golang.org/x/net v0.51.0: verify golang.org/x/net/html parse and render

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/html parse and render
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.51.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html.Parse
  - golang.org/x/net/html.Render
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:f2bf46a26024261c9fdf34d478ed8b1d41644d90599816418cbe0c856513edb7","contract":["html.Parse parses HTML documents into a Node tree with correct hierarchy and attributes","html.Render serializes a Node tree back to valid HTML matching the DOM structure"],"goal":"verify golang.org/x/net/html parse and render","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.51.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.Parse","golang.org/x/net/html.Render"]},"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@v0.51.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.51.0","symbols":["golang.org/x/net/html.Parse","golang.org/x/net/html.Render"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.25.0

require golang.org/x/net v0.51.0

golang.org/x/net v0.51.0 h1:94R/GTO7mt3/4wIKpcR5gkGmRLOuE/2hNGeWq/GBIFo=
golang.org/x/net v0.51.0/go.mod h1:aamm+2QF5ogm02fjy5Bb7CQ0WMt1/WVM7FtyaTLlA9Y=

package main

import (
	"bytes"
	"fmt"
	"log"
	"strings"

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

func main() {
	docHTML := `<!DOCTYPE html><html><head><title>Sample</title></head><body><div class="content"><p>Hello World</p></div></body></html>`

	doc, err := html.Parse(strings.NewReader(docHTML))
	if err != nil {
		log.Fatalf("failed to parse HTML: %v", err)
	}

	var buf bytes.Buffer
	if err := html.Render(&buf, doc); err != nil {
		log.Fatalf("failed to render HTML: %v", err)
	}

	fmt.Println("Rendered HTML:")
	fmt.Println(buf.String())
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html parse and render",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.51.0"
  ],
  "symbols": [
    "golang.org/x/net/html.Parse",
    "golang.org/x/net/html.Render"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"fmt"
	"os"
	"strings"

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

func findFirstElement(n *html.Node, tag string) *html.Node {
	if n.Type == html.ElementNode && n.Data == tag {
		return n
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if res := findFirstElement(c, tag); res != nil {
			return res
		}
	}
	return nil
}

func getAttr(n *html.Node, key string) (string, bool) {
	for _, attr := range n.Attr {
		if attr.Key == key {
			return attr.Val, true
		}
	}
	return "", false
}

func main() {
	// Assertion 1: html.Parse parses HTML documents into a Node tree with correct hierarchy and attributes
	{
		docHTML := `<!DOCTYPE html><html><head><title>Test Page</title></head><body><div id="main" class="container"><p>Sample Text</p></div></body></html>`
		doc, err := html.Parse(strings.NewReader(docHTML))
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: parse error: %v\n", err)
			os.Exit(1)
		}
		if doc.Type != html.DocumentNode {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected DocumentNode, got %v\n", doc.Type)
			os.Exit(1)
		}

		div := findFirstElement(doc, "div")
		if div == nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: div element not found\n")
			os.Exit(1)
		}
		if val, ok := getAttr(div, "id"); !ok || val != "main" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected id='main', got %q (ok=%v)\n", val, ok)
			os.Exit(1)
		}
		if val, ok := getAttr(div, "class"); !ok || val != "container" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected class='container', got %q (ok=%v)\n", val, ok)
			os.Exit(1)
		}

		p := findFirstElement(div, "p")
		if p == nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: p element not found\n")
			os.Exit(1)
		}
		if p.FirstChild == nil || p.FirstChild.Type != html.TextNode || p.FirstChild.Data != "Sample Text" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: p text content mismatch\n")
			os.Exit(1)
		}
	}

	// Assertion 2: html.Render serializes a Node tree back to valid HTML matching the DOM structure
	{
		docHTML := `<!DOCTYPE html><html><head><title>Test Page</title></head><body><div id="main" class="container"><p>Sample Text</p></div></body></html>`
		doc, err := html.Parse(strings.NewReader(docHTML))
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: parse error: %v\n", err)
			os.Exit(1)
		}

		var buf bytes.Buffer
		if err := html.Render(&buf, doc); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: render error: %v\n", err)
			os.Exit(1)
		}

		rendered := buf.String()
		if !strings.Contains(rendered, `<title>Test Page</title>`) ||
			!strings.Contains(rendered, `<div id="main" class="container"><p>Sample Text</p></div>`) {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: rendered HTML missing expected tags: %s\n", rendered)
			os.Exit(1)
		}

		// Round-trip check: parse rendered output again
		doc2, err := html.Parse(strings.NewReader(rendered))
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: roundtrip parse error: %v\n", err)
			os.Exit(1)
		}
		div2 := findFirstElement(doc2, "div")
		if div2 == nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: roundtrip div not found\n")
			os.Exit(1)
		}
	}

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