    001// Copyright 2013 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007// http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.internal.services.assets;
    016
    017import org.apache.tapestry5.internal.services.ResourceStreamer;
    018import org.apache.tapestry5.ioc.Resource;
    019
    020import java.io.IOException;
    021
    022/**
    023 * Utility used by {@link org.apache.tapestry5.services.assets.AssetRequestHandler} implementations
    024 * where the first folder in the extra path is actually a computed checksum of the resource's content.
    025 *
    026 * @since 5.4
    027 */
    028public class ChecksumPath
    029{
    030    private static final String NON_EXISTING_RESOURCE = "_________________________";
    031
    032    public final String checksum;
    033
    034    public final String resourcePath;
    035
    036    private final ResourceStreamer streamer;
    037
    038    public ChecksumPath(ResourceStreamer streamer, String baseFolder, String extraPath)
    039    {
    040        this.streamer = streamer;
    041        int slashx = extraPath.indexOf('/');
    042
    043        checksum = extraPath.substring(0, slashx);
    044
    045        String morePath = extraPath.substring(slashx + 1);
    046
    047        if (!isBlank(morePath)) {
    048            resourcePath = baseFolder == null
    049                    ? morePath
    050                    : baseFolder + "/" + morePath;
    051        }
    052        else {
    053            // When we only have something which looks like a checksum but no actual path.
    054            // For example, /assets/META-INF/
    055            resourcePath = NON_EXISTING_RESOURCE;
    056        }
    057    }
    058
    059    /**
    060     * If the resource exists and the checksum is correct, stream it to the client and return true. Otherwise,
    061     * return false.
    062     *
    063     * @param resource
    064     *         to stream
    065     * @return true if streamed, false otherwise
    066     * @throws IOException
    067     */
    068    public boolean stream(Resource resource) throws IOException
    069    {
    070        if (resource == null || !resource.exists())
    071        {
    072            return false;
    073        }
    074
    075
    076        return streamer.streamResource(resource, checksum, ResourceStreamer.DEFAULT_OPTIONS);
    077    }
    078
    079    /**
    080     * Copied from StringUtils since it's the only method we want from it.
    081     */
    082    private static boolean isBlank(final CharSequence cs) {
    083        int strLen;
    084        if (cs == null || (strLen = cs.length()) == 0) {
    085            return true;
    086        }
    087        for (int i = 0; i < strLen; i++) {
    088            if (!Character.isWhitespace(cs.charAt(i))) {
    089                return false;
    090            }
    091        }
    092        return true;
    093    }
    094
    095}