golang.org/x/time v0.15.0: rate.Reservation, rate.Sometimes

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 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:
  - golang.org/x/time/rate.Reservation
  - golang.org/x/time/rate.Sometimes

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:d7601c54ec72366d16842172e36a28dea4b17f8db2d00fbb9ae40f971eb3f148","contract":["rate.Sometimes with First executes action for the first N calls","rate.Sometimes with Every executes action on the first call and every Nth call","rate.Sometimes zero value executes action exactly once","rate.Limiter.Reserve returns a valid Reservation with OK and Delay","rate.Reservation.Cancel cancels the reservation and restores limiter tokens"],"goal":"verify pkg:golang/golang.org/x/time@v0.15.0","kind":"HOW","packages":["pkg:golang/golang.org/x/time@v0.15.0"],"schemaVersion":1,"symbols":["golang.org/x/time/rate.Reservation","golang.org/x/time/rate.Sometimes"]},"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":["golang.org/x/time/rate.Reservation","golang.org/x/time/rate.Sometimes"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

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 sample

import (
	"context"

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

// RunSometimes executes the function fn governed by Sometimes policy.
func RunSometimes(st *rate.Sometimes, fn func()) {
	st.Do(fn)
}

// ReserveToken creates a reservation for a single event from the limiter.
func ReserveToken(limiter *rate.Limiter) *rate.Reservation {
	return limiter.Reserve()
}

// CancelReservation cancels the given reservation.
func CancelReservation(r *rate.Reservation) {
	r.Cancel()
}

// WaitToken waits until the limiter permits an event or context expires.
func WaitToken(ctx context.Context, limiter *rate.Limiter) error {
	return limiter.Wait(ctx)
}

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

package main

import (
	"context"
	"fmt"
	"os"
	"sync/atomic"
	"time"

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

func main() {
	// Assertion 1: rate.Sometimes with First executes action for the first N calls
	{
		var count int32
		st := rate.Sometimes{First: 3}
		for i := 0; i < 10; i++ {
			sample.RunSometimes(&st, func() {
				atomic.AddInt32(&count, 1)
			})
		}
		if got := atomic.LoadInt32(&count); got != 3 {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected First:3 to run 3 times, got %d\n", got)
			os.Exit(1)
		}
	}

	// Assertion 2: rate.Sometimes with Every executes action on the first call and every Nth call
	{
		var count int32
		st := rate.Sometimes{Every: 3}
		for i := 0; i < 10; i++ {
			sample.RunSometimes(&st, func() {
				atomic.AddInt32(&count, 1)
			})
		}
		// In 10 calls (indices 0..9), executes at indices 0, 3, 6, 9 => 4 times
		if got := atomic.LoadInt32(&count); got != 4 {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed: expected Every:3 in 10 calls to run 4 times, got %d\n", got)
			os.Exit(1)
		}
	}

	// Assertion 3: rate.Sometimes zero value executes action exactly once
	{
		var count int32
		var st rate.Sometimes
		for i := 0; i < 5; i++ {
			sample.RunSometimes(&st, func() {
				atomic.AddInt32(&count, 1)
			})
		}
		if got := atomic.LoadInt32(&count); got != 1 {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected zero Sometimes to run 1 time, got %d\n", got)
			os.Exit(1)
		}
	}

	// Assertion 4: rate.Limiter.Reserve returns a valid Reservation with OK and Delay
	{
		lim := rate.NewLimiter(10, 1)
		r1 := sample.ReserveToken(lim)
		if !r1.OK() {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected r1.OK() to be true\n")
			os.Exit(1)
		}
		if d := r1.Delay(); d != 0 {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected initial delay 0, got %v\n", d)
			os.Exit(1)
		}

		r2 := sample.ReserveToken(lim)
		if !r2.OK() {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected r2.OK() to be true\n")
			os.Exit(1)
		}
		if d := r2.Delay(); d <= 0 {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected delay > 0 for second token, got %v\n", d)
			os.Exit(1)
		}

		// Assertion 5: rate.Reservation.Cancel cancels the reservation and restores limiter tokens
		sample.CancelReservation(r2)

		ctx, cancel := context.WithTimeout(context.Background(), 200*time.Millisecond)
		defer cancel()
		if err := sample.WaitToken(ctx, lim); err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: WaitToken failed after cancel: %v\n", err)
			os.Exit(1)
		}
	}

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