org.fcrepo.kernel.api.utils.ContentDigest.java Source code

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Here is the source code for org.fcrepo.kernel.api.utils.ContentDigest.java

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/*
 * Copyright 2015 DuraSpace, Inc.
 *
 * Licensed 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 org.fcrepo.kernel.api.utils;

import static com.google.common.base.Throwables.propagate;
import static java.util.Collections.singletonMap;
import static org.apache.commons.codec.binary.Hex.encodeHexString;
import static org.slf4j.LoggerFactory.getLogger;

import java.net.URI;
import java.net.URISyntaxException;
import java.util.Map;

import org.slf4j.Logger;

import com.google.common.collect.ImmutableMap;

/**
 * Digest helpers to convert digests (checksums) into URI strings
 * (based loosely on Magnet URIs)
 * @author Chris Beer
 * @since Mar 6, 2013
 */
public final class ContentDigest {

    private static final Logger LOGGER = getLogger(ContentDigest.class);

    public static final Map<String, String> algorithmToScheme = ImmutableMap.of("SHA-1", "urn:sha1", "SHA1",
            "urn:sha1");

    public static final Map<String, String> schemeToAlgorithm = singletonMap("urn:sha1", "SHA-1");

    public static final String DEFAULT_ALGORITHM = "SHA-1";

    private ContentDigest() {
    }

    /**
     * Convert a MessageDigest algorithm and checksum value to a URN
     * @param algorithm the message digest algorithm
     * @param value the checksum value
     * @return URI
     */
    public static URI asURI(final String algorithm, final String value) {
        try {
            final String scheme = algorithmToScheme.get(algorithm);

            return new URI(scheme, value, null);
        } catch (final URISyntaxException unlikelyException) {
            LOGGER.warn("Exception creating checksum URI: {}", unlikelyException);
            throw propagate(unlikelyException);
        }
    }

    /**
     * Convert a MessageDigest algorithm and checksum byte-array data to a URN
     * @param algorithm the message digest algorithm
     * @param data the checksum byte-array data
     * @return URI
     */
    public static URI asURI(final String algorithm, final byte[] data) {
        return asURI(algorithm, asString(data));
    }

    /**
     * Given a digest URI, get the corresponding MessageDigest algorithm
     * @param digestUri the digest uri
     * @return MessageDigest algorithm
     */
    public static String getAlgorithm(final URI digestUri) {
        if (digestUri == null) {
            return DEFAULT_ALGORITHM;
        }
        return schemeToAlgorithm
                .get(digestUri.getScheme() + ":" + digestUri.getSchemeSpecificPart().split(":", 2)[0]);
    }

    private static String asString(final byte[] data) {
        return encodeHexString(data);
    }

    /**
     * Placeholder checksum value.
     * @return URI
     */
    public static URI missingChecksum() {
        return asURI("SHA-1", "missing");
    }

}