This is interesting, I will take it.

The calling code in DFSInputStream already takes into account where the end of the block is. See this code in DFSInputStream:

    if (pos <= targetPos && targetPos <= blockEnd) {
      //
      // If this seek is to a positive position in the current
      // block, and this piece of data might already be lying in
      // the TCP buffer, then just eat up the intervening data.
      //
      int diff = (int)(targetPos - pos);
      if (diff <= blockReader.available()) {
      ...

Notice that we don't call available if targetPos is beyond blockEnd

Also, RemoteBlockReader is deprecated. See the comment at the top:

/**
 * \@deprecated this is an old implementation that is being left around
 * in case any issues spring up with the new {\@link RemoteBlockReader2} implementation.
 * It will be removed in the next release.
 */

We should really fix RemoteBlockReader2 to support SOCKS sockets (those are the only ones without channels, as I recall) and remove RemoteBlockReader as the comment promised we'd do.

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12644364/HDFS-6369.patch
against trunk revision .

+1 @author. The patch does not contain any @author tags.

-1 tests included. The patch doesn't appear to include any new or modified tests.
Please justify why no new tests are needed for this patch.
Also please list what manual steps were performed to verify this patch.

+1 javac. The applied patch does not increase the total number of javac compiler warnings.

+1 javadoc. There were no new javadoc warning messages.

+1 eclipse:eclipse. The patch built with eclipse:eclipse.

+1 findbugs. The patch does not introduce any new Findbugs (version 1.3.9) warnings.

+1 release audit. The applied patch does not increase the total number of release audit warnings.

+1 core tests. The patch passed unit tests in hadoop-hdfs-project/hadoop-hdfs.

+1 contrib tests. The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/6878//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/6878//console

This message is automatically generated.

Hi Colin Patrick McCabe, thank you for the comments, I will update the patch.

As I said earlier, the calling code checks how many bytes are left in the block. So unless I'm missing something, doing this computation just creates extra work, but has no benefit. Another concern is that you only changed the deprecated RemoteBlockReader class, and not the RemoteBlockReader2 class which almost everyone has transitioned to.

How about we should just add a comment on available that it may return more than is actually present in the block? That will make it easier to read the code.

Thanks for this, Ted. Only one comment: I think it would make more sense to add this for the JavaDoc for the base class (BlockReader).

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12648536/hdfs-6369-v3.txt
against trunk revision .

+1 @author. The patch does not contain any @author tags.

-1 tests included. The patch doesn't appear to include any new or modified tests.
Please justify why no new tests are needed for this patch.
Also please list what manual steps were performed to verify this patch.

+1 javac. The applied patch does not increase the total number of javac compiler warnings.

+1 javadoc. There were no new javadoc warning messages.

+1 eclipse:eclipse. The patch built with eclipse:eclipse.

+1 findbugs. The patch does not introduce any new Findbugs (version 1.3.9) warnings.

+1 release audit. The applied patch does not increase the total number of release audit warnings.

+1 core tests. The patch passed unit tests in hadoop-hdfs-project/hadoop-hdfs.

+1 contrib tests. The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/7039//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7039//console

This message is automatically generated.

+1. No tests needed, since this is just a docs change.

committed, thanks.

SUCCESS: Integrated in Hadoop-trunk-Commit #5652 (See https://builds.apache.org/job/Hadoop-trunk-Commit/5652/)
HDFS-6369. Document that BlockReader#available() can return more bytes than are remaining in the block (Ted Yu via Colin Patrick McCabe) (cmccabe: http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1600801)

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java

FAILURE: Integrated in Hadoop-Yarn-trunk #575 (See https://builds.apache.org/job/Hadoop-Yarn-trunk/575/)
HDFS-6369. Document that BlockReader#available() can return more bytes than are remaining in the block (Ted Yu via Colin Patrick McCabe) (cmccabe: http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1600801)

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java

FAILURE: Integrated in Hadoop-Hdfs-trunk #1766 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk/1766/)
HDFS-6369. Document that BlockReader#available() can return more bytes than are remaining in the block (Ted Yu via Colin Patrick McCabe) (cmccabe: http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1600801)

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java

FAILURE: Integrated in Hadoop-Mapreduce-trunk #1793 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk/1793/)
HDFS-6369. Document that BlockReader#available() can return more bytes than are remaining in the block (Ted Yu via Colin Patrick McCabe) (cmccabe: http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1600801)

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java