[bp/1.27] Datadog: restore "resource.name" tag (#30503)

source/extensions/tracers/datadog/demo/docker-compose.yaml

@@ -8,9 +8,11 @@ services:
   dd-agent:
     volumes:
       - '/var/run/docker.sock:/var/run/docker.sock:ro'
+      - '/run/user:/run/user:ro'
       - '/proc/:/host/proc/:ro'
       - '/sys/fs/cgroup/:/host/sys/fs/cgroup:ro'
     environment:
+      - DOCKER_HOST
       - DD_API_KEY
       - DD_APM_ENABLED=true
       - DD_LOG_LEVEL=ERROR

source/extensions/tracers/datadog/demo/envoy

@@ -1,4 +1,4 @@
 #!/bin/sh
 
 here=$(dirname "$0")
-"$(bazelisk info bazel-genfiles)"/source/exe/envoy-static --config-path "$here"/envoy.yaml "$@"
+"$here"/../../../../../bazel-bin/source/exe/envoy-static --config-path "$here"/envoy.yaml "$@"

source/extensions/tracers/datadog/span.cc

@@ -41,15 +41,27 @@ void Span::setOperation(absl::string_view operation) {
     return;
   }
 
-  span_->set_name(operation);
+  // What Envoy calls the operation name more closely corresponds to what
+  // Datadog calls the resource name.
+  span_->set_resource_name(operation);
 }
 
 void Span::setTag(absl::string_view name, absl::string_view value) {
   if (!span_) {
     return;
   }
 
-  span_->set_tag(name, value);
+  // The special "resource.name" tag is a holdover from when the Datadog tracer
+  // was OpenTracing-based, and so there was no way to set the Datadog resource
+  // name directly.
+  // In Envoy, it's still the case that there's no way to set the Datadog
+  // resource name directly; so, here if the tag name is "resource.name", we
+  // actually set the resource name instead of setting a tag.
+  if (name == "resource.name") {
+    span_->set_resource_name(value);
+  } else {
+    span_->set_tag(name, value);
+  }
 }
 
 void Span::log(SystemTime, const std::string&) {

test/extensions/tracers/datadog/span_test.cc

@@ -128,14 +128,18 @@ TEST_F(DatadogTracerSpanTest, SetOperation) {
   ASSERT_NE(nullptr, data_ptr);
   const datadog::tracing::SpanData& data = *data_ptr;
 
-  EXPECT_EQ("gastric bypass", data.name);
+  // Setting the operation name actually sets the resource name, because Envoy's
+  // notion of operation name more closely matches Datadog's notion of resource
+  // name.
+  EXPECT_EQ("gastric bypass", data.resource);
 }
 
 TEST_F(DatadogTracerSpanTest, SetTag) {
   Span span{std::move(span_)};
   span.setTag("foo", "bar");
   span.setTag("boom", "bam");
   span.setTag("foo", "new");
+  span.setTag("resource.name", "vespene gas");
   span.finishSpan();
 
   ASSERT_EQ(1, collector_->chunks.size());
@@ -152,6 +156,12 @@ TEST_F(DatadogTracerSpanTest, SetTag) {
   found = data.tags.find("boom");
   ASSERT_NE(data.tags.end(), found);
   EXPECT_EQ("bam", found->second);
+
+  // The "resource.name" tag is special. It doesn't set a tag, but instead the
+  // span's resource name.
+  found = data.tags.find("resource.name");
+  ASSERT_EQ(data.tags.end(), found);
+  EXPECT_EQ("vespene gas", data.resource);
 }
 
 TEST_F(DatadogTracerSpanTest, InjectContext) {