golang.org/x/net v0.0.0-20210525063256-abc453219eb5: atom.Head

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.Head 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/atom.Head

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:sha256:3389f680fff0d2656cd393e8931e8bd7c29acf78bfb3bb079cc33fd2c777149d","contract":["atom.Head is a non-zero Atom constant whose String() method returns \"head\"","atom.Lookup([]byte(\"head\")) returns atom.Head while uppercase \"HEAD\" returns 0 and \"header\" returns a distinct Atom","html.Parse assigns DataAtom == atom.Head on parsed \u003chead\u003e HTML element nodes"],"goal":"verify golang.org/x/net/html/atom.Head 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/atom.Head"]},"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/atom.Head"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.21

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 main

import (
	"fmt"
	"strings"

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

func main() {
	fmt.Printf("atom.Head = %#x (%q)\n", uint32(atom.Head), atom.Head.String())
	doc, err := html.Parse(strings.NewReader("<!DOCTYPE html><html><head><title>Sample</title></head><body></body></html>"))
	if err != nil {
		panic(err)
	}
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode && n.DataAtom == atom.Head {
			fmt.Printf("matched element Data=%q DataAtom=%v\n", n.Data, n.DataAtom)
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(doc)
}

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

package main

import (
	"fmt"
	"os"
	"strings"

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

func findHeadNode(n *html.Node) *html.Node {
	if n.Type == html.ElementNode && n.DataAtom == atom.Head {
		return n
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if found := findHeadNode(c); found != nil {
			return found
		}
	}
	return nil
}

func main() {
	// 1. atom.Head has a non-zero Atom value and String() returns "head".
	if atom.Head == 0 {
		fmt.Fprintln(os.Stderr, "expected atom.Head to be non-zero")
		os.Exit(1)
	}
	if got := atom.Head.String(); got != "head" {
		fmt.Fprintf(os.Stderr, "expected atom.Head.String() == \"head\", got %q\n", got)
		os.Exit(1)
	}

	// 2. atom.Lookup maps lowercase []byte("head") to atom.Head and distinguishes other byte slices.
	if got := atom.Lookup([]byte("head")); got != atom.Head {
		fmt.Fprintf(os.Stderr, "expected atom.Lookup([]byte(\"head\")) == atom.Head, got %v\n", got)
		os.Exit(1)
	}
	if got := atom.Lookup([]byte("HEAD")); got != 0 {
		fmt.Fprintf(os.Stderr, "expected atom.Lookup([]byte(\"HEAD\")) == 0, got %v\n", got)
		os.Exit(1)
	}
	if got := atom.Lookup([]byte("header")); got == atom.Head || got == 0 {
		fmt.Fprintf(os.Stderr, "expected atom.Lookup([]byte(\"header\")) to be a distinct non-zero atom, got %v\n", got)
		os.Exit(1)
	}

	// 3. html.Parse sets DataAtom to atom.Head on parsed <head> element nodes.
	doc, err := html.Parse(strings.NewReader("<!DOCTYPE html><html><head><meta charset=\"utf-8\"><title>Test</title></head><body><p>Hello</p></body></html>"))
	if err != nil {
		fmt.Fprintf(os.Stderr, "html.Parse failed: %v\n", err)
		os.Exit(1)
	}
	headNode := findHeadNode(doc)
	if headNode == nil {
		fmt.Fprintln(os.Stderr, "expected html.Parse tree to contain an ElementNode with DataAtom == atom.Head")
		os.Exit(1)
	}
	if headNode.Data != "head" {
		fmt.Fprintf(os.Stderr, "expected headNode.Data == \"head\", got %q\n", headNode.Data)
		os.Exit(1)
	}
}