golang.org/x/net v0.0.0-20210525063256-abc453219eb5: 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@v0.0.0-20210525063256-abc453219eb5
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.0.0-20210525063256-abc453219eb5
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:sha256:66ffa40af2dcac2bbe4f9770e373a2328a8ddfb9191e8930d1e88ab3fc7b92d1","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@v0.0.0-20210525063256-abc453219eb5","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.0.0-20210525063256-abc453219eb5"],"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@v0.0.0-20210525063256-abc453219eb5"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.0.0-20210525063256-abc453219eb5","symbols":["golang.org/x/net/html.EndTagToken"],"verifierAdapter":"golang@1"}

module sample

go 1.25.0

require golang.org/x/net v0.0.0-20210525063256-abc453219eb5

golang.org/x/net v0.0.0-20210525063256-abc453219eb5 h1:wjuX4b5yYQnEQHzd+CBcrcC6OVR2J1CN6mUy0oSxIPo=
golang.org/x/net v0.0.0-20210525063256-abc453219eb5/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=

package sample

import (
	"fmt"
	"io"
	"strings"

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

// IsEndTag reports whether the provided TokenType equals html.EndTagToken.
func IsEndTag(tt html.TokenType) bool {
	return tt == html.EndTagToken
}

// NewEndTagToken constructs an html.Token of type html.EndTagToken with the given tag name.
func NewEndTagToken(tagName string) html.Token {
	return html.Token{
		Type: html.EndTagToken,
		Data: tagName,
	}
}

// CollectEndTags tokenizes HTML from the reader and returns all closing tag names in order.
func CollectEndTags(r io.Reader) ([]string, error) {
	z := html.NewTokenizer(r)
	var tags []string

	for {
		tt := z.Next()
		switch tt {
		case html.ErrorToken:
			err := z.Err()
			if err == io.EOF {
				return tags, nil
			}
			return nil, fmt.Errorf("tokenizer error: %w", err)
		case html.EndTagToken:
			name, _ := z.TagName()
			tags = append(tags, string(name))
		}
	}
}

// CheckBalancedEndTags verifies that every StartTagToken has a matching EndTagToken in LIFO order.
func CheckBalancedEndTags(markup string) (bool, error) {
	z := html.NewTokenizer(strings.NewReader(markup))
	var stack []string

	for {
		tt := z.Next()
		switch tt {
		case html.ErrorToken:
			err := z.Err()
			if err == io.EOF {
				return len(stack) == 0, nil
			}
			return false, fmt.Errorf("tokenizer error: %w", err)
		case html.StartTagToken:
			name, _ := z.TagName()
			stack = append(stack, string(name))
		case html.EndTagToken:
			name, _ := z.TagName()
			tag := string(name)
			if len(stack) == 0 || stack[len(stack)-1] != tag {
				return false, nil
			}
			stack = stack[:len(stack)-1]
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.EndTagToken in pkg:golang/golang.org/x/net@v0.0.0-20210525063256-abc453219eb5",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.0.0-20210525063256-abc453219eb5"
  ],
  "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"
	var tt html.TokenType = html.EndTagToken
	if tt.String() != "EndTag" {
		fmt.Fprintf(os.Stderr, "FAIL: expected EndTagToken.String() == 'EndTag', got %q\n", tt.String())
		os.Exit(1)
	}
	if !sample.IsEndTag(html.EndTagToken) {
		fmt.Fprintf(os.Stderr, "FAIL: sample.IsEndTag returned false for html.EndTagToken\n")
		os.Exit(1)
	}

	// Assertion 2: html.EndTagToken is distinct from StartTagToken, SelfClosingTagToken, TextToken, and CommentToken
	otherTypes := []html.TokenType{
		html.ErrorToken,
		html.TextToken,
		html.StartTagToken,
		html.SelfClosingTagToken,
		html.CommentToken,
		html.DoctypeToken,
	}
	for _, ot := range otherTypes {
		if html.EndTagToken == ot {
			fmt.Fprintf(os.Stderr, "FAIL: EndTagToken unexpectedly equals %v\n", ot)
			os.Exit(1)
		}
		if sample.IsEndTag(ot) {
			fmt.Fprintf(os.Stderr, "FAIL: sample.IsEndTag returned true for %v\n", ot)
			os.Exit(1)
		}
	}

	// Assertion 3: html.NewTokenizer emits html.EndTagToken when encountering closing tags
	snippet := `<article><h1>Title</h1><p>Body</p></article>`
	endTags, err := sample.CollectEndTags(strings.NewReader(snippet))
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: CollectEndTags returned error: %v\n", err)
		os.Exit(1)
	}
	expected := []string{"h1", "p", "article"}
	if !reflect.DeepEqual(endTags, expected) {
		fmt.Fprintf(os.Stderr, "FAIL: expected end tags %v, got %v\n", expected, endTags)
		os.Exit(1)
	}

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

	// Assertion 5: Tokenizer.TagName and Tokenizer.Token extract tag name and Token struct for html.EndTagToken
	z := html.NewTokenizer(strings.NewReader("<footer></footer>"))
	seenEnd := false
	for {
		kind := z.Next()
		if kind == html.ErrorToken {
			break
		}
		if kind == html.EndTagToken {
			seenEnd = true
			name, hasAttr := z.TagName()
			if string(name) != "footer" {
				fmt.Fprintf(os.Stderr, "FAIL: expected tag name 'footer', got %q\n", string(name))
				os.Exit(1)
			}
			if hasAttr {
				fmt.Fprintf(os.Stderr, "FAIL: expected hasAttr=false on EndTagToken\n")
				os.Exit(1)
			}
			raw := string(z.Raw())
			if raw != "</footer>" {
				fmt.Fprintf(os.Stderr, "FAIL: expected raw '</footer>', got %q\n", raw)
				os.Exit(1)
			}
		}
	}
	if !seenEnd {
		fmt.Fprintf(os.Stderr, "FAIL: did not encounter EndTagToken\n")
		os.Exit(1)
	}

	ok, err := sample.CheckBalancedEndTags("<div><span>text</span></div>")
	if err != nil || !ok {
		fmt.Fprintf(os.Stderr, "FAIL: CheckBalancedEndTags failed for balanced input: ok=%v, err=%v\n", ok, err)
		os.Exit(1)
	}
	unbalanced, err := sample.CheckBalancedEndTags("<div><span>text</div></span>")
	if err != nil || unbalanced {
		fmt.Fprintf(os.Stderr, "FAIL: CheckBalancedEndTags failed for unbalanced input: unbalanced=%v, err=%v\n", unbalanced, err)
		os.Exit(1)
	}
}