golang.org/x/sys v0.24.0: unix.O_EXCL

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 golang.org/x/sys/unix.O_EXCL in pkg:golang/golang.org/x/sys@v0.24.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.24.0
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.O_EXCL

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:e084f77462043a8843777d5749358bbac11ffbe9b0f3e7e95d374d2d0ee19550","contract":["unix.O_EXCL constant is non-zero and can be combined with unix.O_CREAT and access mode flags","unix.Open with unix.O_CREAT and unix.O_EXCL creates a new file when the file does not already exist","unix.Open with unix.O_CREAT and unix.O_EXCL returns unix.EEXIST if the file already exists"],"goal":"verify golang.org/x/sys/unix.O_EXCL in pkg:golang/golang.org/x/sys@v0.24.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.24.0"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.O_EXCL"]},"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/sys@v0.24.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.24.0","symbols":["golang.org/x/sys/unix.O_EXCL"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require golang.org/x/sys v0.24.0

golang.org/x/sys v0.24.0 h1:Twjiwq9dn6R1fQcyiK+wQyHWfaz/BJB+YIpzU/Cv3Xg=
golang.org/x/sys v0.24.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.O_EXCL in pkg:golang/golang.org/x/sys@v0.24.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.24.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.O_EXCL"
  ]
}

package main

import (
	"errors"
	"os"
	"path/filepath"

	"golang.org/x/sys/unix"
)

func main() {
	if unix.O_EXCL == 0 {
		panic("expected unix.O_EXCL to be non-zero")
	}

	flags := unix.O_CREAT | unix.O_EXCL | unix.O_RDWR
	if flags&unix.O_EXCL == 0 {
		panic("expected combined flags to include unix.O_EXCL")
	}

	dir, err := os.MkdirTemp("", "o-excl-contract-*")
	if err != nil {
		panic(err)
	}
	defer os.RemoveAll(dir)

	target := filepath.Join(dir, "exclusive.txt")

	fd, err := unix.Open(target, flags, 0o600)
	if err != nil {
		panic(err)
	}
	if err := unix.Close(fd); err != nil {
		panic(err)
	}

	_, err = unix.Open(target, flags, 0o600)
	if !errors.Is(err, unix.EEXIST) {
		panic("expected unix.EEXIST when opening existing file with unix.O_CREAT|unix.O_EXCL")
	}
}