github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475: register and update counter and meter in a go-metrics registry

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: register and update counter and meter in a go-metrics registry
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20201227073835-cf1acfcdf475
Demonstrate these symbols/APIs:
  - metrics.NewCounter
  - metrics.NewMeter
  - metrics.NewRegistry

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:e31cf943b383f437c2cec99d6de8c481be26ec64aefcd48b46c8b3ab309faa95","contract":["metrics.NewRegistry creates an empty metric registry","metrics.NewCounter creates a counter that increments and decrements counts","metrics.NewMeter creates a meter that records event marks and counts","Registry.Register adds counter and meter instances to the registry","Registry.Get retrieves registered metric instances by name","Registry.Unregister removes metric instances from the registry","Registry.GetOrRegister registers a new metric or returns an existing metric"],"goal":"register and update counter and meter in a go-metrics registry","kind":"HOW","packages":["pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20201227073835-cf1acfcdf475"],"schemaVersion":1,"symbols":["metrics.NewCounter","metrics.NewMeter","metrics.NewRegistry"]},"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/rcrowley/go-metrics@v0.0.0-20201227073835-cf1acfcdf475"],"schemaVersion":1,"subject":"pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20201227073835-cf1acfcdf475","symbols":["metrics.NewCounter","metrics.NewMeter","metrics.NewRegistry"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475

github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 h1:N/ElC8H3+5XpJzTSTfLsJV/mx9Q9g7kxmchpfZyxgzM=
github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9 h1:bsUq1dX0N8AOIL7EB/X911+m4EHsnWEHeJ0c+3TTBrg=
github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=

package main

import (
	"fmt"

	"github.com/rcrowley/go-metrics"
)

func main() {
	// Create a new metrics registry
	registry := metrics.NewRegistry()

	// Create and register a counter
	counter := metrics.NewCounter()
	if err := registry.Register("requests.total", counter); err != nil {
		panic(err)
	}

	// Update counter
	counter.Inc(10)
	counter.Dec(2)

	// Create and register a meter
	meter := metrics.NewMeter()
	if err := registry.Register("requests.rate", meter); err != nil {
		panic(err)
	}

	// Update meter
	meter.Mark(50)

	// Retrieve and display metrics from the registry
	c := registry.Get("requests.total").(metrics.Counter)
	m := registry.Get("requests.rate").(metrics.Meter)

	fmt.Printf("requests.total count: %d\n", c.Count())
	fmt.Printf("requests.rate count: %d\n", m.Count())
}

{
  "schemaVersion": 1,
  "goal": "register and update counter and meter in a go-metrics registry",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/rcrowley/go-metrics@v0.0.0-20201227073835-cf1acfcdf475"
  ],
  "symbols": [
    "metrics.NewCounter",
    "metrics.NewMeter",
    "metrics.NewRegistry"
  ]
}

package main

import (
	"fmt"
	"os"

	"github.com/rcrowley/go-metrics"
)

func main() {
	// 1. metrics.NewRegistry creates an empty metric registry
	r := metrics.NewRegistry()
	if r == nil {
		fmt.Fprintf(os.Stderr, "metrics.NewRegistry returned nil\n")
		os.Exit(1)
	}

	// 2. metrics.NewCounter creates a counter that increments and decrements counts
	c := metrics.NewCounter()
	if c == nil {
		fmt.Fprintf(os.Stderr, "metrics.NewCounter returned nil\n")
		os.Exit(1)
	}
	if c.Count() != 0 {
		fmt.Fprintf(os.Stderr, "expected initial counter value 0, got %d\n", c.Count())
		os.Exit(1)
	}
	c.Inc(15)
	if c.Count() != 15 {
		fmt.Fprintf(os.Stderr, "expected counter count 15, got %d\n", c.Count())
		os.Exit(1)
	}
	c.Dec(5)
	if c.Count() != 10 {
		fmt.Fprintf(os.Stderr, "expected counter count 10, got %d\n", c.Count())
		os.Exit(1)
	}
	c.Clear()
	if c.Count() != 0 {
		fmt.Fprintf(os.Stderr, "expected cleared counter count 0, got %d\n", c.Count())
		os.Exit(1)
	}

	// 3. metrics.NewMeter creates a meter that records event marks and counts
	m := metrics.NewMeter()
	if m == nil {
		fmt.Fprintf(os.Stderr, "metrics.NewMeter returned nil\n")
		os.Exit(1)
	}
	if m.Count() != 0 {
		fmt.Fprintf(os.Stderr, "expected initial meter count 0, got %d\n", m.Count())
		os.Exit(1)
	}
	m.Mark(42)
	if m.Count() != 42 {
		fmt.Fprintf(os.Stderr, "expected meter count 42, got %d\n", m.Count())
		os.Exit(1)
	}

	// 4. Registry.Register adds counter and meter instances to the registry
	cnt := metrics.NewCounter()
	cnt.Inc(100)
	if err := r.Register("api.counter", cnt); err != nil {
		fmt.Fprintf(os.Stderr, "r.Register counter failed: %v\n", err)
		os.Exit(1)
	}
	mtr := metrics.NewMeter()
	mtr.Mark(200)
	if err := r.Register("api.meter", mtr); err != nil {
		fmt.Fprintf(os.Stderr, "r.Register meter failed: %v\n", err)
		os.Exit(1)
	}
	// duplicate registration must fail
	if err := r.Register("api.counter", cnt); err == nil {
		fmt.Fprintf(os.Stderr, "expected duplicate registration to return error, got nil\n")
		os.Exit(1)
	}

	// 5. Registry.Get retrieves registered metric instances by name
	gotCounter := r.Get("api.counter")
	if gotCounter == nil {
		fmt.Fprintf(os.Stderr, "r.Get('api.counter') returned nil\n")
		os.Exit(1)
	}
	retrievedCounter, ok := gotCounter.(metrics.Counter)
	if !ok || retrievedCounter.Count() != 100 {
		fmt.Fprintf(os.Stderr, "retrieved counter type or count mismatch: ok=%v, count=%v\n", ok, retrievedCounter.Count())
		os.Exit(1)
	}

	gotMeter := r.Get("api.meter")
	if gotMeter == nil {
		fmt.Fprintf(os.Stderr, "r.Get('api.meter') returned nil\n")
		os.Exit(1)
	}
	retrievedMeter, ok := gotMeter.(metrics.Meter)
	if !ok || retrievedMeter.Count() != 200 {
		fmt.Fprintf(os.Stderr, "retrieved meter type or count mismatch: ok=%v, count=%v\n", ok, retrievedMeter.Count())
		os.Exit(1)
	}

	if missing := r.Get("api.nonexistent"); missing != nil {
		fmt.Fprintf(os.Stderr, "expected nil for nonexistent metric, got %v\n", missing)
		os.Exit(1)
	}

	// 6. Registry.Unregister removes metric instances from the registry
	r.Unregister("api.counter")
	if r.Get("api.counter") != nil {
		fmt.Fprintf(os.Stderr, "expected unregistered counter to be nil\n")
		os.Exit(1)
	}

	// 7. Registry.GetOrRegister registers a new metric or returns an existing metric
	gorMetric := r.GetOrRegister("api.gor_counter", metrics.NewCounter)
	if gorMetric == nil {
		fmt.Fprintf(os.Stderr, "r.GetOrRegister returned nil\n")
		os.Exit(1)
	}
	gorCounter, ok := gorMetric.(metrics.Counter)
	if !ok {
		fmt.Fprintf(os.Stderr, "r.GetOrRegister did not return a metrics.Counter\n")
		os.Exit(1)
	}
	gorCounter.Inc(7)

	gorMetric2 := r.GetOrRegister("api.gor_counter", metrics.NewCounter)
	gorCounter2, ok := gorMetric2.(metrics.Counter)
	if !ok || gorCounter2.Count() != 7 {
		fmt.Fprintf(os.Stderr, "expected existing counter count 7, got %v\n", gorCounter2.Count())
		os.Exit(1)
	}

	fmt.Println("All go-metrics contract assertions passed.")
}