December 19th Wednesday (十二月 十九日 水曜日)

Filter Objects

  The filter object is defined in util_filter.h.

/**
  * The representation of a filter chain. Each request has a list
  * of these structures, which are called in turn to filter the data.
  * Subrequests get an exact copy of the main request's filter chain.
  */
struct ap_filter_t {
  /** The internal representation of this filter.  This includes
   *  the filter's name, type, and the actual function pointer.
   */
  ap_filter_rec_t *frec;

  /** A place to store any data associated with the current filter */
  void *ctx;

  /** The next filter in the chain */
  ap_filter_t *next;

  /** The request_rec associated with the current filter.  If a subrequest
   *  adds filters, then the subrequest is the request associated with the
   *  filter.
   */
  request_rec *r;

  /** The conn_rec associated with the current filter.  This is analogous
   *to the request_rec, except that it is used for connection filters.
   */
  conn_rec *c;
};

  The field ctx will use to store application data for the filter between calls, and request_rec, to access all
the normal request data.  (In the case of connection-level filters, there is no valid request_rec field, and the
conn_rec serves a similar purpose.)

/**
* This structure is used for recording information about the
* registered filters. It associates a name with the filter's callback
* and filter type.
*
* At the moment, these are simply linked in a chain, so a ->next pointer
* is available.
*
* It is used for any filter that can be inserted in the filter chain.
* This may be either an httpd-2.0 filter or a mod_filter harness.
* In the latter case, it contains provider and protocol information.
* In the former case, the new fields (from providers) are ignored.
*/

struct ap_filter_rec_t {
  /** The registered name for this filter */
  const char *name;

  /** The function to call when this filter is invoked. */
  ap_filter_func filter_func;

  /** The function to call before the handlers are invoked. Notice
   * that this function is called only for filters participating in
   * the HTTP protocol. Filters for other protocols are to be
   * initialized by the protocols themselves.
   */
  ap_init_filter_func filter_init_func;

  /** 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.
   */
  ap_filter_type ftype;

  /** The next filter_rec in the list */
  struct ap_filter_rec_t *next;

  /** Providers for this filter */
  ap_filter_provider_t *providers;

  /** Trace level for this filter */
  int debug;

  /** Protocol flags for this filter */
  unsigned int proto_flags;
};