Github user brosander commented on a diff in the pull request:
https://github.com/apache/nifi/pull/525#discussion_r68948186
--- Diff:
nifi-nar-bundles/nifi-windows-event-log-bundle/nifi-windows-event-log-processors/src/main/java/org/apache/nifi/processors/windows/event/log/ConsumeWindowsEventLog.java
---
@@ -0,0 +1,282 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.nifi.processors.windows.event.log;
+
+import com.sun.jna.platform.win32.Kernel32;
+import com.sun.jna.platform.win32.Kernel32Util;
+import com.sun.jna.platform.win32.WinNT;
+import org.apache.commons.io.Charsets;
+import org.apache.nifi.annotation.behavior.InputRequirement;
+import org.apache.nifi.annotation.behavior.TriggerSerially;
+import org.apache.nifi.annotation.behavior.WritesAttribute;
+import org.apache.nifi.annotation.behavior.WritesAttributes;
+import org.apache.nifi.annotation.documentation.CapabilityDescription;
+import org.apache.nifi.annotation.documentation.Tags;
+import org.apache.nifi.annotation.lifecycle.OnScheduled;
+import org.apache.nifi.annotation.lifecycle.OnStopped;
+import org.apache.nifi.components.PropertyDescriptor;
+import org.apache.nifi.components.ValidationContext;
+import org.apache.nifi.components.ValidationResult;
+import org.apache.nifi.flowfile.FlowFile;
+import org.apache.nifi.flowfile.attributes.CoreAttributes;
+import org.apache.nifi.processor.AbstractSessionFactoryProcessor;
+import org.apache.nifi.processor.ProcessContext;
+import org.apache.nifi.processor.ProcessSession;
+import org.apache.nifi.processor.ProcessSessionFactory;
+import org.apache.nifi.processor.Relationship;
+import org.apache.nifi.processor.exception.ProcessException;
+import org.apache.nifi.processor.util.StandardValidators;
+import org.apache.nifi.processors.windows.event.log.jna.ErrorLookup;
+import
org.apache.nifi.processors.windows.event.log.jna.EventSubscribeXmlRenderingCallback;
+import org.apache.nifi.processors.windows.event.log.jna.WEvtApi;
+
+import java.net.URI;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+
+
+@InputRequirement(InputRequirement.Requirement.INPUT_FORBIDDEN)
+@Tags({"ingest", "event", "windows"})
+@TriggerSerially
+@CapabilityDescription("Registers a Windows Event Log Subscribe Callback
to receive FlowFiles from Events on Windows. These can be filtered via channel
and XPath.")
+@WritesAttributes({
+ @WritesAttribute(attribute = "mime.type", description = "Will set
a MIME type value of application/xml.")
+})
+public class ConsumeWindowsEventLog extends
AbstractSessionFactoryProcessor {
+ public static final String DEFAULT_CHANNEL = "System";
+ public static final String DEFAULT_XPATH = "*";
+ public static final int DEFAULT_MAX_BUFFER = 1024 * 1024;
+ public static final int DEFAULT_MAX_QUEUE_SIZE = 1024;
+
+ public static final PropertyDescriptor CHANNEL = new
PropertyDescriptor.Builder()
+ .name("channel")
+ .displayName("Channel")
+ .required(true)
+ .defaultValue(DEFAULT_CHANNEL)
+ .description("The Windows Event Log Channel to listen to.")
+ .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+ .build();
+
+ public static final PropertyDescriptor QUERY = new
PropertyDescriptor.Builder()
+ .name("query")
+ .displayName("XPath Query")
+ .required(true)
+ .defaultValue(DEFAULT_XPATH)
+ .description("XPath Query to filter events. (See
https://msdn.microsoft.com/en-us/library/windows/desktop/dd996910(v=vs.85).aspx
for examples.)")
+ .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+ .build();
+
+ public static final PropertyDescriptor MAX_BUFFER_SIZE = new
PropertyDescriptor.Builder()
+ .name("maxBuffer")
+ .displayName("Maximum Buffer Size")
+ .required(true)
+ .defaultValue(Integer.toString(DEFAULT_MAX_BUFFER))
+ .description("The individual Event Log XMLs are rendered to a
buffer." +
+ " This specifies the maximum size in bytes that the
buffer will be allowed to grow to. (Limiting the maximum size of an individual
Event XML.)")
+ .addValidator(StandardValidators.POSITIVE_INTEGER_VALIDATOR)
+ .build();
+
+ public static final PropertyDescriptor MAX_EVENT_QUEUE_SIZE = new
PropertyDescriptor.Builder()
+ .name("maxQueue")
+ .displayName("Maximum queue size")
+ .required(true)
+ .defaultValue(Integer.toString(DEFAULT_MAX_QUEUE_SIZE))
+ .description("Maximum number of events to queue for
transformation into FlowFiles.")
+ .addValidator(StandardValidators.POSITIVE_INTEGER_VALIDATOR)
+ .build();
+
+ public static final List<PropertyDescriptor> PROPERTY_DESCRIPTORS =
Collections.unmodifiableList(Arrays.asList(CHANNEL, QUERY, MAX_BUFFER_SIZE,
MAX_EVENT_QUEUE_SIZE));
+
+ public static final Relationship REL_SUCCESS = new
Relationship.Builder()
+ .name("success")
+ .description("Relationship for successfully consumed events.")
+ .build();
+
+ public static final Set<Relationship> RELATIONSHIPS =
Collections.unmodifiableSet(new HashSet<>(Arrays.asList(REL_SUCCESS)));
+ public static final String APPLICATION_XML = "application/xml";
+ private final WEvtApi wEvtApi;
+ private final Kernel32 kernel32;
+ private final ErrorLookup errorLookup;
+ private final String name;
+
+ private Throwable wEvtApiError = null;
+ private Throwable kernel32Error = null;
+
+ private BlockingQueue<String> renderedXMLs;
+ private WEvtApi.EVT_SUBSCRIBE_CALLBACK evtSubscribeCallback;
+ private WinNT.HANDLE subscriptionHandle;
+ private ProcessSessionFactory sessionFactory;
+ private String provenanceUri;
+
+ /**
+ * Framework constructor
+ */
+ public ConsumeWindowsEventLog() {
+ this(null, null);
+ }
+
+ /**
+ * Constructor that allows injection of JNA interfaces
+ *
+ * @param wEvtApi event api interface
+ * @param kernel32 kernel interface
+ */
+ public ConsumeWindowsEventLog(WEvtApi wEvtApi, Kernel32 kernel32) {
+ this.wEvtApi = wEvtApi == null ? loadWEvtApi() : wEvtApi;
+ this.kernel32 = kernel32 == null ? loadKernel32() : kernel32;
+ this.errorLookup = new ErrorLookup(this.kernel32);
+ if (kernel32 != null) {
+ name = Kernel32Util.getComputerName();
+ } else {
+ // Won't be able to use the processor anyway because native
libraries didn't load
+ name = null;
+ }
+ }
+
+ private WEvtApi loadWEvtApi() {
+ try {
+ return WEvtApi.INSTANCE;
+ } catch (Throwable e) {
+ wEvtApiError = e;
+ return null;
+ }
+ }
+
+ private Kernel32 loadKernel32() {
+ try {
+ return Kernel32.INSTANCE;
+ } catch (Throwable e) {
+ kernel32Error = e;
+ return null;
+ }
+ }
+
+ /**
+ * Register subscriber via native call
+ *
+ * @param context the process context
+ */
+ @OnScheduled
+ public void onScheduled(ProcessContext context) throws Exception {
+ String channel = context.getProperty(CHANNEL).getValue();
+ String query = context.getProperty(QUERY).getValue();
+
+ renderedXMLs = new
LinkedBlockingQueue<>(context.getProperty(MAX_EVENT_QUEUE_SIZE).asInteger());
+ provenanceUri = new URI("winlog", name, "/" + channel, query,
null).toASCIIString();
+
+ evtSubscribeCallback = new
EventSubscribeXmlRenderingCallback(getLogger(), s -> {
+ try {
+ renderedXMLs.put(s);
+ } catch (InterruptedException e) {
+ throw new IllegalStateException("Got interrupted while
waiting to add to queue.", e);
+ }
+ }, context.getProperty(MAX_BUFFER_SIZE).asInteger(), wEvtApi,
kernel32, errorLookup);
+
+ subscriptionHandle = wEvtApi.EvtSubscribe(null, null, channel,
query, null, null,
+ evtSubscribeCallback,
WEvtApi.EvtSubscribeFlags.SUBSCRIBE_TO_FUTURE);
+ if (subscriptionHandle == null || subscriptionHandle.getPointer()
== null) {
+ throw new Exception("Unable to subscribe with provided
parameters, received the following error code: "
+ + errorLookup.getLastError());
+ }
+ }
+
+ /**
+ * Cleanup
+ */
+ @OnStopped
+ public void stop() {
+ wEvtApi.EvtClose(subscriptionHandle);
+ subscriptionHandle = null;
+ evtSubscribeCallback = null;
+ if (!renderedXMLs.isEmpty()) {
+ if (sessionFactory != null) {
+ getLogger().info("Finishing processing leftover events");
+ ProcessSession session = sessionFactory.createSession();
+ processQueue(session);
+ } else {
+ throw new ProcessException("Stopping the processor but
there is no ProcessSessionFactory stored and there are messages in the internal
queue. Removing the processor now will " +
+ "clear the queue but will result in DATA LOSS.
This is normally due to starting the processor, receiving events and stopping
before the onTrigger happens. The messages " +
+ "in the internal queue cannot finish processing
until until the processor is triggered to run.");
+ }
+ }
+ sessionFactory = null;
+ provenanceUri = null;
+ renderedXMLs = null;
+ }
+
+ @Override
+ public void onTrigger(ProcessContext context, ProcessSessionFactory
sessionFactory) throws ProcessException {
+ this.sessionFactory = sessionFactory;
--- End diff --
@JPercivall I'm a little confused here about the GC implications. We're
not creating a new object with this assignment, just reassigning (a copy of
[1]) the same reference to the variable. In that case, we're talking about
either 4 or 8 bytes on the stack, not a heap allocation. [2]
Is there some Java documentation somewhere explaining how this is worse
than a null check?
[1]
http://stackoverflow.com/questions/2776145/how-can-java-assignment-be-made-to-point-to-an-object-instead-of-making-a-copy#answer-2776179
[2]
http://stackoverflow.com/questions/18746801/are-java-primitives-garbage-collected#answer-18746917
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