golang.org/x/sys v0.22.0: unix.Openat

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.Openat 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.Openat

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:b2c751ec25b8125c0164be533a45a1d088a9be78cb7af7c1fcfb5bcecf00c0cd","contract":["unix.Openat opens an existing file relative to a directory file descriptor","unix.Openat with unix.O_CREAT creates and opens a new file relative to a directory file descriptor","unix.Openat with unix.AT_FDCWD opens a file relative to the current working directory","unix.Openat returns unix.ENOENT when opening a non-existent file without O_CREAT","unix.Openat returns unix.EBADF when given an invalid directory file descriptor"],"goal":"verify golang.org/x/sys/unix.Openat 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.Openat"]},"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.Openat"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

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 (
	"fmt"
	"os"

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

func main() {
	tmpDir, err := os.MkdirTemp("", "openat_sample_*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp directory: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	dirFd, err := unix.Open(tmpDir, unix.O_RDONLY|unix.O_DIRECTORY, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to open directory: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(dirFd)

	fileFd, err := unix.Openat(dirFd, "sample.txt", unix.O_CREAT|unix.O_RDWR, 0644)
	if err != nil {
		fmt.Fprintf(os.Stderr, "unix.Openat failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fileFd)

	msg := []byte("verified openat")
	if _, err := unix.Write(fileFd, msg); err != nil {
		fmt.Fprintf(os.Stderr, "unix.Write failed: %v\n", err)
		os.Exit(1)
	}

	if _, err := unix.Seek(fileFd, 0, 0); err != nil {
		fmt.Fprintf(os.Stderr, "unix.Seek failed: %v\n", err)
		os.Exit(1)
	}

	buf := make([]byte, len(msg))
	n, err := unix.Read(fileFd, buf)
	if err != nil || n != len(msg) {
		fmt.Fprintf(os.Stderr, "unix.Read failed: n=%d, err=%v\n", n, err)
		os.Exit(1)
	}

	fmt.Printf("unix.Openat demonstration succeeded, read: %s\n", string(buf))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.Openat 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.Openat"
  ]
}

package main

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

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

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

func runTests() error {
	tmpDir, err := os.MkdirTemp("", "contract_openat_*")
	if err != nil {
		return fmt.Errorf("failed to create temp dir: %w", err)
	}
	defer os.RemoveAll(tmpDir)

	filePath := filepath.Join(tmpDir, "existing.txt")
	expectedContent := []byte("hello from openat")
	if err := os.WriteFile(filePath, expectedContent, 0644); err != nil {
		return fmt.Errorf("failed to write test file: %w", err)
	}

	dirFd, err := unix.Open(tmpDir, unix.O_RDONLY|unix.O_DIRECTORY, 0)
	if err != nil {
		return fmt.Errorf("failed to open directory: %w", err)
	}
	defer unix.Close(dirFd)

	// 1. unix.Openat opens an existing file relative to a directory file descriptor
	fileFd, err := unix.Openat(dirFd, "existing.txt", unix.O_RDONLY, 0)
	if err != nil {
		return fmt.Errorf("unix.Openat failed to open existing file: %w", err)
	}
	buf := make([]byte, len(expectedContent))
	n, err := unix.Read(fileFd, buf)
	unix.Close(fileFd)
	if err != nil {
		return fmt.Errorf("unix.Read failed: %w", err)
	}
	if string(buf[:n]) != string(expectedContent) {
		return fmt.Errorf("content mismatch: expected %q, got %q", string(expectedContent), string(buf[:n]))
	}

	// 2. unix.Openat with unix.O_CREAT creates and opens a new file relative to a directory file descriptor
	createdFd, err := unix.Openat(dirFd, "newfile.txt", unix.O_CREAT|unix.O_WRONLY|unix.O_TRUNC, 0644)
	if err != nil {
		return fmt.Errorf("unix.Openat with O_CREAT failed: %w", err)
	}
	writeData := []byte("new file content")
	if _, err := unix.Write(createdFd, writeData); err != nil {
		unix.Close(createdFd)
		return fmt.Errorf("unix.Write failed: %w", err)
	}
	unix.Close(createdFd)

	createdPath := filepath.Join(tmpDir, "newfile.txt")
	readBack, err := os.ReadFile(createdPath)
	if err != nil {
		return fmt.Errorf("failed to read back created file: %w", err)
	}
	if string(readBack) != string(writeData) {
		return fmt.Errorf("created file content mismatch: expected %q, got %q", string(writeData), string(readBack))
	}

	// 3. unix.Openat with unix.AT_FDCWD opens a file relative to the current working directory
	cwdFd, err := unix.Openat(unix.AT_FDCWD, "go.mod", unix.O_RDONLY, 0)
	if err != nil {
		return fmt.Errorf("unix.Openat with unix.AT_FDCWD failed for go.mod: %w", err)
	}
	unix.Close(cwdFd)

	// 4. unix.Openat returns unix.ENOENT when opening a non-existent file without O_CREAT
	_, err = unix.Openat(dirFd, "does_not_exist.txt", unix.O_RDONLY, 0)
	if err == nil {
		return fmt.Errorf("expected unix.Openat to fail for non-existent file, but succeeded")
	}
	if !errors.Is(err, unix.ENOENT) {
		return fmt.Errorf("expected unix.ENOENT, got: %w", err)
	}

	// 5. unix.Openat returns unix.EBADF when given an invalid directory file descriptor
	_, err = unix.Openat(-1, "existing.txt", unix.O_RDONLY, 0)
	if err == nil {
		return fmt.Errorf("expected unix.Openat(-1) to fail, but succeeded")
	}
	if !errors.Is(err, unix.EBADF) {
		return fmt.Errorf("expected unix.EBADF, got: %w", err)
	}

	return nil
}