nginx/src/http/ngx_http_cache.c

/*
 * small file in malloc()ed memory, mmap()ed file, file descriptor only,
 * file access time only (to estimate could pages still be in memory),
 * translated URI (ngx_http_index_hanlder),
 * compiled script (ngx_http_ssi_filter).
 */


#define NGX_HTTP_CACHE_ENTRY_DELETED  0x00000001
#define NGX_HTTP_CACHE_ENTRY_MMAPED   0x00000002

/* "/" -> "/index.html" in ngx_http_index_handler */
#define NGX_HTTP_CACHE_ENTRY_URI      0x00000004

/* 301 location "/dir" -> "dir/" in ngx_http_core_handler */

/* compiled script in ngx_http_ssi_filter  */
#define NGX_HTTP_CACHE_ENTRY_SCRIPT   0x00000008

#define NGX_HTTP_CACHE_FILTER_FLAGS   0xFFFF0000


typedef struct {
    ngx_fd_t   fd;
    off_t      size;
    void      *data;
    time_t     accessed;
    time_t     last_modified;
    time_t     updated;      /* no needed with kqueue */
    int        refs;
    int        flags;
} ngx_http_cache_entry_t;


typedef struct {
    u_int32_t          crc;
    ngx_str_t          uri;
    ngx_http_cache_t  *cache;
} ngx_http_cache_hash_entry_t;


typedef struct {
    ngx_http_cache_t  *cache;
    u_int32_t          crc;
    int                n;
} ngx_http_cache_handle_t; 


int ngx_http_cache_get(ngx_http_cache_hash_t *cache_hash,
                       ngx_str_t *uri, ngx_http_cache_handle_t *h)
{
    int                           hi;
    ngx_http_cache_hash_entry_t  *entry;

    h->crc = ngx_crc(uri->data, uri->len);

    hi = h->crc % cache_hash->size;
    entry = cache_hash[hi].elts;

    for (i = 0; i < cache_hash[hi].nelts; i++) {
        if (entry[i].crc == crc
            && entry[i].uri.len == uri->len
            && ngx_strncmp(entry[i].uri.data, uri->data, uri->len) == 0
        {
            h->cache = entry[i].cache;
            h->cache->refs++;
            h->n = hi;
            return NGX_OK;
        }
    }

    return NGX_ERROR;
}


/* 32-bit crc16 */

int ngx_crc(char *data, size_t len)
{
    u_int32_t  sum;

    for (sum = 0; len; len--) {
        /*
         * gcc 2.95.2 x86 and icc 7.1.006 compile that operator
         * into the single rol opcode.
         * msvc 6.0sp2 compiles it into four opcodes.
         */
        sum = sum >> 1 | sum << 31;

        sum += *data++;
    }

    return sum;
}