util_filter.h revision 2960eb12428663adcf10ae5b21fcc2b7d85267b9
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#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"
#include "ap_buckets.h"
/**
* @package Apache filter library
*/
#define AP_NOBODY_WROTE -1;
/*
* 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 ap_filter_t ap_filter_t;
/*
* ap_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
* the types and values of the individual buckets should not be altered.
*
* The return value of a filter should be an APR status value.
*/
/*
* 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_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
*
* 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.
*/
/**
* The internal representation of a filter chain. Each request has a list
* of these structures which are called in turn to filter the data. Sub
* requests get an exact copy of the main requests filter chain.
*/
struct ap_filter_t {
/** The current filter function in the chain. The prototype is:
* <PRE>
* apr_status_t (*ap_filter_func)(ap_filter_t *f, ap_bucket_brigade *b);
* </PRE>
*/
/** A place to store any data associated with the current filter */
void *ctx;
/** The type of filter, either AP_FTYPE_CONTENT or AP_FTYPE_CONNECTION.
* An AP_FTYPE_CONTENT filter modifies the data based on information
* found in the content. An AP_FTYPE_CONNECTION filter modifies the
* data based on the type of connection.
*/
/** The next filter in the chain */
/** The request_rec associated with the current filter. If a sub-request
* adds filters, then the sub-request is the request associated with the
* filter.
*/
request_rec *r;
};
/* This function just passes the current bucket brigade down to the next
* filter on the filter stack. When a filter actually writes to the network
* (usually either core or SSL), that filter should return the number of bytes
* actually written and it will get propogated back up to the handler. If
* nobody writes the data to the network, then this function will most likely
* seg fault. I haven't come up with a good way to detect that case yet, and
* it should never happen. Regardless, it's an unrecoverable error for the
* current request. I would just rather it didn't take out the whole child
* process.
*/
/**
* Pass the current bucket brigade down to the next filter on the filter
* stack. The filter should return an apr_status_t value. If the bottom-most
* filter doesn't write to the network, then AP_NOBODY_WROTE is returned.
* @param filter The next filter in the chain
* @param bucket The current bucket brigade
* @return apr_status_t value
* @deffunc apr_status_t ap_pass_brigade(ap_filter_t *filter, ap_bucket_brigade *bucket)
*/
/*
* 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.
*/
/**
* Register a filter for later use. This allows modules to name their filter
* functions for later addition to a specific request
* @param name The name to attach to the filter function
* @param filter_func The filter function to name
* @param The type of filter function, either AP_FTYPE_CONTENT or AP_FTYPE_CONNECTION
* @deffunc void ap_register_filter(const char *name, ap_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.
*
* To re-iterate that last comment. This function is building a FIFO
* list of filters. Take note of that when adding your filter to the chain.
*/
/**
* Add a filter to the current request. Filters are added in a FIFO manner.
* The first filter added will be the first filter called.
* @param name The name of the filter to add
* @param ctx Any filter specific data to associate with the filter
* @param r The request to add this filter for.
* @deffunc void ap_add_filter(const char *name, void *ctx, request_rec *r)
*/
/* The next two filters are for abstraction purposes only. They could be
* done away with, but that would require that we break modules if we ever
* want to change our filter registration method. The basic idea, is that
* all filters have a place to store data, the ctx pointer. These functions
* fill out that pointer with a bucket brigade, and retrieve that data on
* the next call. The nice thing about these functions, is that they
* automatically concatenate the bucket brigades together for you. This means
* that if you have already stored a brigade in the filters ctx pointer, then
* when you add more it will be tacked onto the end of that brigade. When
* you retrieve data, if you pass in a bucket brigade to the get function,
* it will append the current brigade onto the one that you are retrieving.
*/
/**
* Get data that was saved aside for the current filter from an earlier call
* @param f The current filter
* @param b The bucket brigade to append to the data that was saved earlier.
* This should be the brigade that was most recently passed to the
* filter
* @return A single bucket brigade containing all of the data that was set
* aside from a previous call to ap_save_data_to_filter and the data
* that was most recently passed to this filter.
* @deffunc ap_bucket_brigade *ap_get_saved_data(ap_filter_t *f, ap_bucket_brigade **b)
*/
ap_bucket_brigade **b);
/**
* Save a bucket brigade to a filter. This is used to save portions of the
* data off to the side for consumption later
* @param f The current filter
* @param b The bucket brigade to save aside
* @deffunc void ap_save_data_to_filter(ap_filter_t *f, ap_bucket_brigade **b)
*/
#ifdef __cplusplus
}
#endif
#endif /* !AP_FILTER_H */