zeek/scripts/base/frameworks/sumstats/plugins/last.zeek
Benjamin Bannier d5fd29edcd Prefer explicit construction to coercion in record initialization
While we support initializing records via coercion from an expression
list, e.g.,

    local x: X = [$x1=1, $x2=2];

this can sometimes obscure the code to readers, e.g., when assigning to
value declared and typed elsewhere. The language runtime has a similar
overhead since instead of just constructing a known type it needs to
check at runtime that the coercion from the expression list is valid;
this can be slower than just writing the readible code in the first
place, see #4559.

With this patch we use explicit construction, e.g.,

    local x = X($x1=1, $x2=2);
2025-07-11 16:28:37 -07:00

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##! Keep the last X observations.
@load base/frameworks/sumstats
@load base/utils/queue
module SumStats;
export {
redef enum Calculation += {
## Keep last X observations in a queue.
LAST
};
redef record Reducer += {
## Number of elements to keep.
num_last_elements: count &default=0;
};
redef record ResultVal += {
## This is the queue where elements are maintained.
## Don't access this value directly, instead use the
## :zeek:see:`SumStats::get_last` function to get a vector of
## the current element values.
last_elements: Queue::Queue &optional;
};
## Get a vector of element values from a ResultVal.
global get_last: function(rv: ResultVal): vector of Observation;
}
function get_last(rv: ResultVal): vector of Observation
{
local s: vector of any = vector();
if ( rv?$last_elements )
Queue::get_vector(rv$last_elements, s);
local rval: vector of Observation = vector();
for ( i in s )
# When using the cluster-ized version of SumStats, Queue's
# internal table storage uses "any" type for values, so we need
# to cast them here or else they may be left as Broker::Data from
# the unserialization process.
rval += s[i] as Observation;
return rval;
}
hook register_observe_plugins()
{
register_observe_plugin(LAST, function(r: Reducer, val: double, obs: Observation, rv: ResultVal)
{
if ( r$num_last_elements > 0 )
{
if ( ! rv?$last_elements )
rv$last_elements = Queue::init(Queue::Settings($max_len=r$num_last_elements));
Queue::put(rv$last_elements, obs);
}
});
}
hook compose_resultvals_hook(result: ResultVal, rv1: ResultVal, rv2: ResultVal)
{
# Merge $samples
if ( rv1?$last_elements && rv2?$last_elements )
result$last_elements = Queue::merge(rv1$last_elements, rv2$last_elements);
else if ( rv1?$last_elements )
result$last_elements = rv1$last_elements;
else if ( rv2?$last_elements )
result$last_elements = rv2$last_elements;
}