core/src/main/java/org/apache/accumulo/core/constraints/Constraint.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.accumulo.core.constraints;

import java.util.List;

import org.apache.accumulo.core.data.Mutation;
import org.apache.accumulo.core.data.impl.KeyExtent;
import org.apache.accumulo.core.security.AuthorizationContainer;

/**
 * Constraint objects are used to determine if mutations will be applied to a table.
 *
 * <p>
 * This interface expects implementers to return violation codes. The reason codes are returned instead of arbitrary strings to encourage conciseness.
 * Conciseness is needed because violations are aggregated. If a user sends a batch of 10,000 mutations to Accumulo, only aggregated counts about which
 * violations occurred are returned. If the constraint implementer were allowed to return arbitrary violation strings like the following:
 *
 * <p>
 * Value "abc" is not a number<br>
 * Value "vbg" is not a number
 *
 * <p>
 * This would not aggregate very well, because the same violation is represented with two different strings.
 */
public interface Constraint {

  /**
   * The environment within which a constraint exists.
   */
  interface Environment {
    /**
     * Gets the key extent of the environment.
     *
     * @return key extent
     */
    KeyExtent getExtent();

    /**
     * Gets the user within the environment.
     *
     * @return user
     */
    String getUser();

    /**
     * Gets the authorizations in the environment.
     *
     * @return authorizations
     */
    AuthorizationContainer getAuthorizationsContainer();
  }

  /**
   * Gets a short, one-sentence description of what a given violation code means.
   *
   * @param violationCode
   *          numeric violation code
   * @return matching violation description
   */
  String getViolationDescription(short violationCode);

  /**
   * Checks a mutation for constraint violations. If the mutation contains no violations, returns null. Otherwise, returns a list of violation codes.
   *
   * Violation codes must be non-negative. Negative violation codes are reserved for system use.
   *
   * @param env
   *          constraint environment
   * @param mutation
   *          mutation to check
   * @return list of violation codes, or null if none
   */
  List<Short> check(Environment env, Mutation mutation);
}