access log: fix %UPSTREAM_CLUSTER% in upstream http access logs

docs/root/version_history/current.rst

@@ -32,6 +32,7 @@ Bug Fixes
 ---------
 *Changes expected to improve the state of the world and are unlikely to have negative effects*
 
+* access log: fix `%UPSTREAM_CLUSTER%` when used in http upstream access logs. Previously, it was always logging as an unset value.
 * xray: fix the AWS X-Ray tracer bug where span's error, fault and throttle information was not reported properly as per the `AWS X-Ray documentation <https://docs.aws.amazon.com/xray/latest/devguide/xray-api-segmentdocuments.html>`_. Before this fix, server error was reported under 'annotations' section of the segment data.
 
 Removed Config or Runtime

source/common/router/upstream_request.cc

@@ -62,6 +62,11 @@ UpstreamRequest::UpstreamRequest(RouterFilterInterface& parent,
   }
 
   stream_info_.healthCheck(parent_.callbacks()->streamInfo().healthCheck());
+  absl::optional<Upstream::ClusterInfoConstSharedPtr> cluster_info =
+      parent_.callbacks()->streamInfo().upstreamClusterInfo();
+  if (cluster_info.has_value()) {
+    stream_info_.setUpstreamClusterInfo(*cluster_info);
+  }
 }
 
 UpstreamRequest::~UpstreamRequest() {

test/common/router/router_upstream_log_test.cc

@@ -83,6 +83,12 @@ class RouterUpstreamLogTest : public testing::Test {
 public:
   void init(absl::optional<envoy::config::accesslog::v3::AccessLog> upstream_log) {
     envoy::extensions::filters::http::router::v3::Router router_proto;
+    static const std::string cluster_name = "cluster_0";
+
+    cluster_info_ = std::make_shared<NiceMock<Upstream::MockClusterInfo>>();
+    ON_CALL(*cluster_info_, name()).WillByDefault(ReturnRef(cluster_name));
+    ON_CALL(*cluster_info_, observabilityName()).WillByDefault(ReturnRef(cluster_name));
+    ON_CALL(callbacks_.stream_info_, upstreamClusterInfo()).WillByDefault(Return(cluster_info_));
 
     if (upstream_log) {
       ON_CALL(*context_.access_log_manager_.file_, write(_))
@@ -160,6 +166,7 @@ class RouterUpstreamLogTest : public testing::Test {
 
     EXPECT_CALL(context_.cluster_manager_.thread_local_cluster_.conn_pool_.host_->outlier_detector_,
                 putHttpResponseCode(response_code));
+    // NOLINTNEXTLINE(clang-analyzer-core.CallAndMessage)
     response_decoder->decodeHeaders(std::move(response_headers), false);
 
     Http::ResponseTrailerMapPtr response_trailers(
@@ -245,6 +252,7 @@ class RouterUpstreamLogTest : public testing::Test {
   NiceMock<Http::MockStreamDecoderFilterCallbacks> callbacks_;
   std::shared_ptr<FilterConfig> config_;
   std::shared_ptr<TestFilter> router_;
+  std::shared_ptr<NiceMock<Upstream::MockClusterInfo>> cluster_info_;
   NiceMock<StreamInfo::MockStreamInfo> stream_info_;
 };
 
@@ -365,5 +373,27 @@ name: accesslog
   EXPECT_EQ(output_.front(), "110 49 41");
 }
 
+// Test UPSTREAM_CLUSTER log formatter.
+TEST_F(RouterUpstreamLogTest, UpstreamCluster) {
+  const std::string yaml = R"EOF(
+name: accesslog
+typed_config:
+  "@type": type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog
+  log_format:
+    text_format_source:
+      inline_string: "%UPSTREAM_CLUSTER%"
+  path: "/dev/null"
+  )EOF";
+
+  envoy::config::accesslog::v3::AccessLog upstream_log;
+  TestUtility::loadFromYaml(yaml, upstream_log);
+
+  init(absl::optional<envoy::config::accesslog::v3::AccessLog>(upstream_log));
+  run();
+
+  EXPECT_EQ(output_.size(), 1U);
+  EXPECT_EQ(output_.front(), "cluster_0");
+}
+
 } // namespace Router
 } // namespace Envoy