golang.org/x/net v0.51.0: html.ErrorNode

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.ErrorNode 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.ErrorNode

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:sha256:090d1481800a5e636533cfe5de7301c44fcc7b16c78099a76925df79824ad115","contract":["html.ErrorNode is a NodeType constant equal to uint32(0)","uninitialized html.Node struct has Type equal to html.ErrorNode by default","explicitly created html.Node with html.ErrorNode retains its Type and error Data","html.ErrorNode is distinct from TextNode, DocumentNode, ElementNode, CommentNode, DoctypeNode, and RawNode","html.Parse on valid HTML produces a DOM tree where no nodes have Type equal to html.ErrorNode"],"goal":"verify golang.org/x/net/html.ErrorNode 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.ErrorNode"]},"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.ErrorNode"],"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 (
	"fmt"
	"strings"

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

// IsErrorNode checks if an html.Node is an ErrorNode.
func IsErrorNode(n *html.Node) bool {
	return n != nil && n.Type == html.ErrorNode
}

// FindErrorNodes recursively scans an HTML node tree and returns any ErrorNodes found.
func FindErrorNodes(n *html.Node) []*html.Node {
	var errNodes []*html.Node
	if n == nil {
		return errNodes
	}
	if n.Type == html.ErrorNode {
		errNodes = append(errNodes, n)
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		errNodes = append(errNodes, FindErrorNodes(c)...)
	}
	return errNodes
}

// NodeTypeName returns the human-readable string representation of an html.NodeType.
func NodeTypeName(t html.NodeType) string {
	switch t {
	case html.ErrorNode:
		return "ErrorNode"
	case html.TextNode:
		return "TextNode"
	case html.DocumentNode:
		return "DocumentNode"
	case html.ElementNode:
		return "ElementNode"
	case html.CommentNode:
		return "CommentNode"
	case html.DoctypeNode:
		return "DoctypeNode"
	case html.RawNode:
		return "RawNode"
	default:
		return "UnknownNode"
	}
}

func main() {
	// Demonstrating html.ErrorNode as zero-value NodeType
	var defaultNode html.Node
	fmt.Printf("Default node type is %s (is ErrorNode: %t)\n",
		NodeTypeName(defaultNode.Type), IsErrorNode(&defaultNode))

	// Creating an explicit ErrorNode to capture an invalid or failed fragment
	errNode := &html.Node{
		Type: html.ErrorNode,
		Data: "parse error: unclosed tag",
	}
	fmt.Printf("Created ErrorNode with error details: %q\n", errNode.Data)

	// Verifying that a parsed standard HTML document contains no ErrorNodes
	doc, err := html.Parse(strings.NewReader("<p>Hello World</p>"))
	if err != nil {
		panic(err)
	}
	foundErrors := FindErrorNodes(doc)
	fmt.Printf("ErrorNodes in valid parsed document: %d\n", len(foundErrors))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.ErrorNode 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.ErrorNode"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

func main() {
	// 1. html.ErrorNode is a NodeType constant equal to uint32(0)
	{
		if html.ErrorNode != 0 {
			fmt.Fprintf(os.Stderr, "FAIL: expected html.ErrorNode to be 0, got %d\n", html.ErrorNode)
			os.Exit(1)
		}
	}

	// 2. uninitialized html.Node struct has Type equal to html.ErrorNode by default
	{
		var defaultNode html.Node
		if defaultNode.Type != html.ErrorNode {
			fmt.Fprintf(os.Stderr, "FAIL: expected default html.Node.Type to be html.ErrorNode, got %v\n", defaultNode.Type)
			os.Exit(1)
		}
	}

	// 3. explicitly created html.Node with html.ErrorNode retains its Type and error Data
	{
		errMsg := "invalid html token encountered"
		node := &html.Node{
			Type: html.ErrorNode,
			Data: errMsg,
		}
		if node.Type != html.ErrorNode {
			fmt.Fprintf(os.Stderr, "FAIL: expected node.Type to be html.ErrorNode, got %v\n", node.Type)
			os.Exit(1)
		}
		if node.Data != errMsg {
			fmt.Fprintf(os.Stderr, "FAIL: expected node.Data to be %q, got %q\n", errMsg, node.Data)
			os.Exit(1)
		}
	}

	// 4. html.ErrorNode is distinct from TextNode, DocumentNode, ElementNode, CommentNode, DoctypeNode, and RawNode
	{
		otherTypes := []struct {
			name     string
			nodeType html.NodeType
		}{
			{"TextNode", html.TextNode},
			{"DocumentNode", html.DocumentNode},
			{"ElementNode", html.ElementNode},
			{"CommentNode", html.CommentNode},
			{"DoctypeNode", html.DoctypeNode},
			{"RawNode", html.RawNode},
		}
		for _, ot := range otherTypes {
			if ot.nodeType == html.ErrorNode {
				fmt.Fprintf(os.Stderr, "FAIL: html.ErrorNode unexpectedly matches %s\n", ot.name)
				os.Exit(1)
			}
		}
	}

	// 5. html.Parse on valid HTML produces a DOM tree where no nodes have Type equal to html.ErrorNode
	{
		doc, err := html.Parse(strings.NewReader("<!DOCTYPE html><html><head><title>Test</title></head><body><!-- comment --><h1>Title</h1><p>Text</p></body></html>"))
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Parse returned error: %v\n", err)
			os.Exit(1)
		}

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

		if len(errorNodes) != 0 {
			fmt.Fprintf(os.Stderr, "FAIL: expected 0 ErrorNodes in parsed document, found %d\n", len(errorNodes))
			os.Exit(1)
		}
	}

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