golang.org/x/net v0.27.0: html.Parse, html.Render, 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 pkg:golang/golang.org/x/net@v0.27.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.27.0

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:sha256:5f8fab5471c8751c5272e6e70771af63f688c0fd20006056a1be4bf88de02842","contract":["html.Parse parses an HTML document into a node tree from which anchor href attributes are extracted","html.Render serializes a parsed html.Node tree back into valid HTML with entity escaping preserved","publicsuffix.EffectiveTLDPlusOne extracts the effective top-level domain plus one label for multi-level TLDs and returns an error for bare public suffixes"],"goal":"verify pkg:golang/golang.org/x/net@v0.27.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.27.0"],"schemaVersion":1,"symbols":["html.Parse","html.Render","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@v0.27.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.27.0","symbols":["html.Parse","html.Render","publicsuffix.EffectiveTLDPlusOne"],"verifierAdapter":"golang@1"}

module sample

go 1.21

require golang.org/x/net v0.27.0

golang.org/x/net v0.27.0 h1:5K3Njcw06/l2y9vpGCSdcxWOYHOUk3dVNGDXN+FvAys=
golang.org/x/net v0.27.0/go.mod h1:dDi0PyhWNoiUOrAS8uXv/vnScO4wnHQO4mj9fn/RytE=

package sample

import (
	"bytes"
	"strings"

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

// ExtractAnchorHrefs parses an HTML document and returns the href values of all <a> elements.
func ExtractAnchorHrefs(markup string) ([]string, error) {
	doc, err := html.Parse(strings.NewReader(markup))
	if err != nil {
		return nil, err
	}
	var hrefs []string
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode && n.Data == "a" {
			for _, attr := range n.Attr {
				if attr.Key == "href" {
					hrefs = append(hrefs, attr.Val)
				}
			}
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(doc)
	return hrefs, nil
}

// RenderNode renders a parsed HTML node back to its string representation.
func RenderNode(n *html.Node) (string, error) {
	var buf bytes.Buffer
	if err := html.Render(&buf, n); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// ResolveETLDPlusOne extracts the effective TLD plus one label from a domain name.
func ResolveETLDPlusOne(domain string) (string, error) {
	return publicsuffix.EffectiveTLDPlusOne(domain)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/net@v0.27.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.27.0"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"golang.org/x/net/html"
	"sample"
)

func fail(msg string) {
	fmt.Fprintln(os.Stderr, "FAIL:", msg)
	os.Exit(1)
}

func main() {
	markup := `<!DOCTYPE html><html><body><div><a href="http://example.com/one">One</a><p><a href="http://example.com/two">Two</a></p></div></body></html>`

	hrefs, err := sample.ExtractAnchorHrefs(markup)
	if err != nil {
		fail("ExtractAnchorHrefs returned unexpected error: " + err.Error())
	}
	if len(hrefs) != 2 || hrefs[0] != "http://example.com/one" || hrefs[1] != "http://example.com/two" {
		fail(fmt.Sprintf("unexpected hrefs: %v", hrefs))
	}

	doc, err := html.Parse(strings.NewReader("<p>hello &amp; world</p>"))
	if err != nil {
		fail("html.Parse failed: " + err.Error())
	}
	rendered, err := sample.RenderNode(doc)
	if err != nil {
		fail("RenderNode failed: " + err.Error())
	}
	if !strings.Contains(rendered, "<p>hello &amp; world</p>") {
		fail("rendered HTML missing expected paragraph: " + rendered)
	}

	etld, err := sample.ResolveETLDPlusOne("sub.api.example.co.uk")
	if err != nil {
		fail("ResolveETLDPlusOne failed: " + err.Error())
	}
	if etld != "example.co.uk" {
		fail("unexpected eTLD+1: " + etld)
	}

	if _, err := sample.ResolveETLDPlusOne("co.uk"); err == nil {
		fail("expected error for bare public suffix co.uk")
	}
}