chore(userspace/falco): fix build for non linux minimal builds.

Signed-off-by: Federico Di Pierro <[email protected]>

Author: FedeDP

userspace/falco/app/actions/process_events.cpp

@@ -491,8 +491,9 @@ falco::app::run_result falco::app::actions::process_events(falco::app::state& s)
 				}
 
 				if(s.enabled_sources.size() == 1) {
-					// Since the inspector is now opened, we can enable prometheus metrics
-					s.webserver.enable_prometheus_metrics(s);
+					if(s.on_inspectors_opened != nullptr) {
+						s.on_inspectors_opened();
+					}
 
 					// optimization: with only one source we don't spawn additional threads
 					process_inspector_events(s,
@@ -523,9 +524,8 @@ falco::app::run_result falco::app::actions::process_events(falco::app::state& s)
 				break;
 			}
 		}
-		if(s.enabled_sources.size() > 1) {
-			// Since all inspectors are now opened, we can enable prometheus metrics
-			s.webserver.enable_prometheus_metrics(s);
+		if(s.enabled_sources.size() > 1 && s.on_inspectors_opened != nullptr) {
+			s.on_inspectors_opened();
 		}
 
 		// wait for event processing to terminate for all sources

userspace/falco/app/actions/start_webserver.cpp

@@ -44,6 +44,7 @@ falco::app::run_result falco::app::actions::start_webserver(falco::app::state& s
 	                          std::to_string(webserver_config.m_listen_port) + ssl_option + "\n");
 
 	state.webserver.start(state, webserver_config);
+	state.on_inspectors_opened = [&state]() { state.webserver.enable_prometheus_metrics(state); };
 #endif
 	return run_result::ok();
 }

userspace/falco/app/state.h

@@ -116,6 +116,9 @@ struct state {
 
 	falco_webserver webserver;
 #endif
+	// Set by start_webserver to start prometheus metrics
+	// once all inspectors are opened.
+	std::function<void()> on_inspectors_opened = nullptr;
 
 	inline bool is_capture_mode() const { return config->m_engine_mode == engine_kind_t::REPLAY; }