001// Copyright 2006, 2008 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.services;
016
017import org.apache.tapestry5.ioc.annotations.UsesConfiguration;
018
019import java.net.URL;
020
021/**
022 * Responsible for determining which classpath resources require checksums, and for generating checksums for such
023 * resources.
024 * <p/>
025 * The service's configuration identifies which file extensions will be secured using an checksum. The default list is
026 * "class" and "tml".
027 *
028 * @see org.apache.tapestry5.ioc.internal.util.ClasspathResource
029 * @see org.apache.tapestry5.internal.services.ClasspathAssetFactory
030 */
031@UsesConfiguration(String.class)
032public interface ResourceDigestGenerator
033{
034    /**
035     * Examines the path (typically, the file name extension at the end of the path) to determine if a checksum is
036     * required for the path. The path is {@link org.apache.tapestry5.ioc.Resource} style, without a leading slash.
037     */
038    boolean requiresDigest(String path);
039
040    /**
041     * Reads the content of a URL (presumably, for a resource on the classpath) and generates a digest of its content.
042     * This digest will be incorporated into the URL provided to the client, to verify that the client has been
043     * "granted" access to this resource. This is only used for resources where {@link #requiresDigest(String)} is
044     * true.
045     *
046     * @param url
047     * @return the digest for the resource
048     */
049    String generateDigest(URL url);
050}