Add 204 and 308 to heuristically cacheable status codes (#13015)

* Add 204 (No Content) and 308 (Permanent Redirect) to the
  heuristic caching allowlist in is_response_cacheable(),
  per RFC 9110 Section 15.1.
* Add autest validating all seven RFC 9110 heuristically
  cacheable codes (200, 203, 204, 300, 301, 308, 410) are
  cached with only Last-Modified present, and non-cacheable
  codes (302, 307, 400, 403) are not.

Author: bryancall

src/proxy/http/HttpTransact.cc

@@ -6563,7 +6563,8 @@ HttpTransact::is_response_cacheable(State *s, HTTPHdr *request, HTTPHdr *respons
   }
 
   if ((response_code == HTTPStatus::OK) || (response_code == HTTPStatus::NOT_MODIFIED) ||
-      (response_code == HTTPStatus::NON_AUTHORITATIVE_INFORMATION) || (response_code == HTTPStatus::MOVED_PERMANENTLY) ||
+      (response_code == HTTPStatus::NON_AUTHORITATIVE_INFORMATION) || (response_code == HTTPStatus::NO_CONTENT) ||
+      (response_code == HTTPStatus::MOVED_PERMANENTLY) || (response_code == HTTPStatus::PERMANENT_REDIRECT) ||
       (response_code == HTTPStatus::MULTIPLE_CHOICES) || (response_code == HTTPStatus::GONE)) {
     TxnDbg(dbg_ctl_http_trans, "YES response code seems fine");
     return true;

tests/gold_tests/cache/cache-heuristic-status.test.py

@@ -0,0 +1,28 @@
+'''
+Test heuristic caching of status codes per RFC 9110 Section 15.1.
+'''
+#  Licensed to the Apache Software Foundation (ASF) under one
+#  or more contributor license agreements.  See the NOTICE file
+#  distributed with this work for additional information
+#  regarding copyright ownership.  The ASF licenses this file
+#  to you under the Apache License, Version 2.0 (the
+#  "License"); you may not use this file except in compliance
+#  with the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+Test.Summary = '''
+Test heuristic caching of status codes per RFC 9110 Section 15.1.
+
+Verifies that responses with heuristically cacheable status codes (200, 203,
+204, 300, 301, 308, 410) are cached when only Last-Modified is present, and
+that non-cacheable codes (302, 307, 400, 403) are not.
+'''
+
+Test.ATSReplayTest(replay_file="replay/cache-heuristic-status.replay.yaml")