Change precedence of weaken_etag_on_compress

Updated the compressor filter to clarify the precedence of the `weaken_etag_on_compress` option when both it and `disable_on_etag_header` are enabled. Compression will now be applied, and the ETag will be weakened, allowing for better cache management. Documentation and tests have been updated to reflect this behavior.

Signed-off-by: Rafael Antunes <rafael.gaspar@me.com>

api/envoy/extensions/filters/http/compressor/v3/compressor.proto

@@ -69,6 +69,8 @@ message Compressor {
     // When this field is ``true``, disables compression when the response contains an ``ETag`` header.
     // When this field is ``false``, the filter will preserve weak ``ETag`` values and remove those that
     // require strong validation (unless ``weaken_etag_on_compress`` is set).
+    // When both ``disable_on_etag_header`` and ``weaken_etag_on_compress`` are ``true``,
+    // ``weaken_etag_on_compress`` takes precedence (compression is applied and the ETag is weakened).
     bool disable_on_etag_header = 2;
 
     // When this field is ``true``, removes ``Accept-Encoding`` from the request headers before dispatching
@@ -101,8 +103,9 @@ message Compressor {
     // ``ETag``, the filter will weaken the ETag by prepending ``W/`` to its value instead of
     // removing it. This allows caching and conditional requests to work while indicating the
     // response body was modified by compression. When ``false`` (default), strong ETags are
-    // removed when compression is applied. This option has no effect when ``disable_on_etag_header``
-    // is ``true`` (compression is skipped for responses with ETag).
+    // removed when compression is applied. When both ``weaken_etag_on_compress`` and
+    // ``disable_on_etag_header`` are ``true``, this field takes precedence so that compression
+    // is applied and the ETag is weakened, supporting gradual rollout to clients and servers.
     bool weaken_etag_on_compress = 6;
   }
 

changelogs/current.yaml

@@ -278,7 +278,8 @@ new_features:
     to the :ref:`compressor filter <config_http_filters_compressor>`. When enabled in
     ``response_direction_config``, strong ``ETag`` response headers are weakened (``W/`` prefix)
     instead of removed when compression is applied, allowing caches and conditional requests to
-    work while indicating the body was modified by compression.
+    work while indicating the body was modified by compression. When both ``weaken_etag_on_compress``
+    and ``disable_on_etag_header`` are true, the new field takes precedence.
 - area: golang
   change: |
     Added ``DownstreamSslConnection()`` method to the Golang HTTP filter's ``StreamInfo`` interface,

docs/root/configuration/http/http_filters/compressor_filter.rst

@@ -118,9 +118,14 @@ ETag handling
 When a response has an ``ETag`` header, the filter's behavior depends on
 ``response_direction_config``:
 
-- **``disable_on_etag_header: true``** — Compression is *skipped* for responses that
-  contain an ``ETag``. The response is sent unchanged (including the original ``ETag``).
-  This avoids changing the entity tag when the body would be modified by compression.
+- **When both ``disable_on_etag_header`` and ``weaken_etag_on_compress`` are ``true``** —
+  ``weaken_etag_on_compress`` takes precedence. Compression is applied and the strong
+  ``ETag`` is weakened.
+
+- **``disable_on_etag_header: true``** (and ``weaken_etag_on_compress`` is ``false``) —
+  Compression is *skipped* for responses that contain an ``ETag``. The response is sent
+  unchanged (including the original ``ETag``). This avoids changing the entity tag when
+  the body would be modified by compression.
 
 - **``disable_on_etag_header: false``** (default) — Compression is allowed. When compression
   is applied:

source/extensions/filters/http/compressor/compressor_filter.cc

@@ -731,8 +731,13 @@ bool CompressorFilter::checkIsEtagAllowedLogResponseStats(Http::ResponseHeaderMa
 }
 
 bool CompressorFilter::isEtagAllowed(Http::ResponseHeaderMap& headers) const {
-  return !(config_->responseDirectionConfig().disableOnEtagHeader() &&
-           headers.getInline(etag_handle.handle()));
+  const auto& config = config_->responseDirectionConfig();
+  // When both disable_on_etag_header and weaken_etag_on_compress are true, the new field
+  // takes precedence so compression is applied and the ETag is weakened.
+  if (config.weakenEtagOnCompress()) {
+    return true;
+  }
+  return !(config.disableOnEtagHeader() && headers.getInline(etag_handle.handle()));
 }
 
 bool CompressorFilterConfig::ResponseDirectionConfig::areAllResponseCodesCompressible() const {

test/extensions/filters/http/compressor/compressor_filter_test.cc

@@ -1416,6 +1416,35 @@ TEST_F(CompressorFilterTest, WeakenEtagOnCompressWithStatusHeaderEnabled) {
   EXPECT_TRUE(headers.has("x-envoy-compression-status"));
 }
 
+// When both disable_on_etag_header and weaken_etag_on_compress are true, the new field
+// takes precedence: compression is applied and the ETag is weakened.
+TEST_F(CompressorFilterTest, WeakenEtagOnCompressTakesPrecedenceOverDisableOnEtag) {
+  setUpFilter(R"EOF(
+{
+  "response_direction_config": {
+    "disable_on_etag_header": true,
+    "weaken_etag_on_compress": true
+  },
+  "compressor_library": {
+     "name": "test",
+     "typed_config": {
+       "@type": "type.googleapis.com/envoy.extensions.compression.gzip.compressor.v3.Gzip"
+     }
+  }
+}
+)EOF");
+  response_stats_prefix_ = "response.";
+
+  doRequestNoCompression({{":method", "get"}, {"accept-encoding", "test, deflate"}});
+  Http::TestResponseHeaderMapImpl headers{
+      {":method", "get"}, {"content-length", "256"}, {"etag", "\"strong-etag\""}};
+  doResponseCompression(headers, false);
+  EXPECT_EQ(0, stats_.counter("test.compressor.test.test.response.not_compressed_etag").value());
+  EXPECT_EQ("test", headers.get_("content-encoding"));
+  EXPECT_TRUE(headers.has("etag"));
+  EXPECT_EQ(R"(W/"strong-etag")", headers.get_("etag"));
+}
+
 class HasCacheControlNoTransformTest
     : public CompressorFilterTest,
       public testing::WithParamInterface<std::tuple<std::string, bool>> {};