package application import ( "net/http" "time" ) // Fetches data from remote endpoint, parses it and updates in storage. func (a *Application) fetch() { // Do not do anything if fetching is running. // ToDo: maybe another approach? a.fetchIsRunningMutex.RLock() // This is an optimization to avoid excessive waiting when using Lock(). // Most of time application will wait between fetches. // nolint:ifshort isFetching := a.fetchIsRunning a.fetchIsRunningMutex.RUnlock() if isFetching { return } a.fetchIsRunningMutex.Lock() a.fetchIsRunning = true a.fetchIsRunningMutex.Unlock() a.logger.Infoln("Fetching data for", a.name) req, err := http.NewRequestWithContext(a.ctx, "GET", a.config.Endpoint, nil) if err != nil { a.logger.Infoln("Failed to create request for", a.name, "metrics:", err.Error()) return } for header, value := range a.config.Headers { req.Header.Add(header, value) } resp, err := a.httpClient.Do(req) if err != nil { a.logger.Infoln("Failed to execute request for", a.name, "metrics:", err.Error()) return } defer resp.Body.Close() data, err := a.parse(resp.Body) if err != nil { a.logger.Infoln("Failed to parse response body for", a.name, "metrics:", err.Error()) return } a.storage.Put(data) a.fetchIsRunningMutex.Lock() a.fetchIsRunning = false a.fetchIsRunningMutex.Unlock() } // Configures and starts Prometheus data fetching goroutine. func (a *Application) startFetcher() { fetchTicker := time.NewTicker(a.config.TimeBetweenRequests) // nolint:exhaustruct a.httpClient = &http.Client{ Timeout: time.Second * 5, } defer a.logger.Debugln("Fetcher for", a.name, "completed") // First fetch should be executed ASAP. a.fetch() for { select { case <-a.ctx.Done(): return case <-fetchTicker.C: a.fetch() } } }