golang.org/x/net v0.51.0: 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@v0.51.0
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.ElementNode

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:sha256:71bcaa7604ba086e004e7c5211c6ba1445a8e7afc47e5bbb7f4ee2a8d711a758","contract":["html.Parse identifies HTML tag elements with NodeType equal to html.ElementNode and populates Data with the tag name","html.ElementNode nodes contain Attr slice with parsed key-value attribute pairs","Programmatically constructed nodes with html.ElementNode render properly formatted opening and closing tags via html.Render","DOM tree traversal distinguishes html.ElementNode from other node types such as html.TextNode, html.CommentNode, and html.DocumentNode"],"goal":"verify golang.org/x/net/html.ElementNode in pkg:golang/golang.org/x/net@v0.51.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.51.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.ElementNode"]},"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.ElementNode"],"verifierAdapter":"golang@1"}

module 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"
	"strings"

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

// ExtractElements recursively collects all nodes with Type == html.ElementNode.
func ExtractElements(n *html.Node) []*html.Node {
	var elements []*html.Node
	if n == nil {
		return elements
	}
	if n.Type == html.ElementNode {
		elements = append(elements, n)
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		elements = append(elements, ExtractElements(c)...)
	}
	return elements
}

// FindElementByTag finds the first ElementNode with the given tag name.
func FindElementByTag(n *html.Node, tag string) *html.Node {
	if n == nil {
		return nil
	}
	if n.Type == html.ElementNode && n.Data == tag {
		return n
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if found := FindElementByTag(c, tag); found != nil {
			return found
		}
	}
	return nil
}

// GetAttribute returns the value of an attribute on an ElementNode.
func GetAttribute(n *html.Node, key string) (string, bool) {
	if n == nil || n.Type != html.ElementNode {
		return "", false
	}
	for _, attr := range n.Attr {
		if attr.Key == key {
			return attr.Val, true
		}
	}
	return "", false
}

func main() {
	rawHTML := `<div class="container"><a href="https://example.com" id="link-1">Example</a><p>Content</p></div>`
	doc, err := html.Parse(strings.NewReader(rawHTML))
	if err != nil {
		panic(err)
	}

	elements := ExtractElements(doc)
	fmt.Printf("Total ElementNode count: %d\n", len(elements))

	link := FindElementByTag(doc, "a")
	if link != nil {
		href, _ := GetAttribute(link, "href")
		fmt.Printf("Found tag <%s> with href=%s\n", link.Data, href)
	}

	// Programmatic creation of an ElementNode
	customNode := &html.Node{
		Type: html.ElementNode,
		Data: "span",
		Attr: []html.Attribute{
			{Key: "class", Val: "highlight"},
		},
	}
	customNode.AppendChild(&html.Node{
		Type: html.TextNode,
		Data: "Hello World",
	})

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

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.ElementNode in pkg:golang/golang.org/x/net@v0.51.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.51.0"
  ],
  "symbols": [
    "golang.org/x/net/html.ElementNode"
  ]
}

package main

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

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

func main() {
	// 1. html.Parse identifies HTML tag elements with NodeType equal to html.ElementNode and populates Data with the tag name
	{
		doc, err := html.Parse(strings.NewReader("<div><p>Paragraph</p><span>Span</span></div>"))
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Parse returned error: %v\n", err)
			os.Exit(1)
		}

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

		expectedTags := []string{"html", "head", "body", "div", "p", "span"}
		if len(tags) != len(expectedTags) {
			fmt.Fprintf(os.Stderr, "FAIL: expected %d element tags, got %d: %v\n", len(expectedTags), len(tags), tags)
			os.Exit(1)
		}
		for i, expected := range expectedTags {
			if tags[i] != expected {
				fmt.Fprintf(os.Stderr, "FAIL: tag[%d] expected %q, got %q\n", i, expected, tags[i])
				os.Exit(1)
			}
		}
	}

	// 2. html.ElementNode nodes contain Attr slice with parsed key-value attribute pairs
	{
		doc, err := html.Parse(strings.NewReader(`<a href="https://example.com/api" target="_blank" rel="noopener">Link</a>`))
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Parse returned error: %v\n", err)
			os.Exit(1)
		}

		var anchor *html.Node
		var walk func(*html.Node)
		walk = func(n *html.Node) {
			if n.Type == html.ElementNode && n.Data == "a" {
				anchor = n
				return
			}
			for c := n.FirstChild; c != nil; c = c.NextSibling {
				walk(c)
			}
		}
		walk(doc)

		if anchor == nil {
			fmt.Fprintf(os.Stderr, "FAIL: anchor element not found\n")
			os.Exit(1)
		}

		attrMap := make(map[string]string)
		for _, attr := range anchor.Attr {
			attrMap[attr.Key] = attr.Val
		}

		if attrMap["href"] != "https://example.com/api" {
			fmt.Fprintf(os.Stderr, "FAIL: expected href 'https://example.com/api', got %q\n", attrMap["href"])
			os.Exit(1)
		}
		if attrMap["target"] != "_blank" {
			fmt.Fprintf(os.Stderr, "FAIL: expected target '_blank', got %q\n", attrMap["target"])
			os.Exit(1)
		}
		if attrMap["rel"] != "noopener" {
			fmt.Fprintf(os.Stderr, "FAIL: expected rel 'noopener', got %q\n", attrMap["rel"])
			os.Exit(1)
		}
	}

	// 3. Programmatically constructed nodes with html.ElementNode render properly formatted opening and closing tags via html.Render
	{
		elem := &html.Node{
			Type: html.ElementNode,
			Data: "section",
			Attr: []html.Attribute{
				{Key: "id", Val: "feature"},
				{Key: "class", Val: "primary card"},
			},
		}
		elem.AppendChild(&html.Node{
			Type: html.TextNode,
			Data: "Section Body",
		})

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

		expected := `<section id="feature" class="primary card">Section Body</section>`
		if buf.String() != expected {
			fmt.Fprintf(os.Stderr, "FAIL: rendered HTML mismatch:\nexpected: %s\ngot:      %s\n", expected, buf.String())
			os.Exit(1)
		}
	}

	// 4. DOM tree traversal distinguishes html.ElementNode from other node types such as html.TextNode, html.CommentNode, and html.DocumentNode
	{
		doc, err := html.Parse(strings.NewReader(`<!-- notice --><div>text</div>`))
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Parse returned error: %v\n", err)
			os.Exit(1)
		}

		typeCounts := make(map[html.NodeType]int)
		var walk func(*html.Node)
		walk = func(n *html.Node) {
			typeCounts[n.Type]++
			for c := n.FirstChild; c != nil; c = c.NextSibling {
				walk(c)
			}
		}
		walk(doc)

		if typeCounts[html.DocumentNode] < 1 {
			fmt.Fprintf(os.Stderr, "FAIL: expected at least 1 DocumentNode, got %d\n", typeCounts[html.DocumentNode])
			os.Exit(1)
		}
		if typeCounts[html.ElementNode] < 4 { // html, head, body, div
			fmt.Fprintf(os.Stderr, "FAIL: expected at least 4 ElementNodes, got %d\n", typeCounts[html.ElementNode])
			os.Exit(1)
		}
		if typeCounts[html.CommentNode] < 1 {
			fmt.Fprintf(os.Stderr, "FAIL: expected at least 1 CommentNode, got %d\n", typeCounts[html.CommentNode])
			os.Exit(1)
		}
		if typeCounts[html.TextNode] < 1 {
			fmt.Fprintf(os.Stderr, "FAIL: expected at least 1 TextNode, got %d\n", typeCounts[html.TextNode])
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all contract assertions passed")
}