fix(wpt): serve XHR response header fixtures

Model xhr/resources/headers.py with its duplicate, empty, cookie and non-ASCII response headers. Include HEAD behavior and precise fixture discovery regression coverage.

(cherry picked from commit 8557f41b0c)

moli-benchmark/moli_benchmark/wpt_cross/case_set.py

@@ -872,7 +872,7 @@ def _xhr_response_handler_reference_patterns(directory: str) -> tuple[re.Pattern
                  "inspect-headers.py", "echo-headers.py", "content.py",
                  "echo-content-type.py", "win-1252-xml.py", "win-1252-html.py",
                  "invalid-utf8-html.py", "shift-jis-html.py", "img-utf8-html.py",
-                 "empty-div-utf8-html.py", "bad-chunk-encoding.py", "infinite-redirects.py",
+                 "empty-div-utf8-html.py", "headers.py", "bad-chunk-encoding.py", "infinite-redirects.py",
                  "access-control-basic-put-allow.py",
                  "access-control-preflight-request-allow-headers-returns-star.py"):
         resource = f"xhr/resources/{name}"

moli-benchmark/moli_benchmark/wpt_cross/server.py

@@ -93,6 +93,7 @@ XHR_BODY_RESOURCE_PATHS = {
 }
 XHR_RESPONSE_RESOURCE_PATHS = {
     *XHR_BODY_RESOURCE_PATHS,
+    "/xhr/resources/headers.py",
     "/xhr/resources/inspect-headers.py",
     "/xhr/resources/echo-headers.py",
     "/xhr/resources/access-control-basic-put-allow.py",
@@ -3088,6 +3089,19 @@ requestExecutor("{executor_uuid}", {start_on_js});
                     headers, body = _xhr_inspect_headers_fixture_response(
                         parsed.query, list(self.headers.raw_items()),
                     )
+                elif path == "/xhr/resources/headers.py":
+                    status, reason, content_type, body = 200, None, "text/plain", b"TEST"
+                    headers = [
+                        ("X-Custom-Header", "test"),
+                        ("Set-Cookie", "test"),
+                        ("Set-Cookie2", "test"),
+                        ("X-Custom-Header-Empty", ""),
+                        ("X-Custom-Header-Comma", "1"),
+                        ("X-Custom-Header-Comma", "2"),
+                        # send_header encodes strings as Latin-1; preserve the
+                        # UTF-8 ellipsis bytes written by the upstream fixture.
+                        ("X-Custom-Header-Bytes", "\u00e2\u0080\u00a6"),
+                    ]
                 elif path == "/xhr/resources/echo-headers.py":
                     status, reason, content_type = 200, None, "text/plain"
                     headers = []

moli-benchmark/tests/test_wpt_xhr_headers_server.py

@@ -48,6 +48,33 @@ class XhrHeaderFixtureTests(unittest.TestCase):
         finally:
             connection.close()
 
+    def test_fixed_response_preserves_empty_duplicate_cookie_and_non_ascii_headers(self) -> None:
+        server = self.server()
+        for method in ("GET", "HEAD"):
+            with self.subTest(method=method):
+                connection = HTTPConnection("127.0.0.1", server.port, timeout=2)
+                try:
+                    connection.request(method, "/xhr/resources/headers.py")
+                    response = connection.getresponse()
+                    self.assertEqual(response.status, 200)
+                    headers = response.getheaders()
+                    self.assertIn(("Content-Type", "text/plain"), headers)
+                    self.assertIn(("X-Custom-Header", "test"), headers)
+                    self.assertIn(("Set-Cookie", "test"), headers)
+                    self.assertIn(("Set-Cookie2", "test"), headers)
+                    self.assertIn(("X-Custom-Header-Empty", ""), headers)
+                    self.assertEqual(
+                        [value for name, value in headers if name == "X-Custom-Header-Comma"],
+                        ["1", "2"],
+                    )
+                    self.assertEqual(
+                        response.getheader("X-Custom-Header-Bytes").encode("latin-1"),
+                        b"\xe2\x80\xa6",
+                    )
+                    self.assertEqual(response.read(), b"TEST" if method == "GET" else b"")
+                finally:
+                    connection.close()
+
     def test_name_filter_preserves_case_duplicates_whitespace_and_bytes(self) -> None:
         server = self.server()
         status, headers, body = self.request(server.port, "filter_name=X-CaSe", [
@@ -212,12 +239,14 @@ class XhrHeaderFixtureTests(unittest.TestCase):
             "xhr/wrong-root.window.js": "fetch('inspect-headers.py');",
             "xhr/nested/wrong-relative.window.js": "fetch('resources/inspect-headers.py');",
         }
-        sources.update({
-            path.replace(".window.js", "-echo.window.js"): source.replace(
-                "inspect-headers.py", "echo-headers.py"
-            )
-            for path, source in list(sources.items())
-        })
+        base_sources = sources.copy()
+        for suffix, resource in (("fixed", "headers.py"), ("echo", "echo-headers.py")):
+            sources.update({
+                path.replace(".window.js", f"-{suffix}.window.js"): source.replace(
+                    "inspect-headers.py", resource
+                )
+                for path, source in base_sources.items()
+            })
         for path, source in sources.items():
             target = self.root / path
             target.parent.mkdir(parents=True, exist_ok=True)
@@ -225,9 +254,12 @@ class XhrHeaderFixtureTests(unittest.TestCase):
         selected = enumerate_cases(self.root, dir_prefixes=("xhr",))
         self.assertEqual([case.case_path for case in selected], [
             "xhr/absolute-echo.window.js?moli-wpt-script=window",
+            "xhr/absolute-fixed.window.js?moli-wpt-script=window",
             "xhr/absolute.window.js?moli-wpt-script=window",
             "xhr/nested/parent-echo.window.js?moli-wpt-script=window",
+            "xhr/nested/parent-fixed.window.js?moli-wpt-script=window",
             "xhr/nested/parent.window.js?moli-wpt-script=window",
             "xhr/relative-echo.window.js?moli-wpt-script=window",
+            "xhr/relative-fixed.window.js?moli-wpt-script=window",
             "xhr/relative.window.js?moli-wpt-script=window",
         ])