github.com/cenkalti/backoff/v5 v5.0.3: ExponentialBackOff, Permanent, Retry

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/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:
  - ExponentialBackOff
  - Permanent
  - Retry
  - WithMaxTries

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:sha256:2cfe3d518901faaa6c5ea7450a9cb6856ea431c8d38d65570eee874600b02978","contract":["Retry executes operation until success and returns result when transient errors resolve within attempt limits","Retry terminates immediately without further attempts and returns underlying error when operation returns Permanent error","Retry enforces maximum attempts specified by WithMaxTries and returns final operation error upon exhaustion","Retry invokes notification callback with error and next delay on each failed attempt when WithNotify is configured","ExponentialBackOff calculates deterministic exponential delay increments with zero randomization and resets to initial interval"],"goal":"verify 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":["ExponentialBackOff","Permanent","Retry","WithMaxTries"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","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":["ExponentialBackOff","Permanent","Retry","WithMaxTries"],"verifierAdapter":"golang@1"}

module 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 (
	"context"
	"errors"
	"fmt"
	"time"

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

// FetchResource simulates fetching a resource with transient failures.
func FetchResource(ctx context.Context, maxFailures int) (string, error) {
	attempts := 0

	op := func() (string, error) {
		attempts++
		if attempts <= maxFailures {
			return "", errors.New("temporary connection reset")
		}
		return "resource-data", nil
	}

	exp := backoff.NewExponentialBackOff()
	exp.InitialInterval = 10 * time.Millisecond
	exp.Multiplier = 1.5
	exp.MaxInterval = 100 * time.Millisecond

	return backoff.Retry(ctx, op,
		backoff.WithBackOff(exp),
		backoff.WithMaxTries(5),
		backoff.WithNotify(func(err error, d time.Duration) {
			fmt.Printf("Attempt failed with '%v', retrying after %v\n", err, d)
		}),
	)
}

func main() {
	ctx := context.Background()

	result, err := FetchResource(ctx, 2)
	if err != nil {
		fmt.Printf("Fetch failed: %v\n", err)
		return
	}

	fmt.Printf("Fetch succeeded: %s\n", result)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/cenkalti/backoff/v5@v5.0.3"
  ],
  "symbols": [
    "ExponentialBackOff",
    "Permanent",
    "Retry",
    "WithMaxTries"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"context"
	"errors"
	"fmt"
	"os"
	"time"

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

func main() {
	// Assertion 1: Retry executes operation until success and returns result when transient errors resolve within attempt limits
	{
		ctx := context.Background()
		attempts := 0
		res, err := backoff.Retry(ctx, func() (string, error) {
			attempts++
			if attempts < 3 {
				return "", errors.New("transient network timeout")
			}
			return "operation-successful", nil
		}, backoff.WithBackOff(&backoff.ZeroBackOff{}), backoff.WithMaxTries(5))

		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: unexpected error: %v\n", err)
			os.Exit(1)
		}
		if res != "operation-successful" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: unexpected result: %s\n", res)
			os.Exit(1)
		}
		if attempts != 3 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected 3 attempts, got %d\n", attempts)
			os.Exit(1)
		}
	}

	// Assertion 2: Retry terminates immediately without further attempts and returns underlying error when operation returns Permanent error
	{
		ctx := context.Background()
		sentinel := errors.New("fatal configuration error")
		attempts := 0
		_, err := backoff.Retry(ctx, func() (int, error) {
			attempts++
			return 0, backoff.Permanent(sentinel)
		}, backoff.WithBackOff(&backoff.ZeroBackOff{}), backoff.WithMaxTries(5))

		if attempts != 1 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected exactly 1 attempt on Permanent error, got %d\n", attempts)
			os.Exit(1)
		}
		if !errors.Is(err, sentinel) {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected error unwrapped to sentinel, got %v\n", err)
			os.Exit(1)
		}
	}

	// Assertion 3: Retry enforces maximum attempts specified by WithMaxTries and returns final operation error upon exhaustion
	{
		ctx := context.Background()
		sentinel := errors.New("persistent failure")
		attempts := 0
		_, err := backoff.Retry(ctx, func() (int, error) {
			attempts++
			return 0, sentinel
		}, backoff.WithBackOff(&backoff.ZeroBackOff{}), backoff.WithMaxTries(4))

		if attempts != 4 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected 4 attempts, got %d\n", attempts)
			os.Exit(1)
		}
		if !errors.Is(err, sentinel) {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected final error to match sentinel, got %v\n", err)
			os.Exit(1)
		}
	}

	// Assertion 4: Retry invokes notification callback with error and next delay on each failed attempt when WithNotify is configured
	{
		ctx := context.Background()
		attempts := 0
		notifyCount := 0
		var recordedErrors []error

		_, err := backoff.Retry(ctx, func() (int, error) {
			attempts++
			if attempts < 3 {
				return 0, errors.New("retryable fault")
			}
			return 100, nil
		}, backoff.WithBackOff(&backoff.ZeroBackOff{}), backoff.WithNotify(func(err error, d time.Duration) {
			notifyCount++
			recordedErrors = append(recordedErrors, err)
		}))

		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: unexpected error: %v\n", err)
			os.Exit(1)
		}
		if notifyCount != 2 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected 2 notifications, got %d\n", notifyCount)
			os.Exit(1)
		}
		if len(recordedErrors) != 2 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected 2 recorded errors, got %d\n", len(recordedErrors))
			os.Exit(1)
		}
	}

	// Assertion 5: ExponentialBackOff calculates deterministic exponential delay increments with zero randomization and resets to initial interval
	{
		exp := backoff.NewExponentialBackOff()
		exp.InitialInterval = 50 * time.Millisecond
		exp.Multiplier = 2.0
		exp.RandomizationFactor = 0.0
		exp.MaxInterval = 10 * time.Second

		d1 := exp.NextBackOff()
		d2 := exp.NextBackOff()
		d3 := exp.NextBackOff()

		if d1 != 50*time.Millisecond || d2 != 100*time.Millisecond || d3 != 200*time.Millisecond {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: unexpected intervals d1=%v, d2=%v, d3=%v\n", d1, d2, d3)
			os.Exit(1)
		}

		exp.Reset()
		dReset := exp.NextBackOff()
		if dReset != 50*time.Millisecond {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: expected interval after reset 50ms, got %v\n", dReset)
			os.Exit(1)
		}
	}

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