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package org.apache.catalina;

import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;

import javax.servlet.ServletException;
import java.io.IOException;

/**
 * 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
 * @author Gunnar Rjnning
 * @author Peter Donald
 * @version $Revision: 303352 $ $Date: 2004-10-05 19:12:52 +0200 (mar., 05 oct. 2004) $
 */

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 null 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();


    /**
     * 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 context.invokeNext().
     * 
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
     *     invokeNext() method has returned.
     * 
Perform any actions on the output stream associated with the
     *     specified Response after the invokeNext() method has
     *     returned.
     * 
     *
     * @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;


}