github.com/russross/blackfriday/v2 v2.1.0: NewHTMLRenderer

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 github.com/russross/blackfriday/v2.NewHTMLRenderer in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/russross/blackfriday/v2@v2.1.0
Demonstrate these symbols/APIs:
  - github.com/russross/blackfriday/v2.NewHTMLRenderer
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:5137624bac3acfbf8f4a6bbe76fc9d6f2ca35e71702354369bc8b26f84c41daf","contract":["NewHTMLRenderer with HrefTargetBlank and NofollowLinks adds target=\"_blank\" and rel=\"nofollow\" to external links","NewHTMLRenderer with AbsolutePrefix prepends prefix to root-relative URLs","NewHTMLRenderer with HeadingIDPrefix and HeadingIDSuffix customizes generated heading element IDs","NewHTMLRenderer with HeadingLevelOffset shifts heading levels by the specified integer offset","NewHTMLRenderer with CompletePage, Title, and CSS generates full HTML page with metadata tags","NewHTMLRenderer with SkipImages omits image tags from the rendered output"],"goal":"verify github.com/russross/blackfriday/v2.NewHTMLRenderer in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0","kind":"HOW","packages":["pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"],"schemaVersion":1,"symbols":["github.com/russross/blackfriday/v2.NewHTMLRenderer"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/russross/blackfriday/v2@v2.1.0","symbols":["github.com/russross/blackfriday/v2.NewHTMLRenderer"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/russross/blackfriday/v2 v2.1.0

github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=

{
  "schemaVersion": 1,
  "goal": "verify github.com/russross/blackfriday/v2.NewHTMLRenderer in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"
  ],
  "symbols": [
    "github.com/russross/blackfriday/v2.NewHTMLRenderer"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/russross/blackfriday/v2"
)

func main() {
	if err := runTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract tests passed successfully.")
}

func runTests() error {
	// 1. NewHTMLRenderer with HrefTargetBlank and NofollowLinks adds target="_blank" and rel="nofollow" to external links
	{
		params := blackfriday.HTMLRendererParameters{
			Flags: blackfriday.HrefTargetBlank | blackfriday.NofollowLinks,
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("[External](https://example.com/docs)")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer))
		html := strings.TrimSpace(string(output))
		expected := `<p><a href="https://example.com/docs" target="_blank" rel="nofollow">External</a></p>`
		if html != expected {
			return fmt.Errorf("test 1 failed: expected %q, got %q", expected, html)
		}
	}

	// 2. NewHTMLRenderer with AbsolutePrefix prepends prefix to root-relative URLs
	{
		params := blackfriday.HTMLRendererParameters{
			AbsolutePrefix: "https://example.com/static",
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("[Guide](/docs/guide.html)")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer))
		html := strings.TrimSpace(string(output))
		expected := `<p><a href="https://example.com/static/docs/guide.html">Guide</a></p>`
		if html != expected {
			return fmt.Errorf("test 2 failed: expected %q, got %q", expected, html)
		}
	}

	// 3. NewHTMLRenderer with HeadingIDPrefix and HeadingIDSuffix customizes generated heading element IDs
	{
		params := blackfriday.HTMLRendererParameters{
			HeadingIDPrefix: "sec-",
			HeadingIDSuffix: "-top",
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("# Introduction")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer), blackfriday.WithExtensions(blackfriday.AutoHeadingIDs))
		html := strings.TrimSpace(string(output))
		expected := `<h1 id="sec-introduction-top">Introduction</h1>`
		if html != expected {
			return fmt.Errorf("test 3 failed: expected %q, got %q", expected, html)
		}
	}

	// 4. NewHTMLRenderer with HeadingLevelOffset shifts heading levels by the specified integer offset
	{
		params := blackfriday.HTMLRendererParameters{
			HeadingLevelOffset: 2,
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("# Main Heading\n\n## Sub Heading")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer))
		html := strings.TrimSpace(string(output))
		expected := "<h3>Main Heading</h3>\n\n<h4>Sub Heading</h4>"
		if html != expected {
			return fmt.Errorf("test 4 failed: expected %q, got %q", expected, html)
		}
	}

	// 5. NewHTMLRenderer with CompletePage, Title, and CSS generates full HTML page with metadata tags
	{
		params := blackfriday.HTMLRendererParameters{
			Flags: blackfriday.CompletePage,
			Title: "Documentation Page",
			CSS:   "https://example.com/style.css",
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("Hello world")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer))
		html := string(output)
		if !strings.Contains(html, "<!DOCTYPE html>") {
			return fmt.Errorf("test 5 failed: missing doctype: %q", html)
		}
		if !strings.Contains(html, "<title>Documentation Page</title>") {
			return fmt.Errorf("test 5 failed: missing title tag: %q", html)
		}
		if !strings.Contains(html, `<link rel="stylesheet" type="text/css" href="https://example.com/style.css">`) {
			return fmt.Errorf("test 5 failed: missing css link tag: %q", html)
		}
		if !strings.Contains(html, "<p>Hello world</p>") {
			return fmt.Errorf("test 5 failed: missing content: %q", html)
		}
	}

	// 6. NewHTMLRenderer with SkipImages omits image tags from the rendered output
	{
		params := blackfriday.HTMLRendererParameters{
			Flags: blackfriday.SkipImages,
		}
		renderer := blackfriday.NewHTMLRenderer(params)
		input := []byte("Paragraph with ![Logo](https://example.com/logo.png) image")
		output := blackfriday.Run(input, blackfriday.WithRenderer(renderer))
		html := strings.TrimSpace(string(output))
		if strings.Contains(html, "<img") || strings.Contains(html, "logo.png") {
			return fmt.Errorf("test 6 failed: image was rendered: %q", html)
		}
		if !strings.Contains(html, "Paragraph with") || !strings.Contains(html, "image") {
			return fmt.Errorf("test 6 failed: text was omitted: %q", html)
		}
	}

	return nil
}