HDFS-17462. RBF: Fix NPE in Router concat when trg is an empty file.

[fannaihao]

Description of PR

When trg of Router concat is an empty file, it will trigger NPE in Router, and the concat will fail, example:

This is because when trg is an empty file, NameNode will return lastLocatedBlock as null in the response of getBlockLocations. And Router will not check null of lastLocatedBlock returned, instead Router will use it to get block pool id directly.
Trg of concat is an empty file should be allowed in router since this case is supported by concat of NameNode.
This PR fix this NPE exception.

How was this patch tested?

Test cases are:

For code changes:

If lastLocatedBlock returned from getBlockLocations is null in Router concat, it will not be used to get block pool id.
In this case, the block pool id check of trg will be delayed, i.e., concat continues to get and check block pool id of files in src, and only check them.
And the check of trg block pool id can be achieved in following steps, i.e., getLocationForPath and the request of concat forwarded to NameNode.
And exceptions will be thrown if block pool id of trg is not match with the block pool id of any file in src.

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[ayushtkn]

You need to add a test case for the change. I am not sure why are you going with expectedBlockPoolid thing? the getBlockLocations() call succeeded that means the file actually exists on one of the cluster, so you have a way to get the exact block pool id.

Maybe a better approach would be to do a getFileInfo() and verify if they are in same namespace?

[fannaihao]

@ayushtkn Thanks for the comment! I will add tests for this.
Yes, I also think it's better to have a direct way to get the block pool id of an empty file then verify, but I failed to find such methods..
I checked getFileInfo, seems it does not return info about block pool id? If I miss something, please let me know.
The expectedBlockPoolId thing is somehow indirect, but it works right..

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
			_ Prechecks _
+1 💚	dupname	0m 00s		No case conflicting files found.
+0 🆗	spotbugs	0m 00s		spotbugs executables are not available.
+0 🆗	codespell	0m 00s		codespell was not available.
+0 🆗	detsecrets	0m 00s		detect-secrets was not available.
+1 💚	@author	0m 00s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 00s		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	87m 10s		trunk passed
+1 💚	compile	4m 55s		trunk passed
+1 💚	checkstyle	4m 33s		trunk passed
+1 💚	mvnsite	4m 53s		trunk passed
+1 💚	javadoc	4m 31s		trunk passed
+1 💚	shadedclient	137m 05s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	3m 03s		the patch passed
+1 💚	compile	2m 24s		the patch passed
+1 💚	javac	2m 24s		the patch passed
+1 💚	blanks	0m 00s		The patch has no blanks issues.
+1 💚	checkstyle	2m 08s		the patch passed
+1 💚	mvnsite	2m 27s		the patch passed
+1 💚	javadoc	2m 16s		the patch passed
+1 💚	shadedclient	151m 08s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	asflicense	5m 26s		The patch does not generate ASF License warnings.
		398m 52s

Subsystem	Report/Notes
GITHUB PR	#6722
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	MINGW64_NT-10.0-17763 81e6d3c33564 3.4.10-87d57229.x86_64 2024-02-14 20:17 UTC x86_64 Msys
Build tool	maven
Personality	/c/hadoop/dev-support/bin/hadoop.sh
git revision	trunk / cff78d9
Default Java	Azul Systems, Inc.-1.8.0_332-b09
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch-windows-10/job/PR-6722/1/testReport/
modules	C: hadoop-hdfs-project/hadoop-hdfs-rbf U: hadoop-hdfs-project/hadoop-hdfs-rbf
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch-windows-10/job/PR-6722/1/console
versions	git=2.44.0.windows.1
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