Fix ReverseProxied middleware and add docs (spec-first#1873)

Starlette introduced some new changes to how the `root_path` is handled,
which broke our `ReverseProxied` example and test.

This PR fixes both and adds documentation on how to run behind a proxy.

docs/cookbook.rst

@@ -116,3 +116,32 @@ Starlette. You can add it to your application, ideally in front of the ``Routing
                 :noindex:
 
 .. _CORSMiddleware: https://www.starlette.io/middleware/#corsmiddleware
+
+Reverse Proxy
+-------------
+
+When running behind a reverse proxy with stripped path prefix, you need to configure your
+application to properly handle this.
+
+Single known path prefix
+''''''''''''''''''''''''
+
+If there is only a single known prefix your application will be running behind, you can simply
+pass this path prefix as the `root_path` to your ASGI server:
+
+.. code-block:: bash
+
+    $ uvicorn run:app --root-path <root_path>
+
+.. code-block:: bash
+
+    $ gunicorn -k uvicorn.workers.UvicornWorker run:app --root-path <root_path>
+
+
+Dynamic path prefix
+'''''''''''''''''''
+
+If you are running behind multiple proxies, or the path is not known, you can wrap your
+application in a `ReverseProxied` middleware as shown in `this example`_.
+
+.. _this example: https://github.com/spec-first/connexion/tree/main/examples/reverseproxy

examples/reverseproxy/app.py

@@ -54,10 +54,10 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send):
                 root_path = value.decode()
                 break
         if root_path:
-            scope["root_path"] = "/" + root_path.strip("/")
-            path_info = scope.get("PATH_INFO", scope.get("path"))
-            if path_info.startswith(root_path):
-                scope["PATH_INFO"] = path_info[len(root_path) :]
+            root_path = "/" + root_path.strip("/")
+            scope["root_path"] = root_path
+            scope["path"] = root_path + scope.get("path", "")
+            scope["raw_path"] = root_path.encode() + scope.get("raw_path", "")
 
         scope["scheme"] = scope.get("scheme") or self.scheme
         scope["server"] = scope.get("server") or (self.server, None)

pyproject.toml

@@ -53,7 +53,7 @@ Jinja2 = ">= 3.0.0"
 python-multipart = ">= 0.0.5"
 PyYAML = ">= 5.1"
 requests = ">= 2.27"
-starlette = ">= 0.27"
+starlette = ">= 0.35"
 typing-extensions = ">= 4"
 werkzeug = ">= 2.2.1"
 

tests/api/conftest.py

@@ -73,10 +73,10 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send):
                     root_path = value.decode()
                     break
             if root_path:
-                scope["root_path"] = "/" + root_path.strip("/")
-                path_info = scope.get("PATH_INFO", scope.get("path"))
-                if path_info.startswith(root_path):
-                    scope["PATH_INFO"] = path_info[len(root_path) :]
+                root_path = "/" + root_path.strip("/")
+                scope["root_path"] = root_path
+                scope["path"] = root_path + scope.get("path", "")
+                scope["raw_path"] = root_path.encode() + scope.get("raw_path", "")
 
             scope["scheme"] = scope.get("scheme") or self.scheme
             scope["server"] = scope.get("server") or (self.server, None)