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macosxuser3 · Nov 9, 2001, 07:51 AM

Hi,
I am attempting to develop a program that uses multicasting on MacOS 10.1. I found sample programs (MultiCastReceiver/MultiCastSender) of how to do this on the web (at http://sunsite.net.edu.cn/tutorials/...e/24javafi.htm). I verified that these programs do in fact work correctly on another computer (running FreeBSD).

MultiCastReceiver takes a multicast IP and port number, and listens on it until something is received, and once it is, it is displayed to standard out. Below you can see the error I got when attempting to run it. The corresponding MultiCastSender program gives no error when running it.

% java MultiCastReceiver 225.6.2.3 5000
Unable to obtain socket: java.net.SocketException: error setting options
%

After searching the web for a while, I found two things someone suggests to look for when running across this error message:

1) make sure the word "MULTICAST" comes up for every entry when I type "ifconfig -a". It looks like this was alright (I think).

<BLOCKQUOTE>code:<HR><pre>
% ifconfig -a
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet 127.0.0.1 netmask 0xff000000
en0: flags=8863<UP,BROADCAST,b6,RUNNING,SIMPLEX,MULTI CAST> mtu 1500
ether 00:0a:27:b4:9a:18
media: autoselect (none) status: inactive
supported media: none autoselect 10baseT/UTP <half-duplex> 10baseT/UTP <full-duplex> 100baseTX <half-duplex> 100baseTX <full-duplex>
ppp0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST& gt; mtu 1500
inet 129.49.78.230 --> 129.49.76.15 netmask 0xffff0000
%
[/code]

2) add a route if there is not one when listing "netstat -r".

There wasn't a route, so I had to add one:

<BLOCKQUOTE>code:<HR><pre>
% sudo route add 225.6.2.3 localhost
Password:
add host 225.6.2.3: gateway localhost
% netstat -r
Routing tables

Internet:
Destination Gateway Flags Refs Use Netif Expire
default as14.dialup.sunysb UGSc 39 10 ppp0
localhost localhost UH 6 6816 lo0
as14.dialup.sunysb 078-103.dialup.sun UH 40 0 ppp0
225.6.2.3 localhost UGHS 0 0 lo0
%
[/code]

However, this did not fix the problem.

Does anyone know what the problem could be? I am surprised after searching the web I did not see any questions about this anywhere, and nothing on Apple's website. Perhaps I'm the only one having this problem for some reason. Below is the code for MultiCastReceiver (because when I checked the URL I posted above a minute ago, it didn't load). If anyone has time, could you check to see if it works on your computer?

Thanks.
--Daniel

_________________________________________________
<BLOCKQUOTE>code:<HR><pre>
//import sun.net.*; // This will move to java.net soon.
import java.net.*; // Import package names used.
import java.lang.*;
import java.io.*;
/**
* This is a program which allows you to listen
* at a particular multicast IP address/port and
* print out incoming UDP datagrams.
* @author David W. Baker
* @version 1.1
*/
class MultiCastReceiver {
// The length of the data portion of incoming
// datagrams.
private static final int DATAGRAM_BYTES = 256;
private int mcastPort;
private InetAddress mcastIP;
private MulticastSocket mcastSocket;
// Boolean to tell the client to keep looping for
// new datagrams.
private boolean keepReceiving = true;
/**
* This starts up the application
* @param args Program arguments - <ip> <port>
*/
public static void main(String[] args) {
// This must be the same port and IP address
// used by the sender.
if (args.length != 2) {
System.out.print("Usage: MultiCastReceiver <IP "
+ "addr> <port>\n\t<IP addr> can be one of "
+ "224.x.x.x - 239.x.x.x\n");
System.exit(1);
}
MultiCastReceiver send = new MultiCastReceiver(args);
System.exit(0);
}
/**
* The constructor does the work of opening a socket,
* joining the multicast group, and printing out
* incoming data.
* @param args Program arguments - <ip> <port>
*/
public MultiCastReceiver(String[] args) {
DatagramPacket mcastPacket; // Packet to receive.
byte[] mcastBuffer; // byte[] array buffer
InetAddress fromIP; // Sender address.
int fromPort; // Sender port.
String mcastMsg; // String of message.
try {
// First, set up our receiving socket.
mcastIP = InetAddress.getByName(args[0]);
mcastPort = Integer.parseInt(args[1]);
mcastSocket = new MulticastSocket(mcastPort);
// Join the multicast group.
mcastSocket.joinGroup(mcastIP);
} catch(UnknownHostException excpt) {
System.err.println("Unknown address: " + excpt);
System.exit(1);
} catch(SocketException excpt) {
System.err.println("Unable to obtain socket: "
+ excpt);
System.exit(1);
} catch(IOException e) {
System.out.println("IOException \n" + e);
}

while (keepReceiving) {
try {
// Create a new datagram.
mcastBuffer = new byte[DATAGRAM_BYTES];
mcastPacket = new DatagramPacket(mcastBuffer,
mcastBuffer.length);
// Receive the datagram.
mcastSocket.receive(mcastPacket);
fromIP = mcastPacket.getAddress();
fromPort = mcastPacket.getPort();
mcastMsg = new String(mcastPacket.getData(),0);
// Print out the data.
System.out.println("Received from " + fromIP +
" on port " + fromPort + ": " + mcastMsg);
} catch(IOException excpt) {
System.err.println("Failed I/O: " + excpt);
}
}
try {
mcastSocket.leaveGroup(mcastIP); // Leave the group.
} catch(SocketException excpt) {
System.err.println("Socket problem leaving group: "
+ excpt);
} catch(IOException e) {
System.out.println("IOException \n" + e);
}
mcastSocket.close(); // Close the socket.
}
/**
* This method provides a way to stop the program.
*/
public void stop() {
if (keepReceiving) {
keepReceiving = false;
}
}
}
[/code]

Jablabla · Nov 10, 2001, 11:12 AM

Might want to try "netstat -g". It should show you more on the multicast routing table.

Also, here are some useful links. Its c but it might give you some insight. The network you are running on must be multicast enabled. Did not see you set a ttl in your code. Also, might want to be careful about exceptions throwing you out of your while loop.

setting up routes:
http://notch.mathstat.muohio.edu/htm...t-HOWTO-3.html

general multicast info:
http://notch.mathstat.muohio.edu/htm...OWTO.html#toc3

Hope this helps..

ryochiji · Nov 10, 2001, 02:38 PM

I'm not familiar with multicasting or the particular program, but I've done some socket programming in various languages (including Java) so hopfully I'm not too far off mark...

The literal interpretation of the error is that the program is unable to obtain a socket connection to the IP 225.6.2.3 at socket 5000.
This means:
1) the IP is invalid,
2) port 5000 on the specified IP is not broadcasting or otherwise open.

Are you sure the IP and port number is correct? Try "telnet 225.6.2.3 5000" and see if it lets you establish a connection.

macosxuser3 · Nov 11, 2001, 09:29 AM

Thanks for the tip!
When I run "netstat -g", it says nothing is in my multicast routing table (see below). Any idea why this is happening?
Thanks,
--Daniel

<BLOCKQUOTE>code:<HR><pre>
% sudo route add -net 224.0.0.0 -netmask 240.0.0.0 -host localhost
Password:
add net 224.0.0.0: gateway localhost
% netstat -r
Routing tables

Internet:
Destination Gateway Flags Refs Use Netif Expire
default as14.dialup.sunysb UGSc 7 7 ppp0
localhost localhost UH 10 16660 lo0
as14.dialup.sunysb 078-115.dialup.sun UH 8 0 ppp0
224/4 localhost UGS 0 0 lo0
% netstat -g

Virtual Interface Table is empty

Multicast Routing Table is empty

%
[/code]

Originally posted by Jablabla:
Might want to try "netstat -g". It should show you more on the multicast routing table.

Hope this helps..