fix(spanner): use cloudpath channel provider for admin stubs

Author: rahul2393

java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java

@@ -399,6 +399,12 @@ public GapicSpannerRpc(final SpannerOptions options) {
                   options.getChannelEndpointCacheFactory(),
                   endpointChannelConfigurator)
               : baseChannelProvider;
+      TransportChannelProvider adminChannelProvider =
+          useGcpFallback
+              ? createChannelProviderBuilder(
+                      options, headerProviderWithUserAgent, /* isEnableDirectAccess= */ false)
+                  .build()
+              : channelProvider;
 
       spannerWatchdog =
           Executors.newSingleThreadScheduledExecutor(
@@ -497,7 +503,7 @@ public GapicSpannerRpc(final SpannerOptions options) {
                 pdmlSettings.build(), clientContext);
         this.instanceAdminStubSettings =
             options.getInstanceAdminStubSettings().toBuilder()
-                .setTransportChannelProvider(channelProvider)
+                .setTransportChannelProvider(adminChannelProvider)
                 .setCredentialsProvider(credentialsProvider)
                 .setStreamWatchdogProvider(watchdogProvider)
                 .setTracerFactory(
@@ -508,7 +514,7 @@ public GapicSpannerRpc(final SpannerOptions options) {
 
         this.databaseAdminStubSettings =
             options.getDatabaseAdminStubSettings().toBuilder()
-                .setTransportChannelProvider(channelProvider)
+                .setTransportChannelProvider(adminChannelProvider)
                 .setCredentialsProvider(credentialsProvider)
                 .setStreamWatchdogProvider(watchdogProvider)
                 .setTracerFactory(

java-spanner/google-cloud-spanner/src/test/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpcTest.java

@@ -1434,7 +1434,7 @@ private SpannerOptions createSpannerOptions() {
   }
 
   @Test
-  public void testDirectPathFallbackCreatesOneGrpcGcpLayerPerPath() {
+  public void testDirectPathFallbackUsesCloudPathForAdminClients() {
     SpannerOptions.useEnvironment(new SpannerOptions.SpannerEnvironment() {});
     GapicSpannerRpc rpc = null;
     try {
@@ -1445,8 +1445,8 @@ public void testDirectPathFallbackCreatesOneGrpcGcpLayerPerPath() {
       GrpcGcpObjectCounts before = countGrpcGcpObjectsFromChannelz();
       rpc = new GapicSpannerRpc(options);
       GrpcGcpObjectCounts counts = countGrpcGcpObjectsFromChannelz().minus(before);
-      assertEquals(counts.debugString(), 6, counts.gcpManagedChannels);
-      assertEquals(counts.debugString(), 48, counts.channelRefs);
+      assertEquals(counts.debugString(), 4, counts.gcpManagedChannels);
+      assertEquals(counts.debugString(), 32, counts.channelRefs);
     } finally {
       if (rpc != null) {
         rpc.shutdown();