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From "Sebb (Updated) (JIRA)" <>
Subject [jira] [Updated] (NET-73) [net][PATCH] hangs when socket data ends in a command sequence
Date Tue, 31 Jan 2012 13:02:10 GMT


Sebb updated NET-73:

    Affects Version/s: 1.4
        Fix Version/s: 2.0
> [net][PATCH] hangs when socket data ends in a command sequence
> -------------------------------------------------------------------------------------
>                 Key: NET-73
>                 URL:
>             Project: Commons Net
>          Issue Type: Bug
>    Affects Versions: 1.4
>         Environment: Operating System: other
> Platform: All
>            Reporter: Rob Hasselbaum
>             Fix For: 1.5, 2.0
>         Attachments: cmd-seq-hang.patch
> Background: If one calls in single-threaded mode (no 
> reader thread) and there is no data immediately available, the call blocks on 
> a socket read. When data starts to arrive, the stream adds all the available 
> bytes to its internal queue before returning the first one to the caller. To 
> do this, it calls __read() in a loop for as long as there are bytes available. 
> The __read() method returns the first byte of "user data" from the socket. If 
> __read() encounters a Telnet command sequence (IAC, WILL, WONT, DO, DONT, 
> etc.), it handles the negotiation transparently and then returns the first 
> byte of user data.
> In most cases, this works fine, but a problem arises if a chunk of data from 
> the remote host ends in a Telnet command sequence. When that happens, the 
> method hangs, even though it may have already 
> acquired some user data. This is because it calls __read() in a loop as long 
> as super.available() returns true. But if the remaining data from the socket 
> consists entirely of Telnet commands, __read() will process those AND THEN 
> BLOCK waiting for user data.
> Just checking super.available() is not sufficient. We should continue the loop 
> only if there are bytes of USER DATA still available from the socket. Not 
> doing this can cause the client to wait indefinitely.

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