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https://issues.apache.org/jira/browse/HDFS-17803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18063930#comment-18063930
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ASF GitHub Bot commented on HDFS-17803:
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balodesecurity opened a new pull request, #8322:
URL: https://github.com/apache/hadoop/pull/8322
## Summary
`DistributedFileSystem.getFileChecksum()` on an empty (zero-byte) file
always returned an `MD5MD5CRC32GzipFileChecksum` value, even when the client
was configured with `dfs.checksum.combine.mode=COMPOSITE_CRC`. This was
misleading and inconsistent with what non-empty files return in the same mode.
### Root Cause
In `FileChecksumHelper.FileChecksumComputer.compute()`, the empty-file fast
path unconditionally constructed an `MD5MD5CRC32GzipFileChecksum` without
checking `combineMode`.
### Fix
Check `combineMode` in the empty-file path:
- **`COMPOSITE_CRC`**: return `CompositeCrcFileChecksum(crc=0,
configuredChecksumType, configuredBytesPerCrc)` using the client's configured
`ChecksumOpt`.
- **`MD5MD5CRC`**: retain the existing backward-compatible magic value
(`MD5MD5CRC32GzipFileChecksum(0, 0, md5OfZeros)`) to avoid breaking existing
tools.
### Changes
- `FileChecksumHelper.java`: split the empty-file branch on `combineMode`.
- `TestGetFileChecksum.java`: add `testEmptyFileChecksumType` verifying both
modes return the expected `FileChecksum` subclass for a zero-byte file.
## Test plan
- [ ] `TestGetFileChecksum#testEmptyFileChecksumType` passes locally ✅
- [ ] Full module build passes (`mvn package ... -DskipTests`) ✅
> Compute correct checksum type when file is empty/ file length is 0
> ------------------------------------------------------------------
>
> Key: HDFS-17803
> URL: https://issues.apache.org/jira/browse/HDFS-17803
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: dfsclient
> Reporter: Chayanika Bhandary
> Priority: Trivial
> Labels: pull-request-available
>
> When the file is empty or the file size is 0, the checksum returned is always
> MD5MD5CRC type even when the selected checksum type is COMPOSITE_CRC.
> This is misleading and can create confusion while debugging.
>
> Contributing a fix to this. - [https://github.com/apache/hadoop/pull/7764]
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