golang.org/x/sys v0.22.0: 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@v0.22.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.22.0
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:sha256:15ad18f890a548e41bcaeea94e32a4826b2c37f0666a18b62c3d9de39e453921","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@v0.22.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.22.0"],"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@v0.22.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.22.0","symbols":["golang.org/x/sys/unix.O_EXCL"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/sys v0.22.0

golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	tmpFile, err := os.CreateTemp("", "sample_o_excl_*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp file: %v\n", err)
		os.Exit(1)
	}
	path := tmpFile.Name()
	tmpFile.Close()
	os.Remove(path)
	defer os.Remove(path)

	fd, err := unix.Open(path, unix.O_CREAT|unix.O_EXCL|unix.O_RDWR, 0600)
	if err != nil {
		fmt.Fprintf(os.Stderr, "unix.Open with O_CREAT|O_EXCL failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd)

	_, err = unix.Open(path, unix.O_CREAT|unix.O_EXCL|unix.O_RDWR, 0600)
	if !errors.Is(err, unix.EEXIST) {
		fmt.Fprintf(os.Stderr, "expected unix.EEXIST, got: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Successfully demonstrated unix.O_EXCL (0x%x)\n", unix.O_EXCL)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.O_EXCL in pkg:golang/golang.org/x/sys@v0.22.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.22.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.O_EXCL"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract assertions passed.")
}

func runContractTests() error {
	// 1. unix.O_EXCL constant is non-zero and can be combined with unix.O_CREAT and access mode flags
	if unix.O_EXCL == 0 {
		return fmt.Errorf("expected unix.O_EXCL to be non-zero")
	}
	flags := unix.O_CREAT | unix.O_EXCL | unix.O_RDWR
	if (flags & unix.O_EXCL) != unix.O_EXCL {
		return fmt.Errorf("expected flags & unix.O_EXCL == unix.O_EXCL")
	}

	// 2. unix.Open with unix.O_CREAT and unix.O_EXCL creates a new file when the file does not already exist
	tmpFile, err := os.CreateTemp("", "excl_contract_test_*")
	if err != nil {
		return fmt.Errorf("failed to create temp file: %w", err)
	}
	testPath := tmpFile.Name()
	tmpFile.Close()
	if err := os.Remove(testPath); err != nil {
		return fmt.Errorf("failed to remove temp file before test: %w", err)
	}
	defer os.Remove(testPath)

	fd, err := unix.Open(testPath, unix.O_CREAT|unix.O_EXCL|unix.O_RDWR, 0600)
	if err != nil {
		return fmt.Errorf("unix.Open with unix.O_CREAT|unix.O_EXCL failed: %w", err)
	}
	defer unix.Close(fd)

	var stat unix.Stat_t
	if err := unix.Fstat(fd, &stat); err != nil {
		return fmt.Errorf("unix.Fstat failed: %w", err)
	}
	if (stat.Mode & unix.S_IFMT) != unix.S_IFREG {
		return fmt.Errorf("expected regular file mode, got 0%o", stat.Mode&unix.S_IFMT)
	}

	// 3. unix.Open with unix.O_CREAT and unix.O_EXCL returns unix.EEXIST if the file already exists
	_, errExcl := unix.Open(testPath, unix.O_CREAT|unix.O_EXCL|unix.O_RDWR, 0600)
	if errExcl == nil {
		return fmt.Errorf("expected unix.Open with O_CREAT|O_EXCL to fail on existing file")
	}
	if !errors.Is(errExcl, unix.EEXIST) {
		return fmt.Errorf("expected unix.EEXIST, got: %w", errExcl)
	}

	return nil
}