telemetry: Run callbacks at collect time

Calling collect_metrics() from a script would not invoke metric
callbacks, resulting in most of the process metrics to be zero
when a Zeek process isn't scraped via Prometheus.

Fixes #4309

src/telemetry/Manager.cc

@@ -278,6 +278,14 @@ void Manager::InvokeTelemetrySyncHook() {
     in_sync_hook = false;
 }
 
+
+void Manager::UpdateMetrics() {
+    InvokeTelemetrySyncHook();
+
+    for ( const auto& [name, f] : families )
+        f->RunCallbacks();
+}
+
 ValPtr Manager::CollectMetrics(std::string_view prefix_pattern, std::string_view name_pattern) {
     static auto metrics_vector_type = zeek::id::find_type<VectorType>("Telemetry::MetricVector");
     static auto string_vec_type = zeek::id::find_type<zeek::VectorType>("string_vec");
@@ -290,7 +298,7 @@ ValPtr Manager::CollectMetrics(std::string_view prefix_pattern, std::string_view
     static auto metric_opts_type = zeek::id::find_type<zeek::RecordType>("Telemetry::MetricOpts");
     static auto metric_type_idx = metric_opts_type->FieldOffset("metric_type");
 
-    InvokeTelemetrySyncHook();
+    UpdateMetrics();
 
     VectorValPtr ret_val = make_intrusive<VectorVal>(metrics_vector_type);
 
@@ -369,7 +377,7 @@ ValPtr Manager::CollectHistogramMetrics(std::string_view prefix_pattern, std::st
     static auto metric_opts_type = zeek::id::find_type<zeek::RecordType>("Telemetry::MetricOpts");
     static auto metric_type_idx = metric_opts_type->FieldOffset("metric_type");
 
-    InvokeTelemetrySyncHook();
+    UpdateMetrics();
 
     VectorValPtr ret_val = make_intrusive<VectorVal>(metrics_vector_type);
 
@@ -597,10 +605,7 @@ void Manager::ProcessFd(int fd, int flags) {
 
     collector_flare.Extinguish();
 
-    for ( const auto& [name, f] : families )
+    UpdateMetrics();
-        f->RunCallbacks();
-
-    InvokeTelemetrySyncHook();
 
     collector_response_idx = collector_request_idx;
 

src/telemetry/Manager.h

@@ -264,6 +264,11 @@ private:
      */
     void InvokeTelemetrySyncHook();
 
+    /**
+     * Runs the telemetry sync hooks and metric callbacks.
+     */
+    void UpdateMetrics();
+
     bool in_sync_hook = false;
 
     std::map<std::string, std::shared_ptr<MetricFamily>> families;

testing/btest/Baseline/scripts.base.frameworks.telemetry.process-collect/out

@@ -0,0 +1,13 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+zeek_init
+process_cpu_user_seconds_total, [], >0.0, good
+process_cpu_system_seconds_total, [], >0.0, good
+process_resident_memory_bytes, [], >0.0, good
+process_virtual_memory_bytes, [], >0.0, good
+process_open_fds, [], >0.0, good
+zeek_done
+process_cpu_user_seconds_total, [], >0.0, good
+process_cpu_system_seconds_total, [], >0.0, good
+process_resident_memory_bytes, [], >0.0, good
+process_virtual_memory_bytes, [], >0.0, good
+process_open_fds, [], >0.0, good

testing/btest/scripts/base/frameworks/telemetry/process-collect.zeek

@@ -0,0 +1,29 @@
+# @TEST-DOC: Calling collect_metrics() invokes callbacks for process (and other) metrics.
+# Not compilable to C++ due to globals being initialized to a record that
+# has an opaque type as a field.
+# @TEST-REQUIRES: test "${ZEEK_USE_CPP}" != "1"
+#
+# @TEST-EXEC: zeek -r $TRACES/http/get.trace -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+
+@load base/frameworks/telemetry
+
+function print_metrics(ms: vector of Telemetry::Metric) {
+	for (_, m in ms)
+		print m$opts$name, m$label_values, m$value > 0.0 ? ">0.0, good" : "0.0, bad";
+}
+
+event zeek_init()
+	{
+	print "zeek_init";
+	local ms = Telemetry::collect_metrics("process");
+	print_metrics(ms);
+	}
+
+event zeek_done()
+	{
+	print "zeek_done";
+	local ms = Telemetry::collect_metrics("process");
+	print_metrics(ms);
+	}