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

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.Lookup 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.Lookup

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:a1bf6c6cabb99babf015e684e6a829dcb39097b4f2a84e30ed0c9696bce8368e","contract":["idna.Lookup.ToASCII converts internationalized domain names containing Unicode characters to Punycode ASCII format","idna.Lookup.ToUnicode decodes Punycode ASCII domain names back to Unicode format","idna.Lookup.ToASCII leaves standard ASCII domain names unchanged","idna.Lookup.ToASCII returns an error for invalid domain names violating IDNA rules"],"goal":"verify golang.org/x/net/idna.Lookup 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.Lookup"]},"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.Lookup"],"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"
)

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

// DomainToUnicode converts an ASCII (Punycode) domain name back to Unicode representation.
func DomainToUnicode(asciiDomain string) (string, error) {
	return idna.Lookup.ToUnicode(asciiDomain)
}

func main() {
	unicodeDomain := "münchen.de"
	asciiDomain, err := DomainToASCII(unicodeDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error converting %q to ASCII: %v\n", unicodeDomain, err)
		os.Exit(1)
	}
	fmt.Printf("Unicode: %s -> ASCII: %s\n", unicodeDomain, asciiDomain)

	decodedUnicode, err := DomainToUnicode(asciiDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error converting %q to Unicode: %v\n", asciiDomain, err)
		os.Exit(1)
	}
	fmt.Printf("ASCII: %s -> Decoded Unicode: %s\n", asciiDomain, decodedUnicode)

	standardDomain := "example.com"
	asciiStd, err := DomainToASCII(standardDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error converting standard domain: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Standard domain unchanged: %s\n", asciiStd)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/idna.Lookup 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.Lookup"
  ]
}

package main

import (
	"fmt"
	"os"

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

func main() {
	// Assertion 1: idna.Lookup.ToASCII converts internationalized domain names containing Unicode characters to Punycode ASCII format
	unicodeDomain := "münchen.de"
	expectedASCII := "xn--mnchen-3ya.de"
	asciiResult, err := idna.Lookup.ToASCII(unicodeDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToASCII(%q) returned error: %v\n", unicodeDomain, err)
		os.Exit(1)
	}
	if asciiResult != expectedASCII {
		fmt.Fprintf(os.Stderr, "FAIL: ToASCII(%q) = %q, expected %q\n", unicodeDomain, asciiResult, expectedASCII)
		os.Exit(1)
	}

	// Assertion 2: idna.Lookup.ToUnicode decodes Punycode ASCII domain names back to Unicode format
	unicodeResult, err := idna.Lookup.ToUnicode(expectedASCII)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToUnicode(%q) returned error: %v\n", expectedASCII, err)
		os.Exit(1)
	}
	if unicodeResult != unicodeDomain {
		fmt.Fprintf(os.Stderr, "FAIL: ToUnicode(%q) = %q, expected %q\n", expectedASCII, unicodeResult, unicodeDomain)
		os.Exit(1)
	}

	// Assertion 3: idna.Lookup.ToASCII leaves standard ASCII domain names unchanged
	standardDomain := "example.com"
	stdResult, err := idna.Lookup.ToASCII(standardDomain)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToASCII(%q) returned error: %v\n", standardDomain, err)
		os.Exit(1)
	}
	if stdResult != standardDomain {
		fmt.Fprintf(os.Stderr, "FAIL: ToASCII(%q) = %q, expected %q\n", standardDomain, stdResult, standardDomain)
		os.Exit(1)
	}

	// Assertion 4: idna.Lookup.ToASCII returns an error for invalid domain names violating IDNA rules
	invalidDomain := "xn--invalid-punycode-%%%.example.com"
	if _, err := idna.Lookup.ToASCII(invalidDomain); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: ToASCII(%q) expected error, but got nil\n", invalidDomain)
		os.Exit(1)
	}

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