modernc.org/fileutil v1.4.0

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 pkg:golang/modernc.org/fileutil@v1.4.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/modernc.org/fileutil@v1.4.0

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:sha256:20f5175e31979006f73058aaaa468f828c6d3d26a3c4765469d49eb6705de12b","contract":["fileutil.TempFile creates a temporary file with the given prefix and suffix","fileutil.IsEOF reports whether an error is io.EOF","fileutil.Read fills buffer completely from an io.Reader","fileutil.CopyFile copies file content from fs.FS to destination"],"goal":"verify pkg:golang/modernc.org/fileutil@v1.4.0","kind":"HOW","packages":["pkg:golang/modernc.org/fileutil@v1.4.0"],"schemaVersion":1},"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/modernc.org/fileutil@v1.4.0"],"schemaVersion":1,"subject":"pkg:golang/modernc.org/fileutil@v1.4.0","verifierAdapter":"golang@1"}

module sample

go 1.26.6

require modernc.org/fileutil v1.4.0 // indirect

modernc.org/fileutil v1.4.0 h1:j6ZzNTftVS054gi281TyLjHPp6CPHr2KCxEXjEbD6SM=
modernc.org/fileutil v1.4.0/go.mod h1:EqdKFDxiByqxLk8ozOxObDSfcVOv/54xDs/DUHdvCUU=

package main

import (
	"bytes"
	"fmt"
	"io/fs"
	"os"
	"strings"
	"testing/fstest"

	"modernc.org/fileutil"
)

func main() {
	// Demonstrate TempFile
	tempDir, err := os.MkdirTemp("", "sample-fileutil-*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp dir: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tempDir)

	f, err := fileutil.TempFile(tempDir, "example-", ".txt")
	if err != nil {
		fmt.Fprintf(os.Stderr, "TempFile failed: %v\n", err)
		os.Exit(1)
	}
	fName := f.Name()
	_ = f.Close()
	fmt.Printf("Created temp file: %s (has suffix .txt: %t)\n", fName, strings.HasSuffix(fName, ".txt"))

	// Demonstrate Read
	buf := make([]byte, 5)
	reader := bytes.NewReader([]byte("fileutil example"))
	if err := fileutil.Read(reader, buf); err != nil {
		fmt.Fprintf(os.Stderr, "Read failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Read bytes: %s\n", string(buf))

	// Demonstrate CopyFile
	fsys := fstest.MapFS{
		"hello.txt": &fstest.MapFile{
			Data: []byte("sample content"),
			Mode: fs.FileMode(0644),
		},
	}
	dstPath := tempDir + "/copied.txt"
	copiedBytes, err := fileutil.CopyFile(fsys, dstPath, "hello.txt", nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "CopyFile failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Copied %d bytes to %s\n", copiedBytes, dstPath)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/modernc.org/fileutil@v1.4.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/modernc.org/fileutil@v1.4.0"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"testing/fstest"

	"modernc.org/fileutil"
)

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

	// Assertion 1: fileutil.TempFile creates a temporary file with the given prefix and suffix
	prefix := "csx-prefix-"
	suffix := ".suffix"
	tempF, err := fileutil.TempFile(tempDir, prefix, suffix)
	if err != nil {
		fmt.Fprintf(os.Stderr, "fileutil.TempFile failed: %v\n", err)
		os.Exit(1)
	}
	tempName := tempF.Name()
	_ = tempF.Close()

	if !strings.HasPrefix(filepath.Base(tempName), prefix) {
		fmt.Fprintf(os.Stderr, "expected temp file basename to start with %q, got %q\n", prefix, filepath.Base(tempName))
		os.Exit(1)
	}
	if !strings.HasSuffix(tempName, suffix) {
		fmt.Fprintf(os.Stderr, "expected temp file to have suffix %q, got %q\n", suffix, tempName)
		os.Exit(1)
	}

	// Assertion 2: fileutil.IsEOF reports whether an error is io.EOF
	if !fileutil.IsEOF(io.EOF) {
		fmt.Fprintf(os.Stderr, "expected fileutil.IsEOF(io.EOF) to be true\n")
		os.Exit(1)
	}
	if fileutil.IsEOF(io.ErrUnexpectedEOF) {
		fmt.Fprintf(os.Stderr, "expected fileutil.IsEOF(io.ErrUnexpectedEOF) to be false\n")
		os.Exit(1)
	}
	if fileutil.IsEOF(nil) {
		fmt.Fprintf(os.Stderr, "expected fileutil.IsEOF(nil) to be false\n")
		os.Exit(1)
	}

	// Assertion 3: fileutil.Read fills buffer completely from an io.Reader
	srcData := []byte("hello fileutil contract test")
	buf := make([]byte, 5)
	reader := bytes.NewReader(srcData)
	if err := fileutil.Read(reader, buf); err != nil {
		fmt.Fprintf(os.Stderr, "fileutil.Read failed: %v\n", err)
		os.Exit(1)
	}
	if string(buf) != "hello" {
		fmt.Fprintf(os.Stderr, "expected read content 'hello', got %q\n", string(buf))
		os.Exit(1)
	}

	shortReader := bytes.NewReader([]byte("123"))
	shortBuf := make([]byte, 10)
	if err := fileutil.Read(shortReader, shortBuf); err == nil {
		fmt.Fprintf(os.Stderr, "expected fileutil.Read to error when reader runs out of bytes\n")
		os.Exit(1)
	}

	// Assertion 4: fileutil.CopyFile copies file content from fs.FS to destination
	expectedPayload := []byte("sample file copy data content")
	fsys := fstest.MapFS{
		"contract_source.txt": &fstest.MapFile{
			Data: expectedPayload,
			Mode: fs.FileMode(0644),
		},
	}
	dstPath := filepath.Join(tempDir, "contract_dest.txt")
	copiedLen, err := fileutil.CopyFile(fsys, dstPath, "contract_source.txt", nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "fileutil.CopyFile failed: %v\n", err)
		os.Exit(1)
	}
	if copiedLen != int64(len(expectedPayload)) {
		fmt.Fprintf(os.Stderr, "expected copied bytes %d, got %d\n", len(expectedPayload), copiedLen)
		os.Exit(1)
	}

	destContent, err := os.ReadFile(dstPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read copied destination file: %v\n", err)
		os.Exit(1)
	}
	if !bytes.Equal(destContent, expectedPayload) {
		fmt.Fprintf(os.Stderr, "destination file content mismatch\n")
		os.Exit(1)
	}

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