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

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_NONBLOCK 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.O_NONBLOCK
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:sha256:0ca253b25c98fbb71ce398066d1797c1205b49789c0ced2e7abb41aba0e65344","contract":["unix.O_NONBLOCK is a non-zero integer constant representing the non-blocking file descriptor flag","unix.Pipe2 with unix.O_NONBLOCK creates pipe descriptors that return EAGAIN or EWOULDBLOCK on empty read","unix.SetNonblock enables the O_NONBLOCK status flag on an existing file descriptor verifiable via FcntlInt F_GETFL","unix.Write and unix.Read transfer data through non-blocking pipe descriptors without blocking"],"goal":"verify golang.org/x/sys/unix.O_NONBLOCK 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.O_NONBLOCK"]},"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.O_NONBLOCK"],"verifierAdapter":"golang@1"}

module sample

go 1.25.0

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 (
	"errors"
	"fmt"
	"os"

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

// CreateNonBlockingPipe initializes a unidirectional pipe with O_NONBLOCK and O_CLOEXEC flags.
func CreateNonBlockingPipe() ([2]int, error) {
	var fds [2]int
	if err := unix.Pipe2(fds[:], unix.O_NONBLOCK|unix.O_CLOEXEC); err != nil {
		return fds, fmt.Errorf("pipe2 failed: %w", err)
	}
	return fds, nil
}

// SetDescriptorNonBlocking applies unix.O_NONBLOCK mode to an open file descriptor.
func SetDescriptorNonBlocking(fd int, nonblocking bool) error {
	if err := unix.SetNonblock(fd, nonblocking); err != nil {
		return fmt.Errorf("setnonblock failed: %w", err)
	}
	return nil
}

// IsDescriptorNonBlocking checks if O_NONBLOCK flag is active on the given file descriptor.
func IsDescriptorNonBlocking(fd int) (bool, error) {
	flags, err := unix.FcntlInt(uintptr(fd), unix.F_GETFL, 0)
	if err != nil {
		return false, fmt.Errorf("fcntl F_GETFL failed: %w", err)
	}
	return (flags & unix.O_NONBLOCK) != 0, nil
}

// ReadNonBlocking attempts to read from a non-blocking descriptor. Returns true if EAGAIN/EWOULDBLOCK occurred.
func ReadNonBlocking(fd int, buf []byte) (int, bool, error) {
	n, err := unix.Read(fd, buf)
	if err != nil {
		if errors.Is(err, unix.EAGAIN) || errors.Is(err, unix.EWOULDBLOCK) {
			return 0, true, nil
		}
		return 0, false, fmt.Errorf("read failed: %w", err)
	}
	return n, false, nil
}

func main() {
	fds, err := CreateNonBlockingPipe()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error creating non-blocking pipe: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fds[0])
	defer unix.Close(fds[1])

	isNB, err := IsDescriptorNonBlocking(fds[0])
	if err != nil || !isNB {
		fmt.Fprintf(os.Stderr, "Error verifying non-blocking status: %v\n", err)
		os.Exit(1)
	}

	buf := make([]byte, 128)
	n, wouldBlock, err := ReadNonBlocking(fds[0], buf)
	if err != nil || !wouldBlock {
		fmt.Fprintf(os.Stderr, "Expected empty read to return wouldBlock, got n=%d, err=%v\n", n, err)
		os.Exit(1)
	}

	msg := []byte("hello non-blocking pipe")
	if _, err := unix.Write(fds[1], msg); err != nil {
		fmt.Fprintf(os.Stderr, "Error writing: %v\n", err)
		os.Exit(1)
	}

	n, wouldBlock, err = ReadNonBlocking(fds[0], buf)
	if err != nil || wouldBlock || n != len(msg) {
		fmt.Fprintf(os.Stderr, "Error reading message: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Successfully read %d bytes from non-blocking pipe: %s\n", n, string(buf[:n]))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.O_NONBLOCK 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.O_NONBLOCK"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"errors"
	"fmt"
	"os"

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

func main() {
	// Assertion 1: unix.O_NONBLOCK is a non-zero integer constant representing the non-blocking file descriptor flag
	if unix.O_NONBLOCK == 0 {
		fmt.Fprintf(os.Stderr, "FAIL: unix.O_NONBLOCK is 0\n")
		os.Exit(1)
	}

	// Assertion 2: unix.Pipe2 with unix.O_NONBLOCK creates pipe descriptors that return EAGAIN or EWOULDBLOCK on empty read
	var fds [2]int
	if err := unix.Pipe2(fds[:], unix.O_NONBLOCK|unix.O_CLOEXEC); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Pipe2 failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fds[0])
	defer unix.Close(fds[1])

	buf := make([]byte, 64)
	n, err := unix.Read(fds[0], buf)
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected error on empty non-blocking read, got %d bytes\n", n)
		os.Exit(1)
	}
	if !errors.Is(err, unix.EAGAIN) && !errors.Is(err, unix.EWOULDBLOCK) {
		fmt.Fprintf(os.Stderr, "FAIL: expected EAGAIN or EWOULDBLOCK, got %v\n", err)
		os.Exit(1)
	}

	// Assertion 3: unix.SetNonblock enables the O_NONBLOCK status flag on an existing file descriptor verifiable via FcntlInt F_GETFL
	var blockingFds [2]int
	if err := unix.Pipe2(blockingFds[:], unix.O_CLOEXEC); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: pipe creation failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(blockingFds[0])
	defer unix.Close(blockingFds[1])

	flagsBefore, err := unix.FcntlInt(uintptr(blockingFds[0]), unix.F_GETFL, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: fcntl F_GETFL before SetNonblock failed: %v\n", err)
		os.Exit(1)
	}
	if (flagsBefore & unix.O_NONBLOCK) != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: initial pipe descriptor should not have O_NONBLOCK set\n")
		os.Exit(1)
	}

	if err := unix.SetNonblock(blockingFds[0], true); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.SetNonblock failed: %v\n", err)
		os.Exit(1)
	}

	flagsAfter, err := unix.FcntlInt(uintptr(blockingFds[0]), unix.F_GETFL, 0)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: fcntl F_GETFL after SetNonblock failed: %v\n", err)
		os.Exit(1)
	}
	if (flagsAfter & unix.O_NONBLOCK) == 0 {
		fmt.Fprintf(os.Stderr, "FAIL: O_NONBLOCK flag was not set after unix.SetNonblock\n")
		os.Exit(1)
	}

	// Assertion 4: unix.Write and unix.Read transfer data through non-blocking pipe descriptors without blocking
	payload := []byte("non-blocking-contract-test")
	wn, err := unix.Write(fds[1], payload)
	if err != nil || wn != len(payload) {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Write failed: wn=%d, err=%v\n", wn, err)
		os.Exit(1)
	}

	readBuf := make([]byte, 64)
	rn, err := unix.Read(fds[0], readBuf)
	if err != nil || rn != len(payload) || !bytes.Equal(readBuf[:rn], payload) {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Read failed: rn=%d, err=%v, data=%q\n", rn, err, string(readBuf[:rn]))
		os.Exit(1)
	}

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