HDDS-12131. Overwrite an empty file with multipart-upload throws NPE

[k5342]

What changes were proposed in this pull request?

S3MultipartUploadCompleteRequestWithFSO seems to throw NPE when an empty file is being overwritten by non-zero file because omBucketInfo allows null value (null value is passed when non-update needed). This patch fix this by checking omBucketInfo before use.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-12131

How was this patch tested?

I've added annotation for @Nullable.
Local compilation are passed and it'll be checked by CI. Let me know if more tests are suggested.

[adoroszlai]

Thanks @k5342 for reporting this bug and providing the fix.

For reference, this is where bucket info is set to null to prevent unnecessary update for empty file:

ozone/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/s3/multipart/S3MultipartUploadCompleteRequest.java

Lines 338 to 341 in 47525b2

	} else if (!isNamespaceUpdate) {
	// If no bucket size and Namespace changed, prevent from updating
	// bucket object.
	omBucketInfo = null;

Let me know if more tests are suggested

I would like to suggest adding this simple robot test. I reproduced the NPE with it, and verified the fix.

diff --git hadoop-ozone/dist/src/main/smoketest/s3/MultipartUpload.robot hadoop-ozone/dist/src/main/smoketest/s3/MultipartUpload.robot
index e630fe6cda..22e26953f1 100644
--- hadoop-ozone/dist/src/main/smoketest/s3/MultipartUpload.robot
+++ hadoop-ozone/dist/src/main/smoketest/s3/MultipartUpload.robot
@@ -61,6 +61,12 @@ Test Multipart Upload With Adjusted Length
     Perform Multipart Upload    ${BUCKET}    multipart/adjusted_length_${PREFIX}    /tmp/part1    /tmp/part2
     Verify Multipart Upload     ${BUCKET}    multipart/adjusted_length_${PREFIX}    /tmp/part1    /tmp/part2
 
+Overwrite Empty File
+    Execute    touch ${TEMP_DIR}/empty
+    Execute AWSS3Cli        cp ${TEMP_DIR}/empty s3://${BUCKET}/empty_file_${PREFIX}
+    Perform Multipart Upload    ${BUCKET}    empty_file_${PREFIX}    /tmp/part1    /tmp/part2
+    Verify Multipart Upload     ${BUCKET}    empty_file_${PREFIX}    /tmp/part1    /tmp/part2
+
 Test Multipart Upload
     ${uploadID} =       Initiate MPU    ${BUCKET}    ${PREFIX}/multipartKey
     ${nextUploadID} =   Initiate MPU    ${BUCKET}    ${PREFIX}/multipartKey