Java SSL Socket Communication - Both Sending and Receiving

Question

Consider the client send a message to the server, then the server replies to the client.

Client code

public void run() {
    try {
        SSLSocketfactory f = (SSLSocketFactory) SSLSocketFactory.getDefault();
        SSLSocket socket = (SSLSocket) f.createSocket(Common.JSON_SERVER_IP, Integer.parseInt(Common.JSON_SERVER_PORT));
        String[] suites = socket.getSupportedCipherSuites();
        socket.setEnabledCipherSuites(suites);

        Log.i("Socket", "Created");
        DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
        File f = new File(Common.PATH, Common.JSON_FILE_NAME);
        FileInputStream fis = new FileInputStream(f);

        byte sendBytes[] = new byte[1024];
        int fileSize = 0;
        int length = 0;

        // Data Send Start!
        while ((length = fis.read(sendBytes, 0, sendBytes.length)) > 0) {
            fileSize += length;
            dos.write(sendBytes, 0, length);
            dos.flush();
        }

        Log.i("Socket", "Data Send Finish");
        final int final_fileSize = fileSize;
        activity.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(activity.getApplicationContext(), "JSON File Size :" + final_fileSize + "Bytes", Toast.LENGTH_SHORT).show();
            }
        });

        Log.i("Socket", "Output Close");
        // Data Receive Start!
        InputStream is = socket.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));

        // receive the response from Server
        String reply = "";
        String str = "JSON";
        Log.i("Socket", "Receive Ready");
        /* Example result from Server 
        {
            "ret":[{"id":"COM_DATA_002","errCd":0, "errMsg":""}],
            "Value":[{"updateType":0, "fileURL":"http://127.0.0.1/filePath"}]
        }*/
        while ((reply = br.readLine()) != null) {
            Log.i("Socket", "Parsing");
            Object obj_p=JSONValue.parse(reply);
            JSONObject obj_j=(JSONObject)obj_p;
            Object target = obj_j.get("Value");
            JSONArray obj_value = (JSONArray)target;
            JSONObject url_val=(JSONObject)obj_value.get(0);
            String url = (String)url_val.get("fileURL");
            URL urlDB = new URL(url);
            URLConnection getDB = urlDB.openConnection();
            // Get New DB or query
        }
        Log.i("Socket", "File Get");
        if(str.length() != 0) {
            str = "[" + Common.getDateCurrentTimeZone(System.currentTimeMillis()) + "]\n" + str + "\n"; 
            Log.i(Common.TAG, str);
        }

        final String text = str;
        is.close();
        br.close();

    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (dos != null)
            try {
                dos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        if (fis != null)
            try {
                fis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        if (socket != null)
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
    }
}

Server Code

public void run() {
    String fileName = "JSON.txt";

    try {
        // receive file
        receiveFile(fileName);

        // load receive file
        File file = new File(Common.defaultReceivedData, fileName);
        BufferedReader in = new BufferedReader(new FileReader(file));
        // String SendfileName = "ClientVersion.txt";
        String SendfileName = "Return.txt";
        File SendFile = new File(Common.defaultSendData, SendfileName);
        String s;
        Object obj;
        JSONObject obj2;
        String det;

        // File write and send...

        in.close();

    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void receiveFile(String fileName) throws IOException{

    int length = 0;
    int size = 0;

    DataInputStream dis = new DataInputStream(send.getInputStream());
    fileName = "JSON.txt";
    FileOutputStream fos = new FileOutputStream(new File(Common.defaultReceivedData, fileName));

    byte[] inputByte = new byte[1024];
    while ((length = dis.read(inputByte, 0, inputByte.length)) > 0) {
        System.out.println(length);
        size += length;
        fos.write(inputByte, 0, length);
        fos.flush();
    }
    fos.close();
    System.out.println("Received JSON data! [FileSize: " + size + "]");
}

When the client sends a message to the server, the communication stuck.

Client

03-11 15:38:46.476: I/Socket(30160): Created
03-11 15:38:46.606: I/Socket(30160): Data Send Finish
03-11 15:38:46.606: I/Socket(30160): Output Close
03-11 15:38:46.616: I/Socket(30160): Receive Ready

Server

Client is connected: IP is xxx.xxx.xxx.xxx
57

In this code, the server completes receiving the message only after the client has stopped. What can be done in order to complete this communication normally?

Answer 1

The server is reading the file from the socket until end of stream.

The client doesn't close the connection, instead it tries to read a response from the server, again until end of stream.

So neither peer has closed the connection, so end of stream never arrives, so both sides are blocked in read, so you have implemented a networked deadlock.

You need to send the length of the file ahead of the file, so that the server knows when to stop reading.

Or, if you're only going to send one file per connection, the client could shutdown the connection for output, which would give the server the EOS it is looking for, whereupon its read loop would terminate, it would send its reply, and then close the connection, which would give the client the EOS it is looking for, so it would fall out of its read loop and close the connection.