golang.org/x/sys v0.0.0-20220406155245-289d7a0edf71: unix.O_TRUNC

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_TRUNC in pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.O_TRUNC

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:cd1176ae0d5d70f860bb39de6e82509b42a489f8e3df82da769f86aaa421abf6","contract":["unix.O_TRUNC constant flag is defined and non-zero","unix.Open with unix.O_TRUNC truncates existing file to zero bytes","writing to file opened with unix.O_TRUNC replaces prior contents without residual data"],"goal":"verify golang.org/x/sys/unix.O_TRUNC in pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.O_TRUNC"]},"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@v0.0.0-20220406155245-289d7a0edf71"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71","symbols":["golang.org/x/sys/unix.O_TRUNC"],"verifierAdapter":"golang@1"}

module sample

go 1.22

require golang.org/x/sys v0.0.0-20220406155245-289d7a0edf71

golang.org/x/sys v0.0.0-20220406155245-289d7a0edf71 h1:PRD0hj6tTuUnCFD08vkvjkYFbQg/9lV8KIxe1y4/cvU=
golang.org/x/sys v0.0.0-20220406155245-289d7a0edf71/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

package main

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

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

func main() {
	tmpDir, err := os.MkdirTemp("", "csx-trunc-*")
	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")

	// Step 1: Create a file with initial content
	if err := os.WriteFile(filePath, []byte("Initial file content that is relatively long"), 0644); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write initial file: %v\n", err)
		os.Exit(1)
	}

	// Step 2: Open with unix.O_WRONLY | unix.O_TRUNC
	fd, err := unix.Open(filePath, unix.O_WRONLY|unix.O_TRUNC, 0644)
	if err != nil {
		fmt.Fprintf(os.Stderr, "unix.Open failed: %v\n", err)
		os.Exit(1)
	}

	// Step 3: Write new shorter content
	newContent := []byte("Truncated content")
	if _, err := unix.Write(fd, newContent); err != nil {
		unix.Close(fd)
		fmt.Fprintf(os.Stderr, "unix.Write failed: %v\n", err)
		os.Exit(1)
	}
	unix.Close(fd)

	// Step 4: Verify the file content
	readBack, err := os.ReadFile(filePath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "os.ReadFile failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("O_TRUNC flag: %d\n", unix.O_TRUNC)
	fmt.Printf("Resulting content: %s\n", string(readBack))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.O_TRUNC in pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.0.0-20220406155245-289d7a0edf71"
  ],
  "symbols": [
    "golang.org/x/sys/unix.O_TRUNC"
  ]
}

package main

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

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

func main() {
	// Assertion 1: unix.O_TRUNC constant flag is defined and non-zero
	if unix.O_TRUNC == 0 {
		fmt.Fprintf(os.Stderr, "Assertion failed: unix.O_TRUNC expected non-zero, got 0\n")
		os.Exit(1)
	}

	tmpDir, err := os.MkdirTemp("", "csx-trunc-test-*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "Setup failed: os.MkdirTemp error: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	filePath := filepath.Join(tmpDir, "contract_test.txt")
	initialData := []byte("Initial data before truncation with extra bytes to ensure length > 0")
	if err := os.WriteFile(filePath, initialData, 0644); err != nil {
		fmt.Fprintf(os.Stderr, "Setup failed: os.WriteFile error: %v\n", err)
		os.Exit(1)
	}

	// Assertion 2: unix.Open with unix.O_TRUNC truncates existing file to zero bytes
	fd, err := unix.Open(filePath, unix.O_WRONLY|unix.O_TRUNC, 0644)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Assertion failed: unix.Open error: %v\n", err)
		os.Exit(1)
	}

	var stat unix.Stat_t
	if err := unix.Fstat(fd, &stat); err != nil {
		unix.Close(fd)
		fmt.Fprintf(os.Stderr, "Assertion failed: unix.Fstat error: %v\n", err)
		os.Exit(1)
	}
	if stat.Size != 0 {
		unix.Close(fd)
		fmt.Fprintf(os.Stderr, "Assertion failed: expected file size 0 after open with O_TRUNC, got %d\n", stat.Size)
		os.Exit(1)
	}

	// Assertion 3: writing to file opened with unix.O_TRUNC replaces prior contents without residual data
	replacement := []byte("Short new data")
	n, err := unix.Write(fd, replacement)
	if err != nil || n != len(replacement) {
		unix.Close(fd)
		fmt.Fprintf(os.Stderr, "Assertion failed: unix.Write error: %v, written: %d\n", err, n)
		os.Exit(1)
	}
	unix.Close(fd)

	readBack, err := os.ReadFile(filePath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Assertion failed: os.ReadFile error: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(readBack, replacement) {
		fmt.Fprintf(os.Stderr, "Assertion failed: expected content %q, got %q\n", string(replacement), string(readBack))
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed successfully.")
}