golang.org/x/net v0.0.0-20191119073136-fc4aabc6c914: 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 golang.org/x/net/publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914
Demonstrate these symbols/APIs:
  - golang.org/x/net/publicsuffix.EffectiveTLDPlusOne

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:sha256:9457dbb8454facca5cbc78b123563d45b9bfc1054992edf96af4eade4244f997","contract":["publicsuffix.EffectiveTLDPlusOne extracts the effective top-level domain plus one label for valid domains and returns an error for bare public suffixes or malformed domains"],"goal":"verify golang.org/x/net/publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914"],"schemaVersion":1,"symbols":["golang.org/x/net/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@v0.0.0-20191119073136-fc4aabc6c914"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914","symbols":["golang.org/x/net/publicsuffix.EffectiveTLDPlusOne"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.20

require golang.org/x/net v0.0.0-20191119073136-fc4aabc6c914

golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/net v0.0.0-20191119073136-fc4aabc6c914 h1:MlY3mEfbnWGmUi4rtHOtNnnnN4UJRGSyLPx+DXA5Sq4=
golang.org/x/net v0.0.0-20191119073136-fc4aabc6c914/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

package main

import (
	"fmt"
	"log"

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

func main() {
	domain := "sub.example.com"
	etldPlusOne, err := publicsuffix.EffectiveTLDPlusOne(domain)
	if err != nil {
		log.Fatalf("EffectiveTLDPlusOne failed: %v", err)
	}
	fmt.Printf("domain=%s etldPlusOne=%s\n", domain, etldPlusOne)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/publicsuffix.EffectiveTLDPlusOne in pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.0.0-20191119073136-fc4aabc6c914"
  ],
  "symbols": [
    "golang.org/x/net/publicsuffix.EffectiveTLDPlusOne"
  ]
}

package main

import (
	"fmt"
	"os"

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

func main() {
	validCases := []struct {
		domain string
		want   string
	}{
		{"example.com", "example.com"},
		{"sub.example.com", "example.com"},
		{"a.b.c.example.co.uk", "example.co.uk"},
	}

	for _, tc := range validCases {
		got, err := publicsuffix.EffectiveTLDPlusOne(tc.domain)
		if err != nil {
			fmt.Fprintf(os.Stderr, "unexpected error for %q: %v\n", tc.domain, err)
			os.Exit(1)
		}
		if got != tc.want {
			fmt.Fprintf(os.Stderr, "for %q: got %q, want %q\n", tc.domain, got, tc.want)
			os.Exit(1)
		}
	}

	invalidCases := []string{
		"com",
		"co.uk",
		"",
		".",
		".example.com",
		"example.com.",
	}

	for _, inv := range invalidCases {
		got, err := publicsuffix.EffectiveTLDPlusOne(inv)
		if err == nil {
			fmt.Fprintf(os.Stderr, "expected error for invalid domain %q, got %q\n", inv, got)
			os.Exit(1)
		}
	}

	fmt.Println("contract verified")
}