golang.org/x/net v0.24.0: html.ElementNode

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.ElementNode in pkg:golang/golang.org/x/net@v0.24.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.24.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html.ElementNode
Required runtime conditions:
  - ecosystem: golang
  - language: go
  - packageManager: go@1.26.6
  - runtime: go@1.26.6

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:sha256:750bc650a262e0ea7058ada44434a795c3bc8971e8d1e77ddcda2bf569caccff","contract":["html.ElementNode is a NodeType distinguishing HTML element nodes from document and text nodes","html.Parse parses HTML string into a DOM tree containing ElementNode with expected tag names","html.ElementNode contains Attr slice representing HTML attributes with Key and Val","html.ElementNode supports tree mutation via AppendChild and RemoveChild maintaining parent and sibling pointers","html.Render serializes a tree of ElementNode nodes back into valid HTML output","html.ParseFragment parses HTML fragment using an ElementNode context node"],"goal":"verify golang.org/x/net/html.ElementNode in pkg:golang/golang.org/x/net@v0.24.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.24.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.ElementNode"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/golang.org/x/net@v0.24.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.24.0","symbols":["golang.org/x/net/html.ElementNode"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.24.0

require golang.org/x/net v0.24.0

golang.org/x/net v0.24.0 h1:1PcaxkF854Fu3+lvBIx5SYn9wRlBzzcnHZSiaFFAb0w=
golang.org/x/net v0.24.0/go.mod h1:2Q7sJY5mzlzWjKtYUEXSlBWCdyaioyXzRB2RtU8KVE8=

package main

import (
	"bytes"
	"fmt"
	"strings"

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

func main() {
	rawHTML := `<div class="container" id="main"><p>CodeSampleX Demo</p></div>`
	doc, err := html.Parse(strings.NewReader(rawHTML))
	if err != nil {
		panic(err)
	}

	var visit func(*html.Node)
	visit = func(n *html.Node) {
		if n.Type == html.ElementNode {
			fmt.Printf("Element: <%s>\n", n.Data)
			for _, attr := range n.Attr {
				fmt.Printf("  Attr: %s=%s\n", attr.Key, attr.Val)
			}
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			visit(c)
		}
	}
	visit(doc)

	// Create and append an ElementNode programmatically
	newElem := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Span,
		Data:     "span",
		Attr: []html.Attribute{
			{Key: "class", Val: "badge"},
		},
	}
	doc.AppendChild(newElem)

	var buf bytes.Buffer
	if err := html.Render(&buf, doc); err != nil {
		panic(err)
	}
	fmt.Printf("Rendered HTML:\n%s\n", buf.String())
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.ElementNode in pkg:golang/golang.org/x/net@v0.24.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.24.0"
  ],
  "symbols": [
    "golang.org/x/net/html.ElementNode"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

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

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

func main() {
	// 1. html.ElementNode is a NodeType distinguishing HTML element nodes from document and text nodes
	if html.ElementNode == html.DocumentNode {
		fmt.Fprintf(os.Stderr, "Contract 1 failed: ElementNode must not equal DocumentNode\n")
		os.Exit(1)
	}
	if html.ElementNode == html.TextNode {
		fmt.Fprintf(os.Stderr, "Contract 1 failed: ElementNode must not equal TextNode\n")
		os.Exit(1)
	}
	if html.ElementNode == html.CommentNode {
		fmt.Fprintf(os.Stderr, "Contract 1 failed: ElementNode must not equal CommentNode\n")
		os.Exit(1)
	}

	// 2. html.Parse parses HTML string into a DOM tree containing ElementNode with expected tag names
	rawHTML := `<!DOCTYPE html><html><head><title>Test</title></head><body><div id="content"><p>Hello</p></div></body></html>`
	doc, err := html.Parse(strings.NewReader(rawHTML))
	if err != nil {
		fmt.Fprintf(os.Stderr, "Contract 2 failed: html.Parse error: %v\n", err)
		os.Exit(1)
	}
	if doc == nil || doc.Type != html.DocumentNode {
		fmt.Fprintf(os.Stderr, "Contract 2 failed: root node must be DocumentNode\n")
		os.Exit(1)
	}

	var elementTags []string
	var findElements func(*html.Node)
	findElements = func(n *html.Node) {
		if n.Type == html.ElementNode {
			elementTags = append(elementTags, n.Data)
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			findElements(c)
		}
	}
	findElements(doc)

	expectedTags := []string{"html", "head", "title", "body", "div", "p"}
	if len(elementTags) != len(expectedTags) {
		fmt.Fprintf(os.Stderr, "Contract 2 failed: element tags length mismatch: got %v, want %v\n", elementTags, expectedTags)
		os.Exit(1)
	}
	for i, tag := range expectedTags {
		if elementTags[i] != tag {
			fmt.Fprintf(os.Stderr, "Contract 2 failed: tag at %d mismatch: got %s, want %s\n", i, elementTags[i], tag)
			os.Exit(1)
		}
	}

	// 3. html.ElementNode contains Attr slice representing HTML attributes with Key and Val
	var divNode *html.Node
	var findDiv func(*html.Node)
	findDiv = func(n *html.Node) {
		if n.Type == html.ElementNode && n.Data == "div" {
			divNode = n
			return
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			findDiv(c)
		}
	}
	findDiv(doc)
	if divNode == nil {
		fmt.Fprintf(os.Stderr, "Contract 3 failed: div ElementNode not found\n")
		os.Exit(1)
	}
	if len(divNode.Attr) != 1 || divNode.Attr[0].Key != "id" || divNode.Attr[0].Val != "content" {
		fmt.Fprintf(os.Stderr, "Contract 3 failed: div Attr mismatch: got %+v\n", divNode.Attr)
		os.Exit(1)
	}

	// 4. html.ElementNode supports tree mutation via AppendChild and RemoveChild maintaining parent and sibling pointers
	parent := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Ul,
		Data:     "ul",
	}
	child1 := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Li,
		Data:     "li",
	}
	child2 := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Li,
		Data:     "li",
	}

	parent.AppendChild(child1)
	parent.AppendChild(child2)

	if parent.FirstChild != child1 || parent.LastChild != child2 {
		fmt.Fprintf(os.Stderr, "Contract 4 failed: AppendChild pointers mismatch\n")
		os.Exit(1)
	}
	if child1.Parent != parent || child2.Parent != parent {
		fmt.Fprintf(os.Stderr, "Contract 4 failed: child Parent pointer mismatch\n")
		os.Exit(1)
	}
	if child1.NextSibling != child2 || child2.PrevSibling != child1 {
		fmt.Fprintf(os.Stderr, "Contract 4 failed: sibling pointers mismatch\n")
		os.Exit(1)
	}

	parent.RemoveChild(child1)
	if parent.FirstChild != child2 || child1.Parent != nil || child1.NextSibling != nil {
		fmt.Fprintf(os.Stderr, "Contract 4 failed: RemoveChild pointers mismatch\n")
		os.Exit(1)
	}

	// 5. html.Render serializes a tree of ElementNode nodes back into valid HTML output
	var renderBuf bytes.Buffer
	if err := html.Render(&renderBuf, parent); err != nil {
		fmt.Fprintf(os.Stderr, "Contract 5 failed: html.Render error: %v\n", err)
		os.Exit(1)
	}
	expectedRendered := "<ul><li></li></ul>"
	if renderBuf.String() != expectedRendered {
		fmt.Fprintf(os.Stderr, "Contract 5 failed: html.Render mismatch: got %q, want %q\n", renderBuf.String(), expectedRendered)
		os.Exit(1)
	}

	// 6. html.ParseFragment parses HTML fragment using an ElementNode context node
	contextNode := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.Div,
		Data:     "div",
	}
	fragHTML := `<span class="frag">fragment text</span>`
	nodes, err := html.ParseFragment(strings.NewReader(fragHTML), contextNode)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Contract 6 failed: html.ParseFragment error: %v\n", err)
		os.Exit(1)
	}
	if len(nodes) != 1 {
		fmt.Fprintf(os.Stderr, "Contract 6 failed: nodes length mismatch: got %d, want 1\n", len(nodes))
		os.Exit(1)
	}
	fragElem := nodes[0]
	if fragElem.Type != html.ElementNode || fragElem.Data != "span" {
		fmt.Fprintf(os.Stderr, "Contract 6 failed: fragElem mismatch: Type=%v, Data=%s\n", fragElem.Type, fragElem.Data)
		os.Exit(1)
	}
	if len(fragElem.Attr) != 1 || fragElem.Attr[0].Key != "class" || fragElem.Attr[0].Val != "frag" {
		fmt.Fprintf(os.Stderr, "Contract 6 failed: fragElem Attr mismatch: %+v\n", fragElem.Attr)
		os.Exit(1)
	}

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