Receive file via socket, TCP connection freezes

Question

I have stucked for 4h already with the sockets, the way I am using is is that there is only one application as client and server, once the client connect it is opening the theard with new client and waiting for message.

Once the message is send to the server, the client will receive respond, that part is working without any problems.

Part of the Client Theard:

while (true)
        {
            InputStreamReader IR = new InputStreamReader(clientSocket.getInputStream());
            BufferedReader BR = new BufferedReader(IR);
            PrintStream PS = new PrintStream(clientSocket.getOutputStream());
            String message = BR.readLine();
            if (message != null)
            {
                System.out.println(clientSocket.getInetAddress() + ":" + clientSocket.getPort() + " has connected."+message);
                if (message.equals("exit"))
                {
                    PS.println("Exiting...");
                    exit();
                }
                else if (message.equals("list"))
                {
                    getList(PS);
                }
                else if ((message.contains("get") && (message.contains(",") && (message.contains(" ")))))
                {
                    String[] spliter = message.split(" ");
                    String[] file = spliter[1].split(",");
                    String file_name = file[0];
                    String file_md5 = file[1];
                    getFile(file_name, file_md5, clientSocket);
                }
            }
            else
            {
                break;
            }

        }

There are 2 messages that the server is supporting, the first one is "list" and the send one command is "get with values".

if client will request command "list" it will run this: There is a "server/client", it is sending request and receive the one line string and it is working without any problem, I am receiving the list of files from the server.

PrintStream PS = new PrintStream(clientSocket.getOutputStream());
        PS.println("list");
        InputStreamReader IR = new InputStreamReader(clientSocket.getInputStream());
        BufferedReader BR = new BufferedReader(IR);
        String lista_plikow = BR.readLine();
        if ( lista_plikow != null)
        {
            return lista_plikow;
        }

But I have problems to send the files over the sockets using code found on stackoverflow, but the "receiving" is not working, there is my receive function, the loop is always as 0 (even if first bytes length is correct), but the length of the bytes is correct, it is using newly created file but nothing is happening, the file is always on use, and has 0 bytes instead of content of the PS.println.

PrintStream PS = new PrintStream(clientSocket.getOutputStream());
    PS.println("get "+filename+","+file_md5);
    int bytesRead;
    int current = 0;
    FileOutputStream fos = null;
    BufferedOutputStream bos = null;
    try
    {
        byte [] mybytearray  = new byte [Integer.parseInt(size)];
        InputStream is = clientSocket.getInputStream();
        fos = new FileOutputStream(filename + ".recived");
        bos = new BufferedOutputStream(fos);
        bytesRead = is.read(mybytearray,0,mybytearray.length);
        current = bytesRead;
        System.out.println("X" + bytesRead);
        do {
               bytesRead =
                  is.read(mybytearray, current, (mybytearray.length-current));
            System.out.println(bytesRead + " = " + current + " " + (mybytearray.length-current));

               if(bytesRead >= 0) current += bytesRead;
               System.out.println(bytesRead);
        } while(bytesRead > -1);
        bos.write(mybytearray, 0 , current);
        bos.flush();
        System.out.println("File " + "recived." +filename.replace(":", " ")
            + " downloaded (" + current + " bytes read)");
    }catch (Exception e)
    {
        System.out.println(e.getMessage());
    }

And last part of the scrip the "PS.println("get "+filename+","+file_md5);" is doing exactly this one, the sending is working fine:

FileInputStream fis = null;
            BufferedInputStream bis = null;
            OutputStream os = null;

            String the_file = TorrentAppGui.folder+"\\"+file_name.replace(":", " ");
             File myFile = new File (the_file);
              byte [] mybytearray  = new byte [(int)myFile.length()];
              fis = new FileInputStream(myFile);
              bis = new BufferedInputStream(fis);
              bis.read(mybytearray,0,mybytearray.length);
              os = clientSocket.getOutputStream();
              System.out.println("Sending " + the_file + "(" + mybytearray.length + " bytes)");
              os.write(mybytearray, 0, mybytearray.length);
              os.flush();
              System.out.println("Done.");

I have no idea why I cannot save the bytes received by the "get" command, do you have any ideas? I know that only the "receve" function is not working, because if I looged to the application via telnet I could get the file in the console, but it doesnt reach my target. See the screen from cli.

user207421 · Accepted Answer · 2016-01-09 04:36:57Z

5

You can't mixed buffered and unbuffered streams/readers/writers on the same socket. You will lose data in the buffers. Use the same stream pair for the life of the socket. In this case I would use DataInputStream and DataOutputStream, and the readUTF()/writeUTF() methods for the messages and filenames. You will also need to send the file length ahead of the file, unless the file is the last thing sent over the connection: otherwise the peer won't know when to stop reading the file and go back and start reading messages again.

answered Jan 9, 2016 at 4:36

user207421

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3 Comments

WinterTime Over a year ago

Hi @EJP I am already sending the file length in the "send" function, while the function want to download the file from specific server, it is getting the length from the file list, if you perform the "list" command it will add the files on the server to the List, after the list is filled, it has full filenames, md5's, and file lengths, so I am requesting with given file size. What is your suggestion, should I handle it by different way? In future it have to work with multiple hosts, and moreover at this stage I am checking is if the socket isConnected, then I am performing the actions.

WinterTime Over a year ago

Main problem I have only to read the clientSocket.getInputStream, even if the filenames and sum, and size (length) is correct it cannot stop the loop, but while I try do it manually it is working fine, the function just cannot perform the "getInputStream" action, as the "list" command, which is working as you can see in attached script / screenshot.

WinterTime Over a year ago

Thanks @EJP, it seems to that I resolved the error with given answer (Use the same stream pair for the life of the socket.) That was the issue, thanks!

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