[Winpcap-users] Problems with using pcap_getevent

Swaminathan Gurumoorthy swaminathang at yahoo.com
Thu May 17 22:26:03 GMT 2007

I am relatively new to using winpcap library. I am having issues with the Win32 extension pcap_getevent() API call.
  I have a windows application on my host system, asynchronously reading for ethernet type packets sent by another system (again using Winpcap SendPacket() function)  . I am waiting on an event that I am holding from the pcap_getevent() call. I also have my ethereal window open to confirm if my application is reading packets when they arrive.
  The problem is my application is not notified when the packet actually arrives. I looked through old archives and saw a note saying it is due to the kernel buffer being set to some high value. So I modified my open call to include PCAP_OPENFLAG_MAX_RESPONSIVENESS  flag. I was hoping this will ensure the event will be triggered as soon as the packet arrives. But it did not happen. I also realized that I can use the pcap_setmintocopy() to set the buffer value So I went ahead and set this value to a low number (less than my anticipated packet size). This lead to a different problem. I see that my host program is getting the event now but it gets a slew of duplicate packets. I can see my ethereal window on the host system show duplicates as well.
  I am sure the client did not send all those duplicate packets becasue the ethereal window on the client system is showing only one packet. I also confirmed this by commenting out the pcap_setmintocopy() call and see only one packet on my host ethereal window (but not on my application).
  Am I doing something wrong here? The documentation says "use of pcap_getevent is discouraged because it is not portable" but mine is a pure windows app and I am not worried about portability.
  I also do not want to go to a polling mode using pcap_read_next and all that because I am using this in a thread which is waiting for other events as well. I hate to write yet another thread that will poll and send the event.
  Any help will be much appreciated.

Swaminathan Gurumoorthy
1775 Milmont Dr, Apt S101
Milpitas CA 95035

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