Upstream: cache revalidation with conditional requests. The following new directives are introduced: proxy_cache_revalidate, fastcgi_cache_revalidate, scgi_cache_revalidate, uwsgi_cache_revalidate. Default is off. When set to on, they enable cache revalidation using conditional requests with If-Modified-Since for expired cache items. As of now, no attempts are made to merge headers given in a 304 response during cache revalidation with headers previously stored in a cache item. Headers in a 304 response are only used to calculate new validity time of a cache item.

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_SHMEM_H_INCLUDED_
#define _NGX_SHMEM_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


typedef struct {
    u_char      *addr;
    size_t       size;
    ngx_str_t    name;
    ngx_log_t   *log;
    ngx_uint_t   exists;   /* unsigned  exists:1;  */
} ngx_shm_t;


ngx_int_t ngx_shm_alloc(ngx_shm_t *shm);
void ngx_shm_free(ngx_shm_t *shm);


#endif /* _NGX_SHMEM_H_INCLUDED_ */