How to distinguish the broad packets or normal packets?

[wangningyu]

The following is a fragment of code：

sockaddr\_in		from,a;
WSADATA			wsdata;
BOOL			optval = TRUE;
u\_short			uPort  = m\_nPort;

if(WSAStartup(0x0202,&wsdata) != 0)
{
	CString strErr;
	strErr.Format(\_T("WSAStartup Init failed! Error code:%d"),WSAGetLastError());
	AddNote(strErr);
	\_endthreadex(0);
	return FALSE;
}

a.sin\_family		= AF\_INET;
a.sin\_addr.s\_addr	= 0;
a.sin\_port			= htons(uPort);

from.sin\_family			= AF\_INET;
from.sin\_addr.s\_addr	= INADDR\_BROADCAST;
from.sin\_port			= htons(uPort);

int fromlength=sizeof(SOCKADDR);
pThread->m\_socket = socket(AF\_INET,SOCK\_DGRAM,0);
setsockopt(pThread->m\_socket,SOL\_SOCKET,SO\_BROADCAST,(char FAR \*)&optval,sizeof(optval));
bind(pThread->m\_socket,(sockaddr \*)&a,sizeof(sockaddr\_in));

char		buf\[BUF\_MAX\_LEN\] = {0x00};
int			nLen = 0;
char		\*pszIPClient = NULL;
u\_short		uPortClient  = 0;
THREADBOARD	\*pThreadBoard = NULL;
CString		strInit = \_T("");

strInit.Format(\_T("Port: %d Now waiting for clients..."),uPort);
AddNote(strInit);

while(true)
{
	nLen = recvfrom(pThread->m\_socket,buf,BUF\_MAX\_LEN,0,(struct sockaddr FAR \*)&from,(int FAR \*)&fromlength);
	if(nLen > 0)
	{
		// How to distinguish is send broadcast , or normal send ?
	}
}

Thanks for your reply !

[pasztorpisti]

You can do this by using raw sockets but I was raw-socketing only on linux, dont know how it works on windows (if it works at all...). I searched for an example and found this discussion: http://bytes.com/topic/c/answers/900770-how-determine-origin-incoming-message-uincast-multicast-broadcast[^] One of the answers contains source code, read along that thread. Note: I havent tested their code. EDIT: The trick is simple: the sendto address is in the header of the datagram you received, but your recvfrom returns just the payload from that and the address of the sender. You need a method to reach other fields of the received UDP packet header, one way is using raw sockets.

[Software_Developer]

First [this]. Then, Packet Filtering , found [here]. Also [this].

[wangningyu]

Thanks !