Remote cluster license checker and no license info. (#36837)

Fail with a descriptive error when the xpack info returns no license info.

Relates to #36815

Author: martijnvg

x-pack/plugin/core/src/main/java/org/elasticsearch/license/RemoteClusterLicenseChecker.java

@@ -7,6 +7,7 @@
 package org.elasticsearch.license;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.ResourceNotFoundException;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.support.ContextPreservingActionListener;
 import org.elasticsearch.client.Client;
@@ -159,6 +160,10 @@ public void checkRemoteClusterLicenses(final List<String> clusterAliases, final
             @Override
             public void onResponse(final XPackInfoResponse xPackInfoResponse) {
                 final XPackInfoResponse.LicenseInfo licenseInfo = xPackInfoResponse.getLicenseInfo();
+                if (licenseInfo == null) {
+                    listener.onFailure(new ResourceNotFoundException("license info is missing for cluster [" + clusterAlias.get() + "]"));
+                    return;
+                }
                 if ((licenseInfo.getStatus() == LicenseStatus.ACTIVE) == false
                         || predicate.test(License.OperationMode.resolve(licenseInfo.getMode())) == false) {
                     listener.onResponse(LicenseCheck.failure(new RemoteClusterLicenseInfo(clusterAlias.get(), licenseInfo)));

x-pack/plugin/core/src/test/java/org/elasticsearch/license/RemoteClusterLicenseCheckerTests.java

@@ -7,6 +7,7 @@
 package org.elasticsearch.license;
 
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.ResourceNotFoundException;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.common.settings.Settings;
@@ -349,6 +350,41 @@ public void testBuildErrorMessageForInactiveLicense() {
                 equalTo("the license on cluster [expired-cluster] is not active"));
     }
 
+    public void testCheckRemoteClusterLicencesNoLicenseMetadata() {
+        final ThreadPool threadPool = createMockThreadPool();
+        final Client client = createMockClient(threadPool);
+        doAnswer(invocationMock -> {
+            @SuppressWarnings("unchecked") ActionListener<XPackInfoResponse> listener =
+                (ActionListener<XPackInfoResponse>) invocationMock.getArguments()[2];
+            listener.onResponse(new XPackInfoResponse(null, null, null));
+            return null;
+        }).when(client).execute(same(XPackInfoAction.INSTANCE), any(), any());
+
+        final RemoteClusterLicenseChecker licenseChecker =
+            new RemoteClusterLicenseChecker(client, XPackLicenseState::isPlatinumOrTrialOperationMode);
+        final AtomicReference<Exception> exception = new AtomicReference<>();
+
+        licenseChecker.checkRemoteClusterLicenses(
+            Collections.singletonList("remote"),
+            doubleInvocationProtectingListener(new ActionListener<RemoteClusterLicenseChecker.LicenseCheck>() {
+
+                @Override
+                public void onResponse(final RemoteClusterLicenseChecker.LicenseCheck response) {
+                    fail();
+                }
+
+                @Override
+                public void onFailure(final Exception e) {
+                    exception.set(e);
+                }
+
+            }));
+
+        assertNotNull(exception.get());
+        assertThat(exception.get(), instanceOf(ResourceNotFoundException.class));
+        assertThat(exception.get().getMessage(), equalTo("license info is missing for cluster [remote]"));
+    }
+
     private ActionListener<RemoteClusterLicenseChecker.LicenseCheck> doubleInvocationProtectingListener(
             final ActionListener<RemoteClusterLicenseChecker.LicenseCheck> listener) {
         final AtomicBoolean listenerInvoked = new AtomicBoolean();