Fix prometheus passthrough for existing value types (#3351)

plugins/outputs/prometheus_client/prometheus_client.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 	"regexp"
 	"sort"
 	"strings"
@@ -15,6 +16,7 @@ import (
 	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 var invalidNameCharRE = regexp.MustCompile(`[^a-zA-Z0-9_]`)
@@ -46,6 +48,7 @@ type PrometheusClient struct {
 	Listen             string
 	ExpirationInterval internal.Duration `toml:"expiration_interval"`
 	Path               string            `toml:"path"`
+	CollectorsExclude  []string          `toml:"collectors_exclude"`
 
 	server *http.Server
 
@@ -62,11 +65,26 @@ var sampleConfig = `
 
   ## Interval to expire metrics and not deliver to prometheus, 0 == no expiration
   # expiration_interval = "60s"
+
+  ## Collectors to enable, valid entries are "gocollector" and "process".
+  ## If unset, both are enabled.
+  collectors_exclude = ["gocollector", "process"]
 `
 
 func (p *PrometheusClient) Start() error {
 	prometheus.Register(p)
 
+	for _, collector := range p.CollectorsExclude {
+		switch collector {
+		case "gocollector":
+			prometheus.Unregister(prometheus.NewGoCollector())
+		case "process":
+			prometheus.Unregister(prometheus.NewProcessCollector(os.Getpid(), ""))
+		default:
+			return fmt.Errorf("unrecognized collector %s", collector)
+		}
+	}
+
 	if p.Listen == "" {
 		p.Listen = "localhost:9273"
 	}
@@ -76,7 +94,9 @@ func (p *PrometheusClient) Start() error {
 	}
 
 	mux := http.NewServeMux()
-	mux.Handle(p.Path, prometheus.Handler())
+	mux.Handle(p.Path, promhttp.HandlerFor(
+		prometheus.DefaultGatherer,
+		promhttp.HandlerOpts{ErrorHandling: promhttp.ContinueOnError}))
 
 	p.server = &http.Server{
 		Addr:    p.Listen,
@@ -243,10 +263,22 @@ func (p *PrometheusClient) Write(metrics []telegraf.Metric) error {
 			// Special handling of value field; supports passthrough from
 			// the prometheus input.
 			var mname string
-			if fn == "value" {
-				mname = sanitize(point.Name())
-			} else {
-				mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
+			switch point.Type() {
+			case telegraf.Counter:
+				if fn == "counter" {
+					mname = sanitize(point.Name())
+				}
+			case telegraf.Gauge:
+				if fn == "gauge" {
+					mname = sanitize(point.Name())
+				}
+			}
+			if mname == "" {
+				if fn == "value" {
+					mname = sanitize(point.Name())
+				} else {
+					mname = sanitize(fmt.Sprintf("%s_%s", point.Name(), fn))
+				}
 			}
 
 			var fam *MetricFamily