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

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.ToUnicode 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.ToUnicode
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:sha256:944250068ddf372f23724d85a49a1b224d640a975bdbe5e5657ccdd8f9262ff4","contract":["idna.ToUnicode converts ASCII Punycode domain names to their Unicode representation","idna.ToUnicode preserves standard ASCII domain names without modification","idna.ToUnicode returns an error for invalid Punycode labels","idna.Lookup profile converts Punycode domain names according to IDNA2008 lookup rules"],"goal":"verify golang.org/x/net/idna.ToUnicode 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.ToUnicode"]},"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.ToUnicode"],"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"
	"os"

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

// DecodeDomain converts a Punycode ASCII domain string to its Unicode representation.
func DecodeDomain(domain string) (string, error) {
	return idna.ToUnicode(domain)
}

// EncodeDomain converts a Unicode domain string to Punycode ASCII.
func EncodeDomain(domain string) (string, error) {
	return idna.ToASCII(domain)
}

func main() {
	punycode := "xn--bcher-kva.example"
	unicode, err := DecodeDomain(punycode)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Decode error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Punycode %s decoded to Unicode: %s\n", punycode, unicode)

	ascii, err := EncodeDomain(unicode)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Encode error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Unicode %s encoded to ASCII: %s\n", unicode, ascii)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/idna.ToUnicode 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.ToUnicode"
  ],
  "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() {
	// Assertion 1: idna.ToUnicode converts ASCII Punycode domain names to their Unicode representation
	u1, err := idna.ToUnicode("xn--bcher-kva.example")
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToUnicode returned unexpected error: %v\n", err)
		os.Exit(1)
	}
	if u1 != "bücher.example" {
		fmt.Fprintf(os.Stderr, "FAIL: expected 'bücher.example', got %q\n", u1)
		os.Exit(1)
	}

	u2, err := idna.ToUnicode("xn--fsqu00a.xn--0zwm56d")
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToUnicode returned unexpected error for multi-label: %v\n", err)
		os.Exit(1)
	}
	if u2 != "例子.测试" {
		fmt.Fprintf(os.Stderr, "FAIL: expected '例子.测试', got %q\n", u2)
		os.Exit(1)
	}

	// Assertion 2: idna.ToUnicode preserves standard ASCII domain names without modification
	asciiDomain := "example.com"
	uAscii, err := idna.ToUnicode(asciiDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToUnicode error for plain ASCII: %v\n", err)
		os.Exit(1)
	}
	if uAscii != asciiDomain {
		fmt.Fprintf(os.Stderr, "FAIL: plain ASCII modified: expected %q, got %q\n", asciiDomain, uAscii)
		os.Exit(1)
	}

	// Assertion 3: idna.ToUnicode returns an error for invalid Punycode labels
	_, err = idna.ToUnicode("xn--invalidpunycode!!!")
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected error for invalid punycode label, got nil\n")
		os.Exit(1)
	}

	// Assertion 4: idna.Lookup profile converts Punycode domain names according to IDNA2008 lookup rules
	lookupRes, err := idna.Lookup.ToUnicode("xn--mgbh0fb.xn--kgbechtv")
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: idna.Lookup.ToUnicode error: %v\n", err)
		os.Exit(1)
	}
	if lookupRes == "" {
		fmt.Fprintf(os.Stderr, "FAIL: idna.Lookup.ToUnicode returned empty string\n")
		os.Exit(1)
	}

	fmt.Println("PASS: golang.org/x/net/idna.ToUnicode contract verified")
}