tailscale/tsweb/promvarz/promvarz.go

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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package promvarz combines Prometheus metrics exported by our expvar converter
// (tsweb/varz) with metrics exported by the official Prometheus client.
package promvarz
import (
"fmt"
"net/http"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/common/expfmt"
"tailscale.com/tsweb/varz"
)
// OmitPromethusMetrics, if set to true, makes Handler not include native
// Prometheus metrics.
//
// This is useful in some specific cases where the built-in Prometheus
// collectors have poor performance characteristics.
var OmitPromethusMetrics bool
// Handler returns Prometheus metrics exported by our expvar converter
// and the official Prometheus client.
func Handler(w http.ResponseWriter, r *http.Request) {
if err := gatherNativePrometheusMetrics(w); err != nil {
w.WriteHeader(http.StatusInternalServerError)
w.Write([]byte(err.Error()))
return
}
varz.Handler(w, r)
}
// gatherNativePrometheusMetrics writes metrics from the default
// metric registry in text format.
func gatherNativePrometheusMetrics(w http.ResponseWriter) error {
if OmitPromethusMetrics {
return nil
}
enc := expfmt.NewEncoder(w, expfmt.FmtText)
mfs, err := prometheus.DefaultGatherer.Gather()
if err != nil {
return fmt.Errorf("could not gather metrics from DefaultGatherer: %w", err)
}
for _, mf := range mfs {
if err := enc.Encode(mf); err != nil {
return fmt.Errorf("could not encode metric %v: %w", mf, err)
}
}
if closer, ok := enc.(expfmt.Closer); ok {
if err := closer.Close(); err != nil {
return err
}
}
return nil
}