multicast

multicast

[Bruce D. McLeod]

This seems to be due to the mapping of IP_ADD_MEMBERSHIP to 35
in cygwin32/socket.h as opposed to 5 in winsock.h.  I hardcoded
the option at 5, and it works fine.

Bruce

>Date: Wed, 19 Mar 1997 11:16:14 -0500
>To: gnu-win32@cygnus.com
>From: "Bruce D. McLeod" <b.mcleod@opengroup.org>
>Subject: multicast
>
>Has anyone successfully used multicast using the sys/sockets.h version
>of the network stuff?  I am getting "This option is unsupported"
>for the setsockopt:
>
>      err = setsockopt( gListener, IPPROTO_IP, IP_ADD_MEMBERSHIP,
>                        (char *) &multiStruct, sizeof(multiStruct) );
>
>Bruce
>
>The full code...
>
>
>#include <sys/socket.h>
>#include <netinet/in.h>
>#include <netdb.h>
>#include <stdio.h>
>
>#define PANIC() printf("panic\n"); exit(1);
>#define ASSERT( x ) if ( (x) == 0 ) { PANIC(); }
>
>const static int gMyPort = 5500;
>const static char* gMyMultiIp = "225.1.1.88";
>int gListener;
>
>main( int argc, char **argv )
>{
>   if (argc > 1) {
>      struct sockaddr_in localAddr;
>      int err, value;
>      struct ip_mreq multiStruct;
>      char hostName[200];
>      struct hostent* myHostent;
>
>      // Set up listening socket.
>      gListener = socket( AF_INET, SOCK_DGRAM, 0 );
>      ASSERT( gListener != -1 );
>
>      value = 1;
>      err = setsockopt( gListener, SOL_SOCKET, SO_REUSEADDR,
>                        (char *) &value, sizeof(value) );
>      ASSERT( err != -1 );
>
>      err = gethostname( hostName, 200 );
>      ASSERT( err != -1 );
>      myHostent = gethostbyname( hostName );
>      ASSERT( myHostent != NULL );
>
>      localAddr.sin_family = AF_INET;
>      localAddr.sin_addr.s_addr = *((long *) myHostent->h_addr_list[0]);
>      localAddr.sin_port = htons( gMyPort );
>
>      err = bind( gListener, (struct sockaddr *) &localAddr,
sizeof(localAddr) );
>      ASSERT( err != -1 );
>
>      multiStruct.imr_multiaddr.s_addr = inet_addr( gMyMultiIp );
>      multiStruct.imr_interface.s_addr = *((long *) myHostent->h_addr_list[0]);
>      err = setsockopt( gListener, IPPROTO_IP, IP_ADD_MEMBERSHIP,
>                        (char *) &multiStruct, sizeof(multiStruct) );
>      if (err == -1) perror("setsockopt failed");
>      ASSERT( err != -1 );
>
>      for (;;) {
>         static const int bufsize = 200;
>         char buf[bufsize];
>         struct sockaddr fromAddr;
>         int fromAddrLen, bytes;
>
>         printf( "MultiTest: waiting for data\n" );
>
>         fromAddrLen = sizeof(fromAddr);
>         bytes = recvfrom( gListener, buf, bufsize, 0,
>                           &fromAddr, &fromAddrLen );
>         ASSERT( bytes >= 0 );
>
>         if (bytes == 0) {
>            printf( "MultiTest: disconnect received\n" );
>            close( gListener );
>            return 1;
>         }
>
>         printf( "MultiTest: msg received: %s\n", buf );
>      }
>   } else {
>      static const char msg[] = "Hello world.";
>      struct sockaddr_in remoteAddr;
>      int bytes;
>
>      int s = socket( AF_INET, SOCK_DGRAM, 0 );
>      ASSERT( s != -1 );
>
>      remoteAddr.sin_family = AF_INET;
>      remoteAddr.sin_port = htons( gMyPort );
>      remoteAddr.sin_addr.s_addr = inet_addr( gMyMultiIp );
>
>      bytes = sendto( s, msg, strlen( msg ) + 1, 0,
>                      (struct sockaddr *) &remoteAddr, sizeof(remoteAddr) );
>      ASSERT( bytes == (int) strlen( msg ) + 1 );
>      printf("MultiTest: msg sent\n");
>
>      close( s );
>   }
>
>   return 0;
>}
>

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multicast

[Laszlo Vecsey]

I tried a straitforward port of mash.c (monstermash.c, multicast tunneling
program), and ran into a problem when it tries to join a group. I'm trying
to tunnel the sap.mcast.net group of 224.2.127.254. The winsock error I'm
getting is 10022, which means "No error", I think. Has anyone gotten this
to work?


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multicast

[Laszlo Vecsey]

I tried a straitforward port of mash.c (monstermash.c, multicast tunneling
program), and ran into a problem when it tries to join a group. I'm trying
to tunnel the sap.mcast.net group of 224.2.127.254. The winsock error I'm
getting is 10022, which means "No error", I think. Has anyone gotten this
to work?


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Re: multicast

[Chin Chee-Kai]

Interesting trial you have there.  I ran your code as-is on
an SGI (which supports multicast send/receive) and didn't
manage to get multicasting.  Finally, I got a line fixed and
got it running on SGI doing multicast sending/receiving.
Later, I got it compiled on Win95 and tried on the
combination SGI-receiving/Win95-sending and got the right result.
Unfortunately, Win95 doesn't allow me to emulate being on
a multicast network (using Control-Panel to set another 
IP Adapter to 224.x.x.x address), so I can't try the reverse
combination  (Win95-receiving/SGI-sending).


Basically, the change is:

  localAddr.sin_addr.s_addr = *((long *) myHostent->h_addr_list[0]);

to

  localAddr.sin_addr.s_addr = inet_addr(gMyMultiIp);


The idea is that you need to bind to the multicasting
network address, logically as if this host also has a
local address at this multicasting address.  The idea
is much like "localhost" (127.0.0.1) being the address
of the local machine.  So if your machine+OS+network card
supports multicasting, then the Class D networks starting
from "224.0.0.0" are also logically the address of the
local machine.

The operation is not so clear if you first bind a socket
to a unicast IP address (the one returned by gethostbyname())
and subsequently add multicast membership to a unicast-recipient
socket using setsockopt(... IP_ADD_MEMBERSHIP...)
(by which time bind() would have  already named a socket with
a unicast address.  On the other hand, setsockopt() could
undo the semantics of bind() on seeing IP_ADD_MEMBERSHIP
so that the socket can be a recipient of a multicast network.
This is implementation dependent [It's not that clean IMHO].)



Chin Chee-Kai (Last, First)
Internet Email-ID:	cheekai@gen.co.jp



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multicast

[Bruce D. McLeod]

Has anyone successfully used multicast using the sys/sockets.h version
of the network stuff?  I am getting "This option is unsupported"
for the setsockopt:

      err = setsockopt( gListener, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                        (char *) &multiStruct, sizeof(multiStruct) );

Bruce

The full code...


#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>

#define PANIC() printf("panic\n"); exit(1);
#define ASSERT( x ) if ( (x) == 0 ) { PANIC(); }

const static int gMyPort = 5500;
const static char* gMyMultiIp = "225.1.1.88";
int gListener;

main( int argc, char **argv )
{
   if (argc > 1) {
      struct sockaddr_in localAddr;
      int err, value;
      struct ip_mreq multiStruct;
      char hostName[200];
      struct hostent* myHostent;

      // Set up listening socket.
      gListener = socket( AF_INET, SOCK_DGRAM, 0 );
      ASSERT( gListener != -1 );

      value = 1;
      err = setsockopt( gListener, SOL_SOCKET, SO_REUSEADDR,
                        (char *) &value, sizeof(value) );
      ASSERT( err != -1 );

      err = gethostname( hostName, 200 );
      ASSERT( err != -1 );
      myHostent = gethostbyname( hostName );
      ASSERT( myHostent != NULL );

      localAddr.sin_family = AF_INET;
      localAddr.sin_addr.s_addr = *((long *) myHostent->h_addr_list[0]);
      localAddr.sin_port = htons( gMyPort );

      err = bind( gListener, (struct sockaddr *) &localAddr,
sizeof(localAddr) );
      ASSERT( err != -1 );

      multiStruct.imr_multiaddr.s_addr = inet_addr( gMyMultiIp );
      multiStruct.imr_interface.s_addr = *((long *) myHostent->h_addr_list[0]);
      err = setsockopt( gListener, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                        (char *) &multiStruct, sizeof(multiStruct) );
      if (err == -1) perror("setsockopt failed");
      ASSERT( err != -1 );

      for (;;) {
         static const int bufsize = 200;
         char buf[bufsize];
         struct sockaddr fromAddr;
         int fromAddrLen, bytes;

         printf( "MultiTest: waiting for data\n" );

         fromAddrLen = sizeof(fromAddr);
         bytes = recvfrom( gListener, buf, bufsize, 0,
                           &fromAddr, &fromAddrLen );
         ASSERT( bytes >= 0 );

         if (bytes == 0) {
            printf( "MultiTest: disconnect received\n" );
            close( gListener );
            return 1;
         }

         printf( "MultiTest: msg received: %s\n", buf );
      }
   } else {
      static const char msg[] = "Hello world.";
      struct sockaddr_in remoteAddr;
      int bytes;

      int s = socket( AF_INET, SOCK_DGRAM, 0 );
      ASSERT( s != -1 );

      remoteAddr.sin_family = AF_INET;
      remoteAddr.sin_port = htons( gMyPort );
      remoteAddr.sin_addr.s_addr = inet_addr( gMyMultiIp );

      bytes = sendto( s, msg, strlen( msg ) + 1, 0,
                      (struct sockaddr *) &remoteAddr, sizeof(remoteAddr) );
      ASSERT( bytes == (int) strlen( msg ) + 1 );
      printf("MultiTest: msg sent\n");

      close( s );
   }

   return 0;
}

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