CODEWITHSUNDEEP
javafilesocketstcpfile-handling
George Gardner
George Gardner

Reputation: 1

How do I prevent a file from corrupting when I transfer it over a local network using sockets?

I am working on a school project where I want to make a personal storage server. At the moment, what I am trying to achieve is being able to transfer a file from the client machine to the server. However, when testing this with an image, the file partially sends before it corrupts. Please bare in mind that I am a reasonably new programmer and that my technical knowledge may be some-what limited.

I am using a byte array through a DataOutputStream to transfer the file. I want to use this method as it should work for any file type. I've tried to set the buffer size to the exact size of the file and larger but neither have worked.

Server:

public void run() {
            try {
                System.out.println("ip: " + clientSocket.getInetAddress().getHostAddress());

                out = new DataOutputStream(clientSocket.getOutputStream());
                in = new DataInputStream(clientSocket.getInputStream());

                in.read(buffer, 0, buffer.length);

                fileOut = new FileOutputStream("X:\\My Documents\\My 
                Pictures\\gradient.jpg");

                fileOut.write(buffer, 0, buffer.length);
                in.close();
                out.close();
                clientSocket.close();

         } catch (IOException ex) {
                System.out.println(ex.getMessage());
            }
        }

Client:

 public void startConnection(String ip, int port) {
        try {
            clientSocket = new Socket(ip, port);
            out = new DataOutputStream(clientSocket.getOutputStream());
            in = new DataInputStream(clientSocket.getInputStream());

            x = false;
            Path filePath = Paths.get("C:\\Users\\georg\\Documents\\gradient.jpg");
            buffer = Files.readAllBytes(filePath);
            Thread.sleep(3000);
            //Files.write(filePath, buffer);
            //out.write(buffer,0,buffer.length);
            x = true;
            sendMessage(buffer);


        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        } catch (InterruptedException ex) {
            Logger.getLogger(PCS_Client.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public byte[] sendMessage(byte[] buffer) {
        if (x==true){
        try {
            out.write(buffer,0,buffer.length);

        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }

    }
        return null;
    }

Here is a comparison of the files I've tried to send vs the files I receive: https://i.sstatic.net/UuaNh.jpg

Curiously, sending a single colour image produces a single colour image on the server. I believe the issue here may have to be in the timing of code execution however I am not sure and do not know how to go about fixing it.

Upvotes: 0

Views: 79

Answers (1)

StephaneM
StephaneM

Reputation: 4899

The issue is in your server code, at this line:

in.read(buffer, 0, buffer.length);

You expect to read all the data at once, but if you read the doc you will find this:

public final int read(byte[] b, int off, int len) throws IOException

Reads up to len bytes of data from the contained input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

The important part is Reads up to len bytes of data.

You must use the return value of read and call it read repeatedly until the is nothing more to read.

Upvotes: 1

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