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https://issues.apache.org/jira/browse/HDFS-9705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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SammiChen reopened HDFS-9705:
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Assignee: SammiChen (was: Kai Zheng)
Reopen issue for back port to branch-2
> Refine the behaviour of getFileChecksum when length = 0
> -------------------------------------------------------
>
> Key: HDFS-9705
> URL: https://issues.apache.org/jira/browse/HDFS-9705
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Kai Zheng
> Assignee: SammiChen
> Priority: Minor
> Fix For: 3.0.0-alpha3
>
> Attachments: HDFS-9705-v1.patch, HDFS-9705-v2.patch,
> HDFS-9705-v3.patch, HDFS-9705-v4.patch, HDFS-9705-v5.patch,
> HDFS-9705-v6.patch, HDFS-9705-v7.patch
>
>
> {{FileSystem#getFileChecksum}} may accept {{length}} parameter and 0 is a
> valid value. Currently it will return {{null}} when length is 0, in the
> following code block:
> {code}
> //compute file MD5
> final MD5Hash fileMD5 = MD5Hash.digest(md5out.getData());
> switch (crcType) {
> case CRC32:
> return new MD5MD5CRC32GzipFileChecksum(bytesPerCRC,
> crcPerBlock, fileMD5);
> case CRC32C:
> return new MD5MD5CRC32CastagnoliFileChecksum(bytesPerCRC,
> crcPerBlock, fileMD5);
> default:
> // If there is no block allocated for the file,
> // return one with the magic entry that matches what previous
> // hdfs versions return.
> if (locatedblocks.size() == 0) {
> return new MD5MD5CRC32GzipFileChecksum(0, 0, fileMD5);
> }
> // we should never get here since the validity was checked
> // when getCrcType() was called above.
> return null;
> }
> {code}
> The comment says "we should never get here since the validity was checked"
> but it does. As we're using the MD5-MD5-X approach, and {{EMPTY--CONTENT}}
> actually is a valid case in which the MD5 value is
> {{d41d8cd98f00b204e9800998ecf8427e}}, so suggest we return a reasonable value
> other than null. At least some useful information in the returned value can
> be seen, like values from block checksum header.
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