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

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.PermanentError 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.PermanentError

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:sha256:263c620ad75d1c6483ead64a56f0330fabab727ff137c27443539e70283770bd","contract":["PermanentError struct wraps an underlying error in Err field","PermanentError implements Error interface and delegates error string to wrapped error","PermanentError implements Unwrap returning the underlying error","PermanentError unwrapping supports errors.Is and errors.As matching","Returning PermanentError from operation halts backoff.Retry immediately without subsequent retries"],"goal":"verify github.com/cenkalti/backoff/v5.PermanentError 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.PermanentError"]},"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.PermanentError"],"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"
)

var (
	errTransient = errors.New("temporary connection glitch")
	errPermanent = errors.New("invalid request parameters")
)

func performOperation(attempt int) (string, error) {
	if attempt < 2 {
		return "", errTransient
	}
	return "", &backoff.PermanentError{Err: errPermanent}
}

func main() {
	ctx := context.Background()
	attemptCount := 0

	op := func() (string, error) {
		attemptCount++
		fmt.Printf("Attempt %d...\n", attemptCount)
		return performOperation(attemptCount)
	}

	result, err := backoff.Retry(
		ctx,
		op,
		backoff.WithBackOff(backoff.NewConstantBackOff(10*time.Millisecond)),
		backoff.WithMaxTries(5),
	)

	if err != nil {
		fmt.Printf("Operation stopped with error: %v\n", err)
		if errors.Is(err, errPermanent) {
			fmt.Println("Permanent error encountered; retries halted as expected.")
		}
	} else {
		fmt.Printf("Operation succeeded with result: %s\n", result)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/cenkalti/backoff/v5.PermanentError 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.PermanentError"
  ]
}

package main

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

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

func main() {
	// Assertion 1: PermanentError struct wraps an underlying error in Err field
	{
		origErr := errors.New("sentinel permanent error")
		pErr := &backoff.PermanentError{Err: origErr}
		if pErr.Err != origErr {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: pErr.Err mismatch, expected %v, got %v\n", origErr, pErr.Err)
			os.Exit(1)
		}
	}

	// Assertion 2: PermanentError implements Error interface and delegates error string to wrapped error
	{
		msg := "fatal configuration invalid"
		origErr := errors.New(msg)
		pErr := &backoff.PermanentError{Err: origErr}
		if pErr.Error() != msg {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: pErr.Error() = %q, expected %q\n", pErr.Error(), msg)
			os.Exit(1)
		}
	}

	// Assertion 3: PermanentError implements Unwrap returning the underlying error
	{
		origErr := errors.New("nested permanent cause")
		pErr := &backoff.PermanentError{Err: origErr}
		unwrapped := pErr.Unwrap()
		if unwrapped != origErr {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: pErr.Unwrap() = %v, expected %v\n", unwrapped, origErr)
			os.Exit(1)
		}
	}

	// Assertion 4: PermanentError unwrapping supports errors.Is and errors.As matching
	{
		origErr := errors.New("matchable root error")
		pErr := &backoff.PermanentError{Err: origErr}

		if !errors.Is(pErr, origErr) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: errors.Is(pErr, origErr) returned false\n")
			os.Exit(1)
		}

		var target *backoff.PermanentError
		if !errors.As(pErr, &target) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: errors.As failed to match *backoff.PermanentError\n")
			os.Exit(1)
		}
		if target.Err != origErr {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: target.Err mismatch, expected %v, got %v\n", origErr, target.Err)
			os.Exit(1)
		}
	}

	// Assertion 5: Returning PermanentError from operation halts backoff.Retry immediately without subsequent retries
	{
		ctx := context.Background()
		terminalErr := errors.New("halt immediately")
		attempts := 0

		_, err := backoff.Retry(
			ctx,
			func() (string, error) {
				attempts++
				return "", &backoff.PermanentError{Err: terminalErr}
			},
			backoff.WithBackOff(backoff.NewConstantBackOff(10*time.Millisecond)),
			backoff.WithMaxTries(5),
		)

		if attempts != 1 {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: expected 1 attempt, got %d\n", attempts)
			os.Exit(1)
		}
		if !errors.Is(err, terminalErr) {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: returned error does not match terminalErr: %v\n", err)
			os.Exit(1)
		}
	}

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