How to fix "Exception in thread "main" java.net.SocketException: Connection reset"

Question

I am trying to set up a java program that would send and receive a file.

I know there are similar things for this problem on this website, but I was having trouble after reading those.

I followed this video: https://www.youtube.com/watch?v=WeaB8pAGlDw&ab_channel=Thecodersbay

It worked in his video, and I am not sure what I did wrong. The first java file runs just fine, but when I try to run the second I get this error:

Exception in thread "main" java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(Unknown Source)
    at java.net.SocketInputStream.read(Unknown Source)
    at fileSender.fileclient.main(fileclient.java:19)

I tried using some other ports, but that did not solve the problem.

Here is what I have right now:

The fileserver file:

package fileSender;

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

public class fileserver 
{
private static ServerSocket s;
private static FileInputStream fr;

public static void main(String[] args) throws Exception
{
    s = new ServerSocket(1418);
    Socket sr = s.accept();   //accept the connection

    fr = new FileInputStream("C:\\Users\\Anon\\Desktop\\folder\\testfile.txt");
    byte b[] = new byte[2002];   //before reading, a byte has to be declared. byte data includes the size of the file. if the size is unknown, use a random one I guess 
    fr.read(b, 0, b.length);   //the byte b, start reading the file at 0, and stop reading at the end of it. read from start to finish, and store it as b 

    OutputStream os = sr.getOutputStream();   
    os.write(b, 0, b.length);   //b variable will be sent with this. again, starts at 0, and ends at the length of the byte b 


}

}

This is the client file:

package fileSender;

import java.io.*;   //the whole thing
import java.net.*; 

public class fileclient 
{
private static Socket sr;
private static FileOutputStream fr;

public static void main(String[] args) throws Exception
{
    byte []b = new byte[2002];   //size from earlier. what the person gets 

    sr = new Socket("localhost",1418);
    InputStream is = sr.getInputStream();   //capturing the stream

    fr = new FileOutputStream("C:\\Users\\Anon\\Desktop\\testfile.txt");
    is.read(b, 0, b.length);   //will capture the stream of "is". again, whole file, 0 to end 

    fr.write(b, 0, b.length);   //writes the whole content into a file 

}
}

I tried to comment a lot so that I can make sense of things.

Thanks in advance :)

Answer 1

So, Connection Reset means that the socket was closed from the other end. This is quite logical considering what your "server" is doing.

When the client connects, your server is accepting the connection, reading up to 2002 bytes from a file, sending it to the client and terminating the application. At that point the socket sr will just be closed together with the rest of the application's resources. At this point, the client which is still reading from the InputStream would get notified that the socket is no longer valid, and that exception is thrown.

You should check whether testfile.txt is written successfully or not. It might be OK, although I wouldn't have the server disconnect so abruptly. I would let the client close gracefully, or timeout the client connection after inactivity, because you might risk getting that Connection Reset error before reading all the data from the TCP buffers. (TCP Errors tend to be communicated faster.)