ParametersUtils.java

/**
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 * @author Kevin Smith, Boundless, 2017
 */

package org.geowebcache.filter.parameters;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;

import org.apache.commons.codec.digest.DigestUtils;

public class ParametersUtils {
    
    /**
     * 
     * This should be treated as an opaque Identifier and should not be parsed, it is used to 
     * to maintain compatibility with old caches.  For any other uses, {@link getKVP} is preferred
     * as it uses safe escaping of values.
     * 
     * @param parameters
     * @return
     */
    public static String getLegacyParametersKvp(Map<String, String> parameters) {
        StringBuilder sb = new StringBuilder();
        SortedMap<String, String> sorted = new TreeMap<String, String>(parameters);
        for (Map.Entry<String, String> e : sorted.entrySet()) {
            if(sb.length() == 0) {
                sb.append("?");
            } else {
                sb.append("&");
            }
            sb.append(e.getKey()).append('=').append(e.getValue());
        }
        String paramtersKvp = sb.toString();
        return paramtersKvp;
    }
    
    private static String encUTF8(String s) {
        try {
            // This would be much nicer if URLEncoder.encode took a charset object instead of a string
            return URLEncoder.encode(s, StandardCharsets.UTF_8.name());
        } catch (UnsupportedEncodingException e) {
            throw new IllegalStateException("Standard encoding UTF-8 is missing");
        }
    }
    
    private static String decUTF8(String s) {
        try {
            // This would be much nicer if URLDecoder.decode took a charset object instead of a string
            return URLDecoder.decode(s, StandardCharsets.UTF_8.name());
        } catch (UnsupportedEncodingException e) {
            throw new IllegalStateException("Standard encoding UTF-8 is missing");
        }
    }
    
    /**
     * Create a comparator that compares the results of a function applied to both its arguments.
     * @param derivation A function taking a T and returning a Comparable
     * @return A comparator that compares the result of derivation applied to both arguments.
     */
    static <T, U extends Comparable<U>> Comparator<T> derivedComparator(Function<T, U> derivation) {
        return (t1,t2)->derivation.apply(t1).compareTo(derivation.apply(t2));
    }
    
    /**
     * Turns the parameter list into a sorted KVP string
     * 
     * @param parameters
     * @return
     */
    public static String getKvp(Map<String, String> parameters) {
        return parameters.entrySet().stream()
            .sorted(derivedComparator(Entry::getKey))
            .map(e->String.join("=", encUTF8(e.getKey()), encUTF8(e.getValue())))
            .collect(Collectors.joining("&"));
    }
    
    /**
     * Turns the a sorted KVP string into a parameter map.
     * 
     * This should only be used for parsing strings created by {@link getSafeParametersKvp} not for 
     * parsing raw query strings
     * 
     * @param parameters
     * @return
     */
    public static Map<String, String> getMap(String kvp) {
        return Arrays.stream(kvp.split("&"))
            .filter(((Predicate<String>)String::isEmpty).negate())
            .map(pair->pair.split("=", 2))
            .collect(Collectors.toMap(p->decUTF8(p[0]), p->decUTF8(p[1])));
    }
    
    
    /**
     * Returns the parameters identifier for the given parameters map
     * @param parameters
     * @return
     */
    public static String getId(Map<String, String> parameters) {
        if(parameters == null || parameters.size() == 0) {
            return null;
        }
        String parametersKvp = getLegacyParametersKvp(parameters);
        return ParametersUtils.buildKey(parametersKvp);
    }

    public static String buildKey(String parametersKvp) {
        return DigestUtils.sha1Hex(parametersKvp);
    }
    
    
}