2 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.netconf.sal.connect.netconf;
10 import com.google.common.base.Function;
11 import com.google.common.base.Optional;
12 import com.google.common.base.Preconditions;
13 import com.google.common.base.Predicates;
14 import com.google.common.collect.Collections2;
15 import com.google.common.collect.Lists;
16 import com.google.common.collect.Sets;
17 import com.google.common.util.concurrent.CheckedFuture;
18 import com.google.common.util.concurrent.FutureCallback;
19 import com.google.common.util.concurrent.Futures;
20 import com.google.common.util.concurrent.ListenableFuture;
21 import com.google.common.util.concurrent.ListeningExecutorService;
22 import com.google.common.util.concurrent.MoreExecutors;
23 import java.util.Collection;
24 import java.util.LinkedList;
25 import java.util.List;
27 import java.util.concurrent.Callable;
28 import java.util.concurrent.ExecutorService;
29 import org.opendaylight.controller.md.sal.dom.api.DOMNotification;
30 import org.opendaylight.controller.md.sal.dom.api.DOMRpcException;
31 import org.opendaylight.controller.md.sal.dom.api.DOMRpcResult;
32 import org.opendaylight.controller.md.sal.dom.api.DOMRpcService;
33 import org.opendaylight.netconf.api.NetconfMessage;
34 import org.opendaylight.netconf.sal.connect.api.MessageTransformer;
35 import org.opendaylight.netconf.sal.connect.api.RemoteDevice;
36 import org.opendaylight.netconf.sal.connect.api.RemoteDeviceCommunicator;
37 import org.opendaylight.netconf.sal.connect.api.RemoteDeviceHandler;
38 import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfDeviceCapabilities;
39 import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfDeviceCommunicator;
40 import org.opendaylight.netconf.sal.connect.netconf.listener.NetconfSessionPreferences;
41 import org.opendaylight.netconf.sal.connect.netconf.sal.NetconfDeviceRpc;
42 import org.opendaylight.netconf.sal.connect.netconf.schema.NetconfRemoteSchemaYangSourceProvider;
43 import org.opendaylight.netconf.sal.connect.netconf.schema.mapping.NetconfMessageTransformer;
44 import org.opendaylight.netconf.sal.connect.netconf.util.NetconfMessageTransformUtil;
45 import org.opendaylight.netconf.sal.connect.util.RemoteDeviceId;
46 import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.netconf.monitoring.extension.rev131210.$YangModuleInfoImpl;
47 import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.netconf.notifications.rev120206.NetconfCapabilityChange;
48 import org.opendaylight.yang.gen.v1.urn.opendaylight.netconf.node.topology.rev150114.netconf.node.connection.status.unavailable.capabilities.UnavailableCapability;
49 import org.opendaylight.yangtools.sal.binding.generator.impl.ModuleInfoBackedContext;
50 import org.opendaylight.yangtools.yang.common.QName;
51 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
52 import org.opendaylight.yangtools.yang.model.repo.api.MissingSchemaSourceException;
53 import org.opendaylight.yangtools.yang.model.repo.api.SchemaContextFactory;
54 import org.opendaylight.yangtools.yang.model.repo.api.SchemaResolutionException;
55 import org.opendaylight.yangtools.yang.model.repo.api.SchemaSourceRepresentation;
56 import org.opendaylight.yangtools.yang.model.repo.api.SourceIdentifier;
57 import org.opendaylight.yangtools.yang.model.repo.api.YangTextSchemaSource;
58 import org.opendaylight.yangtools.yang.model.repo.spi.PotentialSchemaSource;
59 import org.opendaylight.yangtools.yang.model.repo.spi.SchemaSourceRegistration;
60 import org.opendaylight.yangtools.yang.model.repo.spi.SchemaSourceRegistry;
61 import org.slf4j.Logger;
62 import org.slf4j.LoggerFactory;
65 * This is a mediator between NetconfDeviceCommunicator and NetconfDeviceSalFacade
67 public class NetconfDevice implements RemoteDevice<NetconfSessionPreferences, NetconfMessage, NetconfDeviceCommunicator> {
69 private static final Logger LOG = LoggerFactory.getLogger(NetconfDevice.class);
72 * Initial schema context contains schemas for netconf monitoring and netconf notifications
74 public static final SchemaContext INIT_SCHEMA_CTX;
78 final ModuleInfoBackedContext moduleInfoBackedContext = ModuleInfoBackedContext.create();
79 moduleInfoBackedContext.addModuleInfos(
81 $YangModuleInfoImpl.getInstance(),
82 org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.netconf.notification._1._0.rev080714.$YangModuleInfoImpl.getInstance(),
83 org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.netconf.base._1._0.rev110601.$YangModuleInfoImpl.getInstance()));
84 INIT_SCHEMA_CTX = moduleInfoBackedContext.tryToCreateSchemaContext().get();
85 } catch (final RuntimeException e) {
86 LOG.error("Unable to prepare schema context for netconf initialization", e);
87 throw new ExceptionInInitializerError(e);
91 public static final Function<QName, SourceIdentifier> QNAME_TO_SOURCE_ID_FUNCTION = new Function<QName, SourceIdentifier>() {
93 public SourceIdentifier apply(final QName input) {
94 return new SourceIdentifier(input.getLocalName(), Optional.fromNullable(input.getFormattedRevision()));
98 protected final RemoteDeviceId id;
99 private final boolean reconnectOnSchemasChange;
101 protected final SchemaContextFactory schemaContextFactory;
102 private final RemoteDeviceHandler<NetconfSessionPreferences> salFacade;
103 private final ListeningExecutorService processingExecutor;
104 protected final SchemaSourceRegistry schemaRegistry;
105 private final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver;
106 private final NotificationHandler notificationHandler;
107 protected final List<SchemaSourceRegistration<? extends SchemaSourceRepresentation>> sourceRegistrations = Lists.newArrayList();
109 // Message transformer is constructed once the schemas are available
110 private MessageTransformer<NetconfMessage> messageTransformer;
112 public NetconfDevice(final SchemaResourcesDTO schemaResourcesDTO, final RemoteDeviceId id, final RemoteDeviceHandler<NetconfSessionPreferences> salFacade,
113 final ExecutorService globalProcessingExecutor) {
114 this(schemaResourcesDTO, id, salFacade, globalProcessingExecutor, false);
118 * Create rpc implementation capable of handling RPC for monitoring and notifications even before the schemas of remote device are downloaded
120 static NetconfDeviceRpc getRpcForInitialization(final NetconfDeviceCommunicator listener) {
121 return new NetconfDeviceRpc(INIT_SCHEMA_CTX, listener, new NetconfMessageTransformer(INIT_SCHEMA_CTX, false));
125 // FIXME reduce parameters
126 public NetconfDevice(final SchemaResourcesDTO schemaResourcesDTO, final RemoteDeviceId id, final RemoteDeviceHandler<NetconfSessionPreferences> salFacade,
127 final ExecutorService globalProcessingExecutor, final boolean reconnectOnSchemasChange) {
129 this.reconnectOnSchemasChange = reconnectOnSchemasChange;
130 this.schemaRegistry = schemaResourcesDTO.getSchemaRegistry();
131 this.schemaContextFactory = schemaResourcesDTO.getSchemaContextFactory();
132 this.salFacade = salFacade;
133 this.stateSchemasResolver = schemaResourcesDTO.getStateSchemasResolver();
134 this.processingExecutor = MoreExecutors.listeningDecorator(globalProcessingExecutor);
135 this.notificationHandler = new NotificationHandler(salFacade, id);
139 public void onRemoteSessionUp(final NetconfSessionPreferences remoteSessionCapabilities,
140 final NetconfDeviceCommunicator listener) {
141 // SchemaContext setup has to be performed in a dedicated thread since
142 // we are in a netty thread in this method
143 // Yang models are being downloaded in this method and it would cause a
144 // deadlock if we used the netty thread
145 // http://netty.io/wiki/thread-model.html
146 LOG.debug("{}: Session to remote device established with {}", id, remoteSessionCapabilities);
148 final NetconfDeviceRpc initRpc = getRpcForInitialization(listener);
149 final DeviceSourcesResolver task = new DeviceSourcesResolver(remoteSessionCapabilities, id, stateSchemasResolver, initRpc);
150 final ListenableFuture<DeviceSources> sourceResolverFuture = processingExecutor.submit(task);
152 if (shouldListenOnSchemaChange(remoteSessionCapabilities)) {
153 registerToBaseNetconfStream(initRpc, listener);
156 final FutureCallback<DeviceSources> resolvedSourceCallback = new FutureCallback<DeviceSources>() {
158 public void onSuccess(final DeviceSources result) {
159 addProvidedSourcesToSchemaRegistry(initRpc, result);
163 private void setUpSchema(final DeviceSources result) {
164 processingExecutor.submit(new RecursiveSchemaSetup(result, remoteSessionCapabilities, listener));
168 public void onFailure(final Throwable t) {
169 LOG.warn("{}: Unexpected error resolving device sources: {}", id, t);
170 handleSalInitializationFailure(t, listener);
174 Futures.addCallback(sourceResolverFuture, resolvedSourceCallback);
177 private void registerToBaseNetconfStream(final NetconfDeviceRpc deviceRpc, final NetconfDeviceCommunicator listener) {
178 // TODO check whether the model describing create subscription is present in schema
179 // Perhaps add a default schema context to support create-subscription if the model was not provided (same as what we do for base netconf operations in transformer)
180 final CheckedFuture<DOMRpcResult, DOMRpcException> rpcResultListenableFuture =
181 deviceRpc.invokeRpc(NetconfMessageTransformUtil.toPath(NetconfMessageTransformUtil.CREATE_SUBSCRIPTION_RPC_QNAME), NetconfMessageTransformUtil.CREATE_SUBSCRIPTION_RPC_CONTENT);
183 final NotificationHandler.NotificationFilter filter = new NotificationHandler.NotificationFilter() {
185 public Optional<DOMNotification> filterNotification(final DOMNotification notification) {
186 if (isCapabilityChanged(notification)) {
187 LOG.info("{}: Schemas change detected, reconnecting", id);
188 // Only disconnect is enough, the reconnecting nature of the connector will take care of reconnecting
189 listener.disconnect();
190 return Optional.absent();
192 return Optional.of(notification);
195 private boolean isCapabilityChanged(final DOMNotification notification) {
196 return notification.getBody().getNodeType().equals(NetconfCapabilityChange.QNAME);
200 Futures.addCallback(rpcResultListenableFuture, new FutureCallback<DOMRpcResult>() {
202 public void onSuccess(final DOMRpcResult domRpcResult) {
203 notificationHandler.addNotificationFilter(filter);
207 public void onFailure(final Throwable t) {
208 LOG.warn("Unable to subscribe to base notification stream. Schemas will not be reloaded on the fly", t);
213 private boolean shouldListenOnSchemaChange(final NetconfSessionPreferences remoteSessionCapabilities) {
214 return remoteSessionCapabilities.isNotificationsSupported() && reconnectOnSchemasChange;
217 protected void handleSalInitializationSuccess(final SchemaContext result, final NetconfSessionPreferences remoteSessionCapabilities, final DOMRpcService deviceRpc) {
218 messageTransformer = new NetconfMessageTransformer(result, true);
220 updateTransformer(messageTransformer);
221 // salFacade.onDeviceConnected has to be called before the notification handler is initialized
222 salFacade.onDeviceConnected(result, remoteSessionCapabilities, deviceRpc);
223 notificationHandler.onRemoteSchemaUp(messageTransformer);
225 LOG.info("{}: Netconf connector initialized successfully", id);
228 protected void handleSalInitializationFailure(final Throwable t, final RemoteDeviceCommunicator<NetconfMessage> listener) {
229 LOG.error("{}: Initialization in sal failed, disconnecting from device", id, t);
231 onRemoteSessionDown();
232 resetMessageTransformer();
236 * Set the transformer to null as is in initial state
238 private void resetMessageTransformer() {
239 updateTransformer(null);
242 private void updateTransformer(final MessageTransformer<NetconfMessage> transformer) {
243 messageTransformer = transformer;
246 private void addProvidedSourcesToSchemaRegistry(final NetconfDeviceRpc deviceRpc, final DeviceSources deviceSources) {
247 final NetconfRemoteSchemaYangSourceProvider yangProvider = new NetconfRemoteSchemaYangSourceProvider(id, deviceRpc);
248 for (final SourceIdentifier sourceId : deviceSources.getProvidedSources()) {
249 sourceRegistrations.add(schemaRegistry.registerSchemaSource(yangProvider,
250 PotentialSchemaSource.create(sourceId, YangTextSchemaSource.class, PotentialSchemaSource.Costs.REMOTE_IO.getValue())));
255 public void onRemoteSessionDown() {
256 notificationHandler.onRemoteSchemaDown();
258 salFacade.onDeviceDisconnected();
259 for (final SchemaSourceRegistration<? extends SchemaSourceRepresentation> sourceRegistration : sourceRegistrations) {
260 sourceRegistration.close();
262 resetMessageTransformer();
266 public void onRemoteSessionFailed(final Throwable throwable) {
267 salFacade.onDeviceFailed(throwable);
271 public void onNotification(final NetconfMessage notification) {
272 notificationHandler.handleNotification(notification);
276 * Just a transfer object containing schema related dependencies. Injected in constructor.
278 public static class SchemaResourcesDTO {
279 private final SchemaSourceRegistry schemaRegistry;
280 private final SchemaContextFactory schemaContextFactory;
281 private final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver;
283 public SchemaResourcesDTO(final SchemaSourceRegistry schemaRegistry, final SchemaContextFactory schemaContextFactory, final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver) {
284 this.schemaRegistry = Preconditions.checkNotNull(schemaRegistry);
285 this.schemaContextFactory = Preconditions.checkNotNull(schemaContextFactory);
286 this.stateSchemasResolver = Preconditions.checkNotNull(stateSchemasResolver);
289 public SchemaSourceRegistry getSchemaRegistry() {
290 return schemaRegistry;
293 public SchemaContextFactory getSchemaContextFactory() {
294 return schemaContextFactory;
297 public NetconfStateSchemas.NetconfStateSchemasResolver getStateSchemasResolver() {
298 return stateSchemasResolver;
303 * Schema building callable.
305 private static class DeviceSourcesResolver implements Callable<DeviceSources> {
307 private final NetconfDeviceRpc deviceRpc;
308 private final NetconfSessionPreferences remoteSessionCapabilities;
309 private final RemoteDeviceId id;
310 private final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver;
312 DeviceSourcesResolver(final NetconfDeviceRpc deviceRpc, final NetconfSessionPreferences remoteSessionCapabilities,
313 final RemoteDeviceId id, final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver) {
314 this.deviceRpc = deviceRpc;
315 this.remoteSessionCapabilities = remoteSessionCapabilities;
317 this.stateSchemasResolver = stateSchemasResolver;
320 public DeviceSourcesResolver(final NetconfSessionPreferences remoteSessionCapabilities, final RemoteDeviceId id, final NetconfStateSchemas.NetconfStateSchemasResolver stateSchemasResolver, final NetconfDeviceRpc rpcForMonitoring) {
321 this(rpcForMonitoring, remoteSessionCapabilities, id, stateSchemasResolver);
325 public DeviceSources call() throws Exception {
326 final NetconfStateSchemas availableSchemas = stateSchemasResolver.resolve(deviceRpc, remoteSessionCapabilities, id);
327 LOG.debug("{}: Schemas exposed by ietf-netconf-monitoring: {}", id, availableSchemas.getAvailableYangSchemasQNames());
329 final Set<QName> requiredSources = Sets.newHashSet(remoteSessionCapabilities.getModuleBasedCaps());
330 final Set<QName> providedSources = availableSchemas.getAvailableYangSchemasQNames();
332 final Set<QName> requiredSourcesNotProvided = Sets.difference(requiredSources, providedSources);
333 if (!requiredSourcesNotProvided.isEmpty()) {
334 LOG.warn("{}: Netconf device does not provide all yang models reported in hello message capabilities, required but not provided: {}",
335 id, requiredSourcesNotProvided);
336 LOG.warn("{}: Attempting to build schema context from required sources", id);
339 // Here all the sources reported in netconf monitoring are merged with those reported in hello.
340 // It is necessary to perform this since submodules are not mentioned in hello but still required.
341 // This clashes with the option of a user to specify supported yang models manually in configuration for netconf-connector
342 // and as a result one is not able to fully override yang models of a device. It is only possible to add additional models.
343 final Set<QName> providedSourcesNotRequired = Sets.difference(providedSources, requiredSources);
344 if (!providedSourcesNotRequired.isEmpty()) {
345 LOG.warn("{}: Netconf device provides additional yang models not reported in hello message capabilities: {}",
346 id, providedSourcesNotRequired);
347 LOG.warn("{}: Adding provided but not required sources as required to prevent failures", id);
348 LOG.debug("{}: Netconf device reported in hello: {}", id, requiredSources);
349 requiredSources.addAll(providedSourcesNotRequired);
352 return new DeviceSources(requiredSources, providedSources);
357 * Contains RequiredSources - sources from capabilities.
359 private static final class DeviceSources {
360 private final Set<QName> requiredSources;
361 private final Set<QName> providedSources;
363 public DeviceSources(final Set<QName> requiredSources, final Set<QName> providedSources) {
364 this.requiredSources = requiredSources;
365 this.providedSources = providedSources;
368 public Set<QName> getRequiredSourcesQName() {
369 return requiredSources;
372 public Set<QName> getProvidedSourcesQName() {
373 return providedSources;
376 public Collection<SourceIdentifier> getRequiredSources() {
377 return Collections2.transform(requiredSources, QNAME_TO_SOURCE_ID_FUNCTION);
380 public Collection<SourceIdentifier> getProvidedSources() {
381 return Collections2.transform(providedSources, QNAME_TO_SOURCE_ID_FUNCTION);
387 * Schema builder that tries to build schema context from provided sources or biggest subset of it.
389 private final class RecursiveSchemaSetup implements Runnable {
390 private final DeviceSources deviceSources;
391 private final NetconfSessionPreferences remoteSessionCapabilities;
392 private final RemoteDeviceCommunicator<NetconfMessage> listener;
393 private final NetconfDeviceCapabilities capabilities;
395 public RecursiveSchemaSetup(final DeviceSources deviceSources, final NetconfSessionPreferences remoteSessionCapabilities, final RemoteDeviceCommunicator<NetconfMessage> listener) {
396 this.deviceSources = deviceSources;
397 this.remoteSessionCapabilities = remoteSessionCapabilities;
398 this.listener = listener;
399 this.capabilities = remoteSessionCapabilities.getNetconfDeviceCapabilities();
404 setUpSchema(deviceSources.getRequiredSources());
408 * Recursively build schema context, in case of success or final failure notify device
410 // FIXME reimplement without recursion
411 private void setUpSchema(final Collection<SourceIdentifier> requiredSources) {
412 LOG.trace("{}: Trying to build schema context from {}", id, requiredSources);
414 // If no more sources, fail
415 if(requiredSources.isEmpty()) {
416 final IllegalStateException cause = new IllegalStateException(id + ": No more sources for schema context");
417 handleSalInitializationFailure(cause, listener);
418 salFacade.onDeviceFailed(cause);
422 final CheckedFuture<SchemaContext, SchemaResolutionException> schemaBuilderFuture = schemaContextFactory.createSchemaContext(requiredSources);
424 final FutureCallback<SchemaContext> RecursiveSchemaBuilderCallback = new FutureCallback<SchemaContext>() {
427 public void onSuccess(final SchemaContext result) {
428 LOG.debug("{}: Schema context built successfully from {}", id, requiredSources);
429 final Collection<QName> filteredQNames = Sets.difference(deviceSources.getRequiredSourcesQName(), capabilities.getUnresolvedCapabilites().keySet());
430 capabilities.addCapabilities(filteredQNames);
431 capabilities.addNonModuleBasedCapabilities(remoteSessionCapabilities.getNonModuleCaps());
432 handleSalInitializationSuccess(result, remoteSessionCapabilities, getDeviceSpecificRpc(result));
436 public void onFailure(final Throwable t) {
437 // In case source missing, try without it
438 if (t instanceof MissingSchemaSourceException) {
439 final SourceIdentifier missingSource = ((MissingSchemaSourceException) t).getSourceId();
440 LOG.warn("{}: Unable to build schema context, missing source {}, will reattempt without it", id, missingSource);
441 LOG.debug("{}: Unable to build schema context, missing source {}, will reattempt without it", t);
442 final Collection<QName> qNameOfMissingSource = getQNameFromSourceIdentifiers(Sets.newHashSet(missingSource));
443 if (!qNameOfMissingSource.isEmpty()) {
444 capabilities.addUnresolvedCapabilities(qNameOfMissingSource, UnavailableCapability.FailureReason.MissingSource);
446 setUpSchema(stripMissingSource(requiredSources, missingSource));
448 // In case resolution error, try only with resolved sources
449 } else if (t instanceof SchemaResolutionException) {
450 // TODO check for infinite loop
451 final SchemaResolutionException resolutionException = (SchemaResolutionException) t;
452 final Set<SourceIdentifier> unresolvedSources = resolutionException.getUnsatisfiedImports().keySet();
453 capabilities.addUnresolvedCapabilities(getQNameFromSourceIdentifiers(unresolvedSources), UnavailableCapability.FailureReason.UnableToResolve);
454 LOG.warn("{}: Unable to build schema context, unsatisfied imports {}, will reattempt with resolved only", id, resolutionException.getUnsatisfiedImports());
455 LOG.debug("{}: Unable to build schema context, unsatisfied imports {}, will reattempt with resolved only", resolutionException);
456 setUpSchema(resolutionException.getResolvedSources());
457 // unknown error, fail
459 handleSalInitializationFailure(t, listener);
464 Futures.addCallback(schemaBuilderFuture, RecursiveSchemaBuilderCallback);
467 protected NetconfDeviceRpc getDeviceSpecificRpc(final SchemaContext result) {
468 return new NetconfDeviceRpc(result, listener, new NetconfMessageTransformer(result, true));
471 private Collection<SourceIdentifier> stripMissingSource(final Collection<SourceIdentifier> requiredSources, final SourceIdentifier sIdToRemove) {
472 final LinkedList<SourceIdentifier> sourceIdentifiers = Lists.newLinkedList(requiredSources);
473 final boolean removed = sourceIdentifiers.remove(sIdToRemove);
474 Preconditions.checkState(removed, "{}: Trying to remove {} from {} failed", id, sIdToRemove, requiredSources);
475 return sourceIdentifiers;
478 private Collection<QName> getQNameFromSourceIdentifiers(final Collection<SourceIdentifier> identifiers) {
479 final Collection<QName> qNames = Collections2.transform(identifiers, new Function<SourceIdentifier, QName>() {
481 public QName apply(final SourceIdentifier sourceIdentifier) {
482 return getQNameFromSourceIdentifier(sourceIdentifier);
486 if (qNames.isEmpty()) {
487 LOG.debug("{}: Unable to map any source identifiers to a capability reported by device : {}", id, identifiers);
489 return Collections2.filter(qNames, Predicates.notNull());
492 private QName getQNameFromSourceIdentifier(final SourceIdentifier identifier) {
493 // Required sources are all required and provided merged in DeviceSourcesResolver
494 for (final QName qname : deviceSources.getRequiredSourcesQName()) {
495 if(qname.getLocalName().equals(identifier.getName()) == false) {
499 if(identifier.getRevision().equals(SourceIdentifier.NOT_PRESENT_FORMATTED_REVISION) &&
500 qname.getRevision() == null) {
504 if (qname.getFormattedRevision().equals(identifier.getRevision())) {
508 LOG.warn("Unable to map identifier to a devices reported capability: {} Available: {}",identifier, deviceSources.getRequiredSourcesQName());
509 // return null since we cannot find the QName, this capability will be removed from required sources and not reported as unresolved-capability