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Newsgroups: comp.lang.java.programmer
Date: Fri, 31 May 2019 20:13:37 -0700 (PDT)
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Subject: Re: server-side Socket does not recognize broken connection.
From: trisha guillot <guillottrisha347@gmail.com>
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Xref: csiph.com comp.lang.java.programmer:38975

On Wednesday, May 29, 2019 at 4:03:29 AM UTC-7, Andreas Leitgeb wrote:
> I have a ServerSocket on some port. whenever ".accept()" returns a
> connection, it goes to a loop that (among doing other stuff) polls
> the socket's input stream's ".available()" and if it returns > 0
> it reads and processes that data.  (SSCCE at end of post)
> 
> A client (e.g. using plain old "telnet" on unix) connects, types a
> bit, then breaks the connection using Ctrl-] and "close", and is back
> on the shell. (closing the terminal window that's running telnet
> has same effect, ditto killing the telnet process - apparently
> whatever breaks, or even properly shuts down the connection from
> client side.)
> 
> The Socket on server side, however keeps reporting 0 on .available(),
> rather than throwing some exception for the broken socket.
> 
> Single stepping the .available() method (class AbstractPlainSocketImpl)
> shows that it just never receives the ConnectionResetException, and thus
> won't ever get to throw new IOException("Stream closed.") itself.
> Field resetState never changes away from CONNECTION_NOT_RESET.
> 
> What am I doing wrong wrt. EOF-detection in ".available()" ?
> 
> PS: The real code does more interesting stuff while no input is available,
> so it cannot wait blockingly.  The real code also has other exits from the
> loop (based on input received), but that's not relevant for this SSCCE.
> 
> PS: unlike most of my recent posts, this one is *not* Java11-related.
> 
> 
> SSCCE:  ServerTest.java
> 
> import javax.net.ServerSocketFactory;
> import java.net.ServerSocket;
> import java.net.Socket;
> import java.io.InputStream;
> import java.io.IOException;
> 
> public class ServerTest {
>    public static void main(String[] args) throws IOException,InterruptedException {
> 
>       ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(65432);
>       Socket clientSocket = serverSocket.accept();
>       InputStream is = clientSocket.getInputStream();
> 
>       while (true) {
>          if (is.available() > 0) {
>             System.out.println( is.read() );
>          }
>          Thread.sleep(100);
>       }
>    }
> }