gotosocial/internal/util/punycode.go

// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package util

import (
	"net/url"
	"strings"

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

// Punify converts the given domain to lowercase
// then to punycode (for international domain names).
//
// Returns the resulting domain or an error if the
// punycode conversion fails.
func Punify(domain string) (string, error) {
	domain = strings.ToLower(domain)
	return idna.ToASCII(domain)
}

// DePunify converts the given punycode string
// to its original unicode representation (lowercased).
// Noop if the domain is (already) not puny.
//
// Returns an error if conversion fails.
func DePunify(domain string) (string, error) {
	out, err := idna.ToUnicode(domain)
	return strings.ToLower(out), err
}

// URIMatches returns true if the expected URI matches
// any of the given URIs, taking account of punycode.
func URIMatches(expect *url.URL, uris ...*url.URL) (bool, error) {
	// Normalize expect to punycode.
	expectPuny, err := PunifyURI(expect)
	if err != nil {
		return false, err
	}
	expectStr := expectPuny.String()

	for _, uri := range uris {
		uriPuny, err := PunifyURI(uri)
		if err != nil {
			return false, err
		}

		if uriPuny.String() == expectStr {
			// Looks good.
			return true, nil
		}
	}

	// Didn't match.
	return false, nil
}

// PunifyURI returns a copy of the given URI
// with the 'host' part converted to punycode.
func PunifyURI(in *url.URL) (*url.URL, error) {
	// Take a copy of in.
	out := new(url.URL)
	*out = *in

	// Normalize host to punycode.
	var err error
	out.Host, err = Punify(in.Host)
	return out, err
}

// PunifyURIStr returns a copy of the given URI
// string with the 'host' part converted to punycode.
func PunifyURIStr(in string) (string, error) {
	inURI, err := url.Parse(in)
	if err != nil {
		return "", err
	}

	outURIPuny, err := Punify(inURI.Host)
	if err != nil {
		return "", err
	}

	if outURIPuny == in {
		// Punify did nothing, so in was
		// already punified, return as-is.
		return in, nil
	}

	// Take a copy of in.
	outURI := new(url.URL)
	*outURI = *inURI

	// Normalize host to punycode.
	outURI.Host = outURIPuny
	return outURI.String(), err
}