golang.org/x/sys v0.0.0-20210603081109-ebe580a85c40: unix.Umask

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/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.Umask

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:sha256:2e8b49391eafa6df45d833fd9f4b3e97a1cd4d004935583610191b41ec42d1e7","contract":["unix.Umask sets the file mode creation mask and returns the previous umask value","unix.Umask restores the previous umask properly when called again","unix.Umask restricts file permissions created by os.OpenFile according to the mask","unix.Umask with 0000 mask allows creating files with exact requested permissions"],"goal":"verify pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.Umask"]},"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@v0.0.0-20210603081109-ebe580a85c40"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40","symbols":["golang.org/x/sys/unix.Umask"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require golang.org/x/sys v0.0.0-20210603081109-ebe580a85c40

golang.org/x/sys v0.0.0-20210603081109-ebe580a85c40 h1:JWgyZ1qgdTaF3N3oxC+MdTV7qvEEgHo3otj+HB5CM7Q=
golang.org/x/sys v0.0.0-20210603081109-ebe580a85c40/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

package main

import (
	"fmt"

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

// SetUmask sets the file mode creation mask and returns the previous mask.
func SetUmask(mask int) int {
	return unix.Umask(mask)
}

func main() {
	// Set umask to 0022 (read/execute for group/others, write restricted)
	prev := SetUmask(0022)
	fmt.Printf("Previous umask: 0%o\n", prev)

	// Restore previous umask
	restored := SetUmask(prev)
	fmt.Printf("Restored umask: 0%o\n", restored)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.0.0-20210603081109-ebe580a85c40"
  ],
  "symbols": [
    "golang.org/x/sys/unix.Umask"
  ]
}

package main

import (
	"fmt"
	"os"
	"path/filepath"

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

func main() {
	// Assertion 1: unix.Umask sets the file mode creation mask and returns the previous umask value
	originalMask := unix.Umask(0022)
	currentMask := unix.Umask(0027)
	if currentMask != 0022 {
		fmt.Fprintf(os.Stderr, "FAIL: expected unix.Umask to return previous mask 0022, got 0%o\n", currentMask)
		os.Exit(1)
	}

	// Assertion 2: unix.Umask restores the previous umask properly when called again
	restoredMask := unix.Umask(originalMask)
	if restoredMask != 0027 {
		fmt.Fprintf(os.Stderr, "FAIL: expected unix.Umask to return previous mask 0027, got 0%o\n", restoredMask)
		os.Exit(1)
	}

	// Assertion 3: unix.Umask restricts file permissions created by os.OpenFile according to the mask
	tmpDir, err := os.MkdirTemp("", "umask-contract-*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to create temp dir: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	_ = unix.Umask(0077) // Only owner can read/write
	filePathRestricted := filepath.Join(tmpDir, "restricted.txt")
	f1, err := os.OpenFile(filePathRestricted, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to create restricted file: %v\n", err)
		os.Exit(1)
	}
	f1.Close()

	fi1, err := os.Stat(filePathRestricted)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to stat restricted file: %v\n", err)
		os.Exit(1)
	}
	// With 0077 umask and 0666 requested mode, file mode should be 0600 (0666 & ~0077)
	if fi1.Mode().Perm() != 0600 {
		fmt.Fprintf(os.Stderr, "FAIL: expected file mode 0600 with 0077 umask, got 0%o\n", fi1.Mode().Perm())
		os.Exit(1)
	}

	// Assertion 4: unix.Umask with 0000 mask allows creating files with exact requested permissions
	_ = unix.Umask(0000)
	filePathOpen := filepath.Join(tmpDir, "open.txt")
	f2, err := os.OpenFile(filePathOpen, os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to create open file: %v\n", err)
		os.Exit(1)
	}
	f2.Close()

	fi2, err := os.Stat(filePathOpen)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: failed to stat open file: %v\n", err)
		os.Exit(1)
	}
	if fi2.Mode().Perm() != 0644 {
		fmt.Fprintf(os.Stderr, "FAIL: expected file mode 0644 with 0000 umask, got 0%o\n", fi2.Mode().Perm())
		os.Exit(1)
	}

	// Restore original umask
	unix.Umask(originalMask)

	fmt.Println("PASS: golang.org/x/sys/unix.Umask contract verified successfully")
}