Refactor CORS Middleware to be much faster (#7801)

* changes

* add changeset

* log

* add changeset

* changes

* changes

* lint

* middlware

* lint

* lint

* s
implified docstring

* fix

* revert test change

* docstring

* remove print

* update

---------

Co-authored-by: gradio-pr-bot <gradio-pr-bot@users.noreply.github.com>

.changeset/stale-grapes-roll.md

@@ -0,0 +1,5 @@
+---
+"gradio": patch
+---
+
+feat:Refactor CORS Middleware to be much faster

gradio/route_utils.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import functools
 import hashlib
 import hmac
 import json
@@ -33,9 +34,10 @@ import httpx
 import multipart
 from gradio_client.documentation import document
 from multipart.multipart import parse_options_header
-from starlette.datastructures import FormData, Headers, UploadFile
+from starlette.datastructures import FormData, Headers, MutableHeaders, UploadFile
 from starlette.formparsers import MultiPartException, MultipartPart
-from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import PlainTextResponse, Response
+from starlette.types import ASGIApp, Message, Receive, Scope, Send
 
 from gradio import processing_utils, utils
 from gradio.data_classes import PredictBody
@@ -648,41 +650,86 @@ def get_hostname(url: str) -> str:
         return ""
 
 
-class CustomCORSMiddleware(BaseHTTPMiddleware):
-    async def dispatch(self, request: fastapi.Request, call_next):
-        host: str = request.headers.get("host", "")
-        origin: str = request.headers.get("origin", "")
-        host_name = get_hostname(host)
-        origin_name = get_hostname(origin)
+class CustomCORSMiddleware:
+    # This is a modified version of the Starlette CORSMiddleware that restricts the allowed origins when the host is localhost.
+    # Adapted from: https://github.com/encode/starlette/blob/89fae174a1ea10f59ae248fe030d9b7e83d0b8a0/starlette/middleware/cors.py
 
+    def __init__(
+        self,
+        app: ASGIApp,
+    ) -> None:
+        self.app = app
+        self.all_methods = ("DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT")
+        self.preflight_headers = {
+            "Access-Control-Allow-Methods": ", ".join(self.all_methods),
+            "Access-Control-Max-Age": str(600),
+        }
+        self.simple_headers = {"Access-Control-Allow-Credentials": "true"}
         # Any of these hosts suggests that the Gradio app is running locally.
         # Note: "null" is a special case that happens if a Gradio app is running
         # as an embedded web component in a local static webpage.
-        localhost_aliases = ["localhost", "127.0.0.1", "0.0.0.0", "null"]
-        is_preflight = (
-            request.method == "OPTIONS"
-            and "access-control-request-method" in request.headers
+        self.localhost_aliases = ["localhost", "127.0.0.1", "0.0.0.0", "null"]
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        if scope["type"] != "http":
+            await self.app(scope, receive, send)
+            return
+        headers = Headers(scope=scope)
+        origin = headers.get("origin")
+        if origin is None:
+            await self.app(scope, receive, send)
+            return
+        if scope["method"] == "OPTIONS" and "access-control-request-method" in headers:
+            response = self.preflight_response(request_headers=headers)
+            await response(scope, receive, send)
+            return
+        await self.simple_response(scope, receive, send, request_headers=headers)
+
+    def preflight_response(self, request_headers: Headers) -> Response:
+        headers = dict(self.preflight_headers)
+        origin = request_headers["Origin"]
+        if self.is_valid_origin(request_headers):
+            headers["Access-Control-Allow-Origin"] = origin
+        requested_headers = request_headers.get("access-control-request-headers")
+        if requested_headers is not None:
+            headers["Access-Control-Allow-Headers"] = requested_headers
+        return PlainTextResponse("OK", status_code=200, headers=headers)
+
+    async def simple_response(
+        self, scope: Scope, receive: Receive, send: Send, request_headers: Headers
+    ) -> None:
+        send = functools.partial(self._send, send=send, request_headers=request_headers)
+        await self.app(scope, receive, send)
+
+    async def _send(
+        self, message: Message, send: Send, request_headers: Headers
+    ) -> None:
+        if message["type"] != "http.response.start":
+            await send(message)
+            return
+        message.setdefault("headers", [])
+        headers = MutableHeaders(scope=message)
+        headers.update(self.simple_headers)
+        has_cookie = "cookie" in request_headers
+        origin = request_headers["Origin"]
+        if has_cookie or self.is_valid_origin(request_headers):
+            self.allow_explicit_origin(headers, origin)
+        await send(message)
+
+    def is_valid_origin(self, request_headers: Headers) -> bool:
+        origin = request_headers["Origin"]
+        host = request_headers["Host"]
+        host_name = get_hostname(host)
+        origin_name = get_hostname(origin)
+        return (
+            host_name not in self.localhost_aliases
+            or origin_name in self.localhost_aliases
         )
 
-        if host_name in localhost_aliases and origin_name not in localhost_aliases:
-            allow_origin_header = None
-        else:
-            allow_origin_header = origin
-
-        if is_preflight:
-            response = fastapi.Response()
-        else:
-            response = await call_next(request)
-
-        if allow_origin_header:
-            response.headers["Access-Control-Allow-Origin"] = allow_origin_header
-        response.headers[
-            "Access-Control-Allow-Methods"
-        ] = "GET, POST, PUT, DELETE, OPTIONS"
-        response.headers[
-            "Access-Control-Allow-Headers"
-        ] = "Origin, Content-Type, Accept"
-        return response
+    @staticmethod
+    def allow_explicit_origin(headers: MutableHeaders, origin: str) -> None:
+        headers["Access-Control-Allow-Origin"] = origin
+        headers.add_vary_header("Origin")
 
 
 def delete_files_created_by_app(blocks: Blocks, age: int | None) -> None: