func handler()

in sandbox/ho11y/main.go [253:312]
37 lines of code
5 McCabe index (conditional complexity)

func handler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	traceid := getXrayTraceID(trace.SpanFromContext(ctx))

	// if enabled, we first handle throttling. if the current TPS value
	// is larger than what user told us to, return a 429 and call it a day.
	// we always need to increment the period counter for throttling:
	if enableThrottling {
		invokesInPeriod += 1
		if tpsValue > tpsCutoffVal {
			w.WriteHeader(http.StatusTooManyRequests)
			invokeCounter.WithLabelValues(strconv.Itoa(http.StatusTooManyRequests)).Inc()
			log.Info(fmt.Sprintf("Throttle engaged, got %v TPS with a %v TPS cutoff point", tpsValue, tpsCutoffVal))
			return
		}
	}

	// next, if failure injection is enabled, then we
	// generate a random value (range: 0 to 100)
	// and if this one is above a fixed threshold (50)
	// then we drop the request with a randomly selected
	// status code, bastard-operator-from-hell style.
	// result: in average only half of the requests
	// are successfully served:
	if os.Getenv("HO11Y_INJECT_FAILURE") != "" {
		threshold := 50
		level := rand.Intn(100)
		if level > threshold {
			// now pick a random failure HTTP status code:
			rc := responseCodes[rand.Intn(len(responseCodes))]
			w.WriteHeader(rc)
			invokeCounter.WithLabelValues(strconv.Itoa(rc)).Inc()
			return
		}
	}

	// if we are below the threshold, respond successfully
	// that is with HTTP 200 status code:
	w.Header().Set("Content-Type", "application/json")

	// emit log event for invocation:
	log.WithFields(
		log.Fields{
			"event":   "invoke",
			"traceID": traceid,
			"remote":  r.RemoteAddr,
		},
	).Info("ho11y was invoked")

	// increment counter metric for invocation:
	invokeCounter.WithLabelValues(strconv.Itoa(http.StatusOK)).Inc()

	// emit trace(s) for invocation:
	json := simplejson.New()
	json.Set("traceId", traceid)
	invokeDownstreams(ctx)
	payload, _ := json.MarshalJSON()

	_, _ = w.Write(payload)
}