HTTP缓存

int freshness_limit ()
{
        int heuristic , server_freshness_limit, time_since_last_modified ;
        heuristic = 0;

        if (Max_Age_value_set )
       {
               server_freshness_limit = Max_Age_value ;
       }
        else if ( Expire_value_set)
       {
               server_freshness_limit = Expire_value - Date_value;
       }
        else if ( Last_Modified_value_set)
       {
               time_since_last_modified = max (0, Date_value - Last_Modified_value);
               server_freshness_limit = int ( time_since_last_modified* lm_factor );
               heuristic = 1;
       }
        else
       {
               server_freshness_limit = default_cache_min_lifetime ;
               heuristic = 1;
       }

        if (heuristic )
       {
               if (server_freshness_limit > default_cache_max_lifetime)
                      server_freshness_limit = default_cache_max_lifetime ;
               else if ( server_freshness_limit < default_cache_min_lifetime )
                      server_freshness_limit = default_cache_min_lifetime ;
       }
        return 0;
}

time_since_modify = max(0, server_Date - server_Last_Modified);
server_freshness_limit = int(time_since_modify * lm_factor);

int age ( int time_got_response, int Date_header_value , int Age_header_value)
{      
        int time_issued_request , current_time;
              
        /* 修正时钟偏差造成的负数使用期 */
        int apparent_age = max(0, time_got_response - Date_header_value );
        /* 修正时钟偏差，取最保守的值 */
        int corrected_apparent_age = max( apparent_age, Age_header_value );
        /* 对网络时延的补偿 */
        int response_delay_estimate = ( time_got_response - time_issued_request );
        int age_when_document_arrived_at_our_cache = corrected_apparent_age + response_delay_estimate ;
        int how_long_copy_has_been_in_our_cache = current_time - time_got_response ;
        int age = age_when_document_arrived_at_our_cache + how_long_copy_has_been_in_our_cache ;

        return age ;

}