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pcgallagher 12-27-2008 04:50 AM

Sockets: Why a Connection reset exception on Windows but not on Linuxwhen a client disconnects from a server
 
I'm curious why I get a Connection reset exception when I run this
code on Windows but not on Linux.

It's a client and a server communicating through a socket. The
exception occurs on the server when the client terminates suddenly.
It's ordinary client-server code, but I'll include it for
illustration.

It make sense that the exception occurs - the server is waiting for
the client to send a command, but the client suddenly terminates.
What's odd is that the exception occurs on Windows but not on Linux.

Here are the results on the server side, when run on Windows Vista:

Accepting clients now
Client acquired on port #7777, reading from socket
Hi
java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(Unknown Source)
at sun.nio.cs.StreamDecoder.readBytes(Unknown Source)
at sun.nio.cs.StreamDecoder.implRead(Unknown Source)
at sun.nio.cs.StreamDecoder.read(Unknown Source)
at java.io.InputStreamReader.read(Unknown Source)
at java.io.BufferedReader.fill(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at Server.serviceClient(Server.java:31)
at Server.main(Server.java:51)



Here are the results when run on Linux:

Accepting clients now
Client acquired on port #7777, reading from socket
Hi
Client serviced



Here's the code for the Server and the Client.
Server.java:


import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

private ServerSocket serverSocket;
private BufferedReader bufferedReader;

public Server(int port) throws java.io.IOException {
serverSocket = new ServerSocket(port);
}

/**
* serviceClient accepts a client connection and reads lines from
the socket.
* Each line is handed to executeCommand for parsing and
execution.
*/
public void serviceClient() throws java.io.IOException {
System.out.println("Accepting clients now");
Socket clientConnection = serverSocket.accept();
// Arrange to read input from the Socket
InputStream inputStream = clientConnection.getInputStream();
bufferedReader = new BufferedReader(new InputStreamReader
(inputStream));
// Arrange to write result across Socket back to client
OutputStream outputStream = clientConnection.getOutputStream
();
PrintStream printStream = new PrintStream(outputStream);

System.out.println("Client acquired on port #" +
serverSocket.getLocalPort() + ", reading from socket");

String commandLine;
while ((commandLine = bufferedReader.readLine()) != null) {
try {
System.out.println(commandLine);
} catch (Exception ex) {
System.out.println("ERROR: " + ex);
}
}
}


public static void main(String argv[]) {
int port = 1099;
if (argv.length > 0) {
try {
port = Integer.parseInt(argv[0]);
} catch (Exception e) {
}
}
try {
Server server = new Server(port);
server.serviceClient();
System.out.println("Client serviced");
} catch (Exception ex) {
ex.printStackTrace();
}
}
}




Client.java:

public class Client {
public static void main(String[] args) {
try {
// parse command line arguments
String host = args[0];
int port = Integer.parseInt(args[1]);
SocketWriter sw = new SocketWriter(host, port);
sw.sayHi();
} catch (Exception ae) {
System.out.println("An exception occurred");
ae.printStackTrace();
}
}
}



SocketWriter.java:

import java.io.*;
import java.net.Socket;

class SocketWriter {


private Socket socket;
private PrintStream printStream;
private BufferedReader inputReader;


SocketWriter(String host, int port) throws java.io.IOException {
socket = new Socket(host, port);
OutputStream outputStream = socket.getOutputStream();
printStream = new PrintStream(outputStream);
InputStream inputStream = socket.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader
(inputStream);
inputReader = new BufferedReader(inputStreamReader);
}

void sayHi() {
printStream.println("Hi");
}
}


---
Paul

Michael Rauscher 12-27-2008 03:17 PM

Re: Sockets: Why a Connection reset exception on Windows but noton Linux when a client disconnects from a server
 
pcgallagher wrote:
> I'm curious why I get a Connection reset exception when I run this
> code on Windows but not on Linux.
>
> It's a client and a server communicating through a socket. The
> exception occurs on the server when the client terminates suddenly.
> It's ordinary client-server code, but I'll include it for
> illustration.
>
> It make sense that the exception occurs - the server is waiting for
> the client to send a command, but the client suddenly terminates.


At first, there should be no exception since the client doesn't
terminate suddenly. It finishes its work and should disconnect from the
server (behind the scenes).

Try to close the streams explicitly in SocketWriter and try it again.

Bye
Michael

Mark Space 12-27-2008 08:06 PM

Re: Sockets: Why a Connection reset exception on Windows but noton Linux when a client disconnects from a server
 
pcgallagher wrote:
> I'm curious why I get a Connection reset exception when I run this
> code on Windows but not on Linux.


I re-jiggered your code very slightly to make it an SSCCE, I don't get
an exception. Instead, the server hangs waiting for more input, because
the client doesn't send any more data or close the socket.


debug:
Accepting clients now
Client acquired on port #1099, reading from socket
Hi


And hangs there. I didn't investigate this further, since I did make
changes. You may want to try this code, and report back. If your
behavior is different, then there's some sort of environmental
difference in Windows set-up. I'm running Vista, SP1, I think, within
NetBeans IDE.

This code is now a single file SSCCE. Cut, paste, run.


/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

package socketweirdness;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;


public class Main {

static final int DEFAULT_PORT = 1099;

/**
* @param args the command line arguments
*/
public static void main( final String[] args) throws
InterruptedException {
ServerThread st = new ServerThread( args );
st.start();
Thread.sleep( 500 ); // wait a bit for server to start
Client.main( args );
}
static class ServerThread extends Thread
{
private final String [] args;
ServerThread( final String[] args ) {
this.args = args;
}
@Override
public void run() {
Server.main( args );
}
}

}

//import java.io.*;
//import java.net.ServerSocket;
//import java.net.Socket;

//public class Server
class Server {

private ServerSocket serverSocket;
private BufferedReader bufferedReader;

public Server(int port) throws java.io.IOException {
serverSocket = new ServerSocket(port);
}

/**
* serviceClient accepts a client connection and reads lines from
the socket.
* Each line is handed to executeCommand for parsing and
execution.
*/
public void serviceClient() throws java.io.IOException {
System.out.println("Accepting clients now");
Socket clientConnection = serverSocket.accept();
// Arrange to read input from the Socket
InputStream inputStream = clientConnection.getInputStream();
bufferedReader = new BufferedReader(new InputStreamReader
(inputStream));
// Arrange to write result across Socket back to client
OutputStream outputStream = clientConnection.getOutputStream
();
PrintStream printStream = new PrintStream(outputStream);

System.out.println("Client acquired on port #" +
serverSocket.getLocalPort() + ", reading from socket");

String commandLine;
while ((commandLine = bufferedReader.readLine()) != null) {
try {
System.out.println(commandLine);
} catch (Exception ex) {
System.out.println("ERROR: " + ex);
}
}
}


public static void main(String argv[]) {
int port = Main.DEFAULT_PORT;
if (argv.length > 0) {
try {
port = Integer.parseInt(argv[0]);
} catch (Exception e) {
}
}
try {
Server server = new Server(port);
server.serviceClient();
System.out.println("Client serviced");
} catch (Exception ex) {
ex.printStackTrace();
}
}
}




//Client.java:

//public class Client {
class Client {
public static void main(String[] args) {
try {
String host = "localhost";
int port = Main.DEFAULT_PORT;
if( args.length >= 2 ) {
// parse command line arguments
host = args[0];
port = Integer.parseInt(args[1]);
}
SocketWriter sw = new SocketWriter(host, port);
sw.sayHi();
} catch (Exception ae) {
System.out.println("An exception occurred");
ae.printStackTrace();
}
}
}



//SocketWriter.java:

//import java.io.*;
//import java.net.Socket;

class SocketWriter {


private Socket socket;
private PrintStream printStream;
private BufferedReader inputReader;


SocketWriter(String host, int port) throws java.io.IOException {
socket = new Socket(host, port);
OutputStream outputStream = socket.getOutputStream();
printStream = new PrintStream(outputStream);
InputStream inputStream = socket.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader
(inputStream);
inputReader = new BufferedReader(inputStreamReader);
}

void sayHi() {
printStream.println("Hi");
}
}





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