware_checks(self):
+        errors = []
         for middleware in self.middleware:
             if hasattr(middleware, "checks"):
                 for check in middleware.checks:
-                    check(server=self).check()
+                    if issue := check(server=self).check():
+                        errors.append(issue)
+
+        if errors:
+            # just show the messages
+            sys.tracebacklimit = 0
+            raise StartupErrors(
+                "Problems were identified during startup — cannot continue.", errors
+            )
 
     def process_request_middleware(self, request: Request) -> None | bool:
         for middleware in self.middleware:

spiderweb/middleware/cors.py

@@ -1 +1,137 @@
-# https://gist.github.com/FND/204ba41bf6ae485965ef
+import re
+from urllib.parse import urlsplit, SplitResult
+
+from spiderweb.request import Request
+from spiderweb.response import HttpResponse
+from spiderweb.middleware import SpiderwebMiddleware
+
+ACCESS_CONTROL_ALLOW_ORIGIN = "access-control-allow-origin"
+ACCESS_CONTROL_EXPOSE_HEADERS = "access-control-expose-headers"
+ACCESS_CONTROL_ALLOW_CREDENTIALS = "access-control-allow-credentials"
+ACCESS_CONTROL_ALLOW_HEADERS = "access-control-allow-headers"
+ACCESS_CONTROL_ALLOW_METHODS = "access-control-allow-methods"
+ACCESS_CONTROL_MAX_AGE = "access-control-max-age"
+ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK = "access-control-request-private-network"
+ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK = "access-control-allow-private-network"
+
+
+class CorsMiddleware(SpiderwebMiddleware):
+    # heavily 'based' on https://github.com/adamchainz/django-cors-headers,
+    # which is provided under the MIT license. This is essentially a direct
+    # port, since django-cors-headers is battle-tested code that has been
+    # around for a long time and it works well. Shoutouts to Otto, Adam, and
+    # crew for helping make this a complete non-issue in Django for a very long
+    # time.
+
+    def is_enabled(self, request: Request):
+        return bool(re.match(self.server.cors_urls_regex, request.path))
+
+    def add_response_headers(self, request: Request, response: HttpResponse):
+        enabled = getattr(request, "_cors_enabled", None)
+        if enabled is None:
+            enabled = self.is_enabled(request)
+
+        if not enabled:
+            return response
+
+        if "vary" in response.headers:
+            response.headers["vary"].append("origin")
+        else:
+            response.headers["vary"] = ["origin"]
+
+        origin = request.headers.get("origin")
+        if not origin:
+            return response
+
+        try:
+            url = urlsplit(origin)
+        except ValueError:
+            return response
+
+        if (
+            not self.server.cors_allow_all_origins
+            and not self.origin_found_in_allow_lists(origin, url)
+        ):
+            return response
+
+        if (
+            self.server.cors_allow_all_origins
+            and not self.server.cors_allow_credentials
+        ):
+            response.headers[ACCESS_CONTROL_ALLOW_ORIGIN] = "*"
+        else:
+            response.headers[ACCESS_CONTROL_ALLOW_ORIGIN] = origin
+
+        if self.server.cors_allow_credentials:
+            response.headers[ACCESS_CONTROL_ALLOW_CREDENTIALS] = "true"
+
+        if len(self.server.cors_expose_headers):
+            response.headers[ACCESS_CONTROL_EXPOSE_HEADERS] = ", ".join(
+                self.server.cors_expose_headers
+            )
+
+        if request.method == "OPTIONS":
+            response.headers[ACCESS_CONTROL_ALLOW_HEADERS] = ", ".join(
+                self.server.cors_allow_headers
+            )
+            response.headers[ACCESS_CONTROL_ALLOW_METHODS] = ", ".join(
+                self.server.cors_allow_methods
+            )
+            if self.server.cors_preflight_max_age:
+                response.headers[ACCESS_CONTROL_MAX_AGE] = str(
+                    self.server.cors_preflight_max_age
+                )
+
+        if (
+            self.server.cors_allow_private_network
+            and request.headers.get(ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK) == "true"
+        ):
+            response.headers[ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK] = "true"
+
+        return response
+
+    def origin_found_in_allow_lists(self, origin: str, url: SplitResult) -> bool:
+        return (
+            (origin == "null" and origin in self.server.cors_allowed_origins)
+            or self._url_in_allowlist(url)
+            or self.regex_domain_match(origin)
+        )
+
+    def _url_in_allowlist(self, url: SplitResult) -> bool:
+        origins = [urlsplit(o) for o in self.server.cors_allowed_origins]
+        return any(
+            origin.scheme == url.scheme and origin.netloc == url.netloc
+            for origin in origins
+        )
+
+    def regex_domain_match(self, origin: str) -> bool:
+        return any(
+            re.match(domain_pattern, origin)
+            for domain_pattern in self.server.cors_allowed_origin_regexes
+        )
+
+    def process_request(self, request: Request) -> HttpResponse | None:
+        # Identify and handle a preflight request
+        # origin = request.META.get("HTTP_ORIGIN")
+        request._cors_enabled = self.is_enabled(request)
+        if (
+            request._cors_enabled
+            and request.method == "OPTIONS"
+            and "access-control-request-method" in request.headers
+        ):
+            # this should be 204, but according to mozilla, not all browsers
+            # parse that correctly. See [204] comment below.
+            resp = HttpResponse(
+                "",
+                status_code=200,
+                headers={"content-type": "text/plain", "content-length": 0},
+            )
+            self.add_response_headers(request, resp)
+            return resp
+
+    def process_response(
+        self, request: Request, response: HttpResponse
+    ) -> None:
+        self.add_response_headers(request, response)
+
+# [204]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS#status_code

spiderweb/routes.py

@@ -1,5 +1,5 @@
 import re
-from typing import Callable, Any, Optional
+from typing import Callable, Any, Optional, Sequence
 
 from spiderweb.constants import DEFAULT_ALLOWED_METHODS
 from spiderweb.converters import *  # noqa: F403
@@ -30,7 +30,7 @@ class RoutesMixin:
     # ones that start with underscores are the compiled versions, non-underscores
     # are the user-supplied versions
     _routes: dict
-    routes: list[tuple[str, Callable] | tuple[str, Callable, dict]] = (None,)
+    routes: Sequence[tuple[str, Callable] | tuple[str, Callable, dict]]
     _error_routes: dict
     error_routes: dict[int, Callable]
     append_slash: bool

spiderweb/tests/test_middleware.py

@@ -4,12 +4,16 @@ from datetime import timedelta
 import pytest
 from peewee import SqliteDatabase
 
-from spiderweb import SpiderwebRouter, HttpResponse, ConfigError
+from spiderweb import SpiderwebRouter, HttpResponse, ConfigError, StartupErrors
 from spiderweb.constants import DEFAULT_ENCODING
 from spiderweb.middleware.sessions import Session
 from spiderweb.middleware import csrf
 from spiderweb.tests.helpers import setup
-from spiderweb.tests.views_for_tests import form_view_with_csrf, form_csrf_exempt, form_view_without_csrf
+from spiderweb.tests.views_for_tests import (
+    form_view_with_csrf,
+    form_csrf_exempt,
+    form_view_without_csrf,
+)
 
 
 # app = SpiderwebRouter(
@@ -99,18 +103,21 @@ def test_exploding_middleware():
 
 def test_csrf_middleware_without_session_middleware():
     _, environ, start_response = setup()
-    with pytest.raises(ConfigError) as e:
+    with pytest.raises(StartupErrors) as e:
         SpiderwebRouter(
             middleware=["spiderweb.middleware.csrf.CSRFMiddleware"],
             db=SqliteDatabase("spiderweb-tests.db"),
         )
-
+    exceptiongroup = e.value.args[1]
-    assert e.value.args[0] == csrf.SessionCheck.SESSION_MIDDLEWARE_NOT_FOUND
+    assert (
+        exceptiongroup[0].args[0]
+        == csrf.CheckForSessionMiddleware.SESSION_MIDDLEWARE_NOT_FOUND
+    )
 
 
 def test_csrf_middleware_above_session_middleware():
     _, environ, start_response = setup()
-    with pytest.raises(ConfigError) as e:
+    with pytest.raises(StartupErrors) as e:
         SpiderwebRouter(
             middleware=[
                 "spiderweb.middleware.csrf.CSRFMiddleware",
@@ -118,8 +125,11 @@ def test_csrf_middleware_above_session_middleware():
             ],
             db=SqliteDatabase("spiderweb-tests.db"),
         )
-
+    exceptiongroup = e.value.args[1]
-    assert e.value.args[0] == csrf.SessionCheck.SESSION_MIDDLEWARE_BELOW_CSRF
+    assert (
+        exceptiongroup[0].args[0]
+        == csrf.VerifyCorrectMiddlewarePlacement.SESSION_MIDDLEWARE_BELOW_CSRF
+    )
 
 
 def test_csrf_middleware():
@@ -211,6 +221,7 @@ def test_csrf_expired_token():
         f"swsession={[i for i in Session.select().dicts()][-1]['session_key']}"
     )
     environ["REQUEST_METHOD"] = "POST"
+    environ["HTTP_ORIGIN"] = "example.com"
     environ["HTTP_X_CSRF_TOKEN"] = token
     environ["CONTENT_LENGTH"] = len(formdata)
 
@@ -254,3 +265,44 @@ def test_csrf_exempt():
     environ["PATH_INFO"] = "/2"
     resp2 = app(environ, start_response)[0].decode(DEFAULT_ENCODING)
     assert "CSRF token is invalid" in resp2
+
+
+def test_csrf_trusted_origins():
+    _, environ, start_response = setup()
+    app = SpiderwebRouter(
+        middleware=[
+            "spiderweb.middleware.sessions.SessionMiddleware",
+            "spiderweb.middleware.csrf.CSRFMiddleware",
+        ],
+        csrf_trusted_origins=[
+            "example.com",
+        ],
+        db=SqliteDatabase("spiderweb-tests.db"),
+    )
+
+    app.add_route("/", form_view_without_csrf, ["GET", "POST"])
+
+    environ["HTTP_USER_AGENT"] = "hi"
+    environ["REMOTE_ADDR"] = "1.1.1.1"
+    environ["CONTENT_TYPE"] = "application/x-www-form-urlencoded"
+    environ["REQUEST_METHOD"] = "POST"
+
+    formdata = "name=bob"
+    environ["CONTENT_LENGTH"] = len(formdata)
+    b_handle = BytesIO()
+    b_handle.write(formdata.encode(DEFAULT_ENCODING))
+    b_handle.seek(0)
+    environ["wsgi.input"] = BufferedReader(b_handle)
+
+    environ["HTTP_ORIGIN"] = "notvalid.com"
+    resp = app(environ, start_response)[0].decode(DEFAULT_ENCODING)
+    assert "CSRF token is invalid" in resp
+
+    b_handle = BytesIO()
+    b_handle.write(formdata.encode(DEFAULT_ENCODING))
+    b_handle.seek(0)
+    environ["wsgi.input"] = BufferedReader(b_handle)
+
+    environ["HTTP_ORIGIN"] = "example.com"
+    resp2 = app(environ, start_response)[0].decode(DEFAULT_ENCODING)
+    assert resp2 == '{"name": "bob"}'

spiderweb/utils.py

@@ -1,4 +1,5 @@
 import json
+import re
 import secrets
 import string
 from http import HTTPStatus
@@ -78,3 +79,11 @@ class Headers(dict):
 
     def setdefault(self, key, default=None):
         return super().setdefault(key.lower(), default)
+
+
+def convert_url_to_regex(url: str | re.Pattern) -> re.Pattern:
+    if isinstance(url, re.Pattern):
+        return url
+    url = url.replace(".", "\\.")
+    url = url.replace("*", ".+")
+    return re.compile(url)