/*

 * 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.catalina;

import java.io.IOException;

import javax.servlet.ServletException;

import org.apache.catalina.connector.Request;

import org.apache.catalina.connector.Response;

/**

 * <p>A <b>Valve</b> is a request processing component associated with a

 * particular Container.  A series of Valves are generally associated with

 * each other into a Pipeline.  The detailed contract for a Valve is included

 * in the description of the <code>invoke()</code> method below.</p>

 *

 * <b>HISTORICAL NOTE</b>:  The "Valve" name was assigned to this concept

 * because a valve is what you use in a real world pipeline to control and/or

 * modify flows through it.

 *

 * @author Craig R. McClanahan

 * @author Gunnar Rjnning

 * @author Peter Donald

 */

public interface Valve {

    //-------------------------------------------------------------- Properties

    /**

     * Return descriptive information about this Valve implementation.

     */

    public String getInfo();

    /**

     * Return the next Valve in the pipeline containing this Valve, if any.

     */

    public Valve getNext();

    /**

     * Set the next Valve in the pipeline containing this Valve.

     *

     * @param valve The new next valve, or <code>null</code> if none

     */

    public void setNext(Valve valve);

    //---------------------------------------------------------- Public Methods

    /**

     * Execute a periodic task, such as reloading, etc. This method will be

     * invoked inside the classloading context of this container. Unexpected

     * throwables will be caught and logged.

     */

    public void backgroundProcess();

    /**

     * <p>Perform request processing as required by this Valve.</p>

     *

     * <p>An individual Valve <b>MAY</b> perform the following actions, in

     * the specified order:</p>

     * <ul>

     * <li>Examine and/or modify the properties of the specified Request and

     *     Response.

     * <li>Examine the properties of the specified Request, completely generate

     *     the corresponding Response, and return control to the caller.

     * <li>Examine the properties of the specified Request and Response, wrap

     *     either or both of these objects to supplement their functionality,

     *     and pass them on.

     * <li>If the corresponding Response was not generated (and control was not

     *     returned, call the next Valve in the pipeline (if there is one) by

     *     executing <code>getNext().invoke()</code>.

     * <li>Examine, but not modify, the properties of the resulting Response

     *     (which was created by a subsequently invoked Valve or Container).

     * </ul>

     *

     * <p>A Valve <b>MUST NOT</b> do any of the following things:</p>

     * <ul>

     * <li>Change request properties that have already been used to direct

     *     the flow of processing control for this request (for instance,

     *     trying to change the virtual host to which a Request should be

     *     sent from a pipeline attached to a Host or Context in the

     *     standard implementation).

     * <li>Create a completed Response <strong>AND</strong> pass this

     *     Request and Response on to the next Valve in the pipeline.

     * <li>Consume bytes from the input stream associated with the Request,

     *     unless it is completely generating the response, or wrapping the

     *     request before passing it on.

     * <li>Modify the HTTP headers included with the Response after the

     *     <code>getNext().invoke()</code> method has returned.

     * <li>Perform any actions on the output stream associated with the

     *     specified Response after the <code>getNext().invoke()</code> method has

     *     returned.

     * </ul>

     *

     * @param request The servlet request to be processed

     * @param response The servlet response to be created

     *

     * @exception IOException if an input/output error occurs, or is thrown

     *  by a subsequently invoked Valve, Filter, or Servlet

     * @exception ServletException if a servlet error occurs, or is thrown

     *  by a subsequently invoked Valve, Filter, or Servlet

     */

    public void invoke(Request request, Response response)

        throws IOException, ServletException;

    /**

     * Process a Comet event.

     *

     * @param request The servlet request to be processed

     * @param response The servlet response to be created

     *

     * @exception IOException if an input/output error occurs, or is thrown

     *  by a subsequently invoked Valve, Filter, or Servlet

     * @exception ServletException if a servlet error occurs, or is thrown

     *  by a subsequently invoked Valve, Filter, or Servlet

     */

    public void event(Request request, Response response, CometEvent event)

        throws IOException, ServletException;

}