github.com/prometheus/client_golang v1.19.1: prometheus.Gauge

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify github.com/prometheus/client_golang/prometheus.Gauge in pkg:golang/github.com/prometheus/client_golang@v1.19.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/prometheus/client_golang@v1.19.1
Demonstrate these symbols/APIs:
  - github.com/prometheus/client_golang/prometheus.Gauge

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:fa6f778b69d8f656035512b9cd8c895e83f100df74df978c3d69710bb4e9a04e","contract":["prometheus.NewGauge creates a Gauge metric with GaugeOpts (Name, Help, ConstLabels)","Gauge.Set sets the metric to an arbitrary float64 value","Gauge.Inc increments the metric value by 1.0","Gauge.Dec decrements the metric value by 1.0","Gauge.Add adds a float64 amount to the current metric value","Gauge.Sub subtracts a float64 amount from the current metric value","Gauge.SetToCurrentTime sets the metric value to the current unix epoch timestamp in seconds","prometheus.Registry registers a Gauge and gathers metric families offline"],"goal":"verify github.com/prometheus/client_golang/prometheus.Gauge in pkg:golang/github.com/prometheus/client_golang@v1.19.1","kind":"HOW","packages":["pkg:golang/github.com/prometheus/client_golang@v1.19.1"],"schemaVersion":1,"symbols":["github.com/prometheus/client_golang/prometheus.Gauge"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/prometheus/client_golang@v1.19.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/prometheus/client_golang@v1.19.1","symbols":["github.com/prometheus/client_golang/prometheus.Gauge"],"verifierAdapter":"golang@1"}

package sample

import (
	"errors"

	"github.com/prometheus/client_golang/prometheus"
	dto "github.com/prometheus/client_model/go"
)

// NewTemperatureGauge creates and returns a new prometheus.Gauge metric with given options.
func NewTemperatureGauge(name, help string, constLabels prometheus.Labels) prometheus.Gauge {
	return prometheus.NewGauge(prometheus.GaugeOpts{
		Name:        name,
		Help:        help,
		ConstLabels: constLabels,
	})
}

// AdjustGauge demonstrates various Gauge manipulation methods: Set, Inc, Dec, Add, Sub.
func AdjustGauge(g prometheus.Gauge, initial float64) {
	g.Set(initial)
	g.Inc()
	g.Add(5.5)
	g.Dec()
	g.Sub(2.5)
}

// SetCurrentTime sets the Gauge value to the current unix epoch timestamp in seconds.
func SetCurrentTime(g prometheus.Gauge) {
	g.SetToCurrentTime()
}

// ReadGaugeValue extracts the float64 value directly from the Gauge metric offline via Write.
func ReadGaugeValue(g prometheus.Gauge) (float64, error) {
	var m dto.Metric
	if err := g.Write(&m); err != nil {
		return 0, err
	}
	gauge := m.GetGauge()
	if gauge == nil {
		return 0, errors.New("metric is not a gauge")
	}
	return gauge.GetValue(), nil
}

// RegisterAndGather registers the gauge to a custom registry and gathers the metric value.
func RegisterAndGather(registry *prometheus.Registry, g prometheus.Gauge, metricName string) (float64, error) {
	if err := registry.Register(g); err != nil {
		return 0, err
	}
	mfs, err := registry.Gather()
	if err != nil {
		return 0, err
	}
	for _, mf := range mfs {
		if mf.GetName() == metricName {
			for _, m := range mf.GetMetric() {
				if gauge := m.GetGauge(); gauge != nil {
					return gauge.GetValue(), nil
				}
			}
		}
	}
	return 0, errors.New("metric not found in gathered families")
}

module example.com/prometheus-gauge-sample

go 1.21

require (
	github.com/prometheus/client_golang v1.19.1
	github.com/prometheus/client_model v0.5.0
)

require (
	github.com/beorn7/perks v1.0.1 // indirect
	github.com/cespare/xxhash/v2 v2.2.0 // indirect
	github.com/prometheus/common v0.48.0 // indirect
	github.com/prometheus/procfs v0.12.0 // indirect
	golang.org/x/sys v0.17.0 // indirect
	google.golang.org/protobuf v1.33.0 // indirect
)

github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
github.com/prometheus/client_golang v1.19.1 h1:wZWJDwK+NameRJuPGDhlnFgx8e8HN3XHQeLaYJFJBOE=
github.com/prometheus/client_golang v1.19.1/go.mod h1:mP78NwGzrVks5S2H6ab8+ZZGJLZUq1hoULYBAYBw1Ho=
github.com/prometheus/client_model v0.5.0 h1:VQw1hfvPvk3Uv6Qf29VrPF32JB6rtbgI6cYPYQjL0Qw=
github.com/prometheus/client_model v0.5.0/go.mod h1:dTiFglRmd66nLR9Pv9f0mZi7B7fk5Pm3gvsjB5tr+kI=
github.com/prometheus/common v0.48.0 h1:QO8U2CdOzSn1BBsmXJXduaaW+dY/5QLjfB8svtSzKKE=
github.com/prometheus/common v0.48.0/go.mod h1:0/KsvlIEfPQCQ5I2iNSAWKPZziNCvRs5EC6ILDTlAPc=
github.com/prometheus/procfs v0.12.0 h1:jluTpSng7V9hY0O2R9DzzJHYb2xULk9VTR1V1R/k6Bo=
github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3cnaOZAZEfOo=
golang.org/x/sys v0.17.0 h1:25cE3gD+tdBA7lp7QfhuV+rJiE9YXTcS3VG1SqssI/Y=
golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

{
  "schemaVersion": 1,
  "goal": "verify github.com/prometheus/client_golang/prometheus.Gauge in pkg:golang/github.com/prometheus/client_golang@v1.19.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/prometheus/client_golang@v1.19.1"
  ],
  "symbols": [
    "github.com/prometheus/client_golang/prometheus.Gauge"
  ]
}

package main

import (
	"fmt"
	"math"
	"os"
	"time"

	"example.com/prometheus-gauge-sample"
	"github.com/prometheus/client_golang/prometheus"
)

func main() {
	fmt.Println("Running prometheus.Gauge contract verification...")

	// 1. Creation with GaugeOpts
	labels := prometheus.Labels{"sensor": "temp_1", "unit": "celsius"}
	gauge := sample.NewTemperatureGauge("room_temperature_celsius", "Current room temperature in Celsius", labels)
	if gauge == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected non-nil Gauge instance\n")
		os.Exit(1)
	}

	// 2. Set
	gauge.Set(25.0)
	val, err := sample.ReadGaugeValue(gauge)
	if err != nil || math.Abs(val-25.0) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.Set(25.0) got %v (err: %v)\n", val, err)
		os.Exit(1)
	}

	// 3. Inc
	gauge.Inc()
	val, err = sample.ReadGaugeValue(gauge)
	if err != nil || math.Abs(val-26.0) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.Inc() got %v (err: %v)\n", val, err)
		os.Exit(1)
	}

	// 4. Dec
	gauge.Dec()
	val, err = sample.ReadGaugeValue(gauge)
	if err != nil || math.Abs(val-25.0) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.Dec() got %v (err: %v)\n", val, err)
		os.Exit(1)
	}

	// 5. Add
	gauge.Add(10.5)
	val, err = sample.ReadGaugeValue(gauge)
	if err != nil || math.Abs(val-35.5) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.Add(10.5) got %v (err: %v)\n", val, err)
		os.Exit(1)
	}

	// 6. Sub
	gauge.Sub(5.5)
	val, err = sample.ReadGaugeValue(gauge)
	if err != nil || math.Abs(val-30.0) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.Sub(5.5) got %v (err: %v)\n", val, err)
		os.Exit(1)
	}

	// 7. SetToCurrentTime
	before := float64(time.Now().Unix())
	sample.SetCurrentTime(gauge)
	after := float64(time.Now().Unix())
	val, err = sample.ReadGaugeValue(gauge)
	if err != nil || val < before || val > after+1 {
		fmt.Fprintf(os.Stderr, "FAIL: Gauge.SetToCurrentTime() got %v (expected [%v, %v])\n", val, before, after)
		os.Exit(1)
	}

	// 8. Register and Gather
	reg := prometheus.NewRegistry()
	freshGauge := prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "system_cpu_usage_ratio",
		Help: "Current CPU usage ratio",
	})
	freshGauge.Set(0.75)
	gatheredVal, err := sample.RegisterAndGather(reg, freshGauge, "system_cpu_usage_ratio")
	if err != nil || math.Abs(gatheredVal-0.75) > 1e-6 {
		fmt.Fprintf(os.Stderr, "FAIL: RegisterAndGather got %v (err: %v)\n", gatheredVal, err)
		os.Exit(1)
	}

	fmt.Println("PASS: all prometheus.Gauge contract assertions passed successfully.")
}