How To Use the WSAPROTOCOL_INFO Structure to Create a Socket (192120)

MORE INFORMATION

To choose the correct service provider, examine the capabilities supported by each service provider and choose the one that matches your needs. For example, the following code snippet demonstrates how to obtain a service provider that supports TCP/IP and Quality of Service. It is worth noting that the names of Microsoft service providers differ between the various Windows platforms. Therefore, this article should not form the basis of choosing the appropriate service provider.

Sample Code

   if (WSAStartup(MAKEWORD(2,2), &WSAData))
      printf("WSAStartup %d", WSAGetLastError());
   else
      {
      // First, have WSAEnumProtocols tell you how big a buffer you need.
      nRet = WSAEnumProtocols(NULL, lpProtocolBuf, &dwBufLen);
      if (SOCKET_ERROR != nRet)
         printf("WSAEnumProtocols: should not have succeeded\n");
      else if (WSAENOBUFS != (dwErr = WSAGetLastError()))
         // WSAEnumProtocols failed for some reason not relating to buffer
         // size - also odd.
         printf("WSAEnumProtocols(1): %d\n", WSAGetLastError());
      else
         {
         // WSAEnumProtocols failed for the "expected" reason. Therefore,
         // you need to allocate a buffer of the appropriate size.
         lpProtocolBuf = (WSAPROTOCOL_INFO *)malloc(dwBufLen);
         if (lpProtocolBuf)
            {
            // Now you can call WSAEnumProtocols again with the expectation
            // that it will succeed because you have allocated a big enough
            // buffer.
            nRet = WSAEnumProtocols(NULL, lpProtocolBuf, &dwBufLen);
            if (SOCKET_ERROR == nRet)
               printf("WSAEnumProtocols(3): %d\n", WSAGetLastError());
            else
               {
               // Loop through protocols, looking for the first service
               // provider that meets the matching criteria.
               bProtocolFound = FALSE;
               for (i=0; i<nRet; i++)
                  {
                  if ((IPPROTO_TCP == lpProtocolBuf[i].iProtocol) &&
                      (XP1_QOS_SUPPORTED == (XP1_QOS_SUPPORTED &
                       lpProtocolBuf[i].dwServiceFlags1)))
                     {
                     bProtocolFound = TRUE;
                     break;
                     }
                  }
               }
            }
         }
      }
				

Once you have chosen a service provider, the following sample code demonstrates how to actually create a socket using a supplied WSAPROTOCOL_INFO structure from the service provider you have chosen:

    sd = WSASocket(
        FROM_PROTOCOL_INFO,
        FROM_PROTOCOL_INFO,
        FROM_PROTOCOL_INFO,
        &lpProtocolBuf[i],
        0,
        WSA_FLAG_OVERLAPPED);
    if (INVALID_SOCKET == sd)
        printf("WSASocket %d", WSAGetLastError());
				

Please note that specifying WSA_FLAG_OVERLAPPED is very useful and is recommended. For additional information on specifying WSA_FLAG_OVERLAPPED, please see the following article in the Microsoft Knowledge Base: Also, do not forget to free the lpProtocolInfo buffer when you are finished using it.