[ZOOKEEPER-737] some 4 letter words may fail with netcat (nc)

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 3.3.0
• Fix Version/s: 3.3.1, 3.4.0
• Component/s: server
• Hadoop Flags: Reviewed
• Assignee: Mahadev Konar
• Reporter: Patrick D. Hunt
• Created: 10/Apr/10 21:13
• Updated: 29/Dec/11 23:08
• Resolved: 04/May/10 21:51

Description

nc closes the write channel as soon as it's sent it's information, for example "echo stat|nc localhost 2181"
in general this is fine, however the server code will close the socket as soon as it receives notice that nc has
closed it's write channel. if not all the 4 letter word result has been written back to the client yet, this will cause
some or all of the result to be lost - ie the client will not see the full result. this was introduced in 3.3.0 as part
of a change to reduce blocking of the selector by long running 4letter words.

here's an example of the logs from the server during this

echo -n stat | nc localhost 2181
2010-04-09 21:55:36,124 - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn$Factory@251] - Accepted socket connection from /127.0.0.1:42179
2010-04-09 21:55:36,124 - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@968] - Processing stat command from /127.0.0.1:42179
2010-04-09 21:55:36,125 - WARN [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@606] - EndOfStreamException: Unable to read additional data from client sessionid 0x0, likely client has closed socket
2010-04-09 21:55:36,125 - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@1286] - Closed socket connection for client /127.0.0.1:42179 (no session established for client)
[phunt@gsbl90850 zookeeper-3.3.0]$ 2010-04-09 21:55:36,126 - ERROR [Thread-15:NIOServerCnxn@422] - Unexpected Exception:
java.nio.channels.CancelledKeyException
at sun.nio.ch.SelectionKeyImpl.ensureValid(SelectionKeyImpl.java:55)
at sun.nio.ch.SelectionKeyImpl.interestOps(SelectionKeyImpl.java:59)
at org.apache.zookeeper.server.NIOServerCnxn.sendBuffer(NIOServerCnxn.java:395)
at org.apache.zookeeper.server.NIOServerCnxn$SendBufferWriter.checkFlush(NIOServerCnxn.java:907)
at org.apache.zookeeper.server.NIOServerCnxn$SendBufferWriter.flush(NIOServerCnxn.java:945)
at java.io.BufferedWriter.flush(BufferedWriter.java:236)
at java.io.PrintWriter.flush(PrintWriter.java:276)
at org.apache.zookeeper.server.NIOServerCnxn$2.run(NIOServerCnxn.java:1089)
2010-04-09 21:55:36,126 - ERROR [Thread-15:NIOServerCnxn$Factory$1@82] - Thread Thread[Thread-15,5,main] died
java.nio.channels.CancelledKeyException
at sun.nio.ch.SelectionKeyImpl.ensureValid(SelectionKeyImpl.java:55)
at sun.nio.ch.SelectionKeyImpl.interestOps(SelectionKeyImpl.java:64)
at org.apache.zookeeper.server.NIOServerCnxn$SendBufferWriter.wakeup(NIOServerCnxn.java:927)
at org.apache.zookeeper.server.NIOServerCnxn$SendBufferWriter.checkFlush(NIOServerCnxn.java:909)
at org.apache.zookeeper.server.NIOServerCnxn$SendBufferWriter.flush(NIOServerCnxn.java:945)
at java.io.BufferedWriter.flush(BufferedWriter.java:236)
at java.io.PrintWriter.flush(PrintWriter.java:276)
at org.apache.zookeeper.server.NIOServerCnxn$2.run(NIOServerCnxn.java:1089)

Issue Links

• relates to: ZOOKEEPER-805 four letter words fail with latest ubuntu nc.openbsd
• relates to: ZOOKEEPER-1346 Add Jetty HTTP server support for four letter words.