golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b: unix.RLIMIT_NOFILE

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.RLIMIT_NOFILE in pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.RLIMIT_NOFILE

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:d84fb0399771848a2be7491743fd0e6e58067e53b64144741027f31652f0fe78","contract":["unix.RLIMIT_NOFILE identifies the resource limit constant for open file descriptors","unix.Getrlimit queries current soft and hard limits for RLIMIT_NOFILE","unix.Setrlimit adjusts process soft file descriptor limit within hard limit boundaries and restores original limit","unix.Setrlimit rejects invalid rlimit configurations where soft limit exceeds hard limit"],"goal":"verify golang.org/x/sys/unix.RLIMIT_NOFILE in pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.RLIMIT_NOFILE"]},"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@v0.0.0-20181122145206-62eef0e2fa9b"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b","symbols":["golang.org/x/sys/unix.RLIMIT_NOFILE"],"verifierAdapter":"golang@1"}

module example.com/rlimit-sample

go 1.25.0

require golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b

golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b h1:MQE+LT/ABUuuvEZ+YQAMSXindAdUh7slEmAkup74op4=
golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

package rlimitsample

import (
	"errors"
	"fmt"

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

// Limit represents soft and hard resource limits.
type Limit struct {
	Cur uint64
	Max uint64
}

// GetOpenFileLimit retrieves the file descriptor limit for the current process using unix.RLIMIT_NOFILE.
func GetOpenFileLimit() (Limit, error) {
	var rlim unix.Rlimit
	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &rlim); err != nil {
		return Limit{}, fmt.Errorf("getrlimit(RLIMIT_NOFILE): %w", err)
	}
	return Limit{
		Cur: rlim.Cur,
		Max: rlim.Max,
	}, nil
}

// SetOpenFileLimit sets the soft and hard file descriptor limits using unix.RLIMIT_NOFILE.
func SetOpenFileLimit(limit Limit) error {
	if limit.Cur > limit.Max {
		return errors.New("soft limit cannot exceed hard limit")
	}
	rlim := unix.Rlimit{
		Cur: limit.Cur,
		Max: limit.Max,
	}
	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &rlim); err != nil {
		return fmt.Errorf("setrlimit(RLIMIT_NOFILE): %w", err)
	}
	return nil
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.RLIMIT_NOFILE in pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.0.0-20181122145206-62eef0e2fa9b"
  ],
  "symbols": [
    "golang.org/x/sys/unix.RLIMIT_NOFILE"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

	rlimitsample "example.com/rlimit-sample"
	"golang.org/x/sys/unix"
)

func main() {
	// Assertion 1: RLIMIT_NOFILE is defined and non-zero
	if unix.RLIMIT_NOFILE == 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected unix.RLIMIT_NOFILE to be non-zero\n")
		os.Exit(1)
	}

	// Assertion 2: Query RLIMIT_NOFILE using direct unix.Getrlimit
	var initial unix.Rlimit
	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &initial); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Getrlimit(unix.RLIMIT_NOFILE) failed: %v\n", err)
		os.Exit(1)
	}
	if initial.Cur == 0 || initial.Max == 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected non-zero initial file limits, got cur=%d, max=%d\n", initial.Cur, initial.Max)
		os.Exit(1)
	}
	if initial.Cur > initial.Max {
		fmt.Fprintf(os.Stderr, "FAIL: initial soft limit (%d) exceeds hard limit (%d)\n", initial.Cur, initial.Max)
		os.Exit(1)
	}

	// Assertion 3: Query RLIMIT_NOFILE via helper package
	sampleLimit, err := rlimitsample.GetOpenFileLimit()
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: rlimitsample.GetOpenFileLimit failed: %v\n", err)
		os.Exit(1)
	}
	if sampleLimit.Cur != initial.Cur || sampleLimit.Max != initial.Max {
		fmt.Fprintf(os.Stderr, "FAIL: helper returned mismatched limits: %+v vs %+v\n", sampleLimit, initial)
		os.Exit(1)
	}

	// Assertion 4: Temporarily adjust soft limit downwards and restore
	targetCur := initial.Cur
	if targetCur > 100 {
		targetCur = targetCur - 1
	}
	tempLimit := unix.Rlimit{
		Cur: targetCur,
		Max: initial.Max,
	}
	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &tempLimit); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Setrlimit failed to adjust soft limit: %v\n", err)
		os.Exit(1)
	}

	var verified unix.Rlimit
	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &verified); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to verify adjusted limit: %v\n", err)
		os.Exit(1)
	}
	if verified.Cur != targetCur {
		fmt.Fprintf(os.Stderr, "FAIL: expected adjusted soft limit %d, got %d\n", targetCur, verified.Cur)
		os.Exit(1)
	}

	// Restore original limits
	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &initial); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to restore initial limits: %v\n", err)
		os.Exit(1)
	}

	// Assertion 5: Verify invalid rlimit (cur > max) is rejected by unix.Setrlimit
	invalidLimit := unix.Rlimit{
		Cur: initial.Max + 10,
		Max: initial.Max,
	}
	err = unix.Setrlimit(unix.RLIMIT_NOFILE, &invalidLimit)
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected error when cur > max, got nil\n")
		os.Exit(1)
	}
	if !errors.Is(err, unix.EINVAL) && !errors.Is(err, unix.EPERM) && err != unix.EINVAL && err != unix.EPERM {
		fmt.Fprintf(os.Stderr, "FAIL: expected EINVAL or EPERM, got %v\n", err)
		os.Exit(1)
	}

	fmt.Println("PASS: RLIMIT_NOFILE verified successfully")
}