Properly set host header to ascii string in ProxyFixMiddleware.

src/hypercorn/middleware/proxy_fix.py

@@ -18,9 +18,10 @@ def __init__(
         self.trusted_hops = trusted_hops
 
     async def __call__(self, scope: Scope, receive: Callable, send: Callable) -> None:
-        if scope["type"] in {"http", "websocket"}:
+        # Keep the `or` instead of `in {'http' …}` to allow type narrowing
+        if scope["type"] == "http" or scope["type"] == "websocket":
             scope = deepcopy(scope)
-            headers = scope["headers"]  # type: ignore
+            headers = scope["headers"]
             client: Optional[str] = None
             scheme: Optional[str] = None
             host: Optional[str] = None
@@ -44,19 +45,19 @@ async def __call__(self, scope: Scope, receive: Callable, send: Callable) -> Non
                 host = _get_trusted_value(b"x-forwarded-host", headers, self.trusted_hops)
 
             if client is not None:
-                scope["client"] = (client, 0)  # type: ignore
+                scope["client"] = (client, 0)
 
             if scheme is not None:
-                scope["scheme"] = scheme  # type: ignore
+                scope["scheme"] = scheme
 
             if host is not None:
                 headers = [
                     (name, header_value)
                     for name, header_value in headers
                     if name.lower() != b"host"
                 ]
-                headers.append((b"host", host))
-                scope["headers"] = headers  # type: ignore
+                headers.append((b"host", host.encode()))
+                scope["headers"] = headers
 
         await self.app(scope, receive, send)
 

tests/middleware/test_proxy_fix.py

@@ -26,15 +26,19 @@ async def test_proxy_fix_legacy() -> None:
             (b"x-forwarded-for", b"127.0.0.1"),
             (b"x-forwarded-for", b"127.0.0.2"),
             (b"x-forwarded-proto", b"http,https"),
+            (b"x-forwarded-host", b"example.com"),
         ],
         "client": ("127.0.0.3", 80),
         "server": None,
         "extensions": {},
     }
     await app(scope, None, None)
     mock.assert_called()
-    assert mock.call_args[0][0]["client"] == ("127.0.0.2", 0)
-    assert mock.call_args[0][0]["scheme"] == "https"
+    scope = mock.call_args[0][0]
+    assert scope["client"] == ("127.0.0.2", 0)
+    assert scope["scheme"] == "https"
+    host_headers = [h for h in scope["headers"] if h[0].lower() == b"host"]
+    assert host_headers == [(b"host", b"example.com")]
 
 
 @pytest.mark.asyncio
@@ -52,13 +56,16 @@ async def test_proxy_fix_modern() -> None:
         "query_string": b"",
         "root_path": "",
         "headers": [
-            (b"forwarded", b"for=127.0.0.1;proto=http,for=127.0.0.2;proto=https"),
+            (b"forwarded", b"for=127.0.0.1;proto=http,for=127.0.0.2;proto=https;host=example.com"),
         ],
         "client": ("127.0.0.3", 80),
         "server": None,
         "extensions": {},
     }
     await app(scope, None, None)
     mock.assert_called()
-    assert mock.call_args[0][0]["client"] == ("127.0.0.2", 0)
-    assert mock.call_args[0][0]["scheme"] == "https"
+    scope = mock.call_args[0][0]
+    assert scope["client"] == ("127.0.0.2", 0)
+    assert scope["scheme"] == "https"
+    host_headers = [h for h in scope["headers"] if h[0].lower() == b"host"]
+    assert host_headers == [(b"host", b"example.com")]