UDP Multicast Listener ... setting ports and groups?

[CouponPages]

Based upon some stuff I found on Tek-Tips, I started a project that will involve reading some information from a multicast UDP feed.

The problem is I can't seem to get started on the right foot because there is so little information out there about doing any UDP/TCP/Socket networking out there for FoxPro.

The main objective is pretty simple. I need to set a port and group and then just read strings. I found a lot of things to read from UDP, but nothing about muticast groups.

Can anyone point me to a FAQ or anyplace that can get me started?

Thanks!

 

[CouponPages]

Here's a C/C++ version... most of it is contained in just a dozen or so lines of code, it's driving me crazy that I can't figure out how to get FoxPro to do the same.

#include "winsock2.h"
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
//#include "multicast.h"



 main ()
 {

  WSADATA data;
    WORD version; 
    int ret = 0;  

    version = (MAKEWORD(2, 2)); 
    ret = WSAStartup(version, &data); 
    if (ret != 0) 
    {  
        ret = WSAGetLastError(); 
        
        if (ret == WSANOTINITIALISED) 
        {  
            printf("not initialised"); 
        }
    }


SOCKET udp_socket;
struct sockaddr_in sockaddr;
int peerlen;

char recvbuffer[256];
int retval;


udp_socket = WSASocket(AF_INET, SOCK_DGRAM, IPPROTO_UDP, 
       	0, 0, WSA_FLAG_OVERLAPPED | WSA_FLAG_MULTIPOINT_C_LEAF | WSA_FLAG_MULTIPOINT_D_LEAF); 
    
    if (udp_socket == INVALID_SOCKET)  
    { 
        printf ("WSASocket() failed, Err: %d\n", WSAGetLastError()); 
        return FALSE;  
    }  

// Bind address
SOCKADDR_IN sockAddr;
	memset((char *)&sockAddr, 0, sizeof(sockAddr));   //fooling with memory
   	sockAddr.sin_family = AF_INET;
   	sockAddr.sin_port = htons((WORD)(9051));
	sockAddr.sin_addr.s_addr = inet_addr("230.0.1.1");


udp_socket = WSAJoinLeaf(udp_socket, (SOCKADDR *)&sockAddr,
        	sizeof(sockAddr), 0, 0, 0, 0, JL_RECEIVER_ONLY);

	int result = GetLastError();
    if (INVALID_SOCKET == udp_socket)
   	if( bind(udp_socket, (SOCKADDR *)&sockAddr, sizeof(sockAddr)));

	


   //bind to socket
  bind(udp_socket,(struct sockaddr*) &sockaddr,sizeof(sockaddr)); 

peerlen=sizeof(sockAddr);


while(1) {

  retval = recvfrom(udp_socket, recvbuffer, sizeof(recvbuffer), 0, (struct sockaddr *)&sockAddr, &peerlen);

  //recvfrom returns -1 if it didn't receive anything.
  //If retval is NOT -1, then the recvfrom must have worked, so let's display
  //whatever multicast data was sent.

  if (retval != -1) {printf("%s", recvbuffer);}   //to test my output on the screen and make sure it looks ok.

  }
    return 0;   
}

 

[CouponPages]

For anyone in the future looking to do the same, here's my final solution. I was unable to find a way to call the native libraries myself, and I gave up on trying to encapsulate the C++ solution I described in my last post, so I looked for a third-party library.

I ended up finding a WinSock library from Dart.Com. They have a 30 day trial on the site, so I tried it. The documentation was crude, but ultimately I managed to try the following code and it worked.

From the command window I typed:

_vfp.AutoYield = .f.

otest=CREATEOBJECT("dart.udp.1")dso=CREATEOBJECT("dart.Dartstream.1")

otest.Open(9051)

otest.MaxSubnets = 3

otest.Join("230.0.1.1")

dso.position = 0

Cnt = otest.Receive(dso)

To confirm it worked I typed

? cnt

(# bytes received is printed... which means it worked)


To see the string received, I typed:

dso.position = 0

? dso.readstring()

(the string read from the feed is printed)


It bugs me a bit that I couldn't do this without a third-party library, but as long as it works... I'm happy.

 

[agoeddeke]

Have you tried using the MS Winsock control? There is a UDP example in the link below that can easily be translated into VFP. I have written UDP client apps in VFP before with no trouble.

http://msdn.microsoft.com/library/d...-us/vbcon98/html/vbconusingwinsockcontrol.asp

Andy

 

[CouponPages]

Thanks Andy,

I've experimented, but I can't get past the first line:

oTest = CREATEOBJECT("MSWinSock.WinSock")

Once I create the object, I can't seem to find any properties or methods to support UDP Multicasting. Specifically, I need to join a group, but there is so little written on the subject out there. It's driving me crazy.

This part of my application is pretty simple. I need read a multicast feed of stock quotes, then log them into a database. But without setting the group, I'm stuck.

Do you know how to read such a feed?

 

[agoeddeke]

I have set up a UDP client before by binding to a server IP and port, but I have never heard of UDP Multicasting or joining a group. I'm not sure what that entails. Sorry.

Andy