golang.org/x/time v0.15.0: rate.NewLimiter

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 rate.NewLimiter in pkg:golang/golang.org/x/time@v0.15.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/time@v0.15.0
Demonstrate these symbols/APIs:
  - rate.NewLimiter

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:sha256:6688c967d12875a6f055af65b73e4ea72cb6364a0ca65ca548ec1d7c4ba7d9fe","contract":["rate.NewLimiter creates a token bucket limiter with specified rate and burst size","rate.NewLimiter allows events up to burst size immediately","rate.NewLimiter accepts rate.Every and rate.Inf"],"goal":"verify rate.NewLimiter in pkg:golang/golang.org/x/time@v0.15.0","kind":"HOW","packages":["pkg:golang/golang.org/x/time@v0.15.0"],"schemaVersion":1,"symbols":["rate.NewLimiter"]},"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/golang.org/x/time@v0.15.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/time@v0.15.0","symbols":["rate.NewLimiter"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.25.0

require golang.org/x/time v0.15.0

golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=

package main

import (
	"context"
	"fmt"
	"time"

	"golang.org/x/time/rate"
)

func main() {
	// Create a rate limiter that allows 5 events per second with a burst of 2.
	limiter := rate.NewLimiter(rate.Limit(5), 2)

	fmt.Printf("Rate limit: %v events/sec, burst size: %d\n", limiter.Limit(), limiter.Burst())

	// Consume the initial burst
	for i := 1; i <= 2; i++ {
		if limiter.Allow() {
			fmt.Printf("Event %d allowed immediately\n", i)
		}
	}

	// Next event exceeds burst
	if !limiter.Allow() {
		fmt.Println("Event 3 rate-limited as expected")
	}

	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
	defer cancel()

	if err := limiter.Wait(ctx); err == nil {
		fmt.Println("Event 4 allowed after waiting for token replenishment")
	}
}

{
  "schemaVersion": 1,
  "goal": "verify rate.NewLimiter in pkg:golang/golang.org/x/time@v0.15.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/time@v0.15.0"
  ],
  "symbols": [
    "rate.NewLimiter"
  ]
}

package main

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

	"golang.org/x/time/rate"
)

func main() {
	// 1. rate.NewLimiter creates a token bucket limiter with specified rate and burst size
	lim := rate.NewLimiter(rate.Limit(10), 3)
	if lim.Limit() != rate.Limit(10) {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: Limit() got %v, want 10\n", lim.Limit())
		os.Exit(1)
	}
	if lim.Burst() != 3 {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: Burst() got %d, want 3\n", lim.Burst())
		os.Exit(1)
	}

	// 2. rate.NewLimiter allows events up to burst size immediately
	// Bucket starts full with 3 tokens
	for i := 0; i < 3; i++ {
		if !lim.Allow() {
			fmt.Fprintf(os.Stderr, "Contract assertion failed: Allow() returned false within burst capacity at iteration %d\n", i+1)
			os.Exit(1)
		}
	}
	// 4th event exceeds burst capacity when called immediately
	if lim.Allow() {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: Allow() returned true when burst was exhausted\n")
		os.Exit(1)
	}

	// 3. rate.NewLimiter accepts rate.Every and rate.Inf
	everyLim := rate.NewLimiter(rate.Every(100*time.Millisecond), 1)
	if math.Abs(float64(everyLim.Limit())-10.0) > 1e-6 {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: rate.Every(100ms) limit got %v, want 10\n", everyLim.Limit())
		os.Exit(1)
	}

	infLim := rate.NewLimiter(rate.Inf, 0)
	if infLim.Limit() != rate.Inf {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: rate.Inf limit got %v, want Inf\n", infLim.Limit())
		os.Exit(1)
	}
	if !infLim.Allow() {
		fmt.Fprintf(os.Stderr, "Contract assertion failed: rate.Inf Allow() returned false\n")
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}