[CSM] Add target selector for csm channels (#34311)

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src/cpp/ext/csm/BUILD

@@ -52,9 +52,11 @@ grpc_cc_library(
     language = "c++",
     visibility = ["//:__subpackages__"],
     deps = [
+        "//:gpr",
         "//:gpr_platform",
         "//:grpc_base",
         "//:protobuf_struct_upb",
+        "//:uri_parser",
         "//src/core:env",
         "//src/core:error",
         "//src/core:json",

src/cpp/ext/csm/csm_observability.cc

@@ -20,8 +20,12 @@
 
 #include "src/cpp/ext/csm/csm_observability.h"
 
+#include <string>
 #include <utility>
 
+#include <grpc/support/log.h>
+
+#include "src/core/lib/uri/uri_parser.h"
 #include "src/cpp/ext/otel/otel_plugin.h"
 
 namespace grpc {
@@ -71,8 +75,27 @@ CsmObservabilityBuilder& CsmObservabilityBuilder::SetTargetAttributeFilter(
 
 absl::StatusOr<CsmObservability> CsmObservabilityBuilder::BuildAndRegister() {
   builder_.BuildAndRegisterGlobal();
+  builder_.SetTargetSelector(CsmChannelTargetSelector);
   return CsmObservability();
 }
 
+bool CsmChannelTargetSelector(absl::string_view target) {
+  auto uri = grpc_core::URI::Parse(target);
+  if (!uri.ok()) {
+    gpr_log(GPR_ERROR, "Failed to parse URI: %s", std::string(target).c_str());
+    return false;
+  }
+  // CSM channels should have an "xds" scheme
+  if (uri->scheme() != "xds") {
+    return false;
+  }
+  // If set, the authority should be TD
+  if (!uri->authority().empty() &&
+      uri->authority() != "traffic-director-global.xds.googleapis.com") {
+    return false;
+  }
+  return true;
+}
+
 }  // namespace internal
 }  // namespace grpc

src/cpp/ext/csm/csm_observability.h

@@ -76,6 +76,10 @@ class CsmObservabilityBuilder {
   OpenTelemetryPluginBuilder builder_;
 };
 
+// EXPOSED FOR TESTING PURPOSES ONLY
+// Returns true if the channel is a CSM channel.
+bool CsmChannelTargetSelector(absl::string_view target);
+
 }  // namespace internal
 }  // namespace grpc
 

test/cpp/ext/csm/csm_observability_test.cc

@@ -37,6 +37,29 @@ TEST(GsmDependencyTest, GoogleCloudOpenTelemetryDependency) {
   EXPECT_NE(google::cloud::otel::MakeResourceDetector(), nullptr);
 }
 
+TEST(CsmChannelTargetSelectorTest, NonXdsTargets) {
+  EXPECT_FALSE(internal::CsmChannelTargetSelector("foo.bar.google.com"));
+  EXPECT_FALSE(internal::CsmChannelTargetSelector("dns:///foo.bar.google.com"));
+  EXPECT_FALSE(
+      internal::CsmChannelTargetSelector("dns:///foo.bar.google.com:1234"));
+  EXPECT_FALSE(internal::CsmChannelTargetSelector(
+      "dns://authority/foo.bar.google.com:1234"));
+}
+
+TEST(CsmChannelTargetSelectorTest, XdsTargets) {
+  EXPECT_TRUE(internal::CsmChannelTargetSelector("xds:///foo"));
+  EXPECT_TRUE(internal::CsmChannelTargetSelector("xds:///foo.bar"));
+}
+
+TEST(CsmChannelTargetSelectorTest, XdsTargetsWithNonTDAuthority) {
+  EXPECT_FALSE(internal::CsmChannelTargetSelector("xds://authority/foo"));
+}
+
+TEST(CsmChannelTargetSelectorTest, XdsTargetsWithTDAuthority) {
+  EXPECT_TRUE(internal::CsmChannelTargetSelector(
+      "xds://traffic-director-global.xds.googleapis.com/foo"));
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace grpc