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From "Vincent Bories-Azeau (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (NET-596) NullPointerException when disconnecting TelnetClient twice with JDK 7
Date Tue, 05 Jul 2016 17:31:11 GMT

     [ https://issues.apache.org/jira/browse/NET-596?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Vincent Bories-Azeau updated NET-596:
-------------------------------------
    Description: 
When using the TelnetClient class, a {{NullPointerException}} may occur when calling the {{disconnect}}
method twice, in the {{_closeOutputStream}} method called under the hood, if the Telnet connection
is lost (for instance, server is hardly shut down).

1. The first call to {{disconnect}} resets completely the TelnetClient instance.
2. The second call to {{disconnect}} leads to the NPE exception, because the {{\_output\_}}
property is {{null}}, in the {{_closeOutputStream}} method.

*NOTE: the NPE does not occur with JDK 8, because, the first call to {{disconnect}} throws
an I/O exception (socket is closed), leaving the TelnetClient instance with a non-null {{\_output\_}}
property. Then a second call to disconnect does not throw a NPE. It seems the JDK 8 behaves
differently when a client socket loses a connection. So there is also a bug with JDK 8, as
disconnection shall close quietly resources without an I/O exception, and without leaving
non-null resources, and then disconnect the client socket. The {{SocketClient.disconnect}}
is a good implementation to start with.*

The problem is that the TelnetOutputStream class closes the Socket output stream under the
hood, but doesn't check if it is null and doesn't reset it to null once done. _The implementation
of the TelnetOutputStream is quite strange, as there is a cycling dependency between this
class and the TelnetClient class. The {{TelnetClient}} class shall handle itself the close
of its internal resources, and disconnect the client socket. But this responsibility is delegates
to the TelnetOutputStream._

Here's the stack trace of the NPE exception:
{quote}
|java.lang.NullPointerException
     at org.apache.commons.net.telnet.TelnetClient._closeOutputStream(TelnetClient.java:83)
      at org.apache.commons.net.telnet.TelnetOutputStream.close(TelnetOutputStream.java:163)
      at org.apache.commons.net.telnet.TelnetClient.disconnect(TelnetClient.java:124)
{quote}

A way to workaround this bug, is to always check if the {{TelnetClient}} instance is connected,
before calling the {{disconnect}} method.


  was:
When using the TelnetClient class, a {{NullPointerException}} may occur when calling the {{disconnect}}
method twice, in the {{_closeOutputStream}} method called under the hood, if the Telnet connection
is lost (for instance, server is hardly shut down).

1. The first call to {{disconnect}} resets completely the TelnetClient instance.
2. The second call to {{disconnect}} leads to the NPE exception, because the {{\_output\_}}
property is {{null}}, in the {{_closeOutputStream}} method.

*NOTE: the NPE does not occur with JDK 8, because, the first call to {{disconnect}} throws
an I/O exception (socket is closed), leaving the TelnetClient instance with a non-null {{\_output\_}}
property. Then a second call to disconnect does not throw a NPE. It seems the JDK 8 behaves
differently when a client socket loses a connection. So there is also a bug with JDK 8, as
disconnection shall close quietly resources without an I/O exception, and without leaving
non-null resources, and then disconnect the client socket. The {{SocketClient.disconnect}}
is a good implementation to start with.*

The problem is that the TelnetOutputStream class closes the Socket output stream under the
hood, but doesn't check if it is null and doesn't reset it to null once done. _The implementation
of the TelnetOutputStream is quite strange, as there is a cycling dependency between this
class and the TelnetClient class. The {{TelnetClient}} class shall handle itself the close
of its internal resources, and disconnect the client socket. But this responsibility is delegates
to the TelnetOutputStream._

Here's the stack trace of the NPE exception:
{quote}
|java.lang.NullPointerException
     at org.apache.commons.net.telnet.TelnetClient._closeOutputStream(TelnetClient.java:83)
      at org.apache.commons.net.telnet.TelnetOutputStream.close(TelnetOutputStream.java:163)
      at org.apache.commons.net.telnet.TelnetClient.disconnect(TelnetClient.java:124)
{quote}



> NullPointerException when disconnecting TelnetClient twice with JDK 7
> ---------------------------------------------------------------------
>
>                 Key: NET-596
>                 URL: https://issues.apache.org/jira/browse/NET-596
>             Project: Commons Net
>          Issue Type: Bug
>          Components: Telnet
>    Affects Versions: 3.5
>         Environment: Both telnet client & server with JDK 7.
> Bug not reproduced with JDK 8 (there's another bug with this JDK though, as mentioned
in the description).
>            Reporter: Vincent Bories-Azeau
>
> When using the TelnetClient class, a {{NullPointerException}} may occur when calling
the {{disconnect}} method twice, in the {{_closeOutputStream}} method called under the hood,
if the Telnet connection is lost (for instance, server is hardly shut down).
> 1. The first call to {{disconnect}} resets completely the TelnetClient instance.
> 2. The second call to {{disconnect}} leads to the NPE exception, because the {{\_output\_}}
property is {{null}}, in the {{_closeOutputStream}} method.
> *NOTE: the NPE does not occur with JDK 8, because, the first call to {{disconnect}} throws
an I/O exception (socket is closed), leaving the TelnetClient instance with a non-null {{\_output\_}}
property. Then a second call to disconnect does not throw a NPE. It seems the JDK 8 behaves
differently when a client socket loses a connection. So there is also a bug with JDK 8, as
disconnection shall close quietly resources without an I/O exception, and without leaving
non-null resources, and then disconnect the client socket. The {{SocketClient.disconnect}}
is a good implementation to start with.*
> The problem is that the TelnetOutputStream class closes the Socket output stream under
the hood, but doesn't check if it is null and doesn't reset it to null once done. _The implementation
of the TelnetOutputStream is quite strange, as there is a cycling dependency between this
class and the TelnetClient class. The {{TelnetClient}} class shall handle itself the close
of its internal resources, and disconnect the client socket. But this responsibility is delegates
to the TelnetOutputStream._
> Here's the stack trace of the NPE exception:
> {quote}
> |java.lang.NullPointerException
>      at org.apache.commons.net.telnet.TelnetClient._closeOutputStream(TelnetClient.java:83)
>       at org.apache.commons.net.telnet.TelnetOutputStream.close(TelnetOutputStream.java:163)
>       at org.apache.commons.net.telnet.TelnetClient.disconnect(TelnetClient.java:124)
> {quote}
> A way to workaround this bug, is to always check if the {{TelnetClient}} instance is
connected, before calling the {{disconnect}} method.



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