xds: fix XdsNameResolver blindly propagates XdsClient errors (#8953)

Author: YifeiZhuang

xds/src/main/java/io/grpc/xds/XdsNameResolver.java

@@ -722,7 +722,9 @@ public void run() {
           if (stopped || receivedConfig) {
             return;
           }
-          listener.onError(error);
+          listener.onError(Status.UNAVAILABLE.withCause(error.getCause()).withDescription(
+              String.format("Unable to load LDS %s. xDS server returned: %s: %s.",
+              ldsResourceName, error.getCode(), error.getDescription())));
         }
       });
     }
@@ -920,7 +922,9 @@ public void run() {
             if (RouteDiscoveryState.this != routeDiscoveryState || receivedConfig) {
               return;
             }
-            listener.onError(error);
+            listener.onError(Status.UNAVAILABLE.withCause(error.getCause()).withDescription(
+                String.format("Unable to load RDS %s. xDS server returned: %s: %s.",
+                resourceName, error.getCode(), error.getDescription())));
           }
         });
       }

xds/src/test/java/io/grpc/xds/XdsNameResolverTest.java

@@ -431,7 +431,21 @@ public void resolving_encounterErrorLdsWatcherOnly() {
     verify(mockListener).onError(errorCaptor.capture());
     Status error = errorCaptor.getValue();
     assertThat(error.getCode()).isEqualTo(Code.UNAVAILABLE);
-    assertThat(error.getDescription()).isEqualTo("server unreachable");
+    assertThat(error.getDescription()).isEqualTo("Unable to load LDS " + AUTHORITY
+        + ". xDS server returned: UNAVAILABLE: server unreachable.");
+  }
+
+  @Test
+  public void resolving_translateErrorLds() {
+    resolver.start(mockListener);
+    FakeXdsClient xdsClient = (FakeXdsClient) resolver.getXdsClient();
+    xdsClient.deliverError(Status.NOT_FOUND.withDescription("server unreachable"));
+    verify(mockListener).onError(errorCaptor.capture());
+    Status error = errorCaptor.getValue();
+    assertThat(error.getCode()).isEqualTo(Code.UNAVAILABLE);
+    assertThat(error.getDescription()).isEqualTo("Unable to load LDS " + AUTHORITY
+        + ". xDS server returned: NOT_FOUND: server unreachable.");
+    assertThat(error.getCause()).isNull();
   }
 
   @Test
@@ -441,10 +455,14 @@ public void resolving_encounterErrorLdsAndRdsWatchers() {
     xdsClient.deliverLdsUpdateForRdsName(RDS_RESOURCE_NAME);
     xdsClient.deliverError(Status.UNAVAILABLE.withDescription("server unreachable"));
     verify(mockListener, times(2)).onError(errorCaptor.capture());
-    for (Status error : errorCaptor.getAllValues()) {
-      assertThat(error.getCode()).isEqualTo(Code.UNAVAILABLE);
-      assertThat(error.getDescription()).isEqualTo("server unreachable");
-    }
+    Status error = errorCaptor.getAllValues().get(0);
+    assertThat(error.getCode()).isEqualTo(Code.UNAVAILABLE);
+    assertThat(error.getDescription()).isEqualTo("Unable to load LDS " + AUTHORITY
+        + ". xDS server returned: UNAVAILABLE: server unreachable.");
+    error = errorCaptor.getAllValues().get(1);
+    assertThat(error.getCode()).isEqualTo(Code.UNAVAILABLE);
+    assertThat(error.getDescription()).isEqualTo("Unable to load RDS " + RDS_RESOURCE_NAME
+        + ". xDS server returned: UNAVAILABLE: server unreachable.");
   }
 
   @Test