golang.org/x/net v0.29.0: html.ParseFragment, html.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.Render and ParseFragment in pkg:golang/golang.org/x/net@v0.29.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.29.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html.ParseFragment
  - golang.org/x/net/html.Render

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:sha256:3ef1faa38146a15e1f21189a3e63340b3a8ce79fcfd7e58ee35a2c16ae8625b0","contract":["html.ParseFragment parses HTML fragment string in context node into slice of nodes","html.ParseFragment handles multiple sibling elements and text nodes","html.Render serializes HTML node tree to writer output","html.Render correctly escapes special characters in text nodes","html.ParseFragment and html.Render roundtrip preserve element structure and attributes"],"goal":"verify golang.org/x/net/html.Render and ParseFragment in pkg:golang/golang.org/x/net@v0.29.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.29.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.ParseFragment","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@v0.29.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.29.0","symbols":["golang.org/x/net/html.ParseFragment","golang.org/x/net/html.Render"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require golang.org/x/net v0.29.0

golang.org/x/net v0.29.0 h1:5ORfpBpCs4HzDYoodCDBbwHzdR5UrLBZ3sOnUJmFoHo=
golang.org/x/net v0.29.0/go.mod h1:gLkgy8jTGERgjzMic6DS9+SP0ajcu6Xu3Orq/SpETg0=

package main

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

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

func main() {
	// Parse an HTML fragment in the context of a body element
	fragmentHTML := `<div class="card"><h1 class="title">Item</h1><p>Description &amp; details</p></div>`
	contextNode := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Body,
		Data:     "body",
	}

	nodes, err := html.ParseFragment(strings.NewReader(fragmentHTML), contextNode)
	if err != nil {
		log.Fatalf("ParseFragment failed: %v", err)
	}

	fmt.Printf("Parsed %d top-level node(s)\n", len(nodes))

	// Render the parsed node tree back to an HTML string
	var buf bytes.Buffer
	for _, n := range nodes {
		if err := html.Render(&buf, n); err != nil {
			log.Fatalf("Render failed: %v", err)
		}
	}

	renderedHTML := buf.String()
	fmt.Printf("Rendered HTML:\n%s\n", renderedHTML)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.Render and ParseFragment in pkg:golang/golang.org/x/net@v0.29.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.29.0"
  ],
  "symbols": [
    "golang.org/x/net/html.ParseFragment",
    "golang.org/x/net/html.Render"
  ]
}

package main

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

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

func main() {
	bodyContext := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Body,
		Data:     "body",
	}

	// 1. html.ParseFragment parses HTML fragment string in context node into slice of nodes
	{
		input := `<div id="box" class="highlight"><p>Hello World</p></div>`
		nodes, err := html.ParseFragment(strings.NewReader(input), bodyContext)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: ParseFragment returned error: %v\n", err)
			os.Exit(1)
		}
		if len(nodes) != 1 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected 1 node, got %d\n", len(nodes))
			os.Exit(1)
		}
		div := nodes[0]
		if div.Type != html.ElementNode || div.Data != "div" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected ElementNode 'div', got type=%v, data=%q\n", div.Type, div.Data)
			os.Exit(1)
		}
		var idVal, classVal string
		for _, attr := range div.Attr {
			if attr.Key == "id" {
				idVal = attr.Val
			}
			if attr.Key == "class" {
				classVal = attr.Val
			}
		}
		if idVal != "box" || classVal != "highlight" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected id='box' and class='highlight', got id=%q, class=%q\n", idVal, classVal)
			os.Exit(1)
		}
		p := div.FirstChild
		if p == nil || p.Type != html.ElementNode || p.Data != "p" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected child ElementNode 'p', got %+v\n", p)
			os.Exit(1)
		}
		if p.FirstChild == nil || p.FirstChild.Type != html.TextNode || p.FirstChild.Data != "Hello World" {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected text child 'Hello World', got %+v\n", p.FirstChild)
			os.Exit(1)
		}
	}

	// 2. html.ParseFragment handles multiple sibling elements and text nodes
	{
		input := `<span>First</span> and <span>Second</span>`
		nodes, err := html.ParseFragment(strings.NewReader(input), bodyContext)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: ParseFragment error: %v\n", err)
			os.Exit(1)
		}
		if len(nodes) != 3 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected 3 nodes, got %d\n", len(nodes))
			os.Exit(1)
		}
		if nodes[0].Type != html.ElementNode || nodes[0].Data != "span" {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected node 0 to be span element\n")
			os.Exit(1)
		}
		if nodes[1].Type != html.TextNode || nodes[1].Data != " and " {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected node 1 to be text ' and ', got %q\n", nodes[1].Data)
			os.Exit(1)
		}
		if nodes[2].Type != html.ElementNode || nodes[2].Data != "span" {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected node 2 to be span element\n")
			os.Exit(1)
		}
	}

	// 3. html.Render serializes HTML node tree to writer output
	{
		aNode := &html.Node{
			Type:     html.ElementNode,
			DataAtom: atom.A,
			Data:     "a",
			Attr: []html.Attribute{
				{Key: "href", Val: "https://example.com"},
			},
		}
		textNode := &html.Node{
			Type: html.TextNode,
			Data: "Link",
		}
		aNode.AppendChild(textNode)

		var buf bytes.Buffer
		if err := html.Render(&buf, aNode); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: Render error: %v\n", err)
			os.Exit(1)
		}
		expected := `<a href="https://example.com">Link</a>`
		if buf.String() != expected {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected %q, got %q\n", expected, buf.String())
			os.Exit(1)
		}
	}

	// 4. html.Render correctly escapes special characters in text nodes
	{
		pNode := &html.Node{
			Type:     html.ElementNode,
			DataAtom: atom.P,
			Data:     "p",
		}
		textNode := &html.Node{
			Type: html.TextNode,
			Data: `5 < 10 & 10 > 5`,
		}
		pNode.AppendChild(textNode)

		var buf bytes.Buffer
		if err := html.Render(&buf, pNode); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: Render error: %v\n", err)
			os.Exit(1)
		}
		expected := `<p>5 &lt; 10 &amp; 10 &gt; 5</p>`
		if buf.String() != expected {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected %q, got %q\n", expected, buf.String())
			os.Exit(1)
		}
	}

	// 5. html.ParseFragment and html.Render roundtrip preserve element structure and attributes
	{
		originalHTML := `<section id="sec1"><ul class="list"><li>Item 1</li><li>Item 2</li></ul></section>`
		nodes, err := html.ParseFragment(strings.NewReader(originalHTML), bodyContext)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ParseFragment error: %v\n", err)
			os.Exit(1)
		}
		var buf bytes.Buffer
		for _, n := range nodes {
			if err := html.Render(&buf, n); err != nil {
				fmt.Fprintf(os.Stderr, "assertion 5 failed: Render error: %v\n", err)
				os.Exit(1)
			}
		}
		if buf.String() != originalHTML {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: roundtrip mismatch: expected %q, got %q\n", originalHTML, buf.String())
			os.Exit(1)
		}
	}

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