Uploaded image for project: 'ZooKeeper'
  1. ZooKeeper
  2. ZOOKEEPER-3280

ClientCnxn xid rollover can break sessions



    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Duplicate
    • Affects Version/s: 3.4.6, 3.4.12
    • Fix Version/s: None
    • Component/s: java client
    • Labels:



      2019-02-15 13:40:21,471 [myid:] - DEBUG [main-SendThread(localhost:2181):ClientCnxn$SendThread@759] - Got auth sessionid:0x168f2c5e9c60017
      2019-02-15 13:40:21,472 [myid:] - WARN  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1166] - Session 0x168f2c5e9c60017 for server localhost/0:0:0:0:0:0:0:1:2181, 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$SendThread@1027] - Opening socket connection to server localhost/ Will not attempt to authenticate using SASL (unknown error)
      2019-02-15 13:40:22,521 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@877] - Socket connection established to localhost/, initiating session
      2019-02-15 13:40:22,521 [myid:] - DEBUG [main-SendThread(localhost:2181):ClientCnxn$SendThread@950] - Session establishment request sent on localhost/
      2019-02-15 13:40:22,522 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1301] - Session establishment complete on server localhost/, 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

      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. 



        1. ZKOutOfOrder.java
          1 kB
          Jonathan Park

          Issue Links



              • Assignee:
                parkjsung Jonathan Park
              • Votes:
                0 Vote for this issue
                4 Start watching this issue


                • Created: