golang.org/x/net v0.61.0: html.EndTagToken

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.EndTagToken in pkg:golang/golang.org/x/net@v0.61.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.61.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html.EndTagToken

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:sha256:4759ed07aa717651095533bf85fd4de008241bcef98f0f4628a265882b014942","contract":["html.EndTagToken is a TokenType constant whose String() returns \"EndTag\"","html.EndTagToken is distinct from StartTagToken, SelfClosingTagToken, TextToken, and CommentToken","html.NewTokenizer emits html.EndTagToken when encountering closing tags","html.Token with html.EndTagToken serializes to \u003c/tag\u003e string representation","Tokenizer.TagName returns tag name and no attributes for html.EndTagToken"],"goal":"verify golang.org/x/net/html.EndTagToken in pkg:golang/golang.org/x/net@v0.61.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.61.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.EndTagToken"]},"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@v0.61.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.61.0","symbols":["golang.org/x/net/html.EndTagToken"],"verifierAdapter":"golang@1"}

module sample

go 1.26.0

require golang.org/x/net v0.61.0

golang.org/x/net v0.61.0 h1:RR+6j/BTBCrggOLugxa+66R8FvoN6MHlzDlZIbN9YFw=
golang.org/x/net v0.61.0/go.mod h1:WgDCOTH8iwtB66T4/GfI94AHo/hhdb7Hah9NDseQfiI=

package sample

import (
	"errors"
	"io"
	"strings"

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

// IsEndTag returns true if the token type represents an HTML end/closing tag.
func IsEndTag(tokenType html.TokenType) bool {
	return tokenType == html.EndTagToken
}

// FormatEndTag creates an html.Token of type EndTagToken for the given tag name and returns its string.
func FormatEndTag(tagName string) string {
	tok := html.Token{
		Type: html.EndTagToken,
		Data: tagName,
	}
	return tok.String()
}

// CollectClosingTags parses an HTML fragment and returns the names of all closing tags encountered.
func CollectClosingTags(htmlInput string) ([]string, error) {
	tokenizer := html.NewTokenizer(strings.NewReader(htmlInput))
	var closingTags []string

	for {
		tt := tokenizer.Next()
		switch tt {
		case html.ErrorToken:
			err := tokenizer.Err()
			if errors.Is(err, io.EOF) {
				return closingTags, nil
			}
			return nil, err
		case html.EndTagToken:
			name, _ := tokenizer.TagName()
			closingTags = append(closingTags, string(name))
		}
	}
}

// CheckBalancedTags checks whether every opened tag is matched by a corresponding EndTagToken.
func CheckBalancedTags(htmlInput string) (bool, error) {
	tokenizer := html.NewTokenizer(strings.NewReader(htmlInput))
	var tagStack []string

	for {
		tt := tokenizer.Next()
		switch tt {
		case html.ErrorToken:
			err := tokenizer.Err()
			if errors.Is(err, io.EOF) {
				return len(tagStack) == 0, nil
			}
			return false, err
		case html.StartTagToken:
			name, _ := tokenizer.TagName()
			tagStack = append(tagStack, string(name))
		case html.EndTagToken:
			name, _ := tokenizer.TagName()
			tagName := string(name)
			if len(tagStack) == 0 || tagStack[len(tagStack)-1] != tagName {
				return false, nil
			}
			tagStack = tagStack[:len(tagStack)-1]
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.EndTagToken in pkg:golang/golang.org/x/net@v0.61.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.61.0"
  ],
  "symbols": [
    "golang.org/x/net/html.EndTagToken"
  ]
}

package main

import (
	"fmt"
	"os"
	"reflect"
	"strings"

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

func main() {
	// Assertion 1: html.EndTagToken is a TokenType constant whose String() returns "EndTag"
	if html.EndTagToken.String() != "EndTag" {
		fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected 'EndTag', got %q\n", html.EndTagToken.String())
		os.Exit(1)
	}
	if !sample.IsEndTag(html.EndTagToken) {
		fmt.Fprintf(os.Stderr, "Assertion 1 failed: sample.IsEndTag(html.EndTagToken) was false\n")
		os.Exit(1)
	}

	// Assertion 2: html.EndTagToken is distinct from StartTagToken, SelfClosingTagToken, TextToken, and CommentToken
	if html.EndTagToken == html.StartTagToken ||
		html.EndTagToken == html.SelfClosingTagToken ||
		html.EndTagToken == html.TextToken ||
		html.EndTagToken == html.CommentToken {
		fmt.Fprintf(os.Stderr, "Assertion 2 failed: EndTagToken collides with another TokenType\n")
		os.Exit(1)
	}
	if sample.IsEndTag(html.StartTagToken) || sample.IsEndTag(html.TextToken) {
		fmt.Fprintf(os.Stderr, "Assertion 2 failed: sample.IsEndTag returned true for non-end tag\n")
		os.Exit(1)
	}

	// Assertion 3: html.NewTokenizer emits html.EndTagToken when encountering closing tags
	input := "<div><article><p>Text</p></article></div>"
	tags, err := sample.CollectClosingTags(input)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Assertion 3 failed with error: %v\n", err)
		os.Exit(1)
	}
	expectedTags := []string{"p", "article", "div"}
	if !reflect.DeepEqual(tags, expectedTags) {
		fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected %v, got %v\n", expectedTags, tags)
		os.Exit(1)
	}

	// Assertion 4: html.Token with html.EndTagToken serializes to </tag> string representation
	formatted := sample.FormatEndTag("footer")
	if formatted != "</footer>" {
		fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected '</footer>', got %q\n", formatted)
		os.Exit(1)
	}
	tok := html.Token{Type: html.EndTagToken, Data: "nav"}
	if tok.String() != "</nav>" {
		fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected '</nav>', got %q\n", tok.String())
		os.Exit(1)
	}

	// Assertion 5: Tokenizer.TagName returns tag name and no attributes for html.EndTagToken
	z := html.NewTokenizer(strings.NewReader("</section>"))
	tt := z.Next()
	if tt != html.EndTagToken {
		fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected EndTagToken, got %v\n", tt)
		os.Exit(1)
	}
	name, hasAttr := z.TagName()
	if string(name) != "section" {
		fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected tag name 'section', got %q\n", string(name))
		os.Exit(1)
	}
	if hasAttr {
		fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected hasAttr false for EndTagToken\n")
		os.Exit(1)
	}

	// Helper verification: check balanced tags
	balanced, err := sample.CheckBalancedTags("<ul><li>item</li></ul>")
	if err != nil || !balanced {
		fmt.Fprintf(os.Stderr, "CheckBalancedTags failed for balanced HTML: balanced=%v, err=%v\n", balanced, err)
		os.Exit(1)
	}
	unbalanced, err := sample.CheckBalancedTags("<ul><li>item</ul></li>")
	if err != nil || unbalanced {
		fmt.Fprintf(os.Stderr, "CheckBalancedTags failed for unbalanced HTML: balanced=%v, err=%v\n", unbalanced, err)
		os.Exit(1)
	}

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