sshd-core/src/main/java/org/apache/sshd/common/signature/SignatureFactoriesManager.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * 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 org.apache.sshd.common.signature;

import java.util.List;

import org.apache.sshd.common.NamedFactory;
import org.apache.sshd.common.util.GenericUtils;

/**
 * Manage the list of named factories for <code>Signature</code>.
 *
 * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
 */
public interface SignatureFactoriesManager {
    /**
     * @return The list of named <code>Signature</code> factories
     */
    List<NamedFactory<Signature>> getSignatureFactories();
    void setSignatureFactories(List<NamedFactory<Signature>> factories);

    /**
     * A helper class for signature factories related operations
     * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
     */
    // CHECKSTYLE:OFF
    final class Utils {
        private Utils() {
            throw new UnsupportedOperationException("No instance allowed");
        }

        /**
         * @param manager The {@link SignatureFactoriesManager} instance - ignored if {@code null}
         * @return The associated list of named <code>Signature</code> factories or {@code null} if
         * no manager instance
         */
        public static List<NamedFactory<Signature>> getSignatureFactories(SignatureFactoriesManager manager) {
            return (manager == null) ? null : manager.getSignatureFactories();
        }

        /**
         * Attempts to use the primary manager's signature factories if not {@code null}/empty,
         * otherwise uses the secondary ones (regardless of whether there are any...)
         *
         * @param primary The primary {@link SignatureFactoriesManager}
         * @param secondary The secondary {@link SignatureFactoriesManager}
         * @return The resolved signature factories - may be {@code null}/empty
         * @see #getSignatureFactories(SignatureFactoriesManager)
         */
        public static List<NamedFactory<Signature>> resolveSignatureFactories(
                SignatureFactoriesManager primary, SignatureFactoriesManager secondary) {
            List<NamedFactory<Signature>> factories = getSignatureFactories(primary);
            return GenericUtils.isEmpty(factories) ? getSignatureFactories(secondary) : factories;
        }
    }
}