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Date: Mon, 29 Mar 2010 08:41:27 +0000 (UTC)
From: "Xiao Kang (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-6663) BlockDecompressorStream get EOF
 exception when decompressing the file compressed from empty file
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    [ https://issues.apache.org/jira/browse/HADOOP-6663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850835#action_12850835 ] 

Xiao Kang commented on HADOOP-6663:
-----------------------------------

The EOF exception caused as follow:

BlockCompressorStream compresses the input data block-by-block. For each block, the uncopressed block length is first written to the underlying output stream, followed by compressed chunks, each consists of a chuck-length and compressed chunk-data. 

So BlockCompressorStream writes an int of 0 to the underlying output stream when compressing empty file, without any following chunks. 

BlockDecompressorStream decompresses the underlying compressed input stream block by block. For each block, it reads the uncompressed block length and then reads the chunk length and compressed chunk. 

So BlockDecompressorStream read 0 and get EOF exception trying to read chunk length when decompressing previous compressed empty file.


> BlockDecompressorStream get EOF exception when decompressing the file compressed from empty file
> ------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-6663
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6663
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.20.2
>            Reporter: Xiao Kang
>
> An empty file can be compressed using BlockDecompressorStream, which is for block-based compressiong algorithm such as LZO. However, when decompressing the compressed file, BlockDecompressorStream get EOF exception.
> Here is a typical exception stack:
> java.io.EOFException
> at org.apache.hadoop.io.compress.BlockDecompressorStream.rawReadInt(BlockDecompressorStream.java:125)
> at org.apache.hadoop.io.compress.BlockDecompressorStream.getCompressedData(BlockDecompressorStream.java:96)
> at org.apache.hadoop.io.compress.BlockDecompressorStream.decompress(BlockDecompressorStream.java:82)
> at org.apache.hadoop.io.compress.DecompressorStream.read(DecompressorStream.java:74)
> at java.io.InputStream.read(InputStream.java:85)
> at org.apache.hadoop.util.LineReader.readLine(LineReader.java:134)
> at org.apache.hadoop.mapred.LineRecordReader.next(LineRecordReader.java:134)
> at org.apache.hadoop.mapred.LineRecordReader.next(LineRecordReader.java:39)
> at org.apache.hadoop.mapred.MapTask$TrackedRecordReader.moveToNext(MapTask.java:186)
> at org.apache.hadoop.mapred.MapTask$TrackedRecordReader.next(MapTask.java:170)
> at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:48)
> at org.apache.hadoop.streaming.PipeMapRunner.run(PipeMapRunner.java:18)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:334)
> at org.apache.hadoop.mapred.Child.main(Child.java:196)

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