Re: Compatibility Libpcap/Winpcap and timout of

[Guy Harris <guy () alum mit edu>]

On Jan 28, 2009, at 1:48 AM, Benoit wrote:

> Okay so I should use something like this:
>
> int ret=0;

Assigning 0 to ret isn't necessary, as you're setting it to the return  
value of pcap_select_ms() immediately after assigning 0 to it.

> if((ret =pcap_select_ms(ifhard->adhandle,ifhard->timeout)<=0)) {

As long as you write your own pcap_select_ms() routine - there's no  
such routine in libpcap.

> This might work only on Windows

It will only work on Windows if pcap_select_ms() uses  
WaitForSingleObject() or WaitForMultipleObjects().

> and Linux (This is okay for me because we
> don't use OSX in our lab).

It should work on all OSes other than Mac OS X, possibly AIX, and  
older versions of *BSD.

As per my earlier mail, if you put the pcap_t into non-blocking mode,  
and attempt to read from the handle regardless of whether select times  
out or not, it'll work on those OSes as well.

> Moreover sometimes I need to loop 10 times to be sure to receive
> > correctly the packet,
>
> Why?  Does pcap_next_ex() return 0 or a negative value?
> it return 0 because the timeout is less than the time for: t(PC ->  
> FPGA) +
> t(FPGA setup) + t(FPGA -> PC).

In Linux, libpcap 0.9.8 ignores the timeout passed to  
pcap_open_live(), so the timeout is irrelevant in your case.

There are, however, some cases where it can return 0 regardless of the  
timeout.

There's nothing magic about the number 10.  Don't loop with a count.
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