github.com/cenkalti/backoff/v5 v5.0.3: NewExponentialBackOff

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/cenkalti/backoff/v5.NewExponentialBackOff in pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3
Demonstrate these symbols/APIs:
  - github.com/cenkalti/backoff/v5.NewExponentialBackOff

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:sha256:585c4582a5bf478b2895910bced8bccd9e808753dff73b638b434782ad1747ef","contract":["NewExponentialBackOff returns an ExponentialBackOff instance with default intervals, multiplier, and randomization factor","ExponentialBackOff.NextBackOff returns duration within randomization bounds for initial interval","ExponentialBackOff.NextBackOff increases duration exponentially across successive attempts capped by MaxInterval","ExponentialBackOff.Reset resets backoff interval back to initial interval","ExponentialBackOff implements the BackOff interface"],"goal":"verify github.com/cenkalti/backoff/v5.NewExponentialBackOff in pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3","kind":"HOW","packages":["pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3"],"schemaVersion":1,"symbols":["github.com/cenkalti/backoff/v5.NewExponentialBackOff"]},"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/cenkalti/backoff/v5@v5.0.3"],"schemaVersion":1,"subject":"pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3","symbols":["github.com/cenkalti/backoff/v5.NewExponentialBackOff"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/cenkalti/backoff/v5 v5.0.3

github.com/cenkalti/backoff/v5 v5.0.3 h1:ZN+IMa753KfX5hd8vVaMixjnqRZ3y8CuJKRKj1xcsSM=
github.com/cenkalti/backoff/v5 v5.0.3/go.mod h1:rkhZdG3JZukswDf7f0cwqPNk4K0sa+F97BxZthm/crw=

package main

import (
	"fmt"

	"github.com/cenkalti/backoff/v5"
)

func main() {
	b := backoff.NewExponentialBackOff()

	fmt.Printf("Initial interval: %v\n", b.InitialInterval)
	fmt.Printf("Multiplier: %v\n", b.Multiplier)
	fmt.Printf("Max interval: %v\n", b.MaxInterval)
	fmt.Printf("Randomization factor: %v\n", b.RandomizationFactor)

	for i := 1; i <= 3; i++ {
		d := b.NextBackOff()
		fmt.Printf("Attempt %d backoff: %v\n", i, d)
	}

	b.Reset()
	fmt.Printf("After reset, next backoff: %v\n", b.NextBackOff())
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/cenkalti/backoff/v5.NewExponentialBackOff in pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3"
  ],
  "symbols": [
    "github.com/cenkalti/backoff/v5.NewExponentialBackOff"
  ]
}

package main

import (
	"fmt"
	"os"
	"time"

	"github.com/cenkalti/backoff/v5"
)

func main() {
	// 1. ExponentialBackOff implements the BackOff interface
	var _ backoff.BackOff = (*backoff.ExponentialBackOff)(nil)

	// 2. NewExponentialBackOff initializes ExponentialBackOff with default parameters
	b := backoff.NewExponentialBackOff()
	if b == nil {
		fmt.Fprintf(os.Stderr, "assertion failed: NewExponentialBackOff returned nil\n")
		os.Exit(1)
	}
	if b.InitialInterval != backoff.DefaultInitialInterval {
		fmt.Fprintf(os.Stderr, "assertion failed: expected InitialInterval %v, got %v\n", backoff.DefaultInitialInterval, b.InitialInterval)
		os.Exit(1)
	}
	if b.RandomizationFactor != backoff.DefaultRandomizationFactor {
		fmt.Fprintf(os.Stderr, "assertion failed: expected RandomizationFactor %v, got %v\n", backoff.DefaultRandomizationFactor, b.RandomizationFactor)
		os.Exit(1)
	}
	if b.Multiplier != backoff.DefaultMultiplier {
		fmt.Fprintf(os.Stderr, "assertion failed: expected Multiplier %v, got %v\n", backoff.DefaultMultiplier, b.Multiplier)
		os.Exit(1)
	}
	if b.MaxInterval != backoff.DefaultMaxInterval {
		fmt.Fprintf(os.Stderr, "assertion failed: expected MaxInterval %v, got %v\n", backoff.DefaultMaxInterval, b.MaxInterval)
		os.Exit(1)
	}

	// 3. ExponentialBackOff.NextBackOff returns duration within randomization bounds for initial interval
	d := b.NextBackOff()
	minExpected := time.Duration(float64(backoff.DefaultInitialInterval) * (1.0 - backoff.DefaultRandomizationFactor))
	maxExpected := time.Duration(float64(backoff.DefaultInitialInterval) * (1.0 + backoff.DefaultRandomizationFactor))
	if d < minExpected || d > maxExpected {
		fmt.Fprintf(os.Stderr, "assertion failed: NextBackOff duration %v outside [%v, %v]\n", d, minExpected, maxExpected)
		os.Exit(1)
	}

	// 4. ExponentialBackOff.NextBackOff increases duration exponentially across successive attempts
	custom := backoff.NewExponentialBackOff()
	custom.InitialInterval = 100 * time.Millisecond
	custom.RandomizationFactor = 0
	custom.Multiplier = 2.0
	custom.MaxInterval = 500 * time.Millisecond
	custom.Reset()

	expectedSequence := []time.Duration{
		100 * time.Millisecond,
		200 * time.Millisecond,
		400 * time.Millisecond,
		500 * time.Millisecond,
		500 * time.Millisecond,
	}
	for idx, expected := range expectedSequence {
		got := custom.NextBackOff()
		if got != expected {
			fmt.Fprintf(os.Stderr, "assertion failed at attempt %d: expected %v, got %v\n", idx+1, expected, got)
			os.Exit(1)
		}
	}

	// 5. ExponentialBackOff.Reset resets backoff interval back to initial interval
	custom.Reset()
	firstAfterReset := custom.NextBackOff()
	if firstAfterReset != 100*time.Millisecond {
		fmt.Fprintf(os.Stderr, "assertion failed: expected %v after reset, got %v\n", 100*time.Millisecond, firstAfterReset)
		os.Exit(1)
	}

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