golang.org/x/net v0.12.0: 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@v0.12.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.12.0
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:sha256:639e8601d2ba48ed5fd0f3d7c8e8ac65a9b841f51f29aebc61e12c6eb29245fb","contract":["ErrorToken is a TokenType constant with value 0 representing tokenization termination or errors","ErrorToken String method returns string representation \"Error\"","Tokenizer Next returns ErrorToken and Err returns io.EOF at end of input","Tokenizer Err returns nil prior to reaching ErrorToken","Tokenizer Next returns ErrorToken immediately on empty input reader with Err returning io.EOF","Tokenizer Token returns a Token with Type ErrorToken and empty string representation when ErrorToken is reached","Tokenizer Next returns ErrorToken and preserves underlying custom reader error accessible via Err","Tokenizer Next returns ErrorToken with ErrBufferExceeded when SetMaxBuf limit is exceeded"],"goal":"verify golang.org/x/net/html.ErrorToken in pkg:golang/golang.org/x/net@v0.12.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.12.0"],"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@v0.12.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.12.0","symbols":["golang.org/x/net/html.ErrorToken"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.23.0

require golang.org/x/net v0.12.0

golang.org/x/net v0.12.0 h1:cfawfvKITfUsFCeJIHJrbSxpeu/E81khclypR0GVT50=
golang.org/x/net v0.12.0/go.mod h1:zEVYFnQC7m/vmpQFELhcD1EWkZlX69l4oqgmer6hfKA=

package main

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

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

func main() {
	htmlContent := `<p class="greeting">Hello, <b>CodeSampleX</b>!</p>`
	z := html.NewTokenizer(strings.NewReader(htmlContent))

	fmt.Println("Tokenizing HTML:")
	for {
		tt := z.Next()
		if tt == html.ErrorToken {
			err := z.Err()
			if errors.Is(err, io.EOF) {
				fmt.Println("Reached end of document (io.EOF)")
				break
			}
			fmt.Printf("Tokenization error: %v\n", err)
			break
		}

		token := z.Token()
		fmt.Printf("Token [%s]: %s\n", tt.String(), token.String())
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.ErrorToken in pkg:golang/golang.org/x/net@v0.12.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.12.0"
  ],
  "symbols": [
    "golang.org/x/net/html.ErrorToken"
  ]
}

package main

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

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

type errReader struct {
	err error
}

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

func main() {
	// 1. ErrorToken is a TokenType constant with value 0 representing tokenization termination or errors
	if html.ErrorToken != 0 {
		fmt.Fprintf(os.Stderr, "Expected ErrorToken to have value 0, got %d\n", html.ErrorToken)
		os.Exit(1)
	}

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

	// 3. Tokenizer Next returns ErrorToken and Err returns io.EOF at end of input
	z := html.NewTokenizer(strings.NewReader("<p>test</p>"))
	seenErrorToken := false
	for {
		tt := z.Next()
		if tt == html.ErrorToken {
			seenErrorToken = true
			if !errors.Is(z.Err(), io.EOF) {
				fmt.Fprintf(os.Stderr, "Expected Err() to be io.EOF at end of input, got %v\n", z.Err())
				os.Exit(1)
			}
			break
		}
	}
	if !seenErrorToken {
		fmt.Fprintf(os.Stderr, "Tokenizer did not produce ErrorToken at end of input\n")
		os.Exit(1)
	}

	// 4. Tokenizer Err returns nil prior to reaching ErrorToken
	zPrior := html.NewTokenizer(strings.NewReader("<div>content</div>"))
	if tt := zPrior.Next(); tt == html.ErrorToken {
		fmt.Fprintf(os.Stderr, "Unexpected ErrorToken on first token of non-empty HTML\n")
		os.Exit(1)
	}
	if err := zPrior.Err(); err != nil {
		fmt.Fprintf(os.Stderr, "Expected Err() to be nil before ErrorToken, got %v\n", err)
		os.Exit(1)
	}

	// 5. Tokenizer Next returns ErrorToken immediately on empty input reader with Err returning io.EOF
	zEmpty := html.NewTokenizer(strings.NewReader(""))
	if tt := zEmpty.Next(); tt != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "Expected ErrorToken on empty reader, got %v\n", tt)
		os.Exit(1)
	}
	if !errors.Is(zEmpty.Err(), io.EOF) {
		fmt.Fprintf(os.Stderr, "Expected io.EOF on empty reader, got %v\n", zEmpty.Err())
		os.Exit(1)
	}

	// 6. Tokenizer Token returns a Token with Type ErrorToken and empty string representation when ErrorToken is reached
	zTok := html.NewTokenizer(strings.NewReader(""))
	zTok.Next()
	tok := zTok.Token()
	if tok.Type != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "Expected Token.Type to be ErrorToken, got %v\n", tok.Type)
		os.Exit(1)
	}
	if tok.String() != "" {
		fmt.Fprintf(os.Stderr, "Expected Token.String() to be empty string, got %q\n", tok.String())
		os.Exit(1)
	}

	// 7. Tokenizer Next returns ErrorToken and preserves underlying custom reader error accessible via Err
	customErr := errors.New("custom read failure")
	badReader := &errReader{err: customErr}
	zErr := html.NewTokenizer(badReader)
	if tt := zErr.Next(); tt != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "Expected ErrorToken on custom reader failure, got %v\n", tt)
		os.Exit(1)
	}
	if !errors.Is(zErr.Err(), customErr) {
		fmt.Fprintf(os.Stderr, "Expected custom error %v, got %v\n", customErr, zErr.Err())
		os.Exit(1)
	}

	// 8. Tokenizer Next returns ErrorToken with ErrBufferExceeded when SetMaxBuf limit is exceeded
	longTag := "<div " + strings.Repeat("x", 200) + ">"
	zBuf := html.NewTokenizer(strings.NewReader(longTag))
	zBuf.SetMaxBuf(50)
	if tt := zBuf.Next(); tt != html.ErrorToken {
		fmt.Fprintf(os.Stderr, "Expected ErrorToken when buffer limit exceeded, got %v\n", tt)
		os.Exit(1)
	}
	if !errors.Is(zBuf.Err(), html.ErrBufferExceeded) {
		fmt.Fprintf(os.Stderr, "Expected ErrBufferExceeded, got %v\n", zBuf.Err())
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}