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/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2000 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution,
* if any, must include the following acknowledgment:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgment may appear in the software itself,
* if and wherever such third-party acknowledgments normally appear.
*
* 4. The names "Apache" and "Apache Software Foundation" must
* not be used to endorse or promote products derived from this
* software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache",
* nor may "Apache" appear in their name, without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*/
#ifndef AP_FILTER_H
#define AP_FILTER_H
#ifdef __cplusplus
extern "C" {
#endif
#ifdef APR_HAVE_STDARG_H
#include <stdarg.h>
#endif
#include "httpd.h"
#include "apr.h"
/*
* FILTER CHAIN
*
* Filters operate using a "chaining" mechanism. The filters are chained
* together into a sequence. When output is generated, it is passed through
* each of the filters on this chain, until it reaches the end (or "bottom")
* and is placed onto the network.
*
* The top of the chain, the code generating the output, is typically called
* a "content generator." The content generator's output is fed into the
* filter chain using the standard Apache output mechanisms: ap_rputs(),
* ap_rprintf(), ap_rwrite(), etc.
*
* Each filter is defined by a callback. This callback takes the output from
* the previous filter (or the content generator if there is no previous
* filter), operates on it, and passes the result to the next filter in the
* chain. This pass-off is performed using the ap_fc_* functions, such as
* ap_fc_puts(), ap_fc_printf(), ap_fc_write(), etc.
*
* When content generation is complete, the system will pass an "end of
* stream" marker into the filter chain. The filters will use this to flush
* out any internal state and to detect incomplete syntax (for example, an
* unterminated SSI directive).
*/
/* forward declare the filter type */
typedef struct apr_filter_t apr_filter_t;
/*
* apr_filter_func:
*
* This function type is used for filter callbacks. It will be passed a
* pointer to "this" filter, and a "bucket" containing the content to be
* filtered.
*
* In filter->ctx, the callback will find its context. This context is
* provided here, so that a filter may be installed multiple times, each
* receiving its own per-install context pointer.
*
* Callbacks are associated with a filter definition, which is specified
* by name. See ap_register_filter() for setting the association between
* a name for a filter and its associated callback (and other information).
*
* The *bucket structure (and all those referenced by ->next and ->prev)
* should be considered "const". The filter is allowed to modify the
* next/prev to insert/remove/replace elements in the bucket list, but
* the types and values of the individual buckets should not be altered.
*/
typedef apr_status_t (*apr_filter_func)();
/*
* ap_filter_type:
*
* Filters have different types/classifications. These are used to group
* and sort the filters to properly sequence their operation.
*
* AP_FTYPE_CONTENT:
* These filters are used to alter the content that is passed through
* them. Examples are SSI or PHP.
*
* AP_FTYPE_CONNECTION:
* These filters will alter the content, but in ways that are more
* strongly associated with the output connection. Examples are
* compression, character recoding, or chunked transfer coding.
*
* It is important to note that these types of filters are not allowed
* in a sub-request. A sub-requests output can certainly be filtered
* by AP_FTYPE_CONTENT filters, but all of the "final processing" is
* determined by the main request.
*
* The types have a particular sort order, which allows us to insert them
* into the filter chain in a determistic order. Within a particular grouping,
* the ordering is equivalent to the order of calls to ap_add_filter().
*/
typedef enum {
AP_FTYPE_CONTENT,
AP_FTYPE_CONNECTION
} ap_filter_type;
/*
* apr_filter_t:
*
* This is the request-time context structure for an installed filter (in
* the output filter chain). It provides the callback to use for filtering,
* the request this filter is associated with (which is important when
* an output chain also includes sub-request filters), the context for this
* installed filter, and the filter ordering/chaining fields.
*
* Filter callbacks are free to use ->ctx as they please, to store context
* during the filter process. Generally, this is superior over associating
* the state directly with the request. A callback should not change any of
* the other fields.
*/
struct apr_filter_t {
apr_filter_func filter_func;
void *ctx;
ap_filter_type ftype;
apr_filter_t *next;
};
/*
* ap_register_filter():
*
* This function is used to register a filter with the system. After this
* registration is performed, then a filter may be added into the filter
* chain by using ap_add_filter() and simply specifying the name.
*
* The filter's callback and type should be passed.
*/
API_EXPORT(void) ap_register_filter(const char *name,
apr_filter_func filter_func,
ap_filter_type ftype);
/*
* ap_add_filter():
*
* Adds a named filter into the filter chain on the specified request record.
* The filter will be installed with the specified context pointer.
*
* Filters added in this way will always be placed at the end of the filters
* that have the same type (thus, the filters have the same order as the
* calls to ap_add_filter). If the current filter chain contains filters
* from another request, then this filter will be added before those other
* filters.
*/
API_EXPORT(void) ap_add_filter(const char *name, void *ctx, request_rec *r);
/*
* Things to do later:
* Add parameters to apr_filter_func type. Those parameters will be something
* like:
* (request_rec *r, apr_filter_t *filter, ap_data_list *the_data)
* obviously, the request_rec is the current request, and the filter
* is the current filter stack. The data_list is a bucket list or
* bucket_brigade, but I am trying to keep this patch neutral. (If this
* comment breaks that, well sorry, but the information must be there
* somewhere. :-)
*
* Add a function like ap_pass_data. This function will basically just
* call the next filter in the chain, until the current filter is NULL. If the
* current filter is NULL, that means that nobody wrote to the network, and
* we have a HUGE bug, so we need to return an error and log it to the
* log file.
*/
#ifdef __cplusplus
}
#endif
#endif /* !AP_FILTER_H */
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