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

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.ErrorToken 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.ErrorToken

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:sha256:50e83cd84a25327bad286f5d2e7911a8aa65602807583c6ad0a9e4c6a1b9c9ed","contract":["html.ErrorToken is a TokenType constant representing tokenization error or EOF","html.ErrorToken.String() returns string representation \"Error\"","tokenizer.Next() returns html.ErrorToken when reaching EOF and tokenizer.Err() returns io.EOF","tokenizer.Next() returns html.ErrorToken when underlying reader fails and tokenizer.Err() returns that error","tokenizer.Token().Type equals html.ErrorToken when tokenizer.Next() yields html.ErrorToken"],"goal":"verify golang.org/x/net/html.ErrorToken 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.ErrorToken"]},"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.ErrorToken"],"verifierAdapter":"golang@1"}

module example.com/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"
	"io"
	"strings"

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

// ParseHTMLTokens tokenizes the input HTML string until ErrorToken is encountered.
func ParseHTMLTokens(rawHTML string) ([]string, error) {
	z := html.NewTokenizer(strings.NewReader(rawHTML))
	var tokens []string

	for {
		tt := z.Next()
		if tt == html.ErrorToken {
			err := z.Err()
			if err == io.EOF {
				break
			}
			return nil, err
		}
		tokens = append(tokens, z.Token().String())
	}
	return tokens, nil
}

func main() {
	tokens, err := ParseHTMLTokens("<div><p>Hello CodeSampleX</p></div>")
	if err != nil {
		fmt.Printf("Error: %v\n", err)
		return
	}
	for _, t := range tokens {
		fmt.Println(t)
	}
}

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

package main

import (
	"errors"
	"fmt"
	"io"
	"os"
	"strings"

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

type customFailingReader struct {
	err error
}

func (r *customFailingReader) Read(p []byte) (int, error) {
	return 0, r.err
}

func main() {
	// 1. html.ErrorToken is a TokenType constant representing tokenization error or EOF
	var tt html.TokenType = html.ErrorToken
	if tt != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected html.ErrorToken to have value 0, got %d\n", tt)
		os.Exit(1)
	}

	// 2. html.ErrorToken.String() returns string representation "Error"
	if s := html.ErrorToken.String(); s != "Error" {
		fmt.Fprintf(os.Stderr, "FAIL: expected html.ErrorToken.String() to be %q, got %q\n", "Error", s)
		os.Exit(1)
	}

	// 3. tokenizer.Next() returns html.ErrorToken when reaching EOF and tokenizer.Err() returns io.EOF
	zEOF := html.NewTokenizer(strings.NewReader("<p>text</p>"))
	foundEOFErrorToken := false
	for {
		tokType := zEOF.Next()
		if tokType == html.ErrorToken {
			foundEOFErrorToken = true
			if err := zEOF.Err(); err != io.EOF {
				fmt.Fprintf(os.Stderr, "FAIL: expected io.EOF upon ErrorToken, got %v\n", err)
				os.Exit(1)
			}
			break
		}
	}
	if !foundEOFErrorToken {
		fmt.Fprintf(os.Stderr, "FAIL: did not encounter html.ErrorToken at EOF\n")
		os.Exit(1)
	}

	// 4. tokenizer.Next() returns html.ErrorToken when underlying reader fails and tokenizer.Err() returns that error
	expectedErr := errors.New("underlying stream read failure")
	zFail := html.NewTokenizer(&customFailingReader{err: expectedErr})
	failTokType := zFail.Next()
	if failTokType != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "FAIL: expected html.ErrorToken on reader error, got %v\n", failTokType)
		os.Exit(1)
	}
	if !errors.Is(zFail.Err(), expectedErr) {
		fmt.Fprintf(os.Stderr, "FAIL: expected underlying error %v, got %v\n", expectedErr, zFail.Err())
		os.Exit(1)
	}

	// 5. tokenizer.Token().Type equals html.ErrorToken when tokenizer.Next() yields html.ErrorToken
	errTokenObj := zFail.Token()
	if errTokenObj.Type != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "FAIL: expected token.Type to equal html.ErrorToken, got %v\n", errTokenObj.Type)
		os.Exit(1)
	}

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