Name: dgC58589 Date: 01/27/98


[the text from the user is reformatted and more explanations
are added after exchanging e-mail (###@###.###

The problem appears when a machine that has more than one
IP addresses tries to use a ftp URL to get something. The two
IP addresses are not routable one to another - this situation
is normal for a machine connected to an internal LAN with some
unroutable addresses (example 10.1.1.1) and with a dial up
connection.

When the ftp protocol binds a server socket for receiving data
from the server it send the socj`ket IP and port to the server
so that the server can connect to it. The address sent to the server
is the one returned by InetAddress.getLocalHost().getAddress().
When the host has multiple addresses there is no way to reliably
tell which one should be returned - the internal one will not
wrok when connecting to an external host and the external one
will not work when connecting to an internal host.

A possible suggested fix is to use the local address from the
client socket already connected to the server - if the server can
talk to it and the server socket is bound with inAddrAny then
this should work. The question is wether the getLocalAddress()
[acctually getsockname() in the C library] will return the good
address for a connected socket in the case of multiple IP addresses.

Here is the test case sent by the user:

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

/**
 *
 * Program to snarf files from a random website.
 *
 */
public class Snarf {
  public static void main(String[] args) {
    InputStream inStream = null;
    OutputStream outStream = null;

    try {
      // Check args.
      if (args.length < 2) {
throw new IllegalArgumentException("Wrong number of arguments.");
      } else {
String urlRoot = args[0];
for (int i = 1; i < args.length; i++) {
URL turl = new URL(urlRoot + args[i]);
System.out.println("Snarfing " + turl + " via " +
turl.getProtocol() + " on port " +
turl.getPort() + ".");
String protocol = turl.getProtocol();
int port = turl.getPort();
String host = turl.getHost();
String file = turl.getFile();
turl = null;
URL url = new URL(protocol, host, port, file);
URLConnection urlConnection = url.openConnection();
inStream = urlConnection.getInputStream();
outStream = new FileOutputStream(args[i]);
byte[] buffer = new byte[1096];
int bytes_read = 0;
while((bytes_read = inStream.read(buffer)) != -1) {
outStream.write(buffer, 0, bytes_read);
System.out.print(".");
}
System.out.println("\nDone with " + url);
inStream = null; outStream = null; buffer = null; url = null;
}
      } // Args were OK.
    } catch(Exception e) {
      // Bail informatively.
      System.err.println(e);
      System.err.println("Usage: java Snarf URL files ...");
    } finally { // Always close streams!
      try {
inStream.close();
outStream.close();
      } catch(Exception e) {
/* NOTHING */
      }
    }
  }
}
(Review ID: 22303)
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