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

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.Fstatat 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.Fstatat

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:sha256:2cd6c66a445e5ba907bc3d4c9905871f402821d1feed314376846847489d3df3","contract":["unix.Fstatat retrieves file metadata relative to an open directory file descriptor","unix.Fstatat retrieves file metadata relative to unix.AT_FDCWD","unix.Fstatat with unix.AT_SYMLINK_NOFOLLOW inspects symbolic link without following","unix.Fstatat returns unix.ENOENT for nonexistent relative path","unix.Fstatat returns unix.EBADF for invalid directory file descriptor"],"goal":"verify golang.org/x/sys/unix.Fstatat 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.Fstatat"]},"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.Fstatat"],"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() {
	tmpDir, err := os.MkdirTemp("", "fstatat_demo_*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp dir: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	filePath := filepath.Join(tmpDir, "example.txt")
	content := []byte("fstatat demonstration payload")
	if err := os.WriteFile(filePath, content, 0644); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write file: %v\n", err)
		os.Exit(1)
	}

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

	var stat unix.Stat_t
	if err := unix.Fstatat(dirFd, "example.txt", &stat, 0); err != nil {
		fmt.Fprintf(os.Stderr, "unix.Fstatat failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("unix.Fstatat succeeded: Size=%d, Ino=%d, Mode=0%o\n",
		stat.Size, stat.Ino, stat.Mode)
}

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

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

	fileName := "sample.txt"
	filePath := filepath.Join(tmpDir, fileName)
	content := []byte("fstatat contract test content")
	if err := os.WriteFile(filePath, content, 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 temp dir: %w", err)
	}
	defer unix.Close(dirFd)

	// 1. unix.Fstatat retrieves file metadata relative to an open directory file descriptor
	var stat unix.Stat_t
	if err := unix.Fstatat(dirFd, fileName, &stat, 0); err != nil {
		return fmt.Errorf("unix.Fstatat relative to dirFd failed: %w", err)
	}
	if stat.Size != int64(len(content)) {
		return fmt.Errorf("expected size %d, got %d", len(content), stat.Size)
	}
	if stat.Mode&unix.S_IFMT != unix.S_IFREG {
		return fmt.Errorf("expected regular file mode, got %o", stat.Mode)
	}

	// 2. unix.Fstatat retrieves file metadata relative to unix.AT_FDCWD
	cwd, err := os.Getwd()
	if err != nil {
		return fmt.Errorf("failed to get cwd: %w", err)
	}
	relPath, err := filepath.Rel(cwd, filePath)
	if err != nil {
		return fmt.Errorf("failed to get relative path: %w", err)
	}
	var cwdStat unix.Stat_t
	if err := unix.Fstatat(unix.AT_FDCWD, relPath, &cwdStat, 0); err != nil {
		return fmt.Errorf("unix.Fstatat with AT_FDCWD failed: %w", err)
	}
	if cwdStat.Ino != stat.Ino {
		return fmt.Errorf("expected inode %d, got %d", stat.Ino, cwdStat.Ino)
	}

	// 3. unix.Fstatat with unix.AT_SYMLINK_NOFOLLOW inspects symbolic link without following
	symlinkName := "sample_symlink.txt"
	symlinkPath := filepath.Join(tmpDir, symlinkName)
	if err := os.Symlink(filePath, symlinkPath); err != nil {
		return fmt.Errorf("failed to create symlink: %w", err)
	}

	var symlinkStat unix.Stat_t
	if err := unix.Fstatat(dirFd, symlinkName, &symlinkStat, unix.AT_SYMLINK_NOFOLLOW); err != nil {
		return fmt.Errorf("unix.Fstatat with AT_SYMLINK_NOFOLLOW failed: %w", err)
	}
	if symlinkStat.Mode&unix.S_IFMT != unix.S_IFLNK {
		return fmt.Errorf("expected symlink mode, got %o", symlinkStat.Mode)
	}

	var targetStat unix.Stat_t
	if err := unix.Fstatat(dirFd, symlinkName, &targetStat, 0); err != nil {
		return fmt.Errorf("unix.Fstatat following symlink failed: %w", err)
	}
	if targetStat.Mode&unix.S_IFMT != unix.S_IFREG {
		return fmt.Errorf("expected regular file mode after following symlink, got %o", targetStat.Mode)
	}

	// 4. unix.Fstatat returns unix.ENOENT for nonexistent relative path
	var noentStat unix.Stat_t
	err = unix.Fstatat(dirFd, "nonexistent_file.txt", &noentStat, 0)
	if err == nil {
		return fmt.Errorf("expected error for nonexistent file, got nil")
	}
	if !errors.Is(err, unix.ENOENT) {
		return fmt.Errorf("expected unix.ENOENT, got: %w", err)
	}

	// 5. unix.Fstatat returns unix.EBADF for invalid directory file descriptor
	var badfStat unix.Stat_t
	err = unix.Fstatat(-1, fileName, &badfStat, 0)
	if err == nil {
		return fmt.Errorf("expected error for invalid dirfd, got nil")
	}
	if !errors.Is(err, unix.EBADF) {
		return fmt.Errorf("expected unix.EBADF, got: %w", err)
	}

	return nil
}