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

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_RDWR 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.O_RDWR

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:a6f9f55a93a467038af44fa7155ce49af7837dec146b755f60f13184701c14d3","contract":["unix.O_RDWR matches syscall.O_RDWR flag with access mode value 2","unix.Open with unix.O_RDWR without unix.O_CREAT fails with unix.ENOENT for non-existent file","unix.Open with unix.O_RDWR allows both writing and reading on the file descriptor","file descriptor opened with unix.O_RDONLY fails write with unix.EBADF while unix.O_RDWR succeeds"],"goal":"verify golang.org/x/sys/unix.O_RDWR 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.O_RDWR"]},"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.O_RDWR"],"verifierAdapter":"golang@1"}

module 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=

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

package main

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

	"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("PASS: unix.O_RDWR contract passed")
}

func runTests() error {
	// 1. unix.O_RDWR matches syscall.O_RDWR flag with access mode value 2
	if unix.O_RDWR != 2 {
		return fmt.Errorf("expected unix.O_RDWR to be 2, got %d", unix.O_RDWR)
	}
	if unix.O_RDWR != syscall.O_RDWR {
		return fmt.Errorf("expected unix.O_RDWR to match syscall.O_RDWR (%d), got %d", syscall.O_RDWR, unix.O_RDWR)
	}
	if (unix.O_RDWR & unix.O_ACCMODE) != unix.O_RDWR {
		return fmt.Errorf("expected (unix.O_RDWR & unix.O_ACCMODE) to equal unix.O_RDWR")
	}

	tmpDir, err := os.MkdirTemp("", "ordwr-contract-*")
	if err != nil {
		return fmt.Errorf("failed to create temporary directory: %w", err)
	}
	defer os.RemoveAll(tmpDir)

	filePath := filepath.Join(tmpDir, "rw_test.dat")

	// 2. unix.Open with unix.O_RDWR without unix.O_CREAT fails with unix.ENOENT for non-existent file
	fdMissing, err := unix.Open(filePath, unix.O_RDWR, 0)
	if err == nil {
		unix.Close(fdMissing)
		return fmt.Errorf("expected unix.Open to fail for non-existent file without O_CREAT")
	}
	if !errors.Is(err, unix.ENOENT) {
		return fmt.Errorf("expected error to be unix.ENOENT, got: %w", err)
	}

	// 3. unix.Open with unix.O_RDWR|unix.O_CREAT creates file and allows both writing and reading
	fd, err := unix.Open(filePath, unix.O_RDWR|unix.O_CREAT|unix.O_TRUNC, 0600)
	if err != nil {
		return fmt.Errorf("failed to open file with O_RDWR|O_CREAT: %w", err)
	}
	defer unix.Close(fd)

	payload := []byte("CodeSampleX O_RDWR contract test payload")
	written, err := unix.Write(fd, payload)
	if err != nil {
		return fmt.Errorf("unix.Write failed: %w", err)
	}
	if written != len(payload) {
		return fmt.Errorf("expected to write %d bytes, wrote %d", len(payload), written)
	}

	// Seek to beginning and read back
	offset, err := unix.Seek(fd, 0, unix.SEEK_SET)
	if err != nil {
		return fmt.Errorf("unix.Seek failed: %w", err)
	}
	if offset != 0 {
		return fmt.Errorf("expected offset 0 after seek, got %d", offset)
	}

	readBuf := make([]byte, len(payload))
	nRead, err := unix.Read(fd, readBuf)
	if err != nil {
		return fmt.Errorf("unix.Read failed: %w", err)
	}
	if nRead != len(payload) {
		return fmt.Errorf("expected to read %d bytes, read %d", len(payload), nRead)
	}
	if !bytes.Equal(readBuf, payload) {
		return fmt.Errorf("read data mismatch: expected %q, got %q", payload, readBuf)
	}

	// 4. File descriptor opened with unix.O_RDONLY forbids writing (unix.EBADF)
	fdRO, err := unix.Open(filePath, unix.O_RDONLY, 0)
	if err != nil {
		return fmt.Errorf("failed to open file with O_RDONLY: %w", err)
	}
	defer unix.Close(fdRO)

	_, writeErr := unix.Write(fdRO, []byte("forbidden write"))
	if writeErr == nil {
		return fmt.Errorf("expected write on O_RDONLY fd to fail, but succeeded")
	}
	if !errors.Is(writeErr, unix.EBADF) {
		return fmt.Errorf("expected write error on O_RDONLY to be unix.EBADF, got: %w", writeErr)
	}

	return nil
}