package main import ( "fmt" "github.com/fasthttp/router" "github.com/prometheus/client_golang/prometheus" "github.com/prometheus/client_golang/prometheus/promhttp" "github.com/prometheus/common/expfmt" "github.com/valyala/fasthttp" ) func attachMetrics(r *router.Router, z promhttp.Logger) { r.GET("/metrics/", metricsHandler(prometheus.DefaultGatherer, promhttp.HandlerOpts{ ErrorLog: z, // ErrorHandling: 0, // Registry: nil, // DisableCompression: false, // MaxRequestsInFlight: 0, // Timeout: 0, // EnableOpenMetrics: false, })) } func metricsHandler(reg prometheus.Gatherer, opts promhttp.HandlerOpts) fasthttp.RequestHandler { var ( inFlightSem chan struct{} errCnt = prometheus.NewCounterVec( prometheus.CounterOpts{ Name: "promhttp_metric_handler_errors_total", Help: "Total number of internal errors encountered by the promhttp metric handler.", }, []string{"cause"}, ) ) if opts.MaxRequestsInFlight > 0 { inFlightSem = make(chan struct{}, opts.MaxRequestsInFlight) } if opts.Registry != nil { // Initialize all possibilites that can occur below. errCnt.WithLabelValues("gathering") errCnt.WithLabelValues("encoding") if err := opts.Registry.Register(errCnt); err != nil { if are, ok := err.(prometheus.AlreadyRegisteredError); ok { errCnt = are.ExistingCollector.(*prometheus.CounterVec) } else { panic(err) } } } h := fasthttp.RequestHandler(func(c *fasthttp.RequestCtx) { if inFlightSem != nil { select { case inFlightSem <- struct{}{}: // All good, carry on. defer func() { <-inFlightSem }() default: c.Error(fmt.Sprintf( "Limit of concurrent requests reached (%d), try again later.", opts.MaxRequestsInFlight, ), fasthttp.StatusServiceUnavailable) return } } mfs, err := reg.Gather() if err != nil { if opts.ErrorLog != nil { panic("error gathering metrics:" + err.Error()) } errCnt.WithLabelValues("gathering").Inc() switch opts.ErrorHandling { case promhttp.PanicOnError: panic(err) case promhttp.ContinueOnError: if len(mfs) == 0 { // Still report the error if no metrics have been gathered. c.Error(err.Error(), fasthttp.StatusServiceUnavailable) return } case promhttp.HTTPErrorOnError: c.Error(err.Error(), fasthttp.StatusServiceUnavailable) return } } contentType := expfmt.FmtText c.SetContentType(string(contentType)) enc := expfmt.NewEncoder(c, contentType) var lastErr error // handleError handles the error according to opts.ErrorHandling // and returns true if we have to abort after the handling. handleError := func(err error) bool { if err == nil { return false } lastErr = err if opts.ErrorLog != nil { opts.ErrorLog.Println("error encoding and sending metric family:", err) } errCnt.WithLabelValues("encoding").Inc() switch opts.ErrorHandling { case promhttp.PanicOnError: panic(err) case promhttp.HTTPErrorOnError: c.Error(err.Error(), fasthttp.StatusServiceUnavailable) return true default: // Do nothing in all other cases, including ContinueOnError. return false } } for _, mf := range mfs { if handleError(enc.Encode(mf)) { return } } if closer, ok := enc.(expfmt.Closer); ok { // This in particular takes care of the final "# EOF\n" line for OpenMetrics. if handleError(closer.Close()) { return } } handleError(lastErr) }) if opts.Timeout <= 0 { return h } return fasthttp.TimeoutHandler(h, opts.Timeout, fmt.Sprintf( "Exceeded configured timeout of %v.\n", opts.Timeout, )) }