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

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.Link 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.Link

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:sha256:00a652580645f94d52149c1c38897a029fdcb3422e7d2685b24717370d37f9e0","contract":["Link creates a hard link pointing to an existing file with matching inode","Link fails with ENOENT when the source file does not exist","Link fails with EEXIST when the target path already exists","CreateHardLink helper creates a hard link via unix.Link"],"goal":"verify golang.org/x/sys/unix.Link 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.Link"]},"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.Link"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22.0

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=

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

package src

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

// CreateHardLink creates a hard link pointing to oldPath at newPath.
func CreateHardLink(oldPath, newPath string) error {
	return unix.Link(oldPath, newPath)
}

package main

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

	"example.com/sample/src"
	"golang.org/x/sys/unix"
)

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

	srcFile := filepath.Join(tmpDir, "source.txt")
	linkFile := filepath.Join(tmpDir, "link.txt")
	testPayload := []byte("CodeSampleX verification payload for unix.Link")

	if err := os.WriteFile(srcFile, testPayload, 0600); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write source file: %v\n", err)
		os.Exit(1)
	}

	// 1. Verify unix.Link creates a valid hard link
	if err := unix.Link(srcFile, linkFile); err != nil {
		fmt.Fprintf(os.Stderr, "unix.Link failed: %v\n", err)
		os.Exit(1)
	}

	linkData, err := os.ReadFile(linkFile)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read link file: %v\n", err)
		os.Exit(1)
	}
	if string(linkData) != string(testPayload) {
		fmt.Fprintf(os.Stderr, "link payload mismatch: expected %q, got %q\n", string(testPayload), string(linkData))
		os.Exit(1)
	}

	var statSrc, statLink unix.Stat_t
	if err := unix.Stat(srcFile, &statSrc); err != nil {
		fmt.Fprintf(os.Stderr, "failed to stat source: %v\n", err)
		os.Exit(1)
	}
	if err := unix.Stat(linkFile, &statLink); err != nil {
		fmt.Fprintf(os.Stderr, "failed to stat link: %v\n", err)
		os.Exit(1)
	}
	if statSrc.Ino != statLink.Ino {
		fmt.Fprintf(os.Stderr, "inode mismatch between source (%d) and link (%d)\n", statSrc.Ino, statLink.Ino)
		os.Exit(1)
	}
	if statSrc.Nlink < 2 {
		fmt.Fprintf(os.Stderr, "expected link count >= 2, got %d\n", statSrc.Nlink)
		os.Exit(1)
	}

	// 2. Verify unix.Link returns ENOENT when source path does not exist
	nonExistentSrc := filepath.Join(tmpDir, "missing.txt")
	nonExistentDst := filepath.Join(tmpDir, "missing_link.txt")
	if err := unix.Link(nonExistentSrc, nonExistentDst); !errors.Is(err, unix.ENOENT) {
		fmt.Fprintf(os.Stderr, "expected ENOENT for nonexistent source, got: %v\n", err)
		os.Exit(1)
	}

	// 3. Verify unix.Link returns EEXIST when destination path already exists
	if err := unix.Link(srcFile, linkFile); !errors.Is(err, unix.EEXIST) {
		fmt.Fprintf(os.Stderr, "expected EEXIST for existing target, got: %v\n", err)
		os.Exit(1)
	}

	// 4. Verify helper wrapper
	linkFile2 := filepath.Join(tmpDir, "link2.txt")
	if err := src.CreateHardLink(srcFile, linkFile2); err != nil {
		fmt.Fprintf(os.Stderr, "src.CreateHardLink failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Println("PASS: all contract assertions satisfied")
}