[HDFS-7825] HdfsDataInputStream::read(ByteBuffer) method doesn't conform to its API

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Assignee: Unassigned
• Reporter: Sergey Shelukhin
• Created: 23/Feb/15 23:44
• Updated: 24/Feb/15 00:08
• Resolved: 24/Feb/15 00:04

Description

ByteBufferReadable::read(ByteBuffer) javadoc says:

After a successful call, buf.position() and buf.limit() should be unchanged, and therefore any data can be immediately read from buf. buf.mark() may be cleared or updated. 

I have the following code:

        ByteBuffer directBuf = ByteBuffer.allocateDirect(len);
        int pos = directBuf.position();

            int count = file.read(directBuf);
            if (count < 0) throw new EOFException();
            if (directBuf.position() != pos) {
              RecordReaderImpl.LOG.info("Warning - position mismatch from " + file.getClass()
                  + ": after reading " + count + ", expected " + pos + " but got " + directBuf.position());
            }

and I get:

15/02/23 15:30:56 [pool-4-thread-1] INFO orc.RecordReaderImpl : Warning - position mismatch from class org.apache.hadoop.hdfs.client.HdfsDataInputStream: after reading 6, expected 0 but got 6

So the position is changed, unlike the API doc indicates.

Also, while I haven't verified yet, it may be that the 0-length read is not handled properly.