Is there some way to generate random Multicast address ?

Anticross

I write program which will stream audio to multicast group. I need to generate random multicast ip which is not reserved yet. I need something like chooseRandomIPv4SSMAddress function in live555 library. So it there any way to do this in qt ?

Anticross

The realization of this function in live555 library is seems like this:
@netAddressBits chooseRandomIPv4SSMAddress(UsageEnvironment& env) {
// First, a hack to ensure that our random number generator is seeded:
(void) ourIPAddress(env);

// Choose a random address in the range [232.0.1.0, 232.255.255.255)
// i.e., [0xE8000100, 0xE8FFFFFF)
netAddressBits const first = 0xE8000100, lastPlus1 = 0xE8FFFFFF;
netAddressBits const range = lastPlus1 - first;

return ntohl(first + ((netAddressBits)our_random())%range);
}@

And:
@netAddressBits ourIPAddress(UsageEnvironment& env) {
static netAddressBits ourAddress = 0;
int sock = -1;
struct in_addr testAddr;

if (ourAddress == 0) {
// We need to find our source address
struct sockaddr_in fromAddr;
fromAddr.sin_addr.s_addr = 0;

// Get our address by sending a (0-TTL) multicast packet,
// receiving it, and looking at the source address used.
// (This is kinda bogus, but it provides the best guarantee
// that other nodes will think our address is the same as we do.)
do {
  loopbackWorks = 0; // until we learn otherwise

  testAddr.s_addr = our_inet_addr("228.67.43.91"); // arbitrary
  Port testPort(15947); // ditto

  sock = setupDatagramSocket(env, testPort);
  if (sock < 0) break;

  if (!socketJoinGroup(env, sock, testAddr.s_addr)) break;

  unsigned char testString[] = "hostIdTest";
  unsigned testStringLength = sizeof testString;

  if (!writeSocket(env, sock, testAddr, testPort, 0,
     testString, testStringLength)) break;

  // Block until the socket is readable (with a 5-second timeout):
  fd_set rd_set;
  FD_ZERO(&rd_set);
  FD_SET((unsigned)sock, &rd_set);
  const unsigned numFds = sock+1;
  struct timeval timeout;
  timeout.tv_sec = 5;
  timeout.tv_usec = 0;
  int result = select(numFds, &rd_set, NULL, NULL, &timeout);
  if (result <= 0) break;

  unsigned char readBuffer[20];
  int bytesRead = readSocket(env, sock,
 readBuffer, sizeof readBuffer,
 fromAddr);
  if (bytesRead != (int)testStringLength

|| strncmp((char*)readBuffer, (char*)testString, testStringLength) != 0) {
break;
}

  loopbackWorks = 1;
} while (0);

if (sock >= 0) {
  socketLeaveGroup(env, sock, testAddr.s_addr);
  closeSocket(sock);
}

if (!loopbackWorks) do {
  // We couldn't find our address using multicast loopback,
  // so try instead to look it up directly - by first getting our host name, and then resolving this host name
  char hostname[100];
  hostname[0] = '\0';
  int result = gethostname(hostname, sizeof hostname);
  if (result != 0 || hostname[0] == '\0') {

env.setResultErrMsg("initial gethostname() failed");
break;
}

  // Try to resolve "hostname" to an IP address:
  NetAddressList addresses(hostname);
  NetAddressList::Iterator iter(addresses);
  NetAddress const* address;

  // Take the first address that's not bad:
  netAddressBits addr = 0;
  while ((address = iter.nextAddress()) != NULL) {

netAddressBits a = (netAddressBits)(address->data());
if (!badAddressForUs(a)) {
addr = a;
break;
}
}

  // Assign the address that we found to "fromAddr" (as if the 'loopback' method had worked), to simplify the code below: 
  fromAddr.sin_addr.s_addr = addr;
} while (0);

// Make sure we have a good address:
netAddressBits from = fromAddr.sin_addr.s_addr;
if (badAddressForUs(from)) {
  char tmp[100];
  sprintf(tmp, "This computer has an invalid IP address: %s", AddressString(from).val());
  env.setResultMsg(tmp);
  from = 0;
}

ourAddress = from;

// Use our newly-discovered IP address, and the current time,
// to initialize the random number generator's seed:
struct timeval timeNow;
gettimeofday(&timeNow, NULL);
unsigned seed = ourAddress^timeNow.tv_sec^timeNow.tv_usec;
our_srandom(seed);

}
return ourAddress;
}@

Anticross

So is there any solution on Qt ?

Anticross

How can I check if multicast group exist or not ? If I have it's ip ?

maxim.prishchepa

I need to solve similar issue, some one know how to check is multicast group exists?