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HttpClient-based client for Riak
There is a newer version: 2.1.1
/*
 * This file is provided to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.basho.riak.client.http.util;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Parses the HTTP Link header as described here:
 * 
 * http://tools.ietf.org/html/draft-nottingham-http-link-header
 * 
 * This implementation is more or less a direct port of mnot's Python
 * implementation here:
 * 
 * http://gist.github.com/210535
 * 
 * @author jlee 
 */
public class LinkHeader {

    private static String TOKEN = "(?:[^\\(\\)<>@,;:\\\\\"/\\[\\]\\?={} \\t]+?)";
    private static String QUOTED_STRING = "(?:\"(?:\\\\\"|[^\"])*\")";
    private static String PARAMETER = String.format("(?:%s(?:=(?:%s|%s))?)", TOKEN, TOKEN, QUOTED_STRING);
    private static String LINK = "<[^>]*>\\s*(?:;\\s*" + PARAMETER + "?\\s*)*";
    private static String COMMA = "(?:\\s*(?:,\\s*)+)";
    private static String SEMICOLON = "(?:\\s*(?:;\\s*)+)";
    private static String LINK_SPLIT = LINK + "(?=" + COMMA + "|\\s*$)";
    private static String PARAM_SPLIT = PARAMETER + "(?=" + SEMICOLON + "|\\s*$)";
    private static Pattern LINK_SPLITTER = Pattern.compile(LINK_SPLIT);
    private static Pattern PARAM_SPLITTER = Pattern.compile(PARAM_SPLIT);

    /**
     * Returns a map of links to their parameters. Parameters are a map of
     * parameter name to value.
     * 
     * @param header
     *            Value of the Link header in the format described here:
     * 
     *            http://tools.ietf.org/html/draft-nottingham-http-link-header
     * 
     *            e.g. {@literal ; param="value",
     *            }
     * 
     * @return A map of links to their parameters. Parameters are a list of maps of
     *         parameter name to value. (A URI can appear multiple times in the 
     *         Link header, each Map in the List represents a set of parameters)
     */
    public static Map>> parse(String header) {
        Map>> out = 
            new LinkedHashMap>>();

        if (header == null || header.length() == 0)
            return out;

        Matcher m = LINK_SPLITTER.matcher(header);
        while (m.find()) {
            String link = m.group().trim();
            String[] urlandparams = link.split(">", 2);
            String url = urlandparams[0].substring(1);
            Map parsedLink = new HashMap();

            if (urlandparams.length > 1) {
                String params = urlandparams[1];
                for (String param : splitParams(params)) {
                    String[] parts = param.split("=", 2);
                    if (parts.length > 1) {
                        parsedLink.put(parts[0].toLowerCase(), ClientUtils.unquoteString(parts[1]));
                    } else {
                        parsedLink.put(parts[0].toLowerCase(), null);
                    }
                }
            }
            
            List> existing = out.get(url);
            
            if (existing == null) {
                existing = new LinkedList>();
                out.put(url, existing);
            }
                
            existing.add(parsedLink);
            
        }

        return out;
    }

    private static List splitParams(String s) {

        List items = new ArrayList();
        if (s == null || s.length() == 0)
            return items;

        Matcher m = PARAM_SPLITTER.matcher(s);
        while (m.find()) {
            items.add(m.group().trim());
        }

        return items;
    }

}