# PEP Engine

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

The PEP Manager is a registry for PEP Protocols that follow the generic syntax defined by the HTTP PEP protocol headers. All PEP Protocols are registered at run-time in form of a PEP Module. A PEP Module consists of the following:

protocol
  The name which is used to identify the protocol.
BEFORE Filter
  When a new request is issued, the PEP Manager looks in the URL tree to see if we have any PEP information for this particular request. The search is based on the realm (if known) in which the request belongs and the URL itself. If a record is found then the PEP Manager calls the PEP Module in order to generate the PEP protocol headers.
AFTER Filter
  After a request has terminated and the result was lack of required PEP protocol headers, the request should normally be repeated with a new set of PEP protocol headers. The AFTER filter is responsible for extracting the challenge from the HTTP response and store it in the URL tree, so that we next time we request the same URL we know that it is protected and we can ask the user for the appropriate PRP protocol headers.
garbage collection
  The PEP information is stored in a URL Tree but as it doesn't know the format of the protocol specific parts, you must register a garbage collector (gc). The gc is called when node is deleted in the tree.

Note: The PEP Manager itself consists of BEFORE and an AFTER filter - just like the PEP Modules. This means that any PEP Module also can be registered directly as a BEFORE and AFTER filter by the Net Manager. The reason for having the two layer model is that the PEP Manager maintains a single URL tree for storing PEP information for all PEP Protocols.

A PEP Module has three resources, it can use when creating PEP protocol headers:

- Handle the PEP protocol headers send from the remote party (typically in the form of a HTTP response.
- Handle the PEP protocol headers which typically are to part of the next request.
- Add information to the URL Tree

This module is implemented by HTPEP.c (get it?), and it is a part of the W3C Sample Code Library.

    #ifndef HTPEP_H
    #define HTPEP_H
    #include "HTList.h"
    #include "HTReq.h"
    #include "HTUTree.h"

    typedef struct _HTPEPModule HTPEPModule;

## PEP Module Registration

A PEP Protocol is registered by registering an PEP Module to in the PEP Manager.

### Add a PEP Module

You can add a PEP protocol by using the following method. Each of the callback function must have the type as defined below.

    extern HTPEPModule * HTPEP_newModule(const char *	protocol,
    				     HTNetBefore *	before,
    			             HTNetAfter *	after,
    				     HTUTree_gc *	gc);

### Find a PEP Module

    extern HTPEPModule * HTPEP_findModule (const char * protocol);

### Delete a PEP Module

    extern BOOL HTPEP_deleteModule (const char * protocol);

### Delete ALL PEP modules

    extern BOOL HTPEP_deleteAllModules (void);

## Handling the URL Tree

The PEP information is stored as URL Trees. The root of a URL Tree is identified by a hostname and a port number. Each URL Tree contains a set of templates and realms which can be used to predict what information to use in a hierarchical tree.

The URL trees are automatically collected after some time so the application does not have to worry about freeing the trees. When a node in a tree is freed, the gc registered as part of the PEP Module is called.

Server applications can have different PEP setups for each hostname and port number, they control. For example, a server with interfaces "`www.foo.com`" and "`internal.foo.com`" can have different protection setups for each interface.

### Add information to the Database

Add a PEP information node to the database. If the entry is already found then it is replaced with the new one. The template must follow normal URI syntax but can include a wildcard Return YES if added (or replaced), else NO

    extern HTPEPModule * HTPEP_findModule (const char * name);

## The PEP Manager Filters

As mentioned, the PEP Manager is itself a set of filters that can be registered by the Net manager.

    extern HTNetBefore HTPEP_beforeFilter;
    extern HTNetAfter  HTPEP_afterFilter;

    #endif	/* NOT HTPEP_H */