github.com/prometheus/procfs v0.22.0: FS.Self

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/github.com/prometheus/procfs@v0.22.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/prometheus/procfs@v0.22.0
Demonstrate these symbols/APIs:
  - procfs.FS.Self

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:sha256:6716cb69c03a4fe8facf98d6eea72da2dae15882524affb9564392a2a0d986ce","contract":["procfs.NewDefaultFS() returns (FS, error) where error is nil","fs.Self() returns (Proc, error) where error is nil and PID matches current process","procfs.FS.Self returns an error when reading from a proc mount missing self symlink","fs.Self() resolves self symlink to target PID directory in procfs mount"],"goal":"verify pkg:golang/github.com/prometheus/procfs@v0.22.0","kind":"HOW","packages":["pkg:golang/github.com/prometheus/procfs@v0.22.0"],"schemaVersion":1,"symbols":["procfs.FS.Self"]},"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/github.com/prometheus/procfs@v0.22.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/prometheus/procfs@v0.22.0","symbols":["procfs.FS.Self"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/prometheus/procfs v0.22.0

require golang.org/x/sys v0.47.0 // indirect

github.com/prometheus/procfs v0.22.0 h1:6q9+/JL9IKAPbCmBrv9n5O5Ty3NKnciV5X7YGw0oics=
github.com/prometheus/procfs v0.22.0/go.mod h1:CvmFr/GVhIjIvWJZW3tgkODBQMRIf0EyWMQLHCHab58=
golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=

package main

import (
	"fmt"
	"os"

	"github.com/prometheus/procfs"
)

// ReadSelfProcess returns procfs.Proc representing the current process.
func ReadSelfProcess() (procfs.Proc, error) {
	fs, err := procfs.NewDefaultFS()
	if err != nil {
		return procfs.Proc{}, fmt.Errorf("procfs access failed: %w", err)
	}
	return fs.Self()
}

func main() {
	proc, err := ReadSelfProcess()
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read self process: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Self PID: %d\n", proc.PID)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/prometheus/procfs@v0.22.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/prometheus/procfs@v0.22.0"
  ],
  "symbols": [
    "procfs.FS.Self"
  ]
}

package main

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

	"github.com/prometheus/procfs"
)

func main() {
	// 1. Verify procfs.NewDefaultFS returns a valid FS instance
	fs, err := procfs.NewDefaultFS()
	if err != nil {
		fmt.Fprintf(os.Stderr, "procfs.NewDefaultFS failed: %v\n", err)
		os.Exit(1)
	}

	// 2. Verify fs.Self returns a Proc for the current process
	selfProc, err := fs.Self()
	if err != nil {
		fmt.Fprintf(os.Stderr, "fs.Self failed: %v\n", err)
		os.Exit(1)
	}
	if selfProc.PID <= 0 || selfProc.PID != os.Getpid() {
		fmt.Fprintf(os.Stderr, "expected PID to match os.Getpid() (%d), got: %d\n", os.Getpid(), selfProc.PID)
		os.Exit(1)
	}

	// 3. Verify fs.Self fails when self symlink is missing
	tmpDir, err := os.MkdirTemp("", "proctest*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "os.MkdirTemp failed: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	mockFS, err := procfs.NewFS(tmpDir)
	if err != nil {
		fmt.Fprintf(os.Stderr, "procfs.NewFS failed: %v\n", err)
		os.Exit(1)
	}

	_, err = mockFS.Self()
	if err == nil {
		fmt.Fprintf(os.Stderr, "expected error when self symlink is missing, got nil\n")
		os.Exit(1)
	}

	// 4. Verify mock procfs resolves self symlink to target PID directory
	const mockPID = 42
	mockPIDDir := filepath.Join(tmpDir, "42")
	if err := os.Mkdir(mockPIDDir, 0755); err != nil {
		fmt.Fprintf(os.Stderr, "os.Mkdir failed: %v\n", err)
		os.Exit(1)
	}
	if err := os.Symlink("42", filepath.Join(tmpDir, "self")); err != nil {
		fmt.Fprintf(os.Stderr, "os.Symlink failed: %v\n", err)
		os.Exit(1)
	}

	resolvedProc, err := mockFS.Self()
	if err != nil {
		fmt.Fprintf(os.Stderr, "mockFS.Self failed on valid symlink: %v\n", err)
		os.Exit(1)
	}
	if resolvedProc.PID != mockPID {
		fmt.Fprintf(os.Stderr, "expected mock PID %d, got: %d\n", mockPID, resolvedProc.PID)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}