[jira] [Commented] (NET-596) NullPointerException when disconnecting TelnetClient twice with JDK 7

["Gary Gregory (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/NET-596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15362875#comment-15362875 ] 

Gary Gregory commented on NET-596:
----------------------------------

How about something like:

{code:java}
### Eclipse Workspace Patch 1.0
#P commons-net
Index: src/main/java/org/apache/commons/net/telnet/TelnetClient.java
===================================================================
--- src/main/java/org/apache/commons/net/telnet/TelnetClient.java	(revision 1751512)
+++ src/main/java/org/apache/commons/net/telnet/TelnetClient.java	(working copy)
@@ -80,7 +80,10 @@
     }
     void _closeOutputStream() throws IOException
     {
-        _output_.close();
+        if (_output_!= null) 
+        {
+            _output_.close();
+        }
     }
 
     /***
@@ -120,9 +123,11 @@
         try {
             if (__input != null) {
                 __input.close();
+                __input = null;
             }
             if (__output != null) {
                 __output.close();
+                __output = null;
             }
         } finally { // NET-594
             super.disconnect();
{code}

> 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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