golang.org/x/sys v0.31.0: unix.EFD_CLOEXEC

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.EFD_CLOEXEC in pkg:golang/golang.org/x/sys@v0.31.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.31.0
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.EFD_CLOEXEC
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:3f7f62af2f744ddaf7ee26ec8d99dc1b5b9a41e077039b2b0e986d34415791a4","contract":["unix.Eventfd creates a file descriptor with unix.EFD_CLOEXEC flag setting FD_CLOEXEC","Writing and reading 8-byte uint64 counters transfers data across the eventfd","unix.Eventfd with EFD_CLOEXEC and EFD_NONBLOCK returns EAGAIN when counter is zero","unix.Eventfd with EFD_CLOEXEC and EFD_SEMAPHORE decrements counter by 1 on read"],"goal":"verify golang.org/x/sys/unix.EFD_CLOEXEC in pkg:golang/golang.org/x/sys@v0.31.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.31.0"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.EFD_CLOEXEC"]},"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@v0.31.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.31.0","symbols":["golang.org/x/sys/unix.EFD_CLOEXEC"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/sys v0.31.0

golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=

package main

import (
	"encoding/binary"
	"fmt"
	"os"

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

// CreateEventFD creates an eventfd file descriptor with EFD_CLOEXEC and optional flags.
func CreateEventFD(initval uint, flags int) (int, error) {
	fd, err := unix.Eventfd(initval, flags)
	if err != nil {
		return -1, fmt.Errorf("eventfd failed: %w", err)
	}
	return fd, nil
}

// WriteEventFD writes a 64-bit unsigned integer counter to the eventfd.
func WriteEventFD(fd int, val uint64) error {
	var buf [8]byte
	binary.LittleEndian.PutUint64(buf[:], val)
	n, err := unix.Write(fd, buf[:])
	if err != nil {
		return fmt.Errorf("write to eventfd failed: %w", err)
	}
	if n != 8 {
		return fmt.Errorf("short write to eventfd: %d bytes", n)
	}
	return nil
}

// ReadEventFD reads a 64-bit unsigned integer counter from the eventfd.
func ReadEventFD(fd int) (uint64, error) {
	var buf [8]byte
	n, err := unix.Read(fd, buf[:])
	if err != nil {
		return 0, fmt.Errorf("read from eventfd failed: %w", err)
	}
	if n != 8 {
		return 0, fmt.Errorf("short read from eventfd: %d bytes", n)
	}
	return binary.LittleEndian.Uint64(buf[:]), nil
}

func main() {
	// Create eventfd with EFD_CLOEXEC
	fd, err := CreateEventFD(0, unix.EFD_CLOEXEC)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error creating eventfd: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd)

	// Verify close-on-exec flag is set
	flags, err := unix.FcntlInt(uintptr(fd), unix.F_GETFD, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error getting fd flags: %v\n", err)
		os.Exit(1)
	}
	if flags&unix.FD_CLOEXEC == 0 {
		fmt.Fprintf(os.Stderr, "FD_CLOEXEC not set on eventfd\n")
		os.Exit(1)
	}
	fmt.Printf("Eventfd created successfully with EFD_CLOEXEC (fd: %d, flags: %d)\n", fd, flags)

	// Write counter value
	valToWrite := uint64(42)
	if err := WriteEventFD(fd, valToWrite); err != nil {
		fmt.Fprintf(os.Stderr, "Error writing to eventfd: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Wrote counter %d to eventfd\n", valToWrite)

	// Read counter value back
	valRead, err := ReadEventFD(fd)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error reading from eventfd: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Read counter %d from eventfd\n", valRead)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.EFD_CLOEXEC in pkg:golang/golang.org/x/sys@v0.31.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.31.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.EFD_CLOEXEC"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"encoding/binary"
	"errors"
	"fmt"
	"os"

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

func main() {
	// Assertion 1: unix.Eventfd creates a file descriptor with unix.EFD_CLOEXEC flag setting FD_CLOEXEC
	fd, err := unix.Eventfd(0, unix.EFD_CLOEXEC)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd with EFD_CLOEXEC failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd)

	flags, err := unix.FcntlInt(uintptr(fd), unix.F_GETFD, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.FcntlInt F_GETFD failed: %v\n", err)
		os.Exit(1)
	}
	if flags&unix.FD_CLOEXEC == 0 {
		fmt.Fprintf(os.Stderr, "FAIL: FD_CLOEXEC flag was not set on eventfd\n")
		os.Exit(1)
	}

	// Assertion 2: Writing and reading 8-byte uint64 counters transfers data across the eventfd
	var writeBuf [8]byte
	binary.LittleEndian.PutUint64(writeBuf[:], 7)
	n, err := unix.Write(fd, writeBuf[:])
	if err != nil || n != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Write to eventfd failed: n=%d, err=%v\n", n, err)
		os.Exit(1)
	}

	var readBuf [8]byte
	n, err = unix.Read(fd, readBuf[:])
	if err != nil || n != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Read from eventfd failed: n=%d, err=%v\n", n, err)
		os.Exit(1)
	}
	readVal := binary.LittleEndian.Uint64(readBuf[:])
	if readVal != 7 {
		fmt.Fprintf(os.Stderr, "FAIL: eventfd read value mismatch: got %d, want 7\n", readVal)
		os.Exit(1)
	}

	// Assertion 3: unix.Eventfd with EFD_CLOEXEC and EFD_NONBLOCK returns EAGAIN when counter is zero
	nbFd, err := unix.Eventfd(0, unix.EFD_CLOEXEC|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd with EFD_CLOEXEC|EFD_NONBLOCK failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(nbFd)

	var nbBuf [8]byte
	_, err = unix.Read(nbFd, nbBuf[:])
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected EAGAIN on non-blocking empty eventfd, got nil error\n")
		os.Exit(1)
	}
	if !errors.Is(err, unix.EAGAIN) && !errors.Is(err, unix.EWOULDBLOCK) {
		fmt.Fprintf(os.Stderr, "FAIL: expected EAGAIN/EWOULDBLOCK, got %v\n", err)
		os.Exit(1)
	}

	// Assertion 4: unix.Eventfd with EFD_CLOEXEC and EFD_SEMAPHORE decrements counter by 1 on read
	semFd, err := unix.Eventfd(2, unix.EFD_CLOEXEC|unix.EFD_SEMAPHORE)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd with EFD_CLOEXEC|EFD_SEMAPHORE failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(semFd)

	var semBuf [8]byte
	n, err = unix.Read(semFd, semBuf[:])
	if err != nil || n != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: semFd read failed: n=%d, err=%v\n", n, err)
		os.Exit(1)
	}
	semVal := binary.LittleEndian.Uint64(semBuf[:])
	if semVal != 1 {
		fmt.Fprintf(os.Stderr, "FAIL: semaphore read expected 1, got %d\n", semVal)
		os.Exit(1)
	}

	fmt.Println("PASS: golang.org/x/sys unix.EFD_CLOEXEC contract passed")
}