Don't rewrite Location when absolute_url is True.

Author: ryanlovett

jupyter_server_proxy/handlers.py

@@ -578,13 +578,13 @@ def rewrite_pe(rewritable_response: RewritableResponse):
             self._headers = httputil.HTTPHeaders()
             for header, v in rewritten_response.headers.get_all():
                 if header not in ("Content-Length", "Transfer-Encoding", "Connection"):
-                    # Rewrite Location header in redirects to preserve proxy prefix
-                    if header == "Location" and rewritten_response.code in (
-                        301,
-                        302,
-                        303,
-                        307,
-                        308,
+                    # Rewrite Location header in redirects to preserve proxy prefix.
+                    # If absolute_url is True, the backend already sees the
+                    # full path and handles redirects appropriately.
+                    if (
+                        header == "Location"
+                        and not self.absolute_url
+                        and rewritten_response.code in (301, 302, 303, 307, 308)
                     ):
                         v = self._rewrite_location_header(v, host, port, proxied_path)
                     # some header appear multiple times, eg 'Set-Cookie'

tests/resources/jupyter_server_config.py

@@ -146,6 +146,10 @@ def my_env():
     "python-redirect": {
         "command": [sys.executable, _get_path("redirectserver.py"), "--port={port}"],
     },
+    "python-redirect-abs": {
+        "command": [sys.executable, _get_path("redirectserver.py"), "--port={port}"],
+        "absolute_url": True,
+    },
 }
 
 c.ServerProxy.non_service_rewrite_response = hello_to_foo

tests/test_proxies.py

@@ -558,3 +558,38 @@ def test_server_proxy_redirect_location_header_rewrite(
     # Should be rewritten to include the proxy prefix
     # The token query parameter should be preserved in the redirect
     assert location == f"/python-redirect/target/path?token={TOKEN}"
+
+
+@pytest.mark.parametrize("a_server", ["notebook", "lab"], indirect=True)
+def test_server_proxy_redirect_location_header_absolute_url(
+    a_server_port_and_token: Tuple[int, str],
+) -> None:
+    """
+    Test that Location headers in redirect responses are not rewritten when
+    absolute_url=True is configured.
+
+    When absolute_url=True, the backend server receives the full proxy path
+    (e.g., /python-redirect-abs/mydir instead of just /mydir). The proxy does
+    not rewrite Location headers, passing them through as-is from the backend.
+
+    This means the backend must be aware of the proxy prefix to generate
+    correct redirects, which is the intended behavior of absolute_url=True.
+    """
+    PORT, TOKEN = a_server_port_and_token
+
+    # Test 1: Named server proxy with absolute_url=True, redirect without trailing slash
+    r = request_get(PORT, "/python-redirect-abs/mydir", TOKEN)
+    assert r.code == 301
+    location = r.headers.get("Location")
+    # Location header is not rewritten by proxy, passed through as-is from backend
+    # Backend sees /python-redirect-abs/mydir and adds trailing slash: /python-redirect-abs/mydir/
+    assert location == f"/python-redirect-abs/mydir/?token={TOKEN}"
+
+    # Test 2: Named server proxy with absolute_url=True, verify no rewriting occurs
+    # Request to /python-redirect-abs/abc (without trailing slash)
+    r = request_get(PORT, "/python-redirect-abs/abc", TOKEN)
+    assert r.code == 301
+    location = r.headers.get("Location")
+    # Backend returns whatever it wants, proxy doesn't rewrite it
+    # In this case, backend adds trailing slash to the full path it received
+    assert location == f"/python-redirect-abs/abc/?token={TOKEN}"