reservoir sampler. untested.

scripts/base/frameworks/sumstats/plugins/last.bro

@@ -0,0 +1,49 @@
+@load base/frameworks/sumstats
+@load base/utils/queue
+
+module SumStats;
+
+export {
+	redef record Reducer += {
+		## A number of sample Observations to collect.
+		samples: count &default=0;
+	};
+
+	redef record ResultVal += {
+		## This is the queue where samples are maintained.  Use the
+		## :bro:see:`SumStats::get_samples` function to get a vector of the samples.
+		samples: Queue::Queue &optional;
+	};
+
+	## Get a vector of sample Observation values from a ResultVal.
+	global get_samples: function(rv: ResultVal): vector of Observation;
+}
+
+function get_samples(rv: ResultVal): vector of Observation
+	{
+	local s: vector of Observation = vector();
+	if ( rv?$samples )
+		Queue::get_vector(rv$samples, s);
+	return s;
+	}
+
+hook observe_hook(r: Reducer, val: double, obs: Observation, rv: ResultVal)
+	{
+	if ( r$samples > 0 )
+		{
+		if ( ! rv?$samples )
+			rv$samples = Queue::init([$max_len=r$samples]);
+		Queue::put(rv$samples, obs);
+		}
+	}
+
+hook compose_resultvals_hook(result: ResultVal, rv1: ResultVal, rv2: ResultVal)
+	{
+	# Merge $samples
+	if ( rv1?$samples && rv2?$samples )
+		result$samples = Queue::merge(rv1$samples, rv2$samples);
+	else if ( rv1?$samples )
+		result$samples = rv1$samples;
+	else if ( rv2?$samples )
+		result$samples = rv2$samples;
+	}