UntrackMe-app-android-redirect-nitter-invidious-bibliogram/app/src/main/java/app/fedilab/nitterizeme/Utils.java

package app.fedilab.nitterizeme;
/* Copyright 2020 Thomas Schneider
 *
 * This file is a part of NitterizeMe
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the
 * GNU General Public License as published by the Free Software Foundation; either version 3 of the
 * License, or (at your option) any later version.
 *
 * NitterizeMe 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 General
 * Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with NitterizeMe; if not,
 * see <http://www.gnu.org/licenses>. */
import java.io.IOException;
import java.net.URL;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.net.ssl.HttpsURLConnection;

class Utils {

    static final Pattern urlPattern = Pattern.compile(
            "(?i)\\b((?:[a-z][\\w-]+:(?:/{1,3}|[a-z0-9%])|www\\d{0,3}[.]|[a-z0-9.\\-]+[.][a-z]{2,10}/)(?:[^\\s()<>]+|\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\))+(?:\\(([^\\s()<>]+|(\\([^\\s()<>]+\\)))*\\)|[^\\s`!()\\[\\]{};:'\".,<>?«»“”‘’]))",
            Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);


    /**
     * Returns the unshortened URL
     * @param urlStr String URL to check
     * @return String the Unshortened URL
     */
    static String checkUrl(String urlStr){
        URL url;
        String redirect = null;
        try {
            url = new URL(urlStr);
            HttpsURLConnection httpsURLConnection = (HttpsURLConnection) url.openConnection();
            httpsURLConnection.setRequestProperty("http.keepAlive", "false");
            httpsURLConnection.setInstanceFollowRedirects(false);
            httpsURLConnection.setRequestMethod("HEAD");
            if( httpsURLConnection.getResponseCode() == 301) {
                Map<String, List<String>> map = httpsURLConnection.getHeaderFields();
                for (Map.Entry<String, List<String>> entry : map.entrySet()) {
                    if (entry.toString().toLowerCase().startsWith("location")) {
                        Matcher matcher = urlPattern.matcher(entry.toString());
                        if (matcher.find()) {
                            redirect = matcher.group(1);
                        }
                    }
                }
            }
            httpsURLConnection.getInputStream().close();
            if (redirect != null && redirect.compareTo(urlStr)!=0){
                URL redirectURL = new URL(redirect);
                String host = redirectURL.getHost();
                String protocol = redirectURL.getProtocol();
                if( protocol == null || host == null){
                    redirect = null;
                }
            }
            return redirect;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}