Hello

-
Hello, 

Is there any special consideration for UDP broacasting under Android and OSX ?

I've made a crossplatform socket component to broadcast a message and let different devices knows of each others.

what I don't understand is that Windows receives all the broadcast when Android and OSX don't. The 3 devices are on the same Wifi router.

the socket is setup this way:

so := socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
opt := 1;
setsockopt(so, SOL_SOCKET, SO_REUSEADDR,@opt, SizeOf(opt));
setsockopt(so, SOL_SOCKET, SO_BROADCAST,@opt, SizeOf(opt));
addr.sin_family := AF_INET;
addr.sin_port := htons(2048);
addr.sin_addr := INADDR_ANY;
bind(so, addr, sizeof(addr));

Sending is done this way:
addr.sin_family := AF_INET;
addr.sin_port := htons(2048);
addr.sin_addr := INADDR_BROADCAST;
sendto(so, data, data_len, addr, addr_len);

I've tried to create 2 sockets, one for sending, and the other for reading. the sending socket was bind with
 addr.sin_port := 0;
 addr.sin_addr := my_local_address;
but it changes nothing

I've also tried to replace INADDR_BROADCAST by the network broadcast address...still don't get anything.

Any clue ?

Comments

  1. Paul TOTHJune 8, 2015 at 4:58 AM

    of course the bug seems to be in the unspoken part :D

    I use select(), the first parameter is ignored by Windows, but should be set to the highest socket handle, not the handles count.

    ReplyDelete
  2. Asbjørn HeidJune 8, 2015 at 5:36 AM

    While we're at it, do you clear sin_zero? Heard it could cause issues on some platforms if you don't.

    ReplyDelete
  3. Paul TOTHJune 8, 2015 at 6:17 AM

    yes I do...the MACOS pb was the nfds parameter of select() function...but under Android recvfrom() called directly without select() never returns...

    ReplyDelete
  4. Asbjørn HeidJune 8, 2015 at 6:50 AM

    Paul TOTH The joys of cross-platform programming :)

    ReplyDelete
  5. Paul TOTHJune 9, 2015 at 6:02 AM

    GOT IT !

    ok, they are 2 special things under Android

    1) you have to call WifiManager.createMulticastLock (with android.permission.CHANGE_WIFI_MULTICAST_STATE) to enable your application to receive UDP broadcast, not especially for multicast but also for broadcast messages.

    2) do not bind your socket to the device IP, keep INADDR_ANY with desired port or you'll get nothing.

    ReplyDelete

Post a Comment