Transferring file name then file data over socket

[Mads Nielsen]

Hello

I need to transfer a file over a socket, what i want is to transfer the name of the file then the file data. i have a working server and client.

Server

import java.net.*;   
import java.io.*;   
  
public class FileServer {    
  
  public static void main (String[] args ) throws IOException {   
    
    int bytesRead;
    int current = 0;

	ServerSocket serverSocket = null;
	serverSocket = new ServerSocket(13267);
	  
	while(true) {
		Socket clientSocket = null;
		clientSocket = serverSocket.accept();
		
		InputStream in = clientSocket.getInputStream();
		
		// Writing the file to disk
		// Instantiating a new output stream object
		OutputStream output = new FileOutputStream("E7060v1.2.zip");
		  
		byte[] buffer = new byte[1024];
		while ((bytesRead = in.read(buffer)) != -1) {
			output.write(buffer, 0, bytesRead);
		}
		// Closing the FileOutputStream handle
		output.close();
    }
  }
}

Client

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

public class FileClient {
	
	public static void main(String[] args) throws IOException {

		Socket sock = new Socket("127.0.0.1", 13267);

		// sendfile
		File myFile = new File("E7060v1.2.zip");
		byte[] mybytearray = new byte[(int) myFile.length()];
		
		FileInputStream fis = new FileInputStream(myFile);
		BufferedInputStream bis = new BufferedInputStream(fis);
		bis.read(mybytearray, 0, mybytearray.length);
		
		OutputStream os = sock.getOutputStream();
		
		os.write(mybytearray, 0, mybytearray.length);
		
		os.flush();
		
		sock.close();
	}
}

The file name is hardcoded in the server: FileOutputStream("E7060v1.2.zip"); i would really like this to be dynamic.

What is the best method to use when i need to transfer the file name (string) first then the file data (byte) ?

Kind regards Mads Nielsen

[Rob Spoor]

One approach is to use DataOutputStream on the client. You first use writeUTF to write the file name, then writeLong to write the file size (also very important).
The server then uses DataInputStream. It first uses readUTF to read the file name, then readLong to read the file size. Let's say that value is x. You then read exactly x bytes, not all until the end of the line:

in = new DataInputStream(in);
String fileName = in.readUTF();
OutputStream output = new FileOutputStream(fileName);
long size = in.readLong();
byte[] buffer = new byte[1024];
while (size > 0 && (bytesRead = in.read(buffer, 0, (int)Math.min(buffer.length, size))) != -1)
{
    output.write(buffer, 0, bytesRead);
    size -= bytesRead;
}

Note that the while loop's condition has changed quite a bit. First of all, there's the additional check to see if the remaining size is not 0. Second, the read is limited to the minimum of the buffer length and the remaining size. For most loop iterations this size is the buffer length (and therefore identical to read(buffer)), but the last block(s) will only read as many bytes as necessary; size will be smaller than buffer.length (and therefore can safely be cast to int).

[Mads Nielsen]

Rob Spoor wrote:One approach is to use DataOutputStream on the client. You first use writeUTF to write the file name, then writeLong to write the file size (also very important).
The server then uses DataInputStream. It first uses readUTF to read the file name, then readLong to read the file size. Let's say that value is x. You then read exactly x bytes, not all until the end of the line:

in = new DataInputStream(in);
String fileName = in.readUTF();
OutputStream output = new FileOutputStream(fileName);
long size = in.readLong();
byte[] buffer = new byte[1024];
while (size > 0 && (bytesRead = in.read(buffer, 0, (int)Math.min(buffer.length, size))) != -1)
{
    output.write(buffer, 0, bytesRead);
    size -= bytesRead;
}

Note that the while loop's condition has changed quite a bit. First of all, there's the additional check to see if the remaining size is not 0. Second, the read is limited to the minimum of the buffer length and the remaining size. For most loop iterations this size is the buffer length (and therefore identical to read(buffer)), but the last block(s) will only read as many bytes as necessary; size will be smaller than buffer.length (and therefore can safely be cast to int).

Thank you very much for the server code. It helps a lot getting help on specific code.

I am unsure how to implement the DataOutputStream stream in the client code.?

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

public class FileClient {
	
	public static void main(String[] args) throws IOException {

		Socket sock = new Socket("127.0.0.1", 13267);

		// sendfile
		File myFile = new File("E7060v1.2.zip");
		byte[] mybytearray = new byte[(int) myFile.length()];
		
		FileInputStream fis = new FileInputStream(myFile);
		BufferedInputStream bis = new BufferedInputStream(fis);
		bis.read(mybytearray, 0, mybytearray.length);
		
		OutputStream os = sock.getOutputStream();
		
		os.write(mybytearray, 0, mybytearray.length);
		
		os.flush();
		
		sock.close();
	}
}

Kind regards Mads Nielsen

[Rob Spoor]

Mads Nielsen wrote:I am unsure how to implement the DataOutputStream stream in the client code.?

		OutputStream os = sock.getOutputStream();
		
		//os.write(mybytearray, 0, mybytearray.length);

		//os.flush();

		DataOutputStream dos = new DataOutputStream(os);
		dos.writeUTF(myFile.getName());
		dos.writeLong(mybytearray.length);
		dos.write(mybytearray, 0, mybytearray.length);
		dos.flush();

Also, there is a flaw in your reading code:

		bis.read(mybytearray, 0, mybytearray.length);

This single read operation is not guaranteed to read all of the bytes in one go. You can again use DataInputStream for that:

DataInputStream dis = new DataInputStream(bis);
dis.readFully(mybytearray, 0, mybytearray.length);

Unlike a regular read, readFully is guaranteed to read exactly the requested number of bytes. It will throw an EOFException if there aren't enough bytes to read, but in this case that should not occur.

[Mads Nielsen]

Thank you so very much.

Do you know of a good site where i can read about the many different streams in Java ?

I have tried the java documentation but that is a little heavy.

Kind regards Mads Nielsen

[Mads Nielsen]

import java.net.*;   
import java.io.*;   
  
public class FileServer {    
  
  public static void main (String[] args ) throws IOException {   
    
    int bytesRead;
    int current = 0;

	ServerSocket serverSocket = null;
	serverSocket = new ServerSocket(13267);
	  
	while(true) {
		Socket clientSocket = null;
		clientSocket = serverSocket.accept();
		
		InputStream in = clientSocket.getInputStream();
		
		in = new DataInputStream(in);  
 
		String fileName = in.readUTF();   
		OutputStream output = new FileOutputStream(fileName);   
		long size = in.readLong();   
		byte[] buffer = new byte[1024];   
		while (size > 0 && (bytesRead = in.read(buffer, 0, (int)Math.min(buffer.length, size))) != -1)   
		{   
		    output.write(buffer, 0, bytesRead);   
		    size -= bytesRead;   
		}

		// Writing the file to disk
		// Instantiating a new output stream object
		/*OutputStream output = new FileOutputStream("E7060v1.2.zip");
		  
		byte[] buffer = new byte[1024];
		while ((bytesRead = in.read(buffer)) != -1) {
			output.write(buffer, 0, bytesRead);
		}*/
		// Closing the FileOutputStream handle
		output.close();
    }
  }
}

How do i connect InputStream in = clientSocket.getInputStream(); with in = new DataInputStream(in); ??

I get this error with the above code at compile time:

FileServer.java:22: cannot find symbol
symbol  : method readUTF()
location: class java.io.InputStream
                String fileName = in.readUTF();
                                    ^
FileServer.java:24: cannot find symbol
symbol  : method readLong()
location: class java.io.InputStream
                long size = in.readLong();
                              ^
2 errors

Kind regards Mads Nielsen

[Rob Spoor]

Check the last piece of code in my previous post. I admit I made a mistake by not creating a new variable myself in my first post.

[Mads Nielsen]

Rob Spoor wrote:Check the last piece of code in my previous post. I admit I made a mistake by not creating a new variable myself in my first post.

I got that sorted now.

The server is working now.

import java.net.*;   
import java.io.*;   
  
public class FileServer {    
  
  public static void main (String[] args ) throws IOException {   
    
    int bytesRead;
    int current = 0;

	ServerSocket serverSocket = null;
	serverSocket = new ServerSocket(13267);
	  
	while(true) {
		Socket clientSocket = null;
		clientSocket = serverSocket.accept();
		
		InputStream in = clientSocket.getInputStream();
		
		DataInputStream clientData = new DataInputStream(in); 
		
		String fileName = clientData.readUTF();   
		OutputStream output = new FileOutputStream(fileName);   
		long size = clientData.readLong();   
		byte[] buffer = new byte[1024];   
		while (size > 0 && (bytesRead = clientData.read(buffer, 0, (int)Math.min(buffer.length, size))) != -1)   
		{   
		    output.write(buffer, 0, bytesRead);   
		    size -= bytesRead;   
		}
		
		// Closing the FileOutputStream handle
		output.close();
    }
  }
}

Client

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

public class FileClient {
	
	public static void main(String[] args) throws IOException {

		Socket sock = new Socket("127.0.0.1", 13267);

		//Send file
		File myFile = new File("E7060v1.2.zip");
		byte[] mybytearray = new byte[(int) myFile.length()];
		
		FileInputStream fis = new FileInputStream(myFile);
		BufferedInputStream bis = new BufferedInputStream(fis);
		//bis.read(mybytearray, 0, mybytearray.length);
		
		DataInputStream dis = new DataInputStream(bis);   
		dis.readFully(mybytearray, 0, mybytearray.length);
		
		OutputStream os = sock.getOutputStream();
		
		//Sending file name and file size to the server
		DataOutputStream dos = new DataOutputStream(os);   
        dos.writeUTF(myFile.getName());   
        dos.writeLong(mybytearray.length);   
        dos.write(mybytearray, 0, mybytearray.length);   
        dos.flush();
		
        //Sending file data to the server
		os.write(mybytearray, 0, mybytearray.length);
		os.flush();
		
		//Closing socket
		sock.close();
	}
}

But i am now facing a little problem with the client code, it seems that it is never returning to the prompt. I have tried with dos.close(); but it did not help.

Kind regards Mads Nielsen

[Rob Spoor]

Remove lines 30-32 from FileClient. You are now sending the file data twice, but the server is only expecting it once.

I tried your original code with a 200+MB file and it didn't finish. I then removed those three lines, tried again, and it finished just fine.

[Mauricio Corrêa]

Rob Spoor wrote:Check the last piece of code in my previous post. I admit I made a mistake by not creating a new variable myself in my first post.

For the server code to work correctly, you must close the variables: in and clientData

For example:

        in.close();
        clientData.close();
        

import java.net.*;     
import java.io.*;     
    
public class FileServer {      
    
  public static void main (String[] args ) throws IOException {     
      
    int bytesRead;  
    int current = 0;  
  
    ServerSocket serverSocket = null;  
    serverSocket = new ServerSocket(13267);  
        
    while(true) {  
        Socket clientSocket = null;  
        clientSocket = serverSocket.accept();  
          
        InputStream in = clientSocket.getInputStream();  
          
        DataInputStream clientData = new DataInputStream(in);   
          
        String fileName = clientData.readUTF();     
        OutputStream output = new FileOutputStream(fileName);     
        long size = clientData.readLong();     
        byte[] buffer = new byte[1024];     
        while (size > 0 && (bytesRead = clientData.read(buffer, 0, (int)Math.min(buffer.length, size))) != -1)     
        {     
            output.write(buffer, 0, bytesRead);     
            size -= bytesRead;     
        }  
          
        // Closing the FileOutputStream handle
        in.close();
        clientData.close();
        output.close();  
    }  
  }  
}  

I noticed that the client is also necessary to close some variables.

For example:

        os.close();
        dos.close();

import java.net.*;  
import java.io.*;  
  
public class FileClient {  
      
    public static void main(String[] args) throws IOException {  
  
        Socket sock = new Socket("127.0.0.1", 13267);  
  
        //Send file  
        File myFile = new File("E7060v1.2.zip");  
        byte[] mybytearray = new byte[(int) myFile.length()];  
          
        FileInputStream fis = new FileInputStream(myFile);  
        BufferedInputStream bis = new BufferedInputStream(fis);  
        //bis.read(mybytearray, 0, mybytearray.length);  
          
        DataInputStream dis = new DataInputStream(bis);     
        dis.readFully(mybytearray, 0, mybytearray.length);  
          
        OutputStream os = sock.getOutputStream();  
          
        //Sending file name and file size to the server  
        DataOutputStream dos = new DataOutputStream(os);     
        dos.writeUTF(myFile.getName());     
        dos.writeLong(mybytearray.length);     
        dos.write(mybytearray, 0, mybytearray.length);     
        dos.flush();  
          
        //Sending file data to the server  
        os.write(mybytearray, 0, mybytearray.length);  
        os.flush();  
          
        //Closing socket
        os.close();
        dos.close();  
        sock.close();  
    }  
}

I hope I have contributed.

Hugs...

[Winston Gutkowski]

Mauricio Corrêa wrote:I hope I have contributed...

Maybe so. However, I suspect that Elvis (or Mads) has left the room, considering the thread is more than 2 years old.

Winston

[Campbell Ritchie]

But … welcome to the Ranch