golang.org/x/net v0.17.0: publicsuffix.EffectiveTLDPlusOne

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 publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.17.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.17.0
Demonstrate these symbols/APIs:
  - publicsuffix.EffectiveTLDPlusOne
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:acbfc7eedcb1d4fcbe0294f834cc088ee6585c0f0e141e2a54ccf86ee8b48437","contract":["publicsuffix.EffectiveTLDPlusOne extracts the effective top-level domain plus one label for standard and multi-level TLDs","publicsuffix.EffectiveTLDPlusOne returns an error when given a bare public suffix or invalid domain"],"goal":"verify publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.17.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.17.0"],"schemaVersion":1,"symbols":["publicsuffix.EffectiveTLDPlusOne"]},"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/net@v0.17.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.17.0","symbols":["publicsuffix.EffectiveTLDPlusOne"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.20

require golang.org/x/net v0.17.0

golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=

package main

import (
	"fmt"
	"os"

	"golang.org/x/net/publicsuffix"
)

// ExtractEffectiveTLDPlusOne returns the effective top-level domain plus one label for a domain string.
func ExtractEffectiveTLDPlusOne(domain string) (string, error) {
	return publicsuffix.EffectiveTLDPlusOne(domain)
}

func main() {
	domains := []string{
		"example.com",
		"sub.example.com",
		"deep.sub.example.co.uk",
	}

	for _, d := range domains {
		etld1, err := ExtractEffectiveTLDPlusOne(d)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error processing %s: %v\n", d, err)
			os.Exit(1)
		}
		fmt.Printf("domain: %s -> eTLD+1: %s\n", d, etld1)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.17.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.17.0"
  ],
  "symbols": [
    "publicsuffix.EffectiveTLDPlusOne"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"fmt"
	"os"

	"golang.org/x/net/publicsuffix"
)

func main() {
	// Assertion 1: publicsuffix.EffectiveTLDPlusOne extracts the effective top-level domain plus one label for standard and multi-level TLDs
	cases := []struct {
		input    string
		expected string
	}{
		{"example.com", "example.com"},
		{"sub.example.com", "example.com"},
		{"a.b.c.example.com", "example.com"},
		{"foo.co.uk", "foo.co.uk"},
		{"sub.foo.co.uk", "foo.co.uk"},
		{"golang.org", "golang.org"},
	}

	for _, c := range cases {
		got, err := publicsuffix.EffectiveTLDPlusOne(c.input)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: unexpected error for %q: %v\n", c.input, err)
			os.Exit(1)
		}
		if got != c.expected {
			fmt.Fprintf(os.Stderr, "FAIL: input %q: expected %q, got %q\n", c.input, c.expected, got)
			os.Exit(1)
		}
	}

	// Assertion 2: publicsuffix.EffectiveTLDPlusOne returns an error when given a bare public suffix or invalid domain
	errorCases := []string{
		"com",
		"co.uk",
		"org",
		"",
	}

	for _, input := range errorCases {
		got, err := publicsuffix.EffectiveTLDPlusOne(input)
		if err == nil {
			fmt.Fprintf(os.Stderr, "FAIL: expected error for %q, but got %q\n", input, got)
			os.Exit(1)
		}
	}

	fmt.Println("PASS: publicsuffix.EffectiveTLDPlusOne contract verified")
}