client: return helpful error message when wait-for-ready RPCs fail with timeout (#2777)

Author: yuqitao

Diff for: picker_wrapper.go

@@ -120,6 +120,14 @@ func (bp *pickerWrapper) pick(ctx context.Context, failfast bool, opts balancer.
 			bp.mu.Unlock()
 			select {
 			case <-ctx.Done():
+				if connectionErr := bp.connectionError(); connectionErr != nil {
+					switch ctx.Err() {
+					case context.DeadlineExceeded:
+						return nil, nil, status.Errorf(codes.DeadlineExceeded, "latest connection error: %v", connectionErr)
+					case context.Canceled:
+						return nil, nil, status.Errorf(codes.Canceled, "latest connection error: %v", connectionErr)
+					}
+				}
 				return nil, nil, ctx.Err()
 			case <-ch:
 			}

Diff for: test/end2end_test.go

@@ -6716,6 +6716,29 @@ func (s) TestFailFastRPCErrorOnBadCertificates(t *testing.T) {
 	te.t.Fatalf("TestService/EmptyCall(_, _) = _, %v, want err.Error() contains %q", err, clientAlwaysFailCredErrorMsg)
 }
 
+func (s) TestWaitForReadyRPCErrorOnBadCertificates(t *testing.T) {
+	te := newTest(t, env{name: "bad-cred", network: "tcp", security: "clientAlwaysFailCred", balancer: "round_robin"})
+	te.startServer(&testServer{security: te.e.security})
+	defer te.tearDown()
+
+	opts := []grpc.DialOption{grpc.WithTransportCredentials(clientAlwaysFailCred{})}
+	dctx, dcancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer dcancel()
+	cc, err := grpc.DialContext(dctx, te.srvAddr, opts...)
+	if err != nil {
+		t.Fatalf("Dial(_) = %v, want %v", err, nil)
+	}
+	defer cc.Close()
+
+	tc := testpb.NewTestServiceClient(cc)
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+	if _, err = tc.EmptyCall(ctx, &testpb.Empty{}, grpc.WaitForReady(true)); strings.Contains(err.Error(), clientAlwaysFailCredErrorMsg) {
+		return
+	}
+	te.t.Fatalf("TestService/EmptyCall(_, _) = _, %v, want err.Error() contains %q", err, clientAlwaysFailCredErrorMsg)
+}
+
 func (s) TestRPCTimeout(t *testing.T) {
 	for _, e := range listTestEnv() {
 		testRPCTimeout(t, e)