VWS-Python · adamtheturtle · Aug 16, 2026
diff --git a/docs/source/differences-to-vws.rst b/docs/source/differences-to-vws.rst
@@ -374,7 +374,7 @@ path which does not start with a served path, such as
 For any other request which it does not serve, such as ``DELETE /summary`` or
 ``GET /targetsfoo``, it gives an HTML "Not Found" page which names the method
 and the path of the request.
-The Flask and Docker mock gives an empty body for all of these.
+The Flask and Docker mock reproduces both response shapes.
 
 The ``requests`` and ``httpx`` backends mock only the paths which the mock
 serves, so a request to any other path raises a connection error rather than

diff --git a/src/mock_vws/_flask_server/vws.py b/src/mock_vws/_flask_server/vws.py
@@ -6,6 +6,8 @@
 
 import base64
 import email.utils
+import gzip
+import html
 import json
 import logging
 import threading
@@ -401,14 +403,39 @@ def handle_exceptions(exc: ValidatorError) -> Response:
 @VWS_FLASK_APP.errorhandler(code_or_exception=HTTPStatus.METHOD_NOT_ALLOWED)
 @beartype
 def handle_unrouted_request(exc: NotFound | MethodNotAllowed) -> Response:
-    """Return a 404 response with no body for a request which no route
-    serves.
+    """Return the real Vuforia 404 shape for an unrouted request.
 
-    Real Vuforia returns a 404 response for a request to a path which it does
-    not serve, and for a request to a served path with a method which that
-    path does not serve.
+    Vuforia's edge returns an empty response for unknown path prefixes. Paths
+    routed to the Cloud Targets application return its HTML Not Found page.
     """
     del exc
+    application_prefixes = ("/duplicates", "/summary", "/targets")
+    if request.path.startswith(application_prefixes):
+        request_description = html.escape(
+            s=f"{request.method} {request.path}",
+            quote=True,
+        )
+        body = f"""<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <title>Not Found</title>
+    </head>
+    <body>
+        <h1>Not Found</h1>
+        <p id="detail">For request '{request_description}'</p>
+    </body>
+</html>
+""".encode()
+        return Response(
+            status=HTTPStatus.NOT_FOUND,
+            response=gzip.compress(data=body),
+            headers={
+                "Content-Type": "text/html; charset=UTF-8",
+                "Content-Encoding": "gzip",
+                "x-envoy-upstream-service-time": "5",
+            },
+        )
+
     response = Response(status=HTTPStatus.NOT_FOUND, response=b"")
     del response.headers["Content-Type"]
     return response

diff --git a/tests/mock_vws/test_invalid_given_id.py b/tests/mock_vws/test_invalid_given_id.py
@@ -10,6 +10,7 @@
 there are entries.
 """
 
+import gzip
 from dataclasses import dataclass
 from http import HTTPMethod, HTTPStatus
 
@@ -38,6 +39,8 @@ class _UnroutedResponse:
     status_code: int
     body: bytes
     content_type: str | None
+    content_encoding: str | None
+    upstream_service_time: str | None
 
 
 @beartype
@@ -77,12 +80,22 @@ def _send_unrouted_request(
             method=method,
             headers=headers,
         )
+        response_body = test_client_response.data
+        content_encoding = test_client_response.headers.get(
+            key="Content-Encoding",
+        )
+        if content_encoding == "gzip":
+            response_body = gzip.decompress(data=response_body)
         return _UnroutedResponse(
             status_code=test_client_response.status_code,
-            body=test_client_response.data,
+            body=response_body,
             content_type=test_client_response.headers.get(
                 key="Content-Type",
             ),
+            content_encoding=content_encoding,
+            upstream_service_time=test_client_response.headers.get(
+                key="x-envoy-upstream-service-time",
+            ),
         )
 
     try:
@@ -99,6 +112,10 @@ def _send_unrouted_request(
         status_code=response.status_code,
         body=response.content,
         content_type=response.headers.get("Content-Type"),
+        content_encoding=response.headers.get("Content-Encoding"),
+        upstream_service_time=response.headers.get(
+            "x-envoy-upstream-service-time",
+        ),
     )
 
 
@@ -171,6 +188,8 @@ def test_unknown_path(
         assert response.status_code == HTTPStatus.NOT_FOUND
         assert response.body == b""
         assert response.content_type is None
+        assert response.content_encoding is None
+        assert response.upstream_service_time is None
 
     @staticmethod
     def test_unknown_method(
@@ -194,3 +213,8 @@ def test_unknown_method(
 
         assert response is not None
         assert response.status_code == HTTPStatus.NOT_FOUND
+        assert response.content_type == "text/html; charset=UTF-8"
+        assert response.content_encoding == "gzip"
+        assert response.upstream_service_time is not None
+        assert b"<h1>Not Found</h1>" in response.body
+        assert b"For request 'DELETE /summary'" in response.body