[Click] Accessing element handlers from within a click script

[Eddie Kohler]

Hi David,

Bart, Beyers, and Peter had good feedback for you, but I wanted to point 
specifically at some elements that already pass handlers around.  Most of our 
current elements use HandlerCall objects for write handlers, not read 
handlers.  But you can find a couple that use read handlers.

* elements/analysis/aggregateipflows.* : The _filepos_h HandlerCall object is 
called to fetch the current packet's file position...

HandlerCall *_filepos_h; ...
String s = _filepos_h->call_read();

Also check out elements/standard/script.* and elements/userlevel/progressbar.* 
for examples of using Handler objects directly.  But probably the best thing 
is to look at the HandlerCall documentation Peter mentioned.

Eddie


david johnson wrote:
> Hi
> 
> I've got the following example code in which I'm continuously scanning
> for beacons and storing the results in bs.scan. I then want to send the
> results of the scan to other nodes in the network when I get a certain
> request message.
> 
> To do this I need to access the BeaconScanner handler "scan". I'm new to
> click and maybe I'm breaking some fundamental rule in a click config
> script but is it possible to pass an element handler as a parameter to
> another element. 
> 
> I need to do it at this point in the code:
> 25   -> send_scan_results(### pass bs.scan handler to element ###)
> 
> Thanks
> David
> 
> =========================================
> 
>   1 control :: ControlSocket("TCP", 7777);
>   2 
>   3 rates :: AvailableRates(DEFAULT 2 4 11 22);
>   4 
>   5 FromDevice(ath0, PROMISC true)
>   6   -> RadiotapDecap()
>   7   -> c1 :: Counter
>   8   -> wifi_cl :: Classifier(0/00%0c, /mgt
>   9       0/08%0c, /data);
>  10 
>  11 wifi_cl [0] -> Classifier(0/80%f0)
>  12     -> c2 :: Counter
>  13     -> bs :: BeaconScanner()
>  14     -> Discard;
>  15 
>  16 wifi_cl [1]
>  17   -> WifiDecap()
>  18   -> cognitive :: -> Classifier(//some String 1,
>  19       // Some String 2,
>  20       // Some String 3,
>  21       );
>  22 
>  23 // Respond to Get beacons stored in node
>  24 cognitive [0]
>  25   -> send_scan_results(### pass bs.scan handler to element ###)
>  26   -> q;
>  27 
>  28 
>  29 q :: Queue(10)
>  30 -> wep_encap :: WepEncap(ACTIVE false)
>  31 -> set_rate :: SetTXRate(2)
>  32 -> rate :: ProbeTXRate(OFFSET 4,
>  33            THRESHOLD 0,
>  34            WINDOW 10000,
>  35            RT rates)
>  36 -> SetTXPower(63)
>  37 -> extra_encap :: ExtraEncap()
>  38 -> to_dev :: ToDevice (ath0);
> 
> 
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