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From "Jonathan Park (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-3280) ClientCnxn xid rollover can break sessions
Date Fri, 15 Feb 2019 21:50:00 GMT
Jonathan Park created ZOOKEEPER-3280:
----------------------------------------

             Summary: ClientCnxn xid rollover can break sessions
                 Key: ZOOKEEPER-3280
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3280
             Project: ZooKeeper
          Issue Type: Bug
          Components: java client
    Affects Versions: 3.4.12, 3.4.6
            Reporter: Jonathan Park
         Attachments: ZKOutOfOrder.java

 
{code:java}
181, unexpected error, closing socket connection and attempting reconnect
java.io.IOException: Xid out of order. Got Xid -3 with err 0 expected Xid -4 for a packet
with details: clientPath:null serverPath:null finished:false header:: -4,8 replyHeader:: 0,0,-4
request:: '/,F response:: v{} 
at org.apache.zookeeper.ClientCnxn$SendThread.readResponse(ClientCnxn.java:828)
at org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:94)
at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:366)
at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1143)
2019-02-15 13:40:22,520 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1027]
- Opening socket connection to server localhost/127.0.0.1:2181. Will not attempt to authenticate
using SASL (unknown error)
2019-02-15 13:40:22,521 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@877]
- Socket connection established to localhost/127.0.0.1:2181, initiating session
2019-02-15 13:40:22,521 [myid:] - DEBUG [main-SendThread(localhost:2181):ClientCnxn$SendThread@950]
- Session establishment request sent on localhost/127.0.0.1:2181
2019-02-15 13:40:22,522 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1301]
- Session establishment complete on server localhost/127.0.0.1:2181, sessionid = 0x168f2c5e9c60017,
negotiated timeout = 30000
2019-02-15 13:40:22,525 [myid:] - DEBUG [main-SendThread(localhost:2181):ClientCnxn$SendThread@742]
- Got ping response for sessionid: 0x168f2c5e9c60017 after 235329552ms
{code}
ClientCnxn xid's are tracked as java int's. For long-lived ZK clients this can lead to rollover
into the negative xid space. Xid = -4 is treated as a special xid reserved for auth requests.
With xid rollover, a normal ZK request can also have xid = -4 but the response will be treated
as an auth response making subsequent packet processing error with the exception above. We
can reproduce this more readily by changing the starting xid in ClientCnxn from 1 to -100.
The ZK client will transparently reconnect and establish a new session but features that depended
on the same session persisting will unnecessarily experience a disconnected event.

 

I've attached simple class with a main() method that reproduces the failure quickly against
a local ZK server after modifying the initial value of ClientCnxn.xid from 1 to -100. 

 



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