core: Improve DEADLINE_EXCEEDED message for CallCreds delays

core/src/main/java/io/grpc/internal/DelayedClientTransport.java

@@ -363,6 +363,7 @@ private class PendingStream extends DelayedStream {
     private volatile Status lastPickStatus;
 
     private PendingStream(PickSubchannelArgs args, ClientStreamTracer[] tracers) {
+      super("connecting_and_lb");
       this.args = args;
       this.tracers = tracers;
     }

core/src/main/java/io/grpc/internal/DelayedStream.java

@@ -42,6 +42,7 @@
  * necessary.
  */
 class DelayedStream implements ClientStream {
+  private final String bufferContext;
   /** {@code true} once realStream is valid and all pending calls have been drained. */
   private volatile boolean passThrough;
   /**
@@ -64,6 +65,14 @@ class DelayedStream implements ClientStream {
   // No need to synchronize; start() synchronization provides a happens-before
   private List<Runnable> preStartPendingCalls = new ArrayList<>();
 
+  /**
+   * Create a delayed stream with debug context {@code bufferContext}. The context is what this
+   * stream is delayed by (e.g., "connecting", "call_credentials").
+   */
+  public DelayedStream(String bufferContext) {
+    this.bufferContext = checkNotNull(bufferContext, "bufferContext");
+  }
+
   @Override
   public void setMaxInboundMessageSize(final int maxSize) {
     checkState(listener == null, "May only be called before start");
@@ -104,11 +113,13 @@ public void appendTimeoutInsight(InsightBuilder insight) {
         return;
       }
       if (realStream != null) {
-        insight.appendKeyValue("buffered_nanos", streamSetTimeNanos - startTimeNanos);
+        insight.appendKeyValue(
+            bufferContext + "_delay", "" + (streamSetTimeNanos - startTimeNanos) + "ns");
         realStream.appendTimeoutInsight(insight);
       } else {
-        insight.appendKeyValue("buffered_nanos", System.nanoTime() - startTimeNanos);
-        insight.append("waiting_for_connection");
+        insight.appendKeyValue(
+            bufferContext + "_delay", "" + (System.nanoTime() - startTimeNanos) + "ns");
+        insight.append("was_still_waiting");
       }
     }
   }

core/src/main/java/io/grpc/internal/MetadataApplierImpl.java

@@ -120,7 +120,7 @@ ClientStream returnStream() {
     synchronized (lock) {
       if (returnedStream == null) {
         // apply() has not been called, needs to buffer the requests.
-        delayedStream = new DelayedStream();
+        delayedStream = new DelayedStream("call_credentials");
         return returnedStream = delayedStream;
       } else {
         return returnedStream;

core/src/test/java/io/grpc/internal/DelayedClientTransportTest.java

@@ -742,7 +742,7 @@ public void pendingStream_appendTimeoutInsight_waitForReady() {
     InsightBuilder insight = new InsightBuilder();
     stream.appendTimeoutInsight(insight);
     assertThat(insight.toString())
-        .matches("\\[wait_for_ready, buffered_nanos=[0-9]+\\, waiting_for_connection]");
+        .matches("\\[wait_for_ready, connecting_and_lb_delay=[0-9]+ns\\, was_still_waiting]");
   }
 
   @Test
@@ -759,7 +759,7 @@ public void pendingStream_appendTimeoutInsight_waitForReady_withLastPickFailure(
     assertThat(insight.toString())
         .matches("\\[wait_for_ready, "
             + "Last Pick Failure=Status\\{code=PERMISSION_DENIED, description=null, cause=null\\},"
-            + " buffered_nanos=[0-9]+, waiting_for_connection]");
+            + " connecting_and_lb_delay=[0-9]+ns, was_still_waiting]");
   }
 
   private static TransportProvider newTransportProvider(final ClientTransport transport) {

core/src/test/java/io/grpc/internal/DelayedStreamTest.java

@@ -71,7 +71,7 @@ public class DelayedStreamTest {
   @Mock private ClientStreamListener listener;
   @Mock private ClientStream realStream;
   @Captor private ArgumentCaptor<ClientStreamListener> listenerCaptor;
-  private DelayedStream stream = new DelayedStream();
+  private DelayedStream stream = new DelayedStream("test_op");
 
   @Test
   public void setStream_setAuthority() {
@@ -450,7 +450,7 @@ public void appendTimeoutInsight_realStreamNotSet() {
     InsightBuilder insight = new InsightBuilder();
     stream.start(listener);
     stream.appendTimeoutInsight(insight);
-    assertThat(insight.toString()).matches("\\[buffered_nanos=[0-9]+\\, waiting_for_connection]");
+    assertThat(insight.toString()).matches("\\[test_op_delay=[0-9]+ns\\, was_still_waiting]");
   }
 
   @Test
@@ -469,7 +469,7 @@ public Void answer(InvocationOnMock in) {
     InsightBuilder insight = new InsightBuilder();
     stream.appendTimeoutInsight(insight);
     assertThat(insight.toString())
-        .matches("\\[buffered_nanos=[0-9]+, remote_addr=127\\.0\\.0\\.1:443\\]");
+        .matches("\\[test_op_delay=[0-9]+ns, remote_addr=127\\.0\\.0\\.1:443\\]");
   }
 
   private void callMeMaybe(Runnable r) {