HDFS-16750. NameNode should use NameNode.getRemoteUser() to log audit event to avoid possible NPE

[ZanderXu]

Description of PR

NameNode should use NameNode.getRemoteUser() to log audit event to avoid possible NPE.

The relate code is:

private void logAuditEvent(boolean succeeded, String cmd, String src,
    String dst, FileStatus stat) throws IOException {
  if (isAuditEnabled() && isExternalInvocation()) {
    logAuditEvent(succeeded, Server.getRemoteUser(), Server.getRemoteIp(),
        cmd, src, dst, stat);
  }
}

// the ugi may be null.
private void logAuditEvent(boolean succeeded,
    UserGroupInformation ugi, InetAddress addr, String cmd, String src,
    String dst, FileStatus status) {
  final String ugiStr = ugi.toString();
  ...
} 

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 53s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	41m 10s		trunk passed
+1 💚	compile	1m 38s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	compile	1m 25s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	1m 17s		trunk passed
+1 💚	mvnsite	1m 36s		trunk passed
+1 💚	javadoc	1m 15s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 36s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 40s		trunk passed
+1 💚	shadedclient	25m 41s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 23s		the patch passed
+1 💚	compile	1m 25s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javac	1m 25s		the patch passed
+1 💚	compile	1m 17s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	1m 17s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 59s		the patch passed
+1 💚	mvnsite	1m 24s		the patch passed
+1 💚	javadoc	0m 56s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 28s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 29s		the patch passed
+1 💚	shadedclient	26m 49s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	335m 21s		hadoop-hdfs in the patch passed.
+1 💚	asflicense	1m 13s		The patch does not generate ASF License warnings.
		453m 37s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4821/1/artifact/out/Dockerfile
GITHUB PR	#4821
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux ac8b4a34e3bb 4.15.0-191-generic #202-Ubuntu SMP Thu Aug 4 01:49:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / a207e9d
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4821/1/testReport/
Max. process+thread count	1981 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4821/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[ZanderXu]

@goiri Sir, can help me to merger this pr into trunk?