golang.org/x/net v0.24.0: atom.H4

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/atom.H4 in pkg:golang/golang.org/x/net@v0.24.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.24.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html/atom.H4

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:sha256:0010f8b5015db5705157bb1353268bedc9be7989a9566535859966179c5d818e","contract":["atom.H4 is a non-zero Atom identifier","atom.H4.String returns string h4","atom.Lookup returns atom.H4 for lowercase byte slice h4","atom.String returns string h4 for lowercase byte slice h4","html.Tokenizer identifies h4 start tag with DataAtom matching atom.H4"],"goal":"verify golang.org/x/net/html/atom.H4 in pkg:golang/golang.org/x/net@v0.24.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.24.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html/atom.H4"]},"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@v0.24.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.24.0","symbols":["golang.org/x/net/html/atom.H4"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require golang.org/x/net v0.24.0

golang.org/x/net v0.24.0 h1:1PcaxkF854Fu3+lvBIx5SYn9wRlBzzcnHZSiaFFAb0w=
golang.org/x/net v0.24.0/go.mod h1:2Q7sJY5mzlzWjKtYUEXSlBWCdyaioyXzRB2RtU8KVE8=

package main

import (
	"fmt"
	"strings"

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

// IsH4Element checks if an HTML tag name corresponds to an H4 header atom.
func IsH4Element(tagName string) bool {
	return atom.Lookup([]byte(tagName)) == atom.H4
}

// CountH4Tags parses an HTML fragment and returns the count of <h4> start tags.
func CountH4Tags(htmlDoc string) (int, error) {
	tokenizer := html.NewTokenizer(strings.NewReader(htmlDoc))
	count := 0
	for {
		tt := tokenizer.Next()
		switch tt {
		case html.ErrorToken:
			err := tokenizer.Err()
			if err.Error() == "EOF" {
				return count, nil
			}
			return count, err
		case html.StartTagToken:
			tok := tokenizer.Token()
			if tok.DataAtom == atom.H4 {
				count++
			}
		}
	}
}

func main() {
	doc := `<article><h4>Section Heading</h4><p>Text</p><h4>Another Heading</h4></article>`
	count, err := CountH4Tags(doc)
	if err != nil {
		fmt.Printf("Error: %v\n", err)
		return
	}
	fmt.Printf("atom.H4 name: %s, code: 0x%x, found %d tags\n", atom.H4.String(), uint32(atom.H4), count)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html/atom.H4 in pkg:golang/golang.org/x/net@v0.24.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.24.0"
  ],
  "symbols": [
    "golang.org/x/net/html/atom.H4"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

func main() {
	// 1. atom.H4 is a non-zero Atom identifier
	{
		if atom.H4 == 0 {
			fmt.Fprintf(os.Stderr, "FAIL: atom.H4 must be non-zero\n")
			os.Exit(1)
		}
	}

	// 2. atom.H4.String returns string h4
	{
		name := atom.H4.String()
		if name != "h4" {
			fmt.Fprintf(os.Stderr, "FAIL: atom.H4.String() expected 'h4', got %q\n", name)
			os.Exit(1)
		}
	}

	// 3. atom.Lookup returns atom.H4 for lowercase byte slice h4
	{
		lookedUp := atom.Lookup([]byte("h4"))
		if lookedUp != atom.H4 {
			fmt.Fprintf(os.Stderr, "FAIL: atom.Lookup([]byte(\"h4\")) expected atom.H4 (0x%x), got 0x%x\n", uint32(atom.H4), uint32(lookedUp))
			os.Exit(1)
		}

		// Lookup is case-sensitive: uppercase H4 returns 0
		if atom.Lookup([]byte("H4")) != 0 {
			fmt.Fprintf(os.Stderr, "FAIL: atom.Lookup([]byte(\"H4\")) expected 0, got 0x%x\n", uint32(atom.Lookup([]byte("H4"))))
			os.Exit(1)
		}
	}

	// 4. atom.String returns string h4 for lowercase byte slice h4
	{
		str := atom.String([]byte("h4"))
		if str != "h4" {
			fmt.Fprintf(os.Stderr, "FAIL: atom.String([]byte(\"h4\")) expected 'h4', got %q\n", str)
			os.Exit(1)
		}
	}

	// 5. html.Tokenizer identifies h4 start tag with DataAtom matching atom.H4
	{
		htmlInput := `<h4>Heading Level 4</h4>`
		tokenizer := html.NewTokenizer(strings.NewReader(htmlInput))

		tokenType := tokenizer.Next()
		if tokenType != html.StartTagToken {
			fmt.Fprintf(os.Stderr, "FAIL: expected StartTagToken, got %v\n", tokenType)
			os.Exit(1)
		}

		token := tokenizer.Token()
		if token.DataAtom != atom.H4 {
			fmt.Fprintf(os.Stderr, "FAIL: token.DataAtom expected atom.H4 (0x%x), got 0x%x\n", uint32(atom.H4), uint32(token.DataAtom))
			os.Exit(1)
		}
		if token.Data != "h4" {
			fmt.Fprintf(os.Stderr, "FAIL: token.Data expected 'h4', got %q\n", token.Data)
			os.Exit(1)
		}
	}

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