Copying Multiple Files Over A Socket

[J Mangual]

I want to copy several files over the same stream. These files may have different sources and different destinations, so I'm using standard input to read the source and file destination names. As written, the client program takes all the input and write it to the same destination file. I would like it to receive a file, detect end of file, close it and create a new FileOutputStream object. Closing the server socket is not an option because I would like to send many files over the same session.

Client

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

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

		// localhost for testing
		Socket sock = new Socket("127.0.0.1", 4444);
		System.out.println("Connecting...");

		// receive file
		InputStream in = sock.getInputStream();
		FileOutputStream out = null;

		for (int i = 0; i < args.length; i++) {
			System.out.println(args[i]);
			out = new FileOutputStream(args[i]);

			byte[] mb = new byte[1024];
			for (int c = in.read(mb, 0, 1024); c > 0; c = in.read(mb, 0, 1024)) {
				out.write(mb, 0, c);
			}
			// for(int c = in.read(); c!= -1; c = in.read()){ out.write(c); }
			out.close();
		}
		sock.close();
	}
}

Server

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

public class FileServerW {
	public static void main(String[] args) throws IOException {
		// create socket
		ServerSocket servsock = new ServerSocket(4444);

		while (true) {
			System.out.println("Waiting...");
			Socket sock = servsock.accept();
			System.out.println("Accepted connection : " + sock);
			OutputStream out = sock.getOutputStream();
			
			for (int i = 0; i < args.length; i++) {
				// sendfile
				File myFile = new File(args[i]);
				FileInputStream in = new FileInputStream(myFile);

				System.out.println("Sending...");

				byte[] mb = new byte[1024];
				for (int c = in.read(mb); c > -1; c = in.read(mb)) {
					out.write(mb, 0, c);
				}
				
			}
		}
	}
}

This is really a sequel to an earlier post, but they suggest posting different questions in different threads.

[Paul Clapham]

You can't detect when the other machine stops sending a file. Unless it closes its socket, which you said you don't want. So you need a protocol which tells you how to tell when you have read the whole file.

One easy protocol is to send the number of bytes in the file first, then to send that many bytes. The receiver will read the number of bytes, then it will read that many bytes.

[J Mangual]

All kinds of care has to be made transmitting the file size because read() and write() do not behave reliably. This one seems to work.

Client:

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

public class FileClientW {
	public static void main(String[] args) throws IOException {
		// localhost for testing
		Socket sock = new Socket("127.0.0.1", 4444);
		System.out.println("Connecting...");

		// receive file
		InputStream in = sock.getInputStream();
		FileOutputStream out = null;
		
		for (int i = 0; i < args.length; i++) {
			// open a new file
			out = new FileOutputStream(args[i]);
			
			// read the file size (up to 12 decimal digits long)
			byte[] buf0 = new byte[12];
			int bytesRead = 0;
			while(bytesRead < 12){
				if(bytesRead > 0){
					bytesRead += in.read(buf0, bytesRead, 12 - bytesRead);
				} else bytesRead += in.read(buf0, 0, 12);
			}
			
			int fileLength = 0;
			try{
				fileLength = new Integer(new String(buf0));
			} catch (NumberFormatException e ){
				System.out.println(e);
				System.exit(-1);
			}
			// read upto fileLength bytes from the 'in' and close
			bytesRead = 0;
			byte[] buf = new byte[1024];
			
			int c;
			while(bytesRead  < fileLength){
				if(fileLength - bytesRead > 1024){
				c = in.read(buf, 0, 1024);
				} else{
					c = in.read(buf, 0, fileLength - bytesRead);
				}
				bytesRead += c;
				out.write(buf, 0, c);
			}		
			out.close();
		}
		sock.close();
	}
}

Server:

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

public class FileServerW {
	public static void main(String[] args) throws IOException {
			
		// create socket
		ServerSocket servsock = new ServerSocket(4444);
		while (true) {
			System.out.println("Waiting...");
			Socket sock = servsock.accept();
			System.out.println("Accepted connection : " + sock);
			OutputStream out = sock.getOutputStream();
			
			for (int i = 0; i < args.length; i++) {
				System.out.println(args[i]);
				// sendfile
				File myFile = new File(args[i]);
				
				byte[] head = (myFile.length()+"").getBytes();
				int d = head.length;
				
				for(int k = d-1; d < 12; d++){
					out.write("0".getBytes());
				}
				
				out.write(head);
				System.out.write(head);
				System.out.println();
				
				FileInputStream in = new FileInputStream(myFile);

				System.out.println("Sending...");

				byte[] mb = new byte[1024];
				for (int c = in.read(mb); c > -1; c = in.read(mb)) {
					out.write(mb, 0, c);
				}
				
			}
		}
		//out.close();
		//sock.close();
	}
}

[Paul Clapham]

J Mangual wrote:All kinds of care has to be made transmitting the file size because read() and write() do not behave reliably.

Well, not really. I would just use a DataOutputStream to send the file size (without looking I would guess the method is writeLong) and a DataInputStream to read it at the other end. I'm not aware of any unreliable aspects of that.