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

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.AT_FDCWD 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.AT_FDCWD

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:sha256:9c4277b38d6f9185bd0a8e7dc41950c4d583541bbae6e181bc43c6824e656836","contract":["unix.AT_FDCWD constant equals integer -100","unix.Fstatat with unix.AT_FDCWD resolves relative path against current working directory","unix.Openat with unix.AT_FDCWD opens relative path against current working directory"],"goal":"verify golang.org/x/sys/unix.AT_FDCWD 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.AT_FDCWD"]},"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.AT_FDCWD"],"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 (
	"fmt"
	"os"
	"path/filepath"

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

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

	relName := filepath.Base(tmpFile.Name())
	var stat unix.Stat_t
	if err := unix.Fstatat(unix.AT_FDCWD, relName, &stat, 0); err != nil {
		fmt.Fprintf(os.Stderr, "unix.Fstatat failed: %v\n", err)
		os.Exit(1)
	}

	fd, err := unix.Openat(unix.AT_FDCWD, relName, unix.O_RDONLY, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "unix.Openat failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd)

	fmt.Printf("AT_FDCWD constant: %d\n", unix.AT_FDCWD)
	fmt.Printf("Fstatat succeeded for %s (inode: %d)\n", relName, stat.Ino)
	fmt.Printf("Openat succeeded with fd: %d\n", fd)
}

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

package main

import (
	"bytes"
	"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 {
	// 1. unix.AT_FDCWD constant equals integer -100
	if unix.AT_FDCWD != -100 {
		return fmt.Errorf("expected unix.AT_FDCWD to equal -100, got %d", unix.AT_FDCWD)
	}

	// Setup temporary file in current working directory
	tmpFile, err := os.CreateTemp(".", "at_fdcwd_contract_*")
	if err != nil {
		return fmt.Errorf("failed to create temporary file: %w", err)
	}
	defer os.Remove(tmpFile.Name())
	defer tmpFile.Close()

	payload := []byte("CodeSampleX verification payload for AT_FDCWD")
	if _, err := tmpFile.Write(payload); err != nil {
		return fmt.Errorf("failed to write payload: %w", err)
	}

	relName := filepath.Base(tmpFile.Name())

	// 2. unix.Fstatat with unix.AT_FDCWD resolves relative path against current working directory
	var statDirect unix.Stat_t
	if err := unix.Stat(relName, &statDirect); err != nil {
		return fmt.Errorf("unix.Stat failed: %w", err)
	}

	var statAt unix.Stat_t
	if err := unix.Fstatat(unix.AT_FDCWD, relName, &statAt, 0); err != nil {
		return fmt.Errorf("unix.Fstatat with AT_FDCWD failed: %w", err)
	}

	if statAt.Ino != statDirect.Ino || statAt.Dev != statDirect.Dev {
		return fmt.Errorf("unix.Fstatat with AT_FDCWD did not match direct Stat (ino: %d vs %d)", statAt.Ino, statDirect.Ino)
	}

	// 3. unix.Openat with unix.AT_FDCWD opens relative path against current working directory
	fd, err := unix.Openat(unix.AT_FDCWD, relName, unix.O_RDONLY, 0)
	if err != nil {
		return fmt.Errorf("unix.Openat with AT_FDCWD failed: %w", err)
	}
	defer unix.Close(fd)

	var statFd unix.Stat_t
	if err := unix.Fstat(fd, &statFd); err != nil {
		return fmt.Errorf("unix.Fstat failed: %w", err)
	}
	if statFd.Ino != statDirect.Ino {
		return fmt.Errorf("unix.Openat fd points to different file (ino: %d vs %d)", statFd.Ino, statDirect.Ino)
	}

	buf := make([]byte, len(payload))
	n, err := unix.Read(fd, buf)
	if err != nil {
		return fmt.Errorf("unix.Read failed: %w", err)
	}
	if n != len(payload) || !bytes.Equal(buf[:n], payload) {
		return fmt.Errorf("read content mismatch: expected %q, got %q", string(payload), string(buf[:n]))
	}

	return nil
}