[Click] FromDump restart

[Eddie Kohler]

Hi Robert,

The problem with filepos is that filepos=0 is the pcap file header.  You need 
to set it to the first byte of actual packet data, which might be 24 or 28 
depending on pcap version.

This script works for me.  It relies on the fact that FromDump skips the 
header at initialization time, but does not actually read any packets until 
ACTIVE is true.


fd::FromDump(~/src/ipsumdump/test/one-byte-payload.trace,
	FORCE_IP true, ACTIVE false, END_CALL restarter.step)
	-> IPPrint -> Discard;

restarter::Script(init first_offset $(fd.filepos),
	write fd.active true,
	pause,
	write fd.filepos $first_offset,
	loop)


Eddie


Robert Ross wrote:
> I'm trying to use a Script element along with a FromDump to loop a small PCAP file several times with a delay between replays.  The script basically works except for one critical element:  I cannot seem to reset the FromDump "filepos" handler to the beginning of the file.  As indicated in the documentation, the issue appears to be determining the correct byte offset for the beginning of the first packet in the file.  I've tried the following with no luck:
>  
> 1.  Setting filepos=0.  If only it were that simple...
> 2.  Wait until the first packet has come out and "poke" the script using a Counter element.  Then use the script to calculate various starting positions using a combination of read handlers from FromDump and Counter.
>  
> Some of the questions I have are:
>  
> 1.  Both packet_filepos and filepos provide byte offsets, but the documentation does not adequately describe what these offsets represent.  Is packet_filepos the end point of the last packet read?  The start point of the last packet read?  The start point of the next packet to be read?  Something else?  What is the difference between filepos and packet_filepos?
> 2.  Is there another simpler way to loop a PCAP file that I'm missing?
> 3.  Assuming I knew the correct offset, is it even possible to reset the filepos and re-play the PCAP file again?
>  
> As a general suggestion, added LOOP and LOOP_INTERVAL keywords to the various dump elements could be extremely useful.  In the absence of those, at the very least a "restart" or "start_pos" handler would be equally useful.  I'm currently wondering why the "filepos" handler is even writeable...
>  
> Thanks,
> Robert A. Ross
> DSCI Inc.
> 609-509-5139
> _______________________________________________
> click mailing list
> click at amsterdam.lcs.mit.edu
> https://amsterdam.lcs.mit.edu/mailman/listinfo/click