golang.org/x/net v0.38.0: idna.ToASCII

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/idna.ToASCII in pkg:golang/golang.org/x/net@v0.38.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.38.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/idna.ToASCII
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:sha256:4c88c0634c28ac7df4eed8592931107df7f0dae1a01e01c850ea7715256a3b3b","contract":["idna.ToASCII converts internationalized domain names with unicode characters to ASCII Punycode","idna.ToASCII converts non-Latin scripts such as CJK domain names to ASCII Punycode","idna.ToASCII preserves standard ASCII domain names without modification","idna.ToASCII preserves trailing dot for fully qualified domain names","idna.ToASCII selectively converts internationalized labels within a subdomain hierarchy","idna.ToASCII preserves already-encoded valid Punycode labels","idna.ToASCII accepts empty string and returns empty string without error","idna.ToASCII returns an error when given a malformed Punycode label"],"goal":"verify golang.org/x/net/idna.ToASCII in pkg:golang/golang.org/x/net@v0.38.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.38.0"],"schemaVersion":1,"symbols":["golang.org/x/net/idna.ToASCII"]},"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@v0.38.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.38.0","symbols":["golang.org/x/net/idna.ToASCII"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/net v0.38.0

require golang.org/x/text v0.23.0 // indirect

golang.org/x/net v0.38.0 h1:vRMAPTMaeGqVhG5QyLJHqNDwecKTomGeqbnfZyKlBI8=
golang.org/x/net v0.38.0/go.mod h1:ivrbrMbzFq5J41QOQh0siUuly180yBYtLp+CKbEaFx8=
golang.org/x/text v0.23.0 h1:D71I7dUrlY+VX0gQShAThNGHFxZ13dGLBHQLVl1mJlY=
golang.org/x/text v0.23.0/go.mod h1:/BLNzu4aZCJ1+kcD0DNRotWKage4q2rGVAg4o22unh4=

package main

import (
	"fmt"
	"log"

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

func main() {
	// Convert internationalized domain name to ASCII Punycode
	unicodeDomain := "münchen.de"
	asciiDomain, err := idna.ToASCII(unicodeDomain)
	if err != nil {
		log.Fatalf("ToASCII failed for %q: %v", unicodeDomain, err)
	}
	fmt.Printf("Unicode: %s -> ASCII: %s\n", unicodeDomain, asciiDomain)

	// Preserve standard ASCII domain names
	asciiInput := "example.com"
	converted, err := idna.ToASCII(asciiInput)
	if err != nil {
		log.Fatalf("ToASCII failed for %q: %v", asciiInput, err)
	}
	fmt.Printf("ASCII: %s -> ASCII: %s\n", asciiInput, converted)

	// Convert non-Latin multi-byte scripts
	cjkDomain := "日本語.jp"
	cjkAscii, err := idna.ToASCII(cjkDomain)
	if err != nil {
		log.Fatalf("ToASCII failed for %q: %v", cjkDomain, err)
	}
	fmt.Printf("CJK: %s -> ASCII: %s\n", cjkDomain, cjkAscii)

	// Handle malformed Punycode input with error checking
	invalidPuny := "xn--invalidpunycode-!!!"
	if _, err := idna.ToASCII(invalidPuny); err != nil {
		fmt.Printf("Properly rejected invalid Punycode label %q: %v\n", invalidPuny, err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/idna.ToASCII in pkg:golang/golang.org/x/net@v0.38.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.38.0"
  ],
  "symbols": [
    "golang.org/x/net/idna.ToASCII"
  ],
  "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"

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

func main() {
	// 1. idna.ToASCII converts internationalized domain names with unicode characters to ASCII Punycode
	if ascii, err := idna.ToASCII("münchen.de"); err != nil || ascii != "xn--mnchen-3ya.de" {
		fmt.Fprintf(os.Stderr, "ToASCII(münchen.de) failed: got %q, err: %v; want \"xn--mnchen-3ya.de\"\n", ascii, err)
		os.Exit(1)
	}

	// 2. idna.ToASCII converts non-Latin scripts such as CJK domain names to ASCII Punycode
	if ascii, err := idna.ToASCII("日本語.jp"); err != nil || ascii != "xn--wgv71a119e.jp" {
		fmt.Fprintf(os.Stderr, "ToASCII(日本語.jp) failed: got %q, err: %v; want \"xn--wgv71a119e.jp\"\n", ascii, err)
		os.Exit(1)
	}

	// 3. idna.ToASCII preserves standard ASCII domain names without modification
	if ascii, err := idna.ToASCII("example.com"); err != nil || ascii != "example.com" {
		fmt.Fprintf(os.Stderr, "ToASCII(example.com) failed: got %q, err: %v; want \"example.com\"\n", ascii, err)
		os.Exit(1)
	}

	// 4. idna.ToASCII preserves trailing dot for fully qualified domain names
	if ascii, err := idna.ToASCII("google.com."); err != nil || ascii != "google.com." {
		fmt.Fprintf(os.Stderr, "ToASCII(google.com.) failed: got %q, err: %v; want \"google.com.\"\n", ascii, err)
		os.Exit(1)
	}

	// 5. idna.ToASCII selectively converts internationalized labels within a subdomain hierarchy
	if ascii, err := idna.ToASCII("sub.domain.münchen.de"); err != nil || ascii != "sub.domain.xn--mnchen-3ya.de" {
		fmt.Fprintf(os.Stderr, "ToASCII(sub.domain.münchen.de) failed: got %q, err: %v; want \"sub.domain.xn--mnchen-3ya.de\"\n", ascii, err)
		os.Exit(1)
	}

	// 6. idna.ToASCII preserves already-encoded valid Punycode labels
	if ascii, err := idna.ToASCII("xn--mnchen-3ya.de"); err != nil || ascii != "xn--mnchen-3ya.de" {
		fmt.Fprintf(os.Stderr, "ToASCII(xn--mnchen-3ya.de) failed: got %q, err: %v; want \"xn--mnchen-3ya.de\"\n", ascii, err)
		os.Exit(1)
	}

	// 7. idna.ToASCII accepts empty string and returns empty string without error
	if ascii, err := idna.ToASCII(""); err != nil || ascii != "" {
		fmt.Fprintf(os.Stderr, "ToASCII(\"\") failed: got %q, err: %v; want \"\"\n", ascii, err)
		os.Exit(1)
	}

	// 8. idna.ToASCII returns an error when given a malformed Punycode label
	if ascii, err := idna.ToASCII("xn--invalidpunycode-!!!"); err == nil {
		fmt.Fprintf(os.Stderr, "ToASCII with malformed Punycode expected error, got %q\n", ascii)
		os.Exit(1)
	}

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