Multicasting on Ubuntu - c

Question

My situation is as follows:
I have a windows machine running a UDP Multicast server that is broadcasting packets. I wrote a window client that is able to capture these packets without a problem on a separate windows machine that is connected to the network. I ran into a few firewall problems on the windows machines, but worked that out.
Now, I have an ubuntu 12.04 version of the client; however, my program isn't finding these packets. I ran through all the suggestions provided by other stack overflow posts and some google threads:
when I am running my client, netstat -g shows the IP address of the multicast network
I set the rp_filter to 0 using sysctl
I can see the packets when using tcpdump -i wlan0
Added a route (sudo route add -net 224.0.0.0 netmask 224.0.0.0 wlan0)
For step four, this is a wireless connection established over wlan0, so I add the route on wlan0. Similarly, wlan0's rp_filter=0.
Now, for the code. From the print statements and error checking. I am seeing that I am successfully binding, joining the multicast group, creating the buffer, etc... Then it just blocks at the recvfrom() function call.
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <cstring>
#include <unistd.h>
#include <pthread.h>
#include <fstream>
#pragma warning( disable : 4996 )
#define MAX_PACKETSIZE 100000 // max size of packet (actual packet size is dynamic)
bool IPAddress_StringToAddr(char *szNameOrAddress, struct in_addr *Address);
void Unpack(char* pData);
#define MULTICAST_ADDRESS "239.255.42.99" // IANA, local network
#define PORT_COMMAND 1510
#define PORT_DATA 1511
#define SOCKET_ERROR -1
#define INVALID_SOCKET -1
typedef int SOCKET;
SOCKET DataSocket;
int main(int argc, char* argv[])
{
int retval;
char szMyIPAddress[128] = "";
in_addr MyAddress, MultiCastAddress;
int optval = 0x100000;
int optval_size = 4;
// client address
if(argc>1)
{
strcpy(szMyIPAddress, argv[1]); // specified on command line
IPAddress_StringToAddr(szMyIPAddress, &MyAddress);
}
else
{ printf("usage: ./client [local_ip_address]\n"); return 0; }
MultiCastAddress.s_addr = inet_addr(MULTICAST_ADDRESS);
printf("Client: %s\n", szMyIPAddress);
printf("Multicast Group: %s\n", MULTICAST_ADDRESS);
// create a "Data" socket
printf("Create Socket.\n");
DataSocket = socket(AF_INET, SOCK_DGRAM, 0);
// allow multiple clients on same machine to use address/port
int value = 1;
printf("Set SO_REUSEADDR sockopt.\n");
retval = setsockopt(DataSocket, SOL_SOCKET, SO_REUSEADDR, (char*)&value, sizeof(value));
if (retval == SOCKET_ERROR)
{
close(DataSocket);
return -1;
}
//bind
struct sockaddr_in MySocketAddr;
memset(&MySocketAddr, 0, sizeof(MySocketAddr));
MySocketAddr.sin_family = AF_INET;
MySocketAddr.sin_port = htons(PORT_DATA);
MySocketAddr.sin_addr = MyAddress;
printf("Bind Socket.\n");
if (bind(DataSocket, (struct sockaddr *)&MySocketAddr, sizeof(struct sockaddr)) == SOCKET_ERROR)
{
printf("[PacketClient] bind failed.\n");
return 0;
}
// join multicast group
struct ip_mreq Mreq;
Mreq.imr_multiaddr = MultiCastAddress;
Mreq.imr_interface = MyAddress;
printf("Join multicast group.\n");
retval = setsockopt(DataSocket, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&Mreq, sizeof(Mreq));
if (retval == SOCKET_ERROR)
{
printf("[PacketClient] join failed.\n");
return -1;
}
// create a 1MB buffer
printf("Create 1MB Buffer.\n");
setsockopt(DataSocket, SOL_SOCKET, SO_RCVBUF, (char *)&optval, 4);
getsockopt(DataSocket, SOL_SOCKET, SO_RCVBUF, (char *)&optval, (socklen_t*)&optval_size);
if (optval != 0x100000)
{
printf("[PacketClient] ReceiveBuffer size = %d\n", optval);
}
//listening
printf("Listening...\n");
char szData[20000];
int addr_len = sizeof(struct sockaddr);
sockaddr_in TheirAddress;
while (1)
{
// Block until we receive a datagram from the network (from anyone including ourselves)
int nDataBytesReceived = recvfrom(DataSocket, szData, sizeof(szData), 0, (sockaddr *)&TheirAddress, (socklen_t*)&addr_len);
Unpack(szData);
}
return 0;
}
// convert ipp address string to addr
bool IPAddress_StringToAddr(char *szNameOrAddress, struct in_addr *Address)
{
int retVal;
struct sockaddr_in saGNI;
char hostName[256];
char servInfo[256];
u_short port;
port = 0;
// Set up sockaddr_in structure which is passed to the getnameinfo function
saGNI.sin_family = AF_INET;
saGNI.sin_addr.s_addr = inet_addr(szNameOrAddress);
saGNI.sin_port = htons(port);
// getnameinfo
if ((retVal = getnameinfo((sockaddr *)&saGNI, sizeof(sockaddr), hostName, 256, servInfo, 256, NI_NUMERICSERV)) != 0)
{
printf("[PacketClient] GetHostByAddr failed.\n");
return false;
}
Address->s_addr = saGNI.sin_addr.s_addr;
return true;
}
void Unpack(char* pData)
{
printf("Begin Packet\n-------\n");
}
Any suggestions are appreciated. Here is the question I used as a reference when trying to fix this problem: UDP socket (multicast) not receiving data (Ubuntu)

Answer 1

I paste my answer here instead writing it in comments.
As I understood you have windows machines on both sides, successfully broadcasting udp packets and now you want to replace them with ubuntu machines. And the machines are receiving the packets, but your client isn't notified.
Maybe this will help
SOL_SOCKET is for the socket layer, IPPROTO_IP for the IP layer, etc... For multicast programming, level will always be IPPROTO_IP
Here is the working code for simplified RIPv2 protocol that sends and reives multicast traffic without an problem.
int setup_sender_connection(struct in_addr interface_addr){
//create socket
int sock = socket(AF_INET, SOCK_DGRAM, 0);
if(sock<0){
die("Creating Socket");
}
//set outgoing interface
if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, &interface_addr, sizeof(interface_addr))<0){
die("Setting outgoing interface");
}
//disable loopback
u_char loop = 0;
if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop))<0){
die("Disabling loopback");
}
//allow reusing of port
int reuse = 1;
if(setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0){
die("Allowing reuse");
}
//bind to this port
struct sockaddr_in saddr;
bzero(&saddr, sizeof(struct sockaddr_in));
saddr.sin_family = AF_INET;
saddr.sin_port = htons(520);
saddr.sin_addr = interface_addr;
if(bind(sock, (struct sockaddr *)&saddr, sizeof(struct sockaddr_in))<0){
die("Binding");
}
return sock;
}
void join_group(int sock, struct in_addr interface_addr){
//join gorup
struct ip_mreq mreq;
bzero(&mreq, sizeof(struct ip_mreq));
mreq.imr_multiaddr.s_addr = inet_addr(MULTICAST_IP); /* IP multicast address of group */
mreq.imr_interface = interface_addr; /* local IP address of interface */
if(setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq))<0){
die("Joining group");
}
}
void die(char *error){
perror(error);
exit(1);
}