Java-关闭套接字会产生不同的结果

Question

I'm getting different results while trying to read from a socket while the other socket is closed.

I have two sockets A and B.

1)B sent some data to A --> A has read the data --> A closes --> When B tries to read some data from A, it is getting -1(or EOF).

2)B sent some data to A --> A closes even before reading the data --> Now B tries to read from A, an exception is thrown(java.net.SocketException "Software caused connection abort.")

please excuse me, if you can't understand my question. Please see the code

Server.java

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


class SocketCloser extends Thread
{
    private Socket c;
    public SocketCloser(Socket c) {
        this.c = c;
    }

    public void run()  {

        try{
            this.c.close();
        } catch (Exception e) {}
    }
}


public class Server
{
    public static void main(String argv[]) throws Exception {
        ServerSocket listen = new ServerSocket(6789);

        Socket socket = listen.accept();
        SocketCloser sc = new SocketCloser(socket);
        InputStream is = socket.getInputStream();
        // uncomment below line to get "Software caused connection abort" on client
        //sc.start();
        try {
            Thread.sleep(1000);
            int i = is.read();
            System.out.println("read returned: " + i);
            socket.close();
        } catch (Exception e) {
            System.out.println(e.toString() + " thrown");
        }
    }
}

Client.java

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

public class Client
{
    public static void main(String argv[])
    {
        Socket cSocket;
        try {
            cSocket = new Socket("localhost", 6789);
            InputStream is = cSocket.getInputStream();
            OutputStream os = cSocket.getOutputStream();
            Thread.sleep(1000);
            os.write(200);
            Thread.sleep(1000);
            int i = is.read();
            System.out.println("read returned: " + i);
            cSocket.close();
        } catch (Exception e) {
            System.out.println(e.toString() + " thrown");
        }
    }
}

Can someone please help me figure out why there is an exception in one case and -1 in another. Interestingly on linux both the cases resulted in -1.

Answer 1

1) Because B established a connection, A goes to CLOSE_WAIT. It will be in that state until B closes the connection. There is nothing to read, so the read() call on B's InputStream returns -1.

2) A is blocked in the accept call. The other thread is trying to close the socket, but it can't because accept is blocking it. When B connects, accept unblocks and the socket closes outright. When B tries to read, the socket is not there anymore so you get the exception.

I'm simplifying a bit, but that's the gist of it.

Answer 2

1)B sent some data to A --> A has read the data --> A closes --> When B tries to read some data from A, it is getting -1(or EOF).

I agree. What did you expect? This is the expected behaviour.

2)B sent some data to A --> A closes even before reading the data --> Now B tries to read from A, an exception is thrown(java.net.SocketException "Software caused connection abort.")

I agree. This is one of the expected behaviours in this incorrect situation. What did you expect?

please excuse me, if you can't understand my question.

There is no question here to understand. You haven't asked a question. You close a socket without sending any data and the peer gets EOS without receiving any data. You close a socket while the peer is sending and the peer gets an exception. System is working as designed.