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Simple Socket Problem ( ? )

843790Apr 15 2008 — edited Apr 15 2008

Hey guys,

When I try to run the following code on my system (Linux Kubuntu), I get the exception below (see bottom please):

/*
 * WriteServer.java
 *
 * Created on 15 April 2008, 14:04
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

package org;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.rmi.RMISecurityManager;

/**
 *
 * @author ltsmm
 */
public class WriteServer
{
    public static int            serverPort = 998;
    public static int            clientPort = 999;
    public static int            buffer_size = 1024;
    public static DatagramSocket ds;
    public static byte           buffer[]   = new byte[buffer_size];
    
    public static void TheServer() throws Exception {
        int pos = 0;
        while(true) { //keep looping
            int c = System.in.read();
            switch(c) {
                case -1:
                    echo("Server Quits");
                    return;
                
                case '\r':
                    break;
                
                case '\n':
                    ds.send(new DatagramPacket(buffer, pos, InetAddress.getLocalHost(), clientPort) );
                    pos = 0;
                    break;
                
                default:
                    buffer[pos++] = (byte) c;
            }
        }       
    }
    
    public static void TheClient() throws Exception {
        while(true) {
            DatagramPacket p = new DatagramPacket(buffer, buffer.length);
            ds.receive(p);
            echo( new String(p.getData(), 0, p.getLength()));
        }
        
    }
    
    public static void main(String args[]) throws Exception {
                     
        if(args.length == 1) {
            ds = new DatagramSocket(serverPort); //error occurs here
            TheServer();
        }
        else {
            ds = new DatagramSocket(clientPort); //or here (if args.length == 0)
            TheClient();
        }
    }
    
    
    private static void echo(String s) {
        System.out.println(s);
    }
    
}

Exception in thread "main" java.net.BindException: Permission denied
        at java.net.PlainDatagramSocketImpl.bind0(Native Method)
        at java.net.PlainDatagramSocketImpl.bind(PlainDatagramSocketImpl.java:82)
        at java.net.DatagramSocket.bind(DatagramSocket.java:368)
        at java.net.DatagramSocket.<init>(DatagramSocket.java:210)
        at java.net.DatagramSocket.<init>(DatagramSocket.java:261)
        at java.net.DatagramSocket.<init>(DatagramSocket.java:234)
        at org.WriteServer.main(WriteServer.java:73)

I've tried using a security manager thingie, according to this page: http://www.nabble.com/Permission-denied-td3565150.html
but with no success :-(

If anyone has ideas how to get around this - much appreciated!

Gerry
sockets newbie

Edited by: gvanto on Apr 15, 2008 4:54 AM

EJP

You have a local firewall installed, e.g. a Windows firewall, that is blocking you from using UDP ports 998/999.

843790

Ah sweet, just tried 1200 and 1201 and it works - thanks alot!!

EJP

Actually I am wrong, as you are on Linux you need root privilege to use a port < 1024.

843790

Hey ejp,

Thanks for the ( valuable ) advice!

Ok I got the little java app to talk to itselfs (2 instances, one as client, one as server) which is great.

Ok this is perhaps a little out of line (being C++ and all hehe) but I was wondering if a UDP message sent by my C++ app will be read-able by the java app (in theory it should right?)

I have tried my little C++ app as follows, but the messages do not get received (they DO get received by the client c++ version of this app):

//
// UDP_Talker: Sending some UDP packets
//
// File: main.cc// Author: ltsmm
//
// Created on 6 November 2007, 14:27
//

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define SERVERPORT 1200 // the port users will be connecting to

int main(int argc, char** argv)
{
int sockfd;
struct sockaddr_in their_addr; // connector's address information
struct hostent *he;
int numbytes;

if(argc != 3)
{
fprintf(stderr, "usage: talker hostname message \n");
exit(1);
}

if((he = gethostbyname(argv[1])) == NULL) // get the host info
{
herror("gethostbyname");
exit(1);
}

if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
{
perror("socket");
exit(1);
}

their_addr.sin_family = AF_INET; // HBO
their_addr.sin_port = htons(SERVERPORT); // short, NBO
their_addr.sin_addr = *((struct in_addr *)he->h_addr);
memset(their_addr.sin_zero, '\0', sizeof their_addr.sin_zero);

if((numbytes = sendto(sockfd, argv[2], strlen(argv[2]), 0, (struct sockaddr *)&their_addr, sizeof their_addr)) == -1)
{
printf("error sending!");
perror("sendto");
exit(1);
}

printf("sent %d bytes to %s\n", numbytes, inet_ntoa(their_addr.sin_addr));
close(sockfd);

return (EXIT_SUCCESS);
}

Usage is: ltsmm@gertlx:~/Cpp/UDP_Talker/dist/Debug/GNU-Linux-x86$ ./udp_talker localhost "helloworld"

-G

ps: the listener C++ app for completeness:

// 
// UDP_Listener: Listening to UDP packets coming in
//
// File:   main.cc// Author: ltsmm
//
// Created on 6 November 2007, 14:27
//


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MYPORT 1200 // the port users will be connecting to
#define MAXBUFLEN 100

int main(int argc, char** argv) 
{
    int                 sockfd;
    struct sockaddr_in  my_addr;    // MY address info
    struct sockaddr_in  their_addr; // THEIR address info
    socklen_t           addr_len; 
    int                 numbytes;
    char                buf[MAXBUFLEN];

    printf("****** UPD_Listener Running ********\n");

    /****** Get socket file descriptor **********/
    if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
    {
        perror("socket");
        exit(1);
    }

    /****** Set address info **********/
    my_addr.sin_family = AF_INET;           // HBO
    my_addr.sin_port = htons(MYPORT);       // short, NBO
    my_addr.sin_addr.s_addr = INADDR_ANY;   // Automagically fill with my IP
    memset(my_addr.sin_zero, '\0', sizeof my_addr.sin_zero);

    /****** Bind socket **********/
    if(bind(sockfd, (struct sockaddr *)&my_addr, sizeof my_addr) == -1)
    {
        perror("bind");
        exit(1);
    }

    while(1) // run loop forever
    {
        /******** Do recvfrom() *********/
        addr_len = sizeof their_addr;
        if( (numbytes = recvfrom(sockfd, buf, MAXBUFLEN - 1, 0, (struct sockaddr *)&their_addr, &addr_len)) == -1)
        {
            perror("recvfrom");
            exit(1);
        }

        printf("got packet from %s\n", inet_ntoa(their_addr.sin_addr));
        printf("packet is %d bytes long\n", numbytes);
        buf[numbytes] = '\0';
        printf("packet contains \"%s\" \n", buf);
    }


    // Close socket:
    close(sockfd); 






    return (EXIT_SUCCESS);
}

EJP

Should work as long as you have someone receiving UDP datagrams on port 1200.

843790

ha ha ok thats my bad, i had the talker talkin to PORT 1201 instead of 1200

cheers EJP for your help!!

how sweet is c++ talkin to java over network?! :-D

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Java APIs

Simple Socket Problem ( ? )

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