ContentNegotiation.java

/* Copyright (C) 2013 Tomas Matula <tomas.matula@eea.sk>
 *
 * This file is part of Open Data Node.
 *
 * Open Data Node 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.
 *
 * Open Data Node 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 Open Data Node.  If not, see <http://www.gnu.org/licenses/>.
 */

package sk.opendatanode.utils.http;

import java.util.ArrayList;

import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;

public class ContentNegotiation {

    /**
     * Parses data of Accept field in HTTP header and finds most suitable content form specified content list
     * 
     * @param content of Accept field in HTTP header
     * @param avalContentTypes supported content types
     * @return most suitable content type
     */
    protected static ContentTypes parseHttpContext(String content, ArrayList<ContentTypes> avalContentTypes) {

        String[] tokens = content.split(",");

        return matchContent(fillContentTree(tokens), fillContentTree(avalContentTypes), content);
    }

    /**
     * Fills tree structure with data from list
     * 
     * @param contentTypes list of available content types
     * @return tree object
     */
    private static ContentTree fillContentTree(ArrayList<ContentTypes> contentTypes) {
        String[] tokens = new String[contentTypes.size()];

        for (int i = 0; i < contentTypes.size(); i++) {
            tokens[i] = contentTypes.get(i).getLabel();
        }

        return fillContentTree(tokens);
    }

    /**
     * Fills tree structure with data from tokens
     * 
     * @param tokens input data
     * @return tree object
     */
    private static ContentTree fillContentTree(String[] tokens) {
        ContentTree contentTree = new ContentTree();

        for (String token : tokens) {
            String type;
            String subType;
            Float quality = new Float(1);
            int index, index2, index3;

            index = token.indexOf("/");
            index2 = token.indexOf(";");
            index3 = token.indexOf("q=");

            if (index == -1) {
                // Illegal header data
                throw new AbortWithHttpErrorCodeException(406, "Illegal header format");
            }

            if (index2 == -1) {
                subType = token.substring(index + 1).trim();
            } else {
                subType = token.substring(index + 1, index2).trim();
            }

            if (index3 != -1) {
                index2 = token.indexOf(";", index3);
                if (index2 == -1) {
                    quality = Float.parseFloat(token.substring(index3 + 2));
                } else {
                    quality = Float.parseFloat(token.substring(index3 + 2, index2));
                }
            }

            if (quality > 1 || quality < 0) {
                throw new AbortWithHttpErrorCodeException(406, "Quality parameter out of range <0,1>");
            }

            type = token.substring(0, index).trim();
            contentTree.addContent(type, subType, quality);
        }

        return contentTree;
    }

    /**
     * Matches requested content with available
     */
    private static ContentTypes matchContent(ContentTree contentTree, ContentTree avalContentTypes, String content) {

        ContentTypes contentType = contentTree.searchFromRoots(avalContentTypes.getFirstRoot());
        if (contentType == null) {
            throw new AbortWithHttpErrorCodeException(406, "No such content available: " + content);
        }

        return contentType;
    }
}