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

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.NetDev

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:cce24774281d7df2dbb94daebcd0c9898c484e821f917005987b2a5147a38ee9","contract":["procfs.NewDefaultFS() returns (FS, error) where error is nil","fs.NetDev() returns (NetDev, error) where error is nil and contains network interfaces","procfs.FS.NetDev returns an error when reading from a proc mount missing net/dev","fs.NetDev() parses RxBytes, RxPackets, TxBytes, and TxPackets metrics and NetDev.Total aggregates stats across interfaces"],"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.NetDev"]},"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.NetDev"],"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/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
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"
)

// ReadNetDev returns current network interface statistics.
func ReadNetDev() (procfs.NetDev, error) {
	fs, err := procfs.NewDefaultFS()
	if err != nil {
		return nil, fmt.Errorf("procfs access failed: %w", err)
	}
	return fs.NetDev()
}

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

	total := netDev.Total()
	fmt.Printf("Interfaces=%d TotalRxBytes=%d TotalTxBytes=%d TotalRxPackets=%d TotalTxPackets=%d\n",
		len(netDev), total.RxBytes, total.TxBytes, total.RxPackets, total.TxPackets)
}

{
  "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.NetDev"
  ]
}

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.NetDev parses real /proc/net/dev
	netDev, err := fs.NetDev()
	if err != nil {
		fmt.Fprintf(os.Stderr, "fs.NetDev failed: %v\n", err)
		os.Exit(1)
	}
	if len(netDev) == 0 {
		fmt.Fprintf(os.Stderr, "expected at least one network interface in /proc/net/dev\n")
		os.Exit(1)
	}

	// 3. Verify fs.NetDev fails when net/dev 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.NetDev()
	if err == nil {
		fmt.Fprintf(os.Stderr, "expected error when net/dev file is missing, got nil\n")
		os.Exit(1)
	}

	// 4. Verify mock net/dev parsing and NetDev.Total aggregation
	if err := os.MkdirAll(filepath.Join(tmpDir, "net"), 0755); err != nil {
		fmt.Fprintf(os.Stderr, "os.MkdirAll failed: %v\n", err)
		os.Exit(1)
	}

	mockContent := []byte("Inter-|   Receive                                                |  Transmit\n" +
		" face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed\n" +
		"    lo:    1000      10    0    0    0     0          0         0     2000      20    0    0    0     0       0          0\n" +
		"  eth0:    5000      50    1    0    0     0          0         0     8000      80    2    0    0     0       0          0\n")

	if err := os.WriteFile(filepath.Join(tmpDir, "net", "dev"), mockContent, 0644); err != nil {
		fmt.Fprintf(os.Stderr, "os.WriteFile failed: %v\n", err)
		os.Exit(1)
	}

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

	lo, ok := parsed["lo"]
	if !ok || lo.RxBytes != 1000 || lo.TxBytes != 2000 || lo.RxPackets != 10 || lo.TxPackets != 20 {
		fmt.Fprintf(os.Stderr, "unexpected lo parsed: %+v\n", lo)
		os.Exit(1)
	}

	eth0, ok := parsed["eth0"]
	if !ok || eth0.RxBytes != 5000 || eth0.TxBytes != 8000 || eth0.RxErrors != 1 || eth0.TxErrors != 2 {
		fmt.Fprintf(os.Stderr, "unexpected eth0 parsed: %+v\n", eth0)
		os.Exit(1)
	}

	mockTotal := parsed.Total()
	if mockTotal.RxBytes != 6000 || mockTotal.TxBytes != 10000 || mockTotal.RxPackets != 60 || mockTotal.TxPackets != 100 {
		fmt.Fprintf(os.Stderr, "unexpected total parsed: %+v\n", mockTotal)
		os.Exit(1)
	}

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