/*
 * 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;

A Valve 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 invoke() method below.
HISTORICAL NOTE:  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, Gunnar Rjnning, Peter Donald/**
 * <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

    
Returns:
the next Valve in the pipeline containing this Valve, if any./**
     * @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.
Params:
valve – The new next valve, or null if none/**
     * 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.
/**
     * 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();


    
Perform request processing as required by this Valve.
An individual Valve MAY perform the following actions, in
the specified order:

Examine and/or modify the properties of the specified Request and
    Response.
Examine the properties of the specified Request, completely generate
    the corresponding Response, and return control to the caller.
Examine the properties of the specified Request and Response, wrap
    either or both of these objects to supplement their functionality,
    and pass them on.
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 getNext().invoke().
Examine, but not modify, the properties of the resulting Response
    (which was created by a subsequently invoked Valve or Container).

A Valve MUST NOT do any of the following things:

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).
Create a completed Response AND pass this
    Request and Response on to the next Valve in the pipeline.
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.
Modify the HTTP headers included with the Response after the
    getNext().invoke() method has returned.
Perform any actions on the output stream associated with the
    specified Response after the getNext().invoke() method has
    returned.

Params:
request – The servlet request to be processed
response – The servlet response to be created
Throws:
IOException – if an input/output error occurs, or is thrown
 by a subsequently invoked Valve, Filter, or Servlet
ServletException – if a servlet error occurs, or is thrown
 by a subsequently invoked Valve, Filter, or Servlet/**
     * <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;


    public boolean isAsyncSupported();
}