Can someone share some idea what the Hadoop source code of class
org.apache.hadoop.io.compress.BlockDecompressorStream, method rawReadInt() is
trying to do here?
There is a comment in the code this this method shouldn't return negative
number, but in my testing file, it contains the following bytes from the
inputStream: 248, 19, 20, 116, which corresponding to b1, b2, b3, b4.
After the 4 bytes is read fromt the input stream, then the return result will
be a negative number here, as
(b1 << 24) = -134217728(b2 << 16) = 1245184(b3 << 8) = 5120(b4 << 0) = 116
I am not sure what logic of this method is trying to do here, can anyone share
some idea about it?
Thanks
private int rawReadInt() throws IOException {
int b1 = in.read();
int b2 = in.read();
int b3 = in.read();
int b4 = in.read();
if ((b1 | b2 | b3 | b4) < 0)
throw new EOFException();
return ((b1 << 24) + (b2 << 16) + (b3 << 8) + (b4 << 0));
}
From: [email protected]
To: [email protected]
Subject: Question related to Decompressor interface
Date: Sat, 9 Feb 2013 15:49:31 -0500
HI,
Currently I am researching about options of encrypting the data in the
MapReduce, as we plan to use the Amazon EMR or EC2 services for our data.
I am thinking that the compression codec is good place to integrate with the
encryption logic, and I found out there are some people having the same idea as
mine.
I google around and found out this code:
https://github.com/geisbruch/HadoopCryptoCompressor/
It doesn't seem maintained any more, but it gave me a starting point. I
download the source code, and try to do some tests with it.
It doesn't work out of box. There are some bugs I have to fix to make it work.
I believe it contains 'AES' as an example algorithm.
But right now, I faced a problem when I tried to use it in my testing MapReduer
program. Here is the stack trace I got:
2013-02-08 23:16:47,038 INFO
org.apache.hadoop.io.compress.crypto.CryptoBasicDecompressor: buf length = 512,
and offset = 0, length = -132967308java.lang.IndexOutOfBoundsException at
java.nio.ByteBuffer.wrap(ByteBuffer.java:352) at
org.apache.hadoop.io.compress.crypto.CryptoBasicDecompressor.setInput(CryptoBasicDecompressor.java:100)
at
org.apache.hadoop.io.compress.BlockDecompressorStream.decompress(BlockDecompressorStream.java:97)
at
org.apache.hadoop.io.compress.DecompressorStream.read(DecompressorStream.java:83)
at java.io.InputStream.read(InputStream.java:82) at
org.apache.hadoop.util.LineReader.readDefaultLine(LineReader.java:209) at
org.apache.hadoop.util.LineReader.readLine(LineReader.java:173) at
org.apache.hadoop.mapreduce.lib.input.LineRecordReader.nextKeyValue(LineRecordReader.java:114)
at
org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:458)
at
org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:76)
at
org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:85)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:139) at
org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:645) at
org.apache.hadoop.mapred.MapTask.run(MapTask.java:325) at
org.apache.hadoop.mapred.Child$4.run(Child.java:268) at
java.security.AccessController.doPrivileged(Native Method) at
javax.security.auth.Subject.doAs(Subject.java:396) at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1332)
at org.apache.hadoop.mapred.Child.main(Child.java:262)
I know the error is thrown out of this custom CryptoBasicDecompressor class,
but I really have questions related to the interface it implemented:
Decompressor.
There is limited document about this interface, for example, when and how the
method setInput() will be invoked. If I want to write my own Decompressor, what
do these methods mean in the interface?In the above case, I enable some debug
information, you can see that in this case, the byte[] array passed to setInput
method, only have 512 as the length, but the 3rd parameter of length passed in
is a negative number: -132967308. That caused the IndexOutOfBoundsException. If
I check the GzipDecompressor class of this method in the hadoop, the code will
also throw IndexOutoutBoundsException in this case, so this is a
RuntimeException case. Why it happened in my test case?
Here is my test case:
I have a simpel log text file about 700k. I encrypted it with above code using
'AES'. I can encrypted and decrypted to get my original content. The file name
is foo.log.crypto, this file extension is registered to invoke this
CryptoBasicDecompressor in my testing hadoop using CDH4.1.2 release (hadoop
2.0). Everything works as I expected. The CryptoBasicDecompressor is invoked
when the input file is foo.log.crypto, as you can see in the above stack trace.
But I don't know why the 3rd parameter (length) in setInput() is a negative
number at runtime.
In additional to it, I also have further questions related to use
Compressor/Decompressor to handle the encrypting/decrypting file. Ideally, I
wonder if the encrypting/decrypting can support file splits. This maybe depends
the algorithm we are using, is that right? If so, what kind of algorithm can do
that? I am not sure if it likes the compressor cases, most of them do not
support file split. If so, it maybe not good for my requirements.
If we have a 1G file, encrypted in the Amazone S3, after it copied to the HDFS
of Amazon EMR, can each block of the date be decrypted independently by each
mapper, then passed to the underline RecorderReader to be processed totally
concurrently? Does any one do this before? If so, what encryption algorithm
does support it? Any idea?
Thanks
Yong
