Update dependencies

vendor/tailscale.com/util/usermetric/usermetric.go

@@ -0,0 +1,105 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package usermetric provides a container and handler
+// for user-facing metrics.
+package usermetric
+
+import (
+	"expvar"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"tailscale.com/metrics"
+	"tailscale.com/tsweb/varz"
+)
+
+// Registry tracks user-facing metrics of various Tailscale subsystems.
+type Registry struct {
+	vars expvar.Map
+}
+
+// NewMultiLabelMapWithRegistry creates and register a new
+// MultiLabelMap[T] variable with the given name and returns it.
+// The variable is registered with the userfacing metrics package.
+//
+// Note that usermetric are not protected against duplicate
+// metrics name. It is the caller's responsibility to ensure that
+// the name is unique.
+func NewMultiLabelMapWithRegistry[T comparable](m *Registry, name string, promType, helpText string) *metrics.MultiLabelMap[T] {
+	ml := &metrics.MultiLabelMap[T]{
+		Type: promType,
+		Help: helpText,
+	}
+	var zero T
+	_ = metrics.LabelString(zero) // panic early if T is invalid
+	m.vars.Set(name, ml)
+	return ml
+}
+
+// Gauge is a gauge metric with no labels.
+type Gauge struct {
+	m    *expvar.Float
+	help string
+}
+
+// NewGauge creates and register a new gauge metric with the given name and help text.
+func (r *Registry) NewGauge(name, help string) *Gauge {
+	g := &Gauge{&expvar.Float{}, help}
+	r.vars.Set(name, g)
+	return g
+}
+
+// Set sets the gauge to the given value.
+func (g *Gauge) Set(v float64) {
+	if g == nil {
+		return
+	}
+	g.m.Set(v)
+}
+
+// String returns the string of the underlying expvar.Float.
+// This satisfies the expvar.Var interface.
+func (g *Gauge) String() string {
+	if g == nil {
+		return ""
+	}
+	return g.m.String()
+}
+
+// WritePrometheus writes the gauge metric in Prometheus format to the given writer.
+// This satisfies the varz.PrometheusWriter interface.
+func (g *Gauge) WritePrometheus(w io.Writer, name string) {
+	io.WriteString(w, "# TYPE ")
+	io.WriteString(w, name)
+	io.WriteString(w, " gauge\n")
+	if g.help != "" {
+		io.WriteString(w, "# HELP ")
+		io.WriteString(w, name)
+		io.WriteString(w, " ")
+		io.WriteString(w, g.help)
+		io.WriteString(w, "\n")
+	}
+
+	io.WriteString(w, name)
+	fmt.Fprintf(w, " %v\n", g.m.Value())
+}
+
+// Handler returns a varz.Handler that serves the userfacing expvar contained
+// in this package.
+func (r *Registry) Handler(w http.ResponseWriter, req *http.Request) {
+	varz.ExpvarDoHandler(r.vars.Do)(w, req)
+}
+
+// String returns the string representation of all the metrics and their
+// values in the registry. It is useful for debugging.
+func (r *Registry) String() string {
+	var sb strings.Builder
+	r.vars.Do(func(kv expvar.KeyValue) {
+		fmt.Fprintf(&sb, "%s: %v\n", kv.Key, kv.Value)
+	})
+
+	return sb.String()
+}