Refactor collectors

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

pkg/collector/handler.go

@@ -0,0 +1,77 @@
+//go:build windows
+
+package collector
+
+import (
+	"fmt"
+	stdlog "log"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+	"github.com/prometheus-community/windows_exporter/pkg/types"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/prometheus/common/version"
+)
+
+func (c *Collectors) BuildServeHTTP(disableExporterMetrics bool, timeoutMargin float64) http.HandlerFunc {
+	collectorFactory := func(timeout time.Duration, requestedCollectors []string) (error, *Prometheus) {
+		filteredCollectors := make(map[string]types.Collector)
+		// scrape all enabled collectors if no collector is requested
+		if len(requestedCollectors) == 0 {
+			filteredCollectors = c.collectors
+		}
+		for _, name := range requestedCollectors {
+			col, exists := c.collectors[name]
+			if !exists {
+				return fmt.Errorf("unavailable collector: %s", name), nil
+			}
+			filteredCollectors[name] = col
+		}
+		return nil, NewPrometheus(timeout, c, c.logger)
+	}
+
+	return func(w http.ResponseWriter, r *http.Request) {
+		const defaultTimeout = 10.0
+
+		var timeoutSeconds float64
+		if v := r.Header.Get("X-Prometheus-Scrape-Timeout-Seconds"); v != "" {
+			var err error
+			timeoutSeconds, err = strconv.ParseFloat(v, 64)
+			if err != nil {
+				_ = level.Warn(c.logger).Log("msg", fmt.Sprintf("Couldn't parse X-Prometheus-Scrape-Timeout-Seconds: %q. Defaulting timeout to %f", v, defaultTimeout))
+			}
+		}
+		if timeoutSeconds == 0 {
+			timeoutSeconds = defaultTimeout
+		}
+		timeoutSeconds = timeoutSeconds - timeoutMargin
+
+		reg := prometheus.NewRegistry()
+		err, wc := collectorFactory(time.Duration(timeoutSeconds*float64(time.Second)), r.URL.Query()["collect[]"])
+		if err != nil {
+			_ = level.Warn(c.logger).Log("msg", "Couldn't create filtered metrics handler", "err", err)
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte(fmt.Sprintf("Couldn't create filtered metrics handler: %s", err))) //nolint:errcheck
+			return
+		}
+
+		reg.MustRegister(wc)
+		if !disableExporterMetrics {
+			reg.MustRegister(
+				collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
+				collectors.NewGoCollector(),
+				version.NewCollector("windows_exporter"),
+			)
+		}
+
+		h := promhttp.HandlerFor(reg, promhttp.HandlerOpts{
+			ErrorLog: stdlog.New(log.NewStdlibAdapter(level.Error(c.logger)), "", stdlog.Lshortfile),
+		})
+		h.ServeHTTP(w, r)
+	}
+}