Android Socket Exception "socket is closed"

Question

When I try to run a test composed of an echo server and an android client with the following code, I always get the exception msg "socket is closed". This code can simply send msg to server, and receive msg from server, but if you want to do both at the same time, it just doesn't work... I am very curious why it will lead to this kind of problem, and how should I fix it if I want it to be able to first send msg to echo server

and then receive msg from echo server?

            // Server IP address 
            InetAddress serverIp;

            // try to connect Server
            try {

                // set up server IP address
                serverIp = InetAddress.getByName("192.168.17.1");

                // set up port
                int serverPort=12345;

                // initiate socket connection
                Socket clientSocket=new Socket(serverIp,serverPort);

                BufferedOutputStream out = new BufferedOutputStream(clientSocket.getOutputStream());
                out.write("Send From Android1111, stitch ".getBytes());
                out.flush();

                //wait to receive Server's msg 
                BufferedReader  br =new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); 

                total.toString();*/
            // Display received msg with Toast
                Toast.makeText(getApplicationContext(), br.readLine(), Toast.LENGTH_SHORT ).show();

            //close connection
                clientSocket.close();             

//              out.close();
//              out = null;
            } catch (IOException e) {
                // display exception with Toast
                Toast.makeText(getApplicationContext(),e.toString(), Toast.LENGTH_SHORT).show();
            }

---

unfortunately, it still doesn't work ...I followed your instruction and modify the code to:

            // set up Server IP address 
            serverIp = InetAddress.getByName("192.168.2.2");

            // set up Server port
            int serverPort=12345;

            // initiate socket connection
            Socket clientSocket=new Socket(serverIp,serverPort);

                // open input and output stream
            OutputStream out = clientSocket.getOutputStream();
            InputStream in = clientSocket.getInputStream();

            //send msg
            out.write("Send From Android1111, bitch ".getBytes());


                // receive msg from server
            byte[] buffer = new byte[in.available()];
            in.read(buffer);
            String rMsg = new String(buffer);
            Toast.makeText(getApplicationContext(), rMsg, Toast.LENGTH_LONG ).show();

            //close input and output stream
            in.close();
            out.close();

             //關閉連線
       clientSocket.close(); 
        } catch (IOException e) {
            // 出錯後顯示錯誤訊息Toast
            Toast.makeText(getApplicationContext(),e.toString(), Toast.LENGTH_SHORT).show();
        }

for helper's convenience, here's the python written code for server part:

# Practice Echo Server Program written in Python
import socket

# host = '' means it binds to any available interface
host = ''
port = 12345

# socket() function returns a socket object whose methods implement the various socket system calls.
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

# Bind the socket to address. 
s.bind((host,port))

# Listen for connections made to the socket. The backlog argument specifies 
# the maximum number of queued connections and should be at least 0; 
# the maximum value is system-dependent (usually 5), the minimum value is forced to 0.
s.listen(5)

# Accept a connection. The socket must be bound to an address and listening for 
# connections. The return value is a pair (conn, address) where conn is a new socket 
# object usable to send and receive data on the connection, and address is the address
# bound to the socket on the other end of the connection.
conn, addr = s.accept()
print 'Connected by', addr

# Receive data from the socket. The return value is a string representing the data received.
# The maximum amount of data to be received at once is specified by bufsize. See the Unix
# manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.
# Note For best match with hardware and network realities, the value of bufsize should be 
# a relatively small power of 2, for example, 4096.

while 1:
    data = conn.recv(1024)
    if not data: break 
    print 'received data is : ', repr(data)
    conn.send(data)

conn.close()

Answer 1

I assume you are doing the right things in the wrong order. May be the server is too fast and when you are trying to read the response it is already received and gone.

Following the rules presented in the tutorial Reading from and Writing to a Socket

1. Open a socket
2. Open an input stream and output stream to the socket.
3. Read from and write to the stream according to the server's protocol.
4. Close the streams.
5. Close the socket.

Do you see the difference? First open Input and Output stream and then start sending your request.

I am sure that if you stick to this order it will work.