func main()

in entrypoint.go [101:180]
57 lines of code
13 McCabe index (conditional complexity)

func main() {
	// SIGINT handles Ctrl+C locally.
	// SIGTERM handles Cloud Run termination signal.
	signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)
	ctx := context.Background()

	lastRawConfig, err := getRawUserConfig(userConfigFile)
	if err != nil {
		log.Fatal(err)
	}

	// Generate the OTel config for the first time.
	err = generateOtelConfig(ctx, userConfigFile)
	if err != nil {
		log.Fatal(err)
	}

	entrypointMux := http.NewServeMux()
	entrypointMux.HandleFunc(livenessProbePath, healthcheckHandler)

	go func() {
		err := http.ListenAndServe(fmt.Sprintf(":%d", livenessProbePort), entrypointMux)
		if err != nil && err != http.ErrServerClosed {
			log.Fatal(err)
		}
	}()

	// Spin up new-subprocess that runs the OTel collector and store the PID.
	// This OTel collector should use the generated config.
	var procAttr os.ProcAttr
	procAttr.Files = []*os.File{nil, /* stdin is not needed for the collector */
		os.Stdout, os.Stderr}
	collectorProcess, err := os.StartProcess("./rungmpcol", []string{"./rungmpcol", "--config", otelConfigFile}, &procAttr)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("entrypoint: started OTel successfully")

	refreshTicker := time.NewTicker(configRefreshInterval)
	for {
		select {
		case <-refreshTicker.C:
			rawConfig, err := getRawUserConfig(userConfigFile)
			if err != nil {
				log.Fatal(err)
			}

			// Check if we're using the default config. Only reload if something
			// has changed since the last time we checked.
			if rawConfig == lastRawConfig {
				continue
			}

			// Something changed since the last time we checked the config.
			err = generateOtelConfig(ctx, userConfigFile)
			if err != nil {
				log.Fatal(err)
			}
			lastRawConfig = rawConfig

			// Signal the OTel collector to reload its config
			collectorProcess.Signal(syscall.SIGHUP)
			log.Println("entrypoint: reloaded OTel config")
		case sig := <-signalChan:
			// Wait for signals from Cloud Run. Signal the sub process appropriately
			// after making relevant changes to the config and/or health signals.
			// TODO(b/307317433): Consider having a timeout to shutdown the subprocess
			// non-gracefully.
			log.Printf("entrypoint: %s signal caught", sig)

			collectorProcess.Signal(sig)
			processState, err := collectorProcess.Wait()
			if err != nil {
				log.Fatalf(processState.String(), err)
			}
			log.Print("entrypoint: sidecar exited")
			return
		}
	}
}